Pikey
Dummy Ejection Facilitator..
Go on John give em some advice. It's not like someones gonna dig the thread up in 6months, and use it to start a thread slagging you off
Go on John give em some advice. It's not like someones gonna dig the thread up in 6months, and use it to start a thread slagging you off
I've been telling you that for ages
:mooning::mooning::emps1::lol::lol:
Go on John give em some advice. It's not like someones gonna dig the thread up in 6months, and use it to start a thread slagging you off
You take away Minty's key board?
sijwhite
Active Member
Here's my real world calculations to clarify my statement that under 30mm would be OK in my opinion.
I measured my Summer tyres when I took them off back in November.
All of them are Continental and exactly the same model.
The nearly new rears had a circumference of 2192mm with a tread depth of 8mm.
The fronts with a tread depth of 3.5mm have a circumference of 2164mm
That's a difference of 28mm in circumference.
I intend running the fronts down to 2mm tread depth, at which point the rears will probably have worn down to around 6.5 / 7.0mm.
I firmly believe that if you have the same tyres all round then you need to keep the tread depth difference to 5mm or less.
I now swap my winter tyres round regulary at 5k to equalize them - but I was too late to start doing that with the summer tyres so they are now too big a mismatch to swap front to rear.
So - back to my original opinion that the bigger circumference go on the rear as long as the difference is 30mm or less.
Of course everyone must do as they think best.
I'll get my coat.
I had the 5mm tread depth difference figure in my mind and completely missed the circumference aspect of the point SV was making.
:5bdriving:
Nodge68
Well-Known Member
Also make sure yer tyres are pumped up propper. All with the same pressure including the spare.
I measured my tyres last year when investigating problems. If yer get hold of a flexible sewing measuring tape then yer can easily measure the circumference of yer tyre. Jack up wheel to measure.
Yellow Extra Long Tape Measure Tailor Sewing Measuring Metric Imperial 300cm 256 | eBay
Wecome back JW.
It's better to drive the car onto the tape as the bottom of the tyre will be flattened which will alter it's radius. There is a surprising difference in a tyre in the air and one on the ground with the vehicle weight on it
It's better to drive the car onto the tape as the bottom of the tyre will be flattened which will alter it's radius. There is a surprising difference in a tyre in the air and one on the ground with the vehicle weight on it
dosen't make a difference in how they are measured,on the ground or in the air. As long as they are measured the same way. Then you can do your mathematical equation to determine the difference in circumference to see if the variable is well with in tolerance of a plus or minus
Nodge68
Well-Known Member
It makes a difference front to back with the tyres on the ground! Especially on the diesel and V6 as there I a huge weight difference between front and back axles. You only need look at the front tyres compared to the rear. I measured a 15mm difference in circumference between front and rear even though the tyres are worn to the same depth!!
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Hippo
Lord Hippo
Thats what I expected but I measured mine off the ground (fitted to wheels and inflated to approx 30psi) and then measured them on their own (wheels removed) and the circumference was the same as before.It's better to drive the car onto the tape as the bottom of the tyre will be flattened which will alter it's radius. There is a surprising difference in a tyre in the air and one on the ground with the vehicle weight on it
Mine failed me tests so new tyres fitted. Problem solved. 
Singvogel
Well-Known Member
Well the laws of Physics (or is it Geometry) dictate that the circumference cannot change - no matter what shape the tyre is forced into.
What changes is the radius.
When the tyre is fitted and the tyre 'squidges' down at the bottom the radius from the centre to the ground is a good bit less than the radius from the centre to the top of the tyre.
My 235/55 17 tyres have a overall diameter of 724mm - which would lead you to believe the radius would be 362mm.
That is indeed the radius off the car - or on the car from the centre to the top of the tyre.
But the distance from the centre to the ground is only 335mm - this is know as the 'Static Laden Radius'
That's with a tyre load of around 450Kg at a pressure of 28psi
If the tyre was carrying the max permitted load for a 99 rated tyre of 775Kg it would be even less - at only 325mm. (That's way beyond the max load of a Freelander)
That's enough tyre talk. You are now ready for the Intermediate Level 1 Exam. LOL
What changes is the radius.
When the tyre is fitted and the tyre 'squidges' down at the bottom the radius from the centre to the ground is a good bit less than the radius from the centre to the top of the tyre.
My 235/55 17 tyres have a overall diameter of 724mm - which would lead you to believe the radius would be 362mm.
That is indeed the radius off the car - or on the car from the centre to the top of the tyre.
But the distance from the centre to the ground is only 335mm - this is know as the 'Static Laden Radius'
That's with a tyre load of around 450Kg at a pressure of 28psi
If the tyre was carrying the max permitted load for a 99 rated tyre of 775Kg it would be even less - at only 325mm. (That's way beyond the max load of a Freelander)
That's enough tyre talk. You are now ready for the Intermediate Level 1 Exam. LOL
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Hippo
Lord Hippo
Last year when I was playing with my tyres I set the psi so the tyre centre was the same distance from the ground. Hence the same radius as singvogel mentionned above. Had to put each wheel on a sheet of wood to get it right as the uneven stones in tarmac mess up the measurement when trying to get it mm perfect. Fronts had to be a higher pressure than the rears and it didn't feel right when driving. So I put it back. I have the figures somewhere. I wouldn't advise anyone to try this and I certainly won't do it again.
BothWell the laws of Physics (or is it Geometry) dictate that the circumference cannot change - no matter what shape the tyre is forced into.
What changes is the radius.
When the tyre is fitted and the tyre 'squidges' down at the bottom the radius from the centre to the ground is a good bit less than the radius from the centre to the top of the tyre.
eggszactly
only thing that could make a change in circumferences is PSI but if equal there will be no change. Only thing from front to back would be the flat spot on the bottom being different
Nodge68
Well-Known Member
I hope the designers realized that with equal tyre pressures front and back the front would be more squashed at the bottom which alter the rolling radius between the front and back. It would be unwise in the real world to set the front at a higher pressure than the rear to compensate as it would affect the way the car handles. Manufactures generally set the front tyre pressures equal or lower than the rear as it induces gentle under steer which is safer than over steer for the average driver.
I run my fronts 5psi higher than the back unless hauling or towing a load and watch tyre wear, rotated every 6k with the oil change
