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Negatives of running super short cranks for DH?

HardtailHack

HardtailHack

used an iron once
Jan 20, 2009
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I've just grabbed my set of 155mm cranks for my DH bike and I was wondering if anyone else runs short cranks or why you think it's a bad idea.

From what I can see it's pretty much all positives, more ground clearance when pedalling, stiffer cranks(probably)and less weight. However running shorter cranks will raise your COG slightly and you may have to run a cassette with a slightly larger 1st gear because of the reduction in leverage.

Any opinions?
 
A

aenim

Chimp
Apr 15, 2010
16
0
Poland
You mean 165mm? Most of pro's ride 165mm cranks and I think they know what they do ;)
Reduction in leverage? Who cares! ;) Ground clearance is what we need, especially now in times of low bb's
 
T

trib

not worthy of a Rux.
Jun 22, 2009
1,477
421
With your feet being 4cm closer than a 'conventional' 175mm crankset you may feel a tad unbalanced?

Also pedaling may feel weird with a smaller crank, unless you have a very short inseam I think that 155 would be too short for a lot of pedaling, it is DH though, so that's not really an issue
 
bdamschen

bdamschen

Turbo Monkey
Nov 28, 2005
3,377
156
Spreckels, CA
I used to rock 165mm cranks on my DH, and only really noticed the difference when coming directly off my trail bike with longer cranks. I like 170 now for my dh bike, it feels like I'm getting a little more power when I pedal
 
4130biker

4130biker

PM me about Tantrum Cycles!
May 24, 2007
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I suppose your COG would/could be higher when cornering, depending on pedal position. I'm thinking that when you're riding straight or doing corners without dropping a pedal that it would be the same.
 
toodles

toodles

ridiculously corgi proportioned
Aug 24, 2004
5,499
4,747
Australia
Less power when pedalling and looking like you're riding a circus bike are the only two negatives I'd say. Although longer cranks would give you more leverage for pushing the bike around as well.
 
M

MDJ

Monkey
Dec 15, 2005
669
0
San Jose, CA
If you're racing on a course that you actually have to pedal on, then you will be at a disadvantage running shorter cranks especially if you are a bigger rider. The advantage is that you have slightly more ground clearance. For me, the advantage I get having longer cranks (170s) far outweighs the disadvantages. But then I'm 6'2".
 
HardtailHack

HardtailHack

used an iron once
Jan 20, 2009
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aenim said:
You mean 165mm? Most of pro's ride 165mm cranks and I think they know what they do ;)
Reduction in leverage? Who cares! ;) Ground clearance is what we need, especially now in times of low bb's
Click to expand...
No, I run 165's now and I prefer the feel over 175mm cranks, I think 155's will be fine as well but it might take a couple of runs for them to feel normal under foot.
 
HardtailHack

HardtailHack

used an iron once
Jan 20, 2009
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Socket said:
Slightly off topic, but what cranks actually come in 155?
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I'll just be running Funn Hooka MX(BMX) cranks to see if I like it and may get some Profiles at 150 or 155mm if it works out, The funn cranks are dirt cheap on CRC and I have a couple of BB's from running Middleburn cranks, actually they may come in shorter lengths too.
 
HardtailHack

HardtailHack

used an iron once
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Had my first race on the 155mm cranks today and they feel great however they aren't the worlds stiffest crank but then again they are dirt cheap.
 
bizutch

bizutch

Delicate CUSTOM flower
Dec 11, 2001
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Over your shoulder whispering
I ran 170's on an 06 Demo and smacked cranks occasionally, then 165's on an 07 Sunday and smacked them a hair less and an 08 DHR back to 170's and still just smack occasionally. All the BB's were within 5-10mm of each other.

When my new DHR arrives, I've got an angleset to move between the 13.5" BB/63 degree and a more typical 13.75" at 64 degree head angle. And I'm very much debating which to run on it. Cranks ain't cheap, let alone two pairs.

I'm 5'10" and I'd be interested in what length Hill runs since he's closer to my height than Mig-gnar and Puh-heaty.
 
