Another 944 Spring Rate Recommendation Needed
04-14-2004, 12:18 PM
#16
Race Director
Torsion bar rate is linear.
Honestly I have never liked having both t-bars and coilovers. Due to the issues you just mentioned.
I would do this.
Start with the 140 lber's. Set them to engage right when the tbars stiffen. In this way you should get both springs working at the same time.
Geo...
T-bars and Coilover work in parallell there you may add the spring rates
Two springs on a single shock work in series therefore the total spring rate is 1/ (1/A+1/B).
Remember that when combining T-bars and coilovers there is no place where the T-bar is NOT effective. If you preload the coil spring you are reverse loading the torsion bar. So is probaby best from a theory standpoint to only lightly load the coilspring so that it tight rather than loose (ie 10 lbs preload). That way under the car's weight the load is being taken by both the t-bars and the coilovers. Reverse loading probably faitiuges the t-bars much faster.
Honestly I have never liked having both t-bars and coilovers. Due to the issues you just mentioned.
I would do this.
Start with the 140 lber's. Set them to engage right when the tbars stiffen. In this way you should get both springs working at the same time.
Geo...
T-bars and Coilover work in parallell there you may add the spring rates
Two springs on a single shock work in series therefore the total spring rate is 1/ (1/A+1/B).
Remember that when combining T-bars and coilovers there is no place where the T-bar is NOT effective. If you preload the coil spring you are reverse loading the torsion bar. So is probaby best from a theory standpoint to only lightly load the coilspring so that it tight rather than loose (ie 10 lbs preload). That way under the car's weight the load is being taken by both the t-bars and the coilovers. Reverse loading probably faitiuges the t-bars much faster.
04-14-2004, 04:04 PM
#17
Race Director
Originally posted by M758
Geo...
T-bars and Coilover work in parallell there you may add the spring rates
Geo...
T-bars and Coilover work in parallell there you may add the spring rates
Thanks for the clarification.
04-14-2004, 05:03 PM
#18
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I think its a waste to buy coilovers and then set them level w/ the torsion bars. Kinda eliminates the reason why a lot of people (well maybe just me) buy them (10lbs doesn't provide much room to maneuver).
You are not necessarily reverse loading a torsion bar by setting ride height with the coilovers, you are simply relying less on the torsion bars to support the full weight of the rear end than you would otherwise. They (the torsion bars) would have to be larger than factory sizes to be in reverse load at 1,2,3, even 4 inches from where they would be compressed w/out the coilovers. _Doesn't engage_ was poor wording on my part, static ride height w/out coilovers would have been more accurate.
I don't think you would fatigue torsion bars in reverse load unless you are talking about something pertaining to the splines - seems to me that they have the same spring force in either direction (and wouldn't that say that leaving your car on jack stands fatigues them also??). Actually, I don't see how you have them in reverse load/tension/whatever until you have the rear suspension at full droop. Doesn't seem to me that they pass through a neutral state until you get all of the weight off of them. Now you could be at full droop and have preload on the coils but I think that's excessive or if its happening in that 2 to 3 inch range on factory t-bars, they aren't linear to begin with.
You are not necessarily reverse loading a torsion bar by setting ride height with the coilovers, you are simply relying less on the torsion bars to support the full weight of the rear end than you would otherwise. They (the torsion bars) would have to be larger than factory sizes to be in reverse load at 1,2,3, even 4 inches from where they would be compressed w/out the coilovers. _Doesn't engage_ was poor wording on my part, static ride height w/out coilovers would have been more accurate.
I don't think you would fatigue torsion bars in reverse load unless you are talking about something pertaining to the splines - seems to me that they have the same spring force in either direction (and wouldn't that say that leaving your car on jack stands fatigues them also??). Actually, I don't see how you have them in reverse load/tension/whatever until you have the rear suspension at full droop. Doesn't seem to me that they pass through a neutral state until you get all of the weight off of them. Now you could be at full droop and have preload on the coils but I think that's excessive or if its happening in that 2 to 3 inch range on factory t-bars, they aren't linear to begin with.
04-14-2004, 05:24 PM
#19
Race Director
Adam I guess we meant different things.
The torsion bar is "free" is has zero twist to it. Free could mean out of the car. When the bar in the car with the weight of the car on it it will twist some amount. This is obvious. When the rear is in the air the suspension will droop to a point. The shock can limit this droop if so the load going through the shock is the weight of the suspesion and any force that torsion bar is exerting to get back to the free state.
I also may be possible that the shocks do not limit the droop. I believe this is the case in lowered cars with stiffer bars. Anyway the suspesion will still drop, but if for example it weight in at 50 lbs and the effective torsion bar were rate at the wheel were 100lbs/in the torsion bar would reverse load or droop by 1/2".
Now add in a coilspring on the shock. Lets say it has 100 lbs in effective rate. If at full droop and no shock loading an not preload in the coil it like its not even there. If however the coil spring is aleady compressed by 1/2" then there is 50 lbs of added downward force on the rear suspension. Therefore it will droop 1" lower than before with the same 50lbs weight. So therefore the torsion bar will be subjected added reverse loading of 50lbs more for a total of 100lbs.
Of course if the shock limits downward droop travel then it will take the load and NOT the torsion bar. This will apply no mater how much preload is install in the coil over.
The torsion bar is "free" is has zero twist to it. Free could mean out of the car. When the bar in the car with the weight of the car on it it will twist some amount. This is obvious. When the rear is in the air the suspension will droop to a point. The shock can limit this droop if so the load going through the shock is the weight of the suspesion and any force that torsion bar is exerting to get back to the free state.
I also may be possible that the shocks do not limit the droop. I believe this is the case in lowered cars with stiffer bars. Anyway the suspesion will still drop, but if for example it weight in at 50 lbs and the effective torsion bar were rate at the wheel were 100lbs/in the torsion bar would reverse load or droop by 1/2".
Now add in a coilspring on the shock. Lets say it has 100 lbs in effective rate. If at full droop and no shock loading an not preload in the coil it like its not even there. If however the coil spring is aleady compressed by 1/2" then there is 50 lbs of added downward force on the rear suspension. Therefore it will droop 1" lower than before with the same 50lbs weight. So therefore the torsion bar will be subjected added reverse loading of 50lbs more for a total of 100lbs.
Of course if the shock limits downward droop travel then it will take the load and NOT the torsion bar. This will apply no mater how much preload is install in the coil over.
