Front End Shimmy

Hi, all. This is my first post and want to say hi to everyone. Bought a Unique Cobra a month or so ago (#4279477) :) and have spent most of the time getting the bugs out of it (even though the previous owner said it was "perfect"). It has a Southern Automotive 406 in it and seems to run OK after I re-jetted it. I'm at 5500 feet just outside of Reno and the car came from Georga, near sea level. I do, though, need some advise. I've had all four wheels balanced (they were all off a little with one being way off) but I still have a front end shimmy at between 55 and 60 mph :doh:. Could it be alignment and not just balance? Any experience in this area would be appreciated. I'll attach photos when I learn how to do it.

Welcome to the forum. More than likely it is a balance issue, you might have to put weights outside the wheel and not just on the inside, that is the only way to totally balance your wheel. You might want to check to see if the tires are flat spotted from sitting in one spot too long, this will also cause a shimmy.

Alan

Could very well be the tires, even thought they balance up they may have excessive road force variance. See who has a balancer in your area that can check for road force variance. You can go to the the Hunter Mfg. Site and they will list where the machines are. Anything over 20-25 is really not exceptable on the steering tires (front).

Scotty, it's likely the tires. I have a local shop do my alignment and balancing that is precise beyond the typical tire store. They've had to spin my new tires on the rims to get them to balance half way decently. They also spin the tires on the car after the machine balance to get the last little bit of vibration worked out. Makes a big difference.

Thanks for the feedback guys. I had the balancing done at a shop in Carson City who used the good Hunter machine. They had to dismount, rotate the tire, and remount it before balaning the tire to get it into spec. May have to replace the tires to get rid of the vibration. Have BFG radial TAs on it now but, after doing some research, may buy some Yokohama Avid S/Ts (235x60x15/295x50x15, that is if I can find them. I heard they are no longer being produced but are still around. Any comments?

Most of your problem is probably the BFG tires. I had two sets and it was impossible to keep them balanced. Switched to the Yokohamas about four years ago and they have been flawless but alas, they (Yokohama) are pretty much out of the 15 inch tire business for cars like ours. The selection of tires available is getting smaller and smaller.

Mickey Thompson is making tires in those sizes now. Local guy here bought their S/R Radial tires and loves em.

http://www.mickeythompsontires.com/street.php

Anybody running the Firestone Indy 500 tires? The consumers ratings seem to be better than most others.

http://www.tirerack.com/tires/survey...ireSearch=true

Tony ran the Firehawks for awhile... he'll pop in sooner or later to comment.

Decided to bite the bullit and buy new tires to try to solve my shimmy problem. Just had a set of Cooper Cobra tires (245/60-15, 295/50-16) delivered to my door for $425. Heard that Cooper was out of the 295's and weren't planning on making any more for quite a while. Thought I better get a pair while they were still available. Anyone wanting the website, just ask. I'll have them mounted and balanced next spring. Have a nice winter guys. Scotty

My advice is Mount and Balance your new tires right away.
I'm sure others have had this experience as well, but it's not uncommon to have brand new rubber that is so out of balance or defective that they cannot be balanced properly.
Bought a brand new trailer (C rated tires) and two of the four needed so much weight my tire man said he wouldn't put that much weight on the rims to correct the wheel shake. Guess what - four new tires from same manufacture and it tracks straight as an arrow now. It happens.

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Originally Posted by arrowdriver

Anybody running the Firestone Indy 500 tires? The consumers ratings seem to be better than most others.

http://www.tirerack.com/tires/survey...ireSearch=true

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They are ok . A little shimmy at 60-70 range. Some auto crosses and they are now crap. Will not buy them again.

We spend a lot of money on our cars so I say put some money in our tires. The big problem is no one makes a quality "street" tire for 15' RIMS. I am thinking of buying Avon DOT tires from Krause racing or Goodyear drag radials. Haven't heard any feedback in those yet. Heard guys running the Goodrich drag radials with great results. I am interested in the Mickey Thompson's SR but have not heard any feedback on them being run on a Cobra. Avons get great feedback from Cobra drivers. I have a set of Goodyear Billboards and they look great but are bias ply and until they are heated up are not very pleasant. I also have a set of Goodyear blue streak slicks. Awesome awesome awesome but they are racing slicks and are not good for everyday street driving. Very lightweight and absolutely no shimmy.