Tire guys installed the wrong size.

[ERicincal]

While at the tire shop, the attendent mis-heard what I said, and wound up installing a 255/45/17 tire on my car. (front size is stock 215/40/16- 80%wear)
I have read the posts at: http://www.nsxprime.com/ubb/Forum1/HTML/005742.html

and I am reading that changing the tire sizes can adversely affect the TCS. I was going around a turn today, not terribly fast, but as I accelerated out of the turn the TCS, was limiting my throttle inputs.

This may have been becuase the tires are new and were slipping, but I am wondering based on what I read, is this what happens when you increase the rear tire size? will this increased size continue to cause the TCS on during somewhat spirited driving? do you guys think I should I go get them replaced with the 245 /45 /17? and if I keep them, will the handling change? more understeer?

thanks for your help.

ps.. sorry for the multiple post, I accidently posted in the wrong forum.

 

[nsxtasy]

Originally posted by ERicincal:
While at the tire shop, the attendent mis-heard what I said, and wound up installing a 255/45/17 tire on my car. (front size is stock 215/40/16- 80%wear)

I assume you are using the stock front size, which is 215/45ZR16 (not 40) on a '94-01 car.

The 255/45ZR17 is 5.34 percent larger in outer diameter than stock. Because you are changing the outer diameter in the rear by more than 5 percent, which changes the front-to-rear ratio by the same amount, you are having TCS problems caused by using that tire size.

Even the 245/45ZR17 which you ask about is 3.9 percent larger, which starts to get marginal and may cause TCS problems if the front is worn more than the rear.

I would recommend finding a rear tire with a lower aspect ratio, either the stock 245/40ZR17 or even a 35 aspect tire.

 

[Andrie Hartanto]

I have to disagree with Ken on this one. A Bigger rear should not affect the TCS. I used 275/40/17 with 215/40/16 before with no problem.

Bigger rear, can fool the TCS computer in saying that the rear tire spin less than it should be, and that mean it don't slip. Smaller rear, on the other hand, means the rear tire spins more than it should be (compare to the front). thus the TCS thinks it is slipping, and kicks in.

Most likely on your case is because it is new tire, once the realease mold is gone, the grip should be there.

That being said, 255/45/17 is much larger than stock. I would not accept this tire for tire choice for the NSX.

 

[ERicincal]

whoops... typo. Yes.. front tire is stock, 80% treadware left.

"Even the 245/45ZR17 which you ask about is 3.9 percent larger, which starts to get marginal and may cause TCS problems if the front is worn more than the rear."-

since the rear tires wear out so fast, (4 to 1 ) compared to the fronts, will the TCS issue go away?

[This message has been edited by ERicincal (edited 15 August 2002).]

 

[nsxtasy]

Originally posted by Andrie Hartanto:
I have to disagree with Ken on this one. A Bigger rear should not affect the TCS.

It most certainly does - but it depends on HOW MUCH bigger the outer diameter of the rear tire is than stock, assuming that the front tire size is stock.

Originally posted by Andrie Hartanto:
I used 275/40/17 with 215/40/16 before with no problem.

That's because (a) the outer diameter of the 275/40-17 is significantly smaller than that of the 255/45-17 that are under discussion, and (b) the STOCK rear outer diameter on your '92 is already larger than on ERicincal's '94-01. For Andrie, the 275/40-17 is 3.23 percent larger than '92 stock, which is why it doesn't cause TCS problems. (That size would be 3.82 percent larger than ERinical's '94-01 stock, which is somewhat borderline, but probably okay.) But the 255/45-17 is 5.34 percent larger than '94-01 stock, which will definitely cause problems with the TCS. As you can see.

Originally posted by ERicincal:
since the rear tires wear out so fast, (4 to 1 ) compared to the fronts, will the TCS issue go away?

I wouldn't count on it happening. I would replace the rear tires with a size that works with the TCS, 40 aspect ratio or lower.

[This message has been edited by nsxtasy (edited 15 August 2002).]

 

[Andrie Hartanto]

Originally posted by nsxtasy:
That's because (a) the outer diameter of the 275/40-17 is significantly smaller than that of the 255/45-17 that are under discussion, and (b) the STOCK rear outer diameter on your '92 is already larger than on ERicincal's '94-01. For Andrie, the 275/40-17 is 3.23 percent larger than '92 stock, which is why it doesn't cause TCS problems. (That size would be 3.82 percent larger than ERinical's '94-01 stock, which is somewhat borderline, but probably okay.) But the 255/45-17 is 5.34 percent larger than '94-01 stock, which will definitely cause problems with the TCS. As you can see.

You forgotting one thing. I also have smaller fronts, 215/40/16.

 

[nsxtasy]

Originally posted by Andrie Hartanto:
You forgotting one thing. I also have smaller fronts, 215/40/16.

So your fronts are 1.3 percent smaller than stock; your rears are 3.2 percent larger than stock. Thus you are changing the front-to-rear ratio of the outer diameters by 4.5 percent. Yes, it's borderline, but still below the 5 percent nominal threshold for the TCS to function properly. When you go over that threshold - as ERicincal is doing with the 255/45-17 in the rear - it virtually guarantees problems with the TCS, which is what he's experiencing.

 

[Andrie Hartanto]

sorry, double post

[This message has been edited by Andrie Hartanto (edited 15 August 2002).]

