Trying to figure mph

[rb68rr]

Trying to figure how far off my speedo is. With stock gears and rpm's at 2040 my speedo shows 65mph with 255/60 15's. Is this right? Is there a formula for figuring this? Thanks, R.B.

 

[mikestertwo]

It's close. Your speed should be between 68-69mph at 2040rpm assuming your tires are 26" tall.

 

[rb68rr]

How tall are 255/60/15's?

 

[baller760]

don't mean to butt in but what about 275/50/17 at 60mph. what should the rpms be?

 

[IronCityTurbo6]

Here this might help:Tire size calculator

 

[Blazer406]

Borrow someone's GPS if you don't have one.... then go cruising on the interstate.... with the GPS tracking on the dash.... it will tell you exactly how fast you are going.... then compare it to your speedo.

HTH

 

[mikestertwo]

don't mean to butt in but what about 275/50/17 at 60mph. what should the rpms be?

How tall is the tire?

 

[gsgns4me]

Useful math Formulas for car guys. Scroll down near the bottom for formulas related to determining speed, RPM, gear ratios.