# eccentric bottom bracket



## Monkeybike (Feb 25, 2008)

Hi.

I hate chain guides and tensioners, and as I have a high concentric pivot bike I needed one for tensioning the primary chain from the bottom bracket to the pivot point (similar to a brooklyn but with both chains in the right side.)










given the lack of space, I could only set the tensioner as seen on the image. it worked ok, but not perfect, there was a lot of drag, and in it always becoming loose after a day of use. and I even ripped it of in a couple of occasions.

Bored of dealing with it I decided to fix the problem and I came up with a very simple but effective eccentric bottom bracket. since installed in the bike it has been trouble free. I am using cromo cranks and bb axel (19mm) and the bearings are mounted outside the bottom bracket shell and directly onto the eccentric cup. this could create some space issues.

is it worth it to further develop this thing? or even to patent it?


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## problematiks (Oct 18, 2005)

Sounds like an interesting idea and it might be worth developing.
On the other hand you could try solving the problem with a half-link chain.

Marko


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## ScaryJerry (Jan 12, 2004)

I never thought of using a 19mm axle for eccentric purposes. I've seen the Tr!ckstuff version that works with hollowtech cranks, but given that it uses a 24mm spindle, you don't get much space to work with. A 19mm spindle should give you 2.5mm to mess around with on either side, right?

I'd be highly interested in one for my trials bike. Please keep me posted!


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## Walt (Jan 23, 2004)

*Develop, sure. Patent, no way.*

There is no money in bikes. As such, spending the money to get a patent (assuming you manage to do it - there is a LOT of prior art out there in the bike realm) leaves you in the position of having to spend big $ to sue to actually enforce it. This is the whole "a patent is a $100,000 gun that shoots $1,000,000 bullets" argument that you may have heard before. Bottom line? You'll *never* make a return on the investment, unless you think every bike rider on earth is going to want one.

If you think it has commercial possibilities, make it and figure out a way to sell it. If you're successful enough, someone may copy it from you, and that's a bit of a bummer, but at least you'll end up with money in your pocket when all is said and done, instead of no money and a lot of lawyer's fees.

-Walt



Monkeybike said:


> Hi.
> 
> I hate chain guides and tensioners, and as I have a high concentric pivot bike I needed one for tensioning the primary chain from the bottom bracket to the pivot point (similar to a brooklyn but with both chains in the right side.)
> 
> ...


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## Monkeybike (Feb 25, 2008)

scary jerry, actually I have never measured it, but it allows for a lot of movement, I am guessing about 12 mm to 13 mm. (side to side). Right now the clamping mechanism is placed out side of the bb shell but I see no reason why it couldn't go inside it. (here is where it could get ugly). 

I will try making one for my town bike (..... with horizontal drop outs) just to see if I can fit the fixing mechanism inside the bottom bracket shell. 

And Walt I guess you are right about the patents. its just that I had ideas "borrowed" before and it is a real bummer. I guess we should all start writing song with instant copyright.


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## itsdoable (Jan 6, 2004)

You are describing something that sounds similar to this:








https://www.trickstuff.de/shop/product_info.php?products_id=414


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## ScaryJerry (Jan 12, 2004)

The only problem with the Tr!ckstuff model is it's intended for 24mm spindle Hollowtech cranks. By using a 19mm spindle BMX crank, you get additional room before the spindle contacts the bottom bracket shell. Often times with the Tr!ckstuff BB you still need to use a half-link to get tension just right. Adding another 5mm of play (24mm - 19mm = 5mm) should eliminate the need for a half-link in most installations I would imagine.

Anyway, keep me posted! Still sick of ripping chain-tensioners off my trials bike, so this would be a much better solution.


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## Monkeybike (Feb 25, 2008)

itsdoable said:


> You are describing something that sounds similar to this:
> 
> 
> 
> ...


it is actually a lot simpler, only two cups plus bits to secure it down. I do not use the threads at all.

the before picture is on the first post, here is the after one:










although it will be some time before I'll do another one. but I will post it once it gets done.


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## rocwandrer (Oct 19, 2008)

this going to sound retorical, but it isn't:

why put all that trouble into remote driving the rear wheel, and not put the suspension pivot in line with the line of action of the force from the chain?


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