...and mileage?

Hey All,

I'm in the process of ordering 22" wheels. I was going to go with the 305/45-22 tire, but, the rep that I'm talking to is really pushing the 305/40-22.

Here are the specs:

• The stock diameter is 30".
• The tire I am looking at in the 305/45-22 is 32.8"
• The tire he is recommending is 31.7"

He's telling me that the difference between stock and the 40 in MPH will be about 5% where as with the 45s, the difference is over 9%.

In other words, with the 40s my speedo will be showing 65 and I'll actually be doing 68.6. with the 45s my speedo will be showing 65 and I'll actually be doing 71.

He says that I might have warranty issues if I go too tall. He also said that the service department could recalibrate for the 40s, but, maybe not the 45s. He said even if I re-calibrated with an Edge or other programmer, the warranty on the vehicle still could become an issue.

He also said that because the tires are significantly taller than stock, that the MPG could suffer.

Any thoughts or suggestions?

Thanks, in advance!

Ernie

 

Any change in OEM products can result in a void of warranty. However alot of dealers will not go to drastic measures unless something seriously goes wrong with your truck. To answer the other question yes it will affect gas mileage...Again any change in OEM parts will change mpg for the good or bad. In your case I would say maybe a little worse, I know it was for me. Nice rims by the way!

 

He's right. But let's be real. You are talking about going to a 2 or 3 inch taller tire than stock. It's not like you are mounting a set of 44's on there.

 

Thanks for the comments guys...

Is it possible for the dealer to recalibrate the speedo? Or am I gonna have to use a chip/programmer of some sort?

E

 

Yes the dealer can recalibrate your speedo but it probally going to cost you in the neighboor hood of $200-300 my guess. I had a 78 F-150 recalibrated and that did'nt have any computer crap on it and it was $130. Keep in mind if you switch tires and rims in the winter time you would have to do it again at that point in time.

 

Any Ford dealer can do the speedo recal with the simple stroke of a few keys on the computer. Some dealers don't charge for doing it some do, either way not a big deal or money.
As for warranty, going with that little of a change I wouldn't worry about it. About the only warranty issues thay cold deny would be wheel related..wheel bearing, brakes, suspension, but even that would be a reach since you are not talking monster mudder tires and wheels.
As for MPG, it would depend on what you are installing on the truck. If the new combination is heavier than the stock combination you are going to loose MPG. It takes more power to turn a rolling mass that weigh more. Of course on the flip side if the new weight is less, it could save a few dollars at the pump, but don't count on it.
Remember that if the new tires are not recalibrated on the speedo, then when you figure the mileage per gallon by hand, if the difference is 4.6% off on the speedo then it is also 4.6% off on the odometer. So your figure will also be off by the same amount, you will need to figure this in to the equation when looking for your MPG.
Also the new diameter of the tire will change the effective gearing of your rear end ratio. A simple change in tire size can change a 3:73 ratio to a 3:55.
This normally would mean better mileage and less off the line umph.
There are a number of on line tire calculators that will allow you to compare tire sizes as well as see what the difference to the rear end ratio change will be, check it out and it may make it easier to choose.
Course another then to check into is will the larger of the two tire sizes rub any where. I know that the BFG AT KO 285 18s I put on my 05 F150 did rub in reverse at a full turn.

 

Good info! Thanks!

I can't seem to find anyone that has had any issues with the 305/45-22s rubbing any where...

The wheels I am getting are running a 35mm backspace which sounds pretty standard.

I'll call around to the dealerships and see what they would charge for a recalibration...

Thanks again!

E

 

as others stated- the dealer can update (if they charge, its about .5hrs- $20-30) the pcm with your new tire size- BUT they can only go down to 650 Revs per mile- so if you check your tire specs, and they are below 650, you're speedo still wont be accurate...

good luck-

 

Damn... The tires I'm looking at in the 45 series is listed as 635 revs per mile... In basic math, that's a little over 2% difference if recalculated at 650. That might not be so bad...

 

I wonder how greatly an additional 2.8" will affect my overall gear ratio or off the line take off.

I'm running a 3.55ls rear end right now...