currently have stock set-up for 04 coupe changing to Z06 wheels and need to buy tires. Question is odometer change for more revs. verses less revs.

 

Neither, our cars have a VSS, Vehicle speed sensor. Tire height will not change the speedo

 

Do all C5's have these vehicle speed sensors including the Z06? Are you saying that the sensors automatically detect any wheel or tire size changes and adjust the speedometer accordingly without any reprogramming of the computer or swap-out of a rear speedo gear like in the older cars?

Thanks

 

From what I understand all C5s have VSSs

 

Yes they do have vehicle speed sensors but the speed and miles are calculated by the computer based on info by the speed sensors and compared to a stock tire height. If you go to a shorter tire the computer won't know the diffrence and your mph will read faster than you really are going. When I put on my 315/30-18's they were shorter than stock and my spedo was off. I reprogramed the tire height withh my hp tuners. Now it is ded nuts on. If you go with zo6 wheels just use the stock tire size for a zo6, the overall heights will be the same.

 

Someone else chime in?

TTT

Only changing the gears would throw off the speedo.

 

Changng gears does NOT throw off the speedometer (because the reading is based off wheel speed, not tranny shaft speed) .

Tire height most certainly does affect the read wheel speed, and the speedometer.
Going to a shorter tire will make the speedo read faster than what you're actually going. Most of the prgramming tools out there can plug in a new rear tire height to adjust for that....but the error will be very slight, ie: 1-2mph at freeway speeds, and most people don't bother with it.

 

very helpful as usual. I think I'll get the tires I want and not worry about the small stuff

 

Thanks for the replies on this.

 

Will this also throw off the MPG ??????

I just changed wheel/tires and my milage is lower


DH

 

In effect changing tire is the same thing as changing gears when it relates to speedometer readings. A taller tire is like changing from 4.10 to 3.73 and a shorter tire is like going from 3.73 to 4.10. The tire size changes the revs per mile and WILL throw the speedo off.

 

Most tire company websites will show the overall size and revs per mile for their tire sizes. It is a good place to figure how much percentage wise it will be off.

 

So it would also affect gas milage..........


DH

 

After reading this post I had to throw my 2 cents in... an engineer can't walk away from a math question

Tire height(diameter) * pi (3.14157), will give you the circumference of the tire. A factory tire is ~26" tall with a circumference of ~81", smaller tires would still be ~25" tall with a circumference of ~78.5 inches. sooo... (81/78.5)*60 = 61.9. the speedo(and everything else) would be off slightly less than 2mph(3%) at 60 mph.

I have seen cars come out of the box brand new that were off farther than that. I wouldn't bother unless I had both the time and the equipment in front of me.

To figure what the difference will be for any one particular tire change:

A: Measure the current tires from the ground to the top of the tire, multiply it times 3.14157(pi)

B: Measure the tires you are considering from the ground to the top of the tire, multiply it times 3.14157(still pi )

divide A and B and subtract 1, the answer is percentage that the speedometer readout will change. Multiply this by the speedometer reading at the moment and it will give you actual speed. It will also show that it would take a pretty drastic change to have a big effect.

According to the diagrams, the speed sensor is located on the rear of the transmission, while I could be wrong, that implies that it's attached to an output shaft rather than an input shaft, if this is true a gear change would not affect readings, however a tire change would.

And now, back you your regularly scheduled show.

 

Yes a little bit.