What is a good tire size...

CCKJ03 · **Posted:** Tue Sep 11, 2007 8:52 pm

Thanks to all for the info on my last post.

My next question is...what is a good tire size for a KJ with a 2+" Lift (RRO 2.125). I have heard goodthings about 245/75/16's however, how are 255/70/16's or 265/70/16's? Would like to hear your opinions and inputs.

CCKJ03 · **Posted:** Tue Sep 11, 2007 9:00 pm

oops...looks like a lot of tire questions on the fourm recently. Hope you guys don't mind, I feel like the little brother when I am around the wrangler guys. Sometimes you get overlooked.

DarbyWalters · **Posted:** Tue Sep 11, 2007 9:12 pm

It depends if you want to do any "cutting" or "trimming". Stock tires are 29.2"...I know that 235/75/16s will fit without a lift on stock rims at 29.82". Anything taller on stock rims and you start contact. You also have to worry about tire width, rim width (aftermarket) and backspacing (aftermarket). If you get a wider tire, wider rim or a rim with less backspacing...you can start to hit the outside of the wheelwells and/or the pinch weld. You can also start hitting the front sway bar with 245/70/16s or wider tires ie. 255/70/16s. If you hammer back the front wheelwell pinch weld and use stock width/bs wheels, you will be OK for the most part with a 245/75/16. Anything larger and you will have a few more "creative mods" to perform.

Dje Ryu · **Posted:** Tue Sep 11, 2007 10:00 pm

^ What he said.

ed. · **Posted:** Wed Sep 12, 2007 12:07 am

Would 235/85/16 be an option for this guy with the pinch weld mod?

Alak · **Posted:** Wed Sep 12, 2007 3:18 am

My tires are 225/75R16 at 29.6" and I get no contact except for full flex of the rear axle. No lift.

http://www.lostjeeps.com/forum/phpBB3/vie ... php?t=5375

I keep this link bookmarked so I dont even have to search :lol:

DarbyWalters · **Posted:** Wed Sep 12, 2007 9:34 am

ed. wrote:

Would 235/85/16 be an option for this guy with the pinch weld mod?

I had 235/85/16s on my old KJ (after I wore out the 265/75/16s) and they fit very nicely. They are a bit taller (almost a true 32") than a 265/75/16 but more narrow.

ed. · **Posted:** Wed Sep 12, 2007 6:14 pm

DarbyWalters wrote:

ed. wrote:

Would 235/85/16 be an option for this guy with the pinch weld mod?

I had 235/85/16s on my old KJ (after I wore out the 265/75/16s) and they fit very nicely. They are a bit taller (almost a true 32") than a 265/75/16 but more narrow.

Nice, how much lift did you have though?

Freshmud · **Posted:** Wed Sep 12, 2007 8:08 pm

DarbyWalters wrote:

ed. wrote:

Would 235/85/16 be an option for this guy with the pinch weld mod?

I had 235/85/16s on my old KJ (after I wore out the 265/75/16s) and they fit very nicely. They are a bit taller (almost a true 32") than a 265/75/16 but more narrow.

but you dont really want height though more width i always thought cause the more tire the grabs the bround the better but i could be wrong. IM going with something wider onces i finally order my rustys lift

ATXKJ · **Posted:** Wed Sep 12, 2007 8:27 pm

Actually the amount of tire on the ground is more a function of the tire pressure you run not the tire width
if you have a 4000 lb vehicle - with 33psi - you have 30 square inches of each tire contacting the road surface
- at 40 psi it 25 sq inches - at 25 psi it's 40 sq inches.

With a 235 tire the contact patch is long and narrow - with a 265 tire it's short and wide.

tjkj2002 · **Posted:** Wed Sep 12, 2007 8:36 pm

ATXKJ wrote:

Actually the amount of tire on the ground is more a function of the tire pressure you run not the tire width
if you have a 4000 lb vehicle - with 33psi - you have 30 square inches of each tire contacting the road surface
- at 40 psi it 25 sq inches - at 25 psi it's 40 sq inches.

With a 235 tire the contact patch is long and narrow - with a 265 tire it's short and wide.

Not true at all,a 235/85 and a 265/75 are about the same hieght,but the 265's are 30mm wider(about a 1 1/8") and with both at the same psi the 265 will have a bigger contact patch then the 235/85 does.Two tires with about the same hieght but with one wider then the other the wider tire will always have a bigger contact patch when both are at the same psi,now 2 different hieght(more then a 1" difference) then it's a whole different ballgame.

ATXKJ · **Posted:** Wed Sep 12, 2007 9:27 pm

There is variation due to tire internal construction - i.e. very stiff sidewalls will transmit more force at the edges than just the air pressure alone - thin sidewalls follow the air pressure more, but if the tire construction is the same - the contact patch will match the pressure.

