Comptech bar: 5 way adj. or 20 way adj.?
11-03-2005, 04:11 AM
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Comptech bar: 5 way adj. or 20 way adj.?
The Comptech swaybar has 5 holes for adjusting stiffness. Lets say you have a pin set at full stiff, and than you add a second pin at position one. Would that have any effect on increasing stiffness?
11-03-2005, 06:20 AM
#2
Yes it would... and it does. Currently, I have one bolt in the next to stiff hole and one bolt next to it in the middle hole. The stiffness now feels almost exactly as stiff as one bolt in the stiffest position. It's simple math.
You have the length of the bar which is a constant and you have the cross sectional area of the bar. By moving the bolts around you can change the cross sectional area over the length of the bar... All combinations will result in different stiffnesses. I guess you just have to use a little common sense as to what the differences might be.
You have the length of the bar which is a constant and you have the cross sectional area of the bar. By moving the bolts around you can change the cross sectional area over the length of the bar... All combinations will result in different stiffnesses. I guess you just have to use a little common sense as to what the differences might be.
11-03-2005, 07:44 AM
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Originally Posted by glagola1,Nov 3 2005, 11:20 AM
Yes it would... and it does. Currently, I have one bolt in the next to stiff hole and one bolt next to it in the middle hole. The stiffness now feels almost exactly as stiff as one bolt in the stiffest position. It's simple math.
You have the length of the bar which is a constant and you have the cross sectional area of the bar. By moving the bolts around you can change the cross sectional area over the length of the bar... All combinations will result in different stiffnesses. I guess you just have to use a little common sense as to what the differences might be.
You have the length of the bar which is a constant and you have the cross sectional area of the bar. By moving the bolts around you can change the cross sectional area over the length of the bar... All combinations will result in different stiffnesses. I guess you just have to use a little common sense as to what the differences might be.
All I know is that many people are running full stiff (single pin) with Hoosiers and 710s, but I found 1 hole back from full stiff to be way to stiff with 225/245 RA-1s (this is using AP1 wheels on a new AP2). I had way to much understeer. I also have AP1 rear toe settings on my AP2 (camber -1.5 and -2.5).
I am going to try 1 pin from full soft with 1 pin in the sofest setting to see how that works this weekend.
My AP2 with AP1 wheels/tires and rear toe and the Comptech bar set to 1 hole from full stiff lead to some crazy, terminal understeer (I FELT like I had similar entry speed that I would have used on my older AP1) followed by ass wagging snap oversteer with even the slightest let up of throttle makeing trail braking an advanture. Felt really bad and hard to handle (although I got FTD even with 3 spins in 6 runs).
11-03-2005, 02:52 PM
#4
There are really only sixteen settings.
5, 5-4, 5-3, 5-2, 5-1
4, 4-3, 4-2, 4-1
3, 3-2, 3-1
2, 2-1
1
If you number the bolt holes 1-5, with 5 being the open end of the outer tube, then the stiffness of the section between hole 1 and hole 5 is:
Ki + Ko
--------------------------------------------
1 + (5-A)/4 (Ko/Ki) + (B-1)/4 (Ki/Ko)
Ki is the stiffness of the section of inner bar between holes 1-5.
Ko is the stiffness of the section of outer tube between holes 1-5.
A is the hole that the first bolt is in. 1<=A<=5
B is the hole that the second bolt is in (B=A if not used). 1<=B<=A
If you know the inner and outer diameters of the inner and outer tubes, then you can find the ratio of Ko/Ki and use the formula above to find the relative stiffness of each setting.
5, 5-4, 5-3, 5-2, 5-1
4, 4-3, 4-2, 4-1
3, 3-2, 3-1
2, 2-1
1
If you number the bolt holes 1-5, with 5 being the open end of the outer tube, then the stiffness of the section between hole 1 and hole 5 is:
Ki + Ko
--------------------------------------------
1 + (5-A)/4 (Ko/Ki) + (B-1)/4 (Ki/Ko)
Ki is the stiffness of the section of inner bar between holes 1-5.
Ko is the stiffness of the section of outer tube between holes 1-5.
A is the hole that the first bolt is in. 1<=A<=5
B is the hole that the second bolt is in (B=A if not used). 1<=B<=A
If you know the inner and outer diameters of the inner and outer tubes, then you can find the ratio of Ko/Ki and use the formula above to find the relative stiffness of each setting.
11-04-2005, 03:06 AM
#5
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Well, then there's Comptech's position that FEA showed no difference when designing the bar. There may obviously be a difference between thory and reality but it's also possible that the act of putting two bolts in simply makes you think there's a difference. I'd like to see results of a bench test to prove this definitively.
A local guy did a quick and dirty test by jacking the car with a sheet of paper under the front wheel. At the different combinations of holes there was a difference in measured body height when the paper was able to be moved, more or less proving that multiple bolts do help. Whether it's a limear response, etc., etc., I don't know...
A local guy did a quick and dirty test by jacking the car with a sheet of paper under the front wheel. At the different combinations of holes there was a difference in measured body height when the paper was able to be moved, more or less proving that multiple bolts do help. Whether it's a limear response, etc., etc., I don't know...
11-04-2005, 07:32 AM
#6
It seems to me that I've seen that claim before and there was a big argument about it.
If the inner and outer tubes are welded together at one end of the bar so that only the outer tube is floating, then I would believe that FEA would show no difference.
If on the other hand, the two parts of the bar come apart, then there will be a difference. Without the second bolt, the section of the inner tube between the bolt and the free end will float, and not twist. With the second bolt, the section of the inner tube between the two bolts will twist. That difference in state represents a difference in stored energy, which requires additional force to create.
