Thursday, 1 June 2017

Converting a freewheel to a freehub

I've written in another post about how much I love my Reid Vintage Ladies 7-Speed Classic bike. But that doesn't mean that I'm blind to its vices. In the time since I wrote that piece, another, more serious problem than the flimsy chainguard emerged: the flimsy and fragile wheels. Rear wheels only last me about 6 months or 2,000km (1,250 miles) This post is about how I fixed that problem.

If you just want the take-aways, skip down to the bottom.


My first problem with a Reid wheel occurred when the bike was about four months old. One moment, I was riding along just fine, and the next, the bike came to an abrupt, screeching halt. Dismounting, the cause was obvious: the back wheel was badly bent, preventing it from rotating. I've since learned that the colloquial description for this kind of wheel failure is a "taco", for obvious reasons!

The failure occurred while I was riding along a path shared by cyclists and pedestrians, and I had just maneuvered to avoid a group of people standing still and talking in the middle of it. I thought, at the time, the wheel failed because the spokes had clipped one of the many obstructions jutting into the path.1 In hindsight, I'm not so sure. Either way, the next day, I bought a new wheel from Reid (only available in a set of front and rear, back then, $40) and kept riding. Easy fix.

Reid's target market
for these bikes:
rider weighs less than 80kg.
Everything was fine again for several months, until one day while wheeling my bike to park it after dismounting, I noticed it wasn't rolling smoothly. Specifically, I felt a periodic resistance and heard a dragging noise coming from the rear wheel. Closer inspection showed that once every rotation, part of the wheel rim was dragging on one of the rear brake pads. I assumed that the wheel wasn't sitting square in its dropouts and tried correcting this. I improved the situation, but didn't completely fix it, and on even closer inspection, I discovered that the underlying cause was a broken spoke. At the time, I blamed myself. I was running Tannus solid tyres (more on them another time), and I knew that these handle shocks from the road quite differently from pneumatic tyres. I also suspected that at a bit over 80kg/176lbs, I'm heavier than the riders for whom these bikes are designed. So I forked over another $40 for another wheelset, and switched back to using pneumatic tyres.

So, when several months later, I experienced the same periodic dragging and saw another broken spoke, I was less inclined to blame myself. Rather than go through the waste and inconvenience of replacing wheels a couple of times a year, I was prepared to spend more to get a better-quality wheel. (I summarily dismissed learning to replace spokes as a process more fiddly than I was prepared to undertake, and my growing concerns about the quality of the wheel made me think I'd be doing this often).

As I searched for a compatible replacement, I learned about wheels, their sizes, and about the difference between freewheels (as fitted to this bike) and freehubs (fitted to most other bikes for the last few decades). Sheldon Brown's article "Freewheel or Cassette?" was a great summary for me.

My take-away from all this was that there was no simple, drop-in solution for my problem. That is, I couldn't find a decent-quality 700c-sized wheel designed for either a freewheel or for a 7-speed cassette. Road bike wheels were the right size but designed for 10- or 11-speed cassettes; and mountain bike wheels were different sizes and designed for 8- or 9-speed cassettes. And while I noted some decent-quality mountain bikes fitted with freewheels, the wheels didn't seem to be easily available separately.

Since I rely on my bike for daily transport, expediency prevailed, and I elected just to buy yet another set of wheels (which this time had nearly doubled in price to $70 per set!)

A few months later, a spoke failed again. And, co-incidentally, Reid had withdrawn its physical presence from my city (Brisbane) only a few days earlier, taking with them the expedient solution of just buying more wheels.

Clearly, it was time for a change, even if it proved difficult.

Making the switch

To keep the same size wheel, I figured I'd need to make the switch to a freehub and cassette. After a bit of research, I knew that I would need:
  • a new wheel (duh)
  • a cassette that would work with the shifter and derailleur on the bike, since I didn't want to replace them as well. To be safe, I would aim for as close a match to the freewheel as possible
  • a quick-release skewer to mount the wheel to the frame
  • tools: the tool for tightening and loosening the lock ring on the cassette, and a chain whip in case I needed to get the cassette back off again (which I assumed I would, given my lack of experience and the experimental nature of what I was doing.) I bought Park Tools' FR-5G for the lock ring and their SR-11 chain whip. 
The significant unknown was exactly what would be required to make the cassette work with a hub that was probably designed for one of a different size. I gathered that a spacer would be needed, but I wasn't sure of what size, or whether there was anything else needed too.
I also didn't want to spend too much on the wheel, because I have a grand vision (outlined here) of someday building my "dream" commuting bike around one of the Reid frames I have, so this wheel would be an interim solution only. The cheapest new roadbike wheels sell for nearly as much as the entire bike cost me! A second-hand roadbike wheel on Gumtree seemed to fit the bill: the Shimano WH-R550 had garnered enough favourable reviews in its day (introduced in 2004) and was a reasonably  good-quality wheel from a respected manufacturer. Adjusting for inflation, a set of these when new sold for over $300, so $20 for a second-hand example looked like a good deal.

