Chassis tuning tips to avoid wheel stand

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Chassis tuning tips to avoid wheel stand

Post  Dave De on May 10th 2017, 7:32 pm

3200 pound tube chassis car, 580 cube motor making north of 900 hp. C6, 32" tall tires, stall at 5,000rpm but seems to be higher, leaving off the trans brake and two step at 3600rpm. Car is close to 50/50 weight has ladders with double adjustable rear and single adjustable front. Front is MII suspension only restrained by shock settings. 3.70 gear.

I almost crashed the front end last Saturday when it decided to standup onto the rear quarter panels. Time trials were okay with the wheels lifting about a foot. First round of eliminations and it just went off on me. No videos or photos.

I dont want to change to a glide or pull power out or add wheelie bars. If I crank up the front shocks it blows the tires off. The 60ft seems to be best with the wheels off the ground 1 ft to 1.5 ft and 60's in the 1.25 to 1.29 range.

Ladder bars are level
Front shocks at 8 (15 max)
Rear shocks at 7c and 10r (max is 19)
Tires are Hoosier bias ply, no tubes and 12.5 psi

Doing a little reading and finding Jerry Bickel information to be most straight forward. This is my plan.
lower the shock brackets to the next hole (3/4") this will angle the ladder bar down slightly. The front ladder has only one hole.
Reduce the rear shock settings or at least separate the settings to get it to squat. 3c and 14r
Increase the front shock setting to 10 minimum.
Raise the two step to 4,000 minimum.

Does it seem like I'm going the right way on the adjustments? What else can I do? I am trying to crutch the setup for no bars and make it consistent.

Thanks,
Dave
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Re: Chassis tuning tips to avoid wheel stand

Post  cool40 on May 10th 2017, 10:40 pm

I would think the 370 gear helps with the hit on the tire you get with ladder bars. How does it respond to tightening up the extension on the rear shocks?like a lot to keep separation to a minimum. I never could see any difference with front shock settings but I have the short strange struts with very little travel. My car didn't pick up anything with a glide but it sure made going faster possible...just say'n. Laughing before I abandoned the ladder bars I dropped them down as far in front as possible but it only took away some of the hit and rode the bars way down the track.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 10th 2017, 11:14 pm

I havent changed settings on the the double adjustables yet but you do recommend setting the rebound to be tighter. I do see a change when setting the front shocks tighter.
I see a few 1000 hp cars squat when they leave and still pull good 60's.
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Re: Chassis tuning tips to avoid wheel stand

Post  cool40 on May 10th 2017, 11:51 pm

My setup needed the shocks tight as possible but I was leaving with a 5800 converter. I could never get enough bite out of the ladder bar deal but I know $hocks can be had that will. When you tighten the front it loads the rear tires harder at the hit so I'd bet your bouncing them loose. Good video can be a lot of help.
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Re: Chassis tuning tips to avoid wheel stand

Post  DILLIGASDAVE on May 11th 2017, 3:33 am

If it's aggressively/violently lifting the front tires straight up-out of the beams hard at the hit then adjusting the front shock extension valving/dampening tighter-stiffer will most likely have little/no effect on calming the wheelstand (too much happening all at once & too little time for valving changes to effect it while the pinion gear is climbing the ring gear).

But if the front tires are "driving" out of the beams as the wheelstand is progressing (over a longer period of time) then adjusting the front shock extension valving tighter-stiffer might help calm the wheelstand a given amount.

But the real problem is most likely the car is dead hooking (or damn close to a dead hook) with little/no wheel-speed at the hit. If the car had wheelie bars it would be an easy fix since lowering the w/bars X amount will usually increase wheel-speed X amount in repeatable amounts pass to pass. Adding wheel-speed without wheelie bars can usually be done a number of different ways (but they might not be as "repeatable" as wheelie bars are). One way is to try tightening the rear shock extension valving some more (make it harder to "hit" the tire all at once).

Another way to add/increase wheel-speed is to play with slick air pressures. Depending on the car, the power, & the front/rear weight bias taking away air pressure usually increases wheel-speed.....usually. Buuuuut is some cases the opposite is true and adding air pressure increases wheel-speed (it just depends on the combo).

You could also add weight/move weight up to the nose making it harder to lift the front of the car (which can also sometimes have the side benefit of increasing wheel-speed out back).    

