gesto

I’ve been doing some reading on drag suspension setups. The sticky in the Drag Racing Tech forum is very good but how is that translated into the proper process to tune an f body suspension at the track? Emphasis is not on changing parts but on tuning what I have, although I’m always open to suggestions because I don’t know what I don’t know.

My rear suspension is stock except for adjustable lca’s and relocation brackets, adjustable panhard bar, Viking double-adjustable coilover shocks (springs are 14x175) and 16x50x255 drag radials. Front is stock with sway bar delete and Vikings. I don’t have traction issues at my current power level but I want efficiency and I want to know how to do this when I add power and stall speed. You can see my thread in the Drag Racing Tech forum for a complete diary of my car and runs.

I can think of five basic drag suspension adjustments I can make at the track: 1) ride height via the shocks; 2) percentage of rise via the lca brackets; 3) rear shock valving; 4) front shock valving; and 5) tire pressure. Is this the correct sequence? Are there other suspension specific adjustments that should be added, such as torque arm, phb, drag bar, etc.? If so, where should they go in the sequence?

First, I’m planning on setting ride height so the middle of each fender is right at the top of each tire just enough so I can’t get my fingers between the tire and the fender. Not slammed but lower than stock. By doing this I think both center of gravity (good) and percentage of rise (might be good or bad) are lowered. Is this correct?

Once ride height is in the ballpark I think the lca brackets should be adjusted. They are currently set at the lowest setting which I think increases percentage of rise which pushes more vehicle weight on to the rear tires via leverage. I can’t see a benefit from changing from the lowest setting. Is this correct?

Next is shock valving. I think you want the stiffest settings that hook, so 16c/16r all around to start. If it hooks with 25 – 30 lbs of rear tire pressure, it’s good to go. Energy will be used to propel the car forward instead of up and down. Is that correct or do you want some weight transfer to allow the engine to rev a little quicker?

If it doesn’t hook I get a little confused on what to adjust first. What’s the order of front and rear compression and rebound and rear tire pressure?

I’m thinking you start by lowering rear compression a couple clicks for a little squat. But how much rebound? I know you don’t want it to squat any longer than necessary to hook but you don’t want dangerous bouncing or unloading of the tires a few feet after launch. Would I start at 14c/0r? This would allow a little squat and quick rebound. Then increase rebound as needed.

Do you then change the front shocks to 16c/14r? Seems together the front would come up a little and the rear would squat a little. Then the front would come down quickly and the rear would come back up quickly, which you want until the point of bounce and tire unloading.

Then you adjust tire pressure down a few pounds and repeat until you hook with the maximum amount of rear compression, front rebound and tire pressure. Is this the right process or do you adjust rear tire pressure last?

01ssreda4

iTrader: (96)

Log runs and all settings in a detailed easy to reference format, the put in the seat time. If you hook now, it will be hard to learn, so take some hook away, try on unprepped road or get less sticky tires then get it to hook. If you can hook on an unprepped road you will damn sure hook at a track.

jhshnh

When I put in my Vikings they had recommended settings for different power levels for drag racing. I set mine with what they said, then fine tuned it from there. The end result is the car pulls 1.58 60 fts with just 321 rwhp.

I set my et streets at 18 and made sure they were there before each run.

When fine tuning a suspension, make adjustments on one thing at a time, and log the run in a notebook like what's recommended above. So don't make adjustments on everything... set a baseline setup and then fine tune from there. It takes time and many runs.

Corvett z07

iTrader: (2)

X2

It looks like you know where you have to adjust and how to adjust for tuning a car to launch. I don't think there is a set of adjustments that you do first, then next, then last. I'd imagine you'd set a good stance first that you like, put suspension in line after that (adj control arms), and then lots and lots of launches to tune the weight transfer, tire psi, etc to what gives the best 60' launches. Only change one variable at a time so you know how that variable changed the outcome, then you'll be better prepared on how to tune down the road when you get more horsepower or whatnot. Slowmo videos of your launch could prove useful of where you might need to tune your shocks to as well. A lot of smartphones now have that feature, if you have it you might as well use it to your advantage at the track

gesto

Thanks guys! 01ssredaf, it was one of your posts that got me thinking that maybe I don't want so much rear squat on an auto car. I am going to get a dedicated computer and record everything in excel, store videos and also buy HP tuners. I also need to have someone video my launches up close.

The suspension pros I'm reading focus beyond hooking to suspension efficiency and how you can tune a suspension to reduce ET's. That's what I'm now trying to do.

