Instant center
Originally Posted by FASTFATBOY
Please explain further, I have a Spohn arm in my car with Chrome moly rod-end in the front, the rear does not have a "rod-end" per say, it has a fixed"eyelit", but should pivot around each one when setting pinion angle, should you loosen the bolts when setting pinion angle to prevent bind? Then re-tighten? More info please.
On another note, IMO instant center should be somewhere under the drivers thigh area or close to that point in space..do you agree?
David
On another note, IMO instant center should be somewhere under the drivers thigh area or close to that point in space..do you agree?
David
Draw a triangle, make it so a corner points to the left, (like a long torque arm shape) and the right side is vertical. All the corners are mounting points, the left side corner of the triangle is the front mount, the 2 rod ends on the right vertical side. The vertical right side is the housing bracket and it is a fixed length. Since the arm is welded tubing, it cannot change angles, the angle of the left corner of the triangle cannot change.
If you change the length of the bottom edge of the triangle, say lengthen it, and the left coner angle does not change, then the right vertical side will in theory have to also increase length. However since its mounting points are fixed it cannot change length and will start to bind. Its just triangle geometry.
I never had heard about this binding before, but it makes perfect sense now that I think about it. The only way I can think of now to eliminate the binding is to make the front with 2 hiem joints/rod ends so the angle can change but this seems unpractical.
How much of an issue is this binding, is it just a problem of stress of the arm?
Originally Posted by CHRISPY
Something to think about...
The shorter the arm the faster the tires plant and then unload but with the longer arm it is generally easier to wheelstand the car and that can present its own problems if front suspension limiters do not work...
The shorter the arm the faster the tires plant and then unload but with the longer arm it is generally easier to wheelstand the car and that can present its own problems if front suspension limiters do not work...
Mike
Originally Posted by FASTFATBOY
On another note, IMO instant center should be somewhere under the drivers thigh area or close to that point in space..do you agree?
David
Originally Posted by BigSteele
I believe what he is talking about is the bind in the rear housing bracket. If this is the case I will try to explain it.
Draw a triangle, make it so a corner points to the left, (like a long torque arm shape) and the right side is vertical. All the corners are mounting points, the left side corner of the triangle is the front mount, the 2 rod ends on the right vertical side. The vertical right side is the housing bracket and it is a fixed length. Since the arm is welded tubing, it cannot change angles, the angle of the left corner of the triangle cannot change.
If you change the length of the bottom edge of the triangle, say lengthen it, and the left coner angle does not change, then the right vertical side will in theory have to also increase length. However since its mounting points are fixed it cannot change length and will start to bind. Its just triangle geometry.
I never had heard about this binding before, but it makes perfect sense now that I think about it. The only way I can think of now to eliminate the binding is to make the front with 2 hiem joints/rod ends so the angle can change but this seems unpractical.
How much of an issue is this binding, is it just a problem of stress of the arm?
Draw a triangle, make it so a corner points to the left, (like a long torque arm shape) and the right side is vertical. All the corners are mounting points, the left side corner of the triangle is the front mount, the 2 rod ends on the right vertical side. The vertical right side is the housing bracket and it is a fixed length. Since the arm is welded tubing, it cannot change angles, the angle of the left corner of the triangle cannot change.
If you change the length of the bottom edge of the triangle, say lengthen it, and the left coner angle does not change, then the right vertical side will in theory have to also increase length. However since its mounting points are fixed it cannot change length and will start to bind. Its just triangle geometry.
I never had heard about this binding before, but it makes perfect sense now that I think about it. The only way I can think of now to eliminate the binding is to make the front with 2 hiem joints/rod ends so the angle can change but this seems unpractical.
How much of an issue is this binding, is it just a problem of stress of the arm?
Not sure if you mean this or not....
Adjustment of the rod ended TA: Loosen the jam nuts on both rear housing ends. Adjust the bottom out, you'd adjust the top in or V/V (push and pull theory)? The front pivots, so there is no bind on the front persae. If you attempt to only lengthen the bottom, the front will pivot, but there will still be stress on the top rod end and thus bind. This allows the rear to be rotated, into a desired pinion angle. Hope that makes sense.
Originally Posted by MADMAN
I would obviuosly use my T/A. We normally put weight in the front of these cars anyway so you will be ahead of the game.
Originally Posted by Dear John
Are you saying that weight on the nose is good?
Maybe these modded cars get to a point when you have too much traction/front lift and start to move the other way in tuning to try to keep the nose down but im just guessing.
CAT3,
I meant the front "interior" angle of the torque arm itself is fixed, the angle cannot change between the top and bottom tubes of the arm (they are welded together). The whole TA can pivot with the body at the front point but this wasnt what I was talking about.
Most TAs Ive seen seem to adjust length using only the bottom rod end. I think you would have to take the bracket completely off to adjust the top (as it dosent have an extra "bolt" thing). And even if you could adjust the top there should still be a small bind or stress. I think there would only be 2 angles of the fixed length bracket that would "fit" with the TA back ends. Angles in between should make the rear bracket start to "push or pull" the 2 tubes of the arm apart. Thats what I was talking about with the bind.
Im sure the bind or stress within the arm is pretty small due to the small angle changes but I thought that was what MADMAN was talking about
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So how do you adjust pinion angle WITHOUT stressing the rear mount plate? I think I understand a little better....with the upper shorter than the lower point, it is trying to pull the top of the mounting bracket off before it gets a good push on the bottom of the bracket. There really is no fix for this, you can make the front adjustable(in height) to make the angles minimal in the rear. All cars will be different according to tire size and ride height(for needed pinion angle and instant center adjustment)
David
David
Originally Posted by mongse
Picture your car from the side. Draw a straight line from the axle mount of the LCA to the body mount of the LCA. Now, draw a line from the front mount of your torque arm to the center of the mount on the rear end.
I threw together a quick drawing in CAD to help a little.
http://www.quarter-mile.net/images/instantcenter.gif
I threw together a quick drawing in CAD to help a little.
http://www.quarter-mile.net/images/instantcenter.gif
Originally Posted by critter
That drawing is not correct. I'd post the one I have, but it is copyrighted. The only other choice is to buy the book.
Daren
Joined: Nov 2001
Posts: 8,484
Likes: 0
From: Cecil County Raceway!!!
I originally pointed critter to the correct IC definition. Its described in:
http://www.amazon.com/exec/obidos/tg...books&n=507846
Unfortunately it is copyrighted material.
http://www.amazon.com/exec/obidos/tg...books&n=507846
Unfortunately it is copyrighted material.
