Wheel Bore to Axle Clearance for Graphite

[philm63]

My wheel and axle prep for this year's race didn't work out so well, in my opinion, and it took several hours, so I am looking at purchasing wheels and axles for next year's cars that are already prepped within the pack rules.

Thing is the wheel bores, because they will have been reamed for straightness and polished, are reporting ID specs at 0.098" (says "minimum" but no tolerance cited), and the axles, because they have been deburred and sanded smooth (ready for polish), are coming in at 0.085".

I'm sure there are tolerances at play here, and thus one could conservatively estimate that the actual clearance value could be anywhere between 0.011" and 0.015".

Begs the question - for graphite, what is a tolerable clearance between the hub and axle?

[FatSebastian]

Maybe you meant to name this topic "Wheel Bore to Axle Clearance for Graphite"?

Begs the question - for graphite, what is a tolerable clearance between the hub and axle?

I believe the consensus historically has been that smaller (but not tight) clearances generally offer better performance compared to other extreme of looseness; for example, long-time DT contributor and league-racer Sporty preferred 0.0960" to 0.0965" BSA wheel-bore diameters with graphite. Now, we haven't raced BSA kits for several years, so sadly I am no longer familiar with the bore dimensions to be expected from the latest molds, but we used to measure bores out of the box as low as 0.0955" and as high as 0.0970" when the more recent style of BSA wheels first came out. IIRC, because wheels were rather consistent in their bore diameters at that time, we concentrated more on wheels from molds that were round and well balanced.

A specification of 0.098" minimum (a common spec for commercially reamed wheels) implies that you could be getting a bore size larger than 0.098" in exchange for a trued bore, and there have also been anecdotal reports on DT over the years of quality differences in some commercially modified wheels. If you buy some, it wouldn't hurt to double check the bore sizes with some pin gauges and also their roundness with a concentricity gauge.

[philm63]

Thanks for the info, and the title has now been corrected to "Axle" (good catch).

I could see that too little of a clearance might not allow for a uniform layer of graphite to be deposited on the axle. Conversely, with too much of a clearance perhaps the wheel would be allowed to move too much about the axle causing oscillations that could lead to increased friction associated with binding.

Realizing that having "treated" hubs and axles often means an increased hub diameter and a decreased axle diameter causing the resulting clearance to grow - I don't want this effect to get out of control so I'm looking for some parameters by which to guide my decisions.

I am seeking that sweet spot where there is plenty of clearance to allow for a good coating of graphite on the axle and inside of the hub while not being so sloppy as to cause binding from too much wheel movement. Without the patience to do the necessary experimentation, is there a hard number to use as a ceiling, such as "don't go higher than 0.015" clearance for graphite, or...? Would a simple spin test be sufficient to tell me if the clearances are ok?

[FatSebastian]

...I'm looking for some parameters by which to guide my decisions. I am seeking that sweet spot...

I admittedly don't have a better answer right now beyond my earlier posting, but, if somebody threw out a sweet-spot value (say, 0.01"?), how would you employ that information?

The question implies that an empirical performance graph of "time to finish" v. "bore clearance" might be drawn up via experimentation that has a definite minimum (sweet spot), or there exists a very obvious universal changepoint in performance (hard ceiling number), all other factors being equal. In practice, indicators of performance can flat-line (no obvious "best") or vary subtly in relation to a hypothesized explanatory variable, and it is rare that all other combined factors equate. For example, one can have a very large bore / large axle combination that has exactly the same clearance as a small bore / small axle combination, but the smaller combination should tend to offer better performance. And nail-type axles aren't perfectly round, so the clearance isn't necessarily constant for a single wheel/axle combination, but an average that may have sensitivities to orientation...

[philm63]

I was thinking I might apply such information in my pairing of certain axles with certain bore dimensions to avoid a situation where a given combination is "too tight" or "too loose" but it seems just as well for me to use the ol' spin test - "does it spin well enough? Then all is well."

[Loud2ns]

I was given a tip from a racer that is faster than I am. Use the same axle to bore clearance for graphite as oil. FWIW

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