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PostPosted: Tue Apr 02, 2013 10:50 pm 
Old School Grand Master
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Joined: Sun Aug 21, 2011 11:57 pm
Posts: 4074
Location: Antwerp, Belgium
I took out the Laïti for a 35 mile trip yesterday, and now my knees are swollen and painful. Never had this before.
Could this be caused by the oval (Suntour XCM) chainrings? I do notice that I really get a kick in the knees on every pedal stroke when on the middle and smallest chainring. So those might need to be re-positioned. The big one barely has this, but I still feel that I'm not able to spin it smoothly.

Anyone ever had to switch from ovals to round ones for the same reason? Can you even get round replacement XCM chainrings?


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PostPosted: Tue Apr 02, 2013 11:00 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader
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Joined: Sat Jun 20, 2009 3:45 pm
Posts: 5261
Location: Birmingham
yes it's the rings

http://sheldonbrown.com/biopace.html

i did hear they are again using them on modern racing bikes though


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PostPosted: Tue Apr 02, 2013 11:02 pm 
retrobike rider / Gold Trader
retrobike rider / Gold Trader

Joined: Sat Jul 21, 2007 9:48 am
Posts: 6976
Location: Bristle
the theory of oval chainrings isn't bad, as evidenced by modern road pros using them, it's just that they put the humps in the wrong places back in the day


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PostPosted: Wed Apr 03, 2013 7:21 am 
Retro Guru
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Joined: Thu May 03, 2012 7:13 pm
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Location: The Cock Inn, Tillett, Herts
Even the mighty Geoff Apps reports knee problems from using Fireplace rings.


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PostPosted: Wed Apr 03, 2013 8:07 am 
Retro Guru

Joined: Sun Jun 20, 2010 4:39 pm
Posts: 1455
also check frame size....i once rode my daughter's bike when she was tiny.....and my knees hit the handlebars!!!!! ouch, similar to what you describe....the bendy bit of the leg hurt!! :lol: :wink:


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PostPosted: Wed Apr 03, 2013 9:12 am 
Old School Grand Master
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Joined: Fri May 01, 2009 7:11 pm
Posts: 8479
Location: Fircombe.
I've used oval Rotor Q rings with no problems .
Are you're cranks longer than usual?


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PostPosted: Wed Apr 03, 2013 11:05 am 
retrobike rider
retrobike rider
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Joined: Wed Jul 07, 2010 11:19 am
Posts: 1195
Location: Worthing, W.Sussex
Charlieboy28 wrote:


Are you sure...

from Sheldons conclusion...

"Non-round chainwheels remain controversial, especially among racers who think that everyone should ride racing bikes, but, in my opinion, they are of real value for the vast majority of non-racing cyclists. Unfortunately, this useful option has become all-but-extinct.

Dave


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PostPosted: Wed Apr 03, 2013 11:08 am 
Old School Grand Master
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Joined: Sun Aug 21, 2011 11:57 pm
Posts: 4074
Location: Antwerp, Belgium
@ zetec : pretty sure the bike is a bit on the large side for me, so my knees don't go anywhere near the handlebar.
@Reuben : Crank length is 170mm. I'm used to 175, so they're certainly not too long.

The swelling is gone now, so I'm going to do a 30-40 mile trip with my Scott (round XT M730 rings). If I feel ok tomorrow, I guess I'll need to swith the Laïti's chainrings for round ones.


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PostPosted: Wed Apr 03, 2013 11:15 am 
Dirt Disciple

Joined: Mon Nov 12, 2012 4:06 pm
Posts: 86
Location: NE Scotland
It's a myth


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PostPosted: Wed Apr 03, 2013 12:36 pm 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
Posts: 8658
^^^^^^^^ What he said

Sheldon Brown liked them, so using him as a reference against them suggests the article he wrote was not read properly. Knee problems could be caused by many things, picking the biopace system which was bad mouthed by roadies who incidently used a different oval chainring system does not make sense. However for the OP it could be the rings, everybody is different and reacts differently to pieces of kit others like. I cant get on with SPD's or any system that attaches my feet to the pedals and beliegve me I have persevered.


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