To True or not to True, that is the question!

[Jewel]

Here is what I think the Ultimate wheel would be like.

As big a wheel OD as possible. Find 1.190 OD wheel or better, both from the same mold for the rear wheels if possible. Lathe cut only the high spot on the wheel and polish the tread perfectly flat (that's what is legal at my race). What is good polish to use on the plastic? Test the wheel on a granite block so you know it runs perfectly straight.

Bore out the ID of the tread to make the wheel as light as your rules allow to minimize the rotational inertia of the wheel so it accelerates as fast possible. Any flywheel effect will hinder you in maximizing your forward linear energy because you do not want to maximize the rotational energy held in the wheels, you want forward linear momentum and maximum linear kinetic energy and a minimum rotational energy stored in the wheels. Who cares about getting energy back from the wheels on the flat part of the racetrack the max forward kinetic energy has the best ability to overcome the friction braking the car. All empirical knowledge and I think theory points to light wheels in my opinion. It’s a matter of local rules when making light wheels.

The big OD of the wheel overcomes braking torque, and the low run out of the wheel from the lathe helps you minimize losses in forward momentum from vertical accelerations by the wheel bobbing up and down slightly.

My ideal would be to use a matched pair of wheels with a large ID from the same mold with a small ID that run straight when rolled with a flat thin tread. Since you run on three wheels you only need matched sets in the back of the car so different size wheels fight to turn the car.

[RACER X]

Just adding to the wheel treatment thread:

What are most folks doing for finishing the tread face after trueing ?

polishing

coating [secret sauce]

graphite

[Da Graphite Kid]

Racer X, we use Mother's Chrome Polish on the tread surface after trueing. This year we tried matching an axle to a wheel and using the drill press to run in some grahite-moly before mounting them. As boys do, he started goofing off and ended up with graphite on the wheel tread. We all liked the silvery shine so much that we used graphite all over the wheels. This made the cars really stand out from some of the others and also brought controversy as some thought this was some secret speed technique! If it was, we stumbled on it by accident! My sons cars were almost not allowed at District because of this (rule allowed light sanding only).

Da Graphite Kid

[greg]

I think truing the wheels is a must. The method I use is a drill press with a router bit secured to the press table. With the wheel mounted to a mandrel, I lower the wheel onto the cutting bit allowing a pretty good truing process. However, I race with the awana wheels and the problem that I haven't been able to overcome is the wobbling of the wheels when they are spun on an axle, even after they have been trued. Any suggestions?

[Jewel]

My understanding of wheel woble is that it comes from the difference between the axle diameter and the ID of the wheel. If it is too big it is likely that you will get some woble or buzzing. The wheel kind of orbits around the axle rather than sliding around it.

One solution is to make sure that you have enough lubricant on the alxes, that should cancel the buzzing.

[gpraceman]

However, I race with the awana wheels and the problem that I haven't been able to overcome is the wobbling of the wheels when they are spun on an axle, even after they have been trued. Any suggestions?

This thread http://derbytalk.com/viewtopic.php?t=58 has some info on wheel wobble and axle OD vs wheel ID. That may help.

[greg]

The wobble that I am refering to is from a slow spin on the axle. it appears that the flaw is in the wheel hub. I am not refering to the hum or vibration that comes from not enough lubrication or a smaller diameter axle. Is there something wrong with my truing process?

[MaxV]

Greg,

Truing as you describe will make the tread parallel to the wheel bore (which is certainly important). This corrects problems with variances in the radius of the tread (measured from wheel bore to tread surface at several points on the wheel).

However, many wheels also have a different type of variance. That is, the wheel bore is not perpendicular to the wheel face. This type of defect is obvious when you spin the wheel slowly on an axle. The wheel will have a left-right wobble, once per revolution.

I don't know of any way to totally correct this type of problem short of filling the bore with an epoxy material, and then redrilling it.

