Wheelie bar question???

Hey guys, love the site! It's helped me a bunch. I run outlaw 10.5 with a sbf, blown alky, bruno/lenco, 3400lb ladder bar car. We run a single wheel wheelie bar-62in. My problem is the wheelie bar hits the ground too hard on launch causing the tires to unload. We've limited the front end travel, but the wheelie bar seems to move way quicker in relation to the front end. Is this a rear shock adj problem? We leave around 2200 rpm, 1st gear is 2.60, 4.11 rear end, 33in tall tires. We're thinking of building longer wheelie bars, i'm a little hesitant and thought i'd get some of your guys' input. Thanks in advance!

Josh

 

tires?

what tire combo/ air pressure are you running? if you video your runs you'll see that the first move of the wheelie bar is straight down, as the tire wads. also, how high are bars set, and are they very rigid

 

a long wheelie bar is easier to work with. a short bar is like a hair trigger. you need to be spot on with the adjustment every time. how long is your current bar?

 

Is this a 4 link car? If so, you may need to change the intersect point, but a crutch for the problem is to tighten up the extension side of the shock to slow down the rear end movement towards the ground. Also a little more tire pressure may be in order. How high is the centerline of the wheel from the ground in a race ready position? What is the spring rating of the rear springs? What is the weight of the car?

Rob

 

Bryan you're right, the video shows the wheelie bar going straight down and the tires wod up, when the tires come back they break loose and the car hops when it looses the weight transfer. The tires are M/T slicks, 33x10.5w, we usually run around 10.5lbs or air.

Wheelie bars are ran at about 6-9in above the ground, tried 4in and didn't hook. Ladder bar car (instant center is down a bit, bar slants down slightly), car weighs 3450lbs, bars are 62in and are not rigid at all! I believe the rear springs are 180? We tightened up the rebound on the shocks at a good bite'n track, and it spun terrible. It's been a nightmare really. Oddly enough my ET matches the mph perfectly, but you know how them charts are. Thanks guys for the info!

Josh

 

Josh,
Sounds like your ladder bar instant center needs to be moved up, you are hitting the tire way too hard. A longer wheelie bar is a good idea. But, the longer the wheelie bar the higher up it needs to be off the ground so as not to interfere with the weight transfer. Every car is different, if you can change the ladder bar I would start there rather than paying for new wheelie bars to be built.

 

10 1/2 pounds? Is that a beadlock, or tubes and liners? That sounds high to me either way.

I don't know anything about suspensions or tuning cars that heavy, but I don't think the wheelie bar is your problem. I think shoe is right about hitting the tire too hard. We thought we had the same problem a while back, and kept moving the bar up until it didn't hit them. Problem is, that didn't help. Turns out, we think the beadlocks we were running let the tires wad too much, and when the weight transferred back up off the initial hit, it unloaded the rear of the car, and smoked the tires. The only way to get it off the line was to fatten the launch alot. 2200 sounds like a low launch rpm. I may be wrong, but I think some cars can be much more violent when launching a lower rpms because the clutch locks up and doesn't slip. Yours being an automatic, this may not apply, I don't know, just something to think about.


bryan

 

You may be right...i don't run any beedlocks...infact this year we're putting those tires on a 14" rim...and doubling the wheel screws...sounds crazy i know, but that's what everyone's doing. So we'll probably have to run even more psi to keep the tire from buckling in the middle...

I was always told that raising the instant center allowed the car to separate easier putting more "hit" on the tires. I might be wrong on that. My converter guy (marty chance) did stay i need to be leaving at a higher RPM cause it's flashing the converter too hard. What about the wheelie bars being so flexible....should they be really stiff??

 

???

i do know the lower the launch rpm, the more the converter will multiply touque... a higher launch rpm will calm it down.... i tried this personally..... it does work.... Mike

 

I agree with Marty, too low on the RPM's. You need to leave near where the flash point is. Our 96" bars do not flex, they have a structure built in the middle to prevent this yet allow the tubes to move relative to each other.

 

Agree here too, more tire pressure. Safer and less spooky at the top end.

 

Sorry for any confusion guys, this is an all steel 68 fastback mustang, back-halfed, front strange adjustable struts, strange dual adjustable rear shocks. Mike I agree we should run more psi in the tires. According to the video, the wheelie bar smacks the ground before the front end comes completely up. The tires wrinkle shortly after and then unload and the wheelie bar stays on the ground until about 40 ft out. Shouldn't the wheelie bar mimick what the instant center is doing? I'll be the first to admit i'm not a chassis guy... trying to learn though! lol...

 

Mike i don't want to step on anyone's toes, but if you were to push down on the back of the car the wheelie bar moves upward (frame moves towards the rear end housing causing instant center to move down, in turn the wheelie bar goes up). If I push down on the wheelie bar the back of my car goes up. In my case the wheelie bar would move down because of separation, not because of squat. When my car launches the wheel in relation to the top of the fender stays the same, that tells me the car is not squating or extending. The tires wodding up is really the only downward movement. I usually have them set at 7 (out of ten clicks) on the compression, and 4 or 5 on the rebound. Any more clicks (6 or 7) on the rebound and the tires will usually just blow away because like you said it won't allow separation.

 

You probably don't have the money to change everything so lets work with what you have. The ladder bar will work(look at terry robins old car) but it is probably short(32"?) and high(ic).both of these spell hard instant hit. Because the ic is behind the centre of gravity most of the force of the climbing pinion will lift the back end up. Now because you have the front end tied down, coupled with the fact that you have a very nose heavy car(right?) you will get NO weight transfer. So loosen up the front end as much as possible and raise the wheelie bar. You dont have the criteria to leave like a prostock you must leave like a superstock. Also check out your thrust formula. You do have other options other than changing gear ratios. More on that later.

 

bars

raise the launch RPM you need tire speed,sounds like ur boggin' the motor,tuner up! first over power the tire,then back into the correct RPM launch..less time spent trying to sneek up on it,tuner'up and back down to it.

 

Mike thanks for the clearification...that helps a bunch! I would love for you to look at the video...i'll get a couple of launch shots put together and send them to you and if anyone else would like to see so you can voice your opinion just let me know...i would be very appreciative.

200on10.5>yes the car is very nose heavy, i believe the ladder bars are 32". We actually limited the front to only 2-3" travel to try an keep it off the wheelie bars...should i take that limitation out as well as loosen up the shock? Does more weight transfer=tires buckling more?

 

I'll throw my 2 cents in. 2.60 is WAY too much first gear. Also I run only 7 lbs of air on my 10.5 car (w/ beadocks) because it's way nose heavy and is no prob on the top end from a handling perspective (166 mph in the 1/8th) Everyone's combo is different. All I'm saying is don't be afraid to go away from conventional wisdom to get 'er done.