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Old 12-30-2014, 11:29 AM   #16
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This site is pretty awesome if you are just using four $10 Harbor Freight scales like I am.
http://robrobinette.com/corner_weight_calc.htm
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Old 12-30-2014, 11:39 AM   #17
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Originally Posted by funked1 View Post
This site is pretty awesome if you are just using four $10 Harbor Freight scales like I am.
http://robrobinette.com/corner_weight_calc.htm
I use that all the time when setting up a new ride.
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Old 12-30-2014, 02:46 PM   #18
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Originally Posted by Kraig View Post
So lets take this one step further in our discussion as I think it will help a lot of people.

Chassis, to the best of our knowledge is not tweaked but how would you verify?

The first thing I do is check chassis tweek. If the chassis is twisted, and you can't get it out, and it's the middle of a race day, it's not the end of the world. But the car is never going to be as "right" (which means it's easier to work on) than it will if you got it square to begin with.

You can check chassis tweek by setting the car on setup blocks, on the screws where the front and rear suspension mounts pass through, and then see if the car lies dead flat or "rocks". If it rocks, it's not square and you need to try and get it straight before you move further forward.

In order to untweek it, you are going to need some tools. You can buy something to untweek the car that's really fancy like this:

http://www.redrc.net/2014/06/zen-rac...is-tweak-tool/

Or, you can home brew something. My "home" rig is a piece of 1" x 2 1/2" x by 13" billet aluminum remnant stock I got from a local industrial stainless and aluminum company and the biggest anodized aluminum knitting needle you can find at Hobby Lobby.

(This space reserved for a picture of my $7 setup when photobucket stops being a grump)

At the track, I just use my setup board and the knitting needle because I don't want to haul around this block and my Marc Reinhart setup board is already pretty robust.

At the track, I check it on setup blocks between rounds.

My standard setup regimine is:

- Check/fix chassis tweek
- Set droop (I usually use 20mm blocks and an off-road 20-30mm ride height block, but can use a steel rule and my eyes)
- Put race tires back on in their appropriate wheel positions (I mark my tires in sets, never seperate them and never rotate them) and set the ride height.
- Check cambers and toe, recheck/set ride height.
- Put the car on the scales and see what the L/R, F/R, and split weights look like. There is a way to get the car unwedged/us tweeked without scales using an exacto knife. If you KNOW the car is 50/50 left and right, you can pick up one end with the exacto knife and see which tire comes up first.
- The way you adjustment you make to fix it is remove a small amount of preload the shock DIAGONAL on the chassis to the heavy tire, and add the same amount to the DIAGONAL tire that is light. That way, the ride height isn't disturbed, but you fix the split on the other axle.

Real life MBA case study problem:

The RF and LF tires weight the same. The RR is 30 grams heavier than the LR.

Solution:

Add 1/8 of a turn to the RF (taking weight off the LF and RR, moving it to the LR), remove 1/8 of a turn from the LF (adding weight off the RF and LR, reducing weight on the RR). Recheck and do it again till you are happy.

If I get the car within a couple of grams, I usually quit. If you bump a curb, a board, or another car, it's going to be wrong, especially if you use a plastic chassis car.

Important note:

The above mentioned car is not exactly 50/50 left to right, the math indicates it's 30 grams heavier on the right side. Assuming the car isn't 30 grams underweight or have 30 grams to be relocated, it's probably never going to be. The best you can do in a situation like this is get the cross weights equal (LR+RF = RR+LF) and hope all the high speed sweeper corners are right hand.

IMO the f/r bias is more important than the l/r bias. Moving the weight forward and backward on the chassis has a far greater effect on the car having appropriate handling characteristics getting in the corner and making grip off the corner (slow corners) than having the car be exactly perfect left and right.
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Old 12-30-2014, 03:08 PM   #19
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After posting, I found this older but still valuable article via X-ray. If you got this far, you should take three minutes and read it. It's clear, concise, and has pictures.

http://www.teamxray.com/teamxray/sho...p?file_id=2919
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Old 12-30-2014, 03:37 PM   #20
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Quote:
Originally Posted by Kraig View Post
Chassis, to the best of our knowledge is not tweaked but how would you verify?
Put the car on droop blocks, or directly on the setup board if you don't have battery tape / screws protruding. Make sure it doesn't rock at all. If using droop blocks, you can put a finger on each end of the block and rotate it under the car, to feel where it wants to rotate around. If the chassis is flat, they'll both feel like they're rotating around the middle of the car. If the chassis has a slight tweak, you'll be able to feel the front block rotating around one side of the car, and the rear block rotating around the other side. If they're both rotating around the same side of the car, that side of the car is heavy.

