RPM's vs MPH for M1008 Pickup

[prairie]

A while ago I put 315/70/17 tires on my M1008 pickup. Usually they are called 35" tires, but mine measure 33.5" @ 25-30 psi, and the gear calculator calls them 33.36". Stock tires were 235/85/16's which measured 31", and the gear calculator calls them 31.73"
Have drove it 1500+ miles since then on mainly on gravel roads but some paved roads under all kinds of driving conditions.
My general consensus is that I can go 10 mph faster and it drives, feels and sounds the same as when in stock form. It ran nicely at 45-50 mph in stock form. The gear calculator link that follows tells me that I should only see a 4 mph gain a similar rpm's.

The MPH and RPM's below were calculated from Gear Ratio Calculator

MPH/RPM's

stock 235/85/16---------44/2250----49/2500-----54/2750

315/70/17 ----------------48/2250-----53/2500----58/2750

Should I drive it by the way it feels or should I go by the gear calculator?

I'm taking into consideration that about 2200 rpm's is the max i should regularly run.

 

[Barrman]

I would suggest a different calculator. I just plugged your sizes into this one and got way different answers:

Randy's Ring & Pinion. RPM Calculator.

I would also suggest measuring your tires and using that as a guide instead of a number from the internet.

 

[Iceman3005]

235 x 85 x 16=31.73 x 9.25 x 16............speed=46.57/2250......51.75/2500.......56.92/2750
315 x 70 x 17=34.36 x 12.4 x 17............speed=50.43/2250......56.04/2500.......61.64/2750

 

[WARWAG]

Fist off just measure the rear tire. Measure from the ground to the center of the rear hub. Now take that and multiply it by two. We dont care what the actuall size is. Just what the truck thinks it has in real world figures. For ****s and giggles we will assume your measurement of 33.5 is correct

At 48 MPH your engine's rpm is 2195. There will be a discrepancy between you stock speedo and the actual speed once you installed taller tires. Check your MPH with a GPS unit.

 

[WARWAG]

Fist off just measure the rear tire. Measure from the ground to the center of the rear hub. Now take that and multiply it by two. We dont care what the actuall size is. Just what the truck thinks it has in real world figures. For ****s and giggles we will assume your measurement of 33.5 is correct

At 48 MPH your engine's rpm is 2195. There will be a discrepancy between your stock speedo and the actual speed once you installed taller tires. Check your MPH with a GPS unit.