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UCA - Decisions decisions

14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
Hi all,
Im new to this forum but I have been reading with great interest for a long time and cant help but notice that there is a lot of knowledge in this forum. However, I have read up and down virtually all posts on the UCA upgrade for a long time, and Im struggling to find a conclusion. I read praises of the BMR "ultimate" UCA with spherical joints, I have read that the 11+ longer arm design is for sure the way forward, and that the differential end bushing is to weak and needs an upgrade.

So today I figured Ill add the BMR spherical arm and the diff poly bushings in my basket over at Lethal performance, and in a final search to justify my purchase I stumbled across one of the best threads ever, the project budget 400whp thread... Man.. Now all of the sudden the Roush SHORT 07-10 arm is the way to go and its backed by the a racecar driver. So is that the final answer? Is there no point to use a 11+ longer arm that I thought stabilised the rear end as claimed by.. Well BMR who makes money selling them?

Any help here would be greatly appreciated.

Ill add in a little background information and the problem at hand:

2007 GT500 super snake 660hp
Shelby Eibach suspension system including adjustable panhard bar
Ford Racing 1 pc driveshaft with unknown and potentially incorrect pinion angle
SVE 10" wheels with 275 tires front SVE 11" 295 tires rear

Problem: The car was very unstable in the rear end when I got it. It served little to no confidence, and the rear end was "wobbeling", trailing, just terrible. Pushing it was scary and not fun at all.

Mods:
Ford racing (boss302) LCA and BMR relocation brackets - Top mounting hole is used

Result: Rear end way better, steady state long sweepers etc is now much improved. Still some instability, especially when braking, and bumpy roads when turning, dynamic stuff like right left turns and trailbraking..

I suspect the UCA is causing my problems, but I could be wrong. Ideas anyone?
 

Norm Peterson

Corner Barstool Sitter
939
709
Exp. Type
HPDE
Exp. Level
5-10 Years
a few miles east of Philly
Hi all,
Im new to this forum but I have been reading with great interest for a long time and cant help but notice that there is a lot of knowledge in this forum. However, I have read up and down virtually all posts on the UCA upgrade for a long time, and Im struggling to find a conclusion. I read praises of the BMR "ultimate" UCA with spherical joints, I have read that the 11+ longer arm design is for sure the way forward, and that the differential end bushing is to weak and needs an upgrade.

So today I figured Ill add the BMR spherical arm and the diff poly bushings in my basket over at Lethal performance, and in a final search to justify my purchase I stumbled across one of the best threads ever, the project budget 400whp thread... Man.. Now all of the sudden the Roush SHORT 07-10 arm is the way to go and its backed by the a racecar driver. So is that the final answer? Is there no point to use a 11+ longer arm that I thought stabilised the rear end as claimed by.. Well BMR who makes money selling them?

Any help here would be greatly appreciated.
The longer UCA should stabilize the side view geometry somewhat. You could look at pinion angle changes over suspension travel as being analogous to camber gain with a short-long-arm independent suspension where the further away you can keep the instant center the smaller the angular change (camber or pinion angle).

After that, it still seems a bit muddy to me, and part of that is what do you really want the SVIC and anti-squat to be doing on a road course car. Do you want to get into significant UCA and LCA inclination changes? The extra inch of the later UCA does affect the shape of the anti-squat curve.


Norm
 

Grant 302

basic and well known psychic
Rubber bushings are the main difference regarding grip. Compliance in the 3rd link is more important than most realize.
Anytime I’ve tried to explain why just ends up in arguments.

The short arm geometry isn’t as detrimental as most would think. Or even beneficial if you consider making use of its faster ‘switching’ properties.
 
I went with the BMR adjustable UCA with poly bushings on both ends a couple years ago, and reading Billy's praise on the Roush 3rd link also has me reconsidering that. As Grant above and Billy said in the article, the rubber bushings don't "shock load" the tire as much as a poly bushing or especially a spherical rod end giving less tire load variation. I'm guessing this can help increase rear traction on throttle, and is why they are so popular.

The unknown part for me is the pinion angle. I have a 12' GT with a Magnum XL swap & 1 pc driveshaft like yourself, and the big reason for me to run the adjustable BMR UCA was to bring my pinion angle back into place. With the Roush 3rd link, it's not adjustable so the pinion angle would wind up being out of sync with the engine/trans by ~4 degrees. I realize this won't be great for my U-joints and could increase NVH, but I'm not sure how critical it is if the pinion angle is out 4 degrees from the engine/trans.

