Changing Tire Size

I've done similar tire changes in the past (up 1 size basically) and for me it meant:

1) slightly more sluggish acceleration- noticeable, but not particular bothersome to me
2) a slightly better ride (more sidewall) assuming same tread aggressiveness
3) a small loss in steering sharpness (a touch more 'wander' due to wider tread)
4) a bit more ground clearance & a higher step-in
5) only a slight drop in MPG, if any...more-or-less a wash

Above based on going from 275/70s to 285/75s on a 2002 Land Cruiser, going from 225/70s to 235/75s on a 1990 Cherokee, and downsizing from 285/75s to 265/75s on a 2002 F250 7.3L.

To state the obvious going up more than 1 size will make the above more pronounced.

I have 4:10 gears and was concidering doing that also in hope that the reduced engine speed would help my mileage but many have said the larger tires will eat up any gain. I have a hard time buying that and even if its a wash the lower rpm should be better for the engine. I'll wait to see if someone with real world experience comes along.

My last truck came from the factory with 265's. When they wore out (around 40k) I switched to 285's. Personally, I think they look much better. I did not notice any difference in handling, MPG, etc. I did have the dealer re-set my speedo.

I went from 245/70r17 to 285/70r17 on my 2011 RAM. This was with a 3.77 axle ratio. This was a substantial change in diameter so I had the dealer reprogram the speedometer. I must say the tires look much better on the truck than the old ones.

There was a noticeably reduction in rpm when cruising and it seems like I gained some mpg - I get about 19 MPG on long freeway drives. Around town mileage is about as bad as it was before. I seldom use all the power available from the engine anyway, so acceleration still feels very good. The weight I tow is well below the maximum for my truck so I can't say I've noticed any difference there.

This is what mine looked like with the factory 265's







This is what it looks like now with 285's





My mileage did not change but my rpm did. My truck runs 74 mph @ 2000 rpm now and with the factory tire it run 70 @ 2000 rpm. My truck loves to tow at 1800-2000 rpms so it did hurt the power while towing because I run at about 1800 out on the interstate. When I come up on a big hill I now have to run it on up to 2000 or so and let it back down going up the hill if I don't want it to gear down. Before, I could run it up around 2000-2050 and put my foot down and it would hold it's speed on a 5-6% without gearing down as long as I didn't come up on a gas truck screaming along at 50 mph. LOL!

transamz9,

Nice truck and that does make it look better.

What gears are you running? Any mods?

I'm really leaning towards going with the 285.


Please keep the replies coming.

ldmc wrote:
transamz9,

Nice truck and that does make it look better.

What gears are you running? Any mods?

I'm really leaning towards going with the 285.


Please keep the replies coming.

The truck has 3.73:1 and yes a few mods. Suspension,engine, and as you can tell, body.

I like running my truck level and not jacked up in the rear. After the tire size change I added a 2" level kit and some street Bushwackers. Before I added the level kit I had to run my rear low to be level. Here's a shot of it down the side after I added the flares and level kit.




I don't have any good pictures of it from the side with the level kit and flares yet.

Seems like you could actually increase your mileage according to the charts.

http://i45.photobucket.com/albums/f98/LPG_PWRD/interco.jpg

Interesting chart. It does appear I should get better mileage. I was looking at an F250 with the same size tire on it and it appeared the side wall was bulging a little do to the larger tire size. Wonder if that will impact handling..

You can get a tuner such as Edge and it will reprogram your speedometer according to tire size, neat huh? You can also add up to 60 HP to your engine for towing. Worked for me. You can track and compare injectors and watch 4 engine functions at once, like Trans Temp, Coolant Temp, EGT and Vacuum.