Crank sizes 170mm vs 172.5mm

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Re: Crank sizes 170mm vs 172.5mm

Postby Marty Moose » Thu Nov 29, 2012 2:54 pm

I think the point is many of those guys are not tall. McEwen is not tall and uses 175's pantani not tall etc etc

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Re: Crank sizes 170mm vs 172.5mm

Postby Mulger bill » Thu Nov 29, 2012 8:11 pm

I went from 175 on the commuter to 172.5 thinking it'd help me knees. Tiny adjustment to saddle height and I forgot all about it until I saw this thread. Can't say I've noticed any change but then again, I don't have a wind tunnel and a quiver of sensors hanging off me bike. :?
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Thu Nov 29, 2012 9:49 pm

Hard to see a change from just 2.5mm. I think you need at least 5mm to see if it makes any difference to anything. I took 10mm out of my crank length and it made a difference to me. But so did wedges, lowering my saddle, changing my cadence and doing some other exercises. They are all just small steps than can add up.
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Re: Crank sizes 170mm vs 172.5mm

Postby barefoot » Fri Nov 30, 2012 6:00 am

Nobody wrote:Hard to see a change from just 2.5mm.


I mark my seatpost position with a bit of electrical tape.

One of my bikes felt like the saddle was a touch low, so I raised it slightly. It feels much better now. The electrical tape is now about 2.5mm above the clamp.

2.5mm is definitely noticeable.
2.5mm at the bottom of the pedal stroke + 2.5mm at the top of the pedal stroke would be even more so. Or, if the saddle position is adjusted to suit, 0 at the bottom and 5mm at the top.

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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Fri Nov 30, 2012 7:52 am

OK Tim, then to rephrase:
In the context of whether knee problems can be helped noticeably by shorter cranks, bigger steps are better.

I actually think that 167.5mm would be my ideal crank length as I occasionally ride 170s to find they are too long, but the 165s feel a bit short out of the saddle and sometimes in it even though I ride them regularly. However the rarity of 167.5 means they are expensive and so far I can only find them (from mainstream manufacturers) in Japan.
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Fri Nov 30, 2012 7:57 am

Marty Moose wrote:I think the point is many of those guys are not tall. McEwen is not tall and uses 175's pantani not tall etc etc


barefoot wrote:
Nobody wrote:Hard to see a change from just 2.5mm.


I mark my seatpost position with a bit of electrical tape.

One of my bikes felt like the saddle was a touch low, so I raised it slightly. It feels much better now. The electrical tape is now about 2.5mm above the clamp.

2.5mm is definitely noticeable.
2.5mm at the bottom of the pedal stroke + 2.5mm at the top of the pedal stroke would be even more so. Or, if the saddle position is adjusted to suit, 0 at the bottom and 5mm at the top.

tim


I'm on my old bike at the moment because the new one is creaking like a malaka :x

The seat is a touch higher on it and it is easier on the legs as a result. Both 175mm cranks.

What I'm taking out of that is run your seat as high as you can without over extending your leg or rocking the hips. Those shorter blokes must have done so to save their knees I'm assuming.

I went from 2.5 mm longer on my new bike and haven't noticed any large difference on strava segments, they are short though. I am slightly faster but I'm riding more so slightly fitter :) Then again I'm slightly older :(

I went to 177.5 on my tt bike when I actually got to use it :cry: and went faster over all the same courses than I did on the 175s.
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Fri Nov 30, 2012 9:19 am

warthog1 wrote:I'm on my old bike at the moment because the new one is creaking... :x
Can I assume the press fit BB on the S5? BBright not so bright at the moment?
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Fri Nov 30, 2012 12:33 pm

Nobody wrote:Can I assume the press fit BB on the S5? BBright not so bright at the moment?


Spot on.
Luckily Dr_Mutley has been very patient and thoroughly explained to me, with pictures :oops: , how to fix it. Just waiting for the bits. He's also given me a link to the cervelo forum where the problem has presented itself several times.
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Re: Crank sizes 170mm vs 172.5mm

Postby mrgolf » Sun Dec 02, 2012 7:54 am

Is there a serious suggestion that crank length has some bearing on gearing here? Gearing stays the same, but leverage changes. That's it. So someone with longer cranks pushing the same 53/11 finds it easier than someone on 170's.

Why he pros use longer cranks would be interesting to hear. Can you break the list into sprinters and climbers? That would be interesting

For me, my strength lies in climbing. I am short and run 170's. I ran a set of SRAM red 172.5 for a month or two and found it hard to cadence as naturally as with the slk 170's. I also lost a little av speed. Changing back to 170's fixed it straight away. And yes I adjusted saddle.

I recently bought a cx for commuting which had 172.5 and I changed it to 170 after I found my cadence to be a little lumpy over 110rpm. Now it is much better. Anyone want a set of 172.5 cx gossamer pro cranks?

I might be overly sensitive to change, but I think it's fair to say it is noticeable to some people and not to others.
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Re: Crank sizes 170mm vs 172.5mm

Postby warthog1 » Sun Dec 02, 2012 9:03 am

mrgolf wrote:Why he pros use longer cranks would be interesting to hear.


