Author Topic: eccentric bottom brackets  (Read 637 times)

eccentric bottom brackets
« on: June 07, 2019, 03:33:17 pm »
I'm considering a new fixed gear bike for longer rides (don't get too excited - "longer" means 200km+ in this instance). Most of the track bikes don't strike me as ideal for longer distances. In looking around it's obvious that there are a *lot* more frames available without horizontal dropouts, both new and second hand. Using those frames seems to require either amazing good fortune (a magic gear) or an eccentric bottom bracket or hub. Given that I have a bunch of parts already, an EBB would seem like an easier option.

Is there much existing experience with using an EBB in a regular frame for fixed gear riding around?

Should I stop being silly and just buy a Bob Jackson frame?

As an example of the kind of frame I have in mind, Wiggle are selling Lynskey Ti frames at an attractive price right now and the Spa Audax (either Ti or steel) look interesting. If it works well, I'd even consider a soot frame...

(Another option would perhaps be a chain tensioner, but those that I've looked at suggest they are not suitable for fixed gear, only single speed.)

PaulF

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Re: eccentric bottom brackets
« Reply #1 on: June 07, 2019, 03:41:13 pm »
I've used an EBB with single speed - but not fixed - for many years without a problem.

LittleWheelsandBig

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Re: eccentric bottom brackets
« Reply #2 on: June 07, 2019, 03:48:45 pm »
EBBs are less hassle if you are not very sensitive to saddle position changes. I notice a 1-2mm difference in saddle height on long rides.

Magic gears are a pain for fixed if you do more than ride around the block. Chain wear messes up the wheel position quite quickly.
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Re: eccentric bottom brackets
« Reply #3 on: June 07, 2019, 04:25:23 pm »
You can't use a chain tensioner for fixed gears. The reason is that on a freewheel bike, the top half of the chain can carry force, but the bottom half is just a return, and so doesn't have to transmit force. On a fixed gear, if you slow your pedalling for a second then the bottom half of the chain will be carrying force (to push your legs around) - this force is likely to be too much for a chain tensioner and it would fail.

Out of curiosity, what is it about track bikes that puts you off?  The geometry? The stiffness?  The weight? If you're not too bothered about weight, and you're not necessarily looking for a new frame, then it might be worth looking for an older steel road bike with a forward facing dropout. They usually have enough adjustment room to get a good gearing combination and because they are steel you can cold set to get whatever OLN you need at the dropouts.

Re: eccentric bottom brackets
« Reply #4 on: June 07, 2019, 05:14:04 pm »
Is there much existing experience with using an EBB in a regular frame for fixed gear riding around?
To me an eccentric bottom bracket is of a size that fits the front of a tandem frame i.e. much larger than a usual bottom bracket shell, so this will never fit a "regular frame".  I know you can get very expensive oddities in EBBs such as https://trickstuff.de/exzentriker/ which will give a small degree of adjustability, probably a similar amount to an eccentric rear hub http://www.whiteind.com/eno/

Track bike - I toured extensively on track frames in the 1970s with no comfort issues.

Re: eccentric bottom brackets
« Reply #5 on: June 07, 2019, 07:48:12 pm »
Most steel road/touring bikes up until ca. the late 1980s had horizontal dropouts and will happily bend inwards enough around a standard 120mm track hub (especially the older 126mm spaced bikes). You only need to find one good frame to build your bike.

I have a friend who's a big fan of the white industries eccentric hub. That EBB you link to is a clever idea but only having 3mm of adjustment available is going to get super annoying as any adjustment beyond that is going to mean fiddling with the chain length and half-links.

Re: eccentric bottom brackets
« Reply #6 on: June 08, 2019, 11:54:12 am »
Out of curiosity, what is it about track bikes that puts you off?  The geometry? The stiffness?  The weight?

I’d like mudguards (and not the strap on kind), which rules out most. The Dolan FXE will take them.

Overall I’m after the elusive “comfort”, and have in mind that a stiff aluminium frame with a track geometry is not likely to give me that. That’s not founded on personal experience though. Perhaps I should grab an FXE frame and build it up to see - they aren’t particularly expensive.

Another obvious option is the Condor Tempo. Not much difference in price from Bob Jackson then, though.

Quote
If you're not too bothered about weight, and you're not necessarily looking for a new frame, then it might be worth looking for an older steel road bike with a forward facing dropout. - They usually have enough adjustment room to get a good gearing combination and because they are steel you can cold set to get whatever OLN you need at the dropouts.

Yes, this is an interesting option. I like “cold set” - it sounds so much better than “bend”  :D

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Re: eccentric bottom brackets
« Reply #7 on: June 08, 2019, 04:03:46 pm »
Hi dme

Not that I'm an Audax expert, rather a dabbler Dolan FXE works well for me, currently on 28mm tyres. No stiffness/comfort problems as yet.
Mudguard clearance too.
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