Cant on DFW

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Speedster
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Cant on DFW

Post by Speedster »

I built a stock 3 wheel rail rider except for using Max V's 4094 axles. The axle was bent 1 1/2 degrees using the 5198 Pro-axle bender. Drift was set at 2" in 4' with Positive cant. Test is started by letting the car roll slowly from the end of the curve of a Best track. This is to see if the right rear wheel stays off the rail. I noticed the DFW appeared to be straight up and down, sitting flat on the track, and the inside rim of the wheel flat up against the entire 1/4" of the guide strip. The time recorded was decent but not outstanding. I bent the DFW axle to 3 degrees and the car was faster.
Do racers set their DFW to 1 1/2 degrees and leave it there?
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LightninBoy
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Re: Cant on DFW

Post by LightninBoy »

Most league racers bend about 5 degrees.
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Re: Cant on DFW

Post by Speedster »

That's very informative and makes a lot of sense. If using a stock axle and wheel there is a lot of slop that has to be accounted for. Since this is a test car I will increase the cant to see what happens. Thank you.
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whodathunkit
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Re: Cant on DFW

Post by whodathunkit »

LightninBoy,
Is this so there's better air flow under the car track side as well or to lower the back end of the car?


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chromegsx
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Re: Cant on DFW

Post by chromegsx »

Probably just becuase that's what they found to be faster with their type of builds through testing.
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Vitamin K
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Re: Cant on DFW

Post by Vitamin K »

We drill DFW cant of about 6 degrees and then put a 1 - 1.5 degree bend in the axle that we use to get the drift.

Here's my theory on why a large degree of cant is desirable for the DFW.

When a wheel is rolling on a surface, you have a much lower amount of friction than if the wheel is sliding against the surface. The tricky part with the DFW is that you have two surfaces to contend with: The track surface, and the side of the rail. Now, the DFW is already rolling over the track surface -- that's good. However, when you come up against the rail, you are exposing the inside edge of the wheel. And, with the slop of the axle, the pressing against the rail causes the inside of the wheel to press flat against the rail..thus giving you sliding friction, instead of rolling.

Putting a large amount of cant on the DFW axle keeps this from happening, and gives you a rolling edge on both the track surface AND the side of the rail, which lets the car roll down the rail instead of sliding down it.

At least, that's my theory. ;)
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Stan Pope
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Re: Cant on DFW

Post by Stan Pope »

Vitamin K wrote:...
At least, that's my theory. ;)
A very good theory! :)
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LightninBoy
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Re: Cant on DFW

Post by LightninBoy »

What VK said!

For me personally, I bend *at least* 5 degrees. There's just so much slop - even some aftermarket axles - that in order for the bend to do what its supposed to do it needs to be a generous amount of bend.

@whodathunkit: the fact that the extra bend lifts the front end of the car slightly is actually a disadvantage. In theory it adds both drag and toe-out in the rear axles. I really haven't seen the issues in practice, but I still compensate for that by drilling the DFW axle hole a smidge higher than the rears.
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whodathunkit
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Re: Cant on DFW

Post by whodathunkit »

LightninBoy wrote:

@whodathunkit: the fact that the extra bend lifts the front end of the car slightly is actually a disadvantage. In theory it adds both drag and toe-out in the rear axles. I really haven't seen the issues in practice, but I still compensate for that by drilling the DFW axle hole a smidge higher than the rears.
LightninBoy Thank you!

So if the front end of the car is higher then the rear
there will be more air that cant be expelled out the back and it will cause what some of you pros call a high pressure zone.

The effect is that it will also cause lift to the front end making the cars FDW very unstable
and will cause slowing of the car as well.

So with the front end slightly lower then the rear
The effect would be a low pressure zone to help stabilize the car and cut down on drag.
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LightninBoy
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Re: Cant on DFW

Post by LightninBoy »

whodathunkit wrote: So with the front end slightly lower then the rear
The effect would be a low pressure zone to help stabilize the car and cut down on drag.
I was with you until this last sentence.

In both cases (the nose slightly higher or slightly lower than the rear), there is extra drag. But in once case (nose higher) there is drag and with it the additional effect of some lift. In the other case (nose down), there is drag and with it the additional effect of some down pressure.
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whodathunkit
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Cant on DFW

Post by whodathunkit »

Thanks LightninBoy!
So when you were talking about drilling the DFW axle hole a smudge higher.
We're you talking about keeping the car level
with the 5 dreg of bend
Or were you talking about dropping the front of the car down by 1/32" also.




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LightninBoy
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Re: Cant on DFW

Post by LightninBoy »

I just try to keep the car level. I don't obsess over it, so when I say "smidge" I just basically error on the high side when lining up the bit to drill the DFW hole.
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whodathunkit
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Cant on DFW

Post by whodathunkit »

Ok I'm with you now Thanks LightninBoy!


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Stan Pope
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Re: Cant on DFW

Post by Stan Pope »

The effect of raising the front end by 0.05" (if the wheelbase is 5") is less than 0.6 degrees. I think that few people would be able to twist an axle in increments of 0.6 degrees or less!

Depending on the bend in the rear axle, the change in the angle between the axle and the car path from such a small change is way less than the 0.6 degrees of car rotation. Here is a way to visualize the quantifying: If the rear axle is bent 2.5 degrees and starts at "top dead center" with the car level, raising the front end 90 degrees only makes a 2.5 degree change in the axle angle relative to the car path.
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