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Table of Allowable Wheel Speed Error for TCS

Old Guy

Old Guy

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Somewhere on Prime I stumbled across a table which showed the allowable wheel speed error versus model year for the NSX that would not trigger operation of the TCS. I was looking for it again and have not been able to find it. Does anybody have a copy of it or a link to it that they can share?
 
Are those differences based upon the static outside diameter of the OEM wheel and tire sizes or the revolutions per mile for the OEM wheel and tires? Depending on the tolerance of the TCS for error, that may be a problem. For the Bridgestone RE010 tires on the model year 2000, the difference in the static outside diameter back to front is 4.68%; but, the difference in the revolutions per mile is 4.53%.

When you say that you want to be within a few percent, are you implying say +/- 5% of the OEM difference which would only be .05 x 4.53%= +/-.22% or are you suggesting that 4.53% +/- 5% which is a much larger number? I am curious because the 205/45 16 tire options that I am looking at for the front of my 2000 will result in back to front differences of 6.05% and 6.42% based upon revolutions per mile. Right now I don't have a feel for whether that is within the allowable error for the TCS system.

I know that based upon part numbers, the TCS controller changed in model year 1997 and again in 2002. The 1994-96 cars with 16"/17" wheels appear to use the same TCS unit as the first cars with the smaller wheels. I am curious as to whether the TCS unit in the cars up to 2001 has the same tolerance for wheel speed difference (7.75%) as the first cars or whether the coding got changed and they are perhaps less tolerant of wheel speed differences.
 
The explanation I have always read is that the system tolerates several percent change on an absolute scale, which as you point out is much larger than simply a 5% change from OEM. My numbers are admittedly somewhat crude as based on tire sizes rather than actual miles per rotation. I agree that it is likely that Honda considered the actual tire characteristic of significance.

That's an interesting point about the part numbers and makes me question my entire understanding.

Though I still would be surprised if you had an issue with the 205/45-16. I have maintained that it should be preferable to err on the side of larger rear relative to the front and your proposed size does that. My current tires have a 6.44% diameter ratio on my 2000 (215/40-17 & 265/35-18) without any issue. I can look up the rotations per mile but they are ZII*.
[MENTION=3758]nsxtasy[/MENTION], you're the primary source on a lot of this; available to chime in?
 
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Old Guy said:
Are those differences based upon the static outside diameter of the OEM wheel and tire sizes or the revolutions per mile for the OEM wheel and tires?
Click to expand...
It doesn't matter, because they produce the same result.

And those ratios are based on the calculated outer diameters (or, if you prefer, calculated revolutions per mile) of the tire sizes.

Old Guy said:
For the Bridgestone RE010 tires on the model year 2000, the difference in the static outside diameter back to front is 4.68%; but, the difference in the revolutions per mile is 4.53%.
Click to expand...
Only if you're using some figure other than the precise calculations based on the nominal tire sizes. Tire manufacturers may have specs on their websites showing slightly different numbers, but these are just as likely to be due to rounding in the calculations, as they are to be actual measurements of the tires. Either way, differences under 0.2 percent are pretty insignificant compared with some other factors; see below.

As for the TCS controllers, it's also quite possible that there are errors in the part number database. I've heard about this and consider such errors the most likely explanation. (I base this conclusion in part on the existence of differences in part numbers between the automatic and manual transmission for the same year NSX, for which there is no logical explanation I can think of.)

The fact is, there are lots of sources of possible differences in tire dimensions. Different make/model tires labeled with the same size are not necessarily exactly the same size. The difference in diameter between a tire that is brand new with full tread depth, and the same tire that has worn down to the treadwear indicator bars (2/32"), is about 2 percent. And the TCS operation itself undoubtedly has some variation in it; e.g. if the ratio of rear-to-front stock outer diameters is 1.0775 (as on the '91-93) and the system requires that the ratio stay within 5 percent of that figure, it's not like the TCS will never activate with tire size ratios of 1.1274 and will always activate with tire size ratios of 1.1276. So while you can carry out calculations with total precision, there is always a "fudge factor" representing these and other variables.

