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Thread: Beam Suffering

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2012-07-23 05:17:55
Beam Suffering
2017 Update: Beam suffering is no more, a custom panhard bar solved this problem. See the detailed post here.

The Scott-Russell Link (SRL) is really getting the best of me, especially while being lowered. The rear just seems disconnected from the rest of the car, I can feel the rear also ruining the front traction.

The problem with Scott-Russell link is, when you lower the car, the roll center still remains high, seems to be as high as 12". Mike K also mentions that that link binds and causes uneven wheel rates.

I'm currently exploring these options, I have two beamed cars that I would like this done on. One will be a autocross car, thus it would need a nicer setup, while the other is just a fun daily driver thus it doesn't need as an expensive option. If I could lower the roll center in the rear on the SRL for the daily driver, it would probably be sufficient enough.

For reference Nissan SRL Travel in action:

QT Link, on a lowered car the beam seems to move to the right, this link is adjustable thus it lets you put the beam back in the center and restore the geometry.

SE-R Spec V Scott-Russel Linkage swap
Originally Posted by choaderboy2
The B15 part is much stiffer, being fabricated from stampings so that it is hollow in cross section vs a wimpy I beam like the stock B14 part, with stiffer bushing with a forged aluminum locating link vs a wimpy steel one. I think for a B14 on R compound tires, this might make a big difference. I'll know how it helps handling soon as I can get some track time.

Spec V linkage

Panhard Conversion - Panhard links are a lot simpler then even the Scott-Russell setup, but are very effective, with the conversion you would have adjustable roll center too. Unfortunately it's a bit of an intensive installation, requires lots of welding and tuning.

Moto IQ did it on their B15 Race car:
Originally Posted by MotoIQ
Worse yet the Scott-Russell linkage has a very high rear roll center. To eliminate these issues we have to get rid of the linkage entirely. We replaced the linkage with a Panhard Rod. The Panhard Rod keeps the suspension from flexing sideways at all and lowers the roll center by as much as 6” from stock.

MotoIQ's Panhard:

smokinjoe(2j-racing) did a side by side comparison on the same turn:

Without the Panhard, using the OEM SRL

With the Panhard

Watt's Link - The guys at 2JRacing decided to try to make a Watt's link for our cars. This seems to be the best option, but is also much more complex then the Panhard setup, but it seems to be well worth the trouble.

What an OEM Watt's travel looks like:

Originally Posted by Joe@2J-Racing
I have decent news and unbelievable news. The decent news is the watts link will undergo a redesign on the mounting points. Justin and I would like to make it a bolt in part. Or a partial weld in, secured with bolts. Throughout the winter we'll refine and test the watts to make it available to anyone with decent skills.

After running two sessions I pushed the car harder than I've ever pushed it before, in a on-camber 110 mph turn, probably 1.4gs. I took it flat out. And the mounting bracket pulled away from the chassis. On a first time mock up, that's to be expected.

Now for the unbelievable news. The watts is fcking ridiculous. And I dont use that term lightly. It is the best mod I've ever done since coilovers. Hands down. The car's handling goes from numb to connected. Understeer went from moderate, to ZERO. None. Zilch.
Before when I would pitch the car in a turn, the rear would raise up and the car would begin to push. With the watts the rear squats. Yea, it squats. It's the most unbelievable feeling in the world. Turn in is usually full of drama while the SRL binds up. Now its stable, predictable and connected.

I can't wait for version 2.0. I ran a 1.39.02 at Road Atlanta. That is the fastest N/A FWD. Period. We beat the competition.

Id does seem like 2JRacing guys stuck with the Panhard setup simply because it's simple and easier to do. Plus they had some issues with body flex and welds breaking on the Watt's linkage.
Originally Posted by Joe@2J-Racing
...The big problem with the watts is the roll center, and getting the bell crank low enough (below the beam). Otherwise its just another SRL with spherical bearings...

RedDragon's Watt's Linkage Install

Last edited by Vadim on 2017-05-24 at 14-52-44.
2012-07-23 07:49:28
Do you have rear trailing arm poly bushes? They make a HUGE difference to the car.

2012-07-23 13:47:27
Originally Posted by TheSam
Do you have rear trailing arm poly bushes? They make a HUGE difference to the car.


I haven't yet, I am afraid of doing them on the daily because after I did the front lower control arm bushings the ride comfort went away. For the Sentra I plan on pressing those in though .
2012-07-23 13:57:27
Go, Vadim, Go! Try to make it better, I am all for that, sir.

I just sold my Super Pro rear trailing arm bushings a few months ago, too
Last edited by Kyle on 2012-07-23 at 13-57-49.
2012-07-23 14:54:33
For the record it appears user zero99 I beileve has a panhard bar that can retain exhaust. I have an outstanding pm that hasn't been returned yet but his insight would be great.
2012-07-23 15:55:38
Originally Posted by nissanboi
For the record it appears user zero99 I beileve has a panhard bar that can retain exhaust. I have an outstanding pm that hasn't been returned yet but his insight would be great.

That is a main concern, and for panhard the longer the bar the better it will be, otherwise it can be biased to one side.
2012-07-23 17:53:56
I dont have the funds now but at work we have a PE that said once I layed out materals and all the geometry he would try to see if it would calc out to have the supports for the frame mounting point run perpendicular to the panhard bar thus retaining exhaust.

Also the panhard bar will always be biased to one side but the benifits will outway that. IMHO the roll couple problem in our chasis is a much bigger concern than the thrust angle change thus why the watts link is good in theory but isnt great for our chasis. Yes it does locate the axle better but the roll center is way high so after you lower the car the roll couple is slightly reduced from stock where as the panhard bar puts the roll center very close to the axle. Im actually really excited this topic is being touched as maybe something will finally get done from those of us who have disposible income right now (which I dont).
2012-07-23 17:55:28
BTW 2J ditched the watts link after it broke
2012-07-23 19:23:26
Originally Posted by nissanboi
BTW 2J ditched the watts link after it broke

I was finishing up reading their thread as I was starting to post this. I did notice that they mentioned that the roll center was still way too high. Watt's link looks awesome, but I am doing this mainly to lower the roll center.

I'm going to price out the parts it will take to build this, and probably built two for both of the car
2012-07-23 20:02:53
Fit the trailing arm bushes before you go into all this, honestly the difference they make is incredible.
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