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FB Rear Suspension Geometry Problems/Options/Solutions

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FB Rear Suspension Geometry Problems/Options/Solutions

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Old 01-23-10, 06:50 PM
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Originally Posted by mustanghammer View Post
I pulled the fuel cell out of my car to work on the rear suspension. Here are some pictures of the current panhard bar I have in my car. You can see the Tri Link mount in some of the shots.

I did the fab work on the rear axle housing and made the rod. The rod ends are 3 piece 1/2" stainless. The mount on the chassis has been there for around 10-12 yrs. It looks like crap but has never cracked or failed.

I'll be replacing the chassis mount along with the rear axle housing as a part of my STU build up. The new setup will use a big bearing axle, longer panhard bar, relocated lower control arms and a third link that goes into the car.





Scott, does your exhaust run over or under the axle in this set-up. Would you still go with longer rod if you were staying in IT?
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Old 02-04-10, 12:48 PM
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So, after all this, what is the general consensus for a lowered street car? Tri-link? But for a serious racecar (rules permitting) a redesigned 4-link, or a 3 link going through the floor?
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Old 02-04-10, 11:14 PM
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Originally Posted by kurtf View Post
Scott, does your exhaust run over or under the axle in this set-up. Would you still go with longer rod if you were staying in IT?
Sorry I missed your question. The exhaust is routed over the axle. Yes a longer Panhard rod would be better and I plan on putting one the car as a part of the STU build
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Old 02-04-10, 11:15 PM
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Originally Posted by Electronblue View Post
So, after all this, what is the general consensus for a lowered street car? Tri-link? But for a serious racecar (rules permitting) a redesigned 4-link, or a 3 link going through the floor?
Thats my take!
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Old 02-09-10, 09:12 PM
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Exhaust routing



This is a 2.5" ID pipe.
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Old 02-10-10, 02:01 AM
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This is my all time 2nd favorite thread!
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Old 02-11-10, 10:28 PM
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Originally Posted by Hyper4mance2k View Post
This is my all time 2nd favorite thread!
Lets see if we can make this your FAVORITE thread!

These are some shots of the panhard bar on my friends E Production car. The panhard bar is REALLY long and the car has a 3" stainless exhaust that routes over the axle. This is the car that has the 4 link





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Old 02-12-10, 12:11 AM
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great pic's. Thanks
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Old 03-15-10, 08:56 PM
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How many people out there are running a lowered car on an otherwise completely stock suspension setup? How low can you go before you start to hit any pinion problems realistically?
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Old 03-16-10, 04:39 PM
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If by "otherwise stock suspension" you mean no Trilink/panhard, etc. Then mine is probably one of the lowest around. Using coilovers and the stock Watts. No weird noises from the rear end, or anything else that would imply stress in that area.

Also, damn near no body roll, no snap oversteer, just a very happy car.





.
Attached Thumbnails FB Rear Suspension Geometry Problems/Options/Solutions-csp-98-222.jpg   FB Rear Suspension Geometry Problems/Options/Solutions-csp-98-side.jpg   FB Rear Suspension Geometry Problems/Options/Solutions-csp98.jpg  
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Old 03-17-10, 12:25 PM
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My ITA/PTE (ex PRO7) still sports stock watts, links, bushings, etc. and has ground control Eibach springs with cut dead coils and Koni shocks. Lowered to close to the 5" min per IT rules. Been racing it this way for about seven years. Won a NASA PTE race at Infineon a few weeks ago against a bunch of miatas. So you can race it that way. However, there is room for improvement and Scott has been providing outstanding info/pic's in the areas I am looking to change. I am relatively new here but this IS my favorite thread.