Yes the 265 contact patch will be wider - but it will be shorter than a 235 at the same pressure - This may not be real obvious from just looking at it.

as an example at 25psi - a 265 would have a 10.8 wide x 3.7 long contact patch, 235 would be 9.6 x 4.1 - i.e. .4 difference in length - at 40 psi it's 10.8 x 2.3 vs 9.6 x 2.6 i.e. .3 difference
(assumes xsection ~ tread width which is a marginal assumption)

mattblundell · **Posted:** Thu Sep 13, 2007 2:35 pm

Hey folks,

A couple of people have recommended the Cragar Soft 8's to me. I have found them online at a reasonable price, only what size wheel and tire for a stock KJ (can't afford the lift too, just yet) ?

Matt

Freshmud · **Posted:** Thu Sep 13, 2007 3:33 pm

mattblundell wrote:

Hey folks,

A couple of people have recommended the Cragar Soft 8's to me. I have found them online at a reasonable price, only what size wheel and tire for a stock KJ (can't afford the lift too, just yet) ?

Matt

Ditto except im getting the rustys lift soon

jason thompson · **Posted:** Thu Sep 13, 2007 6:46 pm

mattblundell wrote:

Hey folks,

A couple of people have recommended the Cragar Soft 8's to me. I have found them online at a reasonable price, only what size wheel and tire for a stock KJ (can't afford the lift too, just yet) ?

Matt

I will recommend NOT getting them
if you do you will not be able to run tires that you can on the OE wheels with out rubbing
lots of factors the main one being back spacing cause issues
stick with the OE wheels and you can run bigger tires with less lift
check out some of the pst posts
but in a nut shell
OME lift with 245/75's (31X10.5)on OE wheels rub's less than
Rustys coil lift with 30X9.5's on 15X7 steelies w/3.75 B/S

ROADHAWG · **Posted:** Thu Sep 13, 2007 7:17 pm

I ran my rough country 3" lift with 265/70/r16 and experienced minor rub on the pinch weld but the rub on the fog light doors and the sway bar was pretty bad. When I tossed the R.C. lift and switched to the Frankenlift with an ARB front bumper all the rubbing issues disappeared at the pinch weld. I still have minor rub at the swaybar but now that the fog light doors are gone so is the worst rubbing :twisted:

tjkj2002 · **Posted:** Thu Sep 13, 2007 7:31 pm

ATXKJ wrote:

There is variation due to tire internal construction - i.e. very stiff sidewalls will transmit more force at the edges than just the air pressure alone - thin sidewalls follow the air pressure more, but if the tire construction is the same - the contact patch will match the pressure.

Yes the 265 contact patch will be wider - but it will be shorter than a 235 at the same pressure - This may not be real obvious from just looking at it.

as an example at 25psi - a 265 would have a 10.8 wide x 3.7 long contact patch, 235 would be 9.6 x 4.1 - i.e. .4 difference in length - at 40 psi it's 10.8 x 2.3 vs 9.6 x 2.6 i.e. .3 difference
(assumes xsection ~ tread width which is a marginal assumption)

265's----10.8x3.7=39.9 sq in,235's----9.6x4.1=39.36 sq in,so the 265's DO have a bigger contact patch,It's simple math,the same tires,same hieght,but different widths the wider tire will always have a bigger contact patch.Those #'s look a little fishy anyway's,at least the lengths,the widths are a little off to since a 235mm equals 9.25" not 9.6",and 265mm equals 10.43" not 10.8".

ATXKJ · **Posted:** Thu Sep 13, 2007 9:22 pm

"265's----10.8x3.7=39.9 sq in,235's----9.6x4.1=39.36 sq in,so the 265's DO have a bigger contact patch,It's simple math,the same tires,same hieght,but different widths the wider tire will always have a bigger contact patch.Those #'s look a little fishy anyway's,at least the lengths,the widths are a little off to since a 235mm equals 9.25" not 9.6",and 265mm equals 10.43" not 10.8"."

Yeah - it comes from trying to do things from memory instead look up the conversion factors - I used 24.5 mm/in instead of 25.4 mm/in.

If the tire was solid - you'd be right -but it's not solid - it flexes and it flexes according to the pressure of the air inside.
If you have 10 lbs per sq in of air pressure - then you will have 1 sq inch of rubber on the road for every 10 lbs of vehicle. If you have 40 lbs per sq inch of air pressure - then you will have 1 sq inch of rubber for every 40 lbs of vehicle. It does not matter if that sq inch is long and narrow or short and wide.

Johnboy · **Posted:** Fri Sep 14, 2007 9:16 am

jason thompson wrote:

mattblundell wrote:

Hey folks,

A couple of people have recommended the Cragar Soft 8's to me. I have found them online at a reasonable price, only what size wheel and tire for a stock KJ (can't afford the lift too, just yet) ?

Matt

I will recommend NOT getting them
if you do you will not be able to run tires that you can on the OE wheels with out rubbing
lots of factors the main one being back spacing cause issues
stick with the OE wheels and you can run bigger tires with less lift
check out some of the pst posts
but in a nut shell
OME lift with 245/75's (31X10.5)on OE wheels rub's less than
Rustys coil lift with 30X9.5's on 15X7 steelies w/3.75 B/S

I was under the impression I could get Soft 8's that essentially matched the OE specs, such as diameter width offset and back space? But I guess I have also decided on 245/70/16 so I should have a little more room to play with if I cant get OE sized Cragers...

What is a good tire size...

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