alij2018

Hi,


I am new here and this is my first post.


I am planning to convert my 5 years old mountain geared bike to single speed. I have already removed the shifters but for now, as I have not bought the crankset and rear sprocket yet for single speed, I kept the actual rear sprocket and front chain rings as well as the rear derailleur for chain tension.


I tested my chain on the different rear sprocket and front crank, which obviously gave me different results. After few testings, I found that my smallest front crank of 28T with a rear sprocket of 18T is good. This can permit me to ride uphills quite easily. However, I did not test few of the rest sprocket teeth of both front and rear. But it seems, the smaller the crank, the lower the gear is.


Guys, this is my first time single speed conversion. I cycle since 23 years and I have few mechanical knowkedge on bike. However, I still need help and advise. Here are my questions below:


1/ I will cycle on uphills quite often, road and earthly tracks . What is the appropriate rear sprocket size and number of teeth and front crank size and number of teeth you recommend?


2/ A mechanical scientific question. Is it true size of a front crank does not matter but it is more like the number of teeth which matters the most?


3/ Is it true, the more teeth a sprocket or crank has, the less harder it is to pedal?


4/ Is it true, the smaller the front crank is, the better it is to pedal?


An additional note, I am.using a 26' wheel/tyre.


Thank you very much!

fietsbob

you have to figure out the gear ratio that works for you try 2:1 for a start..
18:36? 18:28 is 1.5:1..

a)There are 135 single speed hubs, to build a wheel around,
b)cassette spacer sets to leave only 1 cog, on an existing cassette hub,
and c) perhaps just get a common freewheel hub , a longer axle ,
and spacers and center that hub
where your single freewheel chainline works best.





....

JohnDThompson 

That depends on your hills and your legs. As I get older, I find I need lower gears. Currently, my fixed gear ride has 44 front/17 rear gearing.

As you still have all your rear cogs and front chainrings installed, try different combinations to see what works for you.

By "size of front crank" do you mean the length of the arms? On a fixed gear bike, shorter arms provide more clearance so you can take corners faster. But it sounds like you'r building a single-speed, not a fixed gear, so you can coast through corners if you need to, and ground clearance isn't a concern.

Tooth count determines the gear ratio. Fewer teeth in front means lower gears, fewer teeth in back means higher gears.

Fewer teeth in front makes it easier to pedal; more teeth in back makes it easier to pedal. But easier to pedal also means you'll hit your maximum pedaling RPMs sooner. On a fixed gear, this can be an issue with long downhills, but if you have a freewheeling cog, you can always coast.


The fewer teeth in front, the easier it is to pedal, but also slower. Whether that makes it "better" is a subjective judgement.

alij2018

Thank you for reply. The size of the front crank I meant the size of the gear. I still have 3 in front as I have not changed to a single speed crankset yet.

When I tested, I placedmy chain to the smallest front gear which has 28T. And I used it with a 18T rear gear. It is good for me.

My question regarding the size was, does gear size plays a role or it's more on the number of teeth? Example, a bigger gear with 28T and a smaller gear with the same number of teeth provides the same performance?

HTupolev

They're directly proportional to each other.

Nearly every single bicycle chain ever made has links that are .5" long. So the teeth on gears are spaced .5" apart from each other. Consequentially, if you're trying to choose between two different 28T cogs for your drivetrain, you'll find that they're the same size.

alij2018

So if I understood, it is more the number of teeth than the size of the gear which affects performance then!
I will test the other gears soon. And will see what's the best for me. Right now I see a rear sprocket of 18T and a front gear of 28T are cool.

HTupolev

Yes, tooth count is the easy-to-use number that matters.

AlmostTrick

Since you're probably going to remove the rear derailer, (if you haven't already) you'll also need to choose a gear combo that gives you good chain tension. You don't want it too tight or too loose. Most geared bikes have vertical drop outs that don't allow fastening the rear wheel in different positions. This is called finding the "Magic Gear".