 

[Andrie Hartanto]

Originally posted by nsxtasy:
So your fronts are 1.3 percent smaller than stock;

Ken, how did you get 1.3% smaller than stock. Enlighten me with your Math please.
The stock O.D. mathemathically is 23.62"
The 215/40/16 O.D. is 22.77"
1.3% of 23.62" is 0.307"
23.62-0.307=23.313

According to my calculation, my fronts are 3.58% smaller. The Rear are 3.82% bigger.

Right now I am using:

215/40/16 front Which is 3.58% smaller than stock.
245/45/17 which is 3.9% bigger.

And I have no problem whatsoever.

The key is to understand TCS. The TCS only kicks in if it senses the rear tire rotating faster than the front. By using bigger rear tire than stock, the TCS don't sense this. TCS doesn't care if the rear spins slower than the front. Cause that means the rear tires don't slip!!

hehehe, let engineer do the calculation...

 

[nsxtasy]

Originally posted by Andrie Hartanto:
Ken, how did you get 1.3% smaller than stock. Enlighten me with your Math please.

Sure, I'll be happy to. (Your number for the outer diameter of the stock front tire appears to be wrong, which is why you're coming up with the wrong result.)

The outer diameter can be calculated as wheel diameter plus twice the sidewall height. For example, on a 205/50-15, the OD = 15 + 2 x (205 * .50 / 25.4) = 23.07087 inches. You can use the same calculation for all the sizes. Alternatively, if you don't want to bother, you can just enter both sizes (stock and modified) into the tire calculator here to find the percentage difference.

Acura has told us that if the ratio of the front outer diameter to the rear outer diameter changes by more than 5 percent, TCS will not work. More on why below.

METHOD 1 - CALCULATING PERCENT CHANGES IN FRONT AND REAR

FRONT
-----

1. OD of '92 stock 205/50-15 is 23.07087 inches (NOT 23.62 inches)

2. OD of your 215/40-16 OD is 22.77165 inches

Percentage difference = 100 * (22.77165 - 23.07087) / 23.07087 = 1.3 percent smaller

REAR
----

1. OD of '92 stock 225/50-16 is 24.85827 inches

You had said that you are using 275/40-17, but now you say that you are using 245/45-17. (Trying to make things more difficult, are we?

) We can calculate it for either of these sizes.

2a. OD of your 275/40-17 OD is 25.66142 inches

Percentage difference = 100 * (25.66142 - 24.85827) / 24.85827 = 3.2 percent larger

2b. OD of your 245/45-17 OD is 25.6811 inches

Percentage difference = 100 * (25.6811 - 24.85827) / 24.85827 = 3.3 percent larger

With either of these sizes, the front-to-rear ratio changes by less than 5 percent, because the front is 1.3 percent smaller and the rear is 3.2 to 3.3 percent larger.

METHOD 2 - CALCULATING ACTUAL FRONT-TO-REAR RATIO

If you like, you can calculate the actual front-to-rear ratio of outer diameters, and see that you are changing it by less than 5 percent:

Stock = 23.07087/24.85827 = 0.928096
Andrie's, using 275/40-17 rear = 22.77165/25.66142 = 0.887389
Percent difference = 100 * (0.887389 - 0.928096) / 0.928096 = -4.4 percent

Stock = 23.07087/24.85827 = 0.928096
Andrie's, using 245/45-17 rear = 22.77165/25.6811 = 0.886709
Percent difference = 100 * (0.886709 - 0.928096) / 0.928096 = -4.5 percent

Again, as you can see, with either of these sizes, the front-to-rear ratio changes by less than 5 percent.

CONCLUSION

The key is indeed to understand TCS. TCS is programmed to look for a difference in the rate of rotation between the front and the rear that is different from the stock normal difference when cruising. The stock normal difference when cruising is the difference in the outer diameters. If you change the outer diameters sufficiently - defined as more than 5 percent in ratio - the difference in the rate of rotation, front vs rear, will ALWAYS be more than 5 percent, not just when the tires are slipping. So TCS will think that you are always slipping your tires (even though you're not) and will retard engine power to compensate. THAT'S why you need to keep the front-to-rear ratio similar to stock, within 5 percent.

You can do the same math with ERicincal's sizes and you'll find that his front-to-rear ratio changes by more than 5 percent.

[This message has been edited by nsxtasy (edited 15 August 2002).]

 

[Andrie Hartanto]

Ken, Why do you use 205/50/15 for the stock O.D calculation, when we are considering it for the 215/45/16 is beyond me. My number is based on the 215/45/16 size.

I guess your understanding of the way the TCS works is different than me.

 

[nsxtasy]

Originally posted by Andrie Hartanto:
Ken, Why do you use 205/50/15 for the stock O.D calculation, when we are considering it for the 215/45/16 is beyond me. My number is based on the 215/45/16 size.

Because your car is a '92, and therefore your TCS is set up to look for variances from the stock '92 sizes, not the later sizes.

ERicincal's car is apparently a '94-01, so his TCS is set up to look for variances from the stock sizes for those years.

 

[ERicincal]

good lord...

my head is spinning.. and I still am not sure what to do.. anyone one want to break this tie?

 

[nsxtasy]

Replace the 255/45-17 tires. (Even Andrie said so.)

Get something with an outer diameter closer to stock.

[This message has been edited by nsxtasy (edited 16 August 2002).]