running 33's
JK Freak
Joined: Sep 2008
Posts: 916
Likes: 3
From: Terryville, LI, NY
Typical changes in true speed vs indicated speed are as follows, based upon using factory tire pressure:
285/70-17: +1.2 mph
33/12.50-17: +2.1 mph
As others have said, the difference is insignificant. Note that during the life of the tire, if you wear the tread half way, you can cut the change in half. Indeed, stock tires worn half way would reverse the equation with your true speed being about 0.5 mph slower than indicated. So, you can see that switching to 33" tires is not something to worry about.
285/70-17: +1.2 mph
33/12.50-17: +2.1 mph
As others have said, the difference is insignificant. Note that during the life of the tire, if you wear the tread half way, you can cut the change in half. Indeed, stock tires worn half way would reverse the equation with your true speed being about 0.5 mph slower than indicated. So, you can see that switching to 33" tires is not something to worry about.
JK Enthusiast
Joined: Dec 2007
Posts: 383
Likes: 0
From: jackson,ms
It will look fine, i ran 1 3/4 spacers in the front and 1 inch spacers in the rear for about 6 months.
JK Newbie
Joined: Jun 2010
Posts: 7
Likes: 0
From: DuBois, PA
Just added Teraflex Leveling Kit, 2" in front, 1" in rear with 285/70/17 Cooper STT. NO Spacers. I love the attitude adjustment. With 2 different GPS units on board, my MPH are exactly correct with these tires. My steering wheel did not need adjusted. I notice no power loss. Just a good looking mod. The height is just right for what I do. I'm not crawling rocks or going mudding just daily use. I just wanted it to look like a jeep should. Tires barely make a noise on the road also.
JK Enthusiast
Joined: Feb 2010
Posts: 422
Likes: 0
From: Plover, WI & Benson, AZ
Funny you should ask ! I came on the forum today to see about the same thing. I have had new tires and rims for about a week and it seems like:
1. I've lost about 2 MGP (according to the avg on the dash computer)
2. have trouble keeping my Jeep cruising at 80 and
3. am downshifting more than before in order to take inclines (sometimes mild)
I have a 6 spd with 3:73 gears, stock tires were 255/75/17 (actual diameter 32.1) on 17 x 7.5 rims.
Went to 255/85/16 (actual diameter 33.1) on 16 x 8 rims
When I am doing 80, my RPMs are at about 2,750, whereas before it would be right at 2,500.
Would a Superchips correct this ?
1. I've lost about 2 MGP (according to the avg on the dash computer)
2. have trouble keeping my Jeep cruising at 80 and
3. am downshifting more than before in order to take inclines (sometimes mild)
I have a 6 spd with 3:73 gears, stock tires were 255/75/17 (actual diameter 32.1) on 17 x 7.5 rims.
Went to 255/85/16 (actual diameter 33.1) on 16 x 8 rims
When I am doing 80, my RPMs are at about 2,750, whereas before it would be right at 2,500.
Would a Superchips correct this ?