Lowering SS gearing - smaller chainring or larger cog?
 

After doing some test riding on the Motobecane SS I built for a friend, I can tell the gearing will certainly need to be changed. The last time I did this I did 42/16 and it was perfect. This time it is 45/16 and it's going to be too steep for her.

Would putting more teeth in the back effectively give me the same result as dropping some teeth in the front? With a 45 up front how could I get closest to the feel of 42/16. I'm not very well versed on ratios. What I know for sure is she doesn't cycle much, wants the bike to get up to speed quickly and with minimal effort, and this is an upright setup. Flat surfaces only and not super long distances. Even for me, someone who rides regularly, this thing is a little tough to get going comfortably.

Said bike:


https://cimg1.ibsrv.net/gimg/bikefor...268e5387d.jpeg

Go here and move the cogs around
Bicycle Gear Calculator
45x18 is 68gi
42x16 is 69.7gi

this should help...

https://cdn.shopify.com/s/files/1/14...g?v=1557265331

45/17 is very close to 42/16.

42x16 = 45x17, around 70 gear inches. In his 1936 Every Cyclist’s Handbook, F.J. Camm recommended a 65-in gear for single freewheel use for gentlemen. He recommended a 60-in gear for ladies riding a single-speed freewheel.

I recommend searching for the late Sheldon Brown’s online gear calculator and keying in the options. If you stick with the 45T ring an 18T cog gets you around a 67-in gear, 19T gets you to 63-inches, and a 20T lands you at 60 gear inches. My vote is a bigger cog in the back, both because it will be cheaper and because there is a case to be made that bigger rings and cogs run smoother and more efficiently.

42 x 16 gives you 71 gear inches, choose any combination that gives the same or close to the same result

For somebody who doesn't ride a lot, wants an easy-to-start bike, and won't be going fast, on an upright townie, 42x16 is way too tall, let alone 45x16. Like, if you don't think it's way too low, it's probably too high for your friend.

I'd go 42x20 to start with, or 45x21. 45x21 is 2% higher than 42x20, both work out to around 13 mph at 80 rpm. 45x20 gets you to 14 mph at 80 rpm, and is as high as I would go.

My bike is set up with a 1x6, 42 x 14, 16, 18, 20, 23, 26. I spend most of my time in the 20 and the 18, depending on the wind. (When I add a 45t outer ring for half-step, the 45x20 will split the 42x20 and 42x18... I bet I'll be in it a lot.)

--Shannon

To be fair, she doesn’t ride a lot, but that’s more due to her current bike. She’s pretty fit and an outdoors person so her legs see some good use, just not in cycling. My thought is that she’ll be riding a lot more and I’m hoping to find a sweet spot for her, but 45x16 definitely won’t be it.

Your advice seems sound though. I’ll try 45x21 to start. The cog will be easier and cheaper for me to replace. This also jives more with rustystrings61’s information above.

Is there any reason to choose even teeth over odd?

You know, I kinda think maybe there is.

The 14-26 Suntour I'm running is the first even-cogged cluster I've ever had, and, while I've been off the bike for 6-7 years, I like 14-16-18-20 better than the 13-15-17-19 that I always had before. It's a feel thing, and there's no obvious reason for it, but I like it a lot.

--Shannon

Well, I’m guessing it won’t be significant enough to matter in my current application.

If it’s really flat surfaces only, a 45/18 might work That’s 67.5 inches. Since you need a freewheel, you will find low cost 18t and 20t more easily than 19 or 21. 45/20 is going to be pretty easy on flat rides Just my 2p.

Otto

Usually swapping out rear cogs is much easier and more effective. One tooth back there is worth 3 or 4 in the front, on average. I was going to say something about 45/16 but figured you picked it for a reason. Yeah, it's pretty high for a 1 speed. 42/16 is more typical, for fit bike enthusiasts...

45/20 or ~61 inches is a good starter gear IMO. Depends on terrain and fitness. 45/21 I feel is a little on the low side. If it's all flat terrain 45/18 is probably going to be better.

I used to ride 44/17 (70 inch) when I rode fix in winter as a young teen but very fit racer, but very hilly terrain. 45/16 would have been way too high. OK for flat terrain I suppose.

Another vote for rear cog and 45/20. 45/18 seems like a possibility too...

Went ahead and picked up a 20t. But I got home and realized I forgot to get a new chain for it! Doh! Will test it out tomorrow.