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Converting off road tire sizes to "standard"
I need to help a friend buy new rims and tires for his recently acquired 1979 Jeep CJ-7.
Now those off road tires have those "weird" sizes and I have no idea what I am dealing with. I would like to know if there is a way to convert them into the normal ( i. e. like 265/60/15) style, so I know what we are dealing with.
He wants to go bigger and wider and unfortunately my tire size simulator only works in passenger car mode.
This question would be better suited for an off road forum but as I know that this is the site for unlimited knowledge and wisdom on almost any subject, I feel confident to ask my brothers in arms. ;-)

[Image: 1z21rv4.png]


"If I were you...... I´d rather be me."  Tongue

Check out my video:

Heres a helpful website to get you close to what you want.


Hope this helps.


1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]

Truck and off road tires are simple for instance if you are looking at a 31-10.50x15, that tells you the tire is 31 inches tall from ground to top of tread, it is 10 1/2 inches wide, and of coarse you know what the 15 is. There are no percentage of width to get height
Ok, Thanks guys!
I'll see if I can work with that. :-)

[Image: 1z21rv4.png]


"If I were you...... I´d rather be me."  Tongue

Check out my video:


31x10.50/R-15 is roughly 245/70-R15
33x12.50/R-15 is roughly 285/70-R15
35x14.50/R-15 is roughly 315/70-R15

These are the common sizes for Jeeps that are going to be streetable. If he's wanting to build an off-road machine, the sky's the limit on tire sizes.

31s will fit in stock configuration. 33s will be better with a 4" lift. And 35's will be better with 6" lift.

My 1980 Jeep CJ-7 came to me with stock suspension, 31x11.50/R-15s on stock rims, and 2.73 gears - I had the most fun with the Jeep in stock configuration, BTW. After about 5 years, I installed a 4" Pro-Comp lift and 33x15.50/R-15 Super Swamper TSX tires on 15x10 chrome/black rims, and with the 2.73s, it was a nightmare to drive (no power whatsoever, and the speedometer read 12% low - indicated speed=65, actual speed=73). in 2004 or so, I changed gears to 4.10s, and the speedometer problems went the other way, reading 15% high (indicated speed=75, actual speed=65). Ideal gears for 33s IMHO are 3.54s.

Just something to consider when picking out bigger tires.

Also, you'll need to extend the brake lines for lift kits over 4", as well as lower the cross-member for the transmission/transfer case mount about an inch (to relax the driveline angle a little).

Here's the drastic change between stock lift and tires, up to 4" lift and 33x15.50 wheels. Here is Day One after getting it home:

[Image: jeepnew1.jpg]

[Image: jeepnew2.jpg]

Sometime in 2005 or 2006, after 4" lift, Swampers, and wide-trac axles:

[Image: EricJeep2.JPG]

[Image: jeepinmud1.jpg]

Hope that helps with the decision.


[Image: mach1sig2.gif]
Something to also consider: the '76-'81 CJs came with what are called "narrow-trac" axles, and in '82 they went with "wide-trac" axles (Dana 30 front, AMC M20 rear). When I first got the Swampers in '96, they were tucked in pretty tight, and even rubbed on the frame/inner wheel wells when the suspension flexed in the rear, while the tread lugs engaged the front springs at full steering lock - as well as caused limitations on the suspension articulation.

Once I swapped in the wide-tracs, all of that went away, and I got my steering radius back as well.

You can see the difference in width by how far the rear tires stick out of the fender flares - about 2.5" on either side.

[Image: Jeep1.jpg]

[Image: widetrac3.jpg]

Hope that helps as well.


[Image: mach1sig2.gif]
That's a nice lookin" Jeep . Cool Remind's me of my old 84 Bronco 4" lift , warmed over 302 4V , 35/14.50/15 monster mudders ,miss playin" off road .

[Image: 1_11_01_14_4_00_47.jpeg]
460 , Edelbrock Performer carb. + intake , 204 / 214 cam , Pertronix Flamethrower 2 billet dizzy + coil , Crites long tubes , C6 .

Thanks! Those shots with the big tires are actually older... somewhere around 2004. Oddly enough, I was getting ready to drop my AMC 360 and TF727 into it, when I found the Mach 1. I had just finished up replacing the rear 'corners,' building the winch bumper, nerf bars, and spare tire rack when it jumped out at me on Craigslist.

The factory tire rack really chewed up the sheet metal corners
[Image: 9728_105046226172971_8215821_n.jpg]

This home-grown rack mounts to the frame - no sheet metal at all
[Image: 27851_123617084315885_5206766_n.jpg?lvh=1]

Welded on the nerf bars - it's actually on the same lift as the Mustang currently inhabits rofl
[Image: 30909_131319173545676_6666590_n.jpg]

Using the bender and welder to get it all together
[Image: 37306_137000419644218_3731774_n.jpg?lvh=1]

All painted up and the Warn 8275 winch mounted. Won a trophy at the car show that day, too Big Grin
[Image: 316262_293672787310313_1370259802_n.jpg]

'84 Bronco... VERY cool thumb


[Image: mach1sig2.gif]
These are 35s..

[Image: IMG_1994_zpsb888de9f.jpg]

[Image: elbe-snow-1_zpscd7ace57.jpg]

And mine's not trail rated, it's trail raped.

[Image: 100_0993Small.jpg]

1973 Mach 1 Q code 351 4V, 9A paint, standard interior, 3.50 rear, C6 trans.
Bronco IIs were WAY under-rated. Nice rig! thumb


[Image: mach1sig2.gif]
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