Unloading the tires.

Looking for some more ideas to aide the problem of unloading the tires off the line.

At the present time, we have tried everything this season. We have ran 9 races and have gone testing 3 separate times, and have tried virtually everything we can try to solve the problem. We have used the same chassis (2001 T&C, S&W clone) for the past several season and have struggled with the same problem. The car was originally built for 36in. Goodyears, and we currently are running 34.5in Hoosiers. I question whether it is a wheelie-bar, balance, or transfer problem? Tune-up wise we have gone from more clutch to virtually no clutch, more timing to less timing, played with wheelie bar height, and tire pressures, and most recently front ballast by adding weight to the weight bar, and all share the same result.

We are hoping that someone might have the cure we are looking for, or has gone through the same problem. If we can't solve the problem soon, I guess we will be looking for a new car for next season!

It could be something simple we have overlooked, so any suggestions would be greatly appreciated.

 

Start line challege

Can you explain a little more detail of whats happening,when,and of course engine/ blower combo/ clutch type & condition/ trans ratios etc
ie. When you say unloading do you mean blowing the tyres off? If so does this happen immediatly on the hit or shortly there after etc.

It may also be benifically to the experienced contributors of this forum to understand what RPM are you launching at, wheelie bar hight settings, current ballast position/ weight, overall vehicle weight.

Parry

 

Sent you a PM

 

i had tommy and chris build me a new ta/fc (firebird ) in 2001 and they front halfed a car for me and built a friend of mine monty todd one at the same time and he still has his car i had killer 60ft time in the mid 90s and so does monty i would like to know more information about the car are you videoing the car from the rear sometimes it takes me watching it 20 are 30 times till i start to see every thing thats going on i know on my car it always hit the wheelie bar pretty hard and you cant see this happening in regular time i had to watch the video over and over in slow motion and it may be hitting the bar so hard it unloads the tire at the hit just somthing to think about i still would like to know more about the combination good luck

ps there wheelie bar was like a spring board

 

I second the videoing, though I'd try to get a slightly side angle, so you can see the wheelie bar and the side of the tire. I assume since your running hoosiers your not running beadlocks? Tire pressure? is it a screw or roots car?

 

Added Videos

I just added a few videos to our website (www.kardiackids.ca) to give a clear view of what exactly is happening. The motor is 65in. out and I believe the crank center-line to be 9 1/2in.
It is an IHRA competitive Roots 14-71, Veney Cylinder Heads, Brad block, running a Crower 3 disc 10.7.
The car is still running 70's with 1.04sec 60fts and is the only roots car to run over 250mph (254.14) so engine wise we are making the power but just not efficiently.

We are leaving @ 6000rpm with soft tranny ratio (doesn't shake at the top of first), with roughly 4in wheelie bar height, Hoosier 34.5in with tubes and liners. We have tried a variety of tire pressures in the tubes and liners, but to no avail.

The car is wrapping the tires (reason we increased liner pressure), then unloading the tires on the wheelie bar within the first few feet. The car isn't shaking it just hazes the tires enough to lose momentum throughout the first 30ft.

I have studied all of the videos frame by frame and can tell exactly what is happening we just can't seem the problem. I am beginning to believe it must deal with wheelie bar stiffness but have no guidelines to go by!

 

its the little things. I just recently found my tire gauge off by 2lbs. if the tire is wrapping up id think it would be then bouncing off the liners? I had that problem awhile back, had to add more tire pressure. 6lbs with a good gauge.

 

I am not expert by any means, but I have seen this type of thing in dragsters mostly. Sometimes in Funny-cars, but that seems to be the exception. The tire pressure too low will cause the tire to squat down too quickly and cause a rebound into tire smoke. People who see this in their car often think that they need more traction so even less tire pressure and it does not fix it.
A pretty small window of chassis work well with very low tire pressure. Most don't like it at all, or very hit and miss one pass to another.
I would try to up the tire pressure. It may be hard rebounding out of the chassis or off of the liner.

 

i had very similar combo in my car and it was T&C car and i was leaving around 5000 to 5500 45lbs in the liner and 5lbs in the tire 198 low gear 430 rear 60s were mid 90s all day long 10.7 crower with the car i have now at 6000 i get a little to much wheel speed and my 60s go to shit

 

I've checked the gauge in the past but just to be safe I'll check it again tomorow. We have been running the liners at 45lbs all year and 5 1/4lbs, but this past weekend we upped the pressure to 50lbs, because we heard of other cars running up to 55lbs.

We added 25lbs to the front weight bar to lessen some of the weight transfer and the car looked like it left better because the tires did not wrap as much. But ultimately the car did the same thing unloading on the wheelie-bar then the tires seemed to haze even more (1.04sec. 60ft).

The troubling thing is that the car still ran 5.82 @248.75mph, we just gave up 0.08ths to the 60ft. and didnt stand a chance against Laurie in the first round.

It just seems that everything equates to the wheelie-bar, so im curious as to what would be standard length, wall thickness, mounting type, that sort of thing most cars are running. Softer wheelie-bar stiffness would make sense; riding the wheelie-bar longer as opposed to unloading but most teams don't seem to have the problems we are facing. I just wish we could use the old "set it and forget it" motto, but thats just not the case!

 

It would be nice to sonic a few bars and see thickness. I have a FED and a short bar, so i can't help much, but good luck.