07 F150 SuperCab 4.6 2WD running 18" wheels no lift. A friend said changing to 20" wheels with 285 x 50 x 20 or 305 will require changing my braking system to larger pads and caliber. By not doing this will cause my stopping distance to increase by 30 to 40 feet. If I keep the 18" wheels will 275 x 65 x 18 rub or what is the largest size tire can I use? (I put the 2" leveling kit on hold). Thanks Guys for your help.

 

Anytime you increase the height of your tire or the weight, braking and acceleration performance will be slightly affect. I seriously doubt your braking distance will be increased enough to notice, much less 30 feet at a given MPH. Has your friend somehow not noticed the 100's of thousands of cars and trucks on the highway with larger than OEM sized wheels and/or tires?
If you keep the OEM wheels you can easily fit a 285/65-18 (33x11.50) or 305/60-18 (33x12.50) tire.

 

Thanks Wandell for your help. By keeping the OEM wheels and using either 285 or 305 will I have to level the front?

 

I went from 265/70/17 to 305/50/20 and can not tell a difference in braking. Just looks as mpg.

 

Probably not, but it would look better with the leveling kit.

 

Is there a significant mpg difference when going from 17's to 20s?

 

I went from 17's to 20's and lost about a mile and a half per gallon. Tire diameter wasn't much bigger but the wieght sure was so I assume that played a factor. To the OP a level kit is one of the easier (if you can work a wrench and have good tools) and cheaper mods you can do to really change the looks of a truck IMO.

 

Not just weight but also resistance due to the increased width. I can really tell the difference on a hill near my home. Where I used to coast and see my speed increase, I now actually slow down while coasting. I too lost close to 1 1/2 mpg.

 

But don't it look soooo much better!!!

 

When you increase the size of the wheel, the averaged center of rotational mass moves farther away from the axle. This makes it more difficult to spin the wheel/tire (Longer moment arm) and is why mpg is affected negatively. Bluejay is also correct. Increasing frictional contact surface area with a wider tire increases resistance too, on top of making the entire assembly heavier.

I moved from 20" rim on 32" tire to 17" rim and 35" tire, and am seeing slight improvements in mpg if you could believe it.

 

Definitley! The price we pay for what we think looks good!

 

Rim size does not have much to do with it, but the overall weight difference is the issue. I went from factory 20s down to an after market 18 and my mileage decreased by about 1.5 MPG. My truck is less responsive and my breaking distance has increased slightly. I have an AF1 intake, true Magna Flow Duals and VMP Tunes.

My factory 20s with Pirelli's weighed 86 lbs and my 18x9 Rockstarts with 33x12.5 Toyo MTs weigh 106 lbs each. The difference of 20 lbs per wheel is what drags your power and MPG down, plus it increases the stopping distance a little.

I do not think you have to change your brakes to handle heavier wheels.

KR-Texas

 

Also, a lot of people install larger tires/wheels and don't correct the speedometer. This means the odometer is off as well. So when they calculate their MPG's it is lower since the truck is traveling more miles than the odometer is showing.

 

Thanks all, this info is very helpful in determine what could or should I do. 20" wheels and a 2" level kit will be next modification.

 

Wish that was my case, unfortunatly, it's not.