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Author Topic:   Tires blow loose on straightaway.
imca01
Dirt Roller

Total posts: 18
posted October 12, 2005 09:03 AM  
Car is hooked up off the corner, but at about the flagman it blows the tires loose. 4-Bar car, spring pull bar with 1050, pre-loaded at 5/16". Any suggestions on a cure.
THANX.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted October 12, 2005 09:26 AM  
How much downhill angle do you have in the pull bar. Too much will cause this. With a low HP application it actually helps to have more Downhill angle, but the Higher HP you're going to have to compensate and give up a tad off to keep your traction going down the straight.

imca01
Dirt Roller

Total posts: 18
posted October 12, 2005 10:53 AM  
If memory serves me correct I think about 18-20 degrees. Is this excessive? Is there a way to keep the forward bite off the corner and maintain it down the straights? What would a spring change or pre-load change do? I've been fighting this problem for a while. I understand every driver is different but, is there a set rule of thumb that you can go by. Thanx for the reply.

Fastride 38
Dirt Maniac

Total posts: 125
posted October 12, 2005 11:16 AM  
You may also have to much pinion angle also. I have had a few nights that would happpen and I took some pinion angle out and it went away. It seems to bite really hard at first then would just go to spinning the tires. When I took some pinion angle out it seemed to gradually gain bite as I got deeper into the throttle.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted October 12, 2005 11:52 AM  
For a 4 link car, I'd start at 15 Degree's.

You can also check pinion angle like Fastride said. Pinion angle really doesn't play that big of a factor as it does on a 2 link car.

How much travel are you getting out of your pullbar spring? You could be bottoming it out right at mid straight and in turn breaking the tires loose. You might consider going to an 1100 or even a 1200 if you feel like playing around. Also make sure your 90/10 shock (If you run one) isn't fully extending.

imca01
Dirt Roller

Total posts: 18
posted October 12, 2005 12:15 PM  
I'm getting aroung 2 1/2" of pull bar travel. We do not run an axle dampner right know but are thinking of trying one again. I will also check pinion angle, thats one thing I over looked. Also, thought of stiffening the spring to see if that helps.I was not sure if it would hurt forward bite off corner or not. Thanx guys for the info. Any thing else you want too add feel free.

ukandesperate
Dirt Full Roller

Total posts: 45
posted October 12, 2005 12:16 PM  
just out of interest,why does pinion angle make any difference to bite,and why more on two link than four??

wfoondirt
Dirt Forum Champ
Total posts: 505
posted October 12, 2005 01:09 PM  
Gains/losses related to pinion angle changes are the result of geometry changes, not a direct effect of the actual pinion angle. Anytime a linkage is solidly attached to the axle housing pinion angle affects the geometry.

On a two link it affects the mounting location of the trailing arms. Thus changing the geometry. Where on a floated suspension (ie 4bar) it is not affected.

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted October 12, 2005 07:10 PM  
2.5" of travel is about right. Make sure that your not running into coil bind like was stated above. Whenever you put a stiffer spring on the pull-bar it will provide more "instant" traction but lose it quicker down the straights. So you problem might be too much preload...... normally a 1050 spring is a good starting point so what I'd do is decrease the preload to 1/4" and take some angle out of the bar, like down to 15 degrees like said above. Then try it and see how it does.

imca01
Dirt Roller

Total posts: 18
posted October 13, 2005 06:01 AM  
Thanks for all the help. Will try a few adjustments this weekend and see how it works.

chapa73
Dirt Maniac

Total posts: 169
posted October 13, 2005 12:36 PM  
I would look at the lower link angles,I had the same problem,had both lowers at about 15* uphill,made the lr about 10* and the rr level and the problems went away.

Sweeney21
Dirt Roller

Total posts: 5
posted October 15, 2005 11:23 PM  
When you take the 90/10 shock off what are the changes to the cars handling and do you change any thing else when you take it off?

imca01
Dirt Roller

Total posts: 18
posted October 16, 2005 06:26 PM  
Took a little angle and preload out and actually put my 90/10 shock back on and car had good bite off and all the way down the straights. Thanx for all the input.

marktires
Dirt Roller

Total posts: 7
posted October 16, 2005 07:42 PM  
quote:
Originally posted by Sweeney21:
When you take the 90/10 shock off what are the changes to the cars handling and do you change any thing else when you take it off?

Leave the 90/10 on kyle


FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted October 17, 2005 04:12 PM  
quote:
Originally posted by Sweeney21:
When you take the 90/10 shock off what are the changes to the cars handling and do you change any thing else when you take it off?


The car will be more free on entry. I do not run a 90-10. I took mine off because of the way the mount was built, it was hyper-extending on accel, and to change the mount to make it work would be a lot of work. My car runs just fine without it. It can cause rear-wheel hop under braking thou. Fortunatly my car doesn't have this problem. There are really no other adjustments you will have to make when removing the 90-10. But it will loosen the car on entry and can cause wheel-hop, so you can try it and see how it works for you but if your not having problems with it now then your probably going to want to leave it on.

Oh and just so you know, NO I have never thrown a driveshaft without it.

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