With adjustable LCA's you could get some of this back, but could result in other issues such as changing the wheelbase, not having the wheels centered in the wheel wells, plus changing anti-squat geometry. How critical that is, I don't know and would like to hear other opinions on.
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
The longer UCA should stabilize the side view geometry somewhat. You could look at pinion angle changes over suspension travel as being analogous to camber gain with a short-long-arm independent suspension where the further away you can keep the instant center the smaller the angular change (camber or pinion angle).

After that, it still seems a bit muddy to me, and part of that is what do you really want the SVIC and anti-squat to be doing on a road course car. Do you want to get into significant UCA and LCA inclination changes? The extra inch of the later UCA does affect the shape of the anti-squat curve.


Norm
The longer UCA should stabilize the side view geometry somewhat. You could look at pinion angle changes over suspension travel as being analogous to camber gain with a short-long-arm independent suspension where the further away you can keep the instant center the smaller the angular change (camber or pinion angle).

After that, it still seems a bit muddy to me, and part of that is what do you really want the SVIC and anti-squat to be doing on a road course car. Do you want to get into significant UCA and LCA inclination changes? The extra inch of the later UCA does affect the shape of the anti-squat curve.
In those very technical terms i have No idea what I want. As a driver I want more stability in the rear end to increase my confidence in the car when pushing it. Obviously without the bind issues of a poly bushing. Im wondering how the short roush compare to the oem 11-14 arm, Both being rubber, but different length?
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
Rubber bushings are the main difference regarding grip. Compliance in the 3rd link is more important than most realize.
Anytime I’ve tried to explain why just ends up in arguments.

The short arm geometry isn’t as detrimental as most would think. Or even beneficial if you consider making use of its faster ‘switching’ properties.

Ive always been a fan of rubber. The No bind, No maintenance with minimal NVH nature of them is ideal.

What benefit Will the faster switching properties of the short arm give me? And Just what does the Long arm do in terms of handling?
 
5,136
5,650
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
My personal favorite:


 

Grant 302

basic and well known psychic
What benefit Will the faster switching properties of the short arm give me? And Just what does the Long arm do in terms of handling?
My opinion is better potential for grip on corner exit with the shorter arm…all depending on the rest of the rear setup in both geometry and hardware used. It’s all in the dynamic changes of instant centers for each side.
The longer arm should have less migration of such points and could potentially be more consistent. I think this is generally true of the OEM setups and why Ford made the update.

I hope that’s not too vague.
 
135
147
2007 GT500? Cast iron block? That's a whole lotta Rosie hanging off the nose - used to have one - great sledge hammer for the highway runs - terrible for the road course tracks but pretty fun at the strip. JS I believe the factory went to the longer UCA because of the increase in horsepower and wanted more forward bite /less axle hop.
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
My personal favorite:


Aah the torque arm, very interesting setup, but if im not mistanken I would need adjustable lca's pushing the price up towards 1500$? Its a bit on the pricey end for me, and this is a street car for the most part, but I would love to hear a detailed handling comparison on the Ta vs 3rd link setup.
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
2007 GT500? Cast iron block? That's a whole lotta Rosie hanging off the nose - used to have one - great sledge hammer for the highway runs - terrible for the road course tracks but pretty fun at the strip. JS I believe the factory went to the longer UCA because of the increase in horsepower and wanted more forward bite /less axle hop.
Yes sir, its nose heavy for sure, but its a street car used for a couple of trackdays a year, not a race car, so Im ok with that.

The problem drives me crazy on spirited drives on twisty Mountain roads, and a fix for this rear end instability would make me very happy with my setup.
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
My opinion is better potential for grip on corner exit with the shorter arm…all depending on the rest of the rear setup in both geometry and hardware used. It’s all in the dynamic changes of instant centers for each side.
The longer arm should have less migration of such points and could potentially be more consistent. I think this is generally true of the OEM setups and why Ford made the update.

I hope that’s not too vague.
So short arm better corner exit.

But Long arm more consistent, what does that mean for handling.

Also, with my fixed lower arms, Will I not need an adjustable upper arm, and what would the result be if I run say a roush uca and run into pinion angles of Day - 4* as js mentioned?

All I really want is to control the rear end from moving around to inspire some confidence in the car, im quite happy with the handling other than that.

Thanks for the answers so far everyone, Great info 🍻
 
5,136
5,650
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
Aah the torque arm, very interesting setup, but if im not mistanken I would need adjustable lca's pushing the price up towards 1500$? Its a bit on the pricey end for me, and this is a street car for the most part, but I would love to hear a detailed handling comparison on the Ta vs 3rd link setup.
I went through several different setups. This one is the smoothest and most predictable IMHO.
Plus it sets the pinion angle. Adjustable lowers will not affect the pinion angle with the Torque arm, its fixed by the arm.
There's more going on here though, suspension is a system. Anti squat, roll steer and roll centers all matter and should be complimentary. Pick a manufacturer and buy all their stuff, don't mix and match. That's the fastest way to a headache I can think of...if you have to do it piece by piece (like most of us) that's cool, just get all the same brand.
Suspension strategies between manufacturers vary wildly and its super easy to get all screwed up with mismatching parts.
 
