I have a single speed bike. I chose a single speed for it’s simplicity. I just get on it and pedal. It has suited me well for about 6 years. The only thing that has changed is kids.
These darn kids, they start at 6 or 7 pounds and eat and grow, and grow and eat and never seem to stop! I used to carry Jules on the back of my bike in a babyseat that attaches to the rear rack. Then Marlo came along and I had the opportunity to buy a Chariot trailer from my friend whose two kids were now riding on their own.
With the added drag of the trailer, and the additional weight of two kids, I found myself doing the walk of shame up steep hills more often than not. I needed another gear, but I’m fond of my good ol’ Redline 29er.
There were a couple of options:
- Nuvinci N360 (which I still might get if I save my duckets)
- Sturmey Archer 2-speed hub like the S2
- SRAM Automatix
I chose the SRAM Automatix because it’s inexpensive, and it’s hackable. There are a few articles out there outlining how to change the shift point on the SRAM Automatix, so I won’t go into the mechanical detail on how to do it. You can read those articles for instructions.
Regular Gear + High Gear
Most people are “unwinding” the shift spring to give the Automatix a shift point at a greater speed. This allows them to have a “normal” gear and then a “high gear” for puttin’ the spurs to it.
I actually wanted to do the opposite.
Low Gear + Regular Gear
I wanted the shift point to be lower, so that I can use the low gear under 10mph for climbing and the high (regular) gear for “normal” cruising.
Trying to get a comfortable shift-point on the Automatix can be tricky because there are a number of factors that determine which speed it shifts at. First is wheel size – the shift point is based on rotation speed, so it will shift at a much faster moving speed on a small-wheeled folding bike than on a 29er. The larger wheel will take you farther per rotation.
You also want it to jive with your cadence. On my 29er with the stock 34t crankset, it shifted at about 14mph. My cadence was ridiculously high at that point.
To get the low-speed gearing right, I switched from the stock 19 tooth to a 20 tooth gear. This gave me the stock mountain bike, low-gear ratio that my Redline came with. Great for going up hills.
I needed to “wind” the shift spring just a tiny bit to bring the shift point down. It doesn’t take much when winding, as winding the spring actually loosens the pressure it puts on the shifting mechanism. Less than 45° did it for me
That change was enough to put the shift point at about 10.5MPH on by bike, which is a good balance for slogging up hills, and just cruisin’. Now I only have to do the walk of shame on the steepest inclines.