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Belt Drive for BMX

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 When you stomp out of the gate, there is no lag time that you traditionally have with taking up the slack in your chain.  

 

 - an immediate transfer of power to the rear wheel.  

 

There is still slack, based on the inherent condition of stacked tolerances between the fit of the spider, chain ring, and chain ring bolts. Those components have fairly loose tolerances, which makes them easy to fit together regardless of what manufacturer made which part. This creates the impossible situation of having a perfectly true (round) front gear in relation to the crank spindle. This is entirely the reason why traditional chains have a "tight spot" and "loose spot". You might not see it as much with a belt, but it's there. And since the belt system relies on a higher degree of precision to perform correctly, it is entirely relevant that one considers those factors. 

 

One way to solve that would be a one-piece sprocket, back-spaced to provide correct chain alignment with today's outboard BB's...which I am unaware of any company making those. And if they did, it would create less flexibility and more effort for a rider to change front gears. 

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 When you stomp out of the gate, there is no lag time that you traditionally have with taking up the slack in your chain.  

 

 - an immediate transfer of power to the rear wheel.  

 

There is still slack, based on the inherent condition of stacked tolerances between the fit of the spider, chain ring, and chain ring bolts. Those components have fairly loose tolerances, which makes them easy to fit together regardless of what manufacturer made which part. This creates the impossible situation of having a perfectly true (round) front gear in relation to the crank spindle. This is entirely the reason why traditional chains have a "tight spot" and "loose spot". You might not see it as much with a belt, but it's there. And since the belt system relies on a higher degree of precision to perform correctly, it is entirely relevant that one considers those factors. 

 

One way to solve that would be a one-piece sprocket, back-spaced to provide correct chain alignment with today's outboard BB's...which I am unaware of any company making those. And if they did, it would create less flexibility and more effort for a rider to change front gears. 

 

 

Yes, the belt drive system will have these stacked tolerances from the spider, belt ring, and belt ring bolts, just like chain drive.

 

But the belt does not have a hundred connection points like the links on a chain, and those connection points also have these stacked tolerances.  That is what creates the slack in a chain which creates the lag time when you crank out of the gate or stop/start pedalling.  And those tolerances between each chain link get worse over time.

 

Every other component on a BMX race bike has been innovated over the years, and now, finally, we have the opportunity to replace the 1880's chain drive technology with this 21st-century drive train.  Gates has covered every angle, and this product is the real deal.   

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 and those connection points also have these stacked tolerances.  That is what creates the slack in a chain which creates the lag time when you crank out of the gate or stop/start pedalling.  And those tolerances between each chain link get worse over time.

  

 

 

A press-fit does not create stacked tolerances. It is, for all practical purposes of discussion on tolerance, a 1-to-1 fit. 

 

Arguing that a chain is inferior (or even gets worse over time) is a losing battle. Timing chains on high-horsepower engines seam to work just fine "with all those stacked tolerances". And when you divide 6,000 RPM by the precision required for correct timing to achieve that RPM in the first place...I think you're going to have a hard time pitching the idea that the chain is the root cause of the problem.  

 

I like the idea of a belt. It's a dream to ride. But the pro's don't outstack the con's IMHO. If a person is comfortable with the drawbacks and wants the latest thing, it's awesome to see this engineering executed so well. They did a great job. A 1-piece front sprocket is a critical next step though IMO. 

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I guess we will have to agree to disagree.

 

Chains definitely lose their efficiency over time.  Their peak efficiency is when you take them out of the box. After that the plates, bushings, and pins start to wear, and dirt or moisture can clog or corrode the links. That decreases efficiency even if you constantly clean and lubricate your chain.

 

The belt is proven to have a much lower wear rate, so its efficiency remains more consistent over time. And no lube required - maintenance consists of hosing it off when needed. To me, that makes the chain inferior.  

 

I like the idea of the 1-piece sprocket.  But since the BMX racing market is so small, not sure if that's going to be a priority for Gates.

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I don't disagree that poor maintenance will cause a chain's efficiency to decrease over time. You could say that about a lot of BMX parts. IMO that the amount is negligible though, and the remedy is to simply buy a new $20 chain. 

 

Belt-drive is cool and fun for sure, but the con's still outweigh the pro's. The proof in that will be how many people actually buy it. So i guess we'll see. 

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I enjoy the interesting, coherent and polite discussion of belts V chain drive.

 

I think that if the belts offer a tangible benefit (as opposed to marketing hype) they will be adapted.

 

Re High horsepower engines I will add the following:

 

Smokey Yunick observed that timing chains (for crank to cam drive in V-8s) moved around so much while under load that it would alter the valve timing. As a result he devised ways to have gear drive for his race engines when the rules allowed such.

