M&H dot tire wadding up on the launch -please look

[dave brode]

All,

I have a new engine in my truck that I'm trying to sort out. I'm running 29x17 M&H dot tires. http://www.mandhtires.com/store.php?...on=show_detail

I have only made 10 passes, but have always felt a "rumbling" on the launch. Not right away, but through most of low gear. It doesn't blow the tires off, I just feel the tires trying to dig. I had a friend watch closely yesterday, and he said the tire wraps up and plants, but about 1.5 truck lengths out, it wads up and deforms badly.

I have done ok with 12.5 to 16 psi, but it "rumbles" with those amounts . I tried 20, but it spins on the hit. It has gone 1.59 in the sixty, but usually goes low 1.7x. On the pass yesterday with 16 psi, it went mid 1.7x, but the tire was wadded up so bad and bouncing that my buddy could see light UNDER the tire.

I have CE adjustable shocks, rears set on 70/30, fronts on 90/10. On the hit, it lifts front up, a little air under the left, and it seems to be all well until 1.5 lengths out. I plan to try tighter shock setting front and rear.

Do I need a stiffer tire? Thanks in advance for any ideas.

Dave

[dave brode]

p.s. - I have tried leaving just above idle to 1400, still "rumbles"

Convertor flashes to 3200.

Dave

[shortbed70]

Sounds like you need to get some laps on them at a steady psi and see how it goes. How are your trailing arm bushings?

[dave brode]

Originally Posted by shortbed70

Sounds like you need to get some laps on them at a steady psi and see how it goes. How are your trailing arm bushings?

Energy Suspension bushings. I tried only one pass at 20 psi, but it didn't even try. That was first pass on the engine and tires, but I drove it 70 miles to the track, so it's not like the tires weren't used at all.

I'm going to call M&H tomorrow, but I'm betting they'll say not enough air, or hitting them too hard initially. I was treating it like a VERY long ladder bar vehicle, so I ASSumed that it would want the rear shocks on 70/30. Maybe not.

Thanks for your reply.

Dave

[Rodms]

Sounds like too much traction and deff low air pressure,Talk to john and see what he says.The hooking it most tire on the market!

[djracer]

try 50/50 on the rear and leave the front alone. Then run as much air as it will allow and still hook.

[71Dragtruck]

You running tubes?

[dave brode]

Thanks, guys.

No tubes. I'd be 1/2 afraid of them pinching, as tight as the tire is wrinkling now. Of course, with more air, they might not wrap up quite as much.

Waiting on a call back from M&H. Will post then. Curious to see if they think a 12" rim would be better than the 14" I have now.

Thanks again.

Dave

[Marv D]

If you use a good tube, don't worry about the wrinkle pinching the tire. I ran 10.25psi in my slicks for a number of years running mid tens and they would 'wad up' and wrinkle pretty good. I was getting tire shake like your talking about. And once the hook let go,, it was all over.



Now I'm hitting the tire with another 200+ horses, pulling 1.2x sixty foot times, and running low 9's with 9.5psi. Yup,, LESS air. Still run tubes and have NO tube issues with them. (I hate having to plug a couple of pounds of air int etired between rounds, and just to hope there is enough to let them down to the right psi just befor ethe pass) But I'm beating the tire up more than I ever have. Used to get 2 years out of a pair of slicks, but now I get nervious those last two races of the year.

Here's the way Alston explained it to me.
Tire shake is 'generally' a issue of not enough power. Like the picture what happens is the tire wads up (well stuck to the track), then because the suspension / power can't maintain the tire 'stretch' it wants to wad up and you drive over the 'lump of air'.

If it were a 4link you would move the IC lower and longer to take hit out of the suspension, and (depending on your setup) probably stiffen the shocks. So where your fixed in suspecsion adjustments,, I agree with Kevin all the way. Take the shocks to 50/50, and put more air in them. Move in small increments in tire PSI and use a GOOD gauge. You need to be consistantly able to SEE 1/4 pound increments CLEARLY on your gauge.

Myself I don't think your going to find a lot that works with that short tire above 15psi. But,, I don't know M&H tires. Everything I run is Hoosier. So thake that with the 2¢ worth of salt it's worth.

[71Dragtruck]

Here's my tires on launch.

[dave brode]

Talked to john at M&H. It was no surprise that he said that I needed more air. He said that the tire was like a spring, and with lower than optimum pressure, I was wrapping it tight, then when the front end tops out hard, the spring unwinds = tire distrortion.

He suggested 18 psi and trying a few things, maybe working up from 18. He said NOT to tighten rear shocks, as he felt that I'll need to hit them due to moving up with tire pressure. I may tighten the front shocks to slow front end rise, and try different launch rpm. Perhaps wrapping the tire up a little before hitting it would help. At least that's my plan.

Thanks all, now if I can just get back before snow flies here.

