gas mileage

[Typrus]

Pi times diameter equals circumference. So if our tires take 913 revs per mile, thats a circumference of.. 5.783 feet? So those 10% increases are 6.361 feet. That equates to 830 revs a mile. Almost a full 100 revs a mile less. Thats 100 revs a mile AT THE WHEELS less at 60 mph, which will likely be in 4th or 5th, so thats, what? 350-430 RPM's less? Or am I just too tired for my own good.

[takza]

not too sure...I use....

<a href='http://350zx.com/tire-wheel.html' target='_blank'>http://350zx.com/tire-wheel.html</a>

Seems the calculations vary at times...or maybe I didn't enter the data correctly...............

[Typrus]

I would suggest trying 185/65R14's. I know they work, I tried them out. My folks have a Passat and it has those tires with 14x6 rims, bolt pattern 4x100 and it worked fine. I tried this a good while ago. So let me calculate....
175/70R13 to 185/65R14

Wheel RPM's at 75

1113---------1074 Not a massive decrease, but enough to get a difference. And they ride nice with proper tires.

3% speedo error (Speedo on 175/70R13 reads 75, 185/65R14's read 78)



0.41 inch increase in ride height (Woo-hoo!)

0.39 inch increase in tire width. This means that assuming the contact patch is 1 inch long, that is an increase in .39 square inches road contact. Assuming 5 inch width, that means you'll increase contact patch size by 0.39 cubuic inches, attaining 5.39 square inches of contact. My not sound like much, but it is about an 8% increase in contact patch. Better traction there.

I have not tried bigger tires, so dunno how well they ride, but it may be that much better.

So not I'll comp the 175/80R13.

75MPH Wheel RPM's
R13 R14
1050 1074

Not a massive difference. Perhaps you would try these to see if you could get a 3-4MPG gain and still have nice handling.


To give an idea, we have driven at 135 MPH in the Passat with this tire size and still it handled well.