GREEN GHOST
Well-Known Member
Got it. 810 would be the 6cyl bar correct ?
Front subframe sitting on bump stop ?
- Thread starter GREEN GHOST
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Professor Fate
Push the button, Max...
Rat Bastid
Dunamis Metron
I think that .810 bar is/was a DC/MP part or maybe Firm Feel made them or someone else in the aftermarket made them.
How is that for a shotgun answer??? Lol
How do you turn? Serious question. Looks like the upper part of the tire is almost touching the fender and that's with no weight in the car.
shittyslant6
Well-Known Member
@Oldmanmopar , he is right....
Mopar Performance Torsion Bar Set
MP torsion bar, do you just not like him?
I don't want to get into any drama but methinks disagreeing on a correct post will be confusing.
jbc426
Well-Known Member
Your best bet for running the car that low is to use drop spindles, because your front suspension was not designed to have optimum geometry when that close to the bottom of it's travel. By using drop spindles, you can crank the torsion bars up to get to the factory specs.
Firm Feel will make you pretty much any torsion bar you want, but right now there is a pretty big gap in production and delivery on some items.
As far as getting the car to hook up, using a drag radial made a huge difference on my Mopars. I've found no downside with running them either. The work as good or better than any wide tire in the rain, but they are only effective in a moderately narrow temperature band. If they are too cold, they don't hook, and if they get too hot, they get greasy feeling. When they are in the sweet spot of temperature, they are actually pretty amazing and make my cars safe to drive on the street.
Firm Feel will make you pretty much any torsion bar you want, but right now there is a pretty big gap in production and delivery on some items.
As far as getting the car to hook up, using a drag radial made a huge difference on my Mopars. I've found no downside with running them either. The work as good or better than any wide tire in the rain, but they are only effective in a moderately narrow temperature band. If they are too cold, they don't hook, and if they get too hot, they get greasy feeling. When they are in the sweet spot of temperature, they are actually pretty amazing and make my cars safe to drive on the street.
This is the best guide I have for relating the ID #'s, part #'s and diameters. The rates listed in this one are calculated by the author of the chart though, and don't exactly match the rates that Mopar published officially. The difference is probably that these were calculated with a generic constant for spring steel, while Mopar actually used the exact constant based on the metallurgy of the bars. Either that or the author of this chart used a slightly different length for the LCA which is totally possible if it was measured. Again Mopar would have had the exact number.
This is a great list of the part #'s and rates, this is the Mopar published data for the rates. But of course it doesn't list the ID #'s on the bars themselves, and it's missing the .85" bar.
Here's another list, this one shows a few of the bars with ID #'s, diameters, and some of the measurements, as well as the factory paint stripe color you can find on the OE bars.
This isn’t actually true.
For radial tires the best suspension geometry occurs when the LCA is parallel to the ground. That’s when the camber gain matches the performance of radial tires the best. The original geometry and specs was designed for bias ply tires, which perform very differently.
Same for the drop spindles replicating stock geometry- not true. The control arm angles might be the same if you drop the car the full 2”, but the bump steer and roll center still change because of the different axle stub location with respect to the ball joints and tie rod ends.
This is a great list of the part #'s and rates, this is the Mopar published data for the rates. But of course it doesn't list the ID #'s on the bars themselves, and it's missing the .85" bar.
Here's another list, this one shows a few of the bars with ID #'s, diameters, and some of the measurements, as well as the factory paint stripe color you can find on the OE bars.
This isn’t actually true.
For radial tires the best suspension geometry occurs when the LCA is parallel to the ground. That’s when the camber gain matches the performance of radial tires the best. The original geometry and specs was designed for bias ply tires, which perform very differently.
Same for the drop spindles replicating stock geometry- not true. The control arm angles might be the same if you drop the car the full 2”, but the bump steer and roll center still change because of the different axle stub location with respect to the ball joints and tie rod ends.
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GREEN GHOST
Well-Known Member
Thanks !
Mic is the easiest and surest way.
Calipers are cheap and often useful!
Calipers are cheap and often useful!
Ironracer
Gearhead
Maybe pull the header and dimple it? I know it's a Pain...
Ironracer
Gearhead
[QUOTE="72bluNblu, post: 1973875384, member: 8182"
For radial tires the best suspension geometry occurs when the LCA is parallel to the ground..[/QUOTE]
Strange Question, I have a 318 car, now 340, rebuilt front end, the heads of the bolts are about 3/4", from bottom of bar, to top of TB adjuster. Bars are not level with ground. What gives?
For radial tires the best suspension geometry occurs when the LCA is parallel to the ground..[/QUOTE]
Strange Question, I have a 318 car, now 340, rebuilt front end, the heads of the bolts are about 3/4", from bottom of bar, to top of TB adjuster. Bars are not level with ground. What gives?
jbc426
Well-Known Member
This isn’t actually true. What is not true? I understand that there are different optimal settings for radial vs bias ply tires, but this person is running his suspension at the bottom of the available travel and actually on the bump stops. That is not good for several reasons, which don't involve the difference between the settings for radials versus bias ply tire settings.
Using a 2 inch drop spindle, and adjusting the torsion bars up so it is closer to the middle of the available travel, is going to allow for be much better ride quality among other benefits than lowering the suspension onto the lower bump stop.
