Help with an unstable/darty car - bad tramlining

[smokinjoe]

I am having a problem with the FWD chassis becoming way to darty at speed - or excessive tramlining. Its to the point where anything over 70mph and the car is difficult to maintain safely.

 

The current specs are hoosier 225/40/17s, set at -3.7 camber fr, -1.4 on the rear beam, 4deg of caster and 10numbers total toe out in fr, 40 numbers total toe in at the rear. thrust angle is .1

 

Coilovers have 10K springs, larger sways and new bushings, ball joints, etc.

 

Should I start with maybe 10numbers toe in at the front, then dial back the camber? I'm thinking at -3.7 I may have too much camber thrust. I prefer the tail to be loose, which is why I run toe out but maybe this is making the tramlining worse.

 

Any thoughts or ideas are greatly appreciated

[mcmmotorsports]

What is this 10numbers/40numbers you speak of?

I am used to 1/8 or 1/16 for toe. Regardless, a toe in condition front OR rear will give you "shopping cart" wheels and feel very unstable.

I prefer to run zero to 1/8 out max on anything I race. In addition, tire temps (taken accurately of course) are the best way to know what suspension settings are ideal for your application.

[kbrew8991]

I'd set the toe much closer to zero - as the Mythbusters would say "There's your problem!"

[smokinjoe]

Thanks guys. Under load the fr wheels toe out so I'll drop the toe to 0' or an 1/8th in (about 10numbers), remove the spacers and take it for a drive. Then dial back the camber.

 

I wasnt sure if other FWD folks have had this experience and remedied the tramlining.

[Greg G.]

Joe,

 

Also, if you are using aftermarket bushings check them very closely--even if you have only had a short amount of track time. In 2008, my car suddenly started eating front control arm bushings within 20 minutes of going on track after using the same setup for two years prior. We never really figured out why it was happening (probably 20 people looked at the car--most with a lot of suspension knowledge and experience). However, when the slop in the bushings first started, it was just a small amount of lateral movement noted on the straights. Ultimately, it would jump 4 feet sideways without any notice by the time the bushing was really torn up. I ended up taking the +3 points for metallic/spherical joints just for the one bushing location and it fixed the problem.

[kbrew8991]

pushing mods on the guy... for an advantage...? (just kidding!!!)

[Greg G.]

pushing mods on the guy... for an advantage...? (just kidding!!!)

Uh, what advantage? I don't compete in his class. I don't compete in any TTA-TTF or PTA-PTF class so that there is no question that my decisions are completely unbiased.

[kbrew8991]

I know, it was a joke man you're not going to run TTB this year?

[smokinjoe]

Joe,

 

Also, if you are using aftermarket bushings check them very closely--even if you have only had a short amount of track time. In 2008, my car suddenly started eating front control arm bushings within 20 minutes of going on track after using the same setup for two years prior. We never really figured out why it was happening (probably 20 people looked at the car--most with a lot of suspension knowledge and experience). However, when the slop in the bushings first started, it was just a small amount of lateral movement noted on the straights. Ultimately, it would jump 4 feet sideways without any notice by the time the bushing was really torn up. I ended up taking the +3 points for metallic/spherical joints just for the one bushing location and it fixed the problem.

 

 

Greg, I heard the same ideas last night from a suspension guru. And your description is dead on to what the car is doing, about 1-2 feet sidways w/o notice. The smallest undulations causes the car to skip out. I was able to get it under control by dialing back the camber to -2.9 and running 1/8th toe in. It still jumps but very, very slightly. Its manageable. I'll pull off the LCAs and inspect the bushings.

 

Good news is the motor made less than I had expected, 250whp and with a cage on the horizon, should come in around 2800. That puts us back into base reclass TTC*, with room from bushings and aero in TTB. Glad to hear I'm not the only FWD who has experienced this.

[Greg G.]

I know, it was a joke man you're not going to run TTB this year?

Nope. I haven't run in TTB or PTB all year.

[smokinjoe]

To close this out, we changed the LCA bushings today. Although not metallic they are a huge improvement. About 90% of the skipping is gone. The rest is probably toe. Thanks Greg

 

 

[Greg G.]

Joe, keep a very close eye on them now. Because they are firmer and not metallic, they may tend to tear up a lot quicker than the old ones. My bushings cost me the PTC Championship at Mid-Ohio in '08.