Shimano still produces 7-speed cassettes, and one of them in the HG200 series has the same range of cogs (14–28) as the Shimano MF-TZ21 freewheel supplied by Reid. This made me confident that the existing derailleur would work. I was less confident about the shifter, because although I could find specs (again, on Sheldon Brown's site) for the cog thickness and spacing of the HG200 cassette, I couldn't find the equivalent numbers for the MF-TZ21 freewheel. I decided to just hope for the best and went ahead and ordered one.

Note the 0.5-mm gap between
the top spacer and lockring
Bringing the wheel and cassette together showed me the missing piece of the equation. With the lockring and smallest cog in place, there was a lot of play for the cassette to slide up and down the hub splines, so the hub had indeed been designed for a cassette wider than mine. Research turned up conflicting information about what cassettes could be used with the WH-R550 wheel, and I also wondered whether there had been different variants of this wheel produced over its lifetime. In the end, I decided to just measure the gap. Lacking a Vernier caliper or any other precision measuring tool, I did the best I could with a ruler and determined that I'd need a 3mm spacer. A quick search of eBay immediately confirmed that such items exist, and I ordered one. On arrival, I found it to be pretty close, but not quite wide enough. Googling to see if anyone made a 3.5mm spacer, I discovered Problem Solvers  — a bike parts company specialising in producing all kinds of adapters so that you can (as they put it) "transform your bike for purposes never conceived by the manufacturer". This is very much My Kind Of Thing. And yes, they make a 3.5mm cassette spacer!2

I ordered one, but in the meantime, figured that the 0.5-mm difference was going to be within the tolerances of the drivetrain components anyway and proceeded to mount the wheel on the bike. A test-ride established that the shifting was terrible — so terrible that I ended up having to extract the chain from where it had wedged between the largest cog and the wheel spokes. Twice.

And that's when I learned about adjusting the rear derailleur, using the excellent video and step-by-step written instructions from Art's Cyclery: "How to Adjust Shimano Rear Derailleurs". With this help, a complete novice like me not only corrected the chain-eating problem described above, but had this bike shifting smoother and quieter than I remember it ever shifting in its life. And all in under 10 minutes!

And that's all there is to it! I'm still waiting on that 3.5-mm cassette spacer to arrive, but in the meantime, the bike is perfectly rideable. In fact, it's much faster and easier to ride, if a little bumpier, than ever before. I'm hoping not to replace this wheel again on this bike, but I'm very grateful for what I've learned along the way.

Project cost

Wheel: $20
Cassette: $23
Skewer: $20
Spacers: $25 ($18 for the right one, including international postage, plus $7 for the almost-right one)
Tools:  $65 ($27 for the lock-ring tool, plus $38 for the chain whip)

Total: $153


If I could distill the lessons and give them to my past self, they would be:
  • You're swapping contemporary components with similar characteristics from the same manufacturer. Don't overly stress about compatibility with the derailleur and shifter. Assume they're going to work until they don't.
  • Fitting a 7-speed cassette onto a hub designed for a larger cassette just requires a spacer. Put the parts together and then measure for the spacer you'll need rather than trying to figure it out from published specs. 
  • Don't be afraid of adjusting the rear derailleur. No matter how complex the mechanism appears, there's a logical sequence to adjusting it, and it's easy to do. 
In short: solve one problem at a time, and approach the project as experimental and requiring some trial-and-error.

1 A staircase! The City Reach Boardwalk is a truly, truly stupid and dangerous design, and I can only assume that whoever thought it was suitable as a shared path to accommodate bicycles (and to use it to link other significant, high-traffic shared paths) was not deeply familiar with the concept of "bicycle". There should be a website for "world's stupidest bicycle infrastructure" and this should get a look-in.

2 Note that they describe their 4.5-mm spacer as "for 7-speed cassettes on 8/9-speed freehub bodies", and there's no way the gap I need to fill is 1.5mm, although the Shimano spec sheet for the WH-R550 (or, at least, one variant of it) specifically states it is for use with a 8/9-speed cassette.

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