TC detecting slip due to bigger diameter than OEM wheels in the front

[Ravi]

Quick question to the owners, does the old ABS/TCS module in the 91 cars have issue with TCS cutting in for slip when you have front wheels which are quite different in diameter from OEM specs ? I know modern cars have a algorithm where by it quickly self learns any change in wheel size as not to be slip and they work just fine ! I've read a bit on this at a few threads but I cant confirm this issue. Has anyone had the same issue before ?

 

[jwmelvin]

Yes, the explanation is that the ratio is programmed (91-93 = 7.75%; 94-01 = 4.65%; 02-05 = 5.3%) and too much deviation from that will trigger TCS. I do not know about ABS.

This is also the reason that I have a theory that larger rear tires (relative to the correct ratio to the front) are better than smaller, as it makes the TCS think the rear tires are rotating slower. As slip occurs, there is more headroom before the TCS triggers. And this headroom also helps accommodate rear tire wear.

 

[91 X]

I've run 17/18 combo on my previous two 91-92 NSX's with no issues ...

 

[jwmelvin]

I've run 17/18 combo on my previous two 91-92 NSX's with no issues ...

Yes, there's nothing wrong with a 17/18 combo as long as the tire sizes are consistent with the ratio that the TCS expects. For example, a typical size of 215/40R17 and 265/35R18 has a rear:front diameter ratio of 1.064:1, and that 6.4% oversize in the rear is well within the +/- ~5% that the TCS will tolerate from the expected 7.75%.

 

[Ravi]

Yes, there's nothing wrong with a 17/18 combo as long as the tire sizes are consistent with the ratio that the TCS expects. For example, a typical size of 215/40R17 and 265/35R18 has a rear:front diameter ratio of 1.064:1, and that 6.4% oversize in the rear is well within the +/- ~5% that the TCS will tolerate from the expected 7.75%.

A bit delayed with the reply, But yeah I actually work with ABS algorithm development and almost all new cars that I work on with have a code which learns fairly quickly even if we had a bigger wheels upto a certain threshold.
I was going to pick up a car which supposedly had the fuse for the ABS/TC pulled out to prevent the issue with mismatched wheels. Its a shame the deal fell through so I do not really know if that was the only reason for the TC acting up
I appreciate your help though, made my decision on the car a little easier !