Drag Racing Tech - scary back and forth wobble at end of the 1/8th

Hey guys, i run 26x9x16" Hoosier QTP's on the rear and 17" ws6 wheels on the front of my 99 TA at the track. I'm a M6 and have to run them at 13lbs to get any kind of traction while launching at 4500-5000 rpm's. I run 1/8th mile and trap at 92mph. The car sways side to side terribly at that speed and scares the hell out of me but i stay in it till i cross the line. Other than putting more air in the tires, reducing my traction, what can i do to stop this? Do i need skinnies up front? Any info would help. Thanks.

Just the nature of a bias ply tire. I run mine at 11 psi and doesnt really do that much swaying to me.

what are you runing up front? would that affect the amount of sway?

I run M/T sportsman 8 ply tire up front. I dont know if that affect it. But dont know other than going to a true stiff wall slick would probly help on the swaying

Thats what im trying to figure out. Do i need skinnies or similiar upfront or just scrap the QTP's and try a full slick. They dont hook as well as i thought they would anyway. I thought i'd blow thru my ls7 clutch before those tires would spin.

You can run a tube in the rear or switch to a bias ply tire in the front

sounds like the bias ply sway from having radials on the front

The mix of bias and radial tires is not really the issue, every drag radial car out there runs a radial rear and bias front with no issues, having a bias ply on the back period does this. Get used to it, only thing you can do is tubes, or a stiff sidewall slick, even then it will still do it some.

Like JL said thats normal its going to feel like that.If you think its moving around alot in the 1/8th wait till you till you do a full pass.Thats were i really noticed the car moving around.I run drag radials now et streets there stable the whole run

Thanks for the replies guys. The sway is so bad that I have to correct it with steering to stay straight. I never had this problem when I ran drag radials on the back. This is my first set of bias ply's. My best 60' was a 1.72 on Hoosier and bfg drag radials. I figured these QTP's would drop me into the 1.50's. I got a 1.68 best short time out of them but all the sway at the end. So... What's my best next move? Bias ply skinnies up front to see if it lessens the sway but also drops my times because of the weight reduction or try the tubes? My goal is to reduce my short time also.

Correcting is not a good practice, that's usually where people lose it and wreck the car

As for the short time improvement, slow motion video from the rear of the drivers side would be very helpful

If you must stick with that tire try tubes first, I dont think changing the front will do much. Stiff side wall slick or drag radial is the easiest fix for this though.

I'm not impressed with the qtp's traction so I think I'll try a different rear tire all together. Probably a full slick. I've got to stay with 26" because of my gearing. Thanks for the help guys. I do have a video but it's from the drivers side, side of the car. I soften up my rear shocks, and play with air pressure. Under 4500, I bog, over, I usually spin.

The mix of bias and radial tires is not really the issue, every drag radial car out there runs a radial rear and bias front with no issues, having a bias ply on the back period does this. Get used to it, only thing you can do is tubes, or a stiff sidewall slick, even then it will still do it some.

I would agree to some point but I have found from my own personal experience that a radial skinny and a Bias ply rear tire is ok and sways very little. But running a Bias ply rear tires and a 17x9 wheel up front with a wide radial makes the car sway a lot more.

I think the OP will notice the car is much more stable switching to a skinny.

Op, how wide is the rim that the rear tire is mounted on?

I have gone 130 mph highway pulls with my qtp and i am just use to it. But its not as bad really as your stating. But as JL said corrcting is not a good practice. Just have to have the feel of tire sway from breaking the tires loose.

I would agree to some point but I have found from my own personal experience that a radial skinny and a Bias ply rear tire is ok and sways very little. But running a Bias ply rear tires and a 17x9 wheel up front with a wide radial makes the car sway a lot more.

I think the OP will notice the car is much more stable switching to a skinny.

Agreed, I ran the last 2 years on QTP's with a radial skinny up front. They had a little sway at the 1/4 but not enough to need to compensate. I run tubes now, they still move but I don't even notice it anymore. I'd guess the wide front radial is very stable making the back feel worse!

I've got ws6 wheels with 275/40's up front. The rear are 16x8 firebird aluminum wheels. The sway is terrible and unsafe. I'm not goin to run them again till I try a new combo. Maybe skinnies up front is the way to go? I was thinking the size of the fronts and the bias ply radial combo was bad originally but I wanted to check with everyone on the forum for insight. Should I run a bias ply or radial skinny up front? For the record, I've learned alot from this forum and I really appreciate all the time you guys are taking to help me sort this out. Thanks.

Bias ply front skinny, you won't find a radial one that's the right size, and a radial would negate a large part of the weight savings. If you must stay on a 16 inch rim there's an et street that's 10 or 11 inches wide that would probably help with traction too fwiw

Is the car going side to side or does it feel like the body is rolling side to side?? If its the body then take the tires off NOW. There is a belt broken in the tire. I have seen this before and replacing the rear tires corrected it.

thats pretty low psi for the qtp as well from my past experience. try and keep it a bit higher. you can call hoosier and see what they suggest i think i ran mine around 17psi.

The whole rear of the car sways side to side and points the front towards the wall, then the centerline causing me to have to compensate. I've only had one night of experience with this. I won't run them again till I can make a change to the setup.

99french, at 17 psi, I blow the tires off at the line. Thats the only reason I drop them down to such a low pressure. But, the sway did get worse as I decreased tire pressure.

The whole rear of the car sways side to side and points the front towards the wall, then the centerline causing me to have to compensate. I've only had one night of experience with this. I won't run them again till I can make a change to the setup.

You haven't messed with your panhard bar lately have you? Something that radical sounds like the panhard bar came loose or you have a broken belt.

maybe soften the shocks some. but hows your 60'? it can be tricky launching a 6spd with a two step i know that much. i also know there was a world of difference between my trutrak and my locker traction wise, plus i broke the trutrak first time out with my two step. why not switch to a 15" wheel on the rear so you can have some more sidewall?

Nope, pan hard bar is a spohn adjustable, it's fine and the axle is centered. I have the relocation brackets on my 9" also and the control arms are in the bottom hole. My shocks are on the softest setting. My 60' sucks to be honest. I bought the tires and wheels from a older guy on Craigslist with hardly any wear. I only ran them one night. My 60' is a best of 1.68 with those tires. 1.72 on drag radials. I am thinkin about switching to 15" rims for more sidewall. Just gotta come up with the dough.

I had this problem when I had 8" wide rims w 26x11.50 et streets. Sway was real bad at 10-11 psi on the big end. Swapped to a 10" rim and it never did it again.