Bumpsteer .... The topic that won't die
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C6 the C5 of tomorrow
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From: Twin Cities Minnesota
Bumpsteer .... The topic that won't die
Hey, it's been way too long since anyone brought up the Bumpsteer topic, time to bore everyone to tears again :crazy:
So I measured bumpsteer on the Rack and pinion I am building, it's based on Gene's work. I used three different tierod lengths, 17.5" 18"and 19.5"
The results are in the chart below.
The chart shows that the shortest tierod is still too long and it needs to be moved up a tad.
For reference I did make some measurements with the tierod 17.5" long and about 1" higher, it's result is in chart 2
This is preliminary data, but I think the results are interesting and it's not bad for a first guess I think.
Now All I need to do is a little curve fitting, a little interpolation and I should be able to nail this BS to almost zero. ( well I have to align the car for castor and camber first too)
Chart 1 ( tie rod needs to be shorter and higher )
Chart 2 ( inner tie rod way too high )
So I measured bumpsteer on the Rack and pinion I am building, it's based on Gene's work. I used three different tierod lengths, 17.5" 18"and 19.5"
The results are in the chart below.
The chart shows that the shortest tierod is still too long and it needs to be moved up a tad.
For reference I did make some measurements with the tierod 17.5" long and about 1" higher, it's result is in chart 2
This is preliminary data, but I think the results are interesting and it's not bad for a first guess I think.
Now All I need to do is a little curve fitting, a little interpolation and I should be able to nail this BS to almost zero. ( well I have to align the car for castor and camber first too)
Chart 1 ( tie rod needs to be shorter and higher )
Chart 2 ( inner tie rod way too high )
Team Owner
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From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (427V8)
427, I would be very interested to see what you come up with, as Pete here recommended raising the center of my tie rods, and yes it did improve the bump on the down swing.....meaning jack the car up and see the tires move....I haven't had time to remove springs and try both ways....
at any rate, my tie rods are 19 and 21 inches long....
and the shortening of them would require a wider mounting bracket to the rack...something that is not so bad tie rod wise, but I question the stresses put on the rack travelor/car....all the increaed twisting/loading...wonder about rack internal stress/wear factors...
GENE
at any rate, my tie rods are 19 and 21 inches long....
and the shortening of them would require a wider mounting bracket to the rack...something that is not so bad tie rod wise, but I question the stresses put on the rack travelor/car....all the increaed twisting/loading...wonder about rack internal stress/wear factors...
GENE
Thread Starter
C6 the C5 of tomorrow
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From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (mrvette)
Well what I se in the data is that tie rod height is much more important than length. Not shown is another test with the inner end down 1" and it looks exactly like chart 2 except going in the negative direction.
I mean look at it, being too high gives almost 1/2 inch of bumpsteer!
While the difference between the longest and shortest tierod was only .020"!
(I'm ignoreing the negative excursion since I think its mostly due to tierod height effects)
So I would look at height a lot more critically
I mean look at it, being too high gives almost 1/2 inch of bumpsteer!
While the difference between the longest and shortest tierod was only .020"!
(I'm ignoreing the negative excursion since I think its mostly due to tierod height effects)
So I would look at height a lot more critically
Team Owner
Joined: Jul 1999
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From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (427V8)
Well, Pete suggested raising the centers tie rod ends by 1.5 inches so I did, and apparently it's helped a LOT, I find the steeroids rack is in fact mounted about an inch off to the driver's side too, from examinaing an install Chris---69my way did down the road here.....so that esplains why their center adaptor/positioning plate is shaped the way it is....I wonder if maybe I should just buy one of their plates before it's all painted up, and adapt the unit to my stock tie rod ends...but then I would have to buy new adjustment collars, and have at it again.....something I feel at this point is fairly moot, so for me it's on to other projects....frankly having my hot tub back in operation took precedence over any car project, and the house is taking on priority these daze....be a while, maybe spring/summer before car get any attention much...
