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MichaelN
07-27-2004, 03:03 PM
Does anyone have any experience (or thoughts) about carbon fiber wheels? I was originally thinking of putting forged magnesium Marchesini's on my 748 (a friend who had them on his 900 couldn't stop raving about how much better the handling, turn-in, suspension, etc. was). But after some research, I read about the CF wheels by BST. The comments on their site (http://www.blackstonetek.com/) are (obviously) quite positive so I was wondering if anyone has comments/opinions. My biggest fear is shattering the wheel(s), but BST is claiming that their wheel is stronger than both aluminium and magnesium.

Thanks,

Michael

Torben
07-27-2004, 03:10 PM
If done right CF can be as strong as magnesium. One of the biggest issued that drive this question is rotating mass. This is a function of the geometry and overall mass of the object. Forged magnesium can be stronger than CF for the simple fact that CF wheels will be near the road surface and high speed chips will cause a stress point in the resin which after time will propogate and cause failure.
Personally I would never use CF for structural items. Magnesium is somewhat heavier than CF but when it comes to wear and tear I'd bet my life on it over CF for critical structural items.

RockStar
07-27-2004, 03:33 PM
I'd second that. I've ridden with a guy who uses CF wheels on his 998 and of course loves them, especially when passing Gixxers.

But Torben is correct. A CF flake will rip like a zipper given continued stress or another trauma.

It'd be great to hear from some of the racers on their experience though.

Y.

DJS
07-27-2004, 03:42 PM
Another issue is when CF fails it can be catastrophic. Also CF is non-repairable and if you happen to damage the rim you will have to buy a new one. Well...you don’t have to and try to repair it but that would be very foolish. Magnesium is the way to go if you want to spend big dough. If you hit a pot hole, the magnesium will bend but you can get it straightened, not having to buy a whole new rim.

Jim is Cool
07-27-2004, 03:47 PM
Ahem.....

Well, I've tried Techno-Magnesio (sp?) wheels, they were pretty cool on the track, faster turn in and transition, but ended up sticking to the stock cast aluminum wheels, mostly for cost. I'm a cheap bastard afterall. Also they will take multiple crashes and off road excursions.

I'd never use Mag or CF on the street, it only takes one good hit to bring the Structural Integrity into question, and the only way to tell is via an NDI inspection. And I would never buy these types of wheels used for that same reason.

For the road, go with Forged Aluminum if you need that "bling" value.

Jim is Cool
07-27-2004, 03:49 PM
Another issue is when CF fails it can be catastrophic. Also CF is non-repairable and if you happen to damage the rim you will have to buy a new one. Well...you don’t have to and try to repair it but that would be very foolish. Magnesium is the way to go if you want to spend big dough. If you hit a pot hole, the magnesium will bend but you can get it straightened, not having to buy a whole new rim.

Not entirely true, cast mag isn't very forgiving, they get stress fractures. Forged is way better.

DJS
07-27-2004, 04:33 PM
Ya that's right. Must have had low blood sugar when i was doing post. Isn't magnesium actually quite brittle? And yes the forged aluminum is the softer and more pliable wheel if you damage it. Damn time to eat the other half of my Subway sandwich and some more of those good chips. Hope they don’t give me a stomach ache. :(

CINDESMO
07-27-2004, 04:39 PM
DJS- Confused, low blood sugar man, the forged aluminum rims are considered the best for the street. They are light and hold up to pot holes. That is what I would get if money weren't an issue.

DJS
07-27-2004, 04:59 PM
That's what I said. I said I had low blood sugar and was going to eat Subway. And that forged aluminum is the way to go. :p

Torben
07-27-2004, 05:32 PM
So did someone actually say these were for street? Did I miss something?
Is my blood sugar low? :happy44:

foggy123
07-27-2004, 07:06 PM
OK. I have them on my bike. :D
They test stronger than any other wheel out there. They are lighter also. Most of the mass is in the the hub so acceleration and turning are quicker.

As far as durability well that has yet to be seen. My thought is if I break them then I've probably screwed up. In that case the bike is toast but at least I'll enjoyed the ride.

DJS
07-27-2004, 11:08 PM
Hey Foggy, that's a very good point if you totally blowup your CF wheel you are probably not going to feel well anyway. I would say buy what you want because otherwise you will/may regret your decision.

