Pluses and minuses for changing either a sprocket or chainring

[in4]

I was thinking about changing my current set up to something that gave me a few lower ( hill climbing ) gears. That got me thinking about the pluses and minuses of changing either a sprocket or a chainring. Is it a simple practicality choice; its easier to change one or the other. Maybe its a cost thing or fitting a chainglider issue. Now that sprockets are easier to change thanks to circlips being used perhaps its almost a personal preference thing. I could of course be barking up the wrong tree here but am happy to be corrected and educated.

[martinf]

Depends on several factors. The first thing is to decide what gear range you want.

Then you can usually get there by changing either the sprocket or the chainring, or maybe both.

If you want to fit a ChainGlider, that limits the options. There are only a few possibilities for compatible chainring size, Chainglider front parts are 38, 42, 44 and 48 IIRC. Same goes for sprockets, with the constraint that smallish sprockets need the special Rohloff compatible Chainglider rear part, which IIRC is different for threaded and splined sprockets. Large sprockets 19,21,22 are in practice compatible with the standard Chainglider rear part as used for Shimano Nexus 8 hubs. Another thing to consider is that Chainglider front parts aren't necessarily compatible with all the rear part options, IIRC the 48T front part won't work properly with the 19-22T rear part. Chaingliders also work best with thin chainrings, the Surly stainless steel chainrings work well for me and are reversible. But I have one bike fitted with a wide TA ring using  1/18" chain and a 1/8" sprocket, this works OK with a Chainglider but needed a "breaking in" period.

Changing the chainring can be economique if you have a stock of spare chainrings. I did this with my Raven Sport Tour, swapping out the 50T TA ring for a 42T TA ring I had in my spares box and leaving the 19T sprocket in place. This also allowed me to fit a Chainglider as I then had a 42x19 combination.

When I lowered the gearing on my Raven Tour I kept the 38T Surly chainring and changed the sprocket from 16T to 21T. I also had to change the Chainglider rear part.

One minor consideration is that for a given gear range a large sprocket/large chainring combination wears more slowly than a small sprocket/small chainring combination. That was the reason I originally chose 50x19 for my Raven Sport Tour. But a transmission that is partially protected by a Chainglider should last a lot longer than an unprotected transmission.

[Andyb1]

What ratio do you have now and what ratios are you considering?

I wanted to lower my gearing and went from 38/16 to 38/17 which effectively added one extra lower gear and removed the very top ratio.  My Raven has the older screw on rear sprocket and as I am near SJS, Nick there swopped sprockets for me (a special tool is needed).  I was lucky that the eccentric BB was initially almost fully tight (even though the chain had little wear) and by going to the fully loose position I could keep the same chain in use.  Chainglider parts were not changed.

The change was definitely worthwhile.  The lowest gear has changed from 17” to 16”.    I don’t miss the loss of the very top ratio and I can cycle up my local steep hill a lot easier.

Having odd number teeth on the back also means the sprocket will wear evenly as narrow and wide links alternate position every revolution (the chainwheel is N/W so the chain always has the same orientation on that).

[in4]

I wanted an extra 'granny gear' So from a 45 x 19 combo to a 39 x 19 combo seems the best option and gives me the 13.33% gearing reduction ie  one full lower gear. Additionally, I read that 'Rohloff only make steel splined sprockets for up to 21 teeth' 22T sprockets are intended for Gates belt drives.
I'm not considering a chainglider.

So, unless I wanted to gear lower again the 39 x 19 combo seems like the best option.
Interestingly the price of a new sprocket or chain ring is about the same in UK.

Many thanks for the helpful posts, appreciated.

[mickeg]

For around town riding with an unladen bike, I use a 44T chainring and 16T sprocket.  That is geared high enough that I still have higher gears on shallow downhills but it is geared low enough that with an unladen bike I have the gears I need for uphills.

But when I go on a bike tour I need lower gears.  I switch to a 36T chainring, stick with the same 16T sprocket. 

I add or subtract four chainlinks when I make the switch.  With the longer chain, I have two quick links installed.

It would be simpler to swap sprockets now with the splined sprockets, I made the choice to switch chainrings when I initially built up the bike, that was back when the sprockets were threaded.

I do not use a chainglider.  I use a five arm crank with 110 BCD.  So swapping chainrings means removing and reinstalling the chainring bolts.

If I was going to do a tour in flatter country, I might try a 40T chainring instead of the 36T, but have not done a tour in an area like that yet.