Stetting up a hardtail chassis

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brechlrl
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Stetting up a hardtail chassis

Post by brechlrl » Thu Jun 05, 2014 12:33 pm

I have a Neil and Parks altered chassis from the 80's It has been modified over the years. WB shortened, engine moved forward. Horsepower dropped from 700+ to 500. C-4 instead of a glide.

Chassis was shortened about 10 inches when it as changed form a solid strut type front to a torsion solid axle.. Engine was moved forward about 8 inches to accommodate new engine trans combo . The car came with a parachute and wheelie bars. But I have never even got close to pulling the front. The car is not fast but very easy to drive as it currently sits. Biggest problem is that it is difficult to launch without tire shake.. My thought is it is all out of whack on where the weight is placed and I am not getting weight transfer on launch.. How should I go about getting the thing to work like it was designed? How do you determine where Engine should be in reference to front and rear axles?

Matt@RFR
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Re: Stetting up a hardtail chassis

Post by Matt@RFR » Thu Jun 05, 2014 12:42 pm

I'm far from an expert, but can tell you our 125" hard tail launches decent with 60/40 weight distribution, 60% on the rear. Our best so far (and still deep in the tuning process) is 1.18 60', 8.52 @ 153 MPH.

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Ken0069
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Re: Stetting up a hardtail chassis

Post by Ken0069 » Fri Jul 04, 2014 12:20 pm

If you're getting tire shake you probably need to play with tire pressure up and down to see if you can stop it with that since you can't make more power to try to drive through it. My 225" Undercover hard tail dragster is super sensitive to as little as .5psig of tire pressure one way or the other!!

I'd go down on tire pressure in 1/4 lb increments to see if it stops. If you go a pound and a half or so and it doesn't stop, then go up the same way from your original starting position.

What tire is on the car now?
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alteredu
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Re: Stetting up a hardtail chassis

Post by alteredu » Thu Aug 28, 2014 3:48 pm

Welcome to the world of tire shake. There is a story about Don Garltis writing everything that he found causing tire shake on his trailer door. He ran out of door before he ran out of things that cause tire shake.

The basic cause is that the car is not getting up on the tire soon enough. This can be caused by lack of launch RPM to not enough HP, along with a dozen other things. I would start by having someone video your car leaving the line. Watch the tires load and unload. Figure how far out you are when getting tire shake. You can learn a lot by seeing what is going on and not guessing. If you make changes, then you can video it again and see what the apparent result was.

Frank makes a good car. First, how long is the wheel base, and second how far out is the motor? Second, how much stall is in your converter? What RPM are you leaving at. What tires are you running?

I race a 125” hardtail Altered, a lot more HP than what your running now, but I did run around 700 for years and will be glad to help if I can.

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Re: Stetting up a hardtail chassis

Post by steve316 » Sat Dec 13, 2014 9:52 am

Your tire compound has a lot to do with shake. Too soft you get slip and grabe then shake. It is a controled spin too much = up in smoke; too little = shake. With a hard tail it is about tire pressure & tire compound. tire shake breaks a lot of parts ; good luck with your fix. Steve

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