DFW behavior

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frontosacam311
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DFW behavior

Post by frontosacam311 »

On a RailRider w/ front positive cant does the DFW ever slide on the outer fluted/beaded area of the rim where it contacts track? Also wondering if this wheel manages to straighten out regarding toe and is oriented parallel to the rail transferring the toe angle to the wheel/ axle slop while still steering the car into the rail? If it does slide at all should the tread be slickened up but if so can being too slick be of detriment? Oww my head hurts now :scratching: :idk:
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Stan Pope
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Re: DFW behavior

Post by Stan Pope »

Here's some "aspirin" and some "hair of the dog":

The toe-in on the DFW is in the vicinity of 0.4 degrees (IIRC). So, a 1.18" diameter wheel would, if not constrained by the rail, move toward the rail 0.007" for every inch of travel down the track. Since the rail is in the way, the wheel slides on the track 0.007" for every inch of travel down the track.

On a typical Piantedosi (28' start to finish) the wheel slides 2.35" sideways during its 336" run!
On a slightly longer Freedom track (about 30' start to finish) the wheel slides a bit more.

If the DFW is displaced from its axle's angle, then the sliding distance will be less.

(Note - according to http://www.stanpope.net/driftcomp.htm, the toe angle for 4" drift on an 8' test ramp for a "stock" wheelbase is about 0.25 degrees, so the sliding distances would be about 1/2 what I computed above.)


One theory says that the DFW rides close to the car body and a bump (irregularity) in the rail can cause the wheel to push out on the axle without disturbing the direction of the car. This isn't always true, in fact, it might seldom be true. I think that if the car's front end is light and the camber of the DFW Axle is too great, then the bump will displace the front end of the car as well as the DFW.


The total sliding distance of the tread edge on the rail is more complicated to compute. The sliding direction depends a lot on where the wheel contacts the rail. And the contact height depends on both the toe and camber angles! The lower it contacts the rail, the better! Still, the total sliding distance is a small fraction of the total track length.


Since energy loss is the product of the coefficient of friction, the force between the two objects, and the distance of the slide, it is important to keep the sliding distance small but still maintain control of the car.
Stan
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frontosacam311
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Re: DFW behavior

Post by frontosacam311 »

Thanks Stan, ton of good info in there.
If I'm understanding correctly having the DFW axle say a thousandth less than normal diameter may reduce the total distance of slide. Also to error on the side of having the tread grip rather than too slick may reduce the amount of side to side movement therefore reduced total distance traveled. For the inner rim surface, having that slick as possible would also seem wise. Now to test what substance to use for an oil car, maybe pure silicone or teflon worked in real good on the inner rim, rather keep graphite off the wheel if at all possible(unless it was an unpowdered graphite that wouldn't shed).
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Re: DFW behavior

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I'm not sure that I concur with your conclusions ... perhaps someone can make direct observations and give you the "straight skinny."
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frontosacam311
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Re: DFW behavior

Post by frontosacam311 »

Track testing would definitely help.
Let me try and explain my logic and hopefully I can learn something in the end.
"If the DFW is displaced from its axle angle sliding will be less"- I figured a slightly smaller axle would achieve this.

Figured having tread with more grip than slickness would result in a straighter line by keeping wheel planted on the rail and less side to side movement.

Not really sure what to use to slicken up the inner rim but that should be a pretty straight forward test for me when I get to testing again. I'll be sure to chime in and share any results, you've been very instrumental in my quest for speed.

Now it's break time- gotta keep that blood sugar maintained or I'll really end up in left field LOL
Thanks again
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Re: DFW behavior

Post by Speedster »

My Mid America car was set up with .093 axles. It was given a drift of 2" in 4' and the time was recorded. The DFW axle was then changed to a .091 axle and set up with a drift of 2" in 4'. The car consistently ran faster with the .091 axle no matter how I adjusted the angles. If I'm understanding this, due to the close clearance of hub to axle, the .093 axle wouldn't allow the wheel to "straighten out" and the wheel had more slide.

frontosacam311. Yes, on my machined 1.169 wheels, the DFW wheel rides on the beaded edge. If you put the 1.169 wheel against a stock wheel under a bright light you can see the difference in the beading. When I run my finger tips across the tread area of the 1.169 wheel I can feel the beads. When I do the same to a stock wheel it is perfectly smooth. On the DFW wheel I take a piece of 2000 grit wet paper and very gently sand the outer beaded edge. I have never used a 1.180 machined wheel so things may be different with that wheel.

I've just been told to lube the inside edge of the DFW with graphite and do it before using the oil. Clean the wheel so there are no flakes.
Last edited by Speedster on Tue Dec 10, 2013 7:54 pm, edited 1 time in total.
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frontosacam311
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Re: DFW behavior

Post by frontosacam311 »

Thanks for the advice Speedster
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