norvalwilhelm

I find that anyone who wants to go to a better handling car seems to automatically throw in heavy springs, 460 or 550's. Why?
Are they just trying to mask a problem or do they really not know that they have a problem and by going to heavy springs mask it?
It's like putting a bandaid on a cut and saying it's better. The cut is still there you just don't notice it.
The same with the springs, the problem is still there but we don't notice it. Heavy springs tie the front end down eliminating the problem but we also have a front end that stops working. We have suspensions to take up irregularities in the road, holes bumps whatever but we go and install heavy springs immobilizing the front end from doing it's job.
Some of you are saying " Here he goes again on this bump steer". YOu are right.
I have spend most of last week chasing that problem. And that is the problem with our front ends and most new cars also.
Go to your local alignment shop and tell them to give you 2 inches of toe in. They will think you are nuts but we drive around daily in cars that have that built in.
I did test a new mustang this week and found at 3 inch lift it have 3/4 inch toe in.
I first started chasing this problem when I went over a rough whoop dee doo bridge hill at 100 mph and almost lost it. The car went right nuts.
Today I can take that same bridge and I do regularly at the same 100 mph with soft front springs and the car doesn't dart, shimmy or anything else other then feeling the wheels moving up and down. Dead true .
When I first started hunting I did some base line bump steer tests with only a tape measure and jacks plus a floor hook to pull the car down.
I don't remember all the figures but 1.250 inches per whee at 3 inch lift comes to mind. That's rediculous.
I did go with extended adjustable ball joints to raise the roll center since then and have some new figures taken this week
Stock tie rod lengths, no bump steer studs. 1 inch up .250 /wheel, 2 inches up .562 /wheel bump in, 3 inches up 1.125 inches in per wheel, total toe in 2.250. This is basically a stock 75.
Added bump steer studs and 1.125 inches lower outer tie rod.
1inch .125, 2 inches .312 , 3 inches .625 toe in per wheel. About 1 1/4 toe in at 3 inches rise like going over a sharp hill.
My toe down at 2 inches down was .015, acceptable.

Then I added a 2.1 inch longer tie rod sleeve and moved the center tie rod 2.1 inches along the center link and at the same time moved it up 1 inch.
Guys I am just filling in space. I ended up moving the tie rod with matching sleeves 2.1 inches then the 3.1 inches then finally 4.1 inches. All the time making new drag links and new tie rod sleeves.
The best for me was the 3.1 inches increased tie rod length. The new sleeve was 14 inches long with the inner hole moved 3.1 inches in plus 1 inch up where the maximum toe in was .312 at 3 inch lift with the same .015 toe in at 2 inches down.
The 4 inch increase in tie rod length just produced more toe in.
For my car so far the best combination is
Outer tie rods moved down 1 1/4 inch with the inner 1 inch higher then stock.
The tie rod sleeve 14 inches with the hole 3.1 inches moved further along the drag or center link.
Another great mod is milling the hole in the cross shafts of the upper A arm an extra 1/4 inch for 5 degrees of positive caster.
I am running 130 mph now on rough roads running 280 front springs and a soft rear spring without any handling problems.
I just don't have the nerve to run faster for now but I am continually pushing.
Don't put a bandaid over your problems by just installing heavier springs,.
FIX THE PROBLEM.
I will not argue this point. I have done extensive testing, I know for me my work is accurate, I know what my car likes and it is working.
I do work as an egineer at an engineering university and I know what accurate tests is all about.
Remember an amature built the arc and engineers built the Titanic.



[Modified by norvalwilhelm, 11:57 AM 8/16/2003]

flynhi

Excellent analysis, Norval. I just installed a Steeroids RP so now I'm wondering how to incorporate your findings with their setup.

Twin_Turbo

To handle the bump steer problem with your setup will require modifying the steering rod bracket and the steering rods. The steeroids kit is a center take off rack and you will want the steering rods as long as possible so the "effective" length changes as little as possible over the entire suspension travel. The greater the angle change the steering rods go through the larger the change in effective length, causing the bump steer. Do a search on this topic and about control arms. It was an older topic by either mr vette or norval. I tried explaining it there and i made some drawings. Mr Vette changed his setup afterwards I think. The trick is to mount the steering rods inner pivots as close to the center of the car as possible.

Matt Gruber

when i first moved to FL my house was on a dirt/shell road. The back way was awful with ruts and bumps. at 20 to 30 mph it would bottom out and scrape the headers!
went to 550 springs and that problem was solved.
not everybody has the same problem!
Now my street is paved so i don't take the back road anymore. i use the stock front sway bar and no rear bar.

you should post in the c2 section, there are 2 GM engineers there that could give you their perspective (SWC Duke & John Z)

Pete79L82

Twin Turbo: what you are saying about tie rod lenght is correct for MacPherson strut style car. It is not correct for cars with unequal lenght a-frame such as our corvettes. Unequal lenght a-frame suspension should be using end take-off racks, not center take-offs. I have not seem a steeroids kit but reading various threads I believe they use some type of adaptor block to compensate for the inner tie rod positions.

