Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497095
05/17/18 08:55 AM
05/17/18 08:55 AM
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Joined: Jan 2005
Posts: 4,243 Charlotte, North Carolina
sgcuda
master
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master
Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
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Ladder bars tend to add stiffness to the suspension and keep the car from rotating the front end. Maybe it's just because they also act as an anti roll bar, but I have set up multiple cars where the car seems to be less active on launch, even though it bites harder. 200 sounds about right for the weight, but if you can swing it, it's never a bad idea to experiment with +/- pressure springs. Just like playing with shock settings. No reason to stagger spring rates. If it's necessary, then something is wrong in the car or suspension. I had problems with tire spin on shifts. It ends up my tires went away. Would still launch fine, but I have videos of tire smoke on gear changes.
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Re: coil over spring rates with ladder bars
[Re: dvw]
#2497124
05/17/18 10:49 AM
05/17/18 10:49 AM
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Joined: Feb 2017
Posts: 566 Texas
RustyM
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mopar
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OP
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DVW: Would you mind sharing a little more data on car? HP/TQ 727? Stall?
This car is 675 hp at flywheel 511 stroker. 5400 stall 727 Rollerized- build, bolt in sprag etc Race only car.
only 60 footing 146-148 weight transfer is basically non-existent 90/10 front shocks/travel limiters.
Its my opinion the 200 lbs are just too tight for the car and thats why there isn't any rear travel to help plant the car i don't think the shocks get a chance to do blooming thing. Ladder bars were set in center hole ( neutral ) I would like to see some compression and the shock controlling rebound long enough to carry the car on the tire so it stays planted. just my thoughts. Am i nuts?
Last edited by RustyM; 05/17/18 10:49 AM.
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497194
05/17/18 01:50 PM
05/17/18 01:50 PM
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Joined: Mar 2006
Posts: 9,861 MI, usa
dvw
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master
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MI, usa
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DVW: Would you mind sharing a little more data on car? HP/TQ 727? Stall?
Never been on a dyno. Best ever 9.00@150@3340lbs.572, guessing 900+, 727, 6100 flash. A 200 lb in my opinion is way to stiff. Rear will have very little help with rear seperation as the springs are barely compressed at ride height. Be aware power affects 60 ft. My bet is your combo has at least .05-.10 left in 60ft. Once the rear is scienced out chances are the 90/10 will be too loose. Just had my front Afco doubles tightened about 50% Doug
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497196
05/17/18 01:59 PM
05/17/18 01:59 PM
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Joined: Aug 2003
Posts: 43,237 Bend,OR USA
Cab_Burge
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I Win
Joined: Aug 2003
Posts: 43,237
Bend,OR USA
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What size torsion bars and what ride height in the front now? How much front end travel before the suspension limiters work? I would lower the torsion bars to the bottom hole and see how much that helps your sixty foot times My old ladder bar coil over Duster(3450Lbs. with me in it) started out with 175 lbs. springs, I switched to a set 150 and that helped, I should have tried a set of 130 Lbs. but I didn't On your deal not knowing on how much weight is on the front and rear I would probably try a set of 140 Lbs. springs next
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497220
05/17/18 02:43 PM
05/17/18 02:43 PM
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Joined: Dec 2005
Posts: 11,621 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,621
Fulton County, PA
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I'm going to assume 3400# with maybe 54% on the nose. That's about 1550 on the rear.
What shock/spring combination is on this? If it's a typical 17" extended length shock, like a 3850 AFCO, or S5206 or S5006 Strange with a 12" spring, a 200# spring has to be holding that shock at full or almost full extended length. It's can't separate without topping the shock. Plus it has to about as stiff as a solid suspension.
So, the shock installed length needs to be correct, about 13 3/4" or so. I would try a 150 if my assumptions are correct. This spring will need to be compressed a bit to hold the shock at the correct length @ ride height. Then a good shock can be used to control the separation at the hit. With that horsepower level, it won't need a lot of separation. You don't want to crush the tire.
90/10s are probably not the best choice for this car. A good adjustable shock, so you can control separation, with a bit smaller than stock torsion bar is where I would start.
Again, this is all based on assumption of what's under that car.
Last edited by CMcAllister; 05/17/18 02:47 PM.
If the results don't match the theory, change the theory.
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497250
05/17/18 04:41 PM
05/17/18 04:41 PM
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Joined: Feb 2017
Posts: 566 Texas
RustyM
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OP
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Cm: Thanks. Stock front suspension other than wilwood drag brakes I would like to see lighter torsion bars and two way adjustable shocks as well.
ladder bars and coil overs in rear- no leaf springs. 8.75 braced, 4.30 gear/spool
Car went 9.80"s on the bottle with cal-tracs - no issues when stock stroked, stroked it and its torn up everything from tranny to driveshafts to rear end housing - made a horseshoe out of it.
Im trying to help him get car sorted as he had ladder bars, coil over installed.
we did an chassis dyno at end of season last year and then took engine to engine dyno- huge chassis loss showed up. New converter based on dyno info , chassis was twisted- put it on a chassis table and had that straightened out, stiffened chassis.
went to test and tune and, car doesn't want to hook, i shot video of the pulls he got before throwing the shaft out - u-joint clamp failure.
rear of chassis has zero movement , front try's to come up but, tire unloads , cant hold separation /rotation. My guess is you are correct- too much spring, shock cannot work. rear of car didn't move up or down- locked out like rear is welded to chassis. Tire bits, lets go, bites, lets go- porpoising the car.
we just had through tranny- it was fine, i then found the tail-shaft bushing was bad, had that changed , sent converter to be checked and should have it back this week and we can get 4 corner weights then.
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2497590
05/18/18 04:38 PM
05/18/18 04:38 PM
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Joined: Dec 2005
Posts: 11,621 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,621
Fulton County, PA
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Correct shock installed length at ride height and good shocks on a ladder bar car with some power are critical. Without those, nothing else matters.
If the results don't match the theory, change the theory.
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2499338
05/23/18 02:38 AM
05/23/18 02:38 AM
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Joined: Aug 2003
Posts: 43,237 Bend,OR USA
Cab_Burge
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I Win
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Last edited by Cab_Burge; 05/23/18 02:46 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: coil over spring rates with ladder bars
[Re: RustyM]
#2499529
05/23/18 03:39 PM
05/23/18 03:39 PM
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Joined: Jan 2003
Posts: 3,505 DFW
mr_340
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DFW
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I never saw how much shock/spring travel you have. More travel should lend to a lower rate spring. For my $.01 (can't afford $.02), here's my calculations.
LR- 737 RR- 845
Total rear weight is 1582 pounds. As stated above, deduct the unsprung weight of the rear axle, wheels and tires, etc. I subtracted 250 pounds here and ended up with 1332 pounds rear sprung weight. Divide that by two (two tires) and I get 666 pounds to be supported per side.
If you have seven inches of total travel, maybe you would want to compress the spring four inches per Cab's 2/3 rule-of-thumb. 666 pounds/4 inches = 166.5 pounds/inch spring rate.
If you have ten inches of total travel, maybe you would want to compress the spring six inches. 666 pounds/6 inches = 111 pounds/inch spring rate.
Q.E.D.
That's my theory anyway. Check some of the chassis books and see what they say. You may have to test a few spring rates and shock settings to find a good setup? Hopefully this can get you in the ballpark.
Floyd Lippencott IV
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