2nd Gen Non-Engine/Transmission Tire Size differences

[DKothe]

My '99 is supposed to have 245/75/16's on it.

It has 235/85/16's... . which I assume is a shorter tire but a bit wider... ... ... is this correct??

But... ... ..... according to OHP and my GPS the truck runs about 3-4 miles an hour faster than the speedo says it's going.

If the tire is shorter than stock the speedo should show more speed than actual instead of less... ... ... ... ... ... ..... right??



Also since I haven't changed tire sizes on my CTD yet and aren't familiar with it... ... ... ... ... ... ... ... ... does a lot taller tire have a big difference on the power like a gasser does???





Thanks

Deano

 

[Cummins4Life]

245's = 30. 5 x 9. 7



235/85's = 31. 7 x 9. 3



Its taller so your GPS is right.

 

[RBratby]

the 245 is how wide the tire is. 75 is the wall profile or how tall the wall of the tire is. the 16 rim size.

 

[Forrest Nearing]

first number = width in milimeters...



second number = sidewall height as a percentage of width...



IE 245/75/16 = 245mm wide (10") 75% of that = 7. 5", times 2 = 15" plus 16" (wheel diameter) = 31" overall diameter

 

[Slick]

Try this site it lets you compare anysize tires and gives the widths, hieght, revs per mile, speedo error etc. http://www.miata.net/garage/tirecalc.html

.

 

[DKothe]

GREAT!

Thanks guys,

I understand now. Appreciate all the info.







Deano

 

[Forrest Nearing]

FWIW, 24. 5mm = 1"



I always use www.randysringandpinion.com for calculations when I'm on the computer... they have calculators for tire height, rpm, mph, gear ratios, etc. etc. etc. very handy.



but sometimes I find myself doing tire calcs by hand



Forrest

 

[Joe Pool]

Correction !!



FWIW, 1" = 25. 4mm NOT 24. 5mm



Joe

 

[Forrest Nearing]

Joe, thanks for the catch! my dyslexia shining through again!



25. 4mm/1inch!



forrest

 

[McCRam]

putting taller tires on your truck make your overall gear ratio higher. So it will probably slow down your acceleration a little bit, and make steep hills a little harder to pull. However when I went from 245/75 to 285/75, my butt-o-meter didn't notice a change