Axle Head Dynamics of Revell vs Box Wheels

[3 Cub Dad]

Hello All,

I've gone through the search and read about every thread I could find on the Revell wheels vs the box or "Made in USA" wheels. But this weekend I ran into an interesting twist while running our workshop.

Our Pack derby is in a week, followed by District. Pack rules are a mirror of the District rule which specify that the step on the outer hub cannot be removed.

While helping a new Tiger and his dad with their car, they had a set of the Revell colored wheels that they wanted to use. Taught them how to prep the axles, including beveling the head. In assembling the car, noticed that the Revell wheels do not have a step on the outer face, or much less of one. Assembled the car, aligned it, and ran it down the track. The car was fast! Very close to the speed of last year's District winner.

In looking at the dynamics, with a beveled head on the Revell wheel, the contact point between the axle head and the wheel is right at the axle. Compare that to the out of the box wheel, and the contact point between the axle head and the wheel is closer to the edge of the axle head.

Given the rule requirement that the step cannot be removed, I'm thinking that the Revell wheels would give a speed benefit. Went out today and bought a couple of sets and am thinking about trying them out.

Anyone have any experience with them or thoughts?

3 Cub Dad

[Speedster]

I agree the step is not as deep. Here are my thoughts. Assuming you did nothing drastic to the wheels , the China wheels are consistently heavier than the wheels made in the U.S. I checked my scale with a 5 oz. weight and a 100 gram weight this morning. The China wheels weigh on average 2.75 grams. One of them weighed 2.80 grams. The U.S. wheels weighed 2.55 grams and were from 3 different mold numbers, 4, 5 and 12. If you are running 4 on the ground you would have U.S wheels 10.2 grams, China wheels 11.0 grams, almost a full 1 gram difference. Not good for all that inertia stuff let alone what quality the China wheels might be. I recently read Stan Pope's explanation why removing the step completely allows the car to go faster, and also Pro racers opinions, but I think it involves a few thousandths of a second. There's been opinions on whether it's advantageous to even taper the head when using the step. The latest China axle is far superior to the U.S. axle and if that's the one you used that might give an advantage. I think to use the China wheel because of the step, without extensive machine work, will not give you an advantage.

[3 Cub Dad]

Speedster -

I appreciate the response. I looked but couldn't find Stan's post on the exact speed contribution. I did notice the weight issue, but also by buying a couple of sets, was able to find three that are relatively close to the BSA wheels. I'm wondering if the benfit of contact closer to the axle will outweigh the lost inital inertia. We run a 3 wheel, standard wheel base rail rider with a COM of just a shade under 1/2 inch. With the step, I have seen the time fall off that others have seen after the first half dozen or so runs. I also think the alignment may be more precise in terms of consistent force on the axle head.

We can't do much to the wheels, but will ream and polish the bore, and slightly sand the outside to help improve concentricity. Our competition keeps getting closer so we've got to keep stepping up our game!

[Stan Pope]

I don't recall what I said about the step before, but it is a small contributor to friction loss to the extent that the hub rubs on the nail head. Looking at the rear wheels, if the car is well aligned, then camber will cause the wheels to drift out. The outward force is very small, so the losses are very small. If the cambered rear axles have slight toe-out, then the losses increase. My guess is that the hub friction losses go away if the rear axles have just a hint of toe-in. (Untested guess! The tuning will be very delicate. The advantage, if any, is easily "lost in the noise.")

I have a problem with the rule if "BSA-licensed product fresh out of the box" fails to satisfy the rule. The rule should be tossed ... promptly! Attempts to enforce the rule will cause "lotsa distress."

[3 Cub Dad]

Just in case anyone if following this or is curious....

Prepped the Revell wheels and ran them last night. While the lack of the step made aligning and tuning much easier, the weight difference was a no-go. Wheels ran about .04 slower than out-of-the-box stock BSA. Swappped back and forth on a couple of cars and the results were consistent.

One note on the Revell axles: There is a single "ridge" on the shaft that can interfere with the stock wheels if they are canted 2.5 degrees if not removed. Not a problem when running the Revell wheels. It's just a weird location. Not so much impact at 1.5 degrees.

Stan:

I have a problem with the rule if "BSA-licensed product fresh out of the box" fails to satisfy the rule. The rule should be tossed ... promptly! Attempts to enforce the rule will cause "lotsa distress."

I'm not sure I understand the reference for this comment? Our rules are the exact opposite.

3 Cub Dad

[Speedster]

For Mr. Pope's explanation of removing the step completely, click on the topic "One small step for Pinekind".

[FatSebastian]

click on the topic "One small step for Pinekind".

... over here.

