Difference btwn 31' and 33' tires on highway

[Dave_in_Texas]

I'm curious, say you have 31 inch tires and your RPMs are 3,000 at 55 MPH. If you put 33 inch tires on, at what speed would you hit 3,000 RPMs? Do you "gain" 5 MPH at the same RPM level?

Thanks,

Dave

 

[vintage bronco]

3.50 ratio with 31in tire at 3,000 rpm = 77 mph
3.50 ratio with 33in tire at 3,000 rpm = 82 mph
so yes you gain approx 5 mph

 

[Dave_in_Texas]

Is there a chart that has that information somewhere?

Dave

 

[73stallion]

http://web.archive.org/web/20050204061805/home.comcast.net/~jcmiley/bronco+gears.html

 

[starkypdx]

Holy charts! I did the Math long hand when I calc'd my gears...

 

[vintage bronco]

Is there a chart that has that information somewhere?

Dave

Dave

I use Randy's Ring and pinion chart. just type in randys ring and pinion on the search bar, also keep in mind all 31in tires are not 31in could be 30.5 30.8 etc.

 

[70_Steve]

I kinda like this one.
http://www.grimmjeeper.com/gears.html

 

[DirtDonk]

And just to mention it again, even if you already know this, but the larger tire is also heavier, with more rubber on the road and, potentially at least, slightly more rolling resistance.
So that minor rpm difference "feels" a lot more than it really is.
Your acceleration and braking will be effected more than the simple speed numbers will indicate. Not enough perhaps to dissuade you from the change, as a huge number of people are running that size on a Bronco, but it's worth mentioning at least.

Paul

 

[vintage bronco]

Holy charts! I did the Math long hand when I calc'd my gears...

nothing wrong with that ! most kids today would have no idea how to do that

 

[DirtDonk]

yeah, no kiddin' there! Heck, I can't even remember half of it. And I was great with math in school too. Favorite subjects all the way through in fact. But forgot more than I'll ever know.
And, when said like that, it's bad...

Paul

 

[tennessee toy]

i never thought about it.
i tell the police - i will get my speedometer checked - NOW I KNOW

 

[mitzel]

33"/31"=1.065 => 6.5% increase in diameter and circumference.
At same RPM you'll be going 6.5% faster than before.
At same MPH engine will be spinning 6.5% slower than before.

 

[Steve83]

...but 31" tires aren't actually 31" tall; likewise 33s. Use the SPECIFICATIONS pages on TireRack.com to find the actual height & RevsPerMile (which is more accurate) for your tires.