FB Rear Suspension Geometry Problems/Options/Solutions
12-09-09, 04:17 PM
#28
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12-09-09, 07:47 PM
#30
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This is something I have became aware of but didn't know what was causing it. I especially noticed it on R-Comps. On my R-comps my car tends to understeer and then be backwards. No in between, lol. When I've raced on my street tires it has felt amazing because the car actually has decent oversteer, something that normally doesn't occur unless its after the word snap. I'd want to do something about it but I have no funds to play with this season, just going to have to drive it as it is.
What does street preppared allow you to do to the rear suspension? Also, there was talk of going with too stiff of springs, noob question but what is wrong with going with really stiff springs on an FB, other than ride quality/shock longevity?
What does street preppared allow you to do to the rear suspension? Also, there was talk of going with too stiff of springs, noob question but what is wrong with going with really stiff springs on an FB, other than ride quality/shock longevity?
12-10-09, 06:47 AM
#32
common sense prevails....
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I was attempting a happy medium, but running an aftermarket front bar and the stock rear bar I was picking up the rear inside wheel, which doesn't help much for exit speed. Plus I think the shock from the tire loading back up when it got back on the ground was helping break my rearends.
First thoughts were that I need to tighten up the rear LSD. Guess from reading this, I might be lifting that tire pretty good... I have the same rear sway bar as Kentetsu and I keep it tight..
Earlier someone was talking about they did not know if they made adjustable watts bars. I run Mazdaspeed adjustable watts bars on mine. Working good!!
The stiff sping vs. lighter spring debate can go on for hours... I am afraid to go too stiff because of loosing "compliance" of the spring. Where we run, it sometimes can get a little rough... Stiff springs seem to work when track conditions are perfect, but race over some rough asphalt or potholes, and you might find yourself just skipping like a rock on a pond!!
12-10-09, 07:12 AM
#33
There you go, actual in the flesh.... Same basic principle but a good bit different.
Panhards are not bad really. The have successfully been used on MANY race cars over the years. Yes they do have the arc motion but it is a minimal issue compared to the stock watts issues.
-billy
12-10-09, 07:24 AM
#34
So, you need to decide if the extra 10lbs of unsprung weight with a watts link like the one above is better than the 1/8" the rear will move side to side in its range of movement.
If you have anything but rod ends in the whole rear suspension your trying to pick the fly **** out of the pepper worrying about it. Even then you won't feel the difference if the roll center is in the same spot.
If you have anything but rod ends in the whole rear suspension your trying to pick the fly **** out of the pepper worrying about it. Even then you won't feel the difference if the roll center is in the same spot.
12-10-09, 06:10 PM
#35
So, you need to decide if the extra 10lbs of unsprung weight with a watts link like the one above is better than the 1/8" the rear will move side to side in its range of movement.
If you have anything but rod ends in the whole rear suspension your trying to pick the fly **** out of the pepper worrying about it. Even then you won't feel the difference if the roll center is in the same spot.
If you have anything but rod ends in the whole rear suspension your trying to pick the fly **** out of the pepper worrying about it. Even then you won't feel the difference if the roll center is in the same spot.
12-10-09, 06:38 PM
#36
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12-10-09, 10:52 PM
#39
I need a new user title
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That's sexy. What kind of car is that in?
I'm looking forward to seeing Billy's solution. I certainly wouldn't mind having a setup like that, but it'll probably be a good while before I'm good enough to make use of it, so I'm in no hurry.
I'm looking forward to seeing Billy's solution. I certainly wouldn't mind having a setup like that, but it'll probably be a good while before I'm good enough to make use of it, so I'm in no hurry.
12-11-09, 05:02 AM
#40
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I think it's a Mustang. I grabbed it off of a random site to show what a watts set-up looks like.
There are lots of aftermarket suspension set-ups for Mustangs available. Google Watts Link and you'll see all sorts of ideas.
RXDad
There are lots of aftermarket suspension set-ups for Mustangs available. Google Watts Link and you'll see all sorts of ideas.
RXDad
12-11-09, 10:32 AM
#42
I helped install one of these on a A Sedan Mustang 10yrs ago. Nice piece but it was not any better than the panhard bar it replaced in terms of on track performance. In other words, the driver didn't win more races with it installed than he did before.
12-11-09, 10:43 AM
#43
First, the stock watts link pivot will fail if not reinforced - been there, seen that. Second, to install a watts link on the back of a rear axle housing requires allot of metal (weight) and a significantly strong (and expensive) pivot bearing because they fail too.....seen that also. Finally, a panhard rod can generate a much lower roll center without putting allot of suspension parts in harms way.
