Garth S

One can change the wheel width from 9" to 11" and not make any significant impact on overall tire diameter (<0.5%) ... that's why I initially stated that wheel width is a non issue re the ABS.
The tire overall diameter directly influences the frequency picked up by the ABS sensor(s) ..... and there is ~5% variance in the two tires in question.

okindao

[QUOTE=Garth S;4578561]One can change the wheel width from 9" to 11" and not make any significant impact on overall tire diameter (<0.5%) ... that's why I initially stated that wheel width is a non issue re the ABS.
The tire overall diameter directly influences the frequency picked up by the ABS sensor(s) ..... and there is ~5% variance in the two tires


iToyo has a chart that shows rev's per miles my original tires were
Original
Fronts 235 40 17's = 852
Rears 255 40 17's = 828

Difference of = 24

Now
Fronts 235 40 17's = 852
Rears 275 40 17's = 812

Difference of = 40

If i switch my fronts to

Fronts 235 45 17's = 834
Rears 275 40 17's = 812

Difference of = 22

Seems to put me back to an even less difference that my original set up , seems that should work , only question is will the turn in be harmed by going to a 45 versus a 40 aspect/profile ??

Dennis

Trevor-uk

If you are worried about turn in with a taller profile front tyre, focus on the rear setup and replace with 275/35 - it will achieve the same effect of reducing the variation in revs/mile to 6 (about 0.7% - perfect).

okindao

toyo does not make a 275 35 17 the only 275 they make is the 40 17

Thanks but .......seems the only option is to go to 35 profile in front

Dennis

Trevor-uk

I'm sure you meant "go to 45 profile in front" and if so I think you're probably right (I don't think anybody makes a 275/35/17 but Toyo certainly make a 235/45/17).

Smiles

Just out of curiosity, why did you go for the 275 40 17's in the rear?

okindao

Friend with a 95 c2 coupe had 275's and just the concept of wider must be grippier/ better ........now unless want to loose the abs with track tires my next set of frronts will be 235 45 17;'s versus the 235 40 17's and according t the toyo calucations i will be nearer to th original diferential in wheel speed for both front and rears

Dennis

Wilder

+1. Width or even size is not the issue; It's the difference in size between fronts and rears that could be causing you grief. You need to be looking for OD or "overall diameter" size which is what dictates RPMs. IIRC, there should be no more than a ~5% variance in OD from front to rear but the ideal scenario is to have fairly well matched diameters all around as per the OE specs.

Greg Fishman

Dennis,
Did you double check the abs sensors on the hub to make sure they haven't been damaged or come loose?

I have run tires up to an 1" difference in diameter with no ABS issues.

okindao

I am assuming that they ar finein that when i restart the car the abs light goes off and does not come on until i have gotten to atleast 45mph ,,,,, then the light comes on, guess i could put on my street tires and drive for a while and if the light does not coe on would prove that it is not the sensor

thanks
Dennis

Martin S.

Your front to rear rolling radius delta is 4.91%. This may be too much for the ABS computer to handle. I have an EXCEL spread sheet I will send you where you can plug in the width of the tire in mm (235), the sidewall hight as a percentage of tread with expressed in %age (40) and wheel diameter (17"). Once this is done, the front to rear rolling radius delta in %age appears, as if by magic!!!

send an e-mail to mfschacht@gmail.com and I'll send the spread sheet to you. I am certain the problem is...the front tires are too short at 40%. You may have to go to 45%.

No worries, there are plenty of cars that use a 235/40/17 tire...GTIs, some BMW cars...you can always sell them.

Don't tell anyone, but I recently bought a pair of 235/40 RA-1 tires by mistake...I sold them to a GTI guy and replaced them with the correct 235/45/17 fronts to go with my 275/40/17 rears. This equates to a 1.3% delta front to rear, no problem for the 993 ABS.

okindao

i agree 100 % when i go to the toyo website and compare the difference of the 45's versus the 40's for the front it seems to make up enough of the difference

iToyo has a chart that shows rev's per miles my original tires were
Original
Fronts 235 40 17's = 852
Rears 255 40 17's = 828

Difference of = 24

Now
Fronts 235 40 17's = 852
Rears 275 40 17's = 812

Difference of = 40

If i switch my fronts to

Fronts 235 45 17's = 834
Rears 275 40 17's = 812

Difference of = 22


thanks for confirming it, looks like i will buy a set of 45''s when my 40's weaqr out ,maybe one more track session !!!!

Thanks
Dennis