[BB]

Everytime someone sees me on my single speed, they say "watch your knees on that". Is this an urban legend or is there a real risk that persistent use of large gearing could have an impact on your knees?

I've nerver met anyone that's had a problem, but people keep on mentioning it!

I currently use a 50x16 and while it doesn't cause me any problems, I'm conscious that as I get older, the knees might not cope!

What's the optimum ratio for preventing knee injury whilst still maintaining a decent average speed.

I'd be interested in what thoughts other SS/fixie users have.

I only use the single speed for commuting and bombing round town (on road only) and it's on 700c wheels btw.

[slackline]

What's the optimum ratio for preventing knee injury whilst still maintaining a decent average speed.

A car! 

[BB]

A car! 

Can you express that as a ratio please Slackers?   

[slackline]

A car! 

Can you express that as a ratio please Slackers?   

Transport by car (for one year) = a
Transport by single-speed (for one year) = b
Injury to knees = c

Injury to knees for a given years travel by car is a : 0c
Injury to knees for a given years travel by single-speed is b : πc

[webbo]

big gears are fine as long as you can actually pedal them.if you are reving them at 80+ most of the time,it shouldn't be a problem.however if you are doing 20 revs a minute and nearly bending the cranks to do it your knees are going to hurt.

[clm]

you need to be able to spin or its horrible. Try to keep the gear inches around or below 70. I always thougt the sore knees bit came from resisting your momentum as you slow. You running a back brake? Anyway, that argument only applies to fixed, if you are riding singlespeed you'll be fine. Ask vicars everywhere.

[webbo]

years ago we all used to ride single free round here in east yorks in winter.used 42 x18 which if you are young and fit means you'll get up most of the hills in the yorkshire wolds and it was on bikes made from japanese gas pipes.now i require something made of aluminimum/carbon  and a more modest 39 x 27.

[northerngreg]

big gears are fine as long as you can actually pedal them.if you are reving them at 80+ most of the time,it shouldn't be a problem.however if you are doing 20 revs a minute and nearly bending the cranks to do it your knees are going to hurt.

 

It's your cadence that matters most when considering the life of your knees. I always aim for 80-90 rpm on the flat road at a sensible aerobic level. Geared for this cadence, I can get up all of Bristol's hills without grinding to a chain-snappingly-strenuous-stamping-on-the-pedals-knee-splittingly-powerful-honk. I think in gear inches it is 68.75. Just to clarify, to calculate gear inches:

Gear inches = (Diameter of rear wheel x teeth on chainring) / teeth on sprocket

For the geeks amongst us gear inches equate to the diameter of wheel a penny farthing (or unicycle) would need to give you the same gear. i.e. my bike equates to a penny farthing with a 68.75 inch diameter wheel!

One last point, if you're riding SPD's, make sure your cleats are in the right place or you'll get knackered knees before you know it. Watch some roadies who's knackered knees seem to 'pop' over to the side at the top of their pedal strokes!

[BB]

Okay, so diameter of a 700c wheels is 29" x 50/16= 90.625 gear inches

That's one hell of a penny farthing!

My commute is downhill on the way and obviously uphill on the way back so the average rpm is probably ok, but the ride home is tough and while i don't have to get out of the saddle, I'm putting a fair bit of power through the cranks. From the comments here, it's probably too much.

[BB]

I've done some more calculations and if i aim for 70ish gear inches as recommended and keep the sprocket the same (because it's screw threaded and harder/more expensive to source that a smaller chainring)...

(70x16)/29=38.621=pronlinged life for my knees

[chappers]

use this: http://www.sheldonbrown.com/gears/
stop all that maths!!

[Percy B]

A 90" gear on a fixie for riding around town, even if its totally flat, is way too big in my opinion. My track bike doesn't have a gear that big! Spinning a smaller gear is going to be way better for you.
As an example, a fit roadie training on a fixie on rolling to hilly terrain might use anything from a 60" to a 65" gear but no more than this unless you're a monster. Shorter trips in town you can get away with a slightly bigger gear, but not that much!

[cowboyhat]

Nice calculator: http://software.bareknucklebrigade.com/rabbit.applet.html

I have 48/18 but it is flat in London.

[chappers]

i ride 48X18 fixed in MCR and training. its good, but i get the occasional "speed wobbles" and i shit myself going down hill at pace due to the high cadence that it produces!

[clm]

...and mines half built and doesnt have foot retention yet. Pegging it for a traffic light i forgot i was fixed, got feet thrown off the pedals and sailed past 6 lanes of traffic with my knees by my chin

[chappers]

where do you live clm? if you wanna go for a ride this winter give me a shout. going on 40 miles with wheelers saturday 9:30 from gateway at parrswood didsbury.

[clm]

prob not riding till after christmas but definately keen. What mph?

[chappers]

if im out for a bike ride i like to enjoy it so, around16mph over to the peak. i go on the chain gang to punish myself, and occasionaly do intervals.

[BB]

I'm finally getting round to replacing the 50T chainring on my SS. However, I'm struggling because of my meagre bike knowledge. It's currently got a Sungino track chainset on it that looks like this:



It's a square taper BB and the cranks are 5 bolt which is about as much as i know. I'm after some recommendations for a suitable chainring that'll actually fit, is around the 38-42T mark and isnt going to cost more than about £40. I don't understand what all this 'BCD' business is about and I'm unsure if there's a specific style of chainring I should be looking at.

Can any of you bike experts help?

[Skinny Pete]

The BCD is the key! Stands for bolt circle diameter and is the diameter of a circle, centred on the BB axle, that passes through all the chainring bolts.  Basically, measure from the centre of the axle out to one of the chainring bolts (in mm), then double it to get the BCD.  Any five-bolt chainring with the same BCD should fit your cranks.

Style is up to you, though for a singlespeed you'll want one with one with no shifting ramps or funny tooth profiles.  Steel are heavier and more durable, Al alloy are lighter and tbh wear is pretty minimal on ss chainrings.

[Duma]

if you're running a 1/8th chain then you'll want a 1/8th ring (3/32 will work, might be a bit noisy and wear quicker though). If t'other way round you definitely need 3/32 ring.
How about this?

[northerngreg]

What they said.

Plenty to choose from here

If you get a reversible one, then when it is looking a bit worn, take it off, flip it over and bolt it back on. Double the life (nearly).

[BB]

Cheers Greg, that place is a goldmine!

[soapy]

also don't forget spa cycles in harrogate