Why are you running the 255/45/20 tires?

[pjw315]

I need to replace the tires (245/45/20) on my 2013 EcoBoost MKS and I noticed allot of people are running 255/45/20's on their SHO's

1. What are the pros and cons of running the 255 tire?
2. Will it work on my MKS without rubbing?
3. Do you need to re-calibrate the speedometer?
4. Will it affect my warranty if I have a PTU or other drive-line issue in the future?

[AJP turbo]

Why do u want that tire? Better handling...u already want it so do it

Pros....more rubber...cons...speedo will need corrected via a tune if u want it perfect...if u don't care that it's off then don't worry....I'd have to figure it out but It may not even be 1mph off

The tire would be .355" taller not even close to rubbing

Don't know about warranty ...I doubt it would be a problem...but the argument could be made...you effectively change the gear ratio of the car....the tire is the last or first gear really...however u look at it...car will get slower

I had a friend that was denied warranty work on his tranny of a gmc truck because he put tiny tires that had a much smaller diameter than stock and they said it increased Rpms of the tranny and motor....they were correct but the argument could've been made that it put less strain on the tranny because of the increased leverage.....the bigger tires u want to install will actually be harder for the car to turn not to mention heavier....albeit not by much

[AJP turbo]

They really only want the size tire that's on the door panel sticker

[FoMoCoSHO]

Ford will typically only have an issue when dealing with mismatched sizes and AWD. That can and does cause awd components to fail.

So moving to the 255's all the way around shouldn't be an issue.

[sunwolf]

I wanted to widen the tires on my car but wasn't sure one size would make that big of a difference. In the end the deciding factor for me was that 255 were actually $200 CHEAPER than 245s. That should be motivation enough.

[PokerMunkee]

Is going from a 245 to a 255 going to affect the speedo??

[AJP turbo]

Is going from a 245 to a 255 going to affect the speedo??

Absolutely

Very minorly though

[ZSHO]

I have 255-45-20 and coudnt be happier and even my service advisor recommended that size,he said just dont jump into a lower profile tire,guess its probably not good for the suspension and probably bend a rim or two depending where you live,cause these flower rims have been through a war zone and never had an issue,kind of makes you laugh when you see brand new Mercedes stuck on the side of the road everyday due to potholes.Z

[SHOdded]

A favorite site for tire size calculation:
http://www.tacomaworld.com/forum/tirecalc.php

Many others found via web search.

[southtxSHO]

Great info here , definitely going with the 255 tire

[sunwolf]

Is going from a 245 to a 255 going to affect the speedo??

I am currently running 255 on the back and 245 on the front. Switching out the fronts next week. Speedometer has moved less than half a mile per hour. I compared the gps speed vs OBDII speed in torque app.

[AJP turbo]

Is going from a 245 to a 255 going to affect the speedo??

I am currently running 255 on the back and 245 on the front. Switching out the fronts next week. Speedometer has moved less than half a mile per hour. I compared the gps speed vs OBDII speed in torque app.

How do u know where the source of speed for the pcm is?...it could be reading from the front....and the speedo inaccuracy will not be linear ...the faster u go the more it will be off...u can gain and lose 1/2 mph with just tread wear so u being off by 1/2 mph is not conclusive because u only have 2 of those tires.

[glock-coma]

Tire 1 is 245/45/20

Tire 2 is 255/45/20

[bpd1151]

Ford will typically only have an issue when dealing with mismatched sizes and AWD.

That can and does cause AWD components to fail.

Although I have been far out of warranty, I wouldn't necessarily agree with the blanket statement of mismatched tires causing AWD component failure.

After all, I've been a running example of not only different tire sizes from factory specs, but also have been running a staggered set, all without any issues whatsoever, for several years now.

Both DD use, as well as track tortured.

So I think that's kind of a premature statement/opinion to haphazardly throw out there for public consumption.

[FoMoCoSHO]

Ford will typically only have an issue when dealing with mismatched sizes and AWD.

That can and does cause AWD components to fail.

Although I have been far out of warranty, I wouldn't necessarily agree with the blanket statement of mismatched tires causing AWD component failure.

After all, I've been a running example of not only different tire sizes from factory specs, but also have been running a staggered set, all without any issues whatsoever, for several years now.

Both DD use, as well as track tortured.

So I think that's kind of a premature statement/opinion to haphazardly throw out there for public consumption.

That is not an opinion.

I sleep with a master certified service adviser who has also spent some time working in the warranty department.

This is a real issue that can and does damage the AWD system. I can also assure you if you have a PTU failure with this setup under warranty, you should be prepared to pay for a PTU.

"Major dissimilar tire sizes between the front and rear axles could cause the AWD system to stop functioning and default to front wheel drive or damage the AWD system.

That quote is from my owners manual.

So which is the haphazard opinion?