Anyone running the MT PBR 32x14 on a bracket car running low 5's or quicker 1/8 mile? I've been trying to get them to work and I have an issue with the car rocking side to side like a boat. It happens mid track and later and gets really sketchy sometimes. I've ran from 9-12lbs of air in them and moved shock settings with no real difference. I'm going to try a different 4 link setting that is a little more traditional radial setup. Any thoughts on how to stop the rocking / wobble?

I don’t know how true it is, but from what I’ve read about radials, you are a good five to six pounds too low on air pressure.

I tried 13 and it blew the tires off instantly, so I'm going to try a 4-link setting that will drive the tire into the track so I can try going up in pressure. At 12 psi seems like the outer edge is not really on the ground but they are kink of build that way it seems like.

Our car did that once real bad. Not with PBRs but it turned out to be a bent wheel. Jack it up and setup a gage and make sure wheel is running true. Ours was bent just a little and it made for some sketchy runs.

May have got bent mounting the tires.

Have you checked your tire gauge lately against another "known good" unit?

I have a friend with a set of the big radials he couldn't make work, went to bias tires, couldn't make them work, checked gauge and it was reading about 8 - 10 p.s.i. low, set tires with good gauge, it has printed tickets since.

It didn't do it with the bias tires on them but I do have another set of wheels I could try. They are beadlock wheels.

quote:

Originally posted by ski_dwn_it:
Our car did that once real bad. Not with PBRs but it turned out to be a bent wheel. Jack it up and setup a gage and make sure wheel is running true. Ours was bent just a little and it made for some sketchy runs.

May have got bent mounting the tires.

I have 3 gauges all read within .1 psi of each other.

quote:

Originally posted by Goob:
Have you checked your tire gauge lately against another "known good" unit?

I have a friend with a set of the big radials he couldn't make work, went to bias tires, couldn't make them work, checked gauge and it was reading about 8 - 10 p.s.i. low, set tires with good gauge, it has printed tickets since.

I talked to Mickey Thompson today and the guy asked how they balanced. They took 15oz on one and 8 on the other, he said that is way too much. I don't think that is a factor as it's not a vibration but more a wobble/rocking. Also said at my weight start at 8psi and go up until the 60' slows then back down one step.

quote:

Originally posted by inferno camaro:
It didn't do it with the bias tires on them but I do have another set of wheels I could try. They are beadlock wheels.

quote:

Originally posted by ski_dwn_it:
Our car did that once real bad. Not with PBRs but it turned out to be a bent wheel. Jack it up and setup a gage and make sure wheel is running true. Ours was bent just a little and it made for some sketchy runs.

May have got bent mounting the tires.

Ours started after a tire change. Assuming the mounting bent them or because it was dead hooking it did something to the wheels and bent them.

Got new wheels and same tires - perfectly smooth sailing.

Its easy enough to check. Jack car up have someone put it in gear. Rig up a stand with a screwdriver close to the wheel and if its moving in and out at all - that is your problem. Its shifting the weight of the car back and forth and it gains momentum and violence as it does it.

If that shows good runout, see if the tire itself. I would expect some on the tire, but not the wheel. If its excessive on the tire it might cause it.

I'll give that a try.

Mine did that same thing with that exact tire. 3200# nova then running 9.25@144 scared the crap out of me. Had them rebalanced and swapped to other sides of the car….no diff. Put new 3074s back on and car was perfect. Good luck

Forgot, also tried 18# 16# 14# 10#. Nothing worked.

I have a buddy fighting this right now with Hoosier radials on his lightweight Vega. I think he's had 3 different sets on there.

New set of them mounted going to try them this weekend. MT wanted me to try another set because it took so much weight to balance the 1st set. Don't think it will help but I also set it up more like a radial car. I'm going to try from 7 to 15 psi in the tire. I really think it needs less air than most are running just because of the weight of the car but we'll see this weekend. This will make or break me on my radial experiment.

quote:

Originally posted by inferno camaro:
New set of them mounted going to try them this weekend. MT wanted me to try another set because it took so much weight to balance the 1st set. Don't think it will help but I also set it up more like a radial car. I'm going to try from 7 to 15 psi in the tire. I really think it needs less air than most are running just because of the weight of the car but we'll see this weekend. This will make or break me on my radial experiment.

How did the runout on the wheel look?

The beadlock ring moves slightly but the wheel itself looked good.

I like racing against Justin; he's one of the best! I've been fortunate enough to have some close/great races against him. I always look forward to racing him & learning.

2BKING

^^^^^ Justin has some interesting advice and especially liked what he said about converters and carburetors. Because of that advice I’m leaving the rear bias tires on longer than when I normally would change.

Took the car out tonight. 4 link change, new set of the same tire took way less weight to balance than the 1st set, car has Penske 8300 piggyback shocks that have 75 clicks on rebound and 22 on compression. I set them at 35 from tight and 11 from tight so basically right in the middle of adjustment. 1st pass kept the timing pulled out of it to make sure it launched straight after 4 link change. I started at 8psi 1st pass. Car went straight 2 small wrinkles in the sidewall, ran 5.07 @ 137 maybe a very slight wobble, DS graph looked very good. Added timing back in left everything else the same went slightly left 5.06 138 graph showed slight spin no wobble. Next pass went up to 10psi no other changes 5.039 138 carried the wheels about 50' 4-5" off the ground no wobble DS graph looked really good. Next pass went up to 12psi slightly higher wheelie to about 60' 5.039 @ 138 .0002 from previous pass no wobble, graph had a couple little spikes down track. 5th pass went down to 11psi and added 500 rpm to the launch, too much wheelie 8-10" off the ground to about 100' no wobble 5.033 @ 138. I'm not sure which change worked but so far so good. The proof will come tomorrow on race day. This track is normally down 1.5-2 mph and .02-.03 from most tracks, runs a little up hill. Different track tomorrow. Fingers crossed it works as well as tonight.

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