Taller tires - computer recalibration

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Gm only gives the dealer the ability to program the truck with the possible
tire combinations available for that truck... meaning is it possible to get
a truck with that engine and chassis with that size tire?? if not , then gm
cannot program the vehicle... you also have to program the abs and pcm
separately... some dealers just program the abs, which is much more lenient,
and the shift points and Speedo are still wrong...If you find someone who
deals in tires, you may be able to find a match of circumference of tires
between what you have and what is available.... as for aftermarket, I don't
know how they do it... must kinda be like hacked firmware for a dvd player
or something....probably works, I just have no experience with it... Bobo

P.S. If you plan on leaving it as it is... I would try to have the dealer
program the abs for the brakes.. the small change in speed may have a
dramatic effect in how the abs works... I know it's a small speed change,
but with thousands of pounds here it wouldn't take a lot to throw a monket
wrench in the works....

"rnf2" <[email protected]> wrote in message
news:[email protected]...
>
> "mxz1972" <[email protected]> wrote in message
> news:ZzRwb.495942$pl3.333975@pd7tw3no...
> > Ok - so i have been to 3 gm dealers today and they all told me it is not
> > possible to recalibrate for 285/75/16 tires. So what is the deal - the
> hand
> > held aftermarket power programmer will work but the dealer says
> impossible.
> > Can anyone shed some light on the topic for my feeble brain. Is it even
> > really necessary except for the speedo and maybe the shift points? The
> tires
> > are only about 1 - 1.5" larger in diameter. What are the consequences of
> > leaving it as is?
> >
> > Thanks
> > Danno
>
> work out the Pi R squared formula from high school and work out how long
the
> circumferance of the 285s are and the originals there will be a
difference,
> divide the number of feet in amile by the circumferance in feet and thats
> how many times the wheels turn in a mile. the smaller wheels will turn
more
> often and the mileometer will be out by however many turns of the wheel
the
> 285s differ from the originals.
>
> fun maths. not sure if it will help.
>
> rhys
>
>


 
Approximately 11/25/03 14:07, Jason Cothran uttered for posterity:

> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
>> Jason Cothran wrote:
>> >
>> > "Mike Romain" <[email protected]> wrote in message
>> > news:[email protected]...
>> > > I would find someone with a GPS and clock it to see.
>> > >
>> > > When I went up from the stock 215's to 235's, my speedo was right on.
> it
>> > > was off before...
>> > >
>> > Going up from a 215 to a 235 will not change the speedo. That is the
> width
>> > of the tire in millimeters. The second number is what determines how
> tall
>> > the tire is.
>>
>> It sure will unless you radically change the profile.
>>
>> I went from P215/75's stock to P235/75's.
>>
>> It is a lot taller tire.
>>
> A lot taller? 15 mm (just over 1/2 inch) is a lot taller?

Whats the increase in circumference? Ignoring the fact that
unless you know the brand and model of tire, you really don't
have anything more than a general idea of the actual tire
diamters involved...


--
Still a Raiders fan, but no longer sure why.

 
On Wed, 26 Nov 2003 12:52:03 +1300, rnf2 wrote:
>
> work out the Pi R squared formula from high school and work out how long
> the circumferance of the 285s are and the originals there will be a
> difference, divide the number of feet in amile by the circumferance in
> feet and thats how many times the wheels turn in a mile. the smaller
> wheels will turn more often and the mileometer will be out by however many
> turns of the wheel the 285s differ from the originals.
>
> fun maths. not sure if it will help.

Fun, yes. Especially when your formula calculates area.

Circumference = PI times diameter

Complicating things a bit more, the rolling circumference of a tire is not
the same thing as one would calculate based on "tire size." The rolling
radius is shorter because the tire deflects under load. However what you
suggest is a good approximation especially when looking to approximate the
differences between two different tire sizes.

Best thing to do is to consult the tire manufacturer's specs. Should be
able to get a very accurate rolling circumference. Is usually
pre-calculated and stated in revolutions per mile.

 

"David Kelly" <[email protected]> wrote in message
news:p[email protected]...
> On Wed, 26 Nov 2003 12:52:03 +1300, rnf2 wrote:
> >
> > work out the Pi R squared formula from high school and work out how long
> > the circumferance of the 285s are and the originals there will be a
> > difference, divide the number of feet in amile by the circumferance in
> > feet and thats how many times the wheels turn in a mile. the smaller
> > wheels will turn more often and the mileometer will be out by however
many
> > turns of the wheel the 285s differ from the originals.
> >
> > fun maths. not sure if it will help.
>
> Fun, yes. Especially when your formula calculates area.
>
> Circumference = PI times diameter
>
OOPS!!

My bad. still you get the idea.

