Shimano Cranks 172.5

kingrollo

Can I get shimano cranks in size 172.5 - I was thing 105 range ?

pompeypoppy

Yes you can:

http://www.totalcycling.com/index.php/product/parts_accessories/cranksets_road/FC_SHIMANO_5600.html

kingrollo

Cheers .....why do bike shops lie so much ???

pompeypoppy

... or if you need a 9-speed:

http://www.chainreactioncycles.com/Models.aspx?PartnerID=79&ModelID=2647

As good as my LBS is, I'm guessing that some bike shops that don't have the right part will bend the truth to get you buying off them.

bompington

While we're being cranky, can anyone enlighten me:
I had 170s on my bike until one fell off (literally), I replaced the whole front end & was so grateful to say goodbye to my old 42 small ring that I never noticed anything untoward. Until a couple of weeks later when I tidied up the garage & threw away the box the new ones came in - and noticed that they were 175s.
The question is: is there a significant difference? I never noticed anything at the time, I put down any feelings of strangeness to the change in ratios, but I still wonder. For the record, I'm 5'8" with relatively short legs.

pompeypoppy

http://www.cptips.com/crnklth.htm

They may be a bit large for you, but shouldn't make a huge difference...

I guess you can lower your saddle by 1/2 - 1 inch if your feeling stretched. If you can't tell the difference I wouldn't worry about it too much.

keef66

This has always perplexed me. Can you really detect a difference in crank length of 2.5 or 5 mm? Surely when I switch from winter to summer socks that has the same effect? Are the cranks longer at 25c than at -5c??

I'd rather spend my time worrying about whether that white van is about to reverse out in front of me, or if I've remembered to reset the QR on my brakes as I hurtle down hill.

kingrollo

keef66 wrote:

This has always perplexed me. Can you really detect a difference in crank length of 2.5 or 5 mm? Surely when I switch from winter to summer socks that has the same effect? Are the cranks longer at 25c than at -5c??

I'd rather spend my time worrying about whether that white van is about to reverse out in front of me, or if I've remembered to reset the QR on my brakes as I hurtle down hill.

You may be right - but when you have a set up that works, after a bout of niggling injuires -Im not about to change !

bompington

Thanks for the link Pompeypoppy, the info there definitely suggests mine are too long.
Changing the saddle height won't work, that just gives me the choice of feet too low at the bottom or kness too high at the top - it's the size of the circle my feet are going in that concerns me.

Pokerface

bompington wrote:

While we're being cranky, can anyone enlighten me:
I had 170s on my bike until one fell off (literally), I replaced the whole front end & was so grateful to say goodbye to my old 42 small ring that I never noticed anything untoward. Until a couple of weeks later when I tidied up the garage & threw away the box the new ones came in - and noticed that they were 175s.
The question is: is there a significant difference? I never noticed anything at the time, I put down any feelings of strangeness to the change in ratios, but I still wonder. For the record, I'm 5'8" with relatively short legs.

Is it possible that you just have the wrong box? I have had stuff come in boxes with the wrong size marked before...

Pokerface

keef66 wrote:

This has always perplexed me. Can you really detect a difference in crank length of 2.5 or 5 mm? Surely when I switch from winter to summer socks that has the same effect? Are the cranks longer at 25c than at -5c??

I'd rather spend my time worrying about whether that white van is about to reverse out in front of me, or if I've remembered to reset the QR on my brakes as I hurtle down hill.

If there was no difference, then cranks would only come in 5 or 10mm increments, not 2.5mm increments.

The answer is YES, there is and YES you can tell the difference.


Plus socks compress, cranks do not.

bompington

Pokerface - as you might guess, I did rush off and measure them as soon as I found out!

Pokerface

Track bikes generally use shorter crank arms. Combination of more clearance needed due to the banked track and (I think) higher RPMs needed. Shorter arms = higher RPMs to get the same speeds.

Even if you are short(er) and have short(er) legs - that is not to say you can't use longer crank arms. It's just easier and more comfortable to generate power with the appropriate size.

mattr2102

kingrollo

Hi,

Just saw on your post that you are looking for a 172.5 crankset. I've got a spare 105 crankset (cranks, bb and rings...) if you're interested, they've done ~900 miles and are in good condition. I'm in Islington (postcode N1) if you're interested at all.

Thanks

Matt

bompington

Pokerface wrote:

Track bikes generally use shorter crank arms. Combination of more clearance needed due to the banked track and (I think) higher RPMs needed. Shorter arms = higher RPMs to get the same speeds.

Even if you are short(er) and have short(er) legs - that is not to say you can't use longer crank arms. It's just easier and more comfortable to generate power with the appropriate size.

Whoops, Pokerface, elementary engineering error there - RPM to wheel speed is determined solely by gearing (that includes wheel size), crank length makes no difference.
What does change with shorter cranks:
- Your feet are following a smaller radius circle, so your feet are going slower for a given cadence: which I guess makes it easier for track riders to push up the RPM
- Shorter cranks mean shorter levers, so you need to push harder for the same torque

Effectively, if you take gearing to include everything from foot speed to road speed, shorter cranks mean higher gears. But not less RPM!

Pokerface

bompington wrote:

Pokerface wrote:

Track bikes generally use shorter crank arms. Combination of more clearance needed due to the banked track and (I think) higher RPMs needed. Shorter arms = higher RPMs to get the same speeds.

Even if you are short(er) and have short(er) legs - that is not to say you can't use longer crank arms. It's just easier and more comfortable to generate power with the appropriate size.

Whoops, Pokerface, elementary engineering error there - RPM to wheel speed is determined solely by gearing (that includes wheel size), crank length makes no difference.
What does change with shorter cranks:
- Your feet are following a smaller radius circle, so your feet are going slower for a given cadence: which I guess makes it easier for track riders to push up the RPM
- Shorter cranks mean shorter levers, so you need to push harder for the same torque

Effectively, if you take gearing to include everything from foot speed to road speed, shorter cranks mean higher gears. But not less RPM!

In the world of track riding - where you have a fixed gear (and thus cannot CHANGE GEAR), would a shorter crank length therefore mean you have to use a higher RPM to achieve the same speed as someone using the same gearing, but a longer crank length? Assuming that the power output of both riders is the same? I think yes.

andy_wrx

Of course not.

If the gearing is the same then the RPM of the cranks will be exactly the same at the same track/roadspeed no matter what your crank length.

That speed is derived from the size of the wheel and the RPM of the wheel, and the RPM of the wheel is related to the RPM of the cranks via the gears being used, i.e. ratio of number of teeth on chainring vs. number of teeth on sprocket

So assuming same wheelsize, same cogs front & back, if you were doing X mph, your cranks would be going round at Y rpm whether those cranks were 160mm long or 180mm