It's the loaded rolling radius. Which changes subject to pressure, tyre wear and load.
It's the loaded rolling radius. Which changes subject to pressure, tyre wear and load.
GrumpyGel
Well-Known Member
I'm not sure what @Hippo is aiming at, cos as @dave12478 says, he aint said. However taking Hippos tyres as an example, the fronts have a rolling circumference of 1.96m, therefore at 100kmh/60mph, they are turning at the rate of 850 times a minute. Given the diff ratio of 3.2:1, this means the props are turning 2,720 times per minute. If there's a 2.1% difference in rear tyre diameter (after the IRD's gearing), this means the VCU slips 57 complete rotations per minute!
In terms of 1 wheel up test, that's a result of 0.26 seconds.
Using Hippos data in his 1 Wheel Up YouTube clip, it appears that the time taken reduces by about 32% as weight doubles. Extrapolating on his timings, the difference in axle speeds at 60mph is the equivalent of about 100kg on the end of a 1.2m bar
I dunno what torque this equates to on the IRD bearings or where tyre meets road.
I'm pretty sure I'm working the diff ratio round the right way. If its the other way round, the prop is turning at a rate of 265 times per minute and the VCU slips 5.4 rotations per minute. This equates to a 1 wheel up test of 2.8 seconds and about 25kg on the 1.2m poll at 60mph.
In terms of 1 wheel up test, that's a result of 0.26 seconds.
Using Hippos data in his 1 Wheel Up YouTube clip, it appears that the time taken reduces by about 32% as weight doubles. Extrapolating on his timings, the difference in axle speeds at 60mph is the equivalent of about 100kg on the end of a 1.2m bar
I dunno what torque this equates to on the IRD bearings or where tyre meets road.I'm pretty sure I'm working the diff ratio round the right way. If its the other way round, the prop is turning at a rate of 265 times per minute and the VCU slips 5.4 rotations per minute. This equates to a 1 wheel up test of 2.8 seconds and about 25kg on the 1.2m poll at 60mph.
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If the prop in front of the VCU was turning at the same rate as the prop behind the VCU technically there would be no drive to the rear wheels. They would just be freewheeling being dragged by the front wheels. The rotational difference ensures the VCU is at least partially engaged at all times driving all the wheels. Freelander is essentially a front wheel drive car that has been adapted to drive all four wheels. Or that's the way it looks to me. Bit Heath Robinson if you ask me.
unless the VCU was seized?
GrumpyGel
Well-Known Member
True, I suppose 100kg on a 1.2m bar "sounds" like an awful lot of something. But how much is it really in the context of a vehicle? If you had a Freelander sitting on level ground in neutral with the brake off... if a 100kg bloke stood on a 1.2m bar fixed to a hub nut, its not going to accellerate (turn the wheel) that quickly. Compare that to the forces pushed through the transmission and tyres when accelerating normally, it ain't much.
With rear tyres being bigger (in an unladen car), they will want to turn slower, so they will be getting a 'hurry up' from the engine.
As the man with the hats says though, if the VCU ain't working well, the actual forces of slipping a VCU at 57rpm, could be a great deal more.
I can see your point, any car with a VCU or Haldex could be described the same (so long as the engine's in the front!), but then how does Range Rover fit into that? So I can see your point, but I think your meaning of it is wrong. VCU technology was in use before Freelander was developed. In traditional LR fashion they went to the Rover parts bin for lots of things, but knowing that VCU tech can be used to provide a good 4x4 system.
Having previously owned Disco and now owning Freelander, the only 'big' Landie I would go back to is a Rangie with a VCU. I'm sold on VCU being better than a traditional transfer box.
Hippo
Lord Hippo
I need peeps to help by answering the questions in the first post, to save me time. Failing that I have to go round measuring wheels meself. I will put up more info at a later date when I have done some more thinking.
In further news, I have always wanted to build a vcu test rig powered by a motor, strong enough to turn a vcu several times per minute constantly. The force required to turn a vcu several times per minute is considerable but I can now confirm a rig has been built at the Hippo Technology centre of Freelandering, and it works. I don't have it for long. Results/info etc to follow at a later date. Get measuring yer wheels...
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B34R
Active Member
I beg to differ
100kg = 1000N give or take, at 1.2 meters that's 1200NM of torque
The K series engine outputs 165NM of torque into the gearbox, which is x3.25 in first gear = 536 NM
The IRD is a ratio of about 1.4 iirc? = 750NM Torque to the wheels.