> Complicating things a bit more, the rolling circumference of a tire is not
> the same thing as one would calculate based on "tire size." The rolling
> radius is shorter because the tire deflects under load. However what you
> suggest is a good approximation especially when looking to approximate the
> differences between two different tire sizes.
>
> Best thing to do is to consult the tire manufacturer's specs. Should be
> able to get a very accurate rolling circumference. Is usually
> pre-calculated and stated in revolutions per mile.
>


 
Leaving it as is will affect your 'perceived' gas mileage and distances
traveled along with a speedometer correction.

As I mentioned, I went one size over anything that was a dealer option
for my Jeep and when I checked the speedo out with a GPS unit, it turned
out to be right on exactly.

They usually calibrate the speedo from the factory to be slightly over
with the largest 'factory option' tires so when the speedo says 65 mph,
you are 'really' only going 63 or 64 mph.

I would just ask the dealer to dial the speedo for the biggest tire they
can and see what the result was.

Meanwhile, all us Jeep folks with really large tires usually just get
paced to find out where the speedo should be and judge the speed
accordingly. It wouldn't hurt my feelings to know I have to be at 63
mph on the speedo to be doing the legal 65 mph. My CJ7 was way off when
I got it with 31" tires on, it read 65 and I was only going 60 before I
went up to 33x9.5 tires. So I just drove at '70 mph' to keep up the
speed limit.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

mxz1972 wrote:
>
> Ok - so i have been to 3 gm dealers today and they all told me it is not
> possible to recalibrate for 285/75/16 tires. So what is the deal - the hand
> held aftermarket power programmer will work but the dealer says impossible.
> Can anyone shed some light on the topic for my feeble brain. Is it even
> really necessary except for the speedo and maybe the shift points? The tires
> are only about 1 - 1.5" larger in diameter. What are the consequences of
> leaving it as is?
>
> Thanks
> Danno
> "Jason Cothran" <[email protected]> wrote in message
> news:[email protected]...
> >
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> > > Jason Cothran wrote:
> > > >
> > > > "Mike Romain" <[email protected]> wrote in message
> > > > news:[email protected]...
> > > > > I would find someone with a GPS and clock it to see.
> > > > >
> > > > > When I went up from the stock 215's to 235's, my speedo was right
> on.
> > it
> > > > > was off before...
> > > > >
> > > > Going up from a 215 to a 235 will not change the speedo. That is the
> > width
> > > > of the tire in millimeters. The second number is what determines how
> > tall
> > > > the tire is.
> > >
> > > It sure will unless you radically change the profile.
> > >
> > > I went from P215/75's stock to P235/75's.
> > >
> > > It is a lot taller tire.
> > >
> > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> >
> >
 
Jason Cothran wrote:
>
> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
> > Jason Cothran wrote:
> > >
> > > "Mike Romain" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > I would find someone with a GPS and clock it to see.
> > > >
> > > > When I went up from the stock 215's to 235's, my speedo was right on.
> it
> > > > was off before...
> > > >
> > > Going up from a 215 to a 235 will not change the speedo. That is the
> width
> > > of the tire in millimeters. The second number is what determines how
> tall
> > > the tire is.
> >
> > It sure will unless you radically change the profile.
> >
> > I went from P215/75's stock to P235/75's.
> >
> > It is a lot taller tire.
> >
> A lot taller? 15 mm (just over 1/2 inch) is a lot taller?

Yo bud, don't know what the heck you are measuring, but in the BFG line,
a P215/75/R15 has a diameter of 27.8".

The P235/75/R15 has a diameter of 29.0"

Just a wee bit more than a 1/2" eh....

http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
 

"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
> Jason Cothran wrote:
> >
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> > > Jason Cothran wrote:
> > > >
> > > > "Mike Romain" <[email protected]> wrote in message
> > > > news:[email protected]...
> > > > > I would find someone with a GPS and clock it to see.
> > > > >
> > > > > When I went up from the stock 215's to 235's, my speedo was right
on.
> > it
> > > > > was off before...
> > > > >
> > > > Going up from a 215 to a 235 will not change the speedo. That is the
> > width
> > > > of the tire in millimeters. The second number is what determines how
> > tall
> > > > the tire is.
> > >
> > > It sure will unless you radically change the profile.
> > >
> > > I went from P215/75's stock to P235/75's.
> > >
> > > It is a lot taller tire.
> > >
> > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
>
> Yo bud, don't know what the heck you are measuring, but in the BFG line,
> a P215/75/R15 has a diameter of 27.8".
>
> The P235/75/R15 has a diameter of 29.0"
>
> Just a wee bit more than a 1/2" eh....
>
> http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's

Think again. that is .6inches (just a wee bit bit over 1/2 inch) per side.
It is simple math. The aspect ratio is simply a percentage of the total
width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim
diameter).
a 235/75/15 is 235mm*.75 inches tall (per side =*2, add rimdiameter), so yes
a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side, but
since we are all assuming, I thought you knew that) taller than a 215/75.
You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6 inches per
side (radius)).