GENE
GENE
Drifting
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From: Shawano WI
Re: Bumpsteer .... The topic that won't die (mrvette)
Gene;
When we made the change on your car, it was from measurement from your car. You cannot assume that the changes made on one car will be the same on another as slight changes in mounting will make huge changes on the car. The race cars that we run are built on a jig, so every one should be the same. Yet when you bump steer them every one takes different adjustments to make them correct. When you guys are doing R&P conversions, the fabrication is done by eyeball and tape measure so no two will ever be the same.
As I stated earlier, Our Corvettes should have a end take off rack to be correct. I do not believe you will ever get a "perfect" bump steer with a center take off rack because the tie rods are too long. So the adjustments you make will have to be the best compromise.
Keith;
Did you get those numbers from accual measurements with a bump steer guage or are they from measuring points on the car and plotting them out? I have been real interested in someone actually bump steering a R&P conversion.
[Modified by Pete79L82, 6:56 AM 11/17/2003]
When we made the change on your car, it was from measurement from your car. You cannot assume that the changes made on one car will be the same on another as slight changes in mounting will make huge changes on the car. The race cars that we run are built on a jig, so every one should be the same. Yet when you bump steer them every one takes different adjustments to make them correct. When you guys are doing R&P conversions, the fabrication is done by eyeball and tape measure so no two will ever be the same.
As I stated earlier, Our Corvettes should have a end take off rack to be correct. I do not believe you will ever get a "perfect" bump steer with a center take off rack because the tie rods are too long. So the adjustments you make will have to be the best compromise.
Keith;
Did you get those numbers from accual measurements with a bump steer guage or are they from measuring points on the car and plotting them out? I have been real interested in someone actually bump steering a R&P conversion.
[Modified by Pete79L82, 6:56 AM 11/17/2003]
Race Director
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Re: Bumpsteer .... The topic that won't die (Pete79L82)
As I stated earlier, Our Corvettes should have a end take off rack to be correct. I do not believe you will ever get a "perfect" bump steer with a center take off rack because the tie rods are too long. So the adjustments you make will have to be the best compromise.
Team Owner
Joined: Jul 1999
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From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (Pete79L82)
I think we mentioned before, Pete, about a company that makes race oriented racks some of them power assisted, and they are very short at about 18 inches long or so, and ETO of course, so we could use them, but the problem is what about the input linkages?? and headers.....
I love the headers I wound up with those Schoenfeldt #151 they fit fine and work well, and are CHEAP....at 150 bux/pair....
At any rate, my buddy the welder is working 7 ten hour days...round the clock untill further notice....lovely....
GENE
I love the headers I wound up with those Schoenfeldt #151 they fit fine and work well, and are CHEAP....at 150 bux/pair....
At any rate, my buddy the welder is working 7 ten hour days...round the clock untill further notice....lovely....
GENE
Race Director
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Re: Bumpsteer .... The topic that won't die (mrvette)
18 inch means it''s a 9x9 rack and it's too long, to position it properly it would have to be mounted way too high and you''d have to space the ball joints at the steering arms. The proper rack must be about 16,5" to 17" long and the only production ETO front steer rack that I have found that MAY fit (the verdict is still out on that one) is from an E36 bimmer
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Drifting
Joined: Oct 2000
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From: Shawano WI
Re: Bumpsteer .... The topic that won't die (mrvette)
Gene: Don't get me wrong. I do beleive you can get an CTO rack to acceptable comprimise with some work like we did with yours. We are not starting out with a clean sheet of paper for suspension design, so we have to work within the boundaries we have. While I believe an ETO would be the best situation, a CTO can be made to work to acceptable levels for street driving. You just can not get a "perfect" bump steer curve with it.
Some of the manufactures of race car P/S racks are Sweet. Appleton and Woodward. And I am sure there are others.
Pete
[Modified by Pete79L82, 7:33 AM 11/17/2003]
Some of the manufactures of race car P/S racks are Sweet. Appleton and Woodward. And I am sure there are others.
Pete
[Modified by Pete79L82, 7:33 AM 11/17/2003]
Thread Starter
C6 the C5 of tomorrow
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From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (Pete79L82)
Pete, these measurements were done with a dial indicator on a home made bumpsteer gauge. they should be failly accurate, but the car does need to be aligned for camber and castor!
