Shorter cranks... Is there a downside?

[Kermit power]

Evening all,

My new MTB seems to ride a little lower than the old one, and I find I'm clipping the pedals on the ground from time to time, which I didn't tend to do on the old one.

Should I come to replace the cranks at any point in the futire, therefore, would there be any reason not to fit shorter cranks? I know it'd make the pedal strokes marginally harder for the same gear, but I'm thinking that would probably be worth it for 5 to 10mm of extra clearance.

[Dammit]

I can't see a downside, just change gear.

[Watchman]

Is the ride height set right? It's unusual for any bike to be intolerant of cranks lengths between 165 and 175mm. I've even had 180s on without really noticing.

[Herman Toothrot]

Have you the same pedals? i have wellgo flats on my current bike, I kept hitting them on things and thought maybe the bb height was lower but it turned out its actually higher and its that the pedals are more rectangular compared to the old DMR V8's I had on the old bike. The DMR's are more sculpted to the shape of a shoe, the corners are cut back giving a lot more ground clearance.

[Kermit power]

Herman Toothrot said:

Have you the same pedals? i have wellgo flats on my current bike, I kept hitting them on things and thought maybe the bb height was lower but it turned out its actually higher and its that the pedals are more rectangular compared to the old DMR V8's I had on the old bike. The DMR's are more sculpted to the shape of a shoe, the corners are cut back giving a lot more ground clearance.

That could be part of it! DMR V12s on the old bike, and Nukeproof Neutrons on the new. Thinner, but a larger platform.

As for the ride height previously mentioned, the rear shock sets its own sag, and if anything, I've got the front set a bit hard, which at 18 stone is not easy to do!

[nike 5]

If you still have your old bike, put your old pedals on new bike.

Some people argue that crank length should be proportion to the persons leg.
http://www.stevehoggbikefitting.com/bikefit/2011/0...

In the scheme of things you're talking about a difference of millimetres - not sure you'd notice a difference with changing crank length.

Sounds more likely that you'd need to look at your riding style. It's also a far cheaper option to look at first. Lots of clips on youtube.
When does pedal strike occur - when going around corners (outside pedal down, as it aids clearance, and helps balance/weight on tyre)
or free wheeling over hazards (at level position, keeping pedals out of way).

Edited by nike 5 on Monday 2nd February 08:44

[scherzkeks]

nike 5 said:

If you still have your old bike, put your old pedals on new bike.

Some people argue that crank length should be proportion to the persons leg.
http://www.stevehoggbikefitting.com/bikefit/2011/0...

In the scheme of things you're talking about a difference of millimetres - not sure you'd notice a difference with changing crank length.

Sounds more likely that you'd need to look at your riding style. It's also a far cheaper option to look at first. Lots of clips on youtube.
When does pedal strike occur - when going around corners (outside pedal down, as it aids clearance, and helps balance/weight on tyre)
or free wheeling over hazards (at level position, keeping pedals out of way).

Edited by nike 5 on Monday 2nd February 08:44

Agreed. Also strictly regarding crank length in relation to leg length, all of this was figured out decades ago. 170 typically works for anyone with an inseam under 90 cm. 165 can be useful if you have very short legs or short femurs.

[anonymous-user]

Mike Burrows has been advocating shorter cranks for years, something to do with increasing cadence and reducing the circle diameter the foot travels which helps the muscles to ensure more efficient pedalling though I may have made that up....

[Kermit power]

nike 5 said:

If you still have your old bike, put your old pedals on new bike.

This is a possibility, although the old pedals are red and the new bike's blue!!

Aesthetics aside, however, I've just checked the sizes, and the Nukeproofs are 98mm (width) x 99mm x 17mm to the DMR's 100 x 95 x 16, so very little in it.

nike 5 said:

In the scheme of things you're talking about a difference of millimetres - not sure you'd notice a difference with changing crank length.

Sounds more likely that you'd need to look at your riding style. It's also a far cheaper option to look at first. Lots of clips on youtube.
When does pedal strike occur - when going around corners (outside pedal down, as it aids clearance, and helps balance/weight on tyre)
or free wheeling over hazards (at level position, keeping pedals out of way).

It's generally when I've got no choice but to pedal around hazards - uphill around roots and rocks, for example. It's only just clipping the pedal, rather than actually digging in, hence thinking just a small reduction in crank length might make all the difference.

[Magic919]

What are the options for the rear shock? Can you not adjust anything there? Sounds like raising the bike would be helpful.

[Kermit power]

Magic919 said:

What are the options for the rear shock? Can you not adjust anything there? Sounds like raising the bike would be helpful.

No. It's self-leveling. You pump it up, then press a button, and it works out the sag itself, and it has absolutely nailed it in terms of pre-loading.

[Magic919]

Says the man whose feet scrape in the ground as he pedals. Can you see how that sounds?

Ok, so what if you don't push the button? Surely you can just pump it up? Don't tell me you need to use the button as you paid so much money for it. :-)

[Kermit power]

Magic919 said:

Says the man whose feet scrape in the ground as he pedals. Can you see how that sounds?

Ok, so what if you don't push the button? Surely you can just pump it up? Don't tell me you need to use the button as you paid so much money for it. :-)

If I press the button, then I get exactly the right amount of sag, but catch the ground a handful of times on any given ride.

If I don't press the button, then I get no sag, and a bloody awful ride.

[Pablo16v]

Are you clipping the pedals when the rear shock is under load or just in general? Most current bikes are low anyway, and slightly shorter crank might help, but if there's any mid-stroke wallow from the shock when under load then that will just exacerbate the problem.

[Magic919]

Doesn't the amount of sag relate to the pressure? I'm sure there's a Law for it. Experiment with lower pressure and no button.

[Kermit power]

Magic919 said:

Doesn't the amount of sag relate to the pressure? I'm sure there's a Law for it. Experiment with lower pressure and no button.

Yes, sag relates to pressure, and the pressure is just right, because the stationary sag is just right.

[Kermit power]

Pablo16v said:

Are you clipping the pedals when the rear shock is under load or just in general? Most current bikes are low anyway, and slightly shorter crank might help, but if there's any mid-stroke wallow from the shock when under load then that will just exacerbate the problem.

Just in general.

It's a shame that I didn't think to check the unladen BB height of the old bike before cannibalizing it to make a Hardtail, but from the web, as stock the BB was about 1/2 inch higher than the new bike, so this probably explains it.

[Kermit power]

Just to close this one out, I've discovered from a couple of reviews that this seems to be something of a design flaw resulting from Spesh trying to rush out a 650 bike.

Still, I'm currently matching (which was bloody frustrating!) or beating my old summer Strava times, so I'll live with the occasional pedal strike!

[MC Bodge]

scherzkeks said:

Agreed. Also strictly regarding crank length in relation to leg length, all of this was figured out decades ago. 170 typically works for anyone with an inseam under 90 cm. 165 can be useful if you have very short legs or short femurs.

I am of fairly average height (~6' on a good day), with a fairly typical inside leg of around 32"/82cm. I seem to have relatively short thighs/long lower legs. My knees are relatively high at the top of the stroke and using drop bars set low, or with a deep drop, my knees hit my chest.

I have my bike seats quite far forward and feel more comfortable with a shorter crank length (as found on road bikes) than typically found on mtbs possibly as it allows me to spin more with less rotation at the knee.

[whatleytom]

I switched to 165mm cranks about a year ago, as I've got tiny legs it helps me to get at least some way towards being more aero. Pedal strokes felt much better and more fluid, but that was probably as the cranks were too long to start with and didn't notice any reduction in power.