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Q-factors(10 posts)

Mar 5, 2002 2:39 PM
Sorme reviewers on this site claim that a Record BB/Chainset combination has a lower Q-factor than, for example, a Daytona BB/Chainset combination. Is this true? And if so, exactly how great is the difference?
And how does Dura Ace compare?

Many thanks.

re: Q-factorsDY
Mar 6, 2002 1:41 PM
They have different axle widths. The Record/Chorus use a 102mm axle and the Daytona/Centaur/Veloce use 111mm. Assuming that the crank arms are all designed the same, you'd have a smaller Q-factor with the Record/Chorus set-up.
they are NOT designed the samenm
Mar 6, 2002 2:17 PM
they are NOT designed the samebugs
Mar 7, 2002 1:03 PM
That's what my question was getting at really (though it was badly worded.)
Given the different axle lengths (103mm, 111mm etc.)AND different chainset desings - do they set up the same? And if not, how big is the difference?

I'd really appreciate any answers.

Mar 7, 2002 3:04 PM
I'd say you have about and 8 mm problem and in the world of BB's this is huge. Most of the bike stuff these days is pretty much optimized and if you try and mix 'n' match you're going to have big problems. Your best bet is to just pony up and get the correct BB for your bike & crank setup.
Mar 8, 2002 1:33 AM
That's not what I meant.
What I mean is, if you have one bike set up with Daytona BB and chainset, and another bike with Chorus BB/chainset would there be any difference in how far apart the pedals are (Q-factor)?
Insufficient data.Spoke Wrench
Mar 8, 2002 7:33 AM
I was hopeing for a full-on Q factor flame war. Grzy wouldn't even bite. What a disappointment.

There are a lot of things that can affect Q factor. I suspect that the two biggest are BB spindle length and the crank offset. Through the years, cranks have become offset more and bottom brackets have become progressively shorter. Q's keep creeping up, but I suspect that might have to do with 130mm rear hub spacing more than the cranks themselves.

The "theoretical Q's" become even more interesting with guys using the shortest possible cranks and chainrings to let them move the crankset closer to the bike's centerline. When the crank arms hit the chainstays, that's your minimum possible Q.

All of this is based on the ASSUMPTION that a smaller Q is better. I'll bet that a discussion about "optimum Q" would be about as much fun as a 2.5mm difference in crank length.
Insufficient data.IF Guy
Mar 8, 2002 8:19 AM
Ah, but you must remeber Spoke Wrench that an difference of 2.5mm of crank length is essetially a 5mm differece in the diameter of the crank arm rotation (2.5mm in the front and 2.5 in the back). Therefore it is a significant change in leverage therby allowing more force to be generated with longer cranks. Conversely it takes less effort to turn shorter cranks. All in all since a change of 2.5mm in crank length is essentailly a 5mm change in a static component, think of how much 5mm change affects other components like stem length or seat post height. Made you think didn't I.
Yeah, right.Spoke Wrench
Mar 8, 2002 10:17 AM
The distance from my pedal at maximum extension to the top of my saddle is 36 inches. As you indicated, a longer or shorter crank will affect my foot at the top of the pedal stroke 5mm, somewhat less than 1/4". The difference is less than 1%. I don't think I've got the touch to notice.
Mar 9, 2002 2:29 PM
hard to find specs for cranks. The Ritchey cranks are supposed to have a low q factor. I know from measuring myself that there was/is a huge difference between the older generation DA and Ultegra cranks which used the same bb width.

some info here

Anyway, I'd go with the Chorus cranks over the Daytona--my guess is that the Chorus setup will have a lower q factor.