[Stan Pope]

Stan:

I have a problem with the rule if "BSA-licensed product fresh out of the box" fails to satisfy the rule. The rule should be tossed ... promptly! Attempts to enforce the rule will cause "lotsa distress."

I'm not sure I understand the reference for this comment? Our rules are the exact opposite.

3 Cub Dad

In the initial post,

Given the rule requirement that the step cannot be removed, ...

To inspection the outer hub of some Revell wheels would appear as prior BSA wheels on which the step had been removed.

Now I think I understand your point ... you "worked around" the prohibition on "removing the step" by selecting wheels that had no step! Since there was no step, you "didn't remove the step" and satisfied the letter of the rule.

[rpcarpe]

So bottom line: BSA wheels are faster, get rid of rules that prohibit step removal!

[3 Cub Dad]

I understand the benefits of removing the step, what I don't get is the comment:

I have a problem with the rule if "BSA-licensed product fresh out of the box" fails to satisfy the rule. The rule should be tossed ... promptly! Attempts to enforce the rule will cause "lotsa distress."

This confused me.

[3 Cub Dad]

So bottom line: BSA wheels are faster, get rid of rules that prohibit step removal!

rpcarpe - I agree with the first part of your bottom line!

In interest of full disclosure, I am the chairman and in charge of the district derby for one of the largest districts of scouts in the US, I also run the pack derby, and wrote the rules for both. The rule specifically prohibiting the removal of the step was put in place last year for a couple of reasons and remains. We take a look at the rules after each derby to see if anything needs to be revised or clarified. That one will remain. Our rules are fairly concise and take less than a page.

3 Cub Dad

[Stan Pope]

I understand the benefits of removing the step, what I don't get is the comment:

I have a problem with the rule if "BSA-licensed product fresh out of the box" fails to satisfy the rule. The rule should be tossed ... promptly! Attempts to enforce the rule will cause "lotsa distress."

This confused me.

Okay, my initial understanding of your post was that "step must be present". This is apparently incorrect, and it is okay to use BSA-licensed wheels which have no step. This eliminates the "lotsa distress" aspect, but leaves difficulties in inspection and some questions of fairness.

It does not make sense to me that one can use wheels from one supplier and can not make wheels from another supplier comparable, i.e. I can use wheels purchased without step but I am prohibited from adjusting wheels from another supplier to make them comparable.

[rpcarpe]

Two items:

3 Cub Dad - I'd love to see a copy of your rules. I write the rules for several local Packs, and am trying to get our District rules to be shorter than 3 pages! I'll gladly reciprocate and send you mine with explanations.

I think Stan has a good point.

It does not make sense to me that one can use wheels from one supplier and can not make wheels from another supplier comparable, i.e. I can use wheels purchased without step but I am prohibited from adjusting wheels from another supplier to make them comparable.

If you don't restrict the supply source (BSA only parts) then the cubs that buy from BSA should be allowed to modify their wheels to be like Revel.

My basic approach is to encourage experimentation, research and testing on the part of the build teams. I strongly discourage lawyer-like rules. I'd rather help raise engineers and inventors than lawyers.

Make it Three Items:
We should start the Rules discussions in July! By the time we realize there's a questionable rule, it's too late for this season.

[3 Cub Dad]

rpcarpe-

1st item:

Shoot me your e-mail on pm and I'll be happy to send you a copy.

2nd item:

Actually, to make the BSA wheels comparable to the Revell wheels that you can buy, you would have to ADD material to the BSA wheel, not remove it. The Revell wheels do not have a step because they have no inset bore face. To put it another way, the end of the bore is flush with the face of the wheel. The Revell wheels are already heavier than the BSA wheels, so allowing more material removal from the BSA wheels has an even greater effect!

On a side note concerning your post on another thread about the Revell axles and that as an inspector you would allow them: I had a discussion with my Distict Activities Chair last night and we agreed that any Revell products that show up at the race WILL be allowed. Given that they have the BSA seal and say "official" BSA product, I am not going to penalize some scout or parent that shows up with them who bought them believing that they were fully legal. No way, not gonna do that! Bad enough if I have to DQ a car because dad did something that is blatently against the rules, but I will not subject someone to that when they are trying to do the right thing.

3rd item

Actually, I usually look to revise the rules the week after the District Derby just so that any issues are fresh.

3 Cub Dad

[Stan Pope]

The Revell wheels are already heavier than the BSA wheels, so allowing more material removal from the BSA wheels has an even greater effect!

Removal of hub mass has negligible effect on the wheel moment.

Hub mass is beneficial, since it is "unsprung weight" which does not contribute to bore friction losses which approx. offsets the slight increse in wheel moment.