What front end mods are absolutely necessary MKIII with a SN95 spindle (2002 GT)?

[skullandbones]

My roadster is on the road now with about 70 miles not counting go karting. My question after reading some of the SAI mod discussion and researching a little is: did I not read far enough into the literature when I changed to the newer spindles? As I understand it, I may have aggrevated the situation by making the geometry of the front end worst by lowering my steering arm an inch or so with the new spindles. Since I went with PS, I can't feel that there is a problem or not. I will be driving mostly on the street but want the added castor so I got the longer adjustable control arms from Speedway (not installed yet). I don't want to overlook a fundamental issue with my steering if the PS just masks the symptoms. Love the PS but also want to have the best solution for suspension geometry for the front.

Thank you,

WEK.:cool::cool:

[FFinisher]

You can have the bump steer measured if you want, if the cars drives well, you are not fighting it, and you are pleased with it leave it alone and drive it. Assuming it has been properly aligned.

you do not automatically have a problem, these parts all work together and are perfectly acceptable.


Don't spend money you don't have too.

[CraigS]

Bump steer can be improved w/ two low cost changes. 1- use the aluminum offset rack mount bushings and lower the rack. 2-Run about 8-9 deg positive caster. As the spindle is tilted back to get the caster, the end of the steering arm raises. I doubt that you will be able to feel any remaining bumpsteer after these mods. I am not saying there isn't any, just that it won't be noticeable.

[skullandbones]

Interesting. I did the initial alignment by following a procedure using a angle gauge and a tool I built to attach it to the wheel and followed the instructions step by step. I have not had a professional alignment done yet. I plan on driving rather conservatively for the first few hundred miles to give me some time to get used to handling the car and also to let the suspension settle in. So I won't be taking it apart at this time. When I do jack it up I will add the new 5 inch adjustment arms on the front to increase the castor. I will re-align at that time and try it out again to see if there is some perceptible difference. I'm hoping to get a more stable feel on the wheel. At this time it is not twitchy or wondering left or right but it does feel very quick. I think the rack is 15 to 1 for the model donor I had. If I do try any quick cornering it will be in a controlled manner away from any obsticles.

Thanks for the advice on the mods. I was planning one already (8 degrees of castor) but did not really associate that with improving the SAI (that's good to know). The rack mod makes a lot of scense too. I have not found the adaptors you mentioned but I will check the various vendors.

I wanted to be able to continue testing the steering without having to stop and take the thing completely apart. So it looks like I can do the one and then test and add the second mod if there are any bump steer symptoms when I start exercising the roadster a little harder. So I think that I am headed in the right direction. I will have it checked by a professional as soon as I re-align just for safety's sake.

If any others want to chime in, suggestions and experiences with this subject are welcomed.

WEK.

[Jeff Kleiner]

I'm in complete agreement with Ron & Craig. So many builders get caught up in throwing every "fix" at the car before they have even determined if they have a problem. Athough bump steer could be measured through the entire range of suspension motion the reality is that in normal driving the actual movement is only over a couple of inches and will most likely be imperceptible. The '02 spindles don't have a dogleg in the steering arm so additional positive caster will bring the end of the arm upwards further improving the tie rod geometry. Should you decide to use the offset offset rack mount bushings they are available through Breeze. For a street car shoot for about 8 degrees positive caster, .5 to .75 negative camber and ~3/32" toe IN. I bet you'll find that it will drive well and no additional "fixes" will be necessary.

Cheers,
Jeff

[skullandbones]

I am following your advice by not replacing components as a "knee jerk" reaction when I read about these possible issues. My main goal is to remove any potential bad behavior from the steering and front suspension geometry that could result in a catistrophic accident like a roll over. I guess that well known picture of Dave's car in the manual with the wheels pointing up stuck with me. It's strange but the only car I can remember feeling like this one is a tiny fiat spyder which I could almost pick up at one end.

Sounds like the car should behave pretty well on the street. What happens when I take it to an off road event? Will there be additional mods that will be necessary before it can handle well enough to enjoy the event or will it be out of it's element until changes are made? By the time I will be doing any such event I will have 9x17 wheels and appropriate tires on the car. So what have you seen as your roadster is used on these varying conditions? Thanks, WEK.

[rich grsc]

I doubt very much you will want to be doing any off-roading in this car.

[skullandbones]

I doubt very much you will want to be doing any off-roading in this car.

You are right! That was a bad choice of words. Actually, what I meant was "off street" stuff like auto X or Track. But that is still a ways away since I am still just getting the street part right. Those that have ventured off the street to do any track or autoX work, what mods have you found necessary to get started off on the right foot, so to speak (pun intended)? And again, I don't plan on doing that sort of thing with the wheels and tires I have now. It will be much more traditional wheels and rubber. Thanks, WEK.

[CHOTIS BILL]

The main problems I have experienced with bump steer is darting side to side under hard braking or at high speeds. Darting under braking can be controlled with the brake pedal but a tank slapper at high speed is very scary and can be controlled be SLOWLY letting up on the throttle

Bill Lomenick

[Jeff Kleiner]

...Those that have ventured off the street to do any track or autoX work, what mods have you found necessary to get started off on the right foot, so to speak...

A properly sorted street car can roll right onto the track or course and be more capable than the vast majority of beginner, or even moderately experienced drivers. After you log some seat time (lots of seat time!) you may find yourself going to more stickier tires and more agressive suspension setups. Therein begins the slippery slope... :)

Jeff

[CraigS]

You won't have any problem. I still have fox spindles. I have been running 8-9 deg. caster for many years now. I did a partial SAI mod last year and did the Ackerman mod by moving the steering rack rearward to the current location. Just last month I finally measured bumpsteer and fixed what was there. Over the last 6 years I have been autocrossing starting w/ street tires and graduated to running used R compound tires for a few years.This is my second season on new A6s. My point is that I am still not quite up to MkIV specs, but have been running the heck out of the car through a lot of upgrades. Each upgrade, there was an improvement, but there was never a wholesale change.

[skullandbones]

[QUOTE=Jeff Kleiner;102844]A properly sorted street car can roll right onto the track or course and be more capable than the vast majority of beginner, or even moderately experienced drivers. After you log some seat time (lots of seat time!) you may find yourself going to more stickier tires and more agressive suspension setups. Therein begins the slippery slope... :)
/QUOTE]

You are talking "seat time" in events like track days and autoX etc, correct (not a lot of those opportunities around here so that could take a while)? I need just regular driving time in the car as it is, having not driven a straight shift car in about five years but I don't think that's going to help me as far as learning how well the car performs as a race car. It's good to know I can get started without a lot of specialized mods.

I am well aware of that slippery slope thing. I can see stuff in my future like a special set of wheels and tires, adjustable shocks, different springs, scales for corner weight and other special tools, 3 link diff, pit crew, and the list goes on and on................ but I will do my best to ease into it like Craig has and try not to get too addicted too fast. Thanks a lot, WEK.

Note: Of course, I will still install the new control arm peices and get that castor up to recommended numbers.