The Moulton TSR as a fixed-gear bike

Can we fix it? Yes, we can!

The TSR has a unified rear triangle. This means the bottom bracket and rear hub are part of the same subframe and therefore the chain length doesn’t vary with suspension movement or pedalling. This makes it possible to run a TSR as a fixed gear bike (and is also beneficial if you want to run one as a singlespeed or with a hub gear). It also has horizontal dropouts (or, at least, my TSR does), which are essential for running a fixed gear as they allow the chain to be tensioned.

A fixed gear bike requires the chain to be as tight as possible without binding, or two things happen:

• There is undesirable free play between “driving” and “braking”, which makes the bike unpleasant to ride
• There is a higher risk of the chain becoming unshipped, which can be disastrous on a fixie, especially if the chain gets caught around a pedal spindle.

Singlespeeds and hub gears can tolerate a bit of chain slack, as they have freewheels and the consequences of an unshipped chain are not usually severe.

Benefits

Turning a TSR into a fixie is the simplest and cheapest way to get the weight down to that approaching a normal road racing bike; in the low 20lb range, if you are prepared to lose the rear brake and mudguards. The other benefits of riding fixed are too many to go into here, but this is about the only way you can ever experience riding fixed with full suspension, something of a revelation on a bike where you have to pedal through the bumps.

Parts swap time

You can (in the UK, at least) lose the rear brake caliper and its cable. If you have dropped bars, you will need to keep the lever so you have the hood to hold onto. Losing the mudguards is optional for maximum weight saving, but not strictly related to the conversion.

I was running 1 x 9, so no changes were needed to the bottom bracket, crank or chainring. The rear mech, bar-end shifter and cabling all come off and go into the TSR spares box. Suddenly there are no cables to the rear of the bike, just like a TSR2 or an old Stowaway. The rear wheel needs to be changed completely, except for the tyre and tube which can be transferred. I used a Surly 130mm fixed hub, a Surly 15T sprocket and an ISO lockring, built onto a Sun CR18 rim to match the front wheel. I could only get a 32h hub, which is probably unnecessarily strong for a 20″ wheel, but it looks fine. The Surly is designed for conversions and gives a chainline of about 45mm from the centreline of the bike. This will line up with many 1 x setups, although you may need a different length bottom bracket for some TSRs. If you have a double or triple chainset, you will want to lose the redundant ring(s) and use single chainring bolts to just fit the outer ring. Finally, you will probably want a new chain to avoid shortening the one from your geared setup, asusming you will be changing back at some point.

My 56 x 15 is just under 70″ in old money, a typical “medium gear” for fixed. This will allow you to keep up down most hills without dragging the front brake, but you can still haul it over a 1 in 6 hill if you need to.

The finished conversion. As minimalist as a TSR can get

Riding experience

I’m assuming that anyone who goes to the trouble of doing this is already an experienced fixie pilot, so I won’t describe the general fixed experience.

Let’s deal with the good parts first. The bike is significantly lighter and there are no rattles due to the tight chain and the lack of, well, stuff (mainly mudguards and 2/3 of the cables). Fixed forces you to pedal through whatever the road can throw at you, and this is where the TSR comes into its own, soaking up the worst of the bumps. The suspension is unfazed by braking through the transmission and works just as normal. It makes for a fun bike for flatter roads, short blasts or just something to freak out fellow cyclists, as if a spaceframe wasn’t enough.

The bad part is that climbing steep hills is harder work than a normal rigid fixie. If I ride fixed on the road, it is usually a track bike. Track bikes have their own problems on the road as the tight angles and very short wheelbase give them toe overlap and the rear wheel can skip over bumps. One thing they have in spades, however, is fork stiffness. Steel track forks, designed for manic sprints, have round fork blades which are stiff in all directions and, when wrestling the thing uphill, there is very little power loss or brake rub. An oval-section road racing fork flexes sideways; a track bike fork does not. So, front end stiffness matters.

The TSR suspension doesn’t help at all when trying to get a 68″ gear over a steep hill. Even with the damping cranked up, the fork turns into a pogo stick and a lot of the effort goes, uselessly, into heating up those Coulomb friction discs. Moultons were designed to be ridden in the saddle, using suitably low gears, not honked uphill with the rider out of the saddle; but that is what you have to do with a fixie, if you ever want to be able to use your knees again. I seriously thought about locking out the fork completely, but that would defeat the whole object of the exercise. I’d just have a slightly heavy fixie with rear suspension.

Verdict

Partial success. I rode the TSR like this for a year, then converted it back to gears (I actually ran it as a 3-speed for a while, then back to 1 x 9). It takes an hour or two to convert between configurations, so I will ride it as a fixie again at some point, but it just doesn’t work well enough for hilly routes. Even a famously flat ride like the Dunwich Dynamo, which I have ridden fixed four times, includes a few hills that require a bit of out-of-the-saddle grunt. To make it a full success would require an on-the-fly fork lockout for the climbs. Most MTB forks have a lockout, and I’m sure Moulton could engineer something suitably lightweight for the road. All it really needs is a beefy locking pin through the bottom of the steerer to restrain the preload adjuster, operated by a thumb or bar end shift lever.