 

Additionally most of the current Moto GP (prototype racers, Yamaha, Honda, Ducati, Aprilla) use gear driven cams on current engines. Honda has used them on certain production (RC-30, RC45, RC51, VFR, etc) bikes that were homolagated for racing as they are always looking for the edge.

 

I certainly get that bicycles use a different power source, so lets see if these belts help out. Color me interested.

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Curt, Nice work with citing a powerplant prodigy, Smokey was a genius! I was going to interject the same info. regarding timing chains VS. gears or timing belts. Timing belts are also superior to chains in terms of keeping precise timing over longer periods of time. However, are more prone to catastrophic failure over the course of it's lifespan, which is the only reason it is recommended to change timing belts more frequently than timing chains. This not to say that timing chains never fail catastrophically, because they do as well.

 

I have seen bicycle chains wear exceedingly quickly, when proper tension is not maintained or chain is not properly lubed. I have seen bicycle chains break. Perhaps belt drive can  provide prolonged service intervals with less chance of catastrophic failure?

 

I will enjoy following the evolution and eventual acceptance or rejection of the concept. Personally I like it, look how long it took the industry to adopt the Cook Uni-Clamp idea. I think the  belt drive concept has taken longer, but it may be here to stay.

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... not sure if that's going to be a priority for Gates.

 

Did Gates manufacture and supply the gear and cog also? Do they have a patent to explicitly prevent other BMX companies from manufacturing the gear and cog? (I've looked at it up close, and technically-speaking there's nothing that would prevent any decent machine shop from making them)

 

If so, that's a bad idea in my opinion. Gears and cogs have historically been generic. If Gates wants to capitalize on the design with the belt that's one thing...but if that includes the gear/cog that's a whole different ball of wax that will hurt more than it helps. 

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Gates manufactures, supplies, and has patented the entire drive train - belt, front sprocket, and rear cog. 

 

Gates is the global leader in power transmission belts, with annual revenue of $3 billion.  The Centertrack design is bicycle-specific and they used their significant resources to develop it with the help of Avid-founder Wayne Lumpkin.  

 

Like any company, Gates is going to protect their intellectual property so that they can insure the quality of their product.

And, of course, they are entitled to receive all the revenue from the patented design they created.

 

I designed a belt drive system back in the 90's that used a generic belt, front sprocket, and rear cog.  I had a lot of issues with belt slippage, even after I added a patented belt tensioning device.  So, unfortunately, generic is not going to work when it comes to belt drive for cycling.

 

But thanks to Gates and their obsession with design and quality, we now have their bulletproof CDX system with Centertrack, which resolves any and all issues of previous attempts at bicycle belt drive.  

 

And they continue to work to improve their product and have some really cool stuff in the pipeline that MIGHT make it's way to BMX.  One innovation that I have been using on my beach cruiser is a molded polycarbonate front sprocket - and this is no Addick's sprocket.  It's super tough, super light, and could reduce friction and improve performance even more.

There is also a molded polycarbonate rear cog that has a steel center where it mounts to the hub - it looks like they are wrapping up the testing on that, so it's almost ready.  And they have a 2.0 version of the belt coming out soon that is even more durable/stronger than the current CDX belt.

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 So, unfortunately, generic is not going to work when it comes to belt drive for cycling.

 

I could've chosen better words. When I said generic, I meant more along the lines of "open source". The front gear is historically a component that offers incredibly diverse design possibilities from many brands, and consumers will want to see aesthetic design choices. Although the gear looks fine for 2015/16, in 2017 it's going to look like it's from 1993 in the eyes of the consumer. BMX is a VERY trendy market, and I doubt Gates will have their finger on the pulse of such subtle issues that equate to sales. If the front gear was open source, Gates could still monetize the system with the sale of the belt and rear cog, yet allow the concept to flourish with letting anyone manufacture the front gear. This is not much different than open-source software, where they give you the bulk for free, but monetize the added features you want. 

 

You are very knowledgeable on this subject. Are you directly affiliated with Gates...or Yess?

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Not directly affiliated with Gates or Yess.  

 

It just gnawed at me over the years that my belt drive system from the 90's did not work out like I had hoped.  

 

But I saw a press release in late 2013 that said Gates was introducing some shorter belt lengths, did some calculations, and determined that it was (coincidentally) the correct length for a BMX bike.

 

So I contacted Gates, then found an elite rider who agreed to test it (he prefers to remain anonymous), and the elite rider had an industry contact who brought Yess into the picture.  Our first test was January 23, 2015 in Vancouver at the Abbotsford indoor.

 

Since then the system has been tested thoroughly, and Yess is now offering complete bikes (a 20" and 24") with Gates Carbon Drive, and I believe they also offer a "rolling chassis" where you add your own components.