This should be done with battery in, and with a clean setup board, and clean bottom side of the chassis.

Note that many modern TC's have so much flex that they will sit flat on the board / droop blocks, but can still be holding a tweak or uneven flex, which will show up on track, and possibly when the sitting on the tires.

Quote:
Originally Posted by Kraig View Post
Body installed
Left and right relationship is how you would be sitting in the car.

I believe my car is ready to race so I scale it. I find that I my left rear has 1 ounce more than the right rear. I find the right front is 1.5 ounces lighter than my left front.

Where do you start to get the same amount of weight across the rear tires and also the front tires?
So, you've got the right front and left rear that are heavy. This is an indication that there's a suspension tweak, and is exactly the situation I was referring to when I said that scales don't tell you which end is tweaked. It's also the situation you can resolve by putting one end of the car on droop blocks (stacked up to match height of the scales as much as possible) with the other end on scales. Tighten the spring on one side while loosening the other side by the same amount, until the weights match. Repeat for the other end of the car, and then re-measure with all 4 wheels on the scales.

This of course assumes the car is balanced left to right. If the car isn't balanced left to right, then you may be able to get left and right to read the same with two scales and blocks, but when you put it back on 4 scales, one side will read heavier on both ends, and the ride height on side of the car will likely be higher. I don't really have experience in what's the best way to set things if the car isn't balanced left to right, because I've only run Mi4's with the motor clamp that makes left/right balance easily adjustable, and Xray T4s which have always balanced well with my electronics.

Also note that a mis-adjusted swaybar can cause a suspension tweak. If you're seeing a lot of tweak, it's worth disconnecting the swaybars to see if it's coming from the springs or the swaybars.

-Mike
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Old 12-30-2014, 04:17 PM   #21
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Quote:
Originally Posted by grippgoat View Post

Also note that a mis-adjusted swaybar can cause a suspension tweak. If you're seeing a lot of tweak, it's worth disconnecting the swaybars to see if it's coming from the springs or the swaybars.

-Mike
Generally, the sway bar shouldn't ever get bent if you went to the trouble to get the preload (tweek) out of it when you built it. Anytime I have the shocks off, I always try to check this because you never know.

Everything else you wrote is correct. I think.
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Old 12-30-2014, 06:31 PM   #22
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This thread is getting GOOD!!!!

Started offroad March 2004, added onroad May 2014 so this tweeking is some what new to me.

Know the blade tweek bit had a AE 12L (white chassis), have a 18" x 24" floor title as a setup board and now four $8 scales from ebay.

The Xray info is a GREAT read!!

THANKS!!!!!!!! :-)
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Old 12-30-2014, 07:08 PM   #23
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Originally Posted by tmail55 View Post
This thread is getting GOOD!!!!

Started offroad March 2004, added onroad May 2014 so this tweeking is some what new to me.

Know the blade tweek bit had a AE 12L (white chassis), have a 18" x 24" floor title as a setup board and now four $8 scales from ebay.

The Xray info is a GREAT read!!

THANKS!!!!!!!! :-)
You can still set tweek with a hobby knife. Just make sure if the car has the same tweek left and right. That is, if you are tweeked a little to the left front, make sure the left rear has the same amount.
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Old 12-31-2014, 07:50 AM   #24
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So important and so simple!!!!!

grippgoat

>>>> a clean setup board, and clean bottom side of the chassis. <<<<

CraigMBA

>>>> If you really want a steering lock, turn the transmitter and the car on. <<<<

"It's the little things that makes a Difference" Stan Brower
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Last edited by tmail55; 12-31-2014 at 08:12 AM.
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