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PostPosted: Wed Jul 17, 2013 7:10 pm 
Retro Guru
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Joined: Mon Jul 26, 2010 10:46 am
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Location: Leamington, UK
Interesting comments, thanks. I should give a bit of background really.

The bike in question is actually a modern carbon racer (sorry). It originally had a 172.5mm crank on it with i think 37/53ish. It is a small frame (I am a shortarse).

On the advice of bike sizing guru mike (forgot his surname) in Leamington, I ditched the cranks and found a 170mm set without rings.

The sram apex crank has a 130bcd bolt pattern so my nos biopace chainrings went straight on. Surprisingly I haven't experienced any trouble using rings originally designed for 7 speed on my 10spd sram rival stuff.

Anyway these biopace rings are 52/42 and combined with the shorter throw of the cranks I'm having real trouble up steeper hills. Been looking for a smaller inner biopace one but no luck so far.

I am fairly out of shape after a heart scare so I'm easing back into things by cycling to/from work - 13mi each way.

Anyway, if any of you have a spare 130bcd ring around 37ish teeth, there's some beer money in it for you. Meanwhile I'll carry on honking up the hills...


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PostPosted: Thu Jul 18, 2013 6:49 pm 
Old School Grand Master

Joined: Tue Oct 09, 2007 1:55 pm
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Location: New Forest, UK
The smallest you can get for a 130pcd crank is 38T.


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PostPosted: Thu Jul 18, 2013 9:22 pm 
Devout Dirtbag

Joined: Sat Apr 07, 2012 1:23 pm
Posts: 104
Also with the hard bottom gear of yore there was very little need to shift when climbing -- i.e. when the hands were on top of the bars.


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PostPosted: Thu Jul 18, 2013 9:51 pm 
PoTM Winner
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Bio pace rings are a disaster. Caused loads of knee issues bitd.

Get some round rings or q rings.


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PostPosted: Thu Jul 18, 2013 10:23 pm 
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Joined: Fri Oct 14, 2011 8:41 pm
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Location: Cumbria
I worked in a bike shop so rode a lot of bikes........not sure I could tell the difference between 170 and 172.5 to be honest.

Depending on where your foot is compared to the centre of the pedal likely exceeds that tolerance.

Have you used ellipsoidal rings before? theoretically your biopace rings have a greater mechanical advantage than removing 2.5mm from the length of the crank arm. If you wanted to reduce the travel of your knees and increase mechanical advantage for hills then stick the biopace rings or Q rings on the longer cranks..

Shaun


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PostPosted: Thu Jul 18, 2013 10:34 pm 
PoTM Winner
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Biopace and q rings are almost opposites. I don't think there is any support for the biopace theory these days.

Go round or q rings. Ditch the biopace.


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PostPosted: Thu Jul 18, 2013 11:51 pm 
Old School Grand Master
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Location: Cumbria
There were Durham chainrings about when I was a lad in the 70's which were eliptical......AFAIK Biopace / q rings / others all had the same principal of increasing mechanical advantage as the pedal passed TDC.

Only Biopace said that cadence would be reduced...

or have I missed something ?

Shaun


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PostPosted: Fri Jul 19, 2013 8:23 am 
Retro Guru

Joined: Wed Dec 10, 2008 9:19 am
Posts: 2095
Location: Sheffield, top city
Montello wrote:
Biopace and q rings are almost opposites.

eh? hows that? are you saying that biopace make it harder top dead centre? Not challenging you, just asking.

BITD biopace were the dogs bollox. I'm still using them on a couple fo rosadbikes and quite like them. I'm betting that in 20 years some scientist will come up with another ring on the same principle and we'll all be dissing Q rings. Fashion and marketing!


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PostPosted: Fri Jul 19, 2013 11:14 am 
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Location: Leamington, UK
Yep I'm a Biopace fan, not everyone is, but works for me and my knees are fine (ish) apart from non-cycling issues that have been there since a kid.

Plus those rings were what was in the spares box and thus have cost me £0.00 to change!

Yes I think the rotor rings/Q rings/Biopace discussion is interesting, but it's driven by fashion and marketing more than science. Next year on the Tour we'll see another variation, I'm sure.

I'm also of the opinion that the differences between Biopace and round are pretty marginal anyway, especially the 'later' Biopace type. I have an early MTB inner ring (26t?) that looks almost square!

I think since I'm looking for a smaller inner ring I'll go for a 38 or 39t round off Ebay and put up with the 'non matchingness'. 38t is the smallest I can find for 130bcd.


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PostPosted: Fri Jul 19, 2013 5:49 pm 
PoTM Winner
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pigman wrote:
Montello wrote:
Biopace and q rings are almost opposites.

eh? hows that? are you saying that biopace make it harder top dead centre? Not challenging you, just asking.


Yes; the axis about which you have maximum mechanical advantage is different between Biopace and all other egg rings like Q rings and Osymetrics.

Biopace give you max mechanical advantage at TDC which is the worst time to have it IMHO; the others give you max advantage when the cranks are level.


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