Adding more power at the launch can also have an effect, sometimes good (more wheel-speed), and sometimes bad (more dead-hook & more violent wheelstand) it can be a crap-shoot what the end result will be when adding more power at the hit.
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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 11th 2017, 1:22 pm

You should first limit the travel of the front suspension. If that doesn't work, add some weight.

I'm guessing you're against wheelie bars?
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 11th 2017, 7:36 pm

Thanks for some insight here. I've read your comments over at least three times.
The car will dead hook at times and if I tighten the front to the maximum it will spin. This tells me that the tires are lifting straight up out of the beams when it dead hooks. If there is a way to set the rear end to allow the front end settings to not be so critical I might be able to get this to work without bars. I can scrub off some ET for consistency. Wouldnt it be better to have more tire pressure than less? Right now it has always dead hooked at 12.5 psi so why not go 13psi and stay above the dead hook?

Daves comments
If it's aggressively/violently lifting the front tires straight up-out of the beams hard at the hit then adjusting the front shock extension valving/dampening tighter-stiffer will most likely have little/no effect on calming the wheelstand (too much happening all at once & too little time for valving changes to effect it while the pinion gear is climbing the ring gear). - Yes it is lifting up and out but adjustments do help and it is not consistent.

One way is to try tightening the rear shock extension valving some more (make it harder to "hit" the tire all at once). Yes I see that and plan to step it up at least 4 clicks

Cools comments
How does it respond to tightening up the extension on the rear shocks?like a lot to keep separation to a minimum. I never could see any difference with front shock settings but I have the short strange struts with very little travel. -MII fronts dont have much travel either but more than your struts. When you say extension that is same as rebound? That being the case I will try that if not then I'm confused as to why.

Curt
I cant see how adding weight to the front will help it be consistent. Yes I dont want bars but if this thing heads to the sky again I might not be so lucky saving the front end coming down.


The rear shock settings will result in compression or squat. This will help the front end not be so violent on going up and be more consistent?
I've outlined changing a number of settings and was thinking to start there on a base line and work my way to a tweeked result. Am I on the right track ?


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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 11th 2017, 7:57 pm

Dave De wrote:

Curt
I cant see how adding weight to the front will help it be consistent. Yes I dont want bars but if this thing heads to the sky again I might not be so lucky saving the front end coming down.

I didn't say that it would help with consistency, you asked how to keep the front end down. Pulling the tires out of the beam the same every time is the only place to start. If you can't limit the travel enough to keep it off the bumper, weight on the front bumper will.

You can't win if your not fully in the throttle until you get to the big end. I too would move from there and deflate the rear tires. If they aren't wadding, they're not working.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 11th 2017, 8:20 pm

Curt wrote:
Dave De wrote:

Curt
I cant see how adding weight to the front will help it be consistent. Yes I dont want bars but if this thing heads to the sky again I might not be so lucky saving the front end coming down.

I didn't say that it would help with consistency, you asked how to keep the front end down.  Pulling the tires out of the beam the same every time is the only place to start. If you can't limit the travel enough to keep it off the bumper, weight on the front bumper will.

You can't win if your not fully in the throttle until you get to the big end.  I too would move from there and deflate the rear tires. If they aren't wadding, they're not working.

Thanks I will try that (lower the tire pressure). I guess I implied consistency was important.
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Re: Chassis tuning tips to avoid wheel stand

Post  cool40 on May 11th 2017, 9:30 pm

Extension or rebound would be the same thing to me. You tighten that up to limit the hit on the tire. I would add air to the tire if I was looking to unhook it some.
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Re: Chassis tuning tips to avoid wheel stand

Post  DILLIGASDAVE on May 12th 2017, 4:25 am

In shock valving/dampening terms "bump" & "compression" mean or describe the same thing/action (compressing the shock). And "rebound" & "extension" mean or describe the same thing/action (extending the shock).

You mentioned that you want the rear of the car to "squat" at the launch. Just remember that what might look like a car's rear suspension "squatting" during the launch (when viewed at real speed) is actually just the rear wheel/tire centerline getting closer to the ground during the sidewall wadded-up at the hit. The rear suspension it's self it actually separating a given amount at the initial hit (usually).

