Ok, I installed larger tires on my F-150 then the small one's it came with. I went from 255/70 17's to 275/70 17's. My question is there a way to change the internal computer to compensate for the larger tires. I know you can do this with a HyperTech but is there a way the dealership, mechanic, or maybe but doubtful way to do it yourself?

In my thinking the computer is still running as if it was at factory settings. Because of this the automatic transmission may not shift correctly and the speedometer readings will not be accurate. I'm not as concerned with the speedometer so much as the transmission. I also think this could help my gas mileage if set right. I could be way off on this thinking but just seeing if there was a way to reprogram.

Thanks

 

Your new tires are 32.2" tall, wheras your stock tires are 31.2" tall. This one inch difference will not make a meaningful difference in the way your truck drives. Look for maybe 2MPH difference at highway speeds, and less of a difference when you're going slower.

My Blazer has 235/75R15s, and it originally came with 235/70R15s. About a 1" difference here, as well. When my speedo says 65, I'm really doing 67. I validated this with a GPS, and it's very consistent.

Just enjoy the tires, and realize you're going a bit faster than you think you are.

 

This may come in handy.
http://www.offroadrecovery.com/categ...torsandtables/

 

The dealership can program your Module to read either different gear ratios or different tire sizes. Take it in and have them reprogram it. I don't know if independents have the proper software in their NGS/Snap-On scanners or not??

 

buy the Edge...it'll do that and alot more for you.

but no, the bigger tire will not affect your shift points. the transmission will shift based upon load applied, gear it's in and speed. your speedo is going to be affected by about 2-5 mph. just keep on driving it. there is no real reason to pay a dealership the money to reprogram your ECM for slightly bigger tires.

 

that one inch difference actually translates into about a 3 inch difference due to larger circumference. and you're doing the next person who buys your truck wrong by outputting the wrong mileage on your odometer. but to each his own.

 

"that one inch difference actually translates into about a 3 inch difference due to larger circumference"

Good point and was helpful. Below not so much.

"and you're doing the next person who buys your truck wrong by outputting the wrong mileage on your odometer. but to each his own."

That is exactly what I was thinking of screwing the next person who buys my truck. I wasn't thinking that I needed to change the tires to fit the needs of what I use it for since I own the truck. That I needed more durable and flat resistant tires because I drive on sharp rocks and thorns on a day to day basis. That I wanted to do the next person wrong even though I'm going to keep the truck for 8-10 years (god willing) since that is better financial since. Nope, nevermind the fact I posted that I wanted to change the internal computer so that the mileage would hopefully be correct. Yes, I guess to each his own.

Also, thanks to all for the input. I'll also look into the Edge, sounds good.

 

The dealership can only program the PCM with tire sizes that were offered by the factory when the truck was manufactured. For any other tire size you will have to buy a tuner in order to compensate for that.