Home Forums Gear Hunting Trucks and Four-Wheel Drives Taller Tires

You guys installing taller tires on your rigs like going from stock 33” diameter up to 35” diameter, are you reprogramming your vehicle computer for proper shift points and accurate Speedo readings?

Thanks.

Yes, I don't want her getting speeding tickets from cameras because the speedometer was off.

Bumped up 2 sizes on my 2020 F150 with a small leveling kit (34” tires). I’m off about 2.5mph at typical 60-65mph highway speeds, so I just drive a couple mph slower than before. I generally don’t push it anyway, regarding the thin line of ticket vs no ticket. Have not needed any shift point mods with the 3.5EB and 10spd. Power delivery is not much different, as there’s a good bit of torque down low. Lost about 2mpg from the worn-down 32” SL-rated factory tires when going to the 34” E-rated AT tires (20.5 vs 18.5).

Jpro, If your circumference went up 6% with that tire upsize, seems like adjusting the 18.5 mpg up by 6% would be accurate? No math guy but the larger tire is going farther per turn. If correct, adjusted mpg might be more like 19.6.

I upsized from 32" to 34" on my F250 and noticed little decline in mpg.

Plug in the numbers here.

https://tiresize.com/comparison/

If you scroll down a bit there is a link to calculate the true axle ratio with bigger tires and what new gears you need to match factory.

Back in the day most factory trucks came with 28-30" tires. Going to 33 or 35" tires was a pretty big jump. But today most trucks have somewhere around 32"-33" tires from the factory. It just isn't that much of a difference to go to 33 or 34" tires. Even 35's. With most swaps you only see about 3 mph difference at 70. Less at slower speeds. I wouldn't worry about re-programing anything unless you go 37" or bigger.

Another thing to keep in mind. Tires get smaller as they are used. With 40,000 miles on them they are about 1 size smaller than when they were new. If you program your speedometer to be right when the tires are new, it won't be right later. If you leave it alone it may be off a bit when the tires are new but will become more accurate as you wear down the tires.

Because of this around 2-3 mph is about as accurate as your speedometer can be from the factory. No one is going to write you a ticket for being 3 mph over. In fact, here in GA in MOST cases they can't write a ticket until you're 11 over. There are exceptions, school and construction zones for example. GSP can write them at less than 11, but unless you're doing something else stupid they leave you alone until you're 11 or more over the limit.

Guys, thanks for your input here.

I’ve got a 2021 F-150 with the 5.0, 10 speed 4x4 that came with 33” tires and I’m thinking about going up to 35” when it’s time to re-shoe.

My concern was more towards the transmission shifting points and the possible continual up shifting and downshifting that might result from the larger diameter tires.

I went to a taller tire on a Tundra without reprogramming and it did the up shift, downshift thing regularly. I’d want to avoid that scenario with this F-150. The gas mileage dropped 3 mpg with the Tundra and taller tires.

Again, thanks gents.

You may be right. I'm just going by the computer calculator, which was pretty close with the factory tires.

My truck will occasionally feed in more turbo boost or drop down to 9th gear on some hills on my daily drive where it did not do such things previously with the smaller and lighter factory tires. There is a little difference, but it's not much. I generally saw much more impact when going up in tire size/weight in older trucks with 4-6spd autos.

Yep it definitely affected the 6 speed Tundra.

I drive manuals, so they shift at the proper shift points regardless, eh.

But yeah, slush boxes need reprogrammed.

No problems. I run about 3-4 mph over at 75 mph, and mileage calculation isn't right in computer. But transmission has no problems. Pulling trailer is easy.

What truck, what tire size and What transmission, TR?

No. I swap gears to compensate so I'm not losing power.