 Excellent question!
As an ex racer myself (Flat track, tt, and eventually MX) from the 60's and 70's I too look at all the weight in the wheels on Harleys. My FXR4 has a pretty front wheel set up but it's heavy for sure. Dual discs and a non-stock chrome plated mag style wheel. The rear is one of those solid rims and chrome plated also. The whole bike looks like not much thought was put into making anything light at all. Now the owner's manual lists the Dry Weight at 601 lbs while the service manual supplement list it at 560 lbs. Whatever... I've always wondered how much fun a sub 500 lb. FXR would be! And like you said, Buzz, lowering unsprung weight in the wheels pays big dividends both in comfort and handling.
So as to what is the lightest wheel setup that would be practical for a street bike here's how I see it:
1) Magnesium wheels, although very light, are no good for street because of porosity and corrosion problems.
2) Cast or forged aluminum wheels are good but not particularly light. The wheel manufacturers could tell you what their lightest setups are. Why don't you, Buzz, ask some of them?
3) Aluminum rims (like Akronts), wire spokes, and light weight racing hubs like you would find on an XRTT would be light and look very trick. This is what I would probably use on my fantasy "Sub 500 lb FXR". Just think of all the old go fast TT and RR big bikes laying around racers' garages with these kind of wheels and brakes. I guess I just like the look of go fast racing stuff anyway.
4) Carbon Fiber wheels...well there are a lot of questions here. For one, CF is only good in tension and laying it up in a mold only works if you lay a big bunch of the Cf cloth in there. When CF is struck from the side it breaks quite easily. Think what an Indy car looks like when it hits something hard. A million black butterflies. Incredibly ridgid stuff until force is applied at an angle other than the load path. Anyway, If you put enough CF cloth in the mold it'll probably be plenty strong enough to resist side loads but you'd lose some of the weight savings.
The other potential problem with CF wheels isn't with the CF but with the epoxy medium the cloth is set in. CF has very high UV resistance but epoxy has very poor resistance to UV rays and it breaks down quickly when exposed to the sun. Just mix up a little batch and leave it outside in the sun, especially here in California, for a year or so and it'll become an ambered, crumbly, useless POS. This poor UV resistance can be improved greatly by adding expensive UV inhibitors to the epoxy but it can never be completely cured. The only sure way to stop the deterioration process is to paint the surface and this is what is done on racing boats and other other outside applications. When I see CF products with the cloth visible it just pisses me off. Looks cool, I guess. That is if you have some idea in your head that if the racers use it then it must be the ultimate and what is cooler than that? The racers always paint it if it is going to be exposed to the sun for extended times. Exposed CF is a marketting ploy to appeal to limited knowledge. The right thing to do with CF wheels is to paint them but then you wouldn't be able to see that that beautiful (?) black cloth that you payed so much for.
Ok, so that's what I see as the downside of CF wheels. Now, if you keep your bike out of the sun as much as possible and the wheel maker has added all the appropriate UV inhibitors to his epoxy, and they have put enough extra CF cloth to overcome its shortcomings in the compression department you might end up with a nice wheel that has saved some weight. I just hope the guy that mounts your tires is aware of the delicate nature nature of your plastic rim.
5) I don't know if there is such a thing but a hybrid wheel with aluminum rim and CF spokes might be something interesting.
Ok and one last little thing, Buzz, one of the very few things that has always bugged me about AIM is that the weight of the feature bikes is almost NEVER given except for the HD lineups! With the stretch jobs and other customs that's no big deal but sometimes, like with that really cool XRTT (Aug. 06) and a couple of the Chopper Guys FXR's, I would have loved to have known how much they weighed. I'd also love to see just how light and quick you could make a Big Twin if you set that as a goal.
Big Mike (milindh)  | 
You all ready chose it! 
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