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Discussion Starter #1
I was wheeling with a friend, I have a stock Rubi, and he's got a YJ with 33x12.50 MTR, and some minor lift ( shackle on the leaf springs, with long shocks). Both vehicles were capable wherever we went, and I did not use any locker. Then I suggested to try some minor rocks in 2wd just to see if he had more traction due to his larger tires ( would not be fair with my lockers and 4:1 T-case). We aired down to 20 PSI. And traction he did have. I noticed the following: his tires were taking the shape of the rocks like they had 10 PSI , and mine were barely bulging, like I had 30 PSI.We were both running 20 PSI, but wherever there was a minor obstacle, I would spin much easier, and he would go. Of course, I'm talking small obstacles, as we were in 2wd and I had no intention of overheating my clutch. On the other hand, he lifted tires much easier in the air, although he's got long shocks. Now after that, I have three questions :
1- Do 33 give better traction due to larger footprint even on rocks ( I know it's better in sand and soft terrain).
2- Do leaf springs add more traction by pressing the tire more on the ground? ( Although his tires were lifting very easy in the air ).
3- Were his tires flexing much better due to his load "C" compared to my "E"? ( If so, what's the point of DC equipping "E" for ultimate rock climbing?
Thanks for anybody who might know one or all the answers.
 

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1. Yes.
2. ??
3. Yes.

My answer to your final question is because it is not a rock crawler. I think this rig was designed specifically for Moab. Low center of gravity, sticky tires, lockers. . . Probably why they named the wheels "Moab"s?
Also, note that Jeep had a Rubicon rally at Easter Jeep Safari held at. . .
Moab, of course.
 

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1. Just marginally. Tire contact area is more an issue of tire cross-section rather than tire diameter.
2. No. It's a function of actual suspension articulation as opposed to the basic design. However, most people believe a coil spring setup gives more flex than a leaf spring design.
3. At the same pressure, yes. Now, air your MT/Rs down to about 12 psi. They'll flex. And when you scrape them against a sharp rock your MT/Rs are going to say, "Oh, a rock." His load range C tires are going to say "Psssssssssssssst' as they deflate from a ripped sidewall. I'll take the stiff sidewall.

The 305/70R16 MT/Rs are load range D. At the same pressure they ride softer than the stock 245/75R16s.

Jerry
 

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Discussion Starter #4
Thanks guys. I'll try 12 PSI next time, although I never complained about traction in 4wd. It's just that funny and probably useless 2wd test. jeepDawg, sorry i'm not familiar with Moab except the Rubi wheels. What does it refer to please? As for my inquiry about DC , I was referring to the 2003 Jeep brochure, where they call the Rubi: EXTREME ROCK CRAWLER. Thanks.
 
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Stock the vehicle is what I would call a moderate Rock Crawler. Extreme is a subjective term indeed. lol

with 3" of lift and some beefy 33's on there, it gets much closer to extreme.

Remember his tires are fatter than yours by a lot. The optimal traction size is generally considered a 12.5" wide tire.

Tire flex has many factors involved...

Side wall strength, the actual ratio of side wall to tire thickness, just to name a few. It common, for one person to have to air down further for the same amount of sidewall flex as somebody else with a different tie.

Did either of you have your swar bars off?? This has a dramatic effect on flex. Just ramp a vehicle with them on then the same vehicle with them off....
 
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