I have seen this much more on BSA wheels than on Awana Wheels. So, it is possible instead that your wheels have a defect in the wheel hub, which causes a sort-of skipping action as the wheel rotates. You might try reaming the bore with a drill bit just a hair larger than the bore.

Good luck!

[RACER X]

When trueing an AWANA wheel, you must be careful not to apply excessive pressure because the wheel will deflect during the process more than a B.S.A. or Pine car will.

If you are mounting wheel straight in a good mandrel, this will establish your centerline. From here you are working to parallel the tread face with the hub bore, the accuracy of this is dependent on your equipment and skill.

When you refer to a wobble, are you refering to the tread going up and down when you test spin the wheel [this would be from truing] or are you refering to the side wall of the wheel going left to right [ this would be a manufacturing defect] you should try another wheel.

Last question, is your wheel centered on the mandrel? If not Max V has a new twist on this.

Have fun.

Racer X

[greg]

Thank you very much. The wheel wobble is a left to right wobble and I am almost positive that it is a manufacturing defect. I do have the new mandrel from MAXV but I still haven't been able to cure the wobble. I will inspect the wheels for mold numbers and try to compare them.

[terryep]

I have tried using mandrels to true wheels but found a better method. I use a steel bushing with a ¼” inside diameter mounted in my drill press. I place the wheel upside down on the table and press fit it’s inside hub into the bushing. I use a combination square resting on the table to give me a true 90-degree surface. Using a low speed I gently slide the square to the wheel with a 220 grit sandpaper. I sand until flat then use wetted 320 grit sandpaper and then polish with pumas on a cloth. Slow and gentle so as not to over heat the plastic.

As for the axel hole, I have learned not to play with that.

[RACER X]

I use a steel bushing with a ¼” inside diameter mounted in my drill press. I place the wheel upside down on the table and press fit it’s inside hub into the bushing.

As for the axel hole, I have learned not to play with that.

I guess that I am confused as to how you are doing this. I am assuming that this bushing is going around the outside of the hub?

I know that a 1/4" or .250" bushing will not fit inside of a .100" hub bore.

You said that you do not mess with the hub bore, I have found them to be too inconsistet from wheel to wheel to not size them so that are all equal.

[terryep]

Re: press fitting in a bushing. Yes, the hub is pressed into the bushing. The hub has a slight taper and is a few thou bigger the 1/4" so it makes a tight fit.

As for not touching the bore. I did a lot of experiments on the bore and found that most everything I tried either made things worse or had no effect. Mostly made things worse. I get a few extra sets of wheels and visually inspect the bore for defects. In a pinch I rolled one on my bench with a drill bit in the bore backward to remove a bump in the plastic when I ran out of wheels. I like to change wheels between district and challenge races.

This is my own experience, I'm not saying you shouldn't experiment yourself

Terry

[RACER X]

My only thought on this is that I do not believe that the outer dimension of the hub is accurate enough to use as a indexing point for doing wheel treatments.

I have found that many wheels do not have the hub bore in the center of the hub, it can be off by several thousandth's.

[terryep]

Re: hole placement in the hub. These wheels are injection molded. Molds are made to fine tolerances because there parts have to fit closely. If the parts are popped out while they are still hot the plastic can deform and warp, plastic can also absorb water from the air. The hole will start out in perfect position but may have voids and depressions if the plastic shrinks while cooling.

A while back I bought a couple lengths of drill blank to make 30 mandrels for my son's pack. I got a couple sizes each 0.001" bigger. I was unhappy that the hole diameter typically varied by 0.003" wheel to wheel and some worse than that. I made a centering piece out of nylon that pressed onto one end of the shaft and centered into the inside hub of the first wheel. Another wheel went on the shaft facing the first wheel then I supplied a rubber washer for the other side of the wheel to contact the drill chuck. I was not happy with the results I got. If the Wheel should spin on the mandrel (happen's with impatient cubs) the center hole can be deformed.

Terry