Radial Tire Top End Violent Wobble At Deceleration

Rusty Davenport · 05-08-2008, 08:55 AM

I'm taking inventory on things to try to keep from wrecking the car before my next experience with radial tires. Under power there are no problems, start slowing down and here we go----hold on for all the excitement. So far I have received the following advice----#1 keep the air pressure low like 11 lbs-----#2 not enough air pressure go to 14-15 lbs----#2 tighten the rebound setting ( Stanhuff ) on the rear to just a couple of sweeps from full tight----ANYONE else care to help before I make another SUICIDE pass ????? PLEASE help....my heart can't take much more.

Angelo DiTocco · 05-08-2008, 09:44 AM

Rusty.... don't roll your ride
Most have had to tighten the rear shock settings W/ radials
Radials also need more air than the bias ply, not less, but that's not the whole story.

They are definitely more sensitive to irregularities in the track surface and even subtle inconsistencies in the suspension setup on the car.

For example, check your front end settings, shock settings, wheel travel, and snubber settings.... if they are uneven and you have one tire hitting the ground before the other coming out of a wheel stand .... or .... one side hitting a snubber before the other when you hit the brakes, those mismatches are transfered to the rear suspension and then oscilate from side to side with the radials. You would not even notice it with bias-plys.
I would check that stuff first, since it is in the shutdown area where the issues arise. Does it start immediately after you lift off the gas, or does it start when you apply the brakes? That's important to know.

I've seen some of the hemi cars rock the whole way down the track when one front wheel lands before the other after the wheelstand.

What weight do you run the car at?
What rear springs do you have?
What brand & size radial?

John Quinn · 05-08-2008, 10:13 AM

If you have bias ply front tires it will cause poor handling. A mix of radial and bias tires was warned against back when radials were new. I hope you solve the problem before any bad events occur.

Rusty Davenport · 05-08-2008, 10:18 AM

Thanks Angelo.....I'm trying to talk my mother-in-law into making the next test run...I'm not looking forward to it. 1996 Camaro........GT/EA.....Car is 3135 lbs-----Hoosier Radials 14.5 X 32------11 lbs air-------very light initial tap the breaks at the finish line, get off the brakes then it goes crazy, let the car coast the to the end after the coronary. I think if I really panicked and got on the breaks hard it would only get worse and roll the car. This is not something you "drive" out of, you have to experience it to understand. It actually feels like the car is leaving the track upward and then side to side....geeeeeeesss.

THE LEGEND · 05-08-2008, 10:38 AM

I don't understand why big radials have this problem and little ones dont.

I had a similar problem with my 10.90 car. We went to the stiff sidewall bias tires.
It was controllable in the 1/8th but it was OH CRAP in the 1/4. I took car to Robbie Draughon(910-988-2619). He reworked shock mounts, put new coilovers on, and replaced all heim joints. The car was backhalfed in the late 90's and everything was old. Robbie said all joints needed to be replaced on a regular basis. That helped the problem a bunch. We finished year out no problem. The next year first race out started up again. We then replaced the front with a set of QA1 coilovers then adjusted the play in the steering box. Put on new front tires. Never had a problem since.
You should probably go over eveything. It could be a combination of small problems causing a big one.
Chip

casper · 05-08-2008, 11:03 AM

I just went thru what you are describing . As soon as I crossed the stripe and got out of the gas the car would begin a violent side to side wobble . I did stiffen up the back shocks but this didn't have much of an effect . Tried the radials at 14.0, up from 13.0 , didn't make much difference . Over the winter I had an anti-roll bar put in , and while this was being done , the chassis guy noticed that the 4-link was out of alignment . After installing the anti-roll and squaring the 4-link , the car is 100% better than it was last year . BTW this is 2002 SS/GA Firebird .
Mike

Dave Goob Cook · 05-08-2008, 03:36 PM

Wow, sounds creepy......
Back in tha day, when radials (passenger tires) were new, you ran the radials on the rear, with bias tires on the front. Or so the old wives tale went.
Sounds like you have something loose, going out of square on deceleration.

