Running bigger tires.

sethc24 · Sep 16, 2012

Guys i have a 2000 f250 7.3 4x4 automatic. And i need some advisement.
I am about ready to buy some new tires and would like to go up from a 265/70/16 tire to a 315/75/16 tire (35x12.50 i believe) and was wondering how much the bigger tire will affect my power and drive-ability as well as cruising rpm etc, braking and steering.

Mods on truck: nadp heavy hauler 4r100, T-500, 6 position chip, gauges, 4" exhaust, 6637, Hutch/pre-pump filter. 2.7" leveling kit.

Also some pictures of leveled super-duties on 35's would be awesome. Especially 99-03 trucks.

ToMang07 · Sep 16, 2012

You're gonna want off-set wheels or you will rub on the leaf springs. I have some rubbing at 3/4+ turns but it's only the plastic fenderwall, so nothing to worry about.

As far as drive-ability, I have had NO issues, and I lost about 1mpg. (3:73 gears) But you really should have the ABS re-set to the right tire size, I did mine with AE. In the event of an emergency or slippery stop, the ABS kicking on can potentially cause issues if it's not reset, not to mention the speedo/odo being off.

Before:

215-75-16E Duratracs after x-code springs and 2" mini-spring pack:

PA Stroker · Sep 17, 2012

I have 35x12.50x18 on my leveled 350srw ill post some pics when it get home. I have some rubbing on the leads at full lock but only if i hit a bounce. Other than that i have noticed any difference with them besides a little better ride,i only run like 40psi or air in them.

Actually my avatar pic is my truck.

Zaairman · Sep 17, 2012

I noticed a slight loss of power. If I was towing regularly over 8000lbs, I would either want a gear change or smaller tires. I noticed about a 1-1.5 MPG loss.

sethc24 · Sep 18, 2012

ah okay thanks for responding guys. Zaairman and tomang how do you guys like your tires. The bfg at and duratrec were 2 of my choices. Zaairman have you used your at's in any mud at all?

Zaairman · Sep 18, 2012

I haven't had the 315s in much mud. Had 285s before, BFG ATs. They are eeeh in mud. Only real reason I went with BFGs again is that because I was spending $1100 on tires, and I knew that these would last a long time.

PA Stroker · Sep 20, 2012

sorry just got a chance to post now

golfer · Sep 21, 2012

if you change nothing else (add no power, no gear change, no chip retune w/ slightly higher shiftpoints, or don't recalibrate the odo w/ a TS ReSpeed or TruSpeed)...

then you'll only really notice the extra weight/height of the tires during stop & go traffic.

If you're 100% happy with your current chip programs..the easiest thing to do, would be to add a TS ReSpeed to correct the odo/speedo so that your shift points will be spot-on.

shift points are based on pedal position & mph (not engine rpm)...so with a larger tire, you'll effectively be going 'faster' with less pedal...which can actually LOWER your shift points...which may cause the truck to feel even more sluggish.

if you PLAN on adding power (injs/turbo) in the future...unless you do a LOT of heavy towing...then I would advise against going with a gear swap...power can overcome a lack of gearing for most milder tire setups.

edit- we've had excellent results with the Mickey Thompson ATZ's for a street/off road tire..good looking/performing tread pattern, and nice and quiet for hwy use.

ToMang07 · Sep 21, 2012

golfer said:
if you change nothing else (add no power, no gear change, no chip retune w/ slightly higher shiftpoints, or don't recalibrate the odo w/ a TS ReSpeed or TruSpeed)...

then you'll only really notice the extra weight/height of the tires during stop & go traffic.

If you're 100% happy with your current chip programs..the easiest thing to do, would be to add a TS ReSpeed to correct the odo/speedo so that your shift points will be spot-on.

shift points are based on pedal position & mph (not engine rpm)...so with a larger tire, you'll effectively be going 'faster' with less pedal...which can actually LOWER your shift points...which may cause the truck to feel even more sluggish.

if you PLAN on adding power (injs/turbo) in the future...unless you do a LOT of heavy towing...then I would advise against going with a gear swap...power can overcome a lack of gearing for most milder tire setups.

edit- we've had excellent results with the Mickey Thompson ATZ's for a street/off road tire..good looking/performing tread pattern, and nice and quiet for hwy use.

I used AE to change the settings in my ABS module for the 315-75 tires I have, and it works great with my original tunes/gearing. It did drop the RPM's down a tad, but overall I am very happy with it, and going from 265-75 to 317-75 I only lost about 1mpg.

Those of you who haven't adjusted the tire size yet...find somebody with AE! (Works up to 35" tires.)

sethc24 · Sep 21, 2012

Awesome guys. I will definitely get my chip re-burnt to work with the bigger tires. Golfer, the atz was also one of the tires i was looking at. But i see there is an atz and atz plus. Does anyone know the differences between them?

b00stleak · Sep 28, 2012

My avatar is 315/75/16 with just a 3" level. Left tire rubs the leaf spring when turned all the way left. Maybe with wheels with a different offset would cure that.