 
Approximately 11/26/03 14:38, Jason Cothran uttered for posterity:

> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
>> Jason Cothran wrote:
>> >
>> > "Mike Romain" <[email protected]> wrote in message
>> > news:[email protected]...
>> > > Jason Cothran wrote:
>> > > >
>> > > > "Mike Romain" <[email protected]> wrote in message
>> > > > news:[email protected]...
>> > > > > I would find someone with a GPS and clock it to see.
>> > > > >
>> > > > > When I went up from the stock 215's to 235's, my speedo was right
> on.
>> > it
>> > > > > was off before...
>> > > > >
>> > > > Going up from a 215 to a 235 will not change the speedo. That is the
>> > width
>> > > > of the tire in millimeters. The second number is what determines how
>> > tall
>> > > > the tire is.
>> > >
>> > > It sure will unless you radically change the profile.
>> > >
>> > > I went from P215/75's stock to P235/75's.
>> > >
>> > > It is a lot taller tire.
>> > >
>> > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
>>
>> Yo bud, don't know what the heck you are measuring, but in the BFG line,
>> a P215/75/R15 has a diameter of 27.8".
>>
>> The P235/75/R15 has a diameter of 29.0"
>>
>> Just a wee bit more than a 1/2" eh....
>>
>> http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
>>
>> Mike
>> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
>> 88 Cherokee 235 BFG AT's
>
> Think again. that is .6inches (just a wee bit bit over 1/2 inch) per side.

Ah, but what is the circumference difference little grasshopper?

87.3 compared to 91.1 inches, or a 3.8 inch difference in circumference,
or just a tad over 4%, not enough to get you a speeding ticket unless
you urinate on the ossifer's foot just before you beer barf on his
nicely pressed uniform, but still enough to bring a slightly out of
true speedometer into line.

> It is simple math. The aspect ratio is simply a percentage of the total
> width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim
> diameter).

Only for a pure and hypothetical tire, little grasshopper. Real
tires are spec'd to the closest standard value and grasshoppers
are encouraged to consult the actual manufacturer's data for the
real tire dimensions. And recall that the difference in diameter
is multipled by 3 in Kentucky and 3.14 elsewhere.



--
Still a Raiders fan, but no longer sure why.

 

"Lon Stowell" <[email protected]> wrote in message
news:i6axb.117879$Dw6.541780@attbi_s02...
> Approximately 11/26/03 14:38, Jason Cothran uttered for posterity:
>
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> >> Jason Cothran wrote:
> >> >
> >> > "Mike Romain" <[email protected]> wrote in message
> >> > news:[email protected]...
> >> > > Jason Cothran wrote:
> >> > > >
> >> > > > "Mike Romain" <[email protected]> wrote in message
> >> > > > news:[email protected]...
> >> > > > > I would find someone with a GPS and clock it to see.
> >> > > > >
> >> > > > > When I went up from the stock 215's to 235's, my speedo was
right
> > on.
> >> > it
> >> > > > > was off before...
> >> > > > >
> >> > > > Going up from a 215 to a 235 will not change the speedo. That is
the
> >> > width
> >> > > > of the tire in millimeters. The second number is what determines
how
> >> > tall
> >> > > > the tire is.
> >> > >
> >> > > It sure will unless you radically change the profile.
> >> > >
> >> > > I went from P215/75's stock to P235/75's.
> >> > >
> >> > > It is a lot taller tire.
> >> > >
> >> > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> >>
> >> Yo bud, don't know what the heck you are measuring, but in the BFG
line,
> >> a P215/75/R15 has a diameter of 27.8".
> >>
> >> The P235/75/R15 has a diameter of 29.0"
> >>
> >> Just a wee bit more than a 1/2" eh....
> >>
> >> http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
> >>
> >> Mike
> >> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> >> 88 Cherokee 235 BFG AT's
> >
> > Think again. that is .6inches (just a wee bit bit over 1/2 inch) per
side.
>
> Ah, but what is the circumference difference little grasshopper?
>
> 87.3 compared to 91.1 inches, or a 3.8 inch difference in circumference,
> or just a tad over 4%, not enough to get you a speeding ticket unless
> you urinate on the ossifer's foot just before you beer barf on his
> nicely pressed uniform, but still enough to bring a slightly out of
> true speedometer into line.
>
> > It is simple math. The aspect ratio is simply a percentage of the total
> > width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim
> > diameter).
>
> Only for a pure and hypothetical tire, little grasshopper. Real
> tires are spec'd to the closest standard value and grasshoppers
> are encouraged to consult the actual manufacturer's data for the
> real tire dimensions. And recall that the difference in diameter
> is multipled by 3 in Kentucky and 3.14 elsewhere.
>

Ah yes, the make it any size you want to rule lol <wink>. Where an inch
equals a mile and pi is forgetten :-D.