With a unequal length a-frame suspension the inner tie rods pivot point should be mounted in a line drawn between the upper and lower inner a-frame pivot points. If you use longer or shorter tie rods then needed you change the radius of the arc and you end up with excessive bump steer.


Norval: I couldn't agree with you more! Stiff springs/stiff shock/stiff bars are all very old school. Modern shock design has moved suspension tuning light years ahead of what it was 10 years ago. 10 years ago we would run 600# front springs and 250# rear spring on a race car. Today, on the same type of race car, we run 350# front springs and 150# rear springs and the cars are running 2 second quicker lap times. I agree, always try to fix the problem rather than try to mask it with another problem.

Cookwithvette

Ohhhhh! Kind of like what the VBP smart struts do in the rear.

I haven't had much time to learn about the steering system/front suspension yet. I don't even know what drag links, ball joints, and tie rod sleeves are let alone what these modifications are trying to accomplish. (aside from stoping toe changes) I also didn't know why our cars suffer from this issue.

Now it is all coming clear to me. Thank you guys very much for taking the time to share this information. This is a topic I've recently taken quite an interest in.

Twin_Turbo

I know what you're saying but the steeroids kit is a CTO unit, not an ETO. I'm gonna install a ETO for that exact reason.

If you look in the topic from some time ago I made some drawings with measurements to determine rack length as opposed to mounting heigth

If you want to adapt the mounting plate so that the CTO rack resembles an ETO it has to be REALLY wide so that the pivot is in the same plane as the upper and lower arm pivot are (green line in pic below). This is such a clumsy way to do it, so IMO it's better to use the steering rods as long sa possible to try to minimize bump steer that way. I know the solution isn't perfect but neither is using a very wide adapter plate.




[Modified by Twin_Turbo, 1:47 PM 8/16/2003]

Pete79L82

Twin_turbo; I agree with you. Our cars should use an ETO racks. I dont know of any ETO racks for rear steer cars. If you can find one that fits it would be a much better situation than CTO racks.

Pete

mrvette

Pete, Norval, all you guys....you all really great at stirring the pot again.....

my driver's side tie rod sleeve is 15 inches...and 17 inches on the pass side...making the C-C LOA of the driver's side....20 inches and pass side 22

SO that is with the inner tire rods about 4-5 inches apart...C-C....

and raised as Pete and I discussed couple of months ago....
NOW I have noticed the bump steer is much less....and the suspension has to go all the way relaxed for the thing to develope maybe a 1/2 inch of turn in...
not so bad....I never figgered on seeing any worse on the driver's side than pass side for that super long tie rod length..but yes....it's noticeable...funny, but true...

all I can say is, truth be known, for doing my OWN wheel alignments in the garage floor with my carpenters levels used very carefully and flipping them around to prove the readings....I have gotten tire wear down to near Zero...
UNLIKE all the so called professional alignmant shops in the Orange Park Florida area.....for the bux...sorry, I"ll do it myself....yet again...sadly....

damned old saw....what it right, DIY!!!

at any rate, going back a few daze ago to the stock front bar, and eliminating the rear bar entirely, has made the ride much better on these crappy roads...

been an interesting discussion all around....even the bridges at high speed are more stable, without the bars....

GENE

PROSOUTH

Marck, thanks for posting the picture again. I will print it this time for future reference.

Check our this set of upper & lower control arms for a Camaro. I am curious as to who makes them.
http://www.classicindustries.com

download catalog, section on 93-02 Camaro suspension-rearend.pdf I think page 22.

Norval, you might be interested in this concept. It is a set of Camaro upper and lower adjustable control arms with a heim joint at each of our present bushing locations.

Says that they allow total adjustment of camber and caster to dial in the front suspension.

They really look trick. It does reccomend them for autocross competition so they must be fairly tough.

I believe if we could come up with a few people that would sign up we could find someone to cast a set of spindles for a C-3. JIM


[Modified by PROSOUTH, 3:13 PM 8/16/2003]

Twin_Turbo

Pete, (norval, sorry for going off topic a bit)

I can't find an ETO rack for rear steer. That's why I'm thinking about converting to front steer. You can just swap spindles left & right, the only thing that changes is the brakes go from leading to trailing.

You also have to mod the lower arms for the sway bar brackets to bne in the rear and mount the bar in the rear (weld mounts on frame)

Look at GregP's site, he has done it. According to him a Fiat X1/9 rack is about the proper width.

