Oval chainrings cause knackered knees?

Perhaps then it's a combination of oval rings and old knees?

40 miles with the Scott yesterday, and no problems whatsoever. Today 10 miles of city traffic with the Laïti and I can already tell that tomorrow I'll be taking painkillers as if they were candy.

I have a feeling that on the middle chainring the humps are in the wrong place indeed. Using the clock as a reference and viewing from the right, I get the proverbial kick in the knees around the 2 and 8 o' clock points. Seeing as this is a 5-arm crankset, it can be turned 72° at a time, which is about that region. So for now I'll rotate it one position at a time until it feels somewhat right, and will see from there.

As for old knees, at 16 I started to have pain in my right knee, usually near the end of longer races. The doctors told me I could either undergo surgery (something about the ligaments) or quit competitive cycling. I haven't touched a road bike since.
I don't put anywhere near as much stress on them nowadays, and certainly not for 100+ miles at a time. As a result, I really doubt the knees themselves are the problem.
Besides, the left knee is also hurting now, and that one has always been perfectly fine.

I notice no ill-effects with Biopace - and my 64 y.o. knees are considerably past their best!

Probably another myth similar to that riding fixed "is bad for the knees".

More usually related (I think) to pushing too high a gear (probably the actual reason for the association with fixed).

Start banging down high doses of Fish Oils. Should sort out joint problems. It did mine. I take 5000mg a day. No problems here.

i agree a lot of it is anecdotal evidence , but have a google of bipoace rings and they are very marmite , with the marmite haters citing knee problems .

seems they work well for some but not for others.

I dont think that biopace didnt take off for the big S because of some nasty urban myth either, it was a failed design

again anecdotally speaking, but my knee's arent great, the only chainset i remember problems with was a biopace , but then it was also a 200gs. i also used to push bigger gears at a lower cadence . now i spin quicker in lower gears and dont have the problems

Charlieboy28":19wziu4b said:

i agree a lot of it is anecdotal evidence , but have a google of bipoace rings and they are very marmite , with the marmite haters citing knee problems .

seems they work well for some but not for others.

I dont think that biopace didnt take off for the big S because of some nasty urban myth either, it was a failed design

again anecdotally speaking, but my knee's arent great, the only chainset i remember problems with was a biopace , but then it was also a 200gs. i also used to push bigger gears at a lower cadence . now i spin quicker in lower gears and dont have the problems

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I went through a period of knee problems - and truth be told, didn't really suffer the symptoms directly from periods of being in the saddle.

I've lifted weights since forever, and have always looked after my knees from that perspective, but strongly believe full squats are helpful for knee health (given work on technique). My knee issues seemed to coincide with perhaps my most active in terms of gym usage, plus my most active in terms of off-roading and hill climbing.

Perhaps BITD, being relatively strong in the leg department, meant I was inclined to push bigger gears than I really should, I'm not sure, but I do know this - once I focused on cadence and being more inclined to spin a bit faster than lug a higher gear, the problem largely went away.

I have used biopace BITD, and one of my current bikes has biopace rings, and although I don't tend to do much miles these days, and little hill climbing, I don't tend to feel anything I'm directly connecting to them. Any minor niggles I have with my knees, these days, is normally one of those biological tells that I should focus more on certain lifts to keep my legs at their fighting strength.

During a full strip of the offending bike, I had the opportunity to look at the chainrings properly. Turns out they aren't just oval, they're some weird shape. Like oval, but with one side more convex than the other.

I noticed that the XCM crankset has a 113mm BB, so switching to an XT wouldn't work without changing the BB itself too (needs 122.5). Altus does have a 113mm BB, but I only have one NOS altus set and I'm saving that for when my Sbike needs it.
However the XCM rings themselves have the same BCD as the XT M735 ones, so I now have a Sunmano crankset ... or is it a Shimtour?



Now I just have to rebuild the bike and take it out for a few test drives to see if the problems are solved.

Raging_Bulls":2skdsl3r said:

@ 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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Is this on the same bike? Have you adjusted the seatpost to take account of this?

At first I was comparing different bikes that had nearly the same riding position. Regular flat pedals too, so I'm sure it's not the result of badly adjusted SPD's.
Now I have put the round chainrings on the bike that had the oval ones, and after 25 miles today I have no pain. Will see if it lasts.