Another thing to think about is the proposed ladder bar (I/C) angle change. True you can set the ladder bar angle (and/or it's I/C) lower and it should theoretically "calm/slow" the mechanical leverage of the initial hit a given amount. But a lower bar angle/lower instant center might also sometimes make the wheelstand climb higher IF the car is (at the same time) also still dead-hooked. Because of this sometimes raising the ladder bar I/C has better results in calming the wheelstand than lowering the bar I/C (again sometimes) because while the higher I/C hits harder, it also doesn't hold "the hit" as long.

As far as adding nose weight causing a loss of consistency goes just remember that we are talking about making small increases in nose weight from pass to pass during testing (think "fine tuning", say in 5 lb increments), vs throwing a bunch of weight on the nose all at once. Adding just 5 pounds on the nose can sometimes make a big difference on some cars. The farther out on the nose you can place a given amount of weight the greater the effect of that given amount of weight.
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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 12th 2017, 10:02 am

You should never try to change the IC with a ladder bar car. All you are going to do is bind up the driveshaft. But hey,, it will calm the car down (due to it's inability to turn the pinion). For maximum performance you need the proper pinion angle. If you already have it, you can't get more.
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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 12th 2017, 10:05 am

Dave De wrote:

I guess I implied consistency was important.

It is important. But if you're dragging the bumper and having to get out of the gas, consistency is something you'll never have.

I had a heavy car that I won 10's of thousand of dollars with. Very consistent.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 12th 2017, 8:53 pm

Lowered the rear at the axle .75 inches. The ladders are 5 degrees down and the pinion angle is under 2 degrees. The ladders were at 4 degrees down.
Going to base line the shocks and go at it again.
Thanks for your help.
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Re: Chassis tuning tips to avoid wheel stand

Post  DILLIGASDAVE on May 13th 2017, 2:17 am

Curt wrote:You should never try to change the IC with a ladder bar car. All you are going to do is bind up the driveshaft. But hey,, it will calm the car down (due to it's inability to turn the pinion).  For maximum performance you need the proper pinion angle. If you already have it, you can't get more.


That may have been somewhat true back in ancient times before the invention of double adjustable ladder bars. But now days double adjustable ladder bars allow you to easily move the ladder bar I/C up or down to whatever front ladder bar chassis bracket/instant center bracket hole you want to use. And then you can independently readjust the pinion U-joint operating angle back to where it needs to be regardless of where the ladder bar I/C was set.
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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 14th 2017, 11:39 am

DILLIGASDAVE wrote:
That may have been somewhat true back in ancient times before the invention of double adjustable ladder bars. But now days double adjustable ladder bars allow you to easily move the ladder bar I/C up or down to whatever front ladder bar chassis bracket/instant center bracket hole you want to use. And then you can independently readjust the pinion U-joint operating angle back to where it needs to be regardless of where the ladder bar I/C was set.

True. As long as he doesn't own ancient ladder bar technology which most do.

In his last post, I didn't see where he corrected the pinion angle after changing his ladder bar angle.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 14th 2017, 12:38 pm

Curt,
I'm at less than 2 degrees pinion angle right now. When I lower the rear end of the car by moving the shock brackets down one hole (3/4") the front ladder bar is still in its original and only hole. This will make the pinion angle lower, previously it was over 2 degrees.
I am concerned about the tire pressure where it has dead hooked 3 times with the old setup when at 12.5 psi. I am thinking about going either 12 or 13 psi and staying away from 12.5 all together.

Thanks for your concerns and I appreciate your suggestions.
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Re: Chassis tuning tips to avoid wheel stand

Post  Curt on May 14th 2017, 1:28 pm

Dave De wrote:Curt,
I'm at less than 2 degrees pinion angle right now. When I lower the rear end of the car by moving the shock brackets down one hole (3/4") the front ladder bar is still in its original and only hole. This will make the pinion angle lower, previously it was over 2 degrees.
I am concerned about the tire pressure where it has dead hooked 3 times with the old setup when at 12.5 psi. I am thinking about going either 12 or 13 psi and staying away from 12.5 all together.

Thanks for your concerns and I appreciate your suggestions.  

So are you saying that your pinion angle is 2° to the earth, or your pinion angle is 1° to the earth and your tailshaft angle is 3°? (or similar)

Or are you calculating the difference between the two?

