How do you choose the right gearing for your fixed?

[edindave]

Do you base it on average cadence for your usual route?
Or just what your legs can take?

I was running 48x16, and my average cadence was in the low 70s.
I swapped the 16t for an 18t and, at roughly the same overall average speed on my normal route, my average cadence went up to about 85.

So on the surface this seems like it should probably a better gear to be running. Or am I wrong?
It certainly feels a bit different, lighter on the legs.

It just got me wondering how others decide on a gear.

 

[Profpointy]

Another thought is crank length. Despite being reasonably tall 6'. i've got 165mm cranks, running a lowish gear 44 x 17 if I recall correctly (hilly city bristol) and I'm not mega fit, and far from young. Spinning quite fast on shortish cranks seems to work for me

 

[Deleted member 1258]

It tends to be trial and error, My Pearson came with 48x18 70 inch gear and 170 cranks, the 70 inch gear was fine on the commute but too high for long lumpier rides, I changed the chainring to 46, about a 68 inch gear which was better, and eventually changed the chainset to give me 165 cranks, which suited me better and settled on 44x18 65 inch gear and ran that for several years, last spring I changed the tires from 700cx28 to 700cx25 and the 65 felt a bit under geared and I went up to 68 again.

 

[GrumpyGregry]

It is determined by the maximum cadence I'm prepared to run on the biggest downhill on my commute home balanced by the longest gear I can honk uphill in on the chevrons I hit coming in to work (different road). A shorter gear makes the latter easier and the former less pleasant. A longer gear eases the former but makes the latter harder. But then your legs soon adapt.

70" or thereabouts works for me. On 175mm cranks. I'm shallow but I prefer the look of a smaller cog and a smaller chainring.

 

[edindave]

Must admit I hadn't thought about crank length. Mine are 165mm and I'm reasonably short at 168cm (5'6").

Interesting that the change of tyres led you to up the gearing @dave r - wouldn't have thought that would make much of a difference. In any case I'm running 23mm Contis.

I've noticed as well that I can at least use my legs a bit more for braking (or rather slowing) with the 18t cog. No skid-stops on the cards though!

 

[edindave]

It is determined by the maximum cadence I'm prepared to run on the biggest downhill on my commute home balanced by the longest gear I can honk uphill in on the chevrons I hit coming in to work (different road). A shorter gear makes the latter easier and the former less pleasant. A longer gear eases the former but makes the latter harder. But then your legs soon adapt.

70" or thereabouts works for me. On 175mm cranks. I'm shallow but I prefer the look of a smaller cog and a smaller chainring.

I was reaching about 120rpm yesterday and today quite comfortably. I'm sure that will increase - I do spin classes in winter so know I can spin faster, but am not used to doing anything higher than that in real life.

 

[HLaB]

My bike came with a 44x16t and I guess I've just adapted to it, if I couldn't I guess I try something different when it wore out.

 

[GrumpyGregry]

I was reaching about 120rpm yesterday and today quite comfortably. I'm sure that will increase - I do spin classes in winter so know I can spin faster, but am not used to doing anything higher than that in real life.

What I can do on a spin bike, 'bolted' to the floor and stationary, and what I'm prepared do on a bumpy Sussex B road, in a crosswind, whilst being passed, despite the oncoming traffic, on the double-whites by a stressed mother in a 4x4 are utterly unrelated.

I can only work out my rpm post-hoc. And then only if I have the gps on the bike to catch the speed to then do the maths.

 

[Deleted member 1258]

Must admit I hadn't thought about crank length. Mine are 165mm and I'm reasonably short at 168cm (5'6").

Interesting that the change of tyres led you to up the gearing @dave r - wouldn't have thought that would make much of a difference. In any case I'm running 23mm Contis.

I've noticed as well that I can at least use my legs a bit more for braking (or rather slowing) with the 18t cog. No skid-stops on the cards though!

700cx28 is about the max for a Pearson with mudguards, I'd put new wheels on the Pearson just before Christmas and was having minor problems with clearance, narrower rims on the new wheels, that was what led to the change to 25's, feeling a difference in the gear was a surprise, I didn't think it would make a difference.

 

[Norry1]

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) ???

 

[GrumpyGregry]

To that I would add consideration of the number of stops and starts encountered. I used an 80ish gear for a while but spent more time cranking it up to speed or slowing to a stop than I did cruising it. A 74" gear proved quicker overall.

I'd concur. I've found that stop/starting in a longer gear that you then have little time to spin in is counter-productive.

 

[GrumpyGregry]

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) ???

I ask someone else to work it out for me.

 

[MrGrumpy]

Started on a 42 x 16 on my original langster, then when the frame broke, the new frame under warranty came with new cranks and a 48t front ring. Did not find it much different, just meant I was not spinning like a looney on my commute. I have now since went to 17t cog and it feels a wee bit better on the hills. Oh could still lock the rear wheel on the 48x16 just took a bit more effort.

 

[Domeo]

I'm shallow but I prefer the look of a smaller cog and a smaller chainring.

I agree with the sentiment. I run 46X14.

edited: should have put 42X14

 

[derrick]

It's what suits you, i have a flattish 3.5 mile comutte and have a 48x14, a bit slow on getaways but once i get it spinning it's fine.