Wheel change - does the computer say no ?

[JonnyCJ]

If you change up or down wheel size would it affect the computer wot controls stuff like that ? I'm thinking that if a car comes with a set rolling radius and it alters in a single incident (rather than gradual wear) would the computer throw a wobbly ?

Similarly, if you put TPMS sensors on a bigger or smaller rolling radius rim, does the signal affect the computer or does it work on radio waves, so rolling radius unimportant ?

 

[EXCF350]

Do a search on maseratilife, people have had lots of trouble when changing wheel size.

 

[CatmanV2]

Can't see that the 'step' change will be an issue. Changing the ratio of front and rear rolling radius will very much so, however. At least I'd expect them to

C

 

[CatmanV2]

Actually I've just had a thought. If the rolling radius changes from what the computer expects, will that change the differential between the speeds of the inside and outside wheels when cornering. That could also stuff things up.

C

 

[JonnyCJ]

So would sticking 20's on a car designed for 19's potentially throw a wobbler ? Then there's the whole spare wheel issue if you're running a GTO spare ?

 

[mjheathcote]

Have a wheel the size of a pram, or a wheel the size of a tractor, won't make any difference. The car computer can't see these. So if pram wheels you might be travelling at 10mph, but the car computer still thinks you are doing say 100mph!.. The wheels are still rotating at the same speed for 100mph but you don't travel as far, hence only doing a real speed of 10mph.
The only problem is if you have different size wheels front to back. Say more taller at the back than standard, compared to the front that are normal height. The computer may get confused. This can happen on a rolling road when the front wheels don't move.
So if you change the wheel height/rolling diameter, do it to the same ratio front and back.

 

[voicey]

Early 360's suffered badly from this. Even fitting the 19" wheels from the Challenge Stradale or F430 was enough of a change to throw the ABS module out of whack. Under braking the ABS was liable to cut in at seemingly random times!

 

[gingeh721]

When I first had my rear tyres changed my MSP and ABS started to randomly kick in at slow speeds on roundabouts or acceleration. After the tyres bedded in it didn't happen again. I've had both the front and the rear tyres changed again since then and it hasn't happened since that first time.

I'm wondering if the systems re-learn that everything is normal, regarding the slight increase in rolling radius, and accept all is fine. This could be the case with slight differences due to changes in alloy wheel sizes?

 

[CatmanV2]

The increase is rolling radius from new tyres must be *tiny*. What's the limit? 4mm? So 8mm total?

C

 

[mjheathcote]

The cars sensors can't measure a change in rolling radius, they can only measure rotation speed. It can measure a change in rotation speed of course, relative to the other wheels of course.
MSP and ABS lights most likely due to slippy new tyres for the first few miles.

 

[EXCF350]

As mentioned earlier, have a look at this http://www.maseratilife.com/forums/granturismo/43601-got-msp-failure-light-4.html
Reading it again I think it's more to do with adding bling wheels with very narrow profile tyres but still worth reading in the context of this thread