thread800-286119
As an update to then original thread on this IRSweheel tramp [Americans incorrectly call IRS tramp as hop}. Live axles do indeed hop vertically, but irs tramp does not actually lift the driven wheels, hence tramp is more accurate.
Update on my experiments and I really hope Greg and Pat and other previous contributors read this and offer comment.
Greg, as a followup to engine torque and the mounts being a source, well after doing extensive gopro filming of all of the likely energy storage bits; engine, gearbox, diff and wheel joints, i found that as expected they all tense up and release energy when wheelspin occurs. No wheelspin = no opportunity to release energy = no tramp. At tramp, the engine rocks the most on its liquid mounts, likewise the gearbox is bolted to the engine and of course rocks to the samne frequency, about 8 Hz. Greg, i fitted a shocker to the engine, mounting it horizontally using one of the few shockers that can work horizontally. I used 2000 QUAD Mustang shockers, as other types get an airlock in their tube that limits use. Result was that the resonance in the engine bay was reduced by about 75%, and reduction at the wheel, where it matters, was also greatly reduced.
The most alarming movement was seen in the diff; mounted with two rubber mounts at the front and a single offset mount at the rear. Gopro movie shows massive vertical resonance with minimal sidways movement. Hence a vertical rubber “snubber” would be a good helper here. A BMW fix in usa seems to be a fabricated rod end as a fourth mount with a solid bush in the original 3 diff mounts, hence solid diff bush with std rubber mounts everywhere else in the rear.
Gopro at the wheels showed the same 8Hz resonance, no vertical lift, only slip/grip cycles with some movement as the rubber mounts compressed causing significant toe change.
My mods, all done separately. Engine damper; excellent mod and the factory should have done it.
Polyurethane diff bush in each of the 3 mounts; NHV increased slightly with poly stiffness 90. Tramp surprisingly little changed. BMW “Guy” confirmed that he also failed with poly but succeded with solid joints. My experiments showed that these claims are dangerous because my experience is that only testing on a wet road is by far the best way to test. When questioned, suppliers of various poly bushes or arms or mounts showed that wet road testing had not been done. This certainly applies to claims from usa suppliers.
The use of big/small diameter axles gave unclear results. I used the Camaro use of differing axles as a guide and built my own axles to a similar torsion ratio. Improvement was minimal and resulted in me following up with GM designers. They also found it didn’t fix the tramp problem and ultimately did what bmw and mercedes did, and that is to use traction control to reduce or even stop all wheelspin. The trick here is that TC is not cancelled when pushed and needs either a 10 second hold down time, or simply cannot be turned off completely. How disappointing that these mega companies cannot engineer a solution and use basically the abs sensors to stop wheelspin rather than fix the cause, I call it waving them white flag!
I have systemically changed rubber bushes for poly or rod ends. The Camaro uses nice rod ends in their toe links, and added another spherical joint to the wheel hub. I can only conclude that GM has failed to find a complete solution and the IT solution used by others really only hides the problem. Electric throttles are part of this stop the wheelspin “cure”. Despite the throttle being 100%, the engine cuts to idle positioning!
Conclusion: i think the “ fellow using a “horizontal damper at the rear wheels is offering the best and certainly simmplest solution, and at minimal cost too. He also found that he needed an engine damper for full 100% wet weather solution. However, the layout of the ve cOMMODORE,/G8 is so far, too difficult to mount a similar damper. It needs innovative brackets to fit whereas hopnot solution is for a Chrysler 300 type car, similar rear IRS but different enough to prohibit it on the Commodore/Pontiac G8
So there it is: use an engine damper, fabricate a diff snubber, mount dampers horizontally at each driven rear wheel if possible! Using poly bushes is dangerous as they can only be used when the geometry allows the particular arm to rotate precisely {rotate over each connecting bolt}. This is not the case when you have semi trailing arm setups, like Camaro, C ommodore and Bmw or similar designs. I found poly suppliers simply do not understand how polyurethane works compared to vulcanised original rubber bushes. The rebound frequency of poly is considerably higher than rubber. Poly also does not like being forced to squish at an angle to the bolt in the joint, and will form an oval shaped hole after a few months in service and can resault in considerable dangerous movement in an arm or link.
After extensive testing, i am sticking with my thought that tramp is a system resonance caused by stored system energy being released through the wheel when wheelspin occurs, that’s energy being again stored and then release resulting in broken slip/grip wheelspin as the car moves along the road. If full wheelspin occurs, this bypasses the tramp mode, but of course forward progress is minimal.