Although the TCS supposedly operates allowing a ratio tolerance of 5 percent, I've found that if you keep the rear-to-front ratio within 3.5 percent of stock, you shouldn't have any problems with the TCS. Go for the full 5 percent, and you might (or might not).

The calculated ratio of the rear-to-front outer diameters (and of revolutions per mile, which is a mile divided by the tire circumference) on a '94-01 NSX is 1.0465. So theoretically you can use tire sizes with a ratio of 0.9965 to 1.0965 (5 percent difference from stock), but as a practical matter, you shouldn't have any problems if you keep it between 1.0115 and 1.0815 (3.5 percent difference).

Here are calculated ratios for the best 16"/17" tire size combinations:

205/45-16 and 245/40-17: 1.0624
205/45-16 and 255/40-17: 1.0760
215/45-16 and 245/40-17: 1.0465 ('94-01 stock)
215/45-16 and 255/40-17: 1.0598

And for the best 17"/18" tire size combinations:

215/40-17 and 255/35-18: 1.0528
215/40-17 and 265/35-18: 1.0644

The bottom line: You shouldn't encounter any TCS problems with any of these combinations of tire sizes on any year NSX. And don't worry about matching the ratio exactly, since differences of a few percent are not a big deal.

(You can look up the ratio of calculated outer diameters of any two tire sizes using a tire calculator like this one.)

HTH
 
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jwmelvin said:
The explanation I have always read is that the system tolerates several percent change on an absolute scale, which as you point out is much larger than simply a 5% change from OEM. My numbers are admittedly somewhat crude as based on tire sizes rather than actual miles per rotation. I agree that it is likely that Honda considered the actual tire characteristic of significance.

That's an interesting point about the part numbers and makes me question my entire understanding.

Though I still would be surprised if you had an issue with the 205/45-16. I have maintained that it should be preferable to err on the side of larger rear relative to the front and your proposed size does that. My current tires have a 6.44% diameter ratio on my 2000 (215/40-17 & 265/35-18) without any issue. I can look up the rotations per mile but they are ZII*.
@nsxtasy, you're the primary source on a lot of this; available to chime in?
Click to expand...

A quick check on Tire Rack for the ZII Star Spec shows that the ratio for the revolutions per mile in your sizes is 1.064 front/back. Very close to the ratio just based upon diameters.

Your turns ratio of 1.064 is almost identical to the 1.064 and 1.0605 for the BFG Sport Comp 2 and Bridgestone 760 in the 205/45 16 and 245/40 size that I am considering as replacements. I also have a 2000 model year so the fact that you have no TCS issues is good to know.

It is interesting to note that unlike the older RE010, for the more current tires, the front / back turns ratios based on the theoretical diameter of the tire are much closer or essentially identical to the turns ratio based on the tires revolutions per mile.
 
nsxtasy said:
As for the TCS controllers, it's also quite possible that there are errors in the part number database. I've heard about this and consider such errors the most likely explanation. (I base this conclusion in part on the existence of differences in part numbers between the automatic and manual transmission for the same year NSX, for which there is no logical explanation I can think of.)
Click to expand...

For the 1991, the TCS units are probably different, mainly because the TCS for an Automatic interfaces with the A/T Control unit (see page 19-81 and 14-17 in the 1991 Service manual that show connections for A/T cars only). Since the manual cars don't have an A/T control unit, I would have no reason to believe the part numbers are incorrect.
 