PS, I purchased Scott's Panasports thru this forum and he has been one of the best individuals I have ever dealt with. The packaging was incredible all by itself. Thanks Scott.
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Old 03-17-10, 10:28 PM
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Originally Posted by kurtf View Post
My ITA/PTE (ex PRO7) still sports stock watts, links, bushings, etc. and has ground control Eibach springs with cut dead coils and Koni shocks. Lowered to close to the 5" min per IT rules. Been racing it this way for about seven years. Won a NASA PTE race at Infineon a few weeks ago against a bunch of miatas. So you can race it that way. However, there is room for improvement and Scott has been providing outstanding info/pic's in the areas I am looking to change. I am relatively new here but this IS my favorite thread.

PS, I purchased Scott's Panasports thru this forum and he has been one of the best individuals I have ever dealt with. The packaging was incredible all by itself. Thanks Scott.
Thanks Kurt! You are a pleasure to work with as well.

I have been making some progress on my STU build and will post up some shots of my new real axle housing. It uses coil-over springs in place of the stock 5" springs. It also has radically revised lower control arm geometry with adjustment options that are 1.5, 3 and 4.5" lower than stock. Pictures tomorrow....
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Old 03-17-10, 11:19 PM
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Originally Posted by mustanghammer View Post
Pictures tomorrow....
Waiting for photos of her rear end
This is one of my favorites too. What is it about rear suspension geometry that gets us all interested?
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Old 03-18-10, 12:44 AM
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because its one of the worst things about our cars
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Old 03-18-10, 02:47 AM
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some really good info here
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Old 03-18-10, 01:12 PM
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Originally Posted by Stevan View Post
Waiting for photos of her rear end
This is one of my favorites too. What is it about rear suspension geometry that gets us all interested?
Because it's critical in a RWD vehicle. Good geometry that also lets the suspension move means you don't need to make the whole suspension incredibly stiff to take out the bad habits. Soft suspension = grip.

I just finished up my 3 link/Panhard arrangement, just need to make the cover and then pull the bits off and paint them. It's all very 5 minutes and 5 dollars kind of work, not picture-worthy at all, but it's a far sight better than the stock 4 link/Watts.

With the 4 link and Watts arrangement, the first thing to hit the floor is either the Watts arm or the driveshaft, depending on how twisted your diff housing is.
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Old 03-18-10, 01:43 PM
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Originally Posted by peejay View Post
Soft suspension = grip.
Agreed, there are so many that do not understand that. They end up running super heavy springs rates with inadequate shocks to control them.

Also, consider this, the only way to accurately tune the suspension is to have known variables. Binding becomes part of the spring rate resulting in an unknown variable.

-billy
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Old 03-18-10, 04:59 PM
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Well, the stock setup binds until the constant forcing against the upper links causes the mounting points to break off of the body. Then it works very freely

I had a weird one. I took my old 3-linked rear and cut the top arm off to fit in a stock shell, after I split that car's rearend down the middle. The 3-linked car did not use the upper links for quite some time. After a few months in the strong shelled car, the right upper link bracket broke off of the rearend. It was rusty, but in the original car, the shell was the weak link...

BTW - I did the 3 link for corner exit power-putdownability. I ditched the Watts for a Panhard because, on grippy tires, in a tight corner, my car would make like a VW and lift the inside rear tire off of the ground. Not from body roll, the back end would rise slightly because the axle was rotating under the car. Down, rollcenter, down!!!
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Old 03-18-10, 10:20 PM
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I don't totally agree with the assertion that soft = grip. Grip is generated as a result of the correct suspension geometry and weight transfer. On a drag car the suspension needs to be soft so that you get allot weight transfer to deal with the shock of a hard launch. But in addition to having a compliant suspension a drag car also has to have a rear suspension that has the correct geometery.

On a solo or club racing car you cannot have a super soft rear suspension and expect the car to be balanced. Basically your car won't turn in properly if the car is too soft in the rear. The STU car I am building will most likely have anywhere from 250-300lb rear springs. This will be a variable depending on the track I am at and the size of the rear sway bar I am using or not using.

