I have been battling tire chatter all year on my dragster. Seems to do worse when sun on track, not immediate but drives into shake/chatter.

Setup:
PAR 632 SR20 Alum Block 1840lb ARC Swingarm
4.10 gear
Ride height 4.5”
Launch 4400
MT Big Bubbas (tried 4.5-5.5psi)

Tried Ohlin TTX (bought from TIBR) Full loose compression, fairly tight rebound
Tried Penske 400# spring, 75psi, 38 compression, 8 Rebound
Tried pulling timing -4 ramped back in

Car has been 0.995 60ft and 4.36 at night with 4.30 gear. Conservative setup 1.02 60 fts

Nothing seems to help graphs/feel consistently

Any advice is appreciated!

Once I figure out how to post pictures I will post graphs.

I had same issues this year 1.00 60ft 4.32 with tire shake starting around .15 into the run. my fix was 6 lbs air and tighten the compression on shocks

In my opinion.

Wrong ride height
Wrong spring rate / psi (on Penske) Never ran the motorcycle shocks.
Not near enough timing out to effect anything

Where are 4) 4 link bars set?

SL...

Pending the ride height will determine 4-link location and vice versa. We run ours at 4 1/4 to achieve a little more lower bar downward angle.

Spring rate. Depends on driver weight in my opinion, but a 400lb is a standard steel block big guy spring. Olines are metric on spring rate and I don't know those. Aluminum block is normally 350 and if it was me at 170lb I'd run a 300. We run 350lb springs with steel blocks.

You can adjust the extension and rebound all you want but if the spring pressure is to stiff to move, the valving is a mute point.

Timing - if you are going to mess with that it's my suggestion to make test runs taking 3 degrees out at a time until you see a move in the way the car reacts.

Again driver weight and 4-link bar locations needed. Do you have an idea as to what the pinion angle is?

SL...

Bottom bar angle is 3 degrees
Pinion I believe is 2.75 (will double check)
4 link holes are 1 down for top bar and 1 up for bottom bar

I’m 180lbs. Penske was from when car was steel block so I threw on to test. Ohlin was sold to me with 550lb spring (no idea why...) so I figured trying 400 penske would help.

I agree with the above. I would try the Penske again and switch to the 350. Too much spring makes it harder for the shock to control the rebound. Anything I service would also be 50psi. In that case at 75psi you are just adding a static spring rate into the equation.

quote:

Originally posted by Sparks3224:
Bottom bar angle is 3 degrees
Pinion I believe is 2.75 (will double check)
4 link holes are 1 down for top bar and 1 up for bottom bar

I’m 180lbs. Penske was from when car was steel block so I threw on to test. Ohlin was sold to me with 550lb spring (no idea why...) so I figured trying 400 penske would help.

I've heard you don't want more than like 1.5* of pinion angle or so.. I'm not positive on the number exactly, but your 2.75 seems like a bit much.

If all else fails put OHLIN back on set it up like a hard tail...full stiff on compression and rebound.....don’t knock it till ya try it...

First of all the spring rate required has much more than the motor size/steel or AL and the driver weight to come up with what's needed. The chassis builder should be able to tell you what you need to start with! Every mono shock car built has a ratio of rear end movement to shock movement! You need to know this in order to A: get the right spring rate for your combo's weight and B: get the shock valved correctly. Without this info your just guessing. If the chassis builder doesn't know this ratio, get another builder.
Also note, if you move the bottom bars up or down, you will change the ratio!

Sparks, when does it start to chatter? How far out time wise? Post a picture of the runs.

I have basically the same combo you do, different chassis & motor builder, I have been .980 in sixty feet and smooth as glass. Raced at the Atco Div 1 race last weekend with a hot track, 5 runs between .991 and .994 over two days. I run a Penske shock also! The MT Big Bubba is a great tire.

BTW my spring rate is 350 lbs/in

Here is one of his graphs

Vid of launch would greatly help also...

quote:

Originally posted by DragRaceResults:
Here is one of his graphs

Can you add the Accel curve too?

I have seen this problem at the Spring Fling this year on a car with Little Bubba's and an aggressive (IMO) setup once the track got hot, right at the same time also (about .8 to 1 second out). By this time in the run the rear end should be pretty much done moving from the launch so shocks changes aren't likely to matter much. Bar angles could help. It is also possible that the combo (including the converter design)is just over powering what that track can handle given the power being applied. You can see the DS get upset from the shift also, just not as bad. So assuming it's not a setup issue, the fix here is to reduce power just before this happens by taking timing away and then ramp it back in. I'd take 8 to 12 degrees for starters away at .5 seconds out and ramp it back in by 1.8 seconds and see how that works and adjust from there. Reducing the launch rpm could also help if it reduces wheel speed in the .4 to .7 second time frame.

Note, I also feel the light weight AL blocks contribute to this issue. Your taking a solid 100 lbs off the rear tires.

"Spring rate. Depends on driver weight in my opinion, but a 400lb is a standard steel block big guy spring. Olines are metric on spring rate and I don't know those. Aluminum block is normally 350 and if it was me at 170lb I'd run a 300. We run 350lb springs with steel blocks."

This /\

Just went through this. Dont overthink the rest of it.
I have the same chassis and basic combo, I'm also 290lbs...switched to a 300 lbs spring to allow the shock to do its job and viola!... like a completely different car.

Frustrated getting there...but 60.00 later (in chrome)....fixed!

lower top bar, down on air,5.2, soften extension slightly

Why soften extension?

quote:

Why soften extension?

it will affect the starting line some but,my thought was it may let the suspension work some at that distance on the track to load the rear tire more.at that spot on the track is very common to see an issue with chatter.i have tried to fix it and other than timing not had much luck.some tires are worse than others also.i think when the tire crushes then springs up is what sets up this action.i like more top bar angle and a different tire.but hey thats just me

quote:

Originally posted by rradracer:
I had same issues this year 1.00 60ft 4.32 with tire shake starting around .15 into the run. my fix was 6 lbs air and tighten the compression on shocks

According to the graph they have power out of it by the flash stall at the hit vs the flash stall at the shift, presumably I'd imagine working on the shake. Put the TTX back on it and the power back in, and maybe the 4.30 gear. Tighten the compression to keep the tire round,,, wheel speed.

quote:

Originally posted by rradracer:
I had same issues this year 1.00 60ft 4.32 with tire shake starting around .15 into the run. my fix was 6 lbs air and tighten the compression on shocks

At .150 into the run is quick different that 0.9 plus or minus! Rear end is not moving at .9 out and the car should be up on the tire well before this point so shock settings won't fix this, air pressure may have some impact but I wouldn't bet on it.

quote:

Originally posted by TOP38:

quote:

Originally posted by rradracer:
I had same issues this year 1.00 60ft 4.32 with tire shake starting around .15 into the run. my fix was 6 lbs air and tighten the compression on shocks

At .150 into the run is quick different that 0.9 plus or minus! Rear end is not moving at .9 out and the car should be up on the tire well before this point so shock settings won't fix this, air pressure may have some impact but I wouldn't bet on it.

In all due respect, You're looking at it from an aspect of an adequate damping system, when the cause of the shake is the result of a inadequate damping system, resulted by an out of phase imbalance between the two tires ,,,, tire shake. This is an objective fact anywhere the shake occurs early in the run.

This message has been edited. Last edited by: Mike Rietow,

Torque converter change will cure it as well. There are so many 4-link dragsters out there that are set up completely wrong and are deadly.