Dave

[Marv D]

Dave, something just hit me,, a ?? 29"x17" tire??? I had no idea ANYONE made a tire that short and that WIDE!!! Is that a DOT slick, or a true treaded tire like the drag radials? Hell the 33x22.50-15 Hoosier DOT slicks on my truck ore only a little over 16 wide @ 33" tall. You got a couple of Tootsierolls under the back there

[dave brode]

Originally Posted by Marv D

Dave, something just hit me,, a ?? 29"x17" tire??? I had no idea ANYONE made a tire that short and that WIDE!!! Is that a DOT slick, or a true treaded tire like the drag radials? Hell the 33x22.50-15 Hoosier DOT slicks on my truck ore only a little over 16 wide @ 33" tall. You got a couple of Tootsierolls under the back there

Hi Marv,

Yes, a dot. Biased. It's the only thing I found that was short. They are a little harder than their smaller "cheater slicks", but still a soft drag type wrinkle wall dot. They also have a 30 x 18"

http://www.mandhtires.com/store.php?...on=show_detail


I went short because it give me more gear. I drive to track on hard 21.5 x 33s. Even with those, the 4.30 gears suck.

Do you feel that a taller tire would work a whole bunch better? I could do that, but I would have to swap gears. I could even try slicks, but I do like being able to legally run on the street with the soft tires if I want to.

Thanks.
Dave

[djracer]

I would try a big drag radial.

[dave brode]

Originally Posted by djracer

I would try a big drag radial.

dj,

You feel the DRs are better than the biased ET streets or the biased Hoosier QT pro?

I don't think I can get a 33" tall on it, due to fender lip clearance. I had 33 x 18.5 ETs on it, but one side was really close, so I sold them. Maybe something 31 or 32"

Thanks.
Dave

[KQQL IT]

16 psi in a hoosier drag radial 325/50 15 just shy of 28" tall it shakes a little.

[Marv D]

Originally Posted by dave brode

Hi Marv,

Yes, a dot. Biased. It's the only thing I found that was short. They are a little harder than their smaller "cheater slicks", but still a soft drag type wrinkle wall dot. They also have a 30 x 18"

http://www.mandhtires.com/store.php?...on=show_detail


I went short because it give me more gear. I drive to track on hard 21.5 x 33s. Even with those, the 4.30 gears suck.

Do you feel that a taller tire would work a whole bunch better? I could do that, but I would have to swap gears. I could even try slicks, but I do like being able to legally run on the street with the soft tires if I want to.

Thanks.
Dave

I would and did. My truck is dipping into the mid 1.5x sixty's on a Hoosier 33x17-15 QTpro (DOT) I run a 5.43 gear and trap only 108-109 with the shift light on from 1000' on ( with a a 6200rpm chip ) It's a little hydraulic roller pump gas 383 street toy that I bracket race once in a while. Kind of hard to see in see in this pic but at 11.5 psi it drives out with no shake at all. Rear shocks are Strange steel adjustables @ 50/50 and fronts are cheepie CE's at 60/40. Have had it shake at the top of 1st and the 1-2 shift, but pretty 'slight' usually.

(edit,, woah that was a big picture!!!)

here's a link to a HUGE pic that you can get a decent eye onthe rear tire
This is a back halfed toy w/ Alston's urethane bushed 4link also so what's working for me may not be right for your setup. But the taller the tire the more contact patch with the track. Means you could put more air in it and still have a better contact than you have now. That would most likely cure the tireshake problem,, but empty your wallet considerably. Changing air pressure and shock settings in whatcha got is pretty cheap right now.

again,, just my 2¢

[djracer]

Originally Posted by dave brode

dj,

You feel the DRs are better than the biased ET streets or the biased Hoosier QT pro?

I don't think I can get a 33" tall on it, due to fender lip clearance. I had 33 x 18.5 ETs on it, but one side was really close, so I sold them. Maybe something 31 or 32"

Thanks.
Dave

Radial racing has gotten real popular around here. In some classes guys who can run slicks are running radials. Steve Jackson has ben 4.60's in the eighth on radials. I would try to go to a radial race and pick up a used set. The big guys get a crazy deal and don't put many passes on them. My buddies little camaro that went 1.449 60ft on a 100 shot did that with a set of 40 dollar used radials.

[dave brode]

Thanks Guys,

If I can bum a tow 185 miles, I'll try more air and 60/40 on the front shocks. All the local tracks are done.

I'll be looking at bigger tires. I assume that you guys are talking about radial slicks, since there are no dot drag radials even as big as what I have now.

thanks again.

Dave

[djracer]

I don't think the size is the problem.

This is what I had in mind.

http://www.jegs.com/i/Mickey-Thompso...3757R/10002/-1

[Super73]

I would probably go with the 315/60/15.. It's at least a 30" vs the 28"

[djracer]

I would go to a radial race and buy either size in a take off to try before dropping the big bucks for new ones.

[swb85]

You're not going to fit any drag radial on a 14" wide rim, even with bead locks.

[dave brode]

I'm thinking that I should just buy slicks. 31" or 32 X 14 ish.

Anyone care to comment on biased vs radial in those? Regular of stiff sidewall? Medium compound best?

Thanks guys.

Dave