You mention that the geometry is altered with drop spindles due to the movement of the spindle location in relation to the ball joint positioning. I learned long ago that you are very knowledgeable in regard to suspension tech, and have enjoyed many of your posts but, I'm still convinced a drop spindle is the way to go if a person wants such a dramatic lowering of the front of the vehicle. I personally don't like my cars that low, but to each his own.
Are you saying that this isn't true? Please elaborate.
Using a 2 inch drop spindle, and adjusting the torsion bars up so it is closer to the middle of the available travel, is going to allow for be much better ride quality among other benefits than lowering the suspension onto the lower bump stop.
You mention that the geometry is altered with drop spindles due to the movement of the spindle location in relation to the ball joint positioning. I learned long ago that you are very knowledgeable in regard to suspension tech, and have enjoyed many of your posts but, I'm still convinced a drop spindle is the way to go if a person wants such a dramatic lowering of the front of the vehicle. I personally don't like my cars that low, but to each his own.
Are you saying that this isn't true? Please elaborate.
First, I agree that for the OP the 2" drop spindles are probably his best option. That's entirely because of the cars use for drag racing and the OP's desire not to upgrade his torsion bars.
The part that isn't true is about the optimum geometry not being at the bottom of the available stock travel- that's exactly where it is.
If you look at the OP's pictures you can see that his LCA's are in fact very close to parallel to the ground. The control arms sitting parallel to the ground is in fact where the best camber curve for radial tires occurs. With the stock ride height the control arms sit at a decent downward angle from the frame. Under compression what that means is that the camber gain is actually positive for part of the initial compression (until the control arms hit parallel to the ground). For a bias ply tire that's ok, because bias ply tires don't do well with negative camber. But the opposite is true for radial tires. For radials to have the best handling performance the static camber setting is best being a little negative, and the camber gain should also be negative to maximize the contact patch on the outside tire, which is getting most of the cornering forces.
So then comes the suspension travel problem. Obviously sitting on the bump stops is not ideal and will not give you good performance or ride quality. But that problem can be solved. Larger torsion bars don't need as much suspension travel. Factory torsion bars had wheel rates in the 90 to 110 lb/in range. That's terrible even for a grocery getter with radial tires. By contrast, the 1.12" torsion bars I run have a 300 lb/in rate (which is much closer to modern performance cars). Clearly with a 300 lb/in wheel rate you don't need as much travel as you do with a 100 lb/in wheel rate. So the car can be lowered substantially from the factory settings. To lower that much you need to modify the bump stops to re-center the available suspension travel. The factory lower bump stops are 1-3/8" tall, the ones I run are 3/8". So you go from touching the top of the factory bump stop to having a full 1" of travel by swapping those out. Now, the factory made use of the bump stop for suspension travel, that's why the lower bump stop is triangular (it's progressive). So you can't just swap out to a 3/8" tall lower bump stop and keep the factory torsion bars, you have to upgrade the bars so you don't use the bump stop very frequently because a 3/8" tall bump stop is not progressive at all. And it turns out the factory must have planned on using that lower bump stop pretty frequently.
So you upgrade the torsion bars to something like 1.08" to 1.12" or better, replace the lower bump stop with a 3/8" tall piece, and replace the upper bump stop with something around 2 to 2-1/4" tall. The taller upper bump stop keeps pressure on the torsion bar adjusters at full extension of the suspension, because the larger bars won't always tolerate having that much down travel without unloading the adjusters. The suspension travel is re-centered around the new lowered ride height and the total amount of travel remains similar to factory (5" to 5.5" ish)
Now, about the 2" drop. So you have a 2" drop spindle, which lowers the ride height of the car 2". Then you have the bump stop deal, that only gets you 1" of clearance at the frame. But you have to do the math, because a 2" drop in ride height (or at the spindle) does not equal a 2" change at the frame. In fact, a 1" change at the part of the LCA where the bumpstop sits works out to about 1.67" of drop at the spindle. You can do the trig on the triangle created by the length of the LCA, the location of the bump stop on the LCA, and the a-b number in the FSM for the lower ball joint height compared to the pivot height (1 7/8" for most A-bodies). The drop at the frame to bumpstop is about 40% less than the drop at the spindle. So even just the smaller bump stop paired with larger torsion bars get the LCA pretty close to parallel to the ground.
There are other tricks out there, I run tubular LCA's on my Duster. The early QA1 LCA's didn't have the bump stop provision so they actually gave about a 1" increase in suspension travel because of their design. I run a bump stop on my frame horn, but the end result is my car is actually lowered about 2" from factory without the use of drop spindles.
The bottom line is that if your goal is best handling performance, you don't need or want drop spindles. You just run larger torsion bars, which you want for handling anyway, and you modify the bump stops and lower the car. And you don't have to go as big as 1.12" bars like I did because most folks probably don't want to use a full 2" drop, so you can trade some of that lowering distance for less torsion bar. Now, if you want to drag race or are lowering the car for purely cosmetic reasons, then drop spindles are fine. They do add bump steer, and they do raise your roll center. And, if you don't lower the car a full 2" you actually make those effects worse, because the angle of control arms is actually worse than stock if you don't drop the car a full 2" with those spindles.
GREEN GHOST
Well-Known Member
After reading post #37 & #38 I short circuited a few times. Then rered and learned alot. Thanks for the detail
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