 
Jason Cothran wrote:
>
> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
> > Jason Cothran wrote:
> > >
> > > "Mike Romain" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > Jason Cothran wrote:
> > > > >
> > > > > "Mike Romain" <[email protected]> wrote in message
> > > > > news:[email protected]...
> > > > > > I would find someone with a GPS and clock it to see.
> > > > > >
> > > > > > When I went up from the stock 215's to 235's, my speedo was right
> on.
> > > it
> > > > > > was off before...
> > > > > >
> > > > > Going up from a 215 to a 235 will not change the speedo. That is the
> > > width
> > > > > of the tire in millimeters. The second number is what determines how
> > > tall
> > > > > the tire is.
> > > >
> > > > It sure will unless you radically change the profile.
> > > >
> > > > I went from P215/75's stock to P235/75's.
> > > >
> > > > It is a lot taller tire.
> > > >
> > > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> >
> > Yo bud, don't know what the heck you are measuring, but in the BFG line,
> > a P215/75/R15 has a diameter of 27.8".
> >
> > The P235/75/R15 has a diameter of 29.0"
> >
> > Just a wee bit more than a 1/2" eh....
> >
> > http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
>
> Think again. that is .6inches (just a wee bit bit over 1/2 inch) per side.
> It is simple math. The aspect ratio is simply a percentage of the total
> width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim
> diameter).
> a 235/75/15 is 235mm*.75 inches tall (per side =*2, add rimdiameter), so yes
> a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side, but
> since we are all assuming, I thought you knew that) taller than a 215/75.
> You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6 inches per
> side (radius)).

Huh???

I really don't get what you are saying....

The damn tire is over 1" taller. Period. Put the two against a wall
and compare, one 'will' be 1.2" taller than the other on the same rim.

In my book that makes it a 'lot taller'. A 'lot taller' enough that it
won't fit on some vehicles too.

The radius has no bearing on this, nor is it what I said in the first
place.

Now if I wanted to figure out how much more ground clearance I would
get, I would divide the diameter in half. In my case on my CJ7, I got
1" more ground clearance by changing from 31's to 33's. I got 2" more
diameter which is the number needed to figure a speedo.

On my Cherokee I only got .6" more ground clearance changing from P215's
to P235's.

If I am figuring out the speedo, I want the diameter measurement to get
the circumference difference.

If you can't understand this simple math, then I give up on you.

I have no urge to argue with someone that wants to talk in circles.

Bye now....

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
 

"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
>
> I really don't get what you are saying....
>
> The damn tire is over 1" taller. Period. Put the two against a wall
> and compare, one 'will' be 1.2" taller than the other on the same rim.
>
> In my book that makes it a 'lot taller'. A 'lot taller' enough that it
> won't fit on some vehicles too.
>
> The radius has no bearing on this, nor is it what I said in the first
> place.

the radius has EVERYTHING to do with it 'being taller'

the RADIUS is half of the DIAMETER

>
> Now if I wanted to figure out how much more ground clearance I would
> get, I would divide the diameter in half. In my case on my CJ7, I got
> 1" more ground clearance by changing from 31's to 33's. I got 2" more
> diameter which is the number needed to figure a speedo.
>
> On my Cherokee I only got .6" more ground clearance changing from P215's
> to P235's.
>
> If I am figuring out the speedo, I want the diameter measurement to get
> the circumference difference.
>
> If you can't understand this simple math, then I give up on you.
>
> I have no urge to argue with someone that wants to talk in circles.
>
> Bye now....
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's


 
This is on an 88 correct?
If so there is no reprogramming needed. The speedo reading from the 215
to the 235 will be off by 3 mph low. So if it says 65 your running 68,
not a big deal.

