Convert an old 10 speed bike to a 15 speed

Posted by on October 29th, 2023  •  0 Comments  •  Full Article

In 1972 I was one year into my tipi phase. I’d dropped out of high school in ’71 to build the tipi on the commune. I’ve written previously about this period. Or use the search function at the top of the page to search for tipi. Anyway, somewhere in that time period family legend has it that I may or may not have bought something as an investment, sold it, and made enough profit to buy this 10 speed bicycle. Or maybe I just dreamed it all. There were so many recreational drugs floating around back in those crazy commune days…who knows what really happened. But two years later when I sobered up, finished high school and went to college, I had (and still have) a nice 1972 Sekai 10 speed. That bike was my first car. I’ve known that old bike longer than I’ve known Sue. The only thing I own that is older is my first harmonica from 1967.

A few years ago I started riding Clint’s 1996 Schwinn Mesa 21 speed mountain bike. He had long moved onto better bikes and left it in our garage. I liked the granny gear for hills, and it was strong enough to fly over curbs without bending the rims.

Clint's Schwinn Mesa
Clint’s Schwinn Mesa

But a couple weeks ago the Schwinn’s frame broke and I had to dust off my 10 speed. It has a granny gear, but it’s a seven inch sprocket. I was spoiled by Clints Schwinn which had a 3.5 inch granny gear. Full disclosure: I already have 7 gears in the back on my 10 speed with an updated rear derailleur. So technically it is a 14 speed, not a ten speed. But to keep this story simpler, I’m still calling it a 10 speed.

At 69 I’m finally too old (or out of shape) to pedal my ten speed up the Tacoma hills. I wanted to change it to a 15 speed. But you can’t just slap on a 3 inch granny gear. The front crank of a ten speed isn’t designed for 3 front gears – sprockets. However, I had the old broken down mountain bike, and those all have 3 gears on the front. In a Eureka moment I wondered: could I swap the front transmission from the 21 speed mtn bike to my ten speed?

I looked online and there is no information on going from 2 to 3 sprockets. In fact, lots of people are going from 3 to 1. 

So I carried my two antique bikes into Second Cycle in Tacoma and explained my crazy idea. They didn’t bat an eye. “Try it!” they said, “it might work”.

The mechanics showed me how to mount my bike in the bike repair stand and pointed to the wall of Park brand specialty bike tools. They explained the hourly rental rates, which were very low, and said to grab them if I had questions.

I’ve worked on bikes for 50 years, but this was uncharted territory for me. I’d completely forgotten how to remove links from a new chain, or how to pull a stuck crank. It was super nice to have friendly and knowledgeable mechanics available when I got over my head. They showed me what to do, but made sure that I did the work. And tools, wow, they had a tool for everything!

Whenever I needed a new part or cable, they had one on hand.  One part isn’t even made any more, so they found a 50 year old used part in a bin that was perfect.

I was there 3 hours, but when I saw that new transmission working, I was pretty stoked. I had so much fun working on the bike that I went next door to their commercial outlet and bought a few Park branded bike tools of my own. Now I have my own crank puller and several specialty chain maintenance tools for the next time I have to mess with transmissions.

Second Cycle is a great resource for Tacoma. There are a few other bike shops in town, but this is the only one offering rental work space for DIY people who need access to specialty bike tools. I was very impressed and will be visiting them again. 

I took the bike for a ride and with the new 3.5 inch granny gear it was much easier on the hills. I did notice that the front derailleur is very touchy. It will shift to the bottom and middle gear, but doesn’t like the biggest gear. Because I was riding a few blocks from what used to be called “Old Town Bikes”, I rode in and had their mechanic look at my Frankenstein bike. He immediately said that my bottom bracket was set up for 10 speeds (naturally).

He explained that the reason my front shifter was struggling was that my bottom bracket needed to have a longer, mountain bike axle, to match up with my mtn bike crank and derailleur. This would move the sprockets farther out…or maybe it was in? Anyway, he seemed quite sure that the proper bottom bracket axle would fix my shifting problems. I also had him order a new front derailleur. Anything would be better than Clint’s worn out 1996 derailleur. Parts totaled $39 and will be here in a couple weeks.

In the meantime, I may buy the tools to fix the bottom bracket myself.