Going up to 17" wheels Question

[mlc]

I am going up to 17" wheels and have a question. The overall tire diameter and RPM of the tires is very close but how much will it affect the speedometer?

16" RPM 837

17" RPM 843

These are from Tirerack.

Are well talking a 1 or 2 MPH or 5 to 6 MPH :yikes: . It can make a BIG difference on the highway for sure.

Or is it measured at the tranny and wont change it at all.


Thanks.
Kevin

[kevos2k]

you wont notice it...

what are the tire sizes check it out here

http://www.miata.net/garage/tirecalc.html

i have had tons of different sizes on my cars over the years its generally not enough to warrant worry unless you are always watching your speed and want to be withing a mile of the limit but even then i wouldnt worry

[mlc]

I am a 8 to 9 over on the highway guy but if that becomes 14 to 15 you can see that might be a problem.

Kevin

[mlc]

Hell, I put in the sizes into the calculator and the speedo will read slightly slower.

Thanks.

Kevin

[mlc]

Okay next question. The stagger of the tires. The OEM RE050 17" suposedly had a very small width front tire. So would you put a 255 rear tire on the car to keep the stagger ratio the same?

So it would be

215/45-17 front
255/40-17 rear verse 245/40-17

Kevin

[4U2NV]

If you stick with the stock sizes you will maintain the factory intended stagger.

[mlc]

I am not sure. Tirerack shows a tread width of 6.7" for the front verse 9" for the rear for the OEM's. Almost all of the other non OEM tire show a front tread width of between 7.6" to 7.9" front and 8.8" and 8.9" rears. Is this just a typo on Tirerack or do you need to increase the rears inorder to keep the stagger ratio?

God knows on a MY00 I don't need any more oversteer.

Kevin

[4U2NV]

You can check with others, but the problem you are referring to was due to AP1 using stock Bridgestone S-02 tires. The S-02 tires were designed for the S2000 by Bridgestone and they had a larger contact patch than other tires of the same size. You may have noticed when you went to buy new S-02 tires that there was a "Honda" and a "Porsche" version. They were two different tires even if they were sized the same. AP2 factory sized tires do not have this anomaly.

Standard sized tires for your AP2 rims should be just what the doctor prescribed.

[desmo4]

On an AP1 putting 17" wheels will actually bring the speedo closer to reality. As The Ap1 speedo's are about 3% fast. I proved it by comparing both 16 and 17 against my gps..

Jonathan

[repiv]

16" RPM 837

17" RPM 843
This is an insignificant difference. One should also point out and clarify that the "RPM" discussed here is NOT revolutions per minute. It's actually revolutions per MILE.
Mathematically, the difference when going from 837 to 843 can be represented in terms of PERCENTAGE. In this case, that would be .............................
(843 - 837) / 837 X 100 = 0.7% That's LESS THAN 1 percent difference. So at 70 mph, you're looking at a difference of less than 1/2 mph. You'll get more than this kind of difference from a brand new tire to one that is down to the wear bars. This is pretty small stuff.

Stock AP2 tire sizing is 215 and 245. Stock CR sizing is 215 and 255. As Jason indicated, don't concern yourself so much about "tread width" as reported by tire manufacturers. The OEM SO2s were an oddball, specially designed tire made by Bridgestone for Honda just for the S2000 back in the day. Also, some "tread width" charts can be confusing as they are talking about "cross sectional tread width". You should be more concerned about actual width of the tread contact patch on the ground. Some charts will give tread width that includes a part of the tread to sidewall interface that doesn't even touch the ground.
Many people have been running 225 and 255 for years. Myself, I'm running 215 and 255 for my winter tires. The difference is so minor from one combination to another that it's simply not worth worrying about. A competent driver can easily compensate for these minor differences without even putting more than 2 neurons into it. It's not different when all of us mentally adjust our driving styles to compensate for worn rear tires when we've got good tread on the front. (Generally, most of us wear out rear tires faster than fronts, at a rate of 2 to 1 for a street driven car.)

[repiv]

On an AP1 putting 17" wheels will actually bring the speedo closer to reality. As The Ap1 speedo's are about 3% fast. I proved it by comparing both 16 and 17 against my gps..

Jonathan
It's not the wheels that alter speedo readings. It's the overall tire diameter and only on the rear as that's the end that the speedo pickup senses. If you have a 3% error on your speedo with your AP1 rims and tires, then going with a 16" tire that is 3% larger in diameter will correct that, if such a size could be found. (eg. If you could get a 245/50/16 tire for the rear, your speedo error would have been nullified.) It is likely that you had to go to 17" rims so that you could have a better selection of 17" tires that were closer to the desired diameter for your speedo error.
Differences in speedo error also depend on the car. Mine was only 1% out.

[rys2kmk]

Stock AP2 tire sizing is 215 and 245. Stock CR sizing is 215 and 255. As Jason indicated, don't concern yourself so much about "tread width" as reported by tire manufacturers. The OEM SO2s were an oddball, specially designed tire made by Bridgestone for Honda just for the S2000 back in the day. Also, some "tread width" charts can be confusing as they are talking about "cross sectional tread width". You should be more concerned about actual width of the tread contact patch on the ground. Some charts will give tread width that includes a part of the tread to sidewall interface that doesn't even touch the ground.
Many people have been running 225 and 255 for years. Myself, I'm running 215 and 255 for my winter tires. The difference is so minor from one combination to another that it's simply not worth worrying about. A competent driver can easily compensate for these minor differences without even putting more than 2 neurons into it. It's not different when all of us mentally adjust our driving styles to compensate for worn rear tires when we've got good tread on the front. (Generally, most of us wear out rear tires faster than fronts, at a rate of 2 to 1 for a street driven car.)

Bottom line is that I agree that small dire differences don't make much difference in normal driving. On my AP2 I plan on moving to 225/255 tires when the original 215/245's wear out. Way more tire choices with the 225.
I will say that the OEM 215 has a much narrower contact patch as Tirerack indicates. I run winter tires in 215/245 and my winter fronts are waaaaaay wider than the OEM 050. I believe the contact patch of the OEM front is really closer to a 195 or 205.

[repiv]

Bottom line is that I agree that small dire differences don't make much difference in normal driving. On my AP2 I plan on moving to 225/255 tires when the original 215/245's wear out. Way more tire choices with the 225.
I will say that the OEM 215 has a much narrower contact patch as Tirerack indicates. I run winter tires in 215/245 and my winter fronts are waaaaaay wider than the OEM 050. I believe the contact patch of the OEM front is really closer to a 195 or 205.
As you've just shown, real world contact patch width don't seem to correlate well with published charts. I run 225 and 255 in the summer.

[desmo4]

Mine has an error which is not even linear. It is larger at high speed than low but that's all I can say with certainty.

Jonathan

[repiv]

Mine has an error which is not even linear. It is larger at high speed than low but that's all I can say with certainty.

Jonathan
One part of the speedo pick-up is a toothed gear spinning past a magnetic sensor. Perhaps you have a tooth that is damaged or missing. Or the VSS is not fully seated into the tranny housing. Or the resistence in one of the sensor wires has changed due to heat or stretching.

[4U2NV]

Mine has an error which is not even linear. It is larger at high speed than low but that's all I can say with certainty.

Jonathan

A 3% error would be off .6 mph at 20 mph. When traveling at 70 mph it would be off by 2.1 mph. That seams linear, but is a constant.