"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
> Jason Cothran wrote:
> >
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> > > Jason Cothran wrote:
> > > >
> > > > "Mike Romain" <[email protected]> wrote in message
> > > > news:[email protected]...
> > > > > Jason Cothran wrote:
> > > > > >
> > > > > > "Mike Romain" <[email protected]> wrote in message
> > > > > > news:[email protected]...
> > > > > > > I would find someone with a GPS and clock it to see.
> > > > > > >
> > > > > > > When I went up from the stock 215's to 235's, my speedo
was right
> > on.
> > > > it
> > > > > > > was off before...
> > > > > > >
> > > > > > Going up from a 215 to a 235 will not change the speedo.
That is the
> > > > width
> > > > > > of the tire in millimeters. The second number is what
determines how
> > > > tall
> > > > > > the tire is.
> > > > >
> > > > > It sure will unless you radically change the profile.
> > > > >
> > > > > I went from P215/75's stock to P235/75's.
> > > > >
> > > > > It is a lot taller tire.
> > > > >
> > > > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> > >
> > > Yo bud, don't know what the heck you are measuring, but in the BFG
line,
> > > a P215/75/R15 has a diameter of 27.8".
> > >
> > > The P235/75/R15 has a diameter of 29.0"
> > >
> > > Just a wee bit more than a 1/2" eh....
> > >
> > > http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
> > >
> > > Mike
> > > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > > 88 Cherokee 235 BFG AT's
> >
> > Think again. that is .6inches (just a wee bit bit over 1/2 inch) per
side.
> > It is simple math. The aspect ratio is simply a percentage of the
total
> > width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add
rim
> > diameter).
> > a 235/75/15 is 235mm*.75 inches tall (per side =*2, add
rimdiameter), so yes
> > a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side,
but
> > since we are all assuming, I thought you knew that) taller than a
215/75.
> > You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6
inches per
> > side (radius)).
>
> Huh???
>
> I really don't get what you are saying....
>
> The damn tire is over 1" taller. Period. Put the two against a wall
> and compare, one 'will' be 1.2" taller than the other on the same rim.
>
> In my book that makes it a 'lot taller'. A 'lot taller' enough that
it
> won't fit on some vehicles too.
>
> The radius has no bearing on this, nor is it what I said in the first
> place.
>
> Now if I wanted to figure out how much more ground clearance I would
> get, I would divide the diameter in half. In my case on my CJ7, I got
> 1" more ground clearance by changing from 31's to 33's. I got 2" more
> diameter which is the number needed to figure a speedo.
>
> On my Cherokee I only got .6" more ground clearance changing from
P215's
> to P235's.
>
> If I am figuring out the speedo, I want the diameter measurement to
get
> the circumference difference.
>
> If you can't understand this simple math, then I give up on you.
>
> I have no urge to argue with someone that wants to talk in circles.
>
> Bye now....
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's




-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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-----== Over 100,000 Newsgroups - 19 Different Servers! =-----
 
ROTFLMAO!!!!

Man, so why would I want to divide the diameter in half to figure out
the circumference?

I don't want the area of the sucker, I want the circumference to figure
the % difference from the smaller tire to the larger.

The speedo will be off by that percent....

Mike

Gary Glaenzer wrote:
>
> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
> >
> > I really don't get what you are saying....
> >
> > The damn tire is over 1" taller. Period. Put the two against a wall
> > and compare, one 'will' be 1.2" taller than the other on the same rim.
> >
> > In my book that makes it a 'lot taller'. A 'lot taller' enough that it
> > won't fit on some vehicles too.
> >
> > The radius has no bearing on this, nor is it what I said in the first
> > place.
>
> the radius has EVERYTHING to do with it 'being taller'
>
> the RADIUS is half of the DIAMETER
>
> >
> > Now if I wanted to figure out how much more ground clearance I would
> > get, I would divide the diameter in half. In my case on my CJ7, I got
> > 1" more ground clearance by changing from 31's to 33's. I got 2" more
> > diameter which is the number needed to figure a speedo.
> >
> > On my Cherokee I only got .6" more ground clearance changing from P215's
> > to P235's.
> >
> > If I am figuring out the speedo, I want the diameter measurement to get
> > the circumference difference.
> >
> > If you can't understand this simple math, then I give up on you.
> >
> > I have no urge to argue with someone that wants to talk in circles.
> >
> > Bye now....
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
 
It isn't 'my' tires in question here, someone else's, I didn't start
this thread.

And as it turns out, I am now running 'exact' to my GPS with the
oversized tires on it.

The factory speedo gear was giving me a 'safe' speedo reading, which was
low compared to 'reality'.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

