Effect of tire size on performance

[smalltownusa]

I've got a 2005 Explorer Sport Trac.
I entered my vin number, and got the original equipment printout.
It's an automatic V6 4.0 liter EFI SOHC engine, with a 3.73 axle ratio, and is the 4WD model.
It's all stock, and has the original stock size P235/70/16 tires that "look" so undersized in the wheel well. In the past I had asked the dealer about upping the tire size, and was told they would not put a sticker on it because of State of Maine rules.

I read that a few years ago the State rules were changed to allow either up to a two tire size upgrade or two inches larger diameter (not sure which one).

I don't want to raise my suspension etc. Reading all the posts, and I mean all the posts it would appear that my max size should be 255/70/16. Not sure about 255/75/16 fitting.

I'm going to the same dealer, and ask about installing these sizes, but before I lay down any hard earned cash. I am hoping this size will look more appropriate.

One nagging question I have, because I don't know an axle ratio from a smakzel ratio is what effect the 255/70/16 or 255/75/16 will have on the driving and performance if any.

 

[SoCal2V]

So, they dick you around over your tires and wheels out there in Maine? And here we all are, thinking California was restrictive on what you can do to your cars....

Anyway, 255/70-16 was an original equipment option on your truck. Definitely fits and definitely fills out the space a little better. Personally I would go for 265/70, but if you can't get past inspection like that then the only way to do it would be mount them on a different set of rims and keep the smaller size around for yearly inspections.

What I would do is go visit an inspection facility and ask them what is and isn't acceptable, get it straight from the horses mouth.

As far as effect on anything, the slightly larger tire will ride a little nicer on imperfect surfaces, washboard dirt roads etc. You probably won't notice any difference in acceleration, it's not like you're putting 35" M/T's or something like that on it. Speedometer reading will remain accurate as well - there's a little wiggle room in thale factory speedo calibration; in my experience most cars read about 3 mph high from the factory. A larger tire in the size you're proposing will drop it down 1 or 2 mph.

 

[01STrunner]

I agree with above as far as performance, you most likely won't feel a difference. I would also suggest trying for a 265/70 as I think my stock 255/70s looked small in these massive wheel wells. Tire type makes a big difference too. I have 255/70s in both of these pictures, but I think the ones in the 2nd picture look much better.

 

[smalltownusa]

Thanks guys. The way the dealer had explained it sometime ago was that the State wanted only the tire size that was on the door sticker. He said that it wasn't unusual for the State Police to show up at the dealership while investigating an accident, and asking what the tire size was from the factory. Ergo all the licensed repair techs did not want to put their license on the line. Can't blame them at least it appears I now have some wiggle room. Yes before I buy my tires I will get the ok ahead of time.

 

[01STrunner]

My advice to you. Don't buy tires or have them installed at a dealer. You'll spend way more than if you were to go to a local place or even discount tire. Dealers are no place to get anything other than vehicle-specific parts.

By the way Maine allows up to a 2" larger diameter than stock (not 2 sizes). So you could run up to 265/70-16s.

 

[smalltownusa]

Yes I planned on getting my tires at a tire discount center. No local place to buy tires here. I only mention the dealer as they will be the ones placing the inspection sticker. I saw posts where people had installed the 265/70/16, and there was rubbing. Trying to avoid rubbing even if it's at the extremes of turning. Since nobody commented on the 75 series I'm guessing they are a no go.

P,S. can't be sure the reported rubbing was on 2005 4x4 models.

 

[01STrunner]

Ah I didn't realize you had to go to a dealer for inspection. In VA we have to go to other shops. Worst case if you get a little rubbing, you could twist the torsion bars up .25" or so.

 

[TGtrac05]

I'll chime in on the rubbing issues. My 05 had the 255/70 stock and it rubbed when turning into a steep driveway. I put 265/70s on and it rubbed quite a bit at stock height, again when turning into driveways or when hitting bumps in turns. I think a lot of people have different experiences, because I've got 5" of lift in the front now on 265/75-16s and they still rub like crazy, which it seems like no one else has that issue with that much lift and 32s.

But I will say the difference in rubbing between the 255/70 and 265/70 at stock height was minimal enough that I would definitely go with the 265 for a little better look.

 

[01STrunner]

I'll chime in on the rubbing issues. My 05 had the 255/70 stock and it rubbed when turning into a steep driveway. I put 265/70s on and it rubbed quite a bit at stock height, again when turning into driveways or when hitting bumps in turns. I think a lot of people have different experiences, because I've got 5" of lift in the front now on 265/75-16s and they still rub like crazy, which it seems like no one else has that issue with that much lift and 32s.

But I will say the difference in rubbing between the 255/70 and 265/70 at stock height was minimal enough that I would definitely go with the 265 for a little better look.

I'm surprised to hear you had rubbing when you had 255s. No matter what I did I didn't ever get rubbing up front, even on trails. How much did you trim after the lift?

 

[TGtrac05]

I'm surprised to hear you had rubbing when you had 255s. No matter what I did I didn't ever get rubbing up front, even on trails. How much did you trim after the lift?

I think the rubbing is all on the sway bar, so I never needed to actually trim. Ive got so much room in the wheel well without hitting anything but you can definitely see where it rubs on the sway bar. Could just get get spacers or wheels but it's not bad enough to justify the money

 

[01STrunner]

That's all the rubbing I had too with my 35s, well after trimming lol. But I only rubbed the sway bar at full lock.