hotrodf1

Hey all,

I finally made a bumpsteer gage and was trying to get the racecar lined out before going to Mid Ohio in about 3 weeks with NASA. This car has a PA Racing tubular K-member installed, with their rack and pinion added as well. I am not sure what the rack is from, was told it was a fourth gen.

The problems start here: the bumpsteer is absolutely ridiculous no matter where I set the tie rod height. And whether the wheel is pointed straight forward or toward the middle of the car, the reading change dramatically. Basically, there is no way to get the bumpsteer down to a reasonable level. I got to thinking and looking etc., and realize that the inner tie rod pivot point is no where close to where it would be on a stock car (which is basically in line with the two lower control arm bolts).

The distance between my inner tie rod pivots points is about 26" now, and I measured on my stock 91 and the inner tie rods are only about 15 or 16" inches apart as measured on the drag link ( or tie bar, whatever its called).

This means with the rack and pinion swap, my tie rods are now much shorter, which appears to be the cause (or main cause) for the wacky incurable bumpsteer reaction.

As I mentioned, the car is a road course racer and I would assume was swapped over to the rack and pinion for weight savings, maybe steering feel ( I didn't build the car).

I can't say I really notice the effect of the bumpsteer on the track, but I'm thinking having .400" of change in 4" of travel (2 bump, 2 droop) is probably not very good, and I'd probably notice more stability in the car if it was corrected.

Does anyone have any info on why the rack & pinion is or is not a good way to go here? The only thing I could do is swap back over to IROC box and the other stock parts and try to bumpsteer the car again.

I used to have a 68 Camaro and I seem to recall the rack and pinion kits were no good on that car either (word on the forums, etc. etc.).

So - should I swap the rack out for the stock style box and links?

Thanks for any help . . . .

572_Rat

I have a rack on my car and do not have the problem that you are having. My rack is a shorten pinto rack, but one thing, I noticed my steering really tighen up when I put a 3 point strut tower brace on the car

Roostmeyer

iTrader: (3)

That's a ton of toe change. I can't believe they'd even sell you their track and pinion setup for road racing. A purpose built circle track racing rack with new mounts welded on is probably your only fix besides going back to a stock recirculating ball setup. Sticking a t-bird or pinto rack on these cars is a drag racing only mod.

The circle track racks are typically 17 or 18" wide, but start around $800 for a power steering rack. If you're running any decently wide tires I'd suggest running power steering anyway.

SlickTrackGod

Are you in camber gain in static A-arm angle? basically what is the static angle of the a-arm to the ground at ride height (from ear to balljoint direction- IE going up 2*, or going down 4* for example.)

You basically will want the car as low as possible to get a decrease in the camber curve. Atart the a-arm at parallel or slightly inverted so as to have the geometry decrease the distance. Then try and get the outer tierod as low as possible to increase. That will hopefully minimize what gain you are getting from the shorter tierod arm change in angle. If you have extended ball joints then yoou will have to take them out. This is all a bandaid fix and you are compromising alot of other benefits (i.e.- the camber curve, the roll centers) the toe gain is great for corners, but you are going to be wandering everywhere.

It its a bumpy course you will be in trouble regardless.

If its a smooth course where you are not experiencing much bump wandering of the car, then use the shorter tierods to your favor. Set the toe about 3/32 in on normal height and when you get hard on the brakes loading the front suspension you will go to about 1/4" toeout (maybe 5/16th but the toeput will make your turn-ins very easy and then tighten up coming off. Again as stated, it will wander on bumps but is the track smooth enough where this is not a big worry?

Just favor a stiffer spring rate to lock up the suspension travel a bit more and lighten the front swaybar.

hotrodf1

Yeah, I'm guessing PA normally sells more to the drag race guys, so maybe it's not an issue with them. I haven't talked to PA or anything, maybe I should get their opinion as well.

Circle track rack is out of the budget it sounds like. And it sounds like it would get me close, but I have suspicions that getting the steering shaft to the rack would be difficult, it's already tight. More narrow would be more problems from that standpoint.

hotrodf1

-- Not sure exact angle, but guessing about 2-3 degrees up at present time.

I think I'm about there, much lower and headers and oil pan are in for real trouble. I think I see what you are saying there. It did respond better with the wheels in straight forward position with the tie rod low. Then I turned the wheel slightly in (so it would be on the loaded side of the car) and then all the readings changed for the worse. It wasn't good straight but was terrible when turned slightly, and I believe was toe in on bump.

We run down at Memphis too, which is a track that's quite bumpy from a few years of neglect.

Ideally I would want the lower a arms about level at ride height correct? So to lower the car properly I would need drop spindles? It has coilover conversion on the front now.