A 100kg bloke stood on a 1.2 meter bar will accelerate the car 1.6 times faster than the K series flat out
Sad I know.
Point is where the VCU is situated. In the Range rover it drives both props equally and slips to compensate for different rotational speeds front to rear if any exist. In the Freelander it is on the rear propshaft and drive and slip is induced by having different diff ratios front and rear. It is bad enough on the Range rover if the VCU seizes but seriously more so on the Freelander because of the builtin front and rear diff ratio mismatch.
Think you will struggle to do that and need an hell of a motor. VCUs are designed to slip slowly but lock up when the input and output shaft speed varies to much. Thus giving a solid connection. You will find if you try it, that when testing the VCU by applying a turning moment to the wheel if you use to much force and apply it quickly the wheel will not turn at all. Only a steady low force will make it turn. If the Freelander VCU has the same properties as the Range rover one that is.
Right :- all tyres same make same pressure. 1mm more tread on fronts - so correcting for that and averaging side to side. Full tank of diesel - TD4 Auto 2005 HSE
Front 346mm Rear 351mm difference 5mm
loaded rolling radius to middle instead of top of insert is circa 320mm - so that's a radius and therefore a circumference difference of 1.6%
As a matter of interest - having glazed over trying to figure out what the front to back drive ratio for a late TD4 Auto was :- I jacked up both wheels one side - Marked with chalk tires to bottom of spring as that was the closest point - marked the VCU - pushed the front wheel forwards 10 turns and keeping the backlash consistent for start and stop positions - I got the rear wheel turning at 2" less in 10 turns - checked the vcu and it had not slipped (the wheels turned very freely - and if I put the handbrake on I could only move the front wheel by forcing the VCU to slip))
26" dia x 3.142 x 10 turns = 817"
2"/817 = .0024 - or very close to Hippo's 0.2% deduction on his thread on the subject ( the other ratio he found being 0.8%)
So my back wheels are pushing my front wheels on a level straight by circa 1.6% - 0.2% = 1.4% (Edit - this should read 1.6% + 0.2% = 1.8% or thereabouts - and I'm using 0.2% as I think my particular TD4 has been fitted with a V6 IRD)
So - Hippo - are we seeing here their thinking behind reducing the drive ratio difference from 0.8% to 0.2%? - Feels right.
Edit - I got this slightly wrong - see the edit above - the 1.6% and 0.2% gearing factors are additive to the effect of the loaded rolling radius difference - so when the heavier V6 generates more compression of the front wheels it did not need so much bias - hence the reduction from 0.8% to 0.2%
So the comparison might look something like :-
Normal TD4 etc :- 1.6 + 0.8 = 2.4% bias towards rear drive
Heavier V6 :- say 2.2 + 0.2% = = 2.4% bias towards rear drive
Hippo's numbers will firm up these Loaded Rolling Radii - keep the wheel measurements coming peeps!
Front 346mm Rear 351mm difference 5mm
loaded rolling radius to middle instead of top of insert is circa 320mm - so that's a radius and therefore a circumference difference of 1.6%
As a matter of interest - having glazed over trying to figure out what the front to back drive ratio for a late TD4 Auto was :- I jacked up both wheels one side - Marked with chalk tires to bottom of spring as that was the closest point - marked the VCU - pushed the front wheel forwards 10 turns and keeping the backlash consistent for start and stop positions - I got the rear wheel turning at 2" less in 10 turns - checked the vcu and it had not slipped (the wheels turned very freely - and if I put the handbrake on I could only move the front wheel by forcing the VCU to slip))
26" dia x 3.142 x 10 turns = 817"
2"/817 = .0024 - or very close to Hippo's 0.2% deduction on his thread on the subject ( the other ratio he found being 0.8%)
So my back wheels are pushing my front wheels on a level straight by circa 1.6% - 0.2% = 1.4% (Edit - this should read 1.6% + 0.2% = 1.8% or thereabouts - and I'm using 0.2% as I think my particular TD4 has been fitted with a V6 IRD)
So - Hippo - are we seeing here their thinking behind reducing the drive ratio difference from 0.8% to 0.2%? - Feels right.
