Grooves in wheel bores?

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davidwilkie
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Grooves in wheel bores?

Post by davidwilkie »

I was searching for something and came across this:... http://hubpages.com/sports/WinningAPinewoodDerby

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...which suggests putting grooves in the wheel bores to retain graphite. Goes against all the polishing strategies my boys have ever done and so I was curious if anyone has any thoughts on this idea? Rubbish or is there merit to the idea? Execution would seem difficult!
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Scrollsawer
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Re: Grooves in wheel bores?

Post by Scrollsawer »

I would lean toward rubbish. Lots of posts here that seem to indicate cars with well administered graphite run quite well 'as-is' for 4-6 runs (which is the duration of most all Pinewood Derbies.

And the author wants folks to apply a "hot screw" to the wheel bore?!? :jawdrop: Yes, I'm going to say it now: Don't do it; It's bunk until someone can prove otherwise."

Theoretically, even if you did get some minuscule graphite retention improvement, as evidenced by lack of speed reduction over more track runs (e.g., 7-10 runs), the risk of trashing your wheel bores far outweighs any minor benefit (which I highly doubt exists), and again, the race would likely be over by runs 4-6 anyway, depending on the number of lanes on the track.

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Gtdhw
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Re: Grooves in wheel bores?

Post by Gtdhw »

I had this come up in my mind a few days ago as well. My thinking on it, was tapping the hub, not burning it though, lol.

I was thinking that it sounded plausible, by threading the bore, it would reduce the axle/hub contact area, that it would allow pockets of graphite, and that if tapped in the right direction, it could aid in getting the wheel to walk to the axle head.

I contacted one of the members here about this/if anyone had experimented with it. Just as I was hoping, he had, and never got good results out of it. His explanation was, that in his testing, it created more concentrated friction and made the graphite less effective. I fully trust his experience, and moved on from the idea.
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Speedster
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Re: Grooves in wheel bores?

Post by Speedster »

We used to run a tap in the bores many years ago thinking it might make a straight bore and possibly remove any imperfections. We had success in our races but I don't really know if the tapped bores helped us. We haven't tapped the bores for many years but with the new tracks and timers it might be fun trying some tests. I have a feeling if it was beneficial the Vendors would be offering it.
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Vitamin K
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Re: Grooves in wheel bores?

Post by Vitamin K »

Grooving axles or wheels is a topic that holds a bit of curiosity for me.

Mathematically, a groove shouldn't reduce overall friction, since friction is not dependent upon surface contact area. What it does do, however, is concentrate pressure onto a smaller surface.

From what I know of graphite, it works best under a lighter load. That's why an unloaded graphite wheel will spin for a lot longer than an unloaded oil wheel. In fact, the graphite-lubed car feels 'looser' than an oil lubed car. Where the graphite starts to fail, however, and the oil starts to shine, is when there are higher loads and higher speeds. Some folks have reported that, when the cars they ran were lubed with oil, the graphite cars would actually be ahead on the slope, but fall off faster down the flat.

So, back to grooving. All the pros say grooves are faster. And, almost universally, all of the pros run oil over graphite. So, my unscientific theory is that grooves are beneficial to an oil car, because they create a higher pressure contact point, which the oil excels with. For graphite, I don't think grooves will help.

Also, as far as the 'lubrication reservoir' thing goes, I think that's hooey. Graphite wants a thin film of only a few molecules thick to work. I can't imagine that pockets of extra graphite will help there.
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whodathunkit
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Re: Grooves in wheel bores?

Post by whodathunkit »

Speedster you have been at this for a good long while haven't you!

Seem's to me that taping the bores would be a auger affect for the graphite to be dumped as the wheel spins around the axle.


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Speedster
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Re: Grooves in wheel bores?

Post by Speedster »

You're probably right. Heaven only knows what was going on inside those bores.
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whodathunkit
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Re: Grooves in wheel bores?

Post by whodathunkit »

Well Speedster,
Here is more reading on grooves in the wheel bores that i came across.
http://www.google.com/patents/US20120187748
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Re: Grooves in wheel bores?

Post by Scrollsawer »

Okay, I see the patent, but I'm still not buying it. There are no empirically derived facts in the patent document that point to a measurable performance improvement. Reduced bore surface area doesn't reduce any amount of friction as it only transfers the static weight of the car onto the ridged surface areas that come into contact with the axle. So, other than what somebody posted about possibly having the grooved wheel bore 'walk' the wheel to the axle head, I don't see the benefit.
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Gtdhw
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Re: Grooves in wheel bores?

Post by Gtdhw »

Are wheels that have had the tread thinned, all but a thin ridge, faster than full tread/contact wheels purely on rotating mass reduction? Or does the thin contact patch add as well?

(I so wish I had a test track)


Edited for clarity
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Scrollsawer
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Re: Grooves in wheel bores?

Post by Scrollsawer »

Gtdhw wrote:Are wheels that have had the tread thinned, all but a thin ridge, faster than full tread/contact wheels purely on rotating mass reduction? Or does the thin contact patch add as well?

(I so wish I had a test track)


Edited for clarity
Now you've got my wheels spinning (in my head :scratching: ). Your question is a good one. Yes, razor wheels are faster than full tread wheels. This is due to a reduced moment of inertia which gets the car moving faster than cars with full tread wheels. It takes more energy to get those full tread wheels moving than those razor disk wheels.

So, the question is...can you reduce the moment of inertia within the bore the same way it's currently done with razor wheels along the tread/track contact surface? Does the moment of inertia behave differently with a spinning motion against two rounded contact surfaces than it does with a rolling motion against one larger round contact surface, and one flat contact surface? Surely, Engineers have solved this question long ago in manufacturing.

A lot to think about..., but on the surface, it would stand to reason that it's a possibility, so long as the same type of razor wheel effect is applicable at the wheel bore/axle contact points.

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