CrateCamaro · 05-08-2008, 07:09 PM

Quote:

Originally Posted by Rusty Davenport

Thanks Angelo.....I'm trying to talk my mother-in-law into making the next test run...I'm not looking forward to it. 1996 Camaro........GT/EA.....Car is 3135 lbs-----Hoosier Radials 14.5 X 32------11 lbs air-------very light initial tap the breaks at the finish line, get off the brakes then it goes crazy, let the car coast the to the end after the coronary. I think if I really panicked and got on the breaks hard it would only get worse and roll the car. This is not something you "drive" out of, you have to experience it to understand. It actually feels like the car is leaving the track upward and then side to side....geeeeeeesss.

Maybe I missed it but I didn't see if you posted what size rim you were running. When we used a set of radials for the first time rocked like crazy with the same tire as you but on a 12in rim. Moved up to a 14in rim and it got better but it was still there. Dropped tire pressure from 17psi (recomended by other racers) to 14.5 and never looked back. I wouldn't run anything under 13.5psi in a radail only because I think that the center of the tire will convex when the car leaves. I could be re-inventing the wheel but 14.5 always works with no "Radial Rock"

Kent Hanley · 05-08-2008, 07:58 PM

A suggestion is to check the alignment and toe in / toe out. When you lift or hit the brakes the frontend changes more than the rear.

Last year at Maple Grove my wishbone broke at about 1200' because of the wobble. Not fun nor anything I will forget soon.

Its gone now sorry I cant tell you what fixed I changed about 100 things. All of which are previously listed just dont discount anything.

Nor are radials worth hurting yourself, put some bias ply tires on. Hoosier makes a real light weight one for superstock that are just about as fast a radial.

Kent

Lynn A McCarty · 05-11-2008, 02:22 PM

Radials all have a different design which is recommended not to mix with bias ply tires. Shock adjustments take care of the wobble, but it is really scary.

05-08-2008, 10:13 AM	#3
John Quinn Member Join Date: Jul 2002 Location: Bison, KS Posts: 97 Likes: 0 Liked 0 Times in 0 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration If you have bias ply front tires it will cause poor handling. A mix of radial and bias tires was warned against back when radials were new. I hope you solve the problem before any bad events occur.

05-08-2008, 10:18 AM	#4
Rusty Davenport Senior Member Join Date: Jun 2005 Location: Nashville N.C. Posts: 505 Likes: 4 Liked 100 Times in 26 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration Thanks Angelo.....I'm trying to talk my mother-in-law into making the next test run...I'm not looking forward to it. 1996 Camaro........GT/EA.....Car is 3135 lbs-----Hoosier Radials 14.5 X 32------11 lbs air-------very light initial tap the breaks at the finish line, get off the brakes then it goes crazy, let the car coast the to the end after the coronary. I think if I really panicked and got on the breaks hard it would only get worse and roll the car. This is not something you "drive" out of, you have to experience it to understand. It actually feels like the car is leaving the track upward and then side to side....geeeeeeesss.

05-08-2008, 10:38 AM	#5
THE LEGEND VIP Member Join Date: Aug 2002 Location: Fayetteville, n.c. Posts: 1,411 Likes: 0 Liked 1 Time in 1 Post	Re: Radial Tire Top End Violent Wobble At Deceleration I don't understand why big radials have this problem and little ones dont. I had a similar problem with my 10.90 car. We went to the stiff sidewall bias tires. It was controllable in the 1/8th but it was OH CRAP in the 1/4. I took car to Robbie Draughon(910-988-2619). He reworked shock mounts, put new coilovers on, and replaced all heim joints. The car was backhalfed in the late 90's and everything was old. Robbie said all joints needed to be replaced on a regular basis. That helped the problem a bunch. We finished year out no problem. The next year first race out started up again. We then replaced the front with a set of QA1 coilovers then adjusted the play in the steering box. Put on new front tires. Never had a problem since. You should probably go over eveything. It could be a combination of small problems causing a big one. Chip