"Steve W." wrote:
>
> This is on an 88 correct?
> If so there is no reprogramming needed. The speedo reading from the 215
> to the 235 will be off by 3 mph low. So if it says 65 your running 68,
> not a big deal.
>
> "Mike Romain" <[email protected]> wrote in message
> news:[email protected]...
> > Jason Cothran wrote:
> > >
> > > "Mike Romain" <[email protected]> wrote in message
> > > news:[email protected]...
> > > > Jason Cothran wrote:
> > > > >
> > > > > "Mike Romain" <[email protected]> wrote in message
> > > > > news:[email protected]...
> > > > > > Jason Cothran wrote:
> > > > > > >
> > > > > > > "Mike Romain" <[email protected]> wrote in message
> > > > > > > news:[email protected]...
> > > > > > > > I would find someone with a GPS and clock it to see.
> > > > > > > >
> > > > > > > > When I went up from the stock 215's to 235's, my speedo
> was right
> > > on.
> > > > > it
> > > > > > > > was off before...
> > > > > > > >
> > > > > > > Going up from a 215 to a 235 will not change the speedo.
> That is the
> > > > > width
> > > > > > > of the tire in millimeters. The second number is what
> determines how
> > > > > tall
> > > > > > > the tire is.
> > > > > >
> > > > > > It sure will unless you radically change the profile.
> > > > > >
> > > > > > I went from P215/75's stock to P235/75's.
> > > > > >
> > > > > > It is a lot taller tire.
> > > > > >
> > > > > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> > > >
> > > > Yo bud, don't know what the heck you are measuring, but in the BFG
> line,
> > > > a P215/75/R15 has a diameter of 27.8".
> > > >
> > > > The P235/75/R15 has a diameter of 29.0"
> > > >
> > > > Just a wee bit more than a 1/2" eh....
> > > >
> > > > http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
> > > >
> > > > Mike
> > > > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > > > 88 Cherokee 235 BFG AT's
> > >
> > > Think again. that is .6inches (just a wee bit bit over 1/2 inch) per
> side.
> > > It is simple math. The aspect ratio is simply a percentage of the
> total
> > > width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add
> rim
> > > diameter).
> > > a 235/75/15 is 235mm*.75 inches tall (per side =*2, add
> rimdiameter), so yes
> > > a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side,
> but
> > > since we are all assuming, I thought you knew that) taller than a
> 215/75.
> > > You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6
> inches per
> > > side (radius)).
> >
> > Huh???
> >
> > I really don't get what you are saying....
> >
> > The damn tire is over 1" taller. Period. Put the two against a wall
> > and compare, one 'will' be 1.2" taller than the other on the same rim.
> >
> > In my book that makes it a 'lot taller'. A 'lot taller' enough that
> it
> > won't fit on some vehicles too.
> >
> > The radius has no bearing on this, nor is it what I said in the first
> > place.
> >
> > Now if I wanted to figure out how much more ground clearance I would
> > get, I would divide the diameter in half. In my case on my CJ7, I got
> > 1" more ground clearance by changing from 31's to 33's. I got 2" more
> > diameter which is the number needed to figure a speedo.
> >
> > On my Cherokee I only got .6" more ground clearance changing from
> P215's
> > to P235's.
> >
> > If I am figuring out the speedo, I want the diameter measurement to
> get
> > the circumference difference.
> >
> > If you can't understand this simple math, then I give up on you.
> >
> > I have no urge to argue with someone that wants to talk in circles.
> >
> > Bye now....
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
>
> -----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
> http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
> -----== Over 100,000 Newsgroups - 19 Different Servers! =-----
 
did you or did you not say that 'the radius has no bearing on this?'

and you don't need to know the circumference..............where S = smaller
tire and L = larger:

circumference L / circumference S = diameter L / diameter S = radius L /
radius S

they are in EXACTLY the same ratios since circumference = 3.1416 diameter =
6.2832 radius


"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
> ROTFLMAO!!!!
>
> Man, so why would I want to divide the diameter in half to figure out
> the circumference?
>
> I don't want the area of the sucker, I want the circumference to figure
> the % difference from the smaller tire to the larger.
>
> The speedo will be off by that percent....
>
> Mike
>
> Gary Glaenzer wrote:
> >
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> > >
> > > I really don't get what you are saying....
> > >
> > > The damn tire is over 1" taller. Period. Put the two against a wall
> > > and compare, one 'will' be 1.2" taller than the other on the same rim.
> > >
> > > In my book that makes it a 'lot taller'. A 'lot taller' enough that
it
> > > won't fit on some vehicles too.
> > >
> > > The radius has no bearing on this, nor is it what I said in the first
> > > place.
> >
> > the radius has EVERYTHING to do with it 'being taller'
> >
> > the RADIUS is half of the DIAMETER
> >
> > >
> > > Now if I wanted to figure out how much more ground clearance I would
> > > get, I would divide the diameter in half. In my case on my CJ7, I got
> > > 1" more ground clearance by changing from 31's to 33's. I got 2" more
> > > diameter which is the number needed to figure a speedo.
> > >
> > > On my Cherokee I only got .6" more ground clearance changing from
P215's
> > > to P235's.
> > >
> > > If I am figuring out the speedo, I want the diameter measurement to
get
> > > the circumference difference.
> > >
> > > If you can't understand this simple math, then I give up on you.
> > >
> > > I have no urge to argue with someone that wants to talk in circles.
> > >
> > > Bye now....
> > >
> > > Mike
> > > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > > 88 Cherokee 235 BFG AT's


 
On Wed, 26 Nov 2003 20:39:26 -0500, Mike Romain wrote:

> ROTFLMAO!!!!
>
> Man, so why would I want to divide the diameter in half to figure out the
> circumference?

