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Old 02-09-08, 12:04 AM   #1
tdister
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Still learning...Oval chainrings...

I picked up a nice little Trek 830 (pearl white, nice condition. she's a beaut) and was going through sorting it out. I'm adjusting the derailleur and notice the chain hopping up and down. I first think it's a stiff link, but realized it occured too often and caused no other issues. Then I'm thinking the chainring is bent/warped, but the big one is round still...

I'm decently mechanically inclined, but this was really messing with my brain. Not round, but no evidence of bash damage. For a brief moment I was picturing the gorilla that must have put enough tq. on these poor rings to warp them like this....people really should warn a guy about these things.

Oh, they are Suntour XCE cranks. I found a minuscule amount of info on these. Basically that they are from '89. Anybody got some info?





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Old 02-09-08, 12:13 AM   #2
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Quote:
Originally Posted by tdister View Post
I picked up a nice little Trek 830 (pearl white, nice condition. she's a beaut) and was going through sorting it out. I'm adjusting the derailleur and notice the chain hopping up and down. I first think it's a stiff link, but realized it occured too often and caused no other issues. Then I'm thinking the chainring is bent/warped, but the big one is round still...

I'm decently mechanically inclined, but this was really messing with my brain. Not round, but no evidence of damage. For a brief moment I was picturing the gorilla that must have put enough tq. on these poor rings to warp them like this....people really should warn a guy.

Oh, they are Suntour XCE cranks. I found a minuscule amount of info on these. Basically that they are from '89. Anybody got some info?
Shimano had Biopace and Suntour answered with Ovaltech. They were supposed to get rid of the dead spots in the pedal stroke. Designed that way. But are they useful? Probably not but they won't hurt anything either.

If you change them, you'll have to lower the front derailer a little for round rings.
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Old 02-09-08, 12:26 AM   #3
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Yeah, they're probably Ovaltech--as the previous post said, they were supposed to reduce the force needed to turn the pedal at the spot where your legs were weakest. For about a year, I think in the late '80s, they were hot. Many experienced riders didn't like them because they felt "wobbly" as the resistance changed. I've only used them a little bit (my wife's mountain bike had them, but she's 5'1" and I'm 6'4", so it wasn't a fair trial), and i didn't care for them. But she still has the bike and has refused several times to let me swap the rings for some from my vast supply of junk bike parts.
Don't worry about them unless they bother you. If you want to change to round, they used a standard bolt circle (might have been 110/74mm, I don't remember for sure), and round ones will bolt right on.
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Old 02-09-08, 12:54 AM   #4
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Bike is too small for me, gonna flip it. I think I would keep it as-is though, if for nothing more than a conversation piece. I gave it a short test ride and it was just slightly weird. Not sure I would have really noticed if i wasn't previously aware. I guess I will see if the new owner, without mentioning anything at first, notices anything on their test ride .

Ovaltech? What a drab name...
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Old 02-09-08, 01:02 AM   #5
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I had a set on a RockHopper rigid and a Raleigh full suspension mtn bike,except all 3 rings were oval(can't remember if they were Shimano or Suntour).I found them hard to get used to.Hard to get a rhythm going.Felt like my pedal speed would speed up ,slow down,speed up,slow down.Really hard to be smooth.On the Raleigh I would actually get a little bit of a bounce happening.I ended up swapping them out in both cases.
It's a love it or hate it thing.You'll soon figure out if it's for you or not.
Ovaltech-sounds like a sports drink for old people

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Old 02-09-08, 11:32 AM   #6
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The oval chain rings were all the thing for some time. The problem with them is the degree of out of round they have to be to be effective is proportional to one's cadence. The small rings on a triple with shimano's biopace were nearly square. It was based on the assumption that people pedalled low gears at about 50 RPM (or so it would seem).

They became nearly standard stuff for awhile there. Then I started seeing bikes sold with this new upgrade, round chain rings!!

They are an interesting curiousity though.
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Old 02-09-08, 12:09 PM   #7
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I used a Sugino Cycloid ring for a while.
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Old 02-09-08, 12:59 PM   #8
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You may have more than ONE stiff link!

I've found that oval rings work well for ME. My right knee is bad, so at a higher cadence, that foot wants to come off the pedal, The oval rings cause the legs to be slower at the 6 & 12 o' clock positions, thus less inertia for my leg to keep traveling up. YMMV.
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Old 11-13-08, 09:34 PM   #9
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interesting stuff... I bought an old road bike and thought I got ripped off because the chainrings were oval. what a mess. did notice it was harder to keep a steady cadence. I guess I'll give it another go before I change the chainrings
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Old 11-13-08, 11:25 PM   #10
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As I recall Shimano had two versions of their Biopace rings, the first more oval than the later version.

Looking at the latest Excel catalog I note that some aftermarket company is trying the idea again, at a very fancy price.

At least Shimano is willing to try new ideas. Some have worked out and others are just historic footnotes. Are the new 11 speed Dura Ace electric shifting derailleurs going to take over and work their way down the price ladder? Index shifting did but many of their ideas did not.
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Old 11-14-08, 03:52 PM   #11
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There's been a few-
http://www.norcom2000.com/users/dcim...hainrings.html
and I couldn't find all of them.
I think when I made this diagram there was about two or three others I could not locate pictures of.

There's also a small company online (UK I think) that makes non-round rings with multiple mounting holes (similar to what the Rotor Q-rings have, but not as many holes) and they have a "stock" product but will basically make whatever CAD shape you send them, so I didn't list that company.

-------

The main issue with non-round rings is that they tend not to shift as well as round ones--although the effect is most noticeable on triple-ring bikes (going from the middle to the granny ring) than double-rings.

Some people found the non-round rings caused knee injuries they didn't get with round rings either, but I wouldn't consider this much of a danger really. You can see from the diagram I made that some of the earlier types varied only slightly from being round. The currently-available Rotor Q-rings vary much more than any of the BioPace, Cycloid and Ovaltech rings did.

-------

I have Rotor Q-rings on both the bikes I have now.

Q-rings have an advantage in that due to the multiple mounting holes you can choose in the pedal stroke where you wish to put the dead spot of the rings. On long rides I would get knee pain but only during the top part of the pedal stroke; getting a set of Q-rings and aligning the short-radius to that point decreased the leg strain considerably, and let me ride significantly farther before knee aching set in (80-90+ miles as opposed to ~60-70 miles with the round rings) .

I started with them on just the "long distance" bike but now have them on the town/commuter bike too (round rings feel "funny" to me now, the Rotors just feel right).... And I have them adjusted about 72 away from the angle they advise for "best power", so I don't know that I'm putting out any more power or going any faster with them. I don't know or care what racers are doing these days; I just know that I can pedal farther in better comfort with the Q-rings than I could with round rings.
~
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