My CP Mustang - pictured earlier in this thread - had a 3 link rear suspension that was very effective. The interesting thing was that rear spring rates had very little to do with how well it hooked up off of a corner. The final spring rate package on that car was 1650lb front springs and 780lb rear springs. The car hooked up so good that it would lift the inside front tire on corner exit anywhere from 2-6 inches with these springs installed. At one event it was so bad I had trouble seeing the next cone/manuver until the front end came back down. I later corrected this by installing a rear swaybar. This really helped with the front end lift issue. This also had no effect on traction.

Okay here are some photos of my progress:



This is the right side lower control arm mount and spring mount. The top hole on the lower control arm mount (the hole closest to the axle tube) is the stock location. The holes below are in 1.5" increments. I anticipate using the mounting hole that is 3" below the stock hole.

The spring perch combines the adjuster with the seat. It is not welded directly to the axle tube. Instead it is located by plates that are welded to it that also welded to the lower control arm mount. This way the axle tube should not be warped.



This is the 3rd link mount. It is off set to the left to by about 2-3 inches. This was done to make the chassis mount more serviceable as the drive shaft in these cars is offset to the right. Since access to the chassis mount will be from under the car I didn't want fight the drive shaft when making adjustments.
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Old 03-19-10, 12:00 PM
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Originally Posted by mustanghammer View Post
I don't totally agree with the assertion that soft = grip. Grip is generated as a result of the correct suspension geometry and weight transfer.
Grip is generated by tread compound and keeping the tires in contact with the ground. Everything else is handling.

On a solo or club racing car you cannot have a super soft rear suspension and expect the car to be balanced. Basically your car won't turn in properly if the car is too soft in the rear.
The point is that you do not need to make the FRONT suspension super-stiff to counteract the fact that the rear suspension sucks.

Look at off-the-shelf performance suspension setups for a prime example. Front spring rates are in the range of double OEM, rear springs are the same or softer, and the sway bar is removed from the rear and/or increased in size for the front.

The front suspension is being stiffened to counteract the rear suspension's not wanting to work. Make the rear work, and you don't need to go overkill on the front end like that.

My CP Mustang - pictured earlier in this thread - had a 3 link rear suspension that was very effective. The interesting thing was that rear spring rates had very little to do with how well it hooked up off of a corner.
I noted something similar in my RX-7. It handled really well at 200lb front and rear, with the 3 link and Watts. With the stock arrangement, 200lb wasn't stiff enough in the front and 100lb was too stiff for the rear...

My first cut this year is 250lb front and 175lb rear, no sways. The suspension already doesn't really move...

The car hooked up so good that it would lift the inside front tire on corner exit anywhere from 2-6 inches with these springs installed.
Some would argue that you'd be better off keeping all four tires on the ground.

Personally, having been in a VW environment, compromises always have to be made. In the case of my VW, stiffening the front to keep the rear tires both on the ground hurt turn-in too much. Lowering the rear excessively helped keep both tires (close to) the ground, and actually helped corner exit power.
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Old 03-19-10, 01:04 PM
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Originally Posted by mustanghammer View Post
My CP Mustang .
two of the guys on our team (25 hour race = 25+ people) were comparing setups between a CSP FB and CSP Fox Body, and the were basically running the same springs and alignment, kinda funny

Originally Posted by peejay View Post
Personally, having been in a VW environment, compromises always have to be made. In the case of my VW, stiffening the front to keep the rear tires both on the ground hurt turn-in too much. Lowering the rear excessively helped keep both tires (close to) the ground, and actually helped corner exit power.
i think with FWD getting the rear tire off the ground might be ok, ours just cause understeer... case in point, at this 25, when the rear tire fell off (pics are in the link in my sig) mario was happier with the balance, and it was only 3 seconds a lap slower, which is about what it ran with Ra1's
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Old 03-19-10, 11:08 PM
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Originally Posted by peejay View Post
Grip is generated by tread compound and keeping the tires in contact with the ground. Everything else is handling.



The point is that you do not need to make the FRONT suspension super-stiff to counteract the fact that the rear suspension sucks.

