Training for higher cadence - crank length

Hi guys,

About 6 months ago I discovered that I tend to ride at fairly low cadences (70-75). As my knees are kinda sensitive this seems like an unwise thing to do, so I've spent a few months now trying to rev up.
This is going so-so.
By now I'm getting into an average of 85 or so, which is keeping my knees happier, but my rides slower.
I have made a dedicated effort to get a smoother pedalling style, but I still have troubles riding smooth when I get into higher cadences.
According to fairly accepted theory shorter cranks will make it easier to spin, but how short is short?
Currently I'm running 170 mm cranks, which according to one sizing formula is abt 5 mm too long.

Should I go for a 165 mm crank(which I'd have to buy somewhere) or do you think I can try going to 160 mm (which is something I could knock together at home at reasonable effort)?

I can believe that shorter cranks might be easier on the knees by increasing leg extension and slowing the foot over the top/bottom of the circle, but I don't think they will change your cadence at all. I'd be interested to read an article or something on that theory if you have a link.


How about knocking together a pair of 160's to see how you like them, then buying a set if they do what you're looking for?

Just out of curiosity, what formula are you using?

The one on this site:

You've gotta keep in mind that I'm a bit biased in this. My knees are a concern, so I'm well motivated to try stuff that might help me out.

Anyhow, here's one:

A forum thread:

Slightly vague article:

And, of course, a Sheldon Brown article about it.

Another forum thread:

I've got a 175 mm crank that I could redrill and rethread for 160 mm at "zero" cost, which is nice if I'd end up not liking it. But If I want to turn it into a 165 I'd have to have the old hole filled first which'd be a more delicate operation. I'd rather not have to do it twice.

Buying is of course always an option. But given that my knees are so-so I prefer not to invest too much in my bikes. There's no telling how long I'll be able to enjoy them.

Just to ask the obvious here, have you payed for a good bike fitting from a professional fitter?

I ask for several reasons. First most cyclists gravitate towards a crank length that feels best to them, but can adapt to a wide range of cranks without problems or big drop in cadence. For instance I ride 165s on the track, 170s on my TT bike, 172.5s on my road bike and 175s on my mountain bike. It's no problem spinning any of them up to 110 rpm or higher on demand. Even if you look at the wide range of inseam lengths among adult cyclists compared to the relatively narrow range of commonly available crankarm lengths it's pretty clear that folks adapt well to the available cranks and don't have dramatic problems spinning a slightly long or short set of cranks.

It makes sense to find your best fit, but I've gotta believe a typical cadence of 70-85 rpm has a lot more to do with: gear selection, skills development, and possibly bike fit than crankarm length.

How long have you been riding seriously and how often do you train and what gears and terrain do you typically ride? Also how is your bike geared, single speed, standard double (53/39), compact double (50/34), triple?

Bikes are often prescribed as rehab for knee troubles and pedaling forces are very low even when compared to things like walking up a flight of stairs. So something isn't adding up here. From what you've described I'd guess that you're either slamming huge gears for the terrain, you're not well fitted to your bike or you just haven't put in enough time to develop your pedaling skills.

FWIW, most folks experience higher heart rates and higher perceived exertion at higher cadences for the same power output. I know I tend to slug a heavier gear in a long flat time trial(80-90 rpm) and spin lighter gears in mass start races to help with the frequent accelerations (100-115 rpm) but spinning efficiently gets easier with practice and is worth the effort if you're concerned about your knees.

Good luck,
-Dave

I'm a bit suspect of any/all "fitting formulas" (I'm familiar with most of the ones you've cited). One needs to remember that a formula simply gets one to a starting point from which to further refine the fit of the bike. It is not a finishing point. Formulas can not take into account all the individual asymmetries and flexibility issues that affect a proper fit.

I second Dave R's suggestion of seeing a qualified fitter as step 1.

Dave

Well, no. Around there there's a total of one to choose from. He charges $200 and don't exactly come highly recommended.

Besides, I have a nagging suspicion that he'd laugh himsef silly if he saw someone riding my class of bikes asking to be fitted....

Can't say I've gravitated towards anything before. First I rode what I had w/o caring. Then as the knee troubles started I kept riding what I had w/o knowing any better. It's only lately that I've begun to be slightly more analytical about it.

When it comes to more relaxed riding, sure, so can I. Until recently the only time I ever considered crank lengths was if I had to do some right/left mix'n matching.
In my case, the problems are already here, and I'm looking high and low to find a way to relieve them.
I can do maybe 95 in a reasonably controlled manner, any higher and I'll get a very pronounced saddle bounce.

Hey, I'm not picky, I'll take any improvement regardless of where it coming from. If painting the frame pink would help I'd get a rattlecan this afternoon!

Joking aside, I think I'm working the gears fairly well (although I'm considering a tighter ratio cassette too). Bike fit feels good, just might drop the bars a little more though.
Skill is an obvious suspect, and I can't say more than I have been doing regular sessions of dedicated pedaling training for some months. Pedaling one legged, focusing on following through the whole rotation, dropping a gear to sort of force a higher cadence.

I used to do XC-MTB which I took fairly seriously, then my riding buddies moved and I guess I just coasted for a few years. Now I've been commuting by bike for about two years and using that as my main work out too. Basic schedule is:
Monday - Ride in, publ.transport home
Tuesday -publ.transport in, ride home
Wednesday - no bike
Thursday - Ride in, publ.transport home
Friday - publ.transport in, ride home

Today's ride in was fairly typical, 1H 5min, peak HR 180, avg HR 145.

The winter bike is basically an old MTB (still got the studded tires on), so it's a 46-36-?? triple to an even older Sachs rear hub at maybe 14-24 or something like that. The terrain is mostly flat, with 3 short, sharp hills that calls for either some serious honking or granny gear. It's 16 miles and the cyclocomputer has it down as around 13 MPH average.

In my early teens I had a paper route, spent maybe 10 hours/week hauling a huge basket loaded with newspapers around in a hilly residential area on a 3-speed, adult-size bike. It ended in tears, rehab and seriously messed up lining on the inside of the kneecap.
If I don't train the knee loses stability and alignment. If I train too hard I overexert an already damaged area.

Damned if I do, and damned if I don't...

Don't think so. Even with my 26-inch wheels it's the 36 in front that sees most of the action.

Could be, but if it isn't an efficient fit it's at least a very comfy fit.

Indeed a possibility. I got the cadence counter in September, so before that I was riding in blissful ignorance.

As a rule I can run fairly high heart rates w/o being particularly bothered by it, so it seems like that could work out for me.

It's about time it got easier then. A 10 rpm improvement over 6 months isn't exactly dazzling.

It sounds like you've eliminated a lot of the common culprits. Definitely double check your seat height, I agree with Dave that formulas are just starting points but make sure your seat height isn't much too high or low. I personally set my seats to 100% of my Greater Trochanter height measured standing upright in bare feet. Other methods should give similar results within a cm or two. It sounds like you could be a tad high (although that usually results in pain behind the knee not in front of the knee, but it can explain bouncing at higher cadences).

The other thing that comes to mind is your shoes, pedals, cleats, etc. Do you pronate or supinate heavily on one or both feet? What pedal & shoe combination do you ride and do they float or are they fixed?

Have you seen these:
http://www.cambriabike.com/shopexd.a...AL+CLEAT+WEDGE

http://www.slowtwitch.com/mainheadin...t/lewedge.html

or these:
http://www.bikescor.com/product/knee.htm

In both cases the concept is to alter your pedal width(Q factor) or shoe angle to improve knee tracking.

Maybe 165mm cranks are exactly what you need, and if you find some to try out you definitely should. But I seriously doubt you'll spin faster and smoother and experience less knee pain by simply dropping half a cm from your cranks. Based on what you've said I'd concentrate on double checking your fit and on your pedal/shoe system.

Good luck,
-Dave

When jogging I've got a fairly moderate pronation that's very symmetrical.

I'm using Crank Brothers Egg Beaters and CB Candy, with either a Shimano MTB winter shoe or a Sidi MTB shoe. The Egg Beater in particular is quite tolerant as to how you angle your foot, and they're both at 6 deg float.

Yes, but I haven't looked into them that close. Right now the canting thingys seems a bit too much like groping in the dark. I'd like a clearer indication that they might offer me some help before trying them out. It seems like they'd make a more significant difference on road shoes/cleats particularly when compared to my Egg Beaters.


Yes, those too. But since I'm riding triples, I'm fairly wide already. I'd be more curious to see if a narrower Q-factor would do me any good.

OK, I'll have a go at redrilling those 175 mm ones sometime soon then.

The knees have been rather pleased with the somewhat higher cadence, so right now pain is a manageable issue.

Darn, I'd quite like to regain that 1-2 MPH that I've dropped in average since I started going for a higher cadence.

I can go to 160 if it's a chance of that having greater effect.

Maybe I'll have to bite the bullet and try that "bike clinic" guy anyhow...

Thanks!

This may be stating the obvious, but BEFORE you re-drill & tap your 175mm cranks to convert them to a shorter length (WOW! That's a potentially tedious effort, particularly tapping in new threads -- use a drill press for the new holes, BTW.), try pedaling in ONE GEAR LOWER (yet another gear lower if you have already downshifted one gear) & see if the higher cadence is agreeable or annoying ...

As suggested, try lowering your saddle height by about a centimeter if you feel as though you are bouncing ... you can raise it back to the "normal" height later IF you acclimate to the higher cadence.

Well, my knees have appreciated that I've dropped a gear or two. And mentally I don't mind it as such. But the issue seems to be twofold:
1) stomping it at a cadence of 75 used to be my "natural" average state. I have no problems as such with dropping a gear and "forcing" myself to ride at 90 or so. But as soon as I quit making a deliberate effort to crank that fast I revert to a "dropped gear average" of 85 at best - which looses me abt 2 mph from the old kneekiller routine.
2) to get a higher average w/o getting carpal tunnel or something from excessive shifting I need to be able to peak higher, and that's when I get that inefficient saddle bounce.

I rather enjoy that kind of work, so thank you for your concern

Maybe I haven't tried it long enough, but I've given that abt 5-6 hours. Feels weird and make me want to ride with my heel dropped and doesn't really seems to do anything for the saddle bounce issue.

10mm can be to much in one go.
Think & pedal in circles.

A bike is a bike is a bike. Doesn't matter what it is - it still has to fit.

Well sure, and I'm happy to take functionality wherever I can find it. But the shop where the bike fitting guy works is more aimed at the shinier (and more expensive) stuff...

I'm a bit concerned that I won't be taken seriously showing up there with a bike whose total value is less than the wheels that his usual clientele uses.