Power Loss with Increase in Tire Size?

I've read a number of threads on here about people with 2.7's losing a few mpg's and some perceivable power loss/decreased rate of acceleration when increasing tire size from the stock 245/75/16 to 265/70/16.

I'm currently running stock steelies and AT20s at 245/75/16. Steels weigh about 32# and AT20s about 32#= ~64#

I want to upgrade to Cooper AT3 4S in either 245/75/16 or 265/70/16, but I'm concerned about power/mpg loss in the 265 size.

The AT3 in the 245 runs 37# and in the 265 runs 39#. I'm planning on putting these on a set of alloys I picked up which reportedly run ~25#.

So with the alloys, the At3s in 245/75/16 would be a little lighter than the current set up, and the 265/70/16 would be about the same weight at ~64# per wheel.

My question is it just the increased mass of the slightly heavier 265/70/16 tire causing the power loss and decreased mpg folks experience? Or would the increased surface area of the slightly wider tire in contact with the pavement be contributing as well?

I'm wondering if I should expect power and mpg loss if the net weight of the new wheel and tire setup is close to same weight of my current set up? Love to hear people's thoughts on this. Thanks!

 

I lost 4-6mpg when I went from the stock tires to 10-ply in my old 2.7. No change in size, just tire weight. Not sure if I really noticed any change in power, though. Hope that helps.

 

Thanks for the feedback. Seems like it doesn't take much weight to drop the mpgs in the 2.7. I do a lot of highway miles so I'm pretty sure I'm going to stick with the stock size for mpgs, noise, etc

 

Check out the tire size calculator. There is a sticky up at the top of the wheel section. You'll find that a 265/70/16 is barely larger in diameter, and just under an inch wider than your stock tires. The only things to compare in the two sizes is weight (ply difference?) and probably a minimal rolling resistance difference. A real change in size would be 265/75/16.

Stock TRD is a 265/70/16, and I dropped down to a 245/75/16 for my snow tires so I had a narrower contact patch, which can be helpful in snow.

 

Going to a 265/70/16 or 265/75/16 isn't that much of a difference so it shouldn't make a big difference. When you lift the vehicle, it catches more wind and taller 285/75/16 that weigh more start to have a bigger effect. I think if you go with the 265/75/16 and aluminum wheels it will be a marginal difference. I'm running 305/65/17 with 3" lift and average around 17 mpg in the warm months. It's getting colder now and I can already see the mpg dropping because of it.

 

Unsprung weight is the enemy.

Diameter changes effective gear ratios.

As others have suggested use the tire calculator to help with the gearing impact.

Don't add any more weight than you have to to achieve the function you are striving for. If you are just doing it for the looks factor, remember the 'pay to play' theme.

 

Get rid of the steel wheels for alloys, immediate weight savings.
Don't be dead set on Cooper tires, notoriously heavy based on my research for 33-35" tires to replace the BFG KM2s.
Upgrade your clutch, intake, and exhaust. Or at least clutch and exhaust. Thank me later.
Regear to ANYTHING over 4.10s if you ever plan to add any weight in any fashion

I've got armor, 255/85r16 KM2s (33s), LCE clutch and header, regeared to 4.88s, lift, and rear lunchbox locker. You won't regret it.

 

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