PS Foggy, If you were the one who got them on Dyno Day your bike looks sweet.

Apostate
07-28-2004, 05:11 PM
Personally I would never use CF for structural items.
Tell that to the Chief Engineer on Boeing's new 7E7 program. The whole fargin' plane is CF!

Carbon fiber is really quite stong, especially when manufactured properly. Its weakness lies in its fracture mechanics properties -- it has none (to speak of)! So you have to pay extra care in manufacturing and maintenance or, as someone pointed out, if you get a nick or a flaw, the crack won't just grow, it'll basically cause the part to explode under load.

Torben
07-28-2004, 07:13 PM
While the 7E7 is mostly CF it has more lams and a different resin than what you'll find in motorcycle bits. I have a degree in mechanical engineering and am familiar with composite materials. My biggest concern would be the fact that wheels are in such close proximity with the ground, which often contains rocks, that the risk of failure is much higher than with a jet liner.
Now if they made CF bits for bikes out of the same layups that the Boeing folks use that'd be a different animal. :happy44:

Buckelew
08-02-2004, 05:55 AM
Let's see....I've seen Marchesini's blow out after losing a bit of the bead when the front wheel hit a pothole (brand new wheels, too).

i've seen more Dymags go to crap than anything else.

I've seen some forged magnesium wheels cracking.

I've seen a BST wheel get bounced off a cement floor and there was no damage.

The BST's are also certified for street use - you try getting something through the certs that BST has - I don't think ANY of the mag wheels are certified for street use - but I'll have to check on that.

Blackstone Tek isn't some fly-by-night outfit that slaps together wheels out of cheesy CF and resin....these guys make rotor blades - one might think that BST might know a bit more than your average mechanical engineer about composites. I would think that they're a bit more than "familiar" with composites.

And....I've actually seen a few sets of BST wheels. Gorgeous. Best looking CF I've seen. Real sexy. I wouldn't mind having a set.

RockStar
08-02-2004, 08:55 AM
No. in a seires of posts. Less generalities and more specificities needed here.

I'd be one for a group sponsored lecture on the comparison of the two materials. I know of some others here who might feel the same and I'll ask my rocket scientist sister if she has any friends from her days at Boeing who could help.

In the mean time here's some material (lol) to chew on.

http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGtext/BDGGraph.html

http://bimmer.roadfly.org/bmw/forums/e90/5387153-1.html

http://power.me.es.osaka-u.ac.jp/research/Mg/Mg_eng.htm

Y.

RockStar
08-02-2004, 09:07 AM
A good example of how and possible 'why's' of changes in product variability over the last several years...end product depends on quality of base materials and style of production...


http://www.caer.uky.edu/carbon/posters/wvufull.pdf

RockStar
08-02-2004, 09:28 AM
Just read the abstract on the PDF paper...Note that explosive destruction was not witnessed during a double notch stress test (not to say that it never happens but 'exploding' could also be fast ripping).

http://doc.tms.org/ezMerchant/prodtms.nsf/ProductLookupItemID/MMTA-0003A-899/$FILE/MMTA-0003A-899F.pdf?OpenElement


Here's a link from a discussion that indicates failure between the hub-composite junction and not so much the wheel. Seems price may determine tensile strength ;)

http://www.bikeforums.net/archive/index.php/t-59042


.....searching for Mg and rate of failure articles.

Apostate
08-02-2004, 05:42 PM
Torben...never meant to slight your experience or intelligence regarding the subject. Mostly, I was poking a tad bit o' fun at me employer (which I try to do at any opportunity). :D

Also just for clarification...anytime I say "explode" in regard to composite crack growth, I only mean it in relation to the way aluminum exhibits crack growth -- i.e. slowly (depending on stress level and cyclic spectrum, of course) as opposed to hypercrazyfast in composites.

Okay, that's enough of that. :indiffere

Torben
08-02-2004, 06:26 PM
Dude I so don't take it as poking fun. No big deal. :happy36:
And yes, I do so enjoy the way CF explodes - it's fun :happy44:

RockStar
08-03-2004, 10:52 AM
I'm having trouble finding a specific article discussing issues with Mg wheels. If anyone has any leads help is welcome.

Y.