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Discussion Starter · #1 ·
When I get over 80-90 MPH my front end tends to feel very loose and twitchy. I'm attributing this to a lack of positive/negative? caster because everything else associated with the steering and suspension is tight as can be.

So, I'm looking having more caster added, but my question is how much is just enough and how much is too much? Steering is 18:1 Flaming River and it's non-power so too much caster at low speeds becomes an issue in the form of overly hard steering. Original caster was set to FF specs, but now I can't find them so all I know is I want more.

BTW, a bump steer kit is on my list for this winter, if that has any bearing on the issue.

Tom
 

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If you have power steering, go to max castor of 6 degrees. If you have any negative camber, reduce it to closer to zero. Everything else is due to a short wheelbase and poor aerodynamics.
 

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air under the hood at 80 mph and above will get you very light. cover the gap on top of rad finish line sells one,i have a rubber air dam made out of 3/8"x6"full width of car wide rubber from mcmaster carr.i get light at 120.plus these cars are for driving not racing .on the sreet! and yes the 120 was done on the street ,no curves no intersections.

paul
 

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I have found my car is very sensitive to the toe setting and tire pressures on the front. I have 17" wheels so the tires are quite low profile but if the pressures are only a few pounds off it will feel darty. Same with the toe, it only has to be slightly off. I am running 1 degree negative camber and 4.5 degrees caster and have the Breeze offset rack bushings and bump steer kit installed along with a 15:1 FR rack.
 

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Originally posted by Mike-Noyes:
I have found my car is very sensitive to the toe setting and tire pressures on the front. I have 17" wheels so the tires are quite low profile but if the pressures are only a few pounds off it will feel darty. Same with the toe, it only has to be slightly off. I am running 1 degree negative camber and 4.5 degrees caster and have the Breeze offset rack bushings and bump steer kit installed along with a 15:1 FR rack.
Mike,
I have the same set up, but note the same alignment specs. Interested in what size tires you are using and tire pressure? I find that roads with a little rutting the car wants to dart a little left and right as it straddles the crown. Most of the other time it is very smooth.
 

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I would check out the bumpsteer . Do a SEARCH above, alot has been written on the subject. Your toe in/out does not have to be off by far. Does the car get twitchy when you hit a bump too? Same thing may be happening when the front end gets light at higher speeds. Do you have a Mark II or III? Do you have aluminum bushings or rubber? Offset?
 

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My car felt light and darty until I installed an air dam from Darkwater Customs. It transformed the handling at higher speed and driving into headwinds. My alignment numbers are 1/8 toe-in,1.5 neg camber, 4.5 castor with 17in wheels and 245/45 tires. Tire pressure is 22psi front,25psi rear. If I had a bigger toy allowance I would think about doing the SAI mod. I have Breeze offset solid rack bushings and bumpsteer kit along with a 15:1 Flaming River manual rack. The best bang for the buck has been the air dam for improving high speed driving. Many times on the way home I have headwinds of 25mph along with 80mph freeway cruising speeds. That adds up to 105mph air speed. That is a lot of aerodynamic lift. You don't have to go to the race track to get some use out of an air dam.
 

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sflaten, the fronts are 245-45-17 Bridestones and I usually run them at 25 psi. The rears are 285-45-17's at 26 psi. I have the toe set to 1/16 toe in.
 

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Discussion Starter · #10 ·
Nothing is ever as simple as we'd like it to be. Now you guys are talking about toe-in, tire pressures, aerodynamics and SAI mods. That's what I love about this forum...ask someone for the time and they'll tell you how to build a clock.

Anyway, I'm intrigued by the SAI mod, but not sure it'll fit with my 15" wheels. So for now, I'm going with the simple fixes first (caster, toe-in change and bumpsteer kit) and see how that goes.

On a related subject, somewhere I recall a post on building your own alignment jig. Sound familiar? and did anyone try it? Aside from the expense, it would sure be easier to make alignment tweaks in your driveway vs running to the shop every time.

Tom
 

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Cheapsnake,
I had exactly the same condition when I first put my car on the road. I already had the tire pressure around 20psi and the caster at 5deg. I got rid of the twitch by carefully setting the toe to 1/16" in and getting the tie rods in the minimum bump steer location. Offsetting the tie rods with spacers at the spindle makes a real big difference in the bump steer. Just remove the shock/spring, take off the wheel and bolt the rotor on with wheel lugs, attach the laser to the rotor (mine had magnets), put a jack under the LCA and move the spindle up and down. Reposition the tie rod attachment with spacers (bump steer kit) until you get minimum steering displacement as the wheel travels up and down. If you point the laser ahead of the car about 20' the steering displacement is real easy to see.
It's a track car so we drive it in the 150-160mph region. I recently added Gordon's adjustable rear control arms to allow me to square up the rears with the fronts. Now the built-in dog track is gone and the beast is steady and predictable.
We align it ourselves each time we race. As long as the surface is flat you can use strings from steel poles of equal length resting on jack stands in front and behind the car to true up the wheels. We set the caster and camber with a Longacre tool. We set the toe with a tape.
I doubt you are getting much aero "unloading" at highway speeds. If you have a bump-steer problem then aero unloading will cause a change in direction. I have never experienced this at highway speeds. You have to get pretty fast to lighten up the front end. Rather, changes in the road surface are the dominant cause of bump steer twitch.
Jim
 

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Discussion Starter · #12 ·
Thanks Jim, that's golden stuff. Can you give me a lead on the laser that you use for the alignment? Thanks.

Tom
 

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Originally posted by Cheapsnake:
Thanks Jim, that's golden stuff. Can you give me a lead on the laser that you use for the alignment? Thanks.

Tom
I used 4 jack stands and wire or string. It is good enough for CART racers, it should be a good start at home. I set mine up, and drove a while to get the suspension droop out and had a pro check it. I was good except 1/16"off in the rear alignment.
 

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Cheap, just as a note, Forte has his bumpsteer kit on sale for 20% off until the end of the month. I got one the other day and it's a quality piece of equipment.
 

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Discussion Starter · #15 ·
Thanks Kevin, I placed my order on Friday. They don't call me Cheapsnake for nothing.

Tom
 
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