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Anybody ever measure the weights of their car's rear suspension components, specifically the trailing arm, hub, rotor, spring plate, shock, and spring? It doesn't have to be dead accurate, but I want to confirm that I'm running close to the correct spring rate, assuming a spring frequency of 135 cycles/minute. I'm running coilovers, with the torsion bars removed, with 800 lb/in springs. Assuming a motion ratio of 0.62, this gives a wheel rate of 307.5 lb/in, which seems pretty reasonable for a track car with no aero. I realize I'd have to divide by two the weights of the compennts that are attached at one end to the chassis (so the trailing arm, spring plate, shock, and spring), but I bet the unsprung weight is still over 100 lb, including the wheel/tire, or course. Again, I'm not looking for accuracy down to the ounce, just a sanity check. Thanks.
without t-bars, couldnt you in theory jack up the car, disconnect the lower shock eye, and let the wheel 'relax' onto your trusty bathroom scale on blocks? that should give you the trailing arm/brake/hub/wheel weight (since the rest of the car is on stands/other tires, and the trailing arm is free to pivot on its bolt/bushing)
Yes, that is an option, but with my coilover setup, the shock eye bolt is torqued to the trailing arm at 150 lb-ft, so I don't like to remove and re-install it any more often than necessary. The reason I'd like to know the unsprung weight is that I bought one of Bruce Karger's last geometry correcting control arm attachment bars, and since I have to remove the springs and shocks to do that, I'd like to know ahead of time if I should swap out the springs for something different. I view the installation of Bruce's bar as a component of a complete package, including installation of longer ball joint pins, bump steer correcting tie rod connectors, softer front springs (I'm currently running 700 lb/in, but 150 cycles/min works out to 500 lb/in), and I'd like to do everything at once, so I don't want to find out I really should be running 750 lb springs in back, and have to delay everything waiting for the springs to arrive.
Thanks - no rush. Yes, I want to see what spring rates are recommended by the formula that correlates suspension frequency to wheel rate. Using assumptions for the unspung weight, I come up with about 775 lb/in for a suspension frequency of 135 cycles/min, which is close to the 800 lb/in springs I'm running, but I think my assumption for unspring weight was low (I think I used 70 lb, and it may be closer to 100 lb.). This is all splitting hairs considering I don't, and never will, race this car; it's just for fun. But since I'm going to have the rear suspension apart installing Bruce's bar, I just want to make sure the springs I'm running aren't too far off.
Well, coincidental or not, and track peers already think I'm way too soft on the SP2 car (separate issue but record speaks for itself), but while switching to the GAZ on the 968, we were going to reconfigure the springs for that car based on a formula of weight differential between the 2 cars.....2600 w/driver vs 2900.
Using what is successful on the 944 x 1.115 (weight factor difference) to quick determine rates for the 968 and they come in at 450F and 750Rr.
Anybody ever measure the weights of their car's rear suspension components, specifically the trailing arm, hub, rotor, spring plate, shock, and spring? It doesn't have to be dead accurate, but I want to confirm that I'm running close to the correct spring rate, assuming a spring frequency of 135 cycles/minute. I'm running coilovers, with the torsion bars removed, with 800 lb/in springs. Assuming a motion ratio of 0.62, this gives a wheel rate of 307.5 lb/in, which seems pretty reasonable for a track car with no aero. I realize I'd have to divide by two the weights of the compennts that are attached at one end to the chassis (so the trailing arm, spring plate, shock, and spring), but I bet the unsprung weight is still over 100 lb, including the wheel/tire, or course. Again, I'm not looking for accuracy down to the ounce, just a sanity check. Thanks.
Ok this is very twilight zone.....I was just thinking about this last night while trying to fall asleep thinking about weighing all the parts......I have everything apart right now in the basement and garage. I will weigh everything tonight an post it...digital weigh scale at home.
If I have not posted this evening someone PM me to remind me.
Wow, what a coincidence. Looking forward to your component weights.
