Originally Posted by
spinconn
I am looking through this forum with interest and think I may want to try single speed ....
Would a new gear train of 48X16 be fairly close to the 40X16 I like, or might I find it too high?
Would the conversion be expensive?
Is there anything about a mtb, other than the drive train, that would make it a bad choice for a single speed?
By tradition, gears are measured in "inches". For example, a "60 inch gear" is equivalent to a 60 inch diameter wheel being driven directly through the hub with no chain or gear mechanism — like an old penny farthing.
To calculate "gear inches" there are 3 things you need to include. The formula is
Number of teeth on the chain ring
divided by number of teeth on the rear sprocket
multiplied by the diameter of the wheel in inches.
As most people ride 700c (roughy 28 inch diameter) it has become common shorthand to refer only to:
Number of teeth on the chain ring
X number of teeth on the sprocket.
If you understand this formula, you will see that if (for simplicity) you double the size of the chain ring, you will double the gear.
Same principle, if you change from a 40t chain ring to 48t, the new gear will be 48/40 of the original. That's an increase of 20%.
A 20% increase is easily enough to make a serious difference.
If you wish to ride single speed, then choose the ratio that will get you up your steepest local hill. You can coast back down.
If you live in a very hilly area, this principle can result in a low ratio that is uncomfortably twiddly to ride on the flat.
This is why gears were invented. Riding single speed is a choice. It gives you savings in terms of weight, complexity and maintenance, but there is a penalty in terms of reduced versatility.
Another option that is simple ad low maintenance is a 3 speed hub gear. Various companies make hub gears. In the UK, the standard for many years was Sturmey Archer.
Set up a bike with a Sturmey Archer 3 speed so that the middle gear is good for general riding. Something like 60 —65 inches.
The higher gear will be 33% higher, and good for down hill, or when the wind is at your back.
The lower gear will be 25% lower, and good for up hill or when the wind is in your face.
Ride a 3 speed like a "selectable single speed".
Alternatively, there is nothing wrong with a derailleur set up. Back in the day, we used to ride simple 5 speed (1 x 5) derailleurs huge distances.
Modern gears are well made and easy to operate. Just because you have gears, doesn't mean you have to keep changing gear every 30 seconds. On my geared bike, I will often complete a 5 or 10 mile ride without changing gear.
There are no prizes for what you choose, except the enjoyment of the ride.