It may be that the difference is very small, depending on the difference in diameters, and that could be what they meant.
The two halves of the bar slide apart, right? Someone post the diameters and I'll plug them in.
If the inner and outer tubes are welded together at one end of the bar so that only the outer tube is floating, then I would believe that FEA would show no difference.
If on the other hand, the two parts of the bar come apart, then there will be a difference. Without the second bolt, the section of the inner tube between the bolt and the free end will float, and not twist. With the second bolt, the section of the inner tube between the two bolts will twist. That difference in state represents a difference in stored energy, which requires additional force to create.
It may be that the difference is very small, depending on the difference in diameters, and that could be what they meant.
The two halves of the bar slide apart, right? Someone post the diameters and I'll plug them in.
11-04-2005, 08:39 AM
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Originally Posted by Orthonormal,Nov 4 2005, 12:32 PM
It seems to me that I've seen that claim before and there was a big argument about it.
If the inner and outer tubes are welded together at one end of the bar so that only the outer tube is floating, then I would believe that FEA would show no difference.
If on the other hand, the two parts of the bar come apart, then there will be a difference. Without the second bolt, the section of the inner tube between the bolt and the free end will float, and not twist. With the second bolt, the section of the inner tube between the two bolts will twist. That difference in state represents a difference in stored energy, which requires additional force to create.
It may be that the difference is very small, depending on the difference in diameters, and that could be what they meant.
The two halves of the bar slide apart, right? Someone post the diameters and I'll plug them in.
If the inner and outer tubes are welded together at one end of the bar so that only the outer tube is floating, then I would believe that FEA would show no difference.
If on the other hand, the two parts of the bar come apart, then there will be a difference. Without the second bolt, the section of the inner tube between the bolt and the free end will float, and not twist. With the second bolt, the section of the inner tube between the two bolts will twist. That difference in state represents a difference in stored energy, which requires additional force to create.
It may be that the difference is very small, depending on the difference in diameters, and that could be what they meant.
The two halves of the bar slide apart, right? Someone post the diameters and I'll plug them in.
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11-04-2005, 09:03 AM
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Orthonormal,
I guess this is a little off topic (but its my thread so I guess I can hijack it
) What % stiffer is a hollow 28.2 x 5mm wall thickness swaybar than a hollow 26.5 x 4.5mm wall thickness bar assuming all else is equal?
I guess this is a little off topic (but its my thread so I guess I can hijack it
) What % stiffer is a hollow 28.2 x 5mm wall thickness swaybar than a hollow 26.5 x 4.5mm wall thickness bar assuming all else is equal?
11-04-2005, 09:56 AM
#9
It's not hard to do that calculation yourself, I'll use your question as an example of how to do it.
Stiffness is proportional to the diameter to the fourth power. Also, superposition works -- if you take a hollow bar and a solid bar that would exactly fill the hole in the middle, and add up the stiffness, the total is the same as the stiffness of a solid bar of the same diameter as the hollow bar.
Using those two rules:
d^4 of the 28.2mm bar is 632,400. The hole down the middle had d=18.2mm, d^4=109,700. Subtract the two to get the number for the hollow bar: 522,700.
Do the same thing for the 26.5mm bar with the 17.5mm hole: 399,400.
Divide to get the result that the 28.2mm bar is 1.31 times as stiff as the 26.5mm bar.
Stiffness is proportional to the diameter to the fourth power. Also, superposition works -- if you take a hollow bar and a solid bar that would exactly fill the hole in the middle, and add up the stiffness, the total is the same as the stiffness of a solid bar of the same diameter as the hollow bar.
Using those two rules:
d^4 of the 28.2mm bar is 632,400. The hole down the middle had d=18.2mm, d^4=109,700. Subtract the two to get the number for the hollow bar: 522,700.
Do the same thing for the 26.5mm bar with the 17.5mm hole: 399,400.
Divide to get the result that the 28.2mm bar is 1.31 times as stiff as the 26.5mm bar.
11-04-2005, 10:31 AM
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Originally Posted by Orthonormal,Nov 4 2005, 02:56 PM
It's not hard to do that calculation yourself, I'll use your question as an example of how to do it.
Stiffness is proportional to the diameter to the fourth power. Also, superposition works -- if you take a hollow bar and a solid bar that would exactly fill the hole in the middle, and add up the stiffness, the total is the same as the stiffness of a solid bar of the same diameter as the hollow bar.
Using those two rules:
d^4 of the 28.2mm bar is 632,400. The hole down the middle had d=18.2mm, d^4=109,700. Subtract the two to get the number for the hollow bar: 522,700.
Do the same thing for the 26.5mm bar with the 17.5mm hole: 399,400.
Divide to get the result that the 28.2mm bar is 1.31 times as stiff as the 26.5mm bar.
Stiffness is proportional to the diameter to the fourth power. Also, superposition works -- if you take a hollow bar and a solid bar that would exactly fill the hole in the middle, and add up the stiffness, the total is the same as the stiffness of a solid bar of the same diameter as the hollow bar.
Using those two rules:
d^4 of the 28.2mm bar is 632,400. The hole down the middle had d=18.2mm, d^4=109,700. Subtract the two to get the number for the hollow bar: 522,700.
Do the same thing for the 26.5mm bar with the 17.5mm hole: 399,400.
Divide to get the result that the 28.2mm bar is 1.31 times as stiff as the 26.5mm bar.