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Discussion Starter #1
This weekend I was replacing the front springs and was checking ride height.

I do this by installing the springs and leaving the shocks off so that I can easily remove them if I need to trim.

I was playing around bouncing the car up and down by pushing on the front fender and watching it rebound. I noticed I could time my downward push and really get the thing to bounce up and down (harmonics).

Then I realized that by doing this I could actually see the camber gain as the front tire/wheel tilted in and out under compression.

Then it hit me.... there was no visible change in toe!

Which there shouldn't be because I previously built a bumpsteer gauge and corrected that.

Then I realized anyone could do this by just removing their front shocks, bouncing the car and monitoring the toe change, adjusting the shims at the tie rod to minimize movement! You could attach a cheap $10 level with a laser to the tire and shoot it at the wall of the garage and just bounce the car watching the toe change and making adjustments.

You can do this without removing your springs!

Charlie ::

::
 

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Good idea. You'll also need to tie the steering wheel off to the pillar as it could move from all the excitement...
 

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Actually, the tire scrubs in & out from the vehicle's centerline as the suspension travels. A laser pointed to the front will move in & out as well, even if there's no toe change. This will LOOK the same as toe change on the wall. ;)

Now, if you took that laser attached to the tire, pointed it at the floor as a front-to-rear line, cycled the suspension, and looked for change in the angle.... :biggrin:
 

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Discussion Starter #4
Right.... yeah... that's what I meant..!

Anyway, thanks Cloney,...

The point is you can easily see the tire move as the suspension loads and unloads.
 

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Very cool. The ultimate in low-cost bump-steer guages.

Wouldn't the bump-steer be limited in this manner by the weight of the car on the tires though? This method would not be as accurate as the other, more involved, methods, would it?
 

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Wouldn't the bump-steer be limited in this manner by the weight of the car on the tires though? This method would not be as accurate as the other, more involved, methods, would it?
I would think that this method might be more accurate because the car has all four tires on the ground, just like it should. Plus you could cycle it through its "normal" suspension travel, which could be beneficial or not depending on how much toe change you are looking for.

Actually, does anybody know what the "normal" amount of suspension travel is for the front suspension from the neutral position? +/- 3 inches? Further in droop than in compression?
 

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Discussion Starter #7
All I'm tellin ya' guys is try it!

You'll feel a little like a lowrider trying to make the car "dance" but you will be amazed what you see.

Since it happens "real time" I expect you could actually improve your bumpsteer by just doing it by sight alone.

It's neat, try it the next time you have your front shocks off.
 

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Now, if you took that laser attached to the tire, pointed it at the floor as a front-to-rear line, cycled the suspension, and looked for change in the angle.... :biggrin:
But wouldn't the changes in Camber now appear as Toe change?

Tim
 

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More accurately, scrub change could look like bumpsteer.

I discussed this with Opentracker and he used a laser attached to the wheel. He also had a way to compensate for the scrub based on the distance to the wall. Hopefully he can chime in to clarify.

While bouncing the car is quick and dirty and can tell you if it's bad or not, I would still prefer to measue it with a gauge to make it quantitative instead of qualitative.
 

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Now, if you took that laser attached to the tire, pointed it at the floor as a front-to-rear line, cycled the suspension, and looked for change in the angle.... :biggrin:
But wouldn't the changes in Camber now appear as Toe change?

Tim
Camber change would move the line in & out from the car CL (but it would stay parallel), whereas toe change would change the ANGLE of the laser line away from parallel with the CL.
 

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A more accurate way to determine bump steer with laser projection would be to mount the laser on the thread of the tire, pointing sidewards. That way, scrub and camber changes do not affect the measurement.

I don't know how to fix the laser to the tire though. Duct tape, maybe. Also, the tire should not rotate. Maybe it's easier to take of the wheel and mount it to the spindle instead. Roadracer's bouncing technique can't be used in that case, of course
 

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I think the tire rotation might be hard to deal with.

When I did my test with a plate mounted to the rotor, the kinematics caused the rotor to seem to spin on the spindle. It wasn't really rotating, but I had to spin the rotor to level out the plate every time I changed the suspension travel.
 