The rack will have to be about 410mm wide from pivot to picot (a little narrower if you mount it lower than the crossmember, a tad wider if mounted above it)


Jim,

I am looking at the pole position stock car products arms, they'r adjustable and available for our stock bolt spacing. That way you can adjust the catser and the camber by adjusting the arms to be narrower. Combined with extended ball joints it will give the desired degree ofm adjustment desired (hopefully, but I'm pretty certain it will)


[Modified by Twin_Turbo, 4:19 PM 8/16/2003]

norvalwilhelm

Gene I am stirring up nothing just passing alot of experimentation allong to maybe help someone else who can not do the work themselves.
This has nothing to do with rack and pinion steering. This is strickly for modifying the stock system, not replacing it.
My tie rod sleeves or for replacing the stock units, with a relocated inner tie rod point.
If someone wanted to try this modification Coleman racing sells these sleeves for about $10.00 each. I make my own in all the different lengths from 10 inches to 14.

Thank you Pete for the input. I know from past posts on this subject that you are the most knowledgeable of any of us. You and redvetracr have real world experience.

Jim I could build a set a custom A arms but my stock units other then looks have everything I want. They have the 5 degrees caster that I want without shims along with -.75 camber. Anything else and I could just start shimming like normal.
I will look closely at them just to see if they temp me.
As for casting spindles think of the work to have them cast then machined? The cost would be high for a few special ones. Let me give it a try first this fall and maybe if they are easy as I think to do I could start doing a few for the forum at a very reasonable cost. Probably just shipping cost.

norvalwilhelm

Twin Turbo you keep comming up with pictures and dimensions that I have to keep for future reference.
I still think that a proper stock steering system works great. When our cars were new they never had a problem with play in the system.
I did bump check a new mustang and it had 3/4 inch toe at 3 iches rise so they still have not gotten rid of the problem.
When Steve Mcqueen took the mustang over the hills of San Fransico in the Movie Bullet he would have had real problems landing with a couple of inches of toe in.

Twin_Turbo

Norval, all that stuff is on my server.

look through the pics here (there is also a bunch on corvettefaq)
http://www.crossfire.homeip.net/twinnie/frsusp1.jpg

and then change 1 to 2.. and so on. Dunno how far it runs

same for
http://www.crossfire.homeip.net/twinnie/frontsusp1.jpg

if you need any dimensions, dust say so. I still ahev the stuff lying around and can emasure whatever you like.

PROSOUTH

As for casting spindles think of the work to have them cast then machined? The cost would be high for a few special ones.

I wonder because of so many being manufactured for drop spindle slammed cars and trucks their market couldn't be that big! I think a couple of hundred bucks will buy a set of them. Why shouldn't we be alble to buy a set for our need?

{b]Let me give it a try first this fall and maybe if they are easy as I think to do I could start doing a few for the forum at a very reasonable cost. Probably just shipping cost.[/b]

I was hoping my friend in Canada would offer that..............lol

jim :smash:

RHD '68 L89

Guys,
There was a good discussion which Norval and I took part in a while back. http://forums.corvetteforum.com/zerothread?&id=557345
I have an end take off rack as part of my RHD steering conversion.
It is a rear mount.
I have zero bump steer but reduced turning circle because I put in the theoretical correct amount of Acherman angle. I used an Australian rack from a Commodore (Holden). This rack will be very similar to the new GTO rack in dimensions( mine was from an older model).
I also used shorter steering arms to give the max wheel angle before the tyre hit the Chassis.
I am looking forward to the taller stub axles. Put me down for a pair when production starts!
Regards,
Cap'n James (retired)

:cheers:

aussiejohn

James, Norval, et al.
Thanks for a great discussion. I thought that I had a pretty good handle on B.S. ( aahhh, Bump Steer, that is ) until I read this. I intend to keep my 1974 left hand drive, as next year it will be 30 years old and I can register it. Only trouble is, I would like to find a nice left hand drive power R&P steering rack to fit my car. What one is used in the Steeroids conversion? What is the measurement of the steering arm pivot points? Just in case I can find one locally. Thanks in advance, guys.

Regards from Down Under

aussiejohn :cheers:

RHD '68 L89

John,
The Steeroids is a Centre take off rack like your Camira.
They bolt a plate on to the centre take off to simulate the drag link
and then have the tierods attached to that.
It means it is easier to adjust the position of the inner tierod points by putting a new plate on.
They would have done a fair bit of engineering to make it work better than the stock setup.
Pics are in August 2002 Vette. Our friend Bob did the article.
If you cant find the article call me. I will bring it to the meeting.
Cap'n James (retired)

:cheers: