spectastic

two questions

why do track sprinters generally use shorter crank lengths while road sprinters generally prefer a longer crank length?

my understanding is that track sprinters value aero and stiffness over weight. it's not uncommon for them to weigh 20 lbs, is that right? is weight really that insignificant?

700wheel

My thoughts:
Because track sprinters use one gear that results in a very high cadence. Short cranks facilitate this.
Road sprinters can upshift to a higher gear when they are already at speed so high cadence is less important.

spectastic

make sense, they're forced to compromise with only one gear, at low and high speeds.

what about bike weight?

Baby Puke

There's a lot of research lately that points to better results on shorter cranks regardless of discipline.

spectastic

can you point me out to these research? the stuff I read list tradeoffs between longer and shorter cranks.

grav.digr

its rather commonplace to see 170mm in the pro ranks these days (on the road)

Baby Puke

I think this is the article that people have been referencing recently:
Are shorter cranks better? - Cycling Weekly

But it's been known for some time that there is virtually no advantage in power in changing your cranks to anything from the 165mm-175mm range that is typical. The conclusion then, is that shorter is better as it allows you to get a more aerodynamic position on the bike with equivalent hip angle. Or allows you to have the same position with a more open hip angle. Pretty easy. I'd like to try 160's myself.

79pmooney

Bike weights matter very little on the track. They never go uphill except to gain height on the banking and much of the reason they do that is to either place themselves where that weight will be used to advantage accelerating as they come off the banking or the rider wants to slow down sharply to force the rider behind to take the lead, again being about to recoup that speed for free coming back down behind the rider he has just forced to pass. Sprinters esp value both stiffness and strength a lot and in general, more of either adds weight. (Track sprinters are the heavyweight wrestlers of the bike world. I've known some whose thighs matched my waist.)

Ben

carleton

Several reasons:

Longer crank arms are great for climbing. Roadies climb. There are no hills on the track.

Roadies usually grind at lower RPMs than the cruising cadences that track racers hold. Cruising RPMs in a peloton are like 80-100 RPM. In a track points race, the cruising RPMs are like 100-110 RPM and sprints are 120-130 RPM.

Most importantly:
Roadies have gears, so they shift their way into maintaining the right amount of torque for a given effort as they increase speed. Trackies don't have gears, so they have to regulate speed with cadence. It's easier to regulate cadence (and spin faster) with shorter cranks than longer cranks.

It's not a weight or stiffness thing at all.

spectastic

yes, there's no climbing, but what about accelerations?

taras0000

Look at the differences between climbing and acceleration and that will answer your questions.

SprintzNKiloz

My fitter is super into the "shorter cranks = better" for most people. For me it was a matter of lessening deadspots. I am short and have short legs but OLD roadie habits had me riding 172.5s on the road. Once I started racing track w 165s, the differences were noticeable once he got my fit sorted on both bikes. Much earlier engagement in the pedal stroke with shorter cranks for me.

andr0id

You use a short crank arm on a track bike so that so your pedal doesn't hit the upside of the bank when you're riding at a walking pace for a matched sprint.

All the other "reasons" about short cranks making your faster or whatever are speculative hooey.

queerpunk

I've known people who use 172.5s on 43-deg banks and have never pedal struck; and I also know that most tracks are not that steep. So banking can't be a great reason.

And, since shorter cranks can accommodate a more aerodynamic position with a hip angle sufficient to generate power, I don't know if you can call increasing your power:cda relationship 'speculative hooey.'

andr0id

Then they have a high BB. My 170's will hit at the Superdrome if I'm going slow enough and it's only 44/45 degrees.

wens

Or they're good at leaning the bike over away from the banking...

dunderhi

I actually think tapping the track with a pedal should be a mandatory drill for newbies. When I rode Giordana last year, I tapped the track with 170's to get a feel for the steepness and felt comfortable with riding 172.5's after that.

wens

. Maybe certain tracks , but I wouldn't want to be the person getting new riders to tap something as step steep as cleveland , because there's just not much main margin for error . I also don't think you even could do this still drill at a lot of wood tracks , yu slide before you arrive strike .

SprintzNKiloz

I rode Giordana with 165s in March to recon for Nats and had ZERO issues then at Nats I tapped twice in my match sprint rounds. DOH.

SprintzNKiloz

Also RE shorter cranks I will second what QP says as my fitter could quantify to a degree the watt delta between short cranks vs long cranks. Not hooey at all.

spectastic

yes, I understand shorter cranks are of greater benefit to shorter people, when speaking in the context of 170-175 cranks. may i ask how tall you are and inseam?

spectastic

what was the delta?

SprintzNKiloz

Nothing massive... 10 watts or so.

SprintzNKiloz

Also, to your other question. Inseam = 28" and height is 5'6" so I for sure fall into the having a lot to gain using shorter cranks perhaps.

Baby Puke

I have reason to believe the GB sprinters have been using cranks shorter than 165 for some time. And some of them are pretty tall. But as with all this stuff, use what you like. It's just for fun.