Rear Suspension Video
 

I am looking for advice for the rear suspension on the SS/L Mustang. Here is a run from Atco this past weekend. Changed springs three times 110lb, 130lb, and in this video 150lb. The front end was not moving much due to coil over setup with not enough shock travel. The car tends to drive the right rear tire down and the left front tire up no matter where the shocks are set. The shocks in this run were set 12 clicks on the rebound and 7 clicks on the compression. When I try the stiff compression and soft rebound the rear tires bounce like a basketball and the sixty foot is very slow. These tires are M/T 29.5/10.5stiff sidewall. Lastly the ladder bars are in the bottom holes for maximum weight transfer. Thanks!

Re: Rear Suspension Video
 

The spring just supports the weight of the car, the shock controls the movement. The spring should compress about 25% of the spring height. I think the 130 & 150 spring are to much. The shock moves much less than you think. The shock will first go into a rebound/compression movement, about .25 - .40/.60 - .80 A rear shock sensor tells alot. With the stick, you need a different setup than an auto. Talk to Randy Mans at Fastshocks, he can help you out. 612-306-5387

Re: Rear Suspension Video
 

Bobby, what a great video. I do not pretend to know anything. But, I would assume that with a stiff sidewall tire it would rebound (bounce very quickly). I would assume it would be the shock adjustment and the clutch setting on the hit vs the importance of the weight of the springs. By the way what camera did you use, it is very clear. I like the car. Thanks again.

Robert

Re: Rear Suspension Video
 

It was hard to tell and correct me if I'm wrong, it looked like the spring was not compressing much if at all.

Re: Rear Suspension Video
 

Thanks Robert, it is a Go Pro 960 that I purchased back in 2011. My uncle and I made a mount for under the car. I just realized that the video looks kind of weird because YouTube has a smoothness enhancement on. That's why the camera is doing weird zooms and what not. I just turned it off and hopefully soon it will be back to original. Also, Thanks for your input Dyno.

Re: Rear Suspension Video
 

" Lastly the ladder bars are in the bottom holes for maximum weight transfer. Thanks!"



I disagree with this statement. As I've never had a car like yours, a 4-speed with a little engine, all I can do is offer an opinion. I'm guessing you only have low 400HP and torque is as bad as it gets because it's a little 289 with low compression and all. That being said, I would think I would place the ladder bars further UP and then make my shock adjustments using the lighter 110# springs. I don't think a car like yours has enough "giddy up and go" to warrant having the IC way up front and attempting to carry the car. I'd hit the slicks harder with the ladder bar moved up. Then you might see some changes with shock adjustments. And of course, I'd have the shocks dyno'd to make sure all is well with the shocks. No matter how new or old they are.

Re: Rear Suspension Video
 

Ahh ok good point Jeff, thanks. That makes sense. Why then would you choose the 110 springs as opposed to the other 2?

Re: Rear Suspension Video
 

It is very hard to tell what is going on at full speed. You can take the video and slow it down using Microsoft Live Movie Maker, its part of the Windows Essentials package. You can slow it down to 1/8 speed and do a better analysis of what is going on, Cool Video !!

Re: Rear Suspension Video
 

springs look as if they are "almost" totally stationary little to no compression or expansion at all on the initial launch leads me to believe they are too stiff--- look at the video if you can put it in "slow motion" things hapenning to fast on the normal speed hard to see whats really going on in 1-2 seconds--I would put ladder bars all the way up to top hole to preload the chassis just to see if it likes it--- if it does then tweak the shocks a bit a little at a time to see what happens if it likes that then go to changing the springs go from the softest or the firmest all the way to the extreme opposite--- I would only do maybe 100-150 foot long plus squirts to see your results--- dont waste time doing anything longer you just want to get the car to launch who cares what it does in the 1/8 or 1/4 work on that later--- just remember for every .01 in the 60 foot usually means .02 in the 1/4---you are not looking for subtle differences now you want radical changes then you can fine tune what ever it is you are trying to do by changing shocks, locating points or spring rates and even rear tire pressure to---- you are not gonna solve this in 2 minutes unless you get lucky and hit the right combo right away----my 2 cents ---FED387

Re: Rear Suspension Video
 

Primarily be because your car is so lite. Springs just hold the car up, if not enough, pre-load them which works better anyways. I bought 110# springs for my AMX as I thought I was going SS. And that would have been 3160#'s with driver and well over 600 HP with a stick.
You may want even lighter than 110# springs.