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Sounds good. You probably don't need me to tell you that by limiting this technology to two companies, that severely restricts the ability for the technology to take off. I don't know if Gates provided exclusivity to Yess, but that would've been a dumb move on their part if they did. This would need to be licensed industry-wide to become mainstream (assuming the mfr's and consumers embrace it, and I'm not sure that they will). 

 

...bulletproof ... 

 

...a molded polycarbonate...

 

Comments about the 2 quoted items above:

 

IMHO, I caution you not to use the word bulletproof on this. For one, you are overselling it. For two, it's not bulletproof. I've pointed out that the setup requires a higher level of stiffness and precision compared to a traditional chain setup. Without that stiffness and precision, it will not work correctly. 

 

Polycarbonate is not a good material for bicycle components. As you may know, PC is referred to as a "notch" plastic. Cutting, machining, sanding, and even normal wear and tear from being used as a sprocket will open the pores of the plastic that will cause degradation and failure. When you injection-mold the part and it is new, you will not have notches (pores), but as the part wears, the material is susceptible to this. I'm assuming you're going to go with a glass-filled PC and possibly add other fillers to increase strength, longevity, lubricity etc. This will help, but still doesn't match the mechanical properties of aluminum at that point. So then you have to ask yourself "what's the point?". The only point worth noting is that you, as a manufacturer, want to make this work because an injection-molded part costs pennies to make, aside from the upfront tooling cost. It isn't about making a better bicycle component...it's about making better profit. 

 

I anticipate that you'll disagree, and hope no offense was taken with my opinion. My career expertise is product development with an emphasis in the plastics industry, and I personally would not venture down this path...at least for use within the BMX racing environment. My $.02

Edited by John De Bruin

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Yess does not have an exclusive.  

 

But I can not say enough about the Yess craftsmanship and quality. Bill and Renny Husada are true artists when it comes to bmx frame design and manufacturing.  And just really good people in general.  

 

When I used the word bulletproof I meant bulletproof in its current configuration on a Yess frame. My description, not Gates.    

 

Yes, chain drive can operate without precision and stiffness, but it will not operate as efficiently. The Yess/Gates combo is about maximizing your drive train efficiency to give you an advantage out of the gate and down the first straight.

 

You are correct about the polycarbonate being glass-filled. The Gates poly sprockets and cogs are intended for the low-end, like my beach cruiser.  But from a design standpoint they are just so trick that I would like to see them in a test on a race bike.  

 

When we did the test in Vancouver, Gates did not send a rep to be there cause I don't think they had a lot of confidence in their product for BMX racing.  Even my wife admitted to me recently that she did not think it would work properly.

 

So now I have decided, why not keep trying different things and it might be OK.  Who knows, the polycarbonate sprockets/cogs might test well and improve performance even more. 

 

I guess we will soon see if the BMX racing community accepts and demands this product.  Thanks for your input.

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I've talked with Bill and Renny at Interbike, Grands, etc. Good people. 

 

I'm gearing up to do a run of frames here shortly, and I'd maybe give this a shot with the Gates drive on a few frames to see how it goes. I've got a half dozen ideas of what I'd do differently than Yess, but in the end that's a good thing because people can decide if they like the Yess version or the JDB version. Not sure if you'd like to share contact info for Gates in a PM. If so, I'd get in touch with them.  

 

Have you looked into the material called Ultem? It's like PC except exotic and expensive. Usually for medical-grade components.Like PC, it comes in solid form so you can CNC some prototypes, and also grains so you can injection-mold it. It is a very stable material to machine on the CNC and a dream to work with. I've never heard of anyone filling it with glass...which means you might be able to try something revolutionary with it for an application such as this. I don't see why you could'nt glass-fill it. It typically is translucent gold color, but you could probably add black color to the injection-mold mix too. For lubricity you could possibly consider a blend of teflon in the mix. I don't know if teflon will blend with PC or Ultem, but it does blend well with acetal (delrin, acetron). 

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Here is the polycarbonate sprocket that I mentioned. It's designed for low mileage pavement bikes, so it might not work for BMX racing. But it certainly is trick!

 

20160531_110827.jpg

 

I wonder if the friction would be reduced because of the slick tooth profile surface, giving an added performance boost!

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saw that on Facebook and thought of this thread, Matt.

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Had a chance to go to the Grands and check out the new model from Yess, the MX-Y (AKA Showstopper).

An evolutionary frame design that eliminates the seat-stay opening (to loop the belt through) on previous models. And check out the built in tensioner called the belt bumper, which guides the belt onto the lower rear cog teeth under high-torque situations. This allows you to run the belt at a lower tension for more efficiency, which could create a performance advantage over the chain. Additional testing needs to be done to make that determination.

 

20171125_114935.jpg

20171125_114923.jpg

20171125_114915.jpg

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Nice to see that the system is working and working well, that video is good stuff.

 

Additionally I like the frame solution above. That could be useful in other bicycle formats.

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