I bought a longacre CC gauge but it hasn't arrived yet..
I agree that the CTO rack is not best of all worlds but it is a big step up in my book and adaptinga CTO I might as well just adapt a C4 system...
I bought a longacre CC gauge but it hasn't arrived yet..
I agree that the CTO rack is not best of all worlds but it is a big step up in my book and adaptinga CTO I might as well just adapt a C4 system...
Race Director
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (427V8)
427V8 I am glad to see someone else taking bump steer seriously. I have been working on my problem alot this summer and will finish it off this winter. I have that Caster Camber gage and really like it. Use 2 greased plates under each wheel and that makes it effortless to turn the wheels 20 degrees in and out.
I can't comment on rack and pinion bump steer but have learned alot about our systems. I found the height of the outer tie rod really makes a big difference. I also found tie rod length played a big part.
Good luck and I will certainly follow this post.
I can't comment on rack and pinion bump steer but have learned alot about our systems. I found the height of the outer tie rod really makes a big difference. I also found tie rod length played a big part.
Good luck and I will certainly follow this post.
Thread Starter
C6 the C5 of tomorrow
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From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
I didn't have much time tonight to do squat wifey's car decided to eat a waterpump, the damn thing locked up tighter than a , well you know...spent all night replacing it and everything else nearby, grrrr
Norval,
Which adapter did you get? They sold me the GM adapter and it was too small so I sent it back to get the magnetic adapter, that way I can do any car.
Yes I am taking Bump steer seriously, I would like to get it as near zero as possible in all attitudes. I was very excited to see the curves that looked exactly like the books say they should. I knew my tierods were too long, I wanted to be able to shorten them since my tierod stretcher is broken...and my tests proved the current height is pretty close, way cool!
One thing I forgot to mention is that I did do a bumpsteer at 30' and it wasn't all that much different than straight ahead, very encouraging!
Gene,
I did sneak over and measure the heights of the tie rod ends and the inner end at it's best height was 3" above the outer end. So I think 3.1 to 3.2 would be about perfect.
Norval,
Which adapter did you get? They sold me the GM adapter and it was too small so I sent it back to get the magnetic adapter, that way I can do any car.
Yes I am taking Bump steer seriously, I would like to get it as near zero as possible in all attitudes. I was very excited to see the curves that looked exactly like the books say they should. I knew my tierods were too long, I wanted to be able to shorten them since my tierod stretcher is broken...and my tests proved the current height is pretty close, way cool!
One thing I forgot to mention is that I did do a bumpsteer at 30' and it wasn't all that much different than straight ahead, very encouraging!
Gene,
I did sneak over and measure the heights of the tie rod ends and the inner end at it's best height was 3" above the outer end. So I think 3.1 to 3.2 would be about perfect.
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (427V8)
427V8 I don't know which adaptor I got. The gage came with a magnetic base that has a large enough hole in the middle to clear the nut as long as the cotter pin is pulled. I remove the dust cover, pull the cotter pin, take a file to the mounting surface to make sure no burrs or paint and carefully, very carefully mount the gage. The magnet is very strong and if you are not carefull the gage will be pulled very aggressively onto the hub and chip the magnet. Be careful.
My curve is confussing. On bump up I toe in regardless of what I do to mounting locations and heights but have only .015 bump in on compression of 3 inches. The amount of bump in at rise varies alot with outer tie rod location and tie rod length.
I tested a brand new Mustang and got 3/4 toe in at 3 inches rise. The factory hasn't worried about this problem obviously.
I am down to 5/16th toe in at 3 inches rise and .015 at 3 inches down. I will get rid of that 5/16 before I am satifified.
My curve is confussing. On bump up I toe in regardless of what I do to mounting locations and heights but have only .015 bump in on compression of 3 inches. The amount of bump in at rise varies alot with outer tie rod location and tie rod length.
I tested a brand new Mustang and got 3/4 toe in at 3 inches rise. The factory hasn't worried about this problem obviously.