Because the tire is 2 * PI radians around. And the circumference is
2 * PI * R.

> I don't want the area of the sucker, I want the circumference to figure
> the % difference from the smaller tire to the larger.

Punch some buttons on your calculator. For percent changed the radius
works exactly as well as the diameter which works exactly as well as the
circumference when comparing speedometer/odometer errors.

A high school student in algebra class should be able to explain why.
Because we are lacking HS algebra graduates I'll explain.

The only difference between circumference and diameter is that diameter is
multiplied by PI to get circumference. When comparing two tires the
constant PI can be factored out from both sides of the equation.

Same applies for radius and 2 * PI.

 
Ouch, ok.... I give up. LOL!

I like simple stuff......

You know, the 'KISS' principal.

If I put a BFG P235/75 against a wall and a BFG P215/75 against a wall I
have a 1.2" height difference.

In my mind that makes one tire taller than the other. 'Lots taller'.

The chart at BFG tells me this.

http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf

So I have a 'diameter' given to me from the tire maker, no radius
mentioned there....

WHY THE HECK SHOULD I DO ANY FANCY MATH CONVERSIONS WHEN THE FORMULA IS
SO SIMPLE! (or even need to know more than basic, which I happen to
anyway)

Excuse me for shouting, but this thread is getting totally silly....

PI times the diameter works for me......

Radius does not come into the equation when figuring out a speedometer
like the original poster asked about!!!!

The tire makers don't give you radius on the tire charts, they give
diameter!

Crap guys....

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

David Kelly wrote:
>
> On Wed, 26 Nov 2003 20:39:26 -0500, Mike Romain wrote:
>
> > ROTFLMAO!!!!
> >
> > Man, so why would I want to divide the diameter in half to figure out the
> > circumference?
>
> Because the tire is 2 * PI radians around. And the circumference is
> 2 * PI * R.
>
> > I don't want the area of the sucker, I want the circumference to figure
> > the % difference from the smaller tire to the larger.
>
> Punch some buttons on your calculator. For percent changed the radius
> works exactly as well as the diameter which works exactly as well as the
> circumference when comparing speedometer/odometer errors.
>
> A high school student in algebra class should be able to explain why.
> Because we are lacking HS algebra graduates I'll explain.
>
> The only difference between circumference and diameter is that diameter is
> multiplied by PI to get circumference. When comparing two tires the
> constant PI can be factored out from both sides of the equation.
>
> Same applies for radius and 2 * PI.
 
Wed, 26 Nov 2003 12:04:05 -0500 Mike Romain <[email protected]>
wrote:

> Jason Cothran wrote:
> > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
>
> Yo bud, don't know what the heck you are measuring, but in the BFG line,
> a P215/75/R15 has a diameter of 27.8".
>
> The P235/75/R15 has a diameter of 29.0"
>
> Just a wee bit more than a 1/2" eh....

Mike,
determining tire height with radius suits better for those who
want more academic conversation and more "convincing" formula.
They have the joy of multiplying the radius by two to get what
we know without multiplying, "how tall the tire is", diameter.