FCLinder

FCLinder

Turbo Monkey
Mar 6, 2002
4,402
0
Greenville, South Carolina
bizutch said:
I'm 5'10" and I'd be interested in what length Hill runs since he's closer to my height than Mig-gnar and Puh-heaty.
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And this is going to make you any faster how??????? He rides a lot different than you do Bro..... I of all people should know this as to why I never could ride behind you. You plow and he doesn't.

Cecil
 
bizutch

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
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Over your shoulder whispering
FCLinder said:
And this is going to make you any faster how??????? He rides a lot different than you do Bro..... I of all people should know this as to why I never could ride behind you. You plow and he doesn't.

Cecil
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has nothing to do with riding style. It has to do with body type, frame size and leg length.

Herndon has been known to run 175's for years (no idea about right now), regardless of BB. Guys like Minarr and Peat have very long legs and 165s would feel goofy as crap to them. I've never seen an article listing their crank lengths, but I assume they run longer arms than Hill (or maybe I'm just secretly in butt love with a guy way younger than me who is pro)
:rolleyes:
 
A

alfonz

Chimp
Jan 28, 2008
60
0
NYC
HardtailHack said:
I've just grabbed my set of 155mm cranks for my DH bike and I was wondering if anyone else runs short cranks or why you think it's a bad idea.

From what I can see it's pretty much all positives, more ground clearance when pedalling, stiffer cranks(probably)and less weight. However running shorter cranks will raise your COG slightly and you may have to run a cassette with a slightly larger 1st gear because of the reduction in leverage.

Any opinions?
Click to expand...
155mm cranks??? are you a midget, or don't ever plan on pedaling?
 
kidwithbike

kidwithbike

Monkey
Apr 16, 2007
466
0
Hoboken, NJ
what are all you on about?
i love this squabbling over minutia, its so rich.

I am 6'3" and I have run 165s on my XC and DH bike for years with various other sizes as well, I have also run 180s on a BMX bike. The enginerd side of me wants to believe those 5mm increments make a perceptible difference in either torque or pedaling ergonomics, but my practical experience tells me, not so much...

Have I been missing out on .0143 ft/lbs (.00342 newton/meters) of Torque on every pedal stroke? The horror! That just ruins all the fun i had previously had on my bike. If I could only turn back time. It would totally be worth the increased risk of catching a pedal and flipping my **** in the Gnartasmic East Coast Rox.
 
bizutch

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
kidwithbike said:
what are all you on about?
i love this squabbling over minutia, its so rich.

I am 6'3" and I have run 165s on my XC and DH bike for years with various other sizes as well, I have also run 180s on a BMX bike. The enginerd side of me wants to believe those 5mm increments make a perceptible difference in either torque or pedaling ergonomics, but my practical experience tells me, not so much...

Have I been missing out on .0143 ft/lbs (.00342 newton/meters) of Torque on every pedal stroke? The horror! That just ruins all the fun i had previously had on my bike. If I could only turn back time. It would totally be worth the increased risk of catching a pedal and flipping my **** in the Gnartasmic East Coast Rox.
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Since you've only ran 1 option for years on all your bikes, you have NO practical input. You just posted 2 paragraphs of nothing. :rolleyes:
 
Racerx7734

Racerx7734

Monkey
Mar 4, 2002
616
0
Hostile Sausage
Almost all of the Pro and Expert riders that we ride or train with, ride 165's regardless of rider height. I'm not saying you should run right out and do what they all do.......but they must do it for a reason. The biggest reason I have heard of is ground clearance. When you are riding at the caliber most Pro's are, you really don't want to ever have to worry about unwarranted clearance problems.

Just like any other part on your bike, you shouldn't be focused on your parts, but instead just your riding. What I mean by this is that you don't want to be worrying about your parts failing or not being able to handle something during a race run.

