Weight bias Equation

General discussions for car and semi-truck racers.
Ratrodsrule1
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Weight bias Equation

Post by Ratrodsrule1 » Sat May 16, 2020 11:59 am

Any advanced crash course in left/right/front/rear weight bias other than 2 oz behind rear axle and the rest in front of rear axle ? thanks.......RRR



Eagle
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Re: Weight bias Equation

Post by Eagle » Sat May 16, 2020 12:21 pm

Depends on the car



Ratrodsrule1
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Re: Weight bias Equation

Post by Ratrodsrule1 » Sat May 16, 2020 12:52 pm

Sorry....BASX 4 3/4" WB, right hand steer. .093 axles, 2.4g machined wheels.



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Re: Weight bias Equation

Post by Speedster » Sun May 17, 2020 9:07 am

I have no answer for the question but because of the specs on the car I would like to go Off Topic a bit and ask a couple of questions.

1. Is the 4 3/4" wheelbase because of rules or is it specifically about Physics? If it's about Physics, other then Doc Jobe, who decided this is the best for speed and how was it determined?

2. When something is changed on a Derby car things become different. If the Dfw is set with 1 1/2 degrees Positive Cant with a .093 axle instead of a .087 axle, does this become an advantage or a disadvantage? Either direction, why?



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Re: Weight bias Equation

Post by Ratrodsrule1 » Tue May 19, 2020 3:01 pm

Not the rule but 4 3/4" WB seems to be the weapon of choice of the BASX League racers. But have the weight bias equation in hand now. The .093's take a LOT of slop out of the bore/axle differential making for a more stable car. Set tight gaps and incorporating derlins as part of the set up seems to help as well. Speedster what trio set of PWD scales would you recommend please ? Thanks



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Re: Weight bias Equation

Post by Speedster » Wed May 20, 2020 7:28 am

I have 3 - Triton T2 scales from Maximum Velocity, $19.95. Calibration weight is extra. I have one calibration weight. These scales are not used in workshops or races. They are strictly for back up.
For Workshops and races I prefer the scale from Hodges Hobby house, $29.95. The scale comes with the calibration weight and batteries.


I'd like to comment on the diameter of the axle for the Dfw.
I experienced using a .093 axle for the Dfw actually slowed the car down compared to using a .087 axle. I learned this when I raced in the Mid America race some time ago. I realize this probably is not a problem with scout racing because of most scout rules. I just wanted to let everyone know what I experienced.
A track and timer will show the difference.



Ratrodsrule1
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Re: Weight bias Equation

Post by Ratrodsrule1 » Wed May 20, 2020 2:24 pm

Curious findings Speedster. Did you uncover what attributed to the better speed with the .087 ? I wouldn't suppose it's more stability. Perhaps less friction area or slightly enough height differential that would affect weight bias loading one or more wheels differently or an overall difference in alignment geometry ? Would love to know.......Thanks RRR

Also thanks for the scale info



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Re: Weight bias Equation

Post by Speedster » Wed May 20, 2020 5:15 pm

I believe the .093 causes more friction because the wheel cannot straighten out as much. With only .004 total clearance the wheel is immediately steered into the rail and held in that position. The wheel is now skidding down the track at a greater angle then if it were allowed to straighten out more. With a .087 nail the 1 1/2 degree bend will still hold the wheel on the rail but the wheel is rolling nearly parallel to the rail. Both nails were set with a 2" in 4' drift. That might have caused the problem. Perhaps the .093 nail needs a much longer drift.

I'll see if I can put something together and do some tests. This might be interesting under a new topic.



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Re: Weight bias Equation

Post by Eagle » Wed May 20, 2020 7:24 pm

Testing and a new thread sounds good - Speedster.

Please make sure to let us know if you are testing oil, graphite, or both.

And, it would be really cool to test on the same car with .087, .089, .091, and .093.



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Re: Weight bias Equation

Post by Speedster » Wed May 20, 2020 8:54 pm

I'll do my best.
It will definitely be on the same car.



Ratrodsrule1
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Re: Weight bias Equation

Post by Ratrodsrule1 » Thu May 21, 2020 4:08 am

Great thought Eagle, kudos !! Speedster you're hypothesis makes total sense.....as usual !! Can't wait for your test results. You may have just given me the handful of hundreths needed to run at least mid pack in BASX if not more. I'm as excited as the ugliest girl in school getting ready for her date with the Quarterback.......RRR



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Re: Weight bias Equation

Post by Ratrodsrule1 » Thu May 21, 2020 5:35 am

Speedster the 1.5 degree bend although standard at many levels pales in comparison to the 6 degree bends used at some higher levels. How do you suppose that equates or should be adjusted into the equation. This could become a long thread LOL LOL.......RRR



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Re: Weight bias Equation

Post by Speedster » Thu May 21, 2020 11:32 am

My test is to get the results of a car using a .087 dfw nail and the same car using a .093 nail. I already have the car which is Commodore Perry District legal.
Lube is Hob-E-Lube graphite. I use the car for demonstration at workshops. The tungsten weights are exposed to show the scouts the different shapes tungsten is available. The car's times are very consistent on Lane 1 of my 30' Best track. The car will travel 30' from pin to timer because of the way I set the timer. The car has less then 10 runs on the wheels from Derby Evolution.

I think the value of the results of this test might be to give thought to building a car for a race where different size axles are allowed. Anyone can do the test that has a track and timer available to them. I'll let you know what happens. The rest is up to you.



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Re: Weight bias Equation

Post by Eagle » Thu May 21, 2020 6:11 pm

Speedster if you only use those two I have no doubt you will get your prior result.

I believe you will find as good or better results with 89 or 91.

I don't know anyone who runs a .093 axle with graphite.

Maybe if you have an old larger bore wheel.



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Re: Weight bias Equation

Post by Ratrodsrule1 » Thu May 21, 2020 7:08 pm

Eagle have you had any success with 91's ?



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