Singlespeed gearing: help please.

jonny_trousers

Okay, I'm getting really confused with gain ratios and whatnot here and not being the most mathmatically minded person in the world I thought I might seek out the advice of you guys.

The bottom line is I am running 50/17 at the moment and I would love to gear my bike the tiniest bit higher without needing to change the chain.

Would 50/16 be a little tough for the commute? Might 51/17 require a change of chain? Does 49/16 sound like a reasonable option? Any thoughts would be appreciated.

Buckled_Rims

Depends on your drop outs, or if you're using a tensioner.

The question can only be answered if you know how much tightness or slackness there's in your chain. It's a "how long is a piece of string" question otherwise.

If for example your chain is stretched to the limit on the dropout, then putting a 16t on is going to need a link taken out.

Personally speaking, if you change the ratio you might as well change the chain as you'll have new on new.

jonny_trousers

Buckled_Rims wrote:

Depends on your drop outs, or if you're using a tensioner.

The question can only be answered if you know how much tightness or slackness there's in your chain. It's a "how long is a piece of string" question otherwise.

If for example your chain is stretched to the limit on the dropout, then putting a 16t on is going to need a link taken out.

Personally speaking, if you change the ratio you might as well change the chain as you'll have new on new.

Thanks! It's a Pearson Touche and there is quite some distance in the horizontal drop out. I don't suppose there is a great deal of space left for using a much bigger chainring, but I could probably get away with going smaller - 49/16 for example. Do you think 49/16 would give me a noticable, but comfortable up shift from 50/17?

Salsa

We don't know things about your bike like tyre size/crank length etc, as you do know these factors use the rabbit single speed calculator to easily find your gear/gain ratios.
That will let you see what your existing ratio is & what effect changing cogs/sprockets will have .
http://software.bareknucklebrigade.com/ ... pplet.html

jonny_trousers

I already checked ratios on the Sheldon Brown site, but the figures that came up didn't mean a great deal to me in a practical sense. I was more looking for someone to say something along the lines of, 'Yes, 50/16 would be a killer' or 'No, moving up to a 51T chainring probably shouldn't require you to buy a new chain.

Thanks anyhow, I guess I'll just have to experiment.

Buckled_Rims

Jonny_Trousers wrote:

I already checked ratios on the Sheldon Brown site, but the figures that came up didn't mean a great deal to me in a practical sense. I was more looking for someone to say something along the lines of, 'Yes, 50/16 would be a killer' or 'No, moving up to a 51T chainring probably shouldn't require you to buy a new chain.

Thanks anyhow, I guess I'll just have to experiment.

Forget the price of a chain, it's only a tenner. What you want to worry about is your knees and can they cope with that gearing? Your commute might be flat but as soon as there's a head wind or there's lots of start/stop traffic, your knees might pop.

I couldn't in a million years use a single speeder on 50/16. I still say for myself the Langster type gearing of 42/16 is just about right for me. I can bike up hills, power into winds and still be pedaling.

jonny_trousers

50/17 actually seems to handle headwinds well and is not too sluggish at the offset so perhaps I should just stick with what I have. Thanks for the advice!

Tom Butcher

Seems a massive gear to me - depends what you are using it for I suppose but I used to do a fairly fast chaingang on 39*16 - OK I did half of it - I got dropped on the descent. Of course only you know what gear suits you best - but for a commuting bike it wouldn't suit me.

vorsprung

I use sheldon browns gear inch calculator to convert the ratio I have into gear inches
And then see what other combinations will give me a similar ratio
And then try it

So I started on 42x17 which is roughly 67" with 28mm tyres

This seemed a bit pedestrian so I had a few days with 52x19 or 73" and that was too much ( I was doing a 70 mile round trip over Exmoor at the time )

I stuck with 42x17 for a year or more and then found a 16T sprocket and did 42x16 which is 70"...this I found to be an excellent ratio

Harveytile

Sounds like you've been tinkering already. The Pearson SS bikes usually come with a 48/18 setup which on a 25mm gives a pretty standard 72 gear inches (if my maths is correct).

Dropping to a 17T rear gave me about 3-4 mph on the flats and a few more drops of sweat on the climbs. I was going to go for a 16T initially but am relieved I went for the 17T as a tester.

A single tooth drop at the rear shouldn't cause any issues in the drop outs. Give it a whirl and see. What's the worst that could happen? :roll:

jonny_trousers

Harveytile wrote:

Sounds like you've been tinkering already. The Pearson SS bikes usually come with a 48/18 setup which on a 25mm gives a pretty standard 72 gear inches (if my maths is correct).

Dropping to a 17T rear gave me about 3-4 mph on the flats and a few more drops of sweat on the climbs. I was going to go for a 16T initially but am relieved I went for the 17T as a tester.

A single tooth drop at the rear shouldn't cause any issues in the drop outs. Give it a whirl and see. What's the worst that could happen? :roll:

The tinkering was already done for me. I bought the Touche second hand and it'd had a lovely Sugino 75 chainset added. The bike came with 50/17 fitted and I have 16T and 15T cogs spare (not tested either yet as I do not have a lock ring removal tool).

According to the Sheldon Brown Gear Calculator, with 700 x 25 tyres and 165mm cranks I am given 77.6 gear inches, which sounds quite high, but it really doesn't feel that bad.

My commute's pretty flat really and the 50/17 does feel good most of the time. There are just a couple of points where I feel my cadence is a touch too high.

Thanks for all the replies!