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Old 06-10-2006, 12:50 PM   #1
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Default Tweak and ride height question.

Im having a little problem with the concept of tweak, i know i should search for the topic but given the tweak search string too many non results appear that are irrelevant. But if there is a relevant topic please redirect me.

This is my understanding so far, tweak occurs when the chassis is bent or twisted. This sets of the balance of the car. If there is a tweak then your car will then to steer always steer one way when going straight.

To compensate for this you use the shock preload collars or the swar bar length to adjust the balance.

1) Is my understanding of this correct?

2) But heres another problem, to adjust the ride height you also use the shock preload collars. So when adjusting for tweak you are also changing the ride height of your car. which property should take presendence in the final setup?

3) Right now im using a tweak station to adjust for the tweak, but my rideheight is all over the place (1mm different from left to right). Also the chassis has minmal tweak (<0.1mm on the rear right) as i have checked this with a setup board. Is the ride height difference normal?

4) My car goes straight (with no steering input) for a while then veers left slowly, is this a result of tweak?

Any help is appreciated.
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Old 06-10-2006, 01:15 PM   #2
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that could be a tweak... when checking my tweak i dont really like messing up with the preload..what i do is unscrew mostly the top deck if you had a 2 deck car...then twist the chassie back and for slowly enough to release the tension,then put it in a flat surface and scre them back(i usually take the tires when im doing it) mostly it will be fixed.. but if still off on your tweak station try checking your droop if they are even..then go check if your chassie is balance...use a hudy chassis balancing tool...it works... then if still have problems then unscrew the lower deck mybe the bulkheads are binding (if you have bulkheads).....if still does just go buy another one..
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Old 06-10-2006, 01:43 PM   #3
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I'd get the car off the tweak station and recheck your steering setup, that sounds like nore of the problem. As for the tweak stations, you'll drive yoursellf nuts trying to get a perfect balance. The only thing I use mine for is my pan cars, I don't bother putting my TC's on it.
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Old 06-10-2006, 02:00 PM   #4
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thanks for the response guys.
I do have a balance tool but i dont think i know how to use it. This is because i always manage to balance the chassis but the chassis is tilted on the balance tool but not touching ground. Also do you need to have a 50/50 front and back weight distribution (out of curiosity?
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Old 06-10-2006, 02:08 PM   #5
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Default Tweak

If your car handles a bt funky, check your droop settings at all 4 corners.
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Old 06-10-2006, 02:24 PM   #6
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not really to be that prescise... just about the same weight... put your chassie on the top of the balancing tool make sure left and right has the same space or height from the table then let go of the chassie if it falls on the left side.add like 5g on the right then do the same procedure..untill you can actually has it balanced on the top of the tool with the tire at the same height away from the table.or setup board..mybe while your adding weights just also balance the weight add mybe a couple of g on the rear too not just the front...
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Old 06-10-2006, 05:14 PM   #7
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I've also noticed that if you can't get the tweek out by taking the tension out of the top plate, try doing the same thing with the shock towers. Make sure you take your tires off and put the car flat on the setup board.
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Old 06-10-2006, 05:17 PM   #8
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I forgot to mention to push down in the middle of the shock tower when you tighten it back up.
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Old 06-12-2006, 08:01 AM   #9
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I like to look at it as there are two different types of tweak.

I refer to the first one as 'chassis tweak', where the chassis becomes twisted and you have to loosen either, or both, the top deck and/or the chassis mounting screws from the bulkheads.

I refer to the second one as 'spring tweak', where there are slight differences in spring height and/or length of the ball ends (where the lower collars settle onto them) between a front or rear pair of shocks.

Even with zero chassis and spring tweak, here are a few things that I've encountered myself that can throw off the readings on a tweak board:

* Uneven shock lengths
* Bent hinge pins (or even the screws for their suspension holders on an XRAY)
* Bent bulkheads
* Mis-aligned shock towers, where there is a little play between the mounting screws and the holes in the shock tower
* Major differences in static weight distribution at either end of the car

I've described how I correct both types of tweak in the Pre-race Alignment & Setup Tips section of the XRAY forum Tech Articles thread. Currently I use the Hudy tweak station for step #9.
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Old 06-12-2006, 10:27 AM   #10
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Random Task - A chassis that twists and can be straightened by loosening screws makes for unpredictable handling. The handling will change in a small crash. I fixed this problem on my JRXS by loosening all the screws that hold the top and bottom plates in alignment and putting blue Loctite under the heads. This creates a nice pin in the head area when the Loctite hardens. The problem was completely solved.

If you grab the front and back of the car and give it a twist and you hear a little creaking sound and then the tweak on the tweak station changes, this is a sign that things have gotten loose and need correction.

I set the ride height on three corners first. This should remove the uneveness you see in ride height left to right on the tweak station. When you remove the tweak on the tweak station the spring collars need only be moved a small amount. If you screw down the left front collar you can unscrew the corresponding right front collar the same amount. This will keep the ride height relatively the same. If you have to do a lot of adjustment you have one of two problems. The chassis is permanently twisted, try to correct this problem, or the weight is poorly placed in the chassis. Try moving weight to the corner that required the most down adjustment on the spring. I use scales to get the weight right on kit assembly, but you can balance the chassis on Xacto knive blade tips and get similar results.

Tweak causes better steering traction in one direction and poor steering traction in the other direction. The car can go quite straight on a straght section.
Here is a post on this Web site with more discussion of this.
http://www.rctech.net/forum/showthre...s-#post1977808
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Last edited by John Stranahan; 06-12-2006 at 10:38 AM.
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