Re: Rear Suspension Video
 

What causes everything to compress on the right rear and not on the left rear? We took out all preload for this weekend and that still didn't prevent it.

Re: Rear Suspension Video
 

All RWD cars with a solid rear axle, as viewed from the rear, the engine twists clockwise and the rear end twists counter clockwise.
A drag car need to keep the left & right drive tire planted equally. Whether by pre-load on a 3 or 4 link, traction bars, air bags, anti-roll bars or springs and shocks is up to you. But "balanced" L/R adjustments can't work due to the nature of the rear axle twist on launch.

Re: Rear Suspension Video
 

coupla things come to mind here--ya might want to switch springs and or shocks side to side not both at the same time but first say the springs see if it does it then the shocks try the same thing---- have you scaled the car to see how much each corner weighs?? might not weigh the same side to side---looking at the pic of the rearend it appears that the left is planting harder than the left=== but when you look at the 2 pix from the right front it appears that the right is planting more than the left---does the car go straight when it leaves ??

Re: Rear Suspension Video
 

I meant to say the left spring is extended more than the right not planting the tire as hard--FED387

Re: Rear Suspension Video
 

Having the right side squat and the other rise is commonly seen on Chevelles with a factory four link. This is because the instant center is too low.

In your case, raising the front mount of the ladder bar will bring the instant center up and back. After doing this, you may find that shock adjustments are a lot more effective.

Re: Rear Suspension Video
 

Can't thank you guys enough for the input! To answer a previous question, yes we have had the car scaled numerous times but it does not seem to do much other than get the car to leave straight. It's kind of difficult to get equal weights on both tires and the ride heights to be similar side to side. It doesn't help with this squat problem nor improve the weight transfer issue but it looks like everyone agrees that I need to raise the ladder bar to move the IC.

Might be SS/LA soon!! This car is worse than a woman! :confused:

Re: Rear Suspension Video
 

I believe it's been mentioned before but if you've got room (and rules permit), an anti-roll bar would make a nice addition.

Re: Rear Suspension Video
 

Well, you would be a woman if you put an automatic in it!
And all the principal of suspension tune would apply with a more feminine transmission.
Have you ever looked under Kips Mustang? Very interesting ladder bar arrangement.

Re: Rear Suspension Video
 

*Like* ^^^^

Re: Rear Suspension Video
 

You definitely need an Anti Roll bar. This will eliminate the twist and keep one side from doing something different than the other.

Re: Rear Suspension Video
 

Beat me to it. I agree. At one time I thought these were a band aid. Now I think they should be on most cars. Get one that's heavy enough to do the job.

Also, IMO 150# springs are way too heavy. Much like a six cylinder type spring on the front stores energy and helps the front suspension to separate and transfer weight, a light spring on the rear wound up a few inches also stores energy and helps get the rear out and applied at the hit. I prefer to use a light spring to accomplish that and use the shock to control the speed. 110s may be a bit too light once you raise the front of the bars, which I agree should be tried. Tightening the compression should help keep the rear out and applied and reduce the basketball effect of the tires. A rough racetrack may limit how tight you can run that knob. Also, I'm not sure a stiff sidewall tire is what you want. The stiffer sidewalls tend to want to bounce the rear back up into the car more so than other style tires.

Re: Rear Suspension Video
 

as an old retired Superstock racer that ran a 283 I was wondering how you were setting your pre-load on your car. I set mine by having the car as level as possible and then adding enough weight in the front seat to equate to my own weight, then set the pre-load. I went through a few adjustments when I first got the car but after I got it set I didn't have to touch it, and the cars 60' was in the very low 1.40's.

Re: Rear Suspension Video
 

You might not want equal weight on the left and right rear tires. My friends ladder bar car required 30 to 50 more pounds on the right rear to leave straight.

Re: Rear Suspension Video
 

You can also straighten out a car the leaves "slightly" left or right (typically it will be right) as simple as adding another 1/2 # of air to the slick. If it's pulling right, add air to the right slick.