T,
The spring rates you came up with are remarkably close to what I've calculated, My car, with me in it, weights about 3040 lbs (depressingly heavy, after all the work I've done to try to lighten it, but it is still streetable, I keep telling myself...). I come up with about 500 lb/in in front, and between 750 and 800 in the back. I'm currently running 700s in the front, simply to compensate for the subterranean roll center, which I will correct with longer ball joint pins at the same time as I install Bruce Karger's torsion tube replacement bar., This will allow me to move my front spring rates closer to the theoretically optimal.
Wow, what a coincidence. Looking forward to your component weights.
T,
The spring rates you came up with are remarkably close to what I've calculated, My car, with me in it, weights about 3040 lbs (depressingly heavy, after all the work I've done to try to lighten it, but it is still streetable, I keep telling myself...). I come up with about 500 lb/in in front, and between 750 and 800 in the back. I'm currently running 700s in the front, simply to compensate for the subterranean roll center, which I will correct with longer ball joint pins at the same time as I install Bruce Karger's torsion tube replacement bar., This will allow me to move my front spring rates closer to the theoretically optimal.
Well, I can share this with you as well; on the similarly weighted car, we ran 475/800 on the car's first outing and it oversteered big time.
The event started on a Friday and I wasn't able to make it that day but I talked to my son several times throughout the day.
Saturday morning we adjusted rear bar to the stop and it made the car driveable but still oversteered.
It was only his driving that kept the car close to P1 and able to make one pass and a couple of other attempts.
Hoping this shift puts a neutral handling with bars neutral as well.
We will see. Testing on same track as race will be in a couple weeks.
Wow, what a coincidence. Looking forward to your component weights.
T,
The spring rates you came up with are remarkably close to what I've calculated, My car, with me in it, weights about 3040 lbs (depressingly heavy, after all the work I've done to try to lighten it, but it is still streetable, I keep telling myself...). I come up with about 500 lb/in in front, and between 750 and 800 in the back. I'm currently running 700s in the front, simply to compensate for the subterranean roll center, which I will correct with longer ball joint pins at the same time as I install Bruce Karger's torsion tube replacement bar., This will allow me to move my front spring rates closer to the theoretically optimal.
Had to bring the parts to work and will weight today. Scale at home not accurate enough. Will post weights and pics of pieces. I am short the rear calipers, rotors and wheel bearings.
edit :
Weights are done. Will post pics when I get home
In case anyone cant read the left rear trailing arm weight it is 14lbs
Rear torsion bar carrier Torsion bar carrier weight Spring Plates Spring plate weights Rear axle components Rear axle component weights Torsion tube ends with bushings Weight for ends Left rear Trailing Arm Weight for left arm Right rear Trailing Arm Weight for right arm
Thanks very much for taking the time to weigh your car's rear suspension parts. The unsprung weight comes out to less than I expected, as it consists of half the weight of the trailing arm, half the weight of the spring plate, the weight of the hubs, plus half the weight of the spring, shock, and their mounting hardware, plus the weight of the wheel bearing, the rotor, caliper, and wheel/tire. I can measure the weights of the caliper, rotor, and wheel next time I rotate my tires, and I have a wheel bearing off the car. But it appears that the unsprung weight will actually be under 100 pounds. I'll let everyone know the total when I have it.
I forgot the torsion bars, however, I can weigh them at home as they are quite heavy and not stock ones. Pics will identify the make of torsion bars...they are the common aftermarket ones but I will have to dig them out from????somewhere in my house.
I forgot the torsion bars, however, I can weigh them at home as they are quite heavy and not stock ones. Pics will identify the make of torsion bars...they are the common aftermarket ones but I will have to dig them out from????somewhere in my house.
Iirc torsion bars do not contribute to unsprung weight whatsoever and their location, very low on the vehicle, only contribute a negligible amount to roll and pitch. They may be heavy but they are optimally placed compared to coil overs.
Iirc torsion bars do not contribute to unsprung weight whatsoever and their location, very low on the vehicle, only contribute a negligible amount to roll and pitch. They may be heavy but they are optimally placed compared to coil overs.
I have a set of brand new koni rear shocks I can add that weight. Forgot I had them. I will throw on the torsion bar weight for fun
12-31-2018, 04:50 PM
944 rear suspension unsprung weight?