Old Guy said:
I know that based upon part numbers, the TCS controller changed in model year 1997 and again in 2002. The 1994-96 cars with 16"/17" wheels appear to use the same TCS unit as the first cars with the smaller wheels. I am curious as to whether the TCS unit in the cars up to 2001 has the same tolerance for wheel speed difference (7.75%) as the first cars or whether the coding got changed and they are perhaps less tolerant of wheel speed differences.
Click to expand...
Actually, the TCS unit part numbers changed in '94 (MT only), '95, '97, and '02. Here are the part numbers for the TCS controller, according to the parts catalog:

39900-SL0-981 or 39900-SL0-982 ('91-93 AT)
39900-SL0-003 or 39900-SL0-023 ('91-94 MT)
39900-SL0-983 ('94 AT)
39900-SL0-033 ('95-96 AT and MT)
39900-SL0-043 ('97-01 AT and MT)
39900-SL0-053 ('02-05 AT and MT)

It's not clear to me why they would change the controller for the '94 AT cars but not for the '94 MT cars. That's why I suspect an error in the part numbers. The alternative explanation is that they didn't get around to changing the controller for the change in tire sizes until the following year.
 
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Would you guys recommend:
205/45/16 and 255/40/17
Or
225/45/16 and 255/40/17

For tracking day tires on 94-01 OEM wheels?
 
piran1 said:
Would you guys recommend:
205/45/16 and 255/40/17
Or
225/45/16 and 255/40/17

For tracking day tires on 94-01 OEM wheels?
Click to expand...
If you plan to also use the tires on the street, I'd definitely get 205/45-16 and 255/40-17.

If this is only for the track and you plan to keep the TCS off, AND if the tires you want to use are only available in the wider front size, then you could consider those sizes.
 
How much does TCS setting off from larger tires affect regular driving? I am curious as to how long it kicks in for or if it just affects those who want peace of mind.
 
When TCS triggers, it is severe. It would not be possible to drive that way; instead, you would have to turn off TCS every time you drive.
 
nsxtasy said:
It doesn't matter, because they produce the same result.

And those ratios are based on the calculated outer diameters (or, if you prefer, calculated revolutions per mile) of the tire sizes.


Only if you're using some figure other than the precise calculations based on the nominal tire sizes. Tire manufacturers may have specs on their websites showing slightly different numbers, but these are just as likely to be due to rounding in the calculations, as they are to be actual measurements of the tires. Either way, differences under 0.2 percent are pretty insignificant compared with some other factors; see below.

As for the TCS controllers, it's also quite possible that there are errors in the part number database. I've heard about this and consider such errors the most likely explanation. (I base this conclusion in part on the existence of differences in part numbers between the automatic and manual transmission for the same year NSX, for which there is no logical explanation I can think of.)

The fact is, there are lots of sources of possible differences in tire dimensions. Different make/model tires labeled with the same size are not necessarily exactly the same size. The difference in diameter between a tire that is brand new with full tread depth, and the same tire that has worn down to the treadwear indicator bars (2/32"), is about 2 percent. And the TCS operation itself undoubtedly has some variation in it; e.g. if the ratio of rear-to-front stock outer diameters is 1.0775 (as on the '91-93) and the system requires that the ratio stay within 5 percent of that figure, it's not like the TCS will never activate with tire size ratios of 1.1274 and will always activate with tire size ratios of 1.1276. So while you can carry out calculations with total precision, there is always a "fudge factor" representing these and other variables.

Although the TCS supposedly operates allowing a ratio tolerance of 5 percent, I've found that if you keep the rear-to-front ratio within 3.5 percent of stock, you shouldn't have any problems with the TCS. Go for the full 5 percent, and you might (or might not).

The calculated ratio of the rear-to-front outer diameters (and of revolutions per mile, which is a mile divided by the tire circumference) on a '94-01 NSX is 1.0465. So theoretically you can use tire sizes with a ratio of 0.9965 to 1.0965 (5 percent difference from stock), but as a practical matter, you shouldn't have any problems if you keep it between 1.0115 and 1.0815 (3.5 percent difference).

