tire size question

[nsxhk]

Hello everyone,

I am running 205/50/16 and 245/40/17 Dunlop D01J on the oem 16/17 wheels and the TCS comes on if I go over 10km/hour.

Will changing the fronts to 225/45/16 solve the TCS problem? I don't quite understand how to calculate the 5% TCS tolerance.
http://tyre.dunlop.co.jp/tyre/lineup/sport/index.html

Thnx in advance.

Henry.

 

[Enzo]

Henry,

FYI, I used 205/45/16 (Pirelli PZero Yellow) on my old 16" wheels without any problems with TCS ! Just too much understeer for my taste !

David

 

[nsxtasy]

Originally posted by nsxhk:
Will changing the fronts to 225/45/16 solve the TCS problem? I don't quite understand how to calculate the 5% TCS tolerance.

Hi Henry,

Here's how.

First, start with a tire calculator such as the one at http://www.powerdog.com/tiresize.cgi and use it to calculate the percentage difference in the outer diameter from stock.

We'll assume that your car is a '91-93. Here is how the tire sizes you're both discussing look, using the tire calculator to determine the percent difference in the outer diameter from the stock size:

Rear
stock 225/50-16
current 245/40-17 0.6 percent smaller

Front
stock 205/50-15
current 205/50-16 4.3 percent larger
proposed 225/45-16 3.9 percent larger
David's 205/45-16 0.8 percent larger

When you change the size in the front and the rear, the change in the front-to-rear ratio is approximately equal to the difference in the percentage of change. For example, when you make the rear tires 0.6 percent smaller, and the front tires 4.3 percent larger, you're changing the front to rear ratio by approximately 4.9 percent, and that's too big - it's enough for the TCS to kick on.

(The threshold is supposedly 5 percent, but there are a lot of other variables that make the exact measurements fluctuate. Different models of tire may have slightly different outer diameter, and even the amount of tread on the tire can change the measurement of the outer diameter by 2 percent from the new tread depth of 10/32" to the treadwear indicator bars which show at 2/32".)

If you're going to continue to use those same rear tires, which are 0.6 percent smaller than stock, then you probably ought to use a front tire size whose change is no more than about 3 percent different from that - in other words, a front tire size whose outer diameter is somewhere between 3.6 percent smaller than stock and 2.4 percent larger than stock.

I would not use the 225/45-16 because it's still too big and doesn't fall within that range. David's 205/45-16 would work. But why not use the '94+ stock size of 215/45-16 (2.4 percent larger)? That way, you can use those terrific OEM tires like the Yokohama A022H. And you'll be certain that the TCS works. (I use the larger OEM tire sizes on my '91 and the TCS works fine.)

[This message has been edited by nsxtasy (edited 09 July 2002).]

 

[nsxhk]

Hi Ken,

Thnx for such a detail explanation. The car is a '91 with oem 16/17 wheels.

I am still kind of confused about the 5% tolerance thing. According to: http://www.powerdog.com/tiresize.cgi , if you input the oem 15/16 tire size, the front-to-rear ratio is 7.7%, which is quite a bit over the 5% tolerance.

I then input the oem 16/17 tire sizes and the front-to -rear ratio is 4.7%, quite borderline to the supposed 5%.

Hmm.....

Further more, I punch in a tire setup that I have been running for 3 years, 215/40/17 and 255/35/18, the ratio is 5.3% but my TCS never had any problem with that setup.

Hmmmm...........

I input my existing tire size, 205/50/16 and 245/40/17. The front-to-rear ratio is only 2.7%! That should be well inside the 5% tolerance, but the TCS doesn't like it.

So.... I'm lost.... I'm starting to wonder about what this '5% tolerance' is?

Henry.

 

[nsxtasy]

Hi Henry,

Okay, you're coming at it a different way - which is also valid.

I had been using the calculator to calculate the change from stock in the front, and the change from stock in the rear; the difference between the two is the change in the front to rear ratio.

You are using the calculator to calculate the actual front to rear ratio, and that's fine too. Here's how to do it that way, and where the 5 percent tolerance comes in.

As you note, the stock front to rear ratio has the rear 7.7 bigger than the front.

If you use other sizes, the TCS won't work if the ratio is off by more than 5 percent. So if the rear is 12.7 percent or more bigger than the front - or if the rear is 2.7 percent or less bigger - then the TCS won't work. As I mentioned, you don't want to cut it TOO close, so I would suggest making the front to rear ratio so that the rear is somewhere between 4 percent and 11 percent bigger than the front. That keeps the ratio within 3.7 percent of stock, instead of 5 percent.

Using this approach:

Originally posted by nsxhk:
I then input the oem 16/17 tire sizes and the front-to -rear ratio is 4.7%

...which is fine, because it's between 4 percent and 11 percent.

Originally posted by nsxhk:
Further more, I punch in a tire setup that I have been running for 3 years, 215/40/17 and 255/35/18, the ratio is 5.3%

...which is also fine, because it's between 4 percent and 11 percent.

Originally posted by nsxhk:
I input my existing tire size, 205/50/16 and 245/40/17. The front-to-rear ratio is only 2.7%!

And now you can see why the TCS doesn't work, because the front-to-rear ratio is outside the 4 to 11 percent range.