Look at off-the-shelf performance suspension setups for a prime example. Front spring rates are in the range of double OEM, rear springs are the same or softer, and the sway bar is removed from the rear and/or increased in size for the front.

The front suspension is being stiffened to counteract the rear suspension's not wanting to work. Make the rear work, and you don't need to go overkill on the front end like that.



I noted something similar in my RX-7. It handled really well at 200lb front and rear, with the 3 link and Watts. With the stock arrangement, 200lb wasn't stiff enough in the front and 100lb was too stiff for the rear...

My first cut this year is 250lb front and 175lb rear, no sways. The suspension already doesn't really move...

Some would argue that you'd be better off keeping all four tires on the ground.

Personally, having been in a VW environment, compromises always have to be made. In the case of my VW, stiffening the front to keep the rear tires both on the ground hurt turn-in too much. Lowering the rear excessively helped keep both tires (close to) the ground, and actually helped corner exit power.
It is really hard to respond to the points that you have made here. To a certain extent I am not sure you understand what I am saying or I am not being clear. Suffice to say I do not agree with many of your opinions but there are allot of ways to skin a cat.

Basically I think you are discounting the effect that a racing tire has on a car's suspension. If we raced on 185/60x13 all season tires then we wouldn't have to work this hard. The reality is that while racing tires provide grip they also introduce loading and forces into the suspension that have to be controlled. The heavy spring rates I listed for my Mustang were not on the car to fix a handling issue that the car had. They were there to fix handling issues the car had BECAUSE of the racing tires.

The spring rates on my Mustang were pretty extreme but then again so were the tires I was trying to control. They were Hoosier 25x12x16 GT1/Trans-Am road racing tires mounted on 16x12 wheels - front and rear. The heavy spring rates were necessary to keep the tires on the ground. The point I was trying to make is that despite the stiff springs the car still hooked up. Soft doesn't = grip.

I Solo'd that car for 15 years and I did use softer springs as well as a more stock suspension early on with the same size tires. It was slow, in part because soft doesn't equal grip. The move to the three link rear suspension, 2.5" drop front spindles, 26 point roll cage, racing shocks/struts, a 400HP engine and heavy springs was necessary to get the most out of the tires. Of note is the fact that the three link was on the car for a long time. But the car wasn't fast until I addressed the whole package.

My RX7 was used for club racing in Improved Touring. The suspension has all spherical bushings - there is no bind. The final spring rates were as follows:

400 Front - racing beat sway bar
250 Rear - no sway bar

The tires were Kumho 215/50x13 ECSTA V710's

I have raced against cars that have softer suspension settings. They were not faster that I was.

It would be incorrect to assume that only the rear suspension on our Rx7's needs attention. It is the most glaring problem because getting a high HP RX7 to hook up is really hard with the stock suspension or with a suspension that is out of geometry. I am fixing that with a 3 link because the rule set I am working with allows it. The front suspension will also be optimized.....more on that when I get to the front end of the car.
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Old 07-02-10, 07:01 PM
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Finally got another front sway bar. Now I'm running RB front sway bar, stock rear, 300/200. RE-speed coils. Car drives amazing. Next step I'm going to do the PB&J racing mod to the upper links then fix the lower control arms mounting on the axle to get them parallel. Then maybe a panhard and 4 link.
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Old 07-02-10, 09:21 PM
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I thought I put my setup in here, but I just looked through and I guess I didn't. Here's what a proper watts link looks like in a fb. It's not finished yet, the bars are a bit too long in this picture, but at least they're equal length and centered on the rear end The reason I didn't go with a panhard bar is because they like to pick up one tire when turning. If the bar is connected to the rear end on the left side, when you turn right it loads the left rear wheel, but when you turn left the bar will unload the left rear and possibly pick it up in the air.



Yes, I'm using 2 forklifts as a lift....
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Old 07-02-10, 11:48 PM
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Fawking beautiful!! Alright I'm back on the Watts wagon.
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