Does an inch in tire diameter really make that big of a difference as far as performance is concerned? I plan on changing out my 265 75 R16 (31.6") tires for 285 75 R16 (32.8"). I don't want to change out the gears if I don't have too.

 

It certainly will make a difference. The difference is caused not only because of the effective gear change, but the extra weight of the tires is out at a larger radius. As the tires get heavier they are in effect four heavy flywheels that you have to spend horsepower and fuel to rotate down the road. They also have more stored energy when it comes time to stop the truck, so your brakes will wear out faster and your truck will not stop as well.

I used to believe that a larger tire would effectively gear it up thus giving better fuel economy but this is not true unless you can somehow change to a featherweight tire. The added flywheel effect of the added weight more than offsets any gearing advantage.

My $0.02,

 

I agree, it does make a difference. I deifinatly feel the difference between my 245's and 285's, and I assume you would between 265's and 285's also. The question is what can you live with? For me I can live with losing a little power and mileage in town, I plainly love the look!

 

........according to the women I have talked to....Yes, it does!!!!!!

 

John, I almost put something in my original post because I knew that someone would jump on it like you did, thanks for the laugh. The only thing I'm worried about is top end speed and acceleration. The truck has a throttle body spacer, cold air intake and I will be adding duals and hopefully the diablo predator.

Correction - the tires on right now are actually 265 70 R17 which is still a 31" tire.

 

In all seriousness.....it will make a little difference but I doubt you will really notice it much and if you install the Predator....you will be able to adjust for the different tire diameter to get the speedo right.....

 

At an actual speed of 60 mph your speedometer will read 57.8 mph. This makes for a 3.756% difference in the speedometer.

 

Do get your puter updated to the new tire sizes. about 2 months ago, I got a ticket for doing 79 in a 55 zone. But my speedo was only showing 73. Luckily, the cop that ticketed me was just having a bad hair day and screwed up just enough for me to get the ticket knocked to a 2 point violation instead of a 10 point violation.

 

I replaced 265/70R17's with 285/70R17's on my '99 OffRoad, and my mileage dropped 1 mpg in the city (14 to 13) and on the highway (17 to 16). The 4.6L is weak as water anyway, so I don't know that I noticed a drop in acceleration - the 4.6L is a factory drop in acceleration. The best thing that I've done to improve acceleration is hang another muffler on it so that I can hear it when I get on it. Now I stick my foot in it more, and the sound just makes it feel better. Of course, that knocks the mileage some more. Drive it like you stole it.

 

The replys are great, thanks. I was just worried that I would have the same problem I had with a previous vehicle. I went from a 31 to a 33 and the truck would only do 75....driving down hill with a big gust of wind.

 

I had 235 75 16's on my 97 then went to 265 70 17's I got from a buddy rims and all then I recently got some goodyear wrangler M/T 285 75 16's. I only noticed a slight power loss and not much diff in gas mileage but when figuring your mileage you have to either correct your speedo/odometer for the new tire size or take the difference into account. I have a 5.4 with a K&N intake kit and a throttle body spacer and Gibson Super Truck exhaust (the gas mileage was never all that great anyway)but these minor mods gave me about 2-2.5 mpg.and boosted the power back up.

 

My .02. With my little 4.2 it made a big diff in mileage and power. I put 255/70-16 yokohama geolanders on the truck when I got it and though it was a pretty weak motor going from the truck I had. Put 235/70-16 nokkian hakka's (dedicated snows) on for the New England winter. It was like a new truck. No more downshifting for the hills and the milage went up far more than the adjusted error accounted for. Did all the calcs but can't recall them now. With both tires the milage calc was done with a GPS for accurate mile measure.

 

every inch bigger you lose .10 off your gear set....only an inch.....you may feel a small difference on hills but it prolly won't be that bad....my 305/70/16's arn't that bad at all...truck still performs well (for a truck) and it just looks soooooo much better....you will defidently be able to go over 75 MPH.....if i get into it i can do about 95 up a local hill.....it's not very steap.....but for PA its not that bad of a hill.....keep in mind thats on the hammer pretty hard but it'll do it every time....

Have fun and make it yours and you'll love it

 

I used to deliver parts for a dealer with a 4.2 reg. cab l/b. Had the same problem, til I started taking it out of O/D. Even on the highway, which is mainly where I drove, it made a big difference. The stupid thing was geared for the salt flats, and the mileage didn't change that I saw, because it was either have the pedal on the floor to keep it moving, or grab a gear and not work as hard, but turn faster. Something like that. (It's late, cut me some slack!)