Advice please on chainset ratios

A 1954 bike deserves to have the gear ratios calculated in inches. Chainwheel divide by cog multiply by wheel diameter in inches.
This dates from the old ordinary, a measure of the equivalent front wheel diameter.

I spent too much time in the 50s sorting out SA hubs that were full of rusty water to ever learn to love them.
The ratios are all available on line, and some catalogues have gear tables in inches. I firmly believe having all gears in direct drive to be preferable.

My own choice of gears in 1950 was 2 chainrings 47 and 50, and 13 to 22 5 speed. This gave a range of 10 gear evenly spaced about 8% between gears.

SA FW gear ratio in inches: 46 x 18 26" would be 84 66 52 44.

By the early 50s I had experienced most of the available gear systems. I always regret never trying the famous Vittoria Margherita as used by Bartali in the 30s, although I may be the last person alive to have used the Campagnolo Paris Roubaix gear in a genuine road race (not historic) in 1956.

Keith
Food for thought, thanks Keith, but for now I rather like my 4speed lever strapped as it is to the bar end, and as everything seems to be running really well I don’t want to make any radical changes just yet. The easiest option for me right now is to swap out the 18t cog for a 16t. I’ll see how I get on with that.
As for water in the hub. This bike doesn’t know what moisture is let alone rain! 😁
 
I seem to remember rain at least 3 times a week when I was riding the 12 miles to work in 1950.
Most of the SA gears were on totally neglected commuter bikes in the 1950s. If a gear cable or toggle chain broke they mostly managed with the high gear only. Water entered through the ball race around the driver, behind the cog.
I must say the AW was a very clever design, as the worst wearing parts were cheap.
 
Thanks for directing me to that thread. It kinda explained things ( I struggle with theory) but don't think it would influence my choice of equipment, mainly because any single speeder I put together would be a collection of what's in the shed to get a given ratio.

What had always perplexed me is how I find it easier to climb using big chainwheels and sprockets. So 34x17 and 50x25 are both the same ratio but I find the 50x25 easier to climb on. The availability of compact chainset and bigger cassettes means I tend to ride most of the day on the outer ring and only drop to the 34 for those noted climbs
 
It’s got a 4 speed wide ratio Sturmey hub with 18t x 44t and on this run I pretty much only used 4th & found myself often freewheeling (the Fiamme rims do roll so well)

Can anyone advise what might be the better option, 18x46 or 16x44? (combined with a 4 speed close ratio Sturmey hub gear)
Is it the close or the wide ratio? Maybe it is stamped with two letters.

AF = close
FC = close
FB = wide
FG = wide
FW = wide
FM = medium
 
Definitely FW, four wide. Mine runs perfectly as I had it fully serviced by @peterwilliamson
 
Why the prime number idea? What advantages does that give?
Chains usually contain an even number of links, because they usually have an equal number of outer links and inner links. The only exception is when someone uses a half link, or they use a chain that is entirely composed of half links. Typically people only use half links when trying to create a 'magic gear' (a combination of chainring and sprocket that gives the correct chain length for bikes with vertical dropouts that have no horizontal movement for adjusting chain tension). Half link chains are also popular with BMX and trials riding.

A typical half link product
econo-kmc-half-link-3-32-silver.jpg

An alternative half link product
112045_half_link.jpg


A chain composed entirely of half links
TFB10_CH4105.jpg





But there are problems when combining a chain with an even number of links, with a sprocket or chainring that also has an even number of teeth.
1. Each tooth will only ever encounter either an inner link or an outer link. But an inner link wears the sides of the teeth more than an outer link, because an outer link has a bigger gap between the side plates, and the narrow inner link each side of an outer link is guiding the outer link.
2. The wear locations that cause distance between the chain rollers to increase is different for inner and outer links:
For an inner link, the distance between two chain rollers increases when the bush and the roller wear
For an outer link, the distance between two chain rollers increases when the bush, the roller, and the pin wear.

So you can see that for outer links, there is an additional wear location.

Eventually you can expect two forms of uneven wear.
1. From the start, alternate teeth will encounter more side wear.
2. As the chain's pins, rollers, and bushes wear, you can expect alternate sprocket teeth and chainring teeth to become more worn and hooked.

There are several answers:
1. Use sprockets and chainrings with tooth counts that are prime numbers, and avoid using a number of chain links that is an exact multiple of the number of sprocket or chainring teeth.
2. If you have an even number of sprocket or chainring teeth, move the chain forwards or backwards one tooth after each ride.
3. Use a half link so that your chain has an uneven number of links, or use a chain composed entirely of half links (not a great solution in my opinion)
4. Replace the chain very regularly. This will help with length related wear issues such as alternate hooked teeth, but not with tooth side wear (unless you take care to put the new chain in the alternate position, displaced one tooth from the old chain position)
5. If you have an unfavourable combination, just ride the whole chain, sprocket and chainring combination to total destruction, then replace.


Why is the 48x16 a poor choice (I guess its something to do with it simply being 3x, but why is that a poor choice?)
Dividing the chainring teeth by the sprocket teeth gives a whole number, not a fraction. That means that the sprocket (and wheel) complete exactly 3 revolutions for each crank revolution. So far so good, but humans don't generate the same force and power all the way around a crank revolution. That means the same sprocket teeth will encounter the most powerful part of the pedal stroke over and over again. Quite a lot of single speed off roaders use something like 36 x 18, because most people use around 2:1 chainring:sprocket ratio for offroad single speed. This is a very bad combination, especially when combined with all the mud and grit found off road. For the same reason, you should regularly rotate the chainring by one bolt hole, so that the same teeth do not encounter the most powerful part of the pedal stroke.

On a fixed wheel bike, ignoring this guidance means that as well as the sprocket possibly wearing unevenly, the tyre may also wear unevenly, although this won't be a problem for single speed because the ability to freewheel means the tyre wear becomes evenly distributed.

Please note that to see any of the uneven wear I've described, you would have to ride thousands of miles without changing the chain position (or just be very unlucky when you remove the wheel and put it back). However, some people do ride long distances without much maintenance (e.g. commuters) and then wonder why a new chain behaves strangely and is extremely noisy. Similarly, if someone were to ride thousands of miles, remove the wheel to fix a puncture, then put it back one link/tooth out, they may wonder why it all suddenly became very noisy.
 
Definitely FW, four wide. Mine runs perfectly as I had it fully serviced by @peterwilliamson
OK, I've got the ratios from Sheldon Brown.


Here is an example calculation.

peachy_ratios.png
 
I think 22.3mph is quite respectable! Or maybe Peachy just isn't pedalling at 90rpm!
Not sure what my regular cadence is but I’m pretty sure I can pedal faster than 90rpm especially down hill.
Here’s a screen grab from Strava, I maxed out downhill at just over 23mph, whereas on my geared Claud I’m normally reaching 35+ on that section and averaging 15.
I think the average would have been more than 12.5mph but I had to pull over for tractors and didn’t pause my phone. 426A65BB-BFF2-48AB-AE26-DD7DF1C1BD7F.png
 
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