My plan to convert Mr Bumble, my Brompton C Line Urban, to single speed should have been a straight forward exercise, however, it’s turning into something of a marathon, like watching all 218 episodes of the X-Files or reading Tolkien’s Lord of the Rings trilogy. I’m thinking, order bike, order parts, bike arrives, parts arrive, fit parts, ride bike. Seems simple enough, yes? But no, some rumbling front wheel bearings bring all progress to a complete standstill.
So, after various emails to Brompton support, and in all fairness, they replied in super quick time and were very helpful, suggesting I can either take the bike to a local dealer for inspection and repair under warranty, or return the bike for an exchange. I also have the option to return the bike within 28-days for a refund, if I choose. The bike is now with Edinburgh Bicycle* at Bruntsfield for a warranty repair which should hopefully resolve the issue.
We popped in on our way to the coast for a walk and they confirmed the front wheel was not right and sometimes faults slip through the net. I’m a bit annoyed by all this. It’s a new bike, straight out of the box and never ridden, not a speck of dirt on the tyres, yet why didn’t someone in quality control simply spin the front wheel and check all was right? Anyway, should be good to go soon, fingers crossed.
Now, that was the middle of January, today is now 10th February, and I have Mr Bumble in my hands again with his new front wheel and we can now get cracking with the single speed conversion. I’m not going to go through the boring nitty-gritty of each and every little task but will list them all here instead, in no particular order. None of the tasks require any professional experience and only a few basic bike tools are required. The final gearing setup is 44T chainring and 12T sprocket.
- Remove chain and lay aside for later.
- Let air out of tyres to allow wheel removal.
- Remove wheels and remove tyres/tubes.
- Fit new Schwalbe Marathon Tour tyres.
- Insert puncture sealant into inner tubes.
- Remove extended seat post and fit standard version.
- Replace 16T sprocket with single spacer.
- Replace 54T chainring with 44T chainring.
- Remove derailleur, gear cable and gear shifter.
- Install Brompton chain tensioner.
- Refit wheels and pump-up tyres.
- Shorten to 96 links and refit existing chain.
- Remove bell and replace with better one.
- Adjust brake lever angle and saddle position.
- Remove handlebar grips and replace with Ergon GP1.
- Install Intralock mobile phone mount.
- Fit frame protection tape where needed.
- Final checks, double checks and road test.
- Cup of coffee and chocolate biscuit.
On Bike Blog 10-01-25, I did mention that I was changing from my initial thoughts on a 44T/12T gear setup for a 54T/16T setup. However, riding the bike back from the warranty repair in Edinburgh revealed this would be far too low for a single gear setup. So, I went back to the drawing board again for another look.
The stock setup on the C Line Urban is a 54T chainring and two sprockets, 12T and 16T. This offers gear inches of 74.7″ (higher gear) and 56.2″ (lower gear) respectively. The average of the two would be 65.5″ and the closest option I can get using the parts I have would be 60.9″, with the 44T/12T setup. I could get 63.9″ with a 50T/13T setup but while I do have a 13T sprocket I do not have the 50T chainring. So, I’ll go with the 44t/12T setup as a starting point for the time being. Can always change later.
Most of the above tasks were fairly straight forwards, even the Schwalbe Marathon Tour tyres which I though would require some careful, and with no small degree, of physical wrangling, but were easy to fit without levers. The gear shifter separated from the combined brake/shifter level easily and I had to resort to watching some videos to remove the gear cable and mechanism. In other words, RTFM. I would advise, if you are carrying out this exercise yourself, to watch any relevant online videos beforehand, just makes life so much easier than thinking you can work out everything yourself. Back again soon once I’ve done a few miles with Mr Bumble.
*Edinburgh Bicycle normally charges £30.00 for Brompton warranty repairs if the bike was not purchased from them. However, as I was not informed of this at the onset, no charge was levied.
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