Here are calculated ratios for the best 16"/17" tire size combinations:

205/45-16 and 245/40-17: 1.0624
205/45-16 and 255/40-17: 1.0760
215/45-16 and 245/40-17: 1.0465 ('94-01 stock)
215/45-16 and 255/40-17: 1.0598

And for the best 17"/18" tire size combinations:

215/40-17 and 255/35-18: 1.0528
215/40-17 and 265/35-18: 1.0644

The bottom line: You shouldn't encounter any TCS problems with any of these combinations of tire sizes on any year NSX. And don't worry about matching the ratio exactly, since differences of a few percent are not a big deal.

(You can look up the ratio of calculated outer diameters of any two tire sizes using a tire calculator like this one.)

HTH
Click to expand...

Based on our calculations...I can put either 215/35 and 275/35 or 215/40 and 275/40 on my 18" wheels and be within 3.5% of original front to back % and not trigger TCS.

Got it.

Will report back when I install and see how they roll.
 
Speedmaster said:
Based on our calculations...I can put either 215/35 and 275/35 or 215/40 and 275/40 on my 18" wheels and be within 3.5% of original front to back % and not trigger TCS.
Click to expand...
On your '95, that's correct.

Here are a couple of other reasons to go with the lower profile sizes. I would avoid the 215/40-18 fronts as there's a good chance they will rub; the 215/35-18 shouldn't. The 275/40-18 rears will also throw off your speedometer by almost 8 percent, while the 275/35-18 should only do so by 3.5 percent.

Good luck.
 
The Michelin Pilot Sport 4S is by far the best tire available in those sizes.

Personally, I would go with a 255/35-18 or 265/35-18 on the rear, for the best handling with a slightly smaller stagger compared with the overwide 275/35-18. (Even though the 255 is the closest match to the ratio of outer diameters of the stock sizes, any of these three should be okay for TCS with the 215 fronts, and shouldn't have rubbing problems.)
 
I have some real world examples as I've pushed 7.75% threshold limit on my 91 over the early years. Ultimately I removed the TCS computer entirely because I found it more trouble than it was worth but that's a different thread. In a nutshell the closer you get to the limits of that ratio the greater the chances your TCS will "freak out". For example going over freeway dividing line bots dots often threw mine into a hissy fit but was fine on regular freeway speeds. Big puddles in the rain and rotted out, pitted roads had a similar effect.

I would propose to stay well within the threshold.
 
Most people who have tried 225/35-18 with stock fenders and wheel well liners have found that it rubs at least some of the time. 215/35-18 generally doesn't. So that's one more thing to consider.
 
Kendo Slice back in the ring!
 
I just purchased a set of factory 16/17 7-spokes. They are mounted with 225/40-16 and 255/40-17 Tires. Based on the math, they are very close to my 92’s original circumference. I am a little worried about front rub at lock, but I expect to be ok with the TCS.

For what I paid for the set, the tires were nearly free, so if I experience rub / TCS issues, I can still sleep at night over my purchase.
 
what tires?
 
The good news is, you shouldn't have any TCS problems with those sizes. The bad news is, those are discontinued all-season tires, and unless you expect freezing temperatures in San Diego, they won't give you the kind of traction and handling your car is capable of. You'll be a whole lot better off with summer tires. There are lots of great summer tires available in 16"/17" sizes. If you want the best grip on dry roads, consider the Hankook Ventus R-S4 in 205/45-16 and 245/40-17 or 255/40-17, the Falken Azenis RT660 in 215/45-16 and 245/40-17 or 255/40-17, or the BFGoodrich g-Force Rival S 1.5 in 215/45-16 and 245/40-17 or 255/40-17. If you also care about treadlife, purchase price, and/or grip in rain, go for the still grippy Continental ExtremeContact Sport in 205/45-16 and 245/40-17 or 255/40-17.

As you aptly note, the all-season tires were virtually free, so you're really not out anything by having bought them.
 
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