05-08-2008, 11:03 AM	#6
casper Member Join Date: Nov 2002 Location: Canada Posts: 111 Likes: 0 Liked 1 Time in 1 Post	Re: Radial Tire Top End Violent Wobble At Deceleration I just went thru what you are describing . As soon as I crossed the stripe and got out of the gas the car would begin a violent side to side wobble . I did stiffen up the back shocks but this didn't have much of an effect . Tried the radials at 14.0, up from 13.0 , didn't make much difference . Over the winter I had an anti-roll bar put in , and while this was being done , the chassis guy noticed that the 4-link was out of alignment . After installing the anti-roll and squaring the 4-link , the car is 100% better than it was last year . BTW this is 2002 SS/GA Firebird . Mike

05-08-2008, 03:36 PM	#7
Dave Goob Cook Member Join Date: Dec 2006 Location: Indy Posts: 422 Likes: 0 Liked 0 Times in 0 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration Wow, sounds creepy...... Back in tha day, when radials (passenger tires) were new, you ran the radials on the rear, with bias tires on the front. Or so the old wives tale went. Sounds like you have something loose, going out of square on deceleration.

05-08-2008, 08:55 AM	#1
Rusty Davenport Senior Member Join Date: Jun 2005 Location: Nashville N.C. Posts: 505 Likes: 4 Liked 100 Times in 26 Posts	Radial Tire Top End Violent Wobble At Deceleration I'm taking inventory on things to try to keep from wrecking the car before my next experience with radial tires. Under power there are no problems, start slowing down and here we go----hold on for all the excitement. So far I have received the following advice----#1 keep the air pressure low like 11 lbs-----#2 not enough air pressure go to 14-15 lbs----#2 tighten the rebound setting ( Stanhuff ) on the rear to just a couple of sweeps from full tight----ANYONE else care to help before I make another SUICIDE pass ????? PLEASE help....my heart can't take much more.

05-08-2008, 09:44 AM	#2
Angelo DiTocco Senior Member Join Date: Dec 2001 Location: NY, NY Posts: 736 Likes: 158 Liked 174 Times in 39 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration Rusty.... don't roll your ride Most have had to tighten the rear shock settings W/ radials Radials also need more air than the bias ply, not less, but that's not the whole story. They are definitely more sensitive to irregularities in the track surface and even subtle inconsistencies in the suspension setup on the car. For example, check your front end settings, shock settings, wheel travel, and snubber settings.... if they are uneven and you have one tire hitting the ground before the other coming out of a wheel stand .... or .... one side hitting a snubber before the other when you hit the brakes, those mismatches are transfered to the rear suspension and then oscilate from side to side with the radials. You would not even notice it with bias-plys. I would check that stuff first, since it is in the shutdown area where the issues arise. Does it start immediately after you lift off the gas, or does it start when you apply the brakes? That's important to know. I've seen some of the hemi cars rock the whole way down the track when one front wheel lands before the other after the wheelstand. What weight do you run the car at? What rear springs do you have? What brand & size radial? __________________ Angelo DiTocco '98 Firebird SS/HA '98 Firebird B/SA Last edited by Angelo DiTocco; 05-08-2008 at 09:55 AM.

05-08-2008, 07:58 PM	#9
Kent Hanley Member Join Date: Mar 2007 Posts: 127 Likes: 69 Liked 0 Times in 0 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration A suggestion is to check the alignment and toe in / toe out. When you lift or hit the brakes the frontend changes more than the rear. Last year at Maple Grove my wishbone broke at about 1200' because of the wobble. Not fun nor anything I will forget soon. Its gone now sorry I cant tell you what fixed I changed about 100 things. All of which are previously listed just dont discount anything. Nor are radials worth hurting yourself, put some bias ply tires on. Hoosier makes a real light weight one for superstock that are just about as fast a radial. Kent

05-11-2008, 02:22 PM	#10
Lynn A McCarty Member Join Date: Jun 2002 Location: Plainfield (INDY) Indiana Posts: 468 Likes: 1 Liked 3 Times in 3 Posts	Re: Radial Tire Top End Violent Wobble At Deceleration Radials all have a different design which is recommended not to mix with bias ply tires. Shock adjustments take care of the wobble, but it is really scary. __________________ Lynn A McCarty 3470 SS Last edited by Lynn A McCarty; 05-11-2008 at 02:26 PM.