I wouldn't change anything from the original set up until you tried the changes on the front end first.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 14th 2017, 2:29 pm

2 degree measurement is from the flat on the yoke to the drive shaft. I'm using a gravity weighted angle tool and calculating the angle.
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Re: Chassis tuning tips to avoid wheel stand

Post  cool40 on May 14th 2017, 9:46 pm

Don't get too caught up in the pinion angle,its only purpose is keeping the ujoint happy. If you want to stop the dead hooking go up on the tire psi and tighten the extension on the rear shocks. Ladder bars are very hard on shocks leaving at higher rpm.
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Re: Chassis tuning tips to avoid wheel stand

Post  Dave De on May 15th 2017, 12:28 pm

I'm going to use Milan's No ET program this Saturday and get this sorted out if the weather holds up. I will mount the camera on the car to see what this is doing and make the adjustments to get this dialed in. Call me a wimp but right now I'm afraid to let go of the button. I keep telling myself all I need is a few good runs and keep it dialed in close to the ground to gain confidence back.
If all goes well I will have a few videos to post next week let's hope none of them pointed to the sky.
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Re: Chassis tuning tips to avoid wheel stand

Post  FalconEh on May 19th 2017, 10:27 pm

DILLIGASDAVE wrote:

But the real problem is most likely the car is dead hooking (or damn close to a dead hook) with little/no wheel-speed at the hit. If the car had wheelie bars it would be an easy fix since lowering the w/bars X amount will usually increase wheel-speed X amount in repeatable amounts pass to pass. Adding wheel-speed without wheelie bars can usually be done a number of different ways (but they might not be as "repeatable" as wheelie bars are). One way is to try tightening the rear shock extension valving some more (make it harder to "hit" the tire all at once).

+1 and with the wheelie bars you can also add the juice although I know you don't like either one, but even with a little plate and no sky wheelie I would bet your after the pass grin will be impossible to hide.Twisted Evil Wink
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Testing at Milan

Post  Dave De on May 20th 2017, 9:17 pm

I got one 1/8th mile hit before the rain came at Milan. No ET is a glorified TnT.
I mounted my cheap camera on the door facing the rear tire and it moved at the brake release. The rear of the car moves sideways when it leaves.
What you dont see is that the front went up equally about 8 inches of space tires to the ground.
Tires were at 11.5 (hot) no tubes,rear shocks at 4-14 compression-rebound (19 max), front shocks at 12 (15 max)
60 ft was 1.27
1/8th mile was 5.72

This probably doesnt say much but if it went straight I think the 60ft would be in the bottom 1.20's
I wanted 12 psi in the slicks but you know how the first run can go. I think the tires could use some more air in them. There doesnt look like any separation took place.

Any comments will be appreciated.

https://youtu.be/EEAjrT2qm7w
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Re: Chassis tuning tips to avoid wheel stand

Post  DILLIGASDAVE on May 21st 2017, 4:37 am

Dave De wrote:..........The rear of the car moves sideways when it leaves.......

It's not really the back end of the car that's moving sideways (to the left), but that the rear end is driving/pushing the front/nose of the car to the right as the launch progresses. This effect can be caused by a number of things.......

(A) a side-to-side ladder bar or 4-link preload problem.
(B) or the slicks don't have the same rollout measurement side-to-side, (or the same air pressure).
(C) or the rear coil overs don't have the same spring rate side-to-side (or possibly a dead spring).
(D) or the rear coil overs don't have the same spring height seat/pedestal adjustment side-to-side.
(E) or the rear housing C/L isn't sitting square in the car in relation to the car's nose-to-tail C/L.
(F) or something is bent/twisted/broke somewhere.

If it turns out it's a preload problem, and if it's driving to the right only a small amount at the launch, but it also drives perfectly straight at the finishline, then it might only need a minor preload adjustment. If that's the case then either take some weight out with the driver side ladder bar turnbuckle adjuster, or add some weight in with the passenger side ladder bar turnbuckle adjuster.
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Re: Chassis tuning tips to avoid wheel stand

Post  DILLIGASDAVE on May 21st 2017, 5:01 am

Dave De wrote:..............There doesnt look like any separation took place.....

From what I could see there was probably around an inch of rear suspension separation at the initial hit. IMO it also wadded up the sidewalls a decent amount too during the launch.

Also if you watch the track surface during the launch you can see the width of the tracks left by the passenger slick shrink/expand in an oscillating pattern for a short time. The engine RPM also came up a little and then fell back during that point. It's possible that there could have been some minor tire shake, or skipping wheel-speed during that point in the launch (or just that one slick slipping/skipping X amount resulting in the launch to the right).
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