I have the issue where basically anywhere in bump or droop I go toe in. This is supposed to be a symptom of tie rods that are too short from what I've read. Seems to make sense. So I guess the above thought may not work. I think when I hit the brakes, it will just toe in more. I don't think my tie rod studs are long enough to get the tie rods low enough to do this.

Like you said about the band aids earlier, I try to avoid doing stuff that way when possible. This car has been modified etc., by multiple people and the problems seem to be compounded, you know how that goes. The balance of the car is really pretty good and I don't want to upset it just yet. The front sway bar is a tubular 1LE piece, and not adjustable.

I'd rather fix it right, for minimal cash if possible. It kind of seems like that means it needs the original style steering hardware back in there.

What's the drawback to doing that? I believe it will pretty much bolt right up, except for the out tie rod heims. Is it just added weight? The rack in the car now seems to be fairly sluggish as far as rate goes, so it's not like I'm used to quick steering anyway (road course this work ok for me, easier to be smoooooth)

BMR Tech

Unless you plan to have a custom, narrow rack built, I wouldn't suggest you have your car converted to rack and pinion for road racing in a Third Gen. There is a dramatic loss in steering angle thanks to the location of the steering arm mounts on the spindles and the packaging concerns for the front of the car. I always talk people out of it when they call about it, unless it's a drag car or they know what they're getting into.

That being said, TurnOne can custom rebuild your steering box and get the thing dialed in very nice for your setup. Give them a call. Might be expensive, but it's quality work and fantastic results. Still cheaper than a custom rack.

- Kevin

hotrodf1

Thanks for the info Kevin, makes sense. I'll look into TurnOne, hadn't hear of them before. I really wish this car hadn't been converted already. Anyone have any steering parts for these cars that they don't need?

I bet whomever converted it thought they were really doing something impressive. Oh well it can be fixed.

hotrodf1

Update:
I have now installed the original style steering hardware in the car. I have the WS style box from a T/A. Also used a modified Astro van steering shaft setup.

The car has bumpsteer studs installed in the steering arms so I can adjust the height of the tie rods.

I got some results from yesterday's bumpsteer measurement. THis is the best. As I moved the tie rod higher, the results were better.

THe right front looks like this: bump +1.5":.135"Out +1.0": .070" Out +.5": .035" Out
Droop -1.5" : .125" IN -1.0": .065" IN -0.5": .030" IN.

This is with the tire rods up as far as I can go with the studs. The studs don't allow for the tie rod to go all the way up to the steering arm due to the design of the studs.

While those above results are in fact much better than they were with the rack & pinion previously installed, it seems there is still room for improvement.

Can anyone recommend the proper path to improve this bumpsteer curve?
I can think of a couple things that I believe might work:
1) More caster - car is not currently setup to have adjustable caster so this is difficult to do. (more caster to effectively raise the tie rod end)
2) Lower outer ball joint with extended length ball joints (this would help the arms be closer to level as well which may be a benefit in roll center on the front of the car)
3) Remove studs in steering arms and use a through bolt (raising the tie rods ends).
4) Find some way to lower the idler arm and steering box, which would lower the center link (same effect as raising height on tie rods???)

Anyone care to weigh in on which option they believe to be the best?

hotrodf1

Quick update:

Moved the idler arm down about .475".
Results are astounding.
1.5 = .000
1.0 = .005 IN
0.5 = .005 IN
00
-.5 = .005OUT
-1.0 = .015 OUT
-1.5 = .025 OUT

I think this will work for now. Could optimize a bit more by moving the idler arm back up maybe .100" or so (or moving outer tie rod down a bit).

The steering box side is going to take a bit more work to complete. . . .

Roostmeyer

iTrader: (3)

I don't think I've ever heard of an acceptable amount of bumpsteer, but I'd think your good there. What's the distance you're measuring across? To the lips of the wheel?

The second posts #'s look very good assuming you're measuring to the lip of the wheel. Sounds like you've got it figured out, but the steering box holes have a lot of slop in those holes as well. It's probably better to adjust the steering boxes position and use the slots in the idle arm to level the centerlink.

I probably should check the passenger side on my car, but if the centerlink is centered side to side and level it shouldn't be any different to the driver side.

SlickTrackGod

Actually a little bumpsteer in corner entrance can do wonders if the track is smooth enough. you can get a toe gain going in under brake compression that will aid in turn-in, and then roll will leave a little bit for help with ackerman- just how much? gotta track test it and also get pyro #'s to see tire heat management. Ive been doing this for years. Its kind of my special trade secret. Its all about driver feel.

My time in NASCAR I was using this to give the RF a little toe loss, and give the LF just a substantial toe gain under compression braking. Overall the cross toe would build an 1/8" more out- the driver did not have to put as much effort intot he wheel and the car turned-in almost by itself like a jetfighter right into the bank without fighting alot of steering movement on a shortrack 1/2mile.