Keep in mind that the roll center on a panhard bar setup is the horizontal axis of the bar itself. The roll center on a Watts Link is the pivot. The lower the pivot is placed on the vehicle the closer to the ground the lower arm in the Watts Link gets.
There are other solutions for a Watts link that helps this a little. For example, it can be mounted to the bottom of the rear axle housing and setup to pivot in a horizontal plane instead of a verticle plane (like the stocker). I have seen setups like this on GT cars.
But no matter how you slice it, a Watts Link adds weight, complexity and expense. A Panhard bar doesn't.
12-11-09, 11:44 AM
#44
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When I purchased my trilink/panhard, I was counseled by the previous owner of it to take steps to reinforce the mounting of the panhard bar. He told me that they are prone to being ripped right off the frame rail.
Another friend, from Detroit area (Bruceman/RotaryReserection (I think)) gave me the same advice upon hearing that I had made the purchase. I believe he was basing that advice on personal experience.
So, I think that Hyper's statement is correct on that point. But of course, the amount of metal needed to reinforce those mounts accordingly probably would not amount to much added weight.
Plenty of options out there to address all of these issues. But for now I'm going to stick with my own philosophy, which is "reduce the amount of rear travel through the use of strong swaybars and reduced ride height, and you reduce the issues associated with the rear end". This seems to be working well for me so far, so I'll continue to see how far I can push the car in it's current state.
Another friend, from Detroit area (Bruceman/RotaryReserection (I think)) gave me the same advice upon hearing that I had made the purchase. I believe he was basing that advice on personal experience.
So, I think that Hyper's statement is correct on that point. But of course, the amount of metal needed to reinforce those mounts accordingly probably would not amount to much added weight.
Plenty of options out there to address all of these issues. But for now I'm going to stick with my own philosophy, which is "reduce the amount of rear travel through the use of strong swaybars and reduced ride height, and you reduce the issues associated with the rear end". This seems to be working well for me so far, so I'll continue to see how far I can push the car in it's current state.
12-11-09, 12:31 PM
#45
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12-11-09, 06:14 PM
#46
I figured as much, just messing with you. 
.....
I also come from the lighter rates, larger bar group. We tried all sorts of heavy *** spring rates up front (450-550), modified stock sway bars and panhards with super low roll centers back in the day. Always went back to softer springs, stiffer bar and rear roll center around 1" above the front. This always felt comfortable and allowed the rear to roll about the front roll center and set the front outside wheel. Granted this was in a class with stock pickup points, 13" wheels, small spec tires, no HP and no brakes to speak of - Also, fast sweeping tracks in the Southeast. The pitch/roll scenario worked well for us.
-billy
.....
I also come from the lighter rates, larger bar group. We tried all sorts of heavy *** spring rates up front (450-550), modified stock sway bars and panhards with super low roll centers back in the day. Always went back to softer springs, stiffer bar and rear roll center around 1" above the front. This always felt comfortable and allowed the rear to roll about the front roll center and set the front outside wheel. Granted this was in a class with stock pickup points, 13" wheels, small spec tires, no HP and no brakes to speak of - Also, fast sweeping tracks in the Southeast. The pitch/roll scenario worked well for us.
-billy
12-12-09, 03:18 AM
#47
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What will the Torque Arm on say the Granny's kit fix? I know its good for straight line squatting, but is it gonna help some of these other problems?
I also agree that the 'fix' is complicated because it depends on alot of fators like suspension and power and even IF you can do alot about it in the class you are racing
I also agree that the 'fix' is complicated because it depends on alot of fators like suspension and power and even IF you can do alot about it in the class you are racing
12-12-09, 10:16 PM
#49
Considering that since 1988 the ESP National Solo II Championship has been won using cars that have torque arms in all but 4 years tells me that they work for more than just drag racing.
It would not be my first choice for an Rx7. A torque arm is heavy and puts allot of stress on a unibody. I mounted one on a mustang and the subframe conectors had to be reinforced quite a bit. An RX7 doesn't have as much meat to work with - the sheet metal is thin.
It would not be my first choice for an Rx7. A torque arm is heavy and puts allot of stress on a unibody. I mounted one on a mustang and the subframe conectors had to be reinforced quite a bit. An RX7 doesn't have as much meat to work with - the sheet metal is thin.