Bump steer gauge

Looking for opinions on bump steer gauge, single vs. dual dial indicator style. I have always used the dual and not sure the accuracy of the single. Using the dual I just note the difference in movement between the two. I have bumped cars that had.250" differential between the front and rear indicator per inch with the front only moving .030". If I used the single style on the front would I be fooled into thinking bump was good? Hope this makes sense. I have read in the ads for the single style and they say you only need 1 indicator and it does the math for you. Not sure how?

How could you have .250 difference between the 2 gauges but front only moved .030? If the front moves out the rear has to move in the same amount at least in my mind. That being said I use bumpsteer with 1 dial indicator

This has really been frustrating. I was hoping someone could explain or help. I keep checking over and over because I think I am doing something wrong. I will spend more time with it this week and see if what I am seeing is correct.

Maybe it's changing caster or camber dramatically, or bad heims in the lower

That was my first thought that caster is changing. That is on tap for this week. Checking for caster change. Thanks

Just think about it .... the bump steer is how much the front is moving in relation to the back , having the back on a roller and the front on a dial indicator measures that amount ... maybe you had one of the indicators topped or bottomed out. Using 2 gauges does not make much sense to me.

when you check toe , you check front and back and compute toe , why wouldn't you do the same with bump steer ?

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Originally Posted by shawburn

Looking for opinions on bump steer gauge, single vs. dual dial indicator style. I have always used the dual and not sure the accuracy of the single. Using the dual I just note the difference in movement between the two. I have bumped cars that had.250" differential between the front and rear indicator per inch with the front only moving .030". If I used the single style on the front would I be fooled into thinking bump was good? Hope this makes sense. I have read in the ads for the single style and they say you only need 1 indicator and it does the math for you. Not sure how?

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Didn't really follow you there on actual measurements, so I'll try to explain.

1. The wheel (least on a LM) is going to move in or out a fair amount towards or away from the engine when it moves up and down. I'm not talking toe, but it's gonna move inboard or outboard as the tire moves from camber change and just the fact that it has control arms. So say you have absolutely no toe change, the wheel can move in say .250 as it goes up so your indicator will show .250 change on both but the toe did not change. You could think of this as measuring toe and both front and back are 88.25" at the tire, but if you remove a 2" wheel spacer the measurement is now 86.25" but the toe is the same.

2. I never used one of the single indicator ones, but the way I see it with the roller as the wheel moves inboard or outboard (as above) to keep the roller on the wheel plate it would appear you would need to move or slide the stand. I don't see how you can move this and not move the other side and mess up the accuracy of the test. That would be the reason most of them are dual indicator ones, is my guess. Again I don't see how you keep the roller on the plate when the wheel is moving a lot inboard/outboard without having to slide the fixture/stand around.

3. The dual simply measure the movement of each end and you just add/subtract the reading to get the overall toe change. Yes it's easy to mess up and add together or subtract when you should have done the opposite. if the indicator dial is moving clockwise then that part of the wheel plate is moving outboard and if rotating counterclockwise the wheel plate is going inboard.

So if both indicators are going the same direction then you subtract the difference in change on both indicators to get toe in or out just like measuring toe with tapes. If one is going clockwise and the other counter clockwise then you need to add them.

Hope that helps

I will spend more time with it this weekend and see what I come up with. This is on a 04' smackdown. I have the setup manual and everything is per the instructions as far as shims on both ends of the tie rod. Only thing is the car has 1 piece lowers. Not sure if the 04's were built with them or did they come with 2 piece? Could there be something that could change with that as far as caster movement if it wasn't checked? That is up next, caster change at different heights. Thanks

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Originally Posted by shawburn

I will spend more time with it this weekend and see what I come up with. This is on a 04' smackdown. I have the setup manual and everything is per the instructions as far as shims on both ends of the tie rod. Only thing is the car has 1 piece lowers. Not sure if the 04's were built with them or did they come with 2 piece? Could there be something that could change with that as far as caster movement if it wasn't checked? That is up next, caster change at different heights. Thanks

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I guess I'm not sure what problem you're having, I assume you have everything to factory specs and maybe it's not coming out right like excessive or too little toe out?

I can say I don't think I ever seen one come out to the spec's I want, so it's very common for it not to be correct with factory setting in my experience. (however I'm not a masters guy so can't say for that type of car.)

That being said if your caster isn't set to specs it will be off, since that raises or lowers the tie rod end of the spindle like having extra or not enough shims there.

billet , i use a home made bump steer plate and i use 2 inch indicators , and thats what i do , subtract and use the difference , i dont see how you could do it with one..

I have a Longacre, which utilizes just one gauge. It is "hinged" at the bottom, so when set-up, the hinge point needs to be outboard of the toe plate (so the upper fixture leans in). Then when moving up (or down), the end opposite the gauge uses a roller to slide up and down the toe plate and you read the change on the gauge.