Alright, the speedometer readout is based on a sensor on the crankshaft or something, so it's calibrated according to stock setup... if I were to get larger aftermarket rims... IE 18's making the circumference of my wheel larger, wouldn't there be a discrepency in the speedometer and actual speed of my car? The crankshaft has to spin less to travel the same amount of distance. Is this the case w/ teh S2k and is there a way to fix this? It would suck to be thinking I'm going the speed limit but in reality I'm going faster... my radar detector would be no good if my speedometer doesn't work

*edit* I'm very tired right now so I can't think straight but doesn't modifry's yellow thing fix it if the car were going faster than the speedometer indicates? and if so how do you adjust it. Thanx a bunch.

 

Yes modifry's mod works in recalibrating the speedo but only if your speedo is going faster than you really are. And yes if you change wheel diameter or final drive ratio's then your speedo will be off. I believe instructions come with the mod.

 

but w/ larger wheels, your speedometer will be slower than actual speed right? so modifry's gadget won't work.

 

Modifry's yellow box can fix your speedo either way. Fast or slow. Yes the rims will knock off your speedo. On a side note, I know the RSX has the speed sensor in a different location than ours so they dont have the same problem with gears or rims.

I am still having trouble adjusting my Yellow box just right. Its a bit off no matter what I do.

 

Incorrect.

Modifry's Yellow Jacket will only help if your speedo is reading faster than normal, i.e., after you install lower gears in the rear.

BTW, changing the wheel diameter won't do a thing to the speedo reading if you sized the tires properly and kept the same overall diameter of the wheel/tire combo.

 

Really, I havent messed with mine in a few months, but I remember it having - and + settings. Tire sizing is not exacly perfect. I have the right size tires, but if I sit them next to the stock wheel, they are smaller by a tiny bit.

 

well, my overall wheel size is still going to be bigger, I've hit plenty of potholes to know that a thin tire + pothole = bent rim so I plan on getting something decent to protect my investment.

 

As already stated by Ludedude, it is NOT your rim size that gives the speedo error. It is the tire size that does. If you got the tire size that gives you the same wheel/tire diameter as stock, then there would be no need for speedo correction. If you go with a tire that is larger in diameter than stock, then this is your choice and has nothing to do with the rim diameter. The Yellow Box will compensate both + and -. I would think that the Modifry unit would do the same.
The bigger from stock that the diameter is, the lower the speedo will read from real life. IE, if you had larger diameter tires and your speedo says 30 mph, you would in fact be going much faster.
FYI, the speedo pick-up is on the final output of the tranny. If it were on the engine's crank, you would see the speedo go up and down with the rpm.

 

Modifry's Yellow Jacket does not allow for increasing the speedo reading. This was a design decision based on two factors:

1) Most people have a speedo that reads too fast (2-4%) from the factory.
2) The most common reason for needing a speedo recalibration, besides the factory error, is after adding lower gearing in the diff.

Since these instances cover the majority of the instances where correction is needed, Bob decided to make his unit address those. The benefit is a lower cost unit. It does not address the very few times that the speedo actually reads too slow since even with somewhat larger overall diameter rims/tires, the factory error is likely enough to cancel out the difference.

Other units on the market might work in both directions, but ours does not.

 

This is good to know for future reference.

You have a good point. Most of our speedometers are off by between 1% and 2%. If you increase the wheel/tire diameter by this same amount, you will be "PERFECT".

I think the Yellow Box is the only other one on the market for this type of application.