I am down to 5/16th toe in at 3 inches rise and .015 at 3 inches down. I will get rid of that 5/16 before I am satifified.
Team Owner
Joined: Jul 1999
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From: Orange Park Florida
Re: Bumpsteer .... The topic that won't die (427V8)
3 inches?? you sure about that 427??.....seems a LOT.....Pete suggested raising them 1.5 inches, which I did, and that has yielded a height differance of only about 1/2-3/4 inch at most.....they are roughly parallel to the lower arm though...my suspension is dropped a bit though with stiff coils of around 460 in front, as I recall...they went in year '95.....but I know they were VBP stiffer coils, NOT in the 500 s anyway....., but like Pete says, it was set up for MY car, other ride heights would of course change everything once again...
GENE
GENE
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (427V8)
427V8 it will be interesting to see what your bump down curve will look like. I have a large nut welded to my crossmember and will a special hook screwed into this nut I can pull the car down any time.
This winter I want to again remove the springs and do it far more accurate then I can do with the springs still installed
This winter I want to again remove the springs and do it far more accurate then I can do with the springs still installed
Thread Starter
C6 the C5 of tomorrow
Joined: Nov 2000
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From: Twin Cities Minnesota
Re: Bumpsteer .... The topic that won't die (mrvette)
Gene,
Boy what a dummy, I measured the rod ends as the car sat but the car is on jack stands so the suspension is at full droop! :bb
I'll have to measure again at ride height, sorry!
Norval,
Do you still have your bumpsteer data?
I'd really like to see it. I have a paper that shows how to decipher the different slopes and curves and I'd like to see how yours looks.
Boy what a dummy, I measured the rod ends as the car sat but the car is on jack stands so the suspension is at full droop! :bb
I'll have to measure again at ride height, sorry!
Norval,
Do you still have your bumpsteer data?
I'd really like to see it. I have a paper that shows how to decipher the different slopes and curves and I'd like to see how yours looks.
Race Director
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (427V8)
don't have the curves like you do. I wrote them down on scraps of paper and put them in a folder. They are still there . I also know how to interpret the curves. They are telling a story.
Until I put my new spindles in I don't want to spend too much time working out the bump steer. This is another winter project. I did try 4 different length tie rods, each 1 inch longer then the other plus 4 different center links, I also spend alot of time lowering the outer tie rod end then made it permanent. I am just finishing the coil overs and should be finished this weekend.
I will then start replacing the spindles and do fine tuning on the bump steer.
So far I have install custom steering arms, tie rods, drag link and adjustable upper ball joints. These spindles are next.
Double click to enlarge
Until I put my new spindles in I don't want to spend too much time working out the bump steer. This is another winter project. I did try 4 different length tie rods, each 1 inch longer then the other plus 4 different center links, I also spend alot of time lowering the outer tie rod end then made it permanent. I am just finishing the coil overs and should be finished this weekend.
I will then start replacing the spindles and do fine tuning on the bump steer.
So far I have install custom steering arms, tie rods, drag link and adjustable upper ball joints. These spindles are next.
Double click to enlarge
Race Director
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From: Waterloo ontario Canada
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
If you guys ever have your spindles out the boss with the big bolt in it that holds the mounting plate for the caliper should be machined down 1/8th of an inch to center the caliper on the rotor. At least my rotors ride a little off center so these will be modified before installation. If you take too much off you can use a washer to center the caliper.
It should be centered.
It should be centered.
Melting Slicks
Joined: Jul 2002
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From: Boulder Creek California
Re: Bumpsteer .... The topic that won't die (norvalwilhelm)
Would this contribute to the common runout/airsucking problem with lipseal calipers, or just cause uneven wear on the rotors/pads?
Edit: That was a little vague, referring to the caliper mount, not bumpsteer of course.
[Modified by RUXperienced, 8:18 PM 11/18/2003]
Edit: That was a little vague, referring to the caliper mount, not bumpsteer of course.
[Modified by RUXperienced, 8:18 PM 11/18/2003]