Evo double down - Page 3 - JKowners.com : Jeep Wrangler JK Forum
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post #51 of 56 Old 05-10-2019, 11:16 PM
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I hear you that there's a lot of people just looking for the bling factor. I was afraid that there was so much in the market that caters to them, that's why I didn't get just a coil over kit. I don't like how the coil overs are at severe angles in the rear. That seemed like too much form over function for me.

I also agree with you that most people won't tune their suspension, and that's going to boil down to the fact that you cannot expect people to understand the complexities of shock tuning and what changes can do for the ride. There's not a dumbed down shock that will get people 90% of the way there. It takes a specialist or someone to dedicate serious time to understand it. I believe money spent on a pro tuning shocks is money well spent. I was so disappointed when I saw the bypass shocks that came in the lever kit. They are like toys!

The reason I wanted coil overs and bypass shocks is because I am coming from buggies back to Jeeps. I have had buggies the last 10 years, dabbled a little in racing and decided that I would rather have a jeep that can take the family for ice cream and can take me through the hammers. Having said that, I still want to be able to drive the thing like a buggy! I know it won't be a buggy, but still want it capable.

I looked at the Genright setup and if it would have been capable with UD 60's I would have gone that route. The deal breaker was that it's cost with the required axles was just too far over what I wanted to spend.

Back to the EVO high clearance arms, the lowers on the axle side are raised substantially over stock. But I'll take a look at raising them in line with the axle tube. I would be concerned that then the uppers would be too low.

For now, I just want to get this thing working well in the form that it's in, then work on the tweaking. Meanwhile I would like to get a clear understanding of it's downfalls and compromises so I can make plans for the next move.

Thanks for everyone's feedback and sorry OP for hijacking your thread!
There really is no reason you can't use UD60's with the genright kit. Its simply a matter of a few axle bracket and if you can do all the welding and cutting on the frame then the axle should not be any big deal. I just finished up a 4 door with out boarded coil overs and a double triangulated rear long arm with a genright rear mounted tank.

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post #52 of 56 Old 05-13-2019, 06:50 AM
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Im sorry but isnt the real issue here that short upper and not the lower?


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post #53 of 56 Old 05-13-2019, 07:02 AM
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Originally Posted by ALASHA View Post
Im sorry but isnt the real issue here that short upper and not the lower?
In general, on a 4x4 (where the lower control arms are much closer to the axle center line than the uppers, something true in 4x4 but not necessarily all vehicles), the lowers set the wheel base which is what will affect rear steer, while the uppers set pinion angle through travel and consistency of the anti-squat through travel. Short uppers can be a big problem to those things, but won't really create rear steer, so long as it's true that the lowers are much closer to the axle tube than the uppers.
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post #54 of 56 Old 05-13-2019, 09:46 AM
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Originally Posted by christensent View Post
In general, on a 4x4 (where the lower control arms are much closer to the axle center line than the uppers, something true in 4x4 but not necessarily all vehicles), the lowers set the wheel base which is what will affect rear steer, while the uppers set pinion angle through travel and consistency of the anti-squat through travel. Short uppers can be a big problem to those things, but won't really create rear steer, so long as it's true that the lowers are much closer to the axle tube than the uppers.
But with a 4 link like the one pictured, its hard for me visualize how the short uppers arent affecting the front to back motion of the axle?


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post #55 of 56 Old 05-13-2019, 09:00 PM
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Originally Posted by ALASHA View Post
But with a 4 link like the one pictured, its hard for me visualize how the short uppers arent affecting the front to back motion of the axle?
Here are pictures that might help visualize how only the lower really matters for front-to-back motion. This graphic assumes the lower is literally at the center of the axle tube which is impossible, so the uppers do matter a little bit, but for any logical 4x4 build the lowers are way more important for wheel-base/front-to-back motion.

These are two totally arbitrary suspensions (not modeling the Evo suspension at all), one with logical upper/lower lengths, and one with uppers that are insanely short compared to the lower.

Here it is at "ride height" showing the pinion angle (depicted by the short vertical line above the axle tube) is the same as well as ride height:



And now we droop out the suspension. Because the lower links are the same length and at the axle tube, the wheel-base and front-to-back motion are precisely the same, only the pinion angle is screwed up due to the short upper links. The anti-squat is also shot through travel. But the wheel base is unaffected and the rear-steer is exactly the same between the two suspensions.



I'm not saying upper length doesn't matter, it's critical to have appropriately matched upper and lower links (usually uppers should be just a bit shorter than lowers, but it depends on the suspension design plan). It just doesn't much matter for wheel-base effects such as rear steer.
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post #56 of 56 Old 05-14-2019, 05:24 AM
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On a JK axle both arms come into play and both have an affect on the pinion angle during articulation since the lower hangs down below the axle centerline by several inches.
The steep angle of the lowers is the real issue, the more angle you have at ride height the more rear steer you will have. Same thing with the track bar, the steeper the angle at ride height the more left/right axle shift you will have.

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