Edit - I got this slightly wrong - see the edit above - the 1.6% and 0.2% gearing factors are additive to the effect of the loaded rolling radius difference - so when the heavier V6 generates more compression of the front wheels it did not need so much bias - hence the reduction from 0.8% to 0.2%
So the comparison might look something like :-
Normal TD4 etc :- 1.6 + 0.8 = 2.4% bias towards rear drive
Heavier V6 :- say 2.2 + 0.2% = = 2.4% bias towards rear drive
Hippo's numbers will firm up these Loaded Rolling Radii - keep the wheel measurements coming peeps!
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whatever the aim of the original post request ..
methinks there are too many variables ..
tyres flex whilst being driven down the road ..
tyre construction varies from make / model / type .. etc
air pressure will vary depending on temperature
getting an accurate height measurement be 'iffy' on most surfaces
placing the vehicle level not too hard .. but the surface needs to be dead smooth ..
like flat steel plate .. or similar ..
as for a measuring device .. i could have done with using something like a combination square set ..
anyhow i tried again .. set all tyres to 31 psi
2006 TD4 commercial:
rear load was about 26 litres diesel + dog
vehicle was level as could be .. but surface were tarmac ..
tried in 2 locations .. 1st one were a rediculous result due to surface undulations of said tarmac
( measured both sides with way different results )
2nd location looked smoother .. measured twice on one side ..
results were different im afraid
350 mm F / 357 mm R
then
349 mm F / 356 mm R
1 mm less tread depth on front .. compared to rear ..
( and that IS as accurate as can be ) ..
tyre .. michelin latitude hp .. 225 / 55 H 17
i'm 62 .. wear varyfocul lens glasses .. 'n have a crap back
trying to spot which mm mark it be while crouching down 'n holding things steady ..
with a cold wind watering up my eyes ..
plus a less than desirable smooth surface on which to stand the steel ruler ..
the potential for an inaccurate reading is definitley there
~~~~~~~~~~~~~
one good thing .. at least i'm reasonably confident now ..
that the rear tyre 'working surface' is greater than the front tyre (s)
( and at my preferred psi loading front-to-rear )
so less chance of fretting / losing sleep .. over the possibility of imminent vcu failure of the stiffening kind
more worried now .. at 109k vehicle miles ..
that the crankshaft sensor will suddenly die mid journey at the worst possible road location
( i think the engine quits totaly .. on the spot .. if that sensor goes kaputski )
best of luck with whatever it is your trying to achieve here 'hippo'
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Hippo
Lord Hippo
Just measure yer fekin wheels as per the original post request and put up yer results.
If the results find the average rear tyre to be Nmm higher than the front, which has a centre Nmm oft the ground, then I is happy with the result. If the tyre pressure are the same with the same make/model/size wheels/tyres then that's good enough for me. Try to measure the wheels in the same way.
Look back at posts from 6 years ago when we were no further forward than we are now, when most were busy arguing the toss. It's no wonder the tratterers take the p***.
I'm not going to tell you what's going on until I get enough results. Yes that's black mail. If I say why it will just descend into argument like the ird ratio fred did.
I bought a brand new gkn vcu some time ago so I don't need to do any of this.
Don't feed the troll. It's about to start posting.
If the results find the average rear tyre to be Nmm higher than the front, which has a centre Nmm oft the ground, then I is happy with the result. If the tyre pressure are the same with the same make/model/size wheels/tyres then that's good enough for me. Try to measure the wheels in the same way.
Look back at posts from 6 years ago when we were no further forward than we are now, when most were busy arguing the toss. It's no wonder the tratterers take the p***.
I'm not going to tell you what's going on until I get enough results. Yes that's black mail. If I say why it will just descend into argument like the ird ratio fred did.
I bought a brand new gkn vcu some time ago so I don't need to do any of this.
Don't feed the troll. It's about to start posting.
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Is that the one were you could not understand why an high revving more powerful engine needs a higher final drive ratio than a four cylinder lower revving diesel?
Hippo
Lord Hippo
No. You chose to argue about the drive ratio's and cause trouble. Most of the fred was deleted. As with this fred it has nothing to do with you. Read my post 29 and your reply post 32 on this fred. Here we go again.Is that the one were you could not understand why an high revving more powerful engine needs a higher final drive ratio than a four cylinder lower revving diesel?
More like adding a bit of sense to a nonsensical imagined problem. But carry on with your sillyness. You can't even explain what all this is trying to prove.
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I am well chilled out, just that the mechanical ineptitude shown on here sometimes is staggering.