I can tell you that MANY Pro riders during the 2010 season ran 2008 and 2009 165 cranks (for their race run's) made by a certain manufacturer on there 2010 Factory bikes because they did not have 165mm cranks in early 2010 made by this un-named manufacturer : ). "new" cranks went right back on after the race. You have have to keep your sponsors happy and they want you to show off the NEW stuff.



right or wrong, that's my 2 cents
 
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J

JRogers

talks too much
Mar 19, 2002
3,785
1
Claremont, CA
From: http://www.pezcyclingnews.com/?pg=fullstory&id=8845&status=True&catname=Latest%20News

They summarize a study on crank lengths with this:

"Of course, the main variable of interest here was maximal power output, and the results are rather surprising. Despite the subjects not really being adapted to the different crank lengths except possibly the 170 mm, the maximal power outputs were only minimally affected. The range was less than 4%, from 1149 W for the 220 mm, to 1194 W for the 145 mm. Overall, the 145 and 170 mm cranks were slightly but statistically greater for maximal power output than the 120 and 220 mm cranks."

Basically, even with huge variations in crank length, the amount of power produced doesn't seem to change much. The test they did was a short warmup followed by very short intense efforts...so it is probably more useful for DH than for other types of riding (the article is from a road blog). Something to think about and compare with all the "common knowledge" about crank length.
 
Sghost

Sghost

Turbo Monkey
Jul 13, 2008
1,038
0
NY
Macdermid 2010 Study said:
There is, of course, a severe caveat that I must emphasize again. This study only looked at maximal power output and NOT anything to do with aerobic performance that might be relevant to the vast majority of cycling. Therefore, while logistically really difficult because of the need for people to be trained and adapted to different crank lengths, the more appropriate study would be replicating this design with more time trial type of tests.

This leads to an interesting Kiwi-Aussie 2010 study that looked at more “realistic” crank lengths and endurance exercise, with the specific context and population of female cross-country mountain bikers (1). In brief, cranks of 170, 172.5, and 175 mm were tested with maximal sprint, a VO2max test, and also an isokinetic (constant velocity) test at 50 rpm. The latter is certainly representative of grinding up a big climb off-road. No differences in the isokinetic or VO2max tests were observed across the three crank lengths. What was really interesting, however, was that, while peak power was not different, the time required to achieve peak power was much lower with the 170 mm (2.57 s) than the 175 mm (3.29 s) cranks.

This has significant practical applications. The shorter cranks permitted you to generate high power outputs faster. This ability is critical in closing a gap, accelerating in a sprint, and also laying out that massive and quick burst of power to get you over an obstacle on the trail or out of a turn in cyclocross.
Click to expand...
Sprinting, fast max power, ground clearance, not having to worry about sustained rpm and long period aerobics. This is a toughie...
 
SuspectDevice

SuspectDevice

Turbo Monkey
Aug 23, 2002
4,160
365
Roanoke, VA
Thanks Mr. Rogers!
I didn't feel like sticking my head in here a week ago dropping heavy spiel to tell all you long-crankers that you don't understand sports science.
/thread
 
kidwithbike

kidwithbike

Monkey
Apr 16, 2007
466
0
Hoboken, NJ
I am 6'3" and I have run 165s on my XC and DH bike for years with various other sizes as well, I have also run 180s on a BMX bike.

bizutch said:
Since you've only ran 1 option for years on all your bikes, you have NO practical input. You just posted 2 paragraphs of nothing. :rolleyes:
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learn how to read Butch! seriously man.
to elaborate I have run 165s through 175s on my DH bikes, even many different sizes in one season, Several times i bent cranks while traveling to races or in Whistler, and took whatever substitute i could find cause I am not a fussypants and can adapt and freaking deal with it. I dont believe its a huge difference.
 
bizutch

bizutch

Delicate CUSTOM flower
Dec 11, 2001
15,928
24
Over your shoulder whispering
kidwithbike said:
I am 6'3" and I have run 165s on my XC and DH bike for years with various other sizes as well, I have also run 180s on a BMX bike.



learn how to read Butch! seriously man.
to elaborate I have run 165s through 175s on my DH bikes, even many different sizes in one season, Several times i bent cranks while traveling to races or in Whistler, and took whatever substitute i could find cause I am not a fussypants and can adapt and freaking deal with it. I dont believe its a huge difference.
Click to expand...
jonKranked said:
sarcasm level 4: butt hurt achieved!
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:rofl:THIS^^^^
 
HardtailHack

HardtailHack

used an iron once
Jan 20, 2009
6,713
5,599
Are there any 155mm cranks other than Profiles that will handle DH use? My Funns seem to twist a fair bit under power so I don't think they will last very long.
 
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