ive got 33 AT's on 15x8 rims. the outer inch or two dont make contact with the ground at 35 psi. i took the down to 30 , now the outer edge makes contact, but the inside edge still doesnt touch.i think its causs the tire rolls over more now on corners. should i air them down more? should i run them at 35 and not worry about it?i dont want to wear the tires out prematurely , and i dont want to hurt my MPG either.
CK5
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BFG tire pressure
- Thread starter Jonny-K5
- Start date
This is why they recommend a 10 inch wide wheel for 12 inch wide tires. An 8 inch wheel is not wide enough for the tread to make full contact with the road at normal pressures. I’m running 33x10.50’s on a stock 8 inch wheel and the tread bows outwards some towards the center, but is fully in contact with the road at 35psi. I would start saving up for either a narrower set of tires or better yet, a 10 inch wide set of wheels.
I played around a lot with putting chalk on the tread, then driving around for a while to see if the chalk wore off evenly. With BFG 35-inch Mud Terrains, mounted on 10-inch-wide wheels, I found that 26 PSI up front and 24 PSI out back put the entire tread in contact with the road. /forums/images/graemlins/eek.gif /forums/images/graemlins/thumb.gif
With a contact patch as big as these tires have, it doesn't take a whole lot of PSI to support the weight of the truck. The PSI posted on the sidewall of the tire is the MAX amount of pressure that you should run, and that's only if you need to support weight that is at the limit of what the tire can safely carry. With less weight you can drop the pressure to keep all of the tread in contact with the road. /forums/images/graemlins/cool.gif
With a contact patch as big as these tires have, it doesn't take a whole lot of PSI to support the weight of the truck. The PSI posted on the sidewall of the tire is the MAX amount of pressure that you should run, and that's only if you need to support weight that is at the limit of what the tire can safely carry. With less weight you can drop the pressure to keep all of the tread in contact with the road. /forums/images/graemlins/cool.gif
i kno my wheels are too narrow, but ive heard that the 8 inch wheel keeps the bead from coming off at low psi trail use. i have a set of 10" steels laying around but dont want them causs my 8s tuck into the fender better and i have no clearance problems with them. plus my 8" rims are stock alloys and ALOT lighter. doesnt it increase rolling resistance with lower pressures? thereby decreasing MPG? how low is too low?
Pookster
1/2 ton status
I've seen either a post/debate somewhere about tirepressure and fuel economy. I forgot where, but there was something about fuel economy due to contact patch,and fuel economy due to rolling resistance.
In short, I think the side I remember is, if you over-inflate your tires, you decrease your contact patch, but you may acutally increase rolling resistance by having the tread lugs "buldge" outward. It made some sense to me, as my MT's are deisigned that where the lug ends, the other lugs on the outside take their place (like an overlapped pattern). Hence, more even truck weight distribution.
In short, I think the side I remember is, if you over-inflate your tires, you decrease your contact patch, but you may acutally increase rolling resistance by having the tread lugs "buldge" outward. It made some sense to me, as my MT's are deisigned that where the lug ends, the other lugs on the outside take their place (like an overlapped pattern). Hence, more even truck weight distribution.
Lower pressures may increase rolling resistance slightly, but the cash you'll lose by wearing the centers off of a set of $600 tires in 15,000 miles will pay for a LOT of gasoline. /forums/images/graemlins/eek.gif I play with the pressures until the entire tread is touching the road at all 4 corners of the rig. That way I don't need my own personal tire store. /forums/images/graemlins/wink.gif
Chris_T
1/2 ton status
I'm with Harry. I have 35" MTs on 10" wheels and I run between 24 and 26 psi in all four for even tire wear.
1972Blazer
1/2 ton status
Just an echo on everyone else that 24-26 psi on a set of 35X12.50 BFG MT's seems to be perfect. I do have mine on a set of 15X8 Ralleys and it makes no difference, BFG says between an 8-10" rim for these tires. I have run this setup on many trucks and love them. A 10" rim will make the tire appear wider but the 8" makes it look taller, I always have people looking for a size on my sidewall thinking they are 37". With inflation set at 24-26 psi the tires measure 35" tall, it all depends on what look you like to have. I can say it does make me dig more in sand then if I run 10" rims, just a thought.
