How do you choose the right gearing for your fixed?

[smutchin]

Most seem to be between 65" and 69".

That sounds about right. When I first started riding fixed, I was riding about 69" and got on fine with it, now my fixed is geared at around 65" and that's fine too.

I think I chose my current gearing because it gives me an overall average cadence of around 90rpm (albeit peaking at a slightly teeth-jangling ~190rpm on certain descents).

Not that there's a huge difference in the way it feels, an inch or two either way, and I really don't think it's worth obsessing over.

 

[fossyant]

I started on 70" with a 74" on the other side. Very soon flipped the hub to 74". Ran that for a couple of years then upped to 77" that gives me a more comfortable cruising speed.

 

[smutchin]

For me, that feels impossibly fast already - and it scares the crap out of me.

At that speed, I'm not pushing, I'm just letting my legs spin away as fastas I can. 170-ish is all I've managed.

When I first started riding fixed (only a few years ago), 150rpm was scary. I've got used to spinning a lot faster but 190rpm is still pretty terrifying - there's one particular local descent where I can hit that speed without much difficulty, but it's mercifully short. I don't think I'd like to be spinning that fast for more than very brief spells at a time. I'd like to break the 200rpm barrier one day though - I've been close a few times.

1. Do people actually push at those sort of cadences? I mean actually gain speed through leg power rather than gradient?

Maybe some people can but not me!

2. I reach higher cadences now than before I put the fixopholous together. Will I gradually be able to creep up towards 190-ish on descents if I keep plugging away at it? These are descents where even my modest levels of skill and courage bring 45mph+ with gears. It's my footspeed that keeps the speed down on fixed.

I've mostly learned to just go with it. Riding a short fixed gear has had other knock-on effects on my cycling. On the flat, my "cruising" cadence on fixed is now around 120rpm, and I find my pedalling style on gears has changed so I now naturally prefer a shorter gear and higher cadence.

 

[Deleted member 1258]

Explain the maths of that to me please. The number of rpm is the same regardless of crank length for a given speed no? Sure my feet might have less distance to travel as the diameter of the circle is less on 165's but would it make a meaningful difference?

Maybe it is only me but footspeed has never been the limiting factor.

For me 165 cranks are more comfortable at high cadence, but I am a short arse.

 

[Deleted member 1258]

1. Do people actually push at those sort of cadences? I mean actually gain speed through leg power rather than gradient?

I'm still pushing the pedals round at 150rpm+

 

[edindave]

Crikey. I have been maxing out at about 120rpm on the flat so far. Some work to be done!

 

[smutchin]

The number of rpm is the same regardless of crank length for a given speed no?

Yes, though strictly speaking, the same combination of chainring and sprocket but different crank length = a different gear. (A crank being a type of lever, a longer crank gives a lower gear.)

Traditional "gear inches" ignore this but Sheldon Brown's "gain ratio" method factors crank length into calculating gear size, and takes into account the actual distance travelled by the pedals.

 

[Sharky]

How exactly do you calculate gear inches? If I have normal 700 wheels, is it just 700/25.4 (to get inches) x 42/16 (gearing) ???

( Wheel size*Chainring teeth)/Sprocket teeth e.g. 27*54/18 = 81"

This equates to riding a penny farthing with a diameter of 81"

Used to be simple when wheels were either 27" or 26", but with metric and different tyre sizes, you need to use a table - look at the Sheldon Brown website - http://sheldonbrown.com/gain.html - also discusses Gain ratios which bring in the difference cranks make.

Cheers Keith

 

[rb58]

I

1. Do people actually push at those sort of cadences? I mean actually gain speed through leg power rather than gradient?

.

I try to. Allows me to feel more in control than when I'm just letting momentum carry my legs round. I max out at about 165/170 rpm these days, although that number has crept up over time.