Drakonchik

Because of the oval shape of the rings, the front derailleur in a BioPace set-up will sit pretty high, and will sit higher still is you are using one of most current MTB front derailleurs because of the shape of the inside wall of the cage on. Which doesn't help shifting speed.

Also none of the MTB BioPace have ramps or pins, although the roadie HP has slight ramps on the large ring, and as a result shifting is no where near as fast as it is with ramped and pinned front rings. So there's a trade-off: gain some traction, lose some shifting speed.

StokerPoker

I've been riding the Trek for a few days now and My legs don't hurt a bit during or after I ride. I do find that I have to learn to pace myself on this bike because I'm riding harder and faster because I'm more comfortable. I'm getting out of breath...

jordanb

One question about these things: I assume they only work with derailleurs? It seems that the length of chain wrapped around the sprocket would change as it rotated and if you didn't have a springed tensioner it would be going from taught to slack and back again. Even with a tensioner I'd think that if the cyclist really started spinning the chain would start flopping around.

Eatadonut

theoRETICALLY, the length of chain stays the same, Sheldon has an article on this. As well, he's made a Biopace-equipped fixie. I've never had that luck, but I haven't tried too hard.

Lurch

Two of my bikes have biopace chainrings and when spinning the crank on the repair stand I can observe only a slight bit of possible rear derailler motion if any. If you look down while pedaling the chainrings are obviously "out of round" but there isn't nearly as obvious a motion in the chain tensioner function of the rear derailler. My limited intellect has trouble with the effect of chainwheel shape plus the number of teeth. However, if I think about an extreme case such as an almost bar shaped chainwheel, the effect seems more obvious. Such a chainwheel would result in pronounced "power pulses" to the rear wheel. The effective diameter of the chainwheel would change drastically as it spun as would the number of teeth engaged with the chain. However, I suspect the two effects would cancel out to a great extent as far as chain slack is concerned. Does anyone else think this is the case? Does anyone care at this point?

StokerPoker

if you put any bike on a stand and turn the pedals there will most likely be movement in the derailleur

jcm

BioPace and OvalTech are not oval. They are subtley trapazoidal. My '88 Trek 830 mtb has the Sakae Ovaltech in 48/38/28. Among other reasons, this is the main factor as to why this old nag is my favorite bike for all purpose riding. I mean for everything, including centuries. I always have my eyes open for a BioPace road triple so I can somehow put it on my '98 Trek 520. Then I might ride that more.

I suspect that BioPace fell out of favor because of the cost of manufacture and the rise to prominence of the race crowd because of the advent of American racing success, ala Gregg Lemond. So followed the Bike Writers, as opposed to Riders, and thus the industry 'discovered' the New Wisdom: Round Is Better.

It's all marketing in the end. If the writers and industry suddenly began to spout about the virtues of BioPace under another name, it would be all the rage all over.

To those who have tried it and didn't notice a difference: Seriously, were you coasting? You got me muttering to myself here. To me, the difference is nothing short of astounding on hills with a loaded bike. The torque is unbelievable at the power stroke. You can kick back and spin or mash 'em with what seems like half the effort. That 830 with me aboard and another 15-25 pounds just crushes hills.

jcm

Yes, the derailleur moves forward and back with each crank-over.

StokerPoker

it is amazing for hills. there is one hill on the way back to my dad's apartment that can be a killer if our wednesday morning rides are too long. I used to keep pace with my dad on that hill because that was my pace too. he just turned 59 and I'm 23. my MTB and his hybrid with a megarange gear... Now with my trek 800 with BioPace I had to wait at the top of the hill for almost 2 minutes for him to reach the top. my legs used to burn up that hill. now I'm just out of breath when I ride this bike cause I'm able to ride so darn fast... if I quit smoking I'll never get off of this bike!!!

jcm

You are right about the construction differences but I have to say that my Trek 830 shifts as fast and reliably as both of my 105 equipped bikes. Both at the front and rear. Quiet, too. I can't explain that, though.