My mistake, I thought you were refering to the yellow box to begin with

 

If you have larger overall wheel/tire diameter, you are correct. You'll need the Yellow Box to compensate, but like I said, if you are out by within a couple %, you should need to worry too much about it.

 

[QUOTE=revhi,Jan 2 2005, 12:26 AM] Really, I havent messed with mine in a few months, but I remember it having - and + settings.

 

Alright, stock MY00 S2K rims are 16" w/ like 215 something front... something back... anywho. I'm prolly going to get 18" rims... now if I wanted to keep the overall wheel size the same, that means that the tires are going to be thin... the backs are going to be like 245/20? that's a no no for expensive rims that are driven on the streets of Houston... I plan on getting something thick enough so that if I accidently hit a pothole... I won't own a rim. That means my overall wheel size will be bigger, thus throwing off the speedometer, but I guess if it's off anyways by like 2%, maybe I'll be fine. The only thing that worries me is like my speedometer reads 75 but I'm actually going like 80... that would be bad.

 

You can go to the Bridgestone site to find out exactly what the diameter of an "S2000" OEM SO2 is. It'll be "about" 25 inches. Then, you can go to the manufacturer's site for the tire you are going by for your 18" tire and see what the various diameters are of different aspect ratios.

I don't think you'll be going to a 245/20. It'll be more like 245/35 or 245/30 at the extreme. Many people run aspect ratios of 40 on the rear with no problems regarding daily driving. If you hit a pothole hard enough, even the OEM sizing won't save you. It won't matter, except for looks and extreme handling characteristics what you run on the front as this won't affect speedo.

 

I'm running 255/35/18's, but like xviper said I could have gone to 40's to. Its just SO3's are not made with 40 side walls for 18's. Ive hit some pretty large pot holes with no ill effects. The sidewalls are usually all reinforced when they are low profile.


xviper, I tried adjusting my yellow box before to make the speedo perfect, but just not working. I went up one setting from where it is now and it was still off and went down one setting and it was still off. I dont think it will ever be dead on.

 

Hmmmm, a 1/4% is a pretty fine adjustment. I'm surprised it's not working for you. You didn't "hot" wire the YB, did you? I mean, is it wired for power to "ignition" such that each time you turn the engine off, the power goes off to the YB? The YB will not use a new setting if the power is not disconnected momentarily.
In any case, a speedo that is out up to 2% on our cars is acceptable.

 

It is wired to go off when I shut off the car, but your saying I have to turn it off after I put new settings in for it to take effect? I dont think I did that.

 

This is correct. If you changed it while it was on, until you turn it off, it will use the last setting it had. By now, I'm sure it has been off many times. It should be using your most recent change by now. Do another speed check.