14
3
Exp. Type
Circle Track
Exp. Level
10-20 Years
Norway
I went through several different setups. This one is the smoothest and most predictable IMHO.
Plus it sets the pinion angle. Adjustable lowers will not affect the pinion angle with the Torque arm, its fixed by the arm.
There's more going on here though, suspension is a system. Anti squat, roll steer and roll centers all matter and should be complimentary. Pick a manufacturer and buy all their stuff, don't mix and match. That's the fastest way to a headache I can think of...if you have to do it piece by piece (like most of us) that's cool, just get all the same brand.
Suspension strategies between manufacturers vary wildly and its super easy to get all screwed up with mismatching parts.
Hm. The torque arm makes a lot of sense. It says on the cortex site that it requires adjustable lower arms, not sure why. Does it move the axle off center maybe?

On a sidenote, have you ever tried the oem uca with upgraded lower arms and did you feel that the rear end was instable with that uca like i do?
 
5,136
5,650
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
Hm. The torque arm makes a lot of sense. It says on the cortex site that it requires adjustable lower arms, not sure why. Does it move the axle off center maybe?

On a sidenote, have you ever tried the oem uca with upgraded lower arms and did you feel that the rear end was instable with that uca like i do?
I've had a ton of different setups, can't really remember what each one was like, just that I kept searching for something that felt right. I ended up with the current setup and that was it for me.
There are other great setups also, but you are likely to get the best results with a package system from one manufacturer. If you are trying to keep it mostly stock you can't go wrong with the ford racing catalogue.
Just, and I can't say this enough, don't add things willy nilly from different manufacturers because somebody said this part or that part was the cats meow. This sport is full of experts that speak from inexperience.
Seek proven professionals.
 
5,136
5,650
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
Hm. The torque arm makes a lot of sense. It says on the cortex site that it requires adjustable lower arms, not sure why. Does it move the axle off center maybe?

On a sidenote, have you ever tried the oem uca with upgraded lower arms and did you feel that the rear end was instable with that uca like i do?
The stock 3rd link was the first thing to go in my build, though I always retained the factory rubber in the diff mount. I ran a number of lower trailing arms and axel brackets and pan hard bars and sway bars, springs and shocks.
A 3rd link is a good place to have rubber as it cushions the shock of hammering the gas, banging gears and standing on the brakes. It doesn't have any of the bad traits like excessively soft bushings in control arms which allow the rear end to move forward and back under acceleration/de acceleration or cause wheel hop. Rear trailing arms need to articulate though and a lot of after market arms do not provide enough movement. You can't beat rod ends but the NVH tends to go up. I'm focused on racing so NVH is not a consideration for me. I think Cortex has some street trailing arms with something the off roaders call "Johnny Joints". Kind of a bridge between street and race. As for why the Torque arm "requires" adjustable lower arms I can't say. The front of the arm slips in its mount so changing the wheel base has little effect. It just slips forward and back. They might be referring to the kit with adjustable arms and drop brackets to optimize the trailing arm angle. You might try different holes in your drop brackets as that affects both roll steer and anti squat. A big angle with the front pivot much higher than the rear will cause a lot of roll oversteer and that's very unsettling. Cortex recommends 3 to 5* up. Mine are at set at the minimum.
 
807
418
I think you guys missed Billy’s response about using the short arm. He used it because it’s the only one available from Rousch. He was also pretty clear about wanting to keep from shocking the tires because he wasn’t running slicks or a lot of aero. He also didn’t change the lower control arms and add relocation brackets for more anti-squat, which would help from shocking the tires if using a UCA with bearings vs. rubber.

Billy is building a street car that is a reasonably capable HPDE car. If that is not your goal, then there are better choices.

From having driven S197s with rubber UCAs and full bearing setups, I found the bearings worked better on track. But, I also was running slicks (Hoosiers, Pirellis, Michelins) along with relocation brackets.
 
5,136
5,650
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
Billy is building a street car that is a reasonably capable HPDE car. If that is not your goal, then there are better choices.

From having driven S197s with rubber UCAs and full bearing setups, I found the bearings worked better on track. But, I also was running slicks (Hoosiers, Pirellis, Michelins) along with relocation brackets.
I read it and agree completely. The right amount of rubber is good, even if I you have to use a short arm to get it.
 

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