Gear Ratios

[NickGM]

Hi Folks,

So I managed to pick up an old cannondale road bike that I want to turn into a single speed but I'm not sure what gear ratios are "standard" or common. All I want it for is for commuting to work. I'm not trying to break any land speed records but at the same time only have a few gentle hills to climb on my ride.

 

So what the bike has at the moment is a Shimano RX100 crank that has 2 chanrings - the bigger one had 53 teeth and the smaller one has 39. I've attached a pic of the crank, although have already taken the chain rings off.

 

Then at the back I have a 4 cog casette (see pic) with 18-27 teeth. Luckily it also has a lot of spacers which (I presume) will help me get the alignment right between the front chain ring and back cog.

 

Anyway, my question is, what sort of gear ratio should I be going for? Is 53-18 crazy? Perhaps 39-18... Suggestions appreciated

 

Thanks for the help.

[porqui]

Get yourself a used chain and try out each back gear individually ans see which one you prefer.

You will have to change the length of the chain for each gear.

[Cois]

I am going to run a 52x21 at the moment on my SS. Still have to go ride it. SS build was done last night

[Letum911]

I run 39*17, works well for Pta with the amount of hills.

[NickGM]

OK - well I'm going to test out the 53-18 I started with tonight. I'm not sure my little chicken legs will handle it, and if so, will swap the big chainring in the front for the medium (39 tooth) one. I have a flatish ride to work, but I'm not exactly Fabian Cancellara either.

[Cois]

Just work out the ratios. I am just glad my Uncle knows a lot about ratios and how to get the correct ratio.

You might have to run a soup plate at the back, but might be worth it

[Old School Rookie]

Recently did the same for the same purpose. Some advice. If the bike included a rear derailleur, leave it on to use as chain guide if you want to try out a couple of ratios 1st. Doing this will avoid having to mess around with the chain length while experimenting. You probably need to fit a chain tensioner on that frame in any case, so if you don't have an old derailleur you can fit this so long. Ride ur regular route and experiment with different gears. However. Keep the following in mind to skip the teething lessons I had to learn. You can probably use any of the front chain rings. At the back you probably gonna end up using ss specific gears, as you might lose some chain wrap using a tensioner, slipage on regular gears might be an issue. SS specific gears have longer teeth and thus provides better grip. They are however pretty limited in size, i think around 14 smallest up to 20 odd. I therefore decided to use a 53 ring up front with a 18 at the back. This provides a 1/3 ratio which seems to be pretty much the baseline. Om my 15km return route i encounter a 3km hill ranging from 5 to 7 %. With these gears I make to the top with considerable effort, which is the whole idea for me as the bike needs to get my lazy bones stronger.

The SS purists will give the best advice etc. I endeavored to keep the project cheap and simple using whatever i had on hand. Outlay that you might expect can include:

I use a standard 9spd chain which is pretty cheap. (Half link chains an option and might exclude the use of a tensioner. I wont go that way as I'd prefer not messing with a just too tight chain that could hurt the wheel hub) Rear SS kit cost around R200. Simple tensioner like a On One Doofus R200 from Rapide. (They are noisy though and I will try a more expensive gusset type when i get round to it)

You might need shorter chain bolts up front. R100 should do for a set. Except for further SS pimping purposes you shouldn't need much more than that to get the wheels turning. I turned and old GT road bike into a SS and dropped more than 1.6kg on its original weight. Quite a sweet deal considering the expense. Also keep this weight loss in mind when U experiment with the gears, I makes a helluva diffs up the hills. Enjoy it!

[NickGM]

Thanks for the superb feedback. I've used the old derailleur as a tensioner, trimmed the bars and turned upright and got lucky with the gear ratios - perfect for my ride in to work.

 

Currently the old derailleur is a bit noisy, so with time I may look at alternatives, but it all works fine for me now.

[MoreTrails]

Bike looks rad, nice and stripped.

 

If it ain't a fixie you may want to consider a rear brake?

[NickGM]

Yeah it isn't. I just went with the front brake because it mean an easier job with using the old cable housing!

 

Do you suggest the back brake as opposed to the front brake, or in addition? I do fear that I will jam on the front brake one day and, well it never ends well.

 

Will give it a paint job eventually, when time and funds allow.

[Tankman]

No need for a rear brake, leave as is.

 

You have more than enough stopping power on the front only.