Different Tyre Diameters

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3rd June 2012, 01:50 PM
Dougal

Quote:

Originally Posted by gghaggis

The car measures individual wheel speeds and compares that to the known attitude and trajectory of the car. If they don't match, the DSC will decide whether to activate - if it does, you'll feel a grinding sensation as it tries to match the wheel speeds. Continual running like this will escalate the priority of the logged fault. Eventually the EAS will throw a hissy fit. Mine also disabled TR, HDC and may or may not have contributed to a temporary transmission fault.

Unless you absolutely have to (the tsunami is lapping at your heels), don't do it. If you absolutely have to, stop every 40 k's or so and reset the car, drive in Sand mode to reduce ABS interference, with the DSC off.

Cheers,

Gordon

I'd expect the car to trigger a tyre inflation error long before traction/stability control will kick in.
What are the thresholds for each in the RRS? In other vheicles I have heard 1/8th of a wheel revolution (12%) is needed for action to be taken.
3rd June 2012, 02:21 PM
Scouse

D3s & early Sports didn't have the tyre pressure warning system, out here at least.
4th June 2012, 12:43 PM
jonesy63

Out of interest... what difference in tyre diameter is required to trigger DSC?

For instance, I have 4 worn tyres and put on a spare which has 5mm more tread depth (10mm bigger diameter)... would that be enough?

Cheers.
4th June 2012, 12:48 PM
Dougal

Quote:

Originally Posted by Scouse

D3s & early Sports didn't have the tyre pressure warning system, out here at least.

A quick read of the owners manual shows the TPM system if fitted to these usese sensors on the valve stems, you get some quite different looking valves poking out of your rims if you have it.
This is different to the system used by some cars to simply monitor the different abs sensors and flag if one wheel consistently turns faster or slower than the rest.

Jonesy, I'm quite confident stability and traction control aren't going to trigger based off a constant wheel speed difference of that little. Stability control is tied into steering wheel sensors and yaw sensors, exactly how it's coded will be a well kept secret.
Traction control is based on wheel spin/slip, not a minor difference in speed.
4th June 2012, 01:46 PM
101RRS

Quote:

Originally Posted by jonesy63

Out of interest... what difference in tyre diameter is required to trigger DSC?

For instance, I have 4 worn tyres and put on a spare which has 5mm more tread depth (10mm bigger diameter)... would that be enough?

Cheers.

Based on my experience I doubt it - however a tyre with about 5 psi in it compared to all the others with about 40psi in them will set DSC off - not sure what the different in tyre dia is between a deflating tyre and an inflated tyre is but was enough to set DSC off - I had not other indication that the tyre was going down.

Garry
4th June 2012, 01:53 PM
Redback

Quote:

Originally Posted by jonesy63

Out of interest... what difference in tyre diameter is required to trigger DSC?

For instance, I have 4 worn tyres and put on a spare which has 5mm more tread depth (10mm bigger diameter)... would that be enough?

Cheers.

I don't think 5mm would be an issue Rob, 10mm + might be though, if fitted to the front not as much of an issue, given the 60/40 ratio on AWD systems, probable not a problem on a gravel road, I wouldn't do it on the tar, it's a no no on the D2 because of diff/transfer case wind up, I suspect maybe the same on the D3/D4/RRS, but not to the same extent as long as the difference wasn't to great.

Just my 2 cents

Baz.
4th June 2012, 02:00 PM
Dougal

Quote:

Originally Posted by Redback

I don't think 5mm would be an issue Rob, 10mm + might be though, if fitted to the front not as much of an issue, given the 60/40 ratio on AWD systems, probable not a problem on a gravel road, I wouldn't do it on the tar, it's a no no on the D2 because of diff/transfer case wind up, I suspect maybe the same on the D3/D4/RRS, but not to the same extent as long as the difference wasn't to great.

Just my 2 cents

Baz.

D2's have three open diffs. There is no diff/TC windup unless you drive around on tarmac with the CDL in. There are many reasons to not drive around with the CDL in on tarmac even with four equal tyres.
4th June 2012, 04:04 PM
jonesy63

Quote:

Originally Posted by Redback

I don't think 5mm would be an issue Rob, 10mm + might be though, if fitted to the front not as much of an issue, given the 60/40 ratio on AWD systems, probable not a problem on a gravel road, I wouldn't do it on the tar, it's a no no on the D2 because of diff/transfer case wind up, I suspect maybe the same on the D3/D4/RRS, but not to the same extent as long as the difference wasn't to great.

Just my 2 cents

Baz.

Thanks Baz. In future, I guess I will need to do 5 wheel rotations on the MT tyres. :angel:
4th June 2012, 04:37 PM
Redback

Quote:

Originally Posted by jonesy63

Thanks Baz. In future, I guess I will need to do 5 wheel rotations on the MT tyres. :angel:

It is recommended on AWD vehicles to include the spare in rotations.

Baz.
5th June 2012, 07:36 AM
Learner

[QUOTE=Redback;1695 Snip
given the 60/40 ratio on AWD systems,
SNIP z.[/QUOTE]

Hi Baz,
Would you please explain what you mean by this and its relevance to D3/D4/RRS

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