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Discussion Starter #1
I have some basic questions as i try to understand the nuances of suspension and handling.

I see most tires run rather small vs advertised size, for instance my duratrac 285/70/17 measure just 31 7/8 mounted on my light jk 2dr and at 32 psi. Those are sold as 33. The 315/70/17 of my neighbor measure 33 7/8 those are sold as 35. In both cases we measured it by using a level and confirmed it by measuring circumference using chalk inprints and dividing it by pi (3.141592) then we used closest measure (¾ or 6/8 instead of 7/8) in procal and xonfirmed speed with speedometer app.

So a duratrac 33 is just adding 1 inch versus stock, a 35 adds 3.

What is most damaging to the axles? The extra inch in diameter, the extra weight or the extra ½ inch of backspace in 4.5 bs wheels?

Duratrac are small but are also the lightest (less rubber i guess) so a 35 duratrac weights less than most real 33 and 34. Am i right to think that in a rubi with 4.1 and dana 44 the duratrac 35 are as good or as damaging as the 33s on a 3.73 with dana 30 on a sport jk? Bs 4.5 in both cases.

So assuming 3" lift in both cases, with the aev 2.5 dualsport lift (it renders 3" in jk 2 dr), with geometry correction brackets and with teraflex forged front trackbar i am as good with 35 on the rubi as with 33 on the sport?

Usage is camping, fishing, backroard traveling in routes that i would classify always as easy to moderate trails but never epic rock climbing or rubicon class trails. Just classic expedition.
 

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It's diameter that does damage to axles. Imagine trying to loosen a tight bolt with a 6" long wrench. And then try it with a 12" long wrench. The longer wrench will allow you to apply far more torque to the bolt. Whether the 6" wrench weighs 1 pound or 5 pounds won't make any difference. It's all about leverage.

Less back spacing will put more strain on your ball joints, Cs, and rear axle flanges. Tire diameter has a significant impact here as well. Large tire diameter + low backspace is a lot of leverage. Weight is a minor player in all of this.

Now with that said I wouldn't have a problem with running 35s on either setup for what you want to do. Gusset the Cs, replace the ball joints, and tac weld the front u joint caps and you will be fine.
 

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As far as stresses and strength, there is absolutely no difference between the structural strength of the Sport D30 and the Rubi D44. They share the same axle tubes C's knuckles balljoints bearings etc. So the only difference is the physical size of R&P and axles.
As mentioned anything weight and physical size wise more then stock will add stress but regular maintenance will always allow you to monitor wear so worn parts can be changed before breakdowns occur.
 

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Discussion Starter #5
Thanks, assuming that tolerances and margins of safety are at least 5% then the duratrac 33 are basicalky stock as diameter is 5% larger. I can see how 34 s are probably out of margin and ideally reinforcement of the components listed would be the right thing to do.

Weight should affect mpg, brakes and engine performance for sure because of the additional unsprung weight and rotational dynamics. What about tire width? I assume the width been 35% or more than stock will cause stress on steering components, is that correct?

So the whole " use 4.5 bs" for 33 and "2.5 lift" for 35. Is just the basic bare minimum to not to cause rubbing or break factory fenders, but the stress on the stuff that keeps one safe and the car working: axles, joints, steering, etc. is not addressed by these mods. So let me rethink my build :)

The reality is i wheel only on weekends and while i do it almost every week, 80% of the time the car is at highway speed as DD. at highway speed is where a failure of any of those component is a disaster; in a backroad expedidtion going at 10 - 20 mph max, a failure would be a minor or major inconvenience but unlikely a disaster.
 

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WOW Dude you are way overthinking this. I have run heavy 35" tires on 4.5" backspace for my Jeeps entire life. At 170,000klm I changed balljoints, while it was apart I changed driveshaft UJoints and unit bearings. Not because they were totally worn out out but because they were worn.
For a DD and mild off-roading you will have no issues with 35s for a long time as long as you do regular maintenance...
Build it, Drive it, enjoy it, and upgrade parts as they wear.
 

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Discussion Starter #7
WOW Dude you are way overthinking this. I have run heavy 35" tires on 4.5" backspace for my Jeeps entire life. At 170,000klm I changed balljoints, while it was apart I changed driveshaft UJoints and unit bearings. Not because they were totally worn out out but because they were worn. For a DD and mild off-roading you will have no issues with 35s for a long time as long as you do regular maintenance... Build it, Drive it, enjoy it, and upgrade parts as they wear.
Yes i know i am over thinking it but it is part of the fun of owning a jeep. Learning, doing mechanical work, understanding why and exploring new places.

I got very useful info here as to why... What to do is ok but i find fascinating the why which helps me with my learning

On our way to trail with the new aev 2.5 and teraflex forged bar! I like the 33s on a 2 door but keep overthinking 33 or 35 for the new ruby hardrock 2 dr coming next week.
 

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