--
Jukka
 
Well, Mike, you are right about the thread getting silly. I also don't care
about radius or diameter or circumference or any mathematical ****. So
here's the only way for you to get it. Stand the tires against the wall.
One tire is 2 inches taller than the other one. The taller tire will raise
the truck by ONE INCH!!! The other inch is at the top of the tire. Holy
****, this is getting to be some boring reading! However much taller the
one tire is, divide by 2. It bolts on in the middle!!!!
..
"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
> Ouch, ok.... I give up. LOL!
>
> I like simple stuff......
>
> You know, the 'KISS' principal.
>
> If I put a BFG P235/75 against a wall and a BFG P215/75 against a wall I
> have a 1.2" height difference.
>
> In my mind that makes one tire taller than the other. 'Lots taller'.
>
> The chart at BFG tells me this.
>
> http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
>
> So I have a 'diameter' given to me from the tire maker, no radius
> mentioned there....
>
> WHY THE HECK SHOULD I DO ANY FANCY MATH CONVERSIONS WHEN THE FORMULA IS
> SO SIMPLE! (or even need to know more than basic, which I happen to
> anyway)
>
> Excuse me for shouting, but this thread is getting totally silly....
>
> PI times the diameter works for me......
>
> Radius does not come into the equation when figuring out a speedometer
> like the original poster asked about!!!!
>
> The tire makers don't give you radius on the tire charts, they give
> diameter!
>
> Crap guys....
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
>
> David Kelly wrote:
> >
> > On Wed, 26 Nov 2003 20:39:26 -0500, Mike Romain wrote:
> >
> > > ROTFLMAO!!!!
> > >
> > > Man, so why would I want to divide the diameter in half to figure out
the
> > > circumference?
> >
> > Because the tire is 2 * PI radians around. And the circumference is
> > 2 * PI * R.
> >
> > > I don't want the area of the sucker, I want the circumference to
figure
> > > the % difference from the smaller tire to the larger.
> >
> > Punch some buttons on your calculator. For percent changed the radius
> > works exactly as well as the diameter which works exactly as well as the
> > circumference when comparing speedometer/odometer errors.
> >
> > A high school student in algebra class should be able to explain why.
> > Because we are lacking HS algebra graduates I'll explain.
> >
> > The only difference between circumference and diameter is that diameter
is
> > multiplied by PI to get circumference. When comparing two tires the
> > constant PI can be factored out from both sides of the equation.
> >
> > Same applies for radius and 2 * PI.


 

"Mike Romain" <[email protected]> wrote in message
news:[email protected]...
> Jason Cothran wrote:
> >
> > "Mike Romain" <[email protected]> wrote in message
> > news:[email protected]...
> > > Jason Cothran wrote:
> > > >
> > > > "Mike Romain" <[email protected]> wrote in message
> > > > news:[email protected]...
> > > > > Jason Cothran wrote:
> > > > > >
> > > > > > "Mike Romain" <[email protected]> wrote in message
> > > > > > news:[email protected]...
> > > > > > > I would find someone with a GPS and clock it to see.
> > > > > > >
> > > > > > > When I went up from the stock 215's to 235's, my speedo was
right
> > on.
> > > > it
> > > > > > > was off before...
> > > > > > >
> > > > > > Going up from a 215 to a 235 will not change the speedo. That is
the
> > > > width
> > > > > > of the tire in millimeters. The second number is what determines
how
> > > > tall
> > > > > > the tire is.
> > > > >
> > > > > It sure will unless you radically change the profile.
> > > > >
> > > > > I went from P215/75's stock to P235/75's.
> > > > >
> > > > > It is a lot taller tire.
> > > > >
> > > > A lot taller? 15 mm (just over 1/2 inch) is a lot taller?
> > >
> > > Yo bud, don't know what the heck you are measuring, but in the BFG
line,
> > > a P215/75/R15 has a diameter of 27.8".
> > >
> > > The P235/75/R15 has a diameter of 29.0"
> > >
> > > Just a wee bit more than a 1/2" eh....
> > >
> > > http://www.bfgoodrichtires.com/assets/pdf/radial_long_trail_ta.pdf
> > >
> > > Mike
> > > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > > 88 Cherokee 235 BFG AT's
> >
> > Think again. that is .6inches (just a wee bit bit over 1/2 inch) per
side.
> > It is simple math. The aspect ratio is simply a percentage of the total
> > width. E.G., a 215/75 is 215mm*.75 inches tall (per side =*2, add rim
> > diameter).
> > a 235/75/15 is 235mm*.75 inches tall (per side =*2, add rimdiameter), so
yes
> > a 235/75 is, like I said, just a wee bit over a 1/2 inch (per side, but
> > since we are all assuming, I thought you knew that) taller than a
215/75.
> > You even showed it yourself off the chart (29-27.8=1.2 / 2 = .6 inches
per
> > side (radius)).
>
> Huh???
>
> I really don't get what you are saying....
>
> The damn tire is over 1" taller. Period. Put the two against a wall
> and compare, one 'will' be 1.2" taller than the other on the same rim.
>
> In my book that makes it a 'lot taller'. A 'lot taller' enough that it
> won't fit on some vehicles too.
>
> The radius has no bearing on this, nor is it what I said in the first
> place.
>
> Now if I wanted to figure out how much more ground clearance I would
> get, I would divide the diameter in half. In my case on my CJ7, I got
> 1" more ground clearance by changing from 31's to 33's. I got 2" more
> diameter which is the number needed to figure a speedo.
>
> On my Cherokee I only got .6" more ground clearance changing from P215's
> to P235's.
>
> If I am figuring out the speedo, I want the diameter measurement to get
> the circumference difference.
>
> If you can't understand this simple math, then I give up on you.
>
> I have no urge to argue with someone that wants to talk in circles.
>
> Bye now....
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's

You're the one that admitted you dont get. rofl.


 
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