1995 Honda Civic h/b tire size puzzle

[Bill in Houston]

Originally Posted by cems70

Bill, the old tires (Firestone) only had about 9000 miles on them, so tread depth shouldn't make a huge difference. Besides, I measured the circumference of the old and new tires, and they were within .2% of each other.

Oh fine, then. Shot down again. :-) I'm stumped.

[GasSavers_bobski]

Originally Posted by thisisntjared

all tires allow slippage in the treads, especially during acceleration and deceleration and different tire designs allow different amounts of slippage.

You may be confusing sidewall flex for slip. If they slipped, the tread would shift relative to the sidewall/wheel and stay there. When the sidewall flexes under strong braking or acceleration, it's merely acting as a spring. The tread and sidewall/wheel return to their original positions relative to eachother once force is removed.

[VetteOwner]

Originally Posted by cems70

"If it's really bugging you, you could put them back on the car, measure the rolling diameter while in use, and see if you agree with the manufacturer as far as revs per mile.

Ooo, ooo, I figured it out, maybe. The spec is for a tire at full tread depth. you were comparing worn old tires to full tread new tires. That makes a pretty stout difference, esp in a small tire like yours."

Bill, the old tires (Firestone) only had about 9000 miles on them, so tread depth shouldn't make a huge difference. Besides, I measured the circumference of the old and new tires, and they were within .2% of each other. This is why I'm perplexed about why the odometer is now registering 4% low w/ the new tires when it was only registering 2.6% low with the old tires. It must be the flex in the old tires causing more RPMs.

"ok so you swapped trannys now your speedo/odometers off...."

Vette, the speedo is actually precise now, whereas before the tranny swap it was about 2 - 3 mph high at 60 mph. The odometer changed from being 1.6% high to 2.6% low. I figured the new tires w/ a claimed 927 RPMs versus old tires w/ a claimed 919 RPMs would make the odometer a little more accurate...like closer to only 1.7% low instead of 2.6% low.

I did not swap my speed sensor from the DX tranny to the CX tranny because the CX tranny had a broken bolt on it, and I didn't want to mess around with it. I may swap them now to see if it makes a difference. It certainly can't get any worse than 4%!

worth a shot i mean you already have the part it sounds now if you can get to it...thats a whole nother can of worms. (i hate working on FWD cars)

[cems70]

Originally Posted by bobski

You may be confusing sidewall flex for slip. If they slipped, the tread would shift relative to the sidewall/wheel and stay there. When the sidewall flexes under strong braking or acceleration, it's merely acting as a spring. The tread and sidewall/wheel return to their original positions relative to eachother once force is removed.

You're right, I was confusing sidewall flex for slip. In that case, slip has to be the only plausible explanation for the additional low odometer reading. The new tires must be slipping less than the old tires which causes fewer Revs Per Mile. Who would have thought there could be such a difference in two different brands of the same size tire??