running dif size tires front to rear

[e30turbo2]

right now im running fairly bald baja claws 35/12.50.15's a friend of mine just gave me a pair of old school granp prix 4 wheel rvt's. on the sidewall they say 36/15/15. with no wieght on them they measure out to about 34.5 and my claws are within 3/4" of that. this is a off orad only truck im wondering if i can run the 36's on the rear without killing my t case. if anyone has ever done this or heard of probs i would appreciate hearing about it.

 

[Surrey]

The real question is not in the difference in height, its a matter of circumference.

with the numbers you give me, I come up with aprox. 105.2 inches, compared to 109.9 inches, or a difference of about 4.5%.

 

[CHKNFKR]

If you're 2wd, you're good. Generally speaking if you are 4x4 its a bad idea, particularly on pavement. There are exceptions to this, mud boggers tend to mix and match tire sizes and gear ratios to make the fronts [travel a greater distance] it helps the stay pointed forward. Also when i was in colorado i noticed lots of 4x4s of all sizes running larger tires up front than out back, not real sure of their purpose.

 

[Tony Raine]

"static load radius"

-measurement from the ground to the center of the hub, with tires on the truck.

adjust air pressure until the front and rear are pretty close to each other


you'll be fine. i ran 33's with 3.73 front and 3.45 rear gears for a few years. when i went offroad, i just aired down the rear tires a bit, and left the fronts at street pressure

 

[e30turbo2]

i kinda figured airing down the rears would get them really close. the truck spends its life in low range with 5:13 gears thats not moving very fast and always on dirt. im probably gonna do this either way unless somebody really thinks this is a bad idea. im pretty sure i have seen trucks out wheeling with mis matched slightly dif size tires front to rear

 

[Surrey]

"static load radius"

-measurement from the ground to the center of the hub, with tires on the truck.

adjust air pressure until the front and rear are pretty close to each other


you'll be fine. i ran 33's with 3.73 front and 3.45 rear gears for a few years. when i went offroad, i just aired down the rear tires a bit, and left the fronts at street pressure

As stated you need to factor in circumference, not radius.
If that worked, airing down a 35 enough would make it run with 30s on the other axle. Airing down will change your radius, but the elliptical shape your tire takes doesn't magically shorten the total distance covered in 1 full rotation of a tire.

 

[e30turbo2]

lol duh i never thought of it that way...... makes sense. well with that said does anyone see it being a huge issue in the dirt?

 

[Surrey]

Less than 5% is not a huge diff. You could probably get away with it... that's not to say I advise it, but I am sure people have ran worse without breaking stuff. I would advise against any fast driving in 4x4 at the least.

 

[CHKNFKR]

"static load radius"

-measurement from the ground to the center of the hub, with tires on the truck.

adjust air pressure until the front and rear are pretty close to each other


you'll be fine. i ran 33's with 3.73 front and 3.45 rear gears for a few years. when i went offroad, i just aired down the rear tires a bit, and left the fronts at street pressure

There is some truth to this so long as the difference in distance per drive shaft revs is minimal (i'd say 5% max)

As stated you need to factor in circumference, not radius.
If that worked, airing down a 35 enough would make it run with 30s on the other axle. Airing down will change your radius, but the elliptical shape your tire takes doesn't magically shorten the total distance covered in 1 full rotation of a tire.

While i mostly agree with this, airing up and down can change the real world circumference of a tire. Imagine yoir tire aired up to 40psi or so, the center will bulge out and that center bulge will nearly be the only part of the tire touching the ground.

Now air that tire down to single digits and the center will collapse and the sidewall may even roll in under tge weight of the vehicle. At this point the real world circumference will be less than the same tire aired up.

I wouldn't count on This principal saving a t-case/diff. On top of that, the aired down tires will turn into a slicks in no time

 

[e30turbo2]

why would the aired down rears turn into slicks? this truck is never on the street. i run very low psi all the time beadlocks in the near future for that reason. anyway im just trying to get through the spring wheeling season with these until work picks up.

 

[CHKNFKR]

I guess i missed the part about never seeing pavement. If thats the case you might get away with it for a while before putting your driveline in a bind. Its not something i recommend or endorse though.

 

[e30turbo2]

fair enough i think im going to go for it. the grand prix's look allot like tsl's and are almost new. should be a big improvment over my claws.