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Hmmm I seem to recognize a few people here...

Isn't the easiest, most simple method to just remove the springs (my lowered springs fall out after I jack the car up and remove the shocks) and then move the car through its travel with a jack, checking change in toe for every inch of vertical travel?

I watched the old-time alignment shop I used to use simply spray a little silver paint on the tread, spin the tire and mark a line. I think he used an awl. That was his centerline on each tire.

After removing the springs and marking the tires we lower the car to full bump. Measure the toe (measure front, measure rear - same height) and chart it.
Jack the car up an inch and do it again until you're at full rebound.

Isn't bump steering a car really the measurement of toe change while the suspension is cycled through its usable travel?

Easier than the Longacre setup and on-the-car accurate. No special tools required.

BillGear -- great looking car.
 

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I checked mine with a sturdy rectangular metal frame. It's about 25 inches wide and about as tall. This is a method that I learned of in the Herb Adams Chassis Engineering handbook... I used it to set the position of the rack and pinion steering in my car.
Basically with the car level on jackstands, remove the springs / shocks, and use a jack to cycle the suspension. Starting with the suspension set around "normal" ride height, lean your frame against the outside of the tire so that it touches both the front and rear sections of the sidewall. about midway up the tire. Make sure the base of the frame does not slip or slide on the floor, and also make sure your steering is locked. Jack the wheel up 2 or 3 inches. If there is bumpsteer you will see a gap open up at either the front or rear between the frame and the tire. gap on the rear is understeer, gap on the front is oversteer. I kept adjusting the hieght of the rack until I got the virtually no change within a 5" cycle (+ 2.5 / - 2.5 of normal ride height) . Going to a full cycle (~ 7" ) I think I got a little bump steer near both ends of the cycle...

This is a less sophisticated method than what an alignment shop can do, but It certainly highlighted some issues with my original setup. I'm confident it got me in the ballbark... Once I drive the car I'll know if it actually worked!!!
 

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Dug this out of the abbiss............

I just spent about 2 days adjusting the total toe change on my 68 Mustang. I say total toe change because thats how I measured it,Like BossBill above,I removed the shocks and springs after measuring the ride hieght. Then set the toe,adjusted the hieght 1" and reread the toe and recorded the change. I measured 3" either side of ride hieght,because I only had 3" of travel in Bump (down) at body,up at spindle. Seemed like a good number. I was working alone so it took about 30 mins to check each posible setting with my Bump Steer kit. Truth is I hit the spot in 4 changes,plus 1 check to verify my setting. I also played with castor and found that has a measurable effect on toe change on my car,more seems better. My castor is limited by my arms as I have manual steering and an FE. 3.5* Positive is my limit.
I ended up with 0 toe change 2" either side of static ride hieght and 1/16" at 3", -1/16th at 3"bump,-1/16 at 3" rebound. I have to say thats pretty good for a 40+yo car.

Car has most of OpenTracker's front end catalog,roller upper and lower control arms,roller perches,adjustable strut arms. Miaer 600 springs and Bilstien Sport shocks,BTW best money you'll spend KYBs suck with heavy springs.
Upper control arms lowered 1.5".
I get 3* of camber gain at 3" of bump and camber does not go positive in drop.
 

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I'll say it's an old post but very worthwhile. I remember another cool way to check bumpsteer Opentracker posted I thought was pretty slick. He had the car facing the garage wall. With the car at ride height, springs,shocks out' he placed a laser level on the hub shining at the wall. Where the beam hit, he drew a vertical line. As he raised and lowered the suspension he could see how much toe changed and make corrections easily.a
 

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Huskinhano,
I read about shining a laser here or there but I dont know how it would work,or why.

As my car gets lower,bump,the track width gets wider. The change is about 1/4" per inch of travel.

Maybe if the car was in a box and the laser projected forwards and back you could calculate toe change,but just measuring it at the tires may be easier.

Anyway now I need to go drive mine and see if the Bump Steer Effect is reduced,Opentrackers term IIRC.
 
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