My guess,given they are racing, is they tend to run longer cranks as they find them faster or more comfortable to maintain a high average speed.

mrgolf wrote:For me, my strength lies in climbing. I am short and run 170's.


Pantani 170mm -180mm in the mountains

mrgolf wrote:For me, my strength lies in climbing. I am short and run 170's. I ran a set of SRAM red 172.5 for a month or two and found it hard to cadence as naturally as with the slk 170's. I also lost a little av speed. Changing back to 170's fixed it straight away. And yes I adjusted saddle.


If you are short then 170 is probably right for you.
However I am a never was and really have NFI apart from what works for me anyway :roll: :lol:
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Re: Crank sizes 170mm vs 172.5mm

Postby mikesbytes » Sun Dec 02, 2012 9:59 am

mrgolf wrote:Is there a serious suggestion that crank length has some bearing on gearing here? Gearing stays the same, but leverage changes. That's it. So someone with longer cranks pushing the same 53/11 finds it easier than someone on 170's.


Yes, there is relationship between crank length and gearing, as the length of the cranks affects foot velocity, so a different gear will give the same foot velocity with different crank lengths.

I did the maths a long time ago and in simple terms, about 5mm of crank length is equal a tooth on the big ring.

Hence
165/50 is approx 175/52
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Re: Crank sizes 170mm vs 172.5mm

Postby dougalh » Sun Dec 02, 2012 5:51 pm

Thanks for all of the helpful replies everyone! It's overwhelming the help and insight here :)
I've currently got 170mm and I'm 6'2 with long legs so I think I shall go 175mm when I upgrade.
If only they made a 10T :twisted:
Thanks everyone :D
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Re: Crank sizes 170mm vs 172.5mm

Postby cpical » Sun Dec 02, 2012 6:08 pm

toolonglegs wrote:
Great moments... but got to admit I cringed a bit when I heard Liggets voice commentating :| .



Not worse than the guys on France Television during Tour de France. I just can't understand they keep them... I much prefer Eurosport, Virenque is a laugh, despite his poor command of French (much better now actually), Jacky Durand and JF Bernard are very good.
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Re: Crank sizes 170mm vs 172.5mm

Postby toolonglegs » Sun Dec 02, 2012 6:19 pm

dougalh wrote:If only they made a 10T :twisted: :D

you can get bigger chain rings... I am a big fan of my 55 on my 180's. I will run a 56 on my TT bike next year... Although it is more about having a good chain line than actually using a 56 / 11 all the time ;-) .
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Re: Crank sizes 170mm vs 172.5mm

Postby dougalh » Sun Dec 02, 2012 7:10 pm

toolonglegs wrote:
dougalh wrote:If only they made a 10T :twisted: :D

you can get bigger chain rings... I am a big fan of my 55 on my 180's. I will run a 56 on my TT bike next year... Although it is more about having a good chain line than actually using a 56 / 11 all the time ;-) .


What are you running?
The biggest option I can find is 53/39T 175mm for Ultegra. Can I swap chainrings for a 55?
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Re: Crank sizes 170mm vs 172.5mm

Postby mikesbytes » Sun Dec 02, 2012 7:38 pm

Of course you can get a bigger chain ring. The other option is to learn to spin a bit more
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Re: Crank sizes 170mm vs 172.5mm

Postby toolonglegs » Sun Dec 02, 2012 8:05 pm

I run DuraAce 180mm cranks ( only DuraAce runs longer than 175 in road cranks ) ... but XT runs 175,177.5 & 180mm in mtb cranks.
I run 55 chain rings... probably a 54 is closer to standard on the longer cranks... it isn't about spinning more, it's about having a better chain line and the option of slightly bigger gearing if needed. I don't want to spin, I don't like to spin... I am quite happy at 88-90 rpm average.
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Re: Crank sizes 170mm vs 172.5mm

Postby Nobody » Sun Dec 02, 2012 8:42 pm

toolonglegs wrote:I run DuraAce 180mm cranks ( only DuraAce runs longer than 175 in road cranks ) ...

Apparently they do exist in other brands. Probably just harder to find.
http://www.campagnolo.com/jsp/en/groups ... tid_12.jsp
http://www.wiggle.com.au/sram-rival-dou ... pQodHWMArg
http://www.amazon.com/Crankset-180mm-Wh ... B005DUCQ68

toolonglegs wrote:I run 55 chain rings... probably a 54 is closer to standard on the longer cranks... it isn't about spinning more, it's about having a better chain line and the option of slightly bigger gearing if needed. I don't want to spin, I don't like to spin... I am quite happy at 88-90 rpm average.
Being able to use a bigger cog on the back with the bigger chainring is probably more efficient too.
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Re: Crank sizes 170mm vs 172.5mm

Postby toolonglegs » Sun Dec 02, 2012 8:53 pm

Tony Martin thinks so... he runs a 58 quite often :shock: .
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Re: Crank sizes 170mm vs 172.5mm

Postby mikesbytes » Mon Dec 03, 2012 9:04 am

It's also possible to get custom rings made up, if you want something huge. Cycle underground comes to mind.

Make sure it will fit under your FD
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