Hope that explains it; if not, feel free to ask.

 

[HUNTJAMES]

Originally posted by nsxtasy:
Hi Henry,

Okay, you're coming at it a different way - which is also valid.

I had been using the calculator to calculate the change from stock in the front, and the change from stock in the rear; the difference between the two is the change in the front to rear ratio.

You are using the calculator to calculate the actual front to rear ratio, and that's fine too. Here's how to do it that way, and where the 5 percent tolerance comes in.

As you note, the stock front to rear ratio has the rear 7.7 bigger than the front.

If you use other sizes, the TCS won't work if the ratio is off by more than 5 percent. So if the rear is 12.7 percent or more bigger than the front - or if the rear is 2.7 percent or less bigger - then the TCS won't work. As I mentioned, you don't want to cut it TOO close, so I would suggest making the front to rear ratio so that the rear is somewhere between 4 percent and 11 percent bigger than the front. That keeps the ratio within 3.7 percent of stock, instead of 5 percent.

Using this approach:

And now you can see why the TCS doesn't work, because the front-to-rear ratio is outside the 4 to 11 percent range.

Hope that explains it; if not, feel free to ask.

I have the same problem when I put new rear tires on. Here are my Tire numbers;

235/40-17 3.7 in 12.2 in 24.4 in 76.7 in 827 / mile 0.0%
205/50-15 4.0 in 11.5 in 23.1 in 72.5 in 874 / mile -5.5%
225/35-18 3.1 in 12.1 in 24.2 in 76.0 in 833 / mile -0.8%
225/50-16 4.4 in 12.4 in 24.9 in 78.1 in 811 / mile 1.9%

 

[nsxtasy]

HUNTJAMES,

Your 225/35-18 rear tires are actually smaller in outside diameter, and narrower in treadwidth, than your 235/40-17 front tires.

This is highly unusual, to say the least. The TCS is definitely not going to work with these sizes, and the handling is probably going to suffer noticeably as well.

I think the size tires that most people are using with 17" front and 18" rear wheels are front 215/40-17 and rear 255/35-18 or 265/35-18.

 

[HUNTJAMES]

Originally posted by nsxtasy:
HUNTJAMES,

Your 225/35-18 rear tires are actually smaller in outside diameter, and narrower in treadwidth, than your 235/40-17 front tires.

This is highly unusual, to say the least. The TCS is definitely not going to work with these sizes, and the handling is probably going to suffer noticeably as well.

I think the size tires that most people are using with 17" front and 18" rear wheels are front 215/40-17 and rear 255/35-18 or 265/35-18.

I just bought it and the kid that put it together didn't know what he was doing. Too many dollars not enough sence. Like I said the rears are brand new! Is there a way to match the rears with something that works?

 

[nsxtasy]

Originally posted by HUNTJAMES:
Like I said the rears are brand new! Is there a way to match the rears with something that works?

Well... those fronts are REALLY BIG (I'm surprised if they don't rub the wheel wells) and the rears are REALLY SMALL. So you're going to have to replace at least one or the other. The rears would work with the stock 205/50-15, but I don't think there's anything that will fit on a 17" front wheel that will be small enough. I think the smallest 17" size tire you can get would be a 205/40 and that's questionable for getting the TCS to work.

I think your best bet would be to ditch the new rear tires (sorry) and get a different size. If you're looking to find something that will work with those really big front tires you currently have, a 275/35-18 (or even 285/35-18, although that's REALLY wide) should work with the TCS.

Maybe Chris SoS has some additional suggestions here...

 

[nsxhk]

Ken,

Thnx for clarification. I see the light!

I think this "4%-11%" front-to-rear ratio should be added to the faq, Lud?

I have now narrowed down my tire choices for the oem 16/17 wheels:

Yokohama A038
215/45/16
245/45/17
8.7% diff

Yokohama A048
225/45/16
255/40/17
4.4% diff

Thnx Ken

Henry.

 

[Andrie Hartanto]

Originally posted by HUNTJAMES:
I just bought it and the kid that put it together didn't know what he was doing. Too many dollars not enough sence. Like I said the rears are brand new! Is there a way to match the rears with something that works?

225/35/18, sounds like the wheel width is in the range of 7" - 8". which is very skinny and the max size you can get away with is 245. This is not the right wheels for the rear of NSX. It will look very funny. I would suggest to get rear wheel width of at least 9" width to compensate your pretty wide front tires.

 

[nsxtasy]

Originally posted by Andrie Hartanto:
225/35/18, sounds like the wheel width is in the range of 7" - 8". which is very skinny and the max size you can get away with is 245. This is not the right wheels for the rear of NSX. It will look very funny. I would suggest to get rear wheel width of at least 9" width to compensate your pretty wide front tires.

Andrie, I'm not so sure about that. You're assuming that the wheels are narrow because the tire guy knew enough to match the tread width to the wheel width. But if the tire guy was stupid enough not to know how to match the outer diameter on the tire size, he may have also been stupid enough not to match the tread width to the wheel width. I bet the wheels he has are already wider than that!

 

[Andrie Hartanto]

Ken, you might be right. I assume the tire guy is smart enough not to mount 225 in 9" width wheels. I guess, there is a possibility of him being that stupid.