Viking recommends high compression/low rebound for the fronts and low compression/mid rebound for the rears if you want weight transfer. That's how I currently have mine set with tire pressure at 20 lbs and the car is too bouncy.

I am going to take your collective advice and make one small adjustment at a time and log and hopefully get video.

BMR Sales2

iTrader: (40)

whew, a lot to go over here, so I will cover some basics;

You are correct with the correlation of ride height to lower control arm angle. You want a slightly positive (going up towards the body) angle on the lower control arms to provide lift and keep the tires planted.
Another factor to this is torque arm angle and mounting height. The lower control arm angle and mounting position of the torque arm together figure your Instant Center.

Under ideal conditions, a car on a radial tire will see no squat in the rear. I usually like to get the car close to staying neutral with control arm and torque arm adjustment, then do the fine tuning with shock valving. You said you have a 175 rear spring rate, which is a little higher than I like to see on a street/strip car, but it is manageable. This will just mean you will need less compression on the rear shock valving. What spring rate do you have on the front? On a low powered car you will want a soft rate and loose extension rate to promote transfer. But if you go too far, it will result in the car coming up too fast and unloading the rear.

The Best bet would be to get videos of the car launching. I can tell a lot about what adjustments need to be made just from seeing the car leave. Not only for traction, but efficiency. Also as mentioned above, keep careful log on shock settings, tire pressure etc that way you have reference to work with

01ssreda4

iTrader: (96)

At my power level, cutting mid 1.4s, the car does best with full loose on the front. The quicker it comes up for me the better, if I slow it at all it makes finding traction harder. So my front setting stays on c15r0. I generally focus on tire pressure and rear shock adjustment. I havent had a ton of passes to figure that out yet but it will come in time. I have my arms at the lowest hole and the ta at the lowest hole and my back end seems to stay neutral so I leave them where they are.

SoFla01SSLookinstok

Do you still think the front torque arm "height" mounting point is adjusting something with your IC/AS?

BMR Sales2

iTrader: (40)

That is exactly what that adjustment does

gesto

Eric, thanks for taking time to respond. Lowering ride height reduces center of gravity which is good but won't it also lower percentage of rise? Higher PR puts more leverage on the rear tires. With lca in the lowest position the only way I can adjust PR is by ride height????? Is there an ideal range of PR or lca angle? This is overkill but now I'm curious.

I plan on staying stock t/a until I get a 9" or S60 rear because I hear an aftermarket drag t/a will murder my 10 bolt. So I can only adjust instant center through the lca, even if I knew what range of IC I should be in. Again, overkill.

I think I'm going to switch to a 12x150 rear spring set up for now. Current ride height gives me at least 2 - 3 inches between the top of the tire and the fenders. Any lower and the springs flop around when the car is jacked up and the suspension hangs. I don't like the idea of having to make sure the spring sets right every time I have to jack the rear up.

Fronts are 300 lbs. I will try to get some video if/when I get back to the track in January. Last Friday was my first trip with this rear set up and I don't have any video.

gesto

01ssreda4, I read in one of your posts that your rears were set at something like 12c/8r, which is what I thought would be a starting range for an a4 car -- fronts loose and rear stiff.

BMR Sales2

iTrader: (40)

Correct. Changing ride height completely changes all of your calculations. There isn't nearly as much resources and information avaliable for torque arm cars as there is a 4 link, but they work on similar principles. Finding the instant center is a bit of a different configuration but the calcualtion of anti-squat percentage versus the anti-squat line is the same concept. Here are about the best diagrams I have been able to find relating to this

gesto

Thanks!

01ssreda4

iTrader: (96)

They were, I keep a pen and paper in the driver door with the current settings. I was at the track with less then stellar prep and those settings werent working perfect so I started adjusting. Cant remember what I ended up at at the end of the night.

jhshnh

This maybe nerding out, but I keep a logbook that I record shock settings, tire psi, da, etc. after every run. That way I can make adjustments and look at what I've already tried.

01ssreda4

iTrader: (96)

Thats what I need to be doing. I'm just too lazy and dont get out as much as I should. I may change that this year coming up though.

BMR Sales2

iTrader: (40)

Not nerding out at all. That is a good practice. I have done this with several cars including my own. Many times I will make the notes right on the time slip for that run so I can see what changes made difference in each run. The last shop I worked for I actually had a spread sheet for keeping track of data from every run. Shock settings, tire pressure, launch rpm, boost at launch, ramp in rate, weather conditions etc. This gives you a record of stuff you know works, that way when you go to the track you can look back through your past logs and make adjustments based on past similar conditions