D/A 7410 cranks - the all-time narrow champion?

[über-goober]

Here's my product review.. for a crank released in 1993.


These were the last square taper Dura Ace cranks and are known for their narrow tread AKA 'Q-factor'. I have always liked a narrow pedaling stance and was intrigued to try these on a modern 11sp drivetrain.

And the elegant shape has really grown on me - the slender curves for lightness and bringing all your massive soul-crushing forces in toward the center of the bike.


The stats:
With a Phil 103mm BB mine have a 138mm q-factor, and a 118mm width at the center (the 'u-factor' measurement for heel clearance). Compared with the Super Record ti cranks that are narrower than most, but measure 145.5mm and 128mm.



The narrowest current production cranks I know of are Extralites; about the same as the 7410s at ~138mm but with a wide U-factor that may actually exceed the SR cranks.

Here's are some published numbers from BB30 cranks:


And then weights:
604g for the arms plus Phil ti BB, alloy cups, and alloy crank bolts. And a complete crankset with 53/39t rings and alloy chainring bolts they are 743g. (vs 638g for the full SR set). Stiffness is probably about as impressive and then a stiffness-to-weight number way down in the basement showing the 20 years' lag in technology.


But nevertheless I'm in love. Thanks for retrogrouching with me this far. More to come.

[pritchet74]

Completely agree. One of my favorite cranksets of all time! Nice write-up too.

[über-goober]

borat.jpg (40.55 KiB) Viewed 2770 times

Very nice!

[pritchet74]

Nice pic!

How'd you polish those chainrings?

[über-goober]

I like shiny. Those are stock Truvativ rings -- never intended for 11sp but they work well.

[Boonen]

Nice write-up über-goober! Nice thing about these is you can tune them to your frame with the right bb if you want them to be really narrow. Bet these won't fit some wide carbon frames like this!

Anybody has a set of super record cranks they could measure in comparison? From the article on Sheldonbrown you linked to it seems those might be even narrower?

[über-goober]

Some last thoughts. The Q-factor thing can be a real can o' worms. Biomechanics is complicated stuff and I have a lot of respect for those who know how to fit people on bikes.

While some of us prefer narrow (some militantly so) there are many others on the opposite end of the spectrum having to go wide. I have a couple friends who had to widen their BB and shim their pedals out or else get IT band flare-ups and knee problems. I've heard many correlate it with hip width but the bottom line is people can and do ride anything on the spectrum and it generally works OK.

And honestly when I ride a MTB with an inch more width it's noticeably different at first but not so bad. I have a set of Morati cranks at 158mm, not a deal breaker because of the coolness factor. (Until they broke.. now that's your deal breaker.)

So why think about it? Besides how you pedal, what about for aerodynamics? Graham Obree was obsessed with narrowing his cranks for his hour record, hence his famous modified washing machine part. With everything people are doing to get lower -- isn't getting narrower just as important?

And then cornering clearance.. what if your criterium bike could lean a centimeter more on each side before scraping?

TImely stuff because the 135mm rear spacing that may be inevitable on road bikes in the next few years = wider at the cranks most likely.

Lastly - about measuring the Q-factor: an easy way is to use a ruler and measure from the crankarm face right at the pedal to a particular spot on the seattube or chainstays, and then rotate the cranks to the other side and measure to that same spot. (you don't need to take anything off).

[pritchet74]

I would much prefer to have a very narrow q-factor for aero purposes, but a well respected local bike fitter added shims to my pedals to widen my stance and it is more comfortable and alleviated a problem I had with my hamstring.

[Xavier]

Actually, if you can get hold of a set of 7400 or 7402 square taper cranks, then paired with a 103mm BB they will give you a Q Factor of 128mm. You might have issues with the chainstay clearance and/or inner ring, but I've fitted sets to quite a few bikes, especially TT bikes where you can get away with the single ring. If you can find some FSA Vigorelli track cranks (the older ones with the circular central section) and then lose the pedal washers, they get you down to 133mm (single ring 144bcd), which is another good option for non BB30 frames. Otherwise use the Cannondale Hollowgram cranks.

Hip width does not correlate with preferred Q Factor - it's likely to be related to muscle insertion points, muscle lengths and flexibility/range of motion at the hip. A higher Q Angle* may influence your preferred Q Factor as well.

During Project 94 they had a go at narrowing legs against frames and seeing if it was more aerodynamic, but it could have been done better I feel (they didn't find any differences).

B Xavier Disley

*not to be confused with Q Factor, Q Angle is the angle of the quadriceps to the hip. A higher Q Angle means that your knees are closer together, and women have higher Q Angles than men - which is partly why we see more knee injuries in women as the side loads on the patella are greater.

[über-goober]

Thanks for the info. How is the heel clearance on 7400s? Do you know about any efforts by Walser or others to make TT bikes narrower?

When I got some shorter Speedplay spindles I ran into the limits of low Q at least for this bike, when the heels rub the chainstays.

[über-goober]

During Project 94 they had a go at narrowing legs against frames and seeing if it was more aerodynamic, but it could have been done better I feel (they didn't find any differences).

What is Project 94?
Thanks.

[pritchet74]

He means Project 96, which was for the development of new bikes and other cycling equipment for the USA track racing team for the 1996 Atlanta Olympics.

[Xavier]

Sorry, I did mean Project 96

Heel clearance is just related to the chainstay shape really - on most track bikes we've used the DA 7402s are fine but you do just have to try and see! Luckily the 740x cranks and a 103mm 7410 BB aren't too expensive secondhand nowadays.

We presented some data at ECSS this year about Q Factor in the laboratory showing a (small) improvement in efficiency with narrower Q Factors, the full study will be published soon:

http://www.ecss2006.com/asp/congress/Sc ... ractID=948

Xavier

[über-goober]

One of the original GT Super Bikes is on display at a shop that makes roof racks in Boulder.

Different wheels but very close to this:


It looks invisible from straight ahead...

[pritchet74]

I love that bike. One (and maybe that exact one) was sold on eBay several years ago by the US Olympic committee. I bid, but couldn't afford the final price. That would have been nice to have.