Perhaps I should join the white flag crew and use electronics to stop wheelspin. I look forward to reading your comments. Please foregive typos, hard going on my iphone at night. Cheers
As an update to then original thread on this IRSweheel tramp [Americans incorrectly call IRS tramp as hop}. Live axles do indeed hop vertically, but irs tramp does not actually lift the driven wheels, hence tramp is more accurate.
Update on my experiments and I really hope Greg and Pat and other previous contributors read this and offer comment.
Greg, as a followup to engine torque and the mounts being a source, well after doing extensive gopro filming of all of the likely energy storage bits; engine, gearbox, diff and wheel joints, i found that as expected they all tense up and release energy when wheelspin occurs. No wheelspin = no opportunity to release energy = no tramp. At tramp, the engine rocks the most on its liquid mounts, likewise the gearbox is bolted to the engine and of course rocks to the samne frequency, about 8 Hz. Greg, i fitted a shocker to the engine, mounting it horizontally using one of the few shockers that can work horizontally. I used 2000 QUAD Mustang shockers, as other types get an airlock in their tube that limits use. Result was that the resonance in the engine bay was reduced by about 75%, and reduction at the wheel, where it matters, was also greatly reduced.
The most alarming movement was seen in the diff; mounted with two rubber mounts at the front and a single offset mount at the rear. Gopro movie shows massive vertical resonance with minimal sidways movement. Hence a vertical rubber “snubber” would be a good helper here. A BMW fix in usa seems to be a fabricated rod end as a fourth mount with a solid bush in the original 3 diff mounts, hence solid diff bush with std rubber mounts everywhere else in the rear.
Gopro at the wheels showed the same 8Hz resonance, no vertical lift, only slip/grip cycles with some movement as the rubber mounts compressed causing significant toe change.
My mods, all done separately. Engine damper; excellent mod and the factory should have done it.
Polyurethane diff bush in each of the 3 mounts; NHV increased slightly with poly stiffness 90. Tramp surprisingly little changed. BMW “Guy” confirmed that he also failed with poly but succeded with solid joints. My experiments showed that these claims are dangerous because my experience is that only testing on a wet road is by far the best way to test. When questioned, suppliers of various poly bushes or arms or mounts showed that wet road testing had not been done. This certainly applies to claims from usa suppliers.
The use of big/small diameter axles gave unclear results. I used the Camaro use of differing axles as a guide and built my own axles to a similar torsion ratio. Improvement was minimal and resulted in me following up with GM designers. They also found it didn’t fix the tramp problem and ultimately did what bmw and mercedes did, and that is to use traction control to reduce or even stop all wheelspin. The trick here is that TC is not cancelled when pushed and needs either a 10 second hold down time, or simply cannot be turned off completely. How disappointing that these mega companies cannot engineer a solution and use basically the abs sensors to stop wheelspin rather than fix the cause, I call it waving them white flag!
I have systemically changed rubber bushes for poly or rod ends. The Camaro uses nice rod ends in their toe links, and added another spherical joint to the wheel hub. I can only conclude that GM has failed to find a complete solution and the IT solution used by others really only hides the problem. Electric throttles are part of this stop the wheelspin “cure”. Despite the throttle being 100%, the engine cuts to idle positioning!
Conclusion: i think the “ fellow using a “horizontal damper at the rear wheels is offering the best and certainly simmplest solution, and at minimal cost too. He also found that he needed an engine damper for full 100% wet weather solution. However, the layout of the ve cOMMODORE,/G8 is so far, too difficult to mount a similar damper. It needs innovative brackets to fit whereas hopnot solution is for a Chrysler 300 type car, similar rear IRS but different enough to prohibit it on the Commodore/Pontiac G8
So there it is: use an engine damper, fabricate a diff snubber, mount dampers horizontally at each driven rear wheel if possible! Using poly bushes is dangerous as they can only be used when the geometry allows the particular arm to rotate precisely {rotate over each connecting bolt}. This is not the case when you have semi trailing arm setups, like Camaro, C ommodore and Bmw or similar designs. I found poly suppliers simply do not understand how polyurethane works compared to vulcanised original rubber bushes. The rebound frequency of poly is considerably higher than rubber. Poly also does not like being forced to squish at an angle to the bolt in the joint, and will form an oval shaped hole after a few months in service and can resault in considerable dangerous movement in an arm or link.
After extensive testing, i am sticking with my thought that tramp is a system resonance caused by stored system energy being released through the wheel when wheelspin occurs, that’s energy being again stored and then release resulting in broken slip/grip wheelspin as the car moves along the road. If full wheelspin occurs, this bypasses the tramp mode, but of course forward progress is minimal.
Perhaps I should join the white flag crew and use electronics to stop wheelspin. I look forward to reading your comments. Please foregive typos, hard going on my iphone at night. Cheers
