So there you are, pedaling hard at the last stretch of a 20 mile commute home from work – your blood is pumping, your energy is holding strong, and with any luck you’ll beat your best time and make it to your uncle’s annual chile cook off before sun down. And then POW!!!! Two pedals into Nail Alley you get a flat on your rear tire, and in a single moment all hope of a delicious steaming pile of cooked beans and spices have been obliterated forever.
Fixing a flat on the rear wheel of a Brompton is known the world round as “a little tricky.” But I promise, once you get the hang of it, you’ll be fixing your own flats in no time! While my co-worker Josh was replacing a tube on a Brompton, I asked him if I could take a few closeups:
What do you need to fix the flat?
All you need to fix a flat on a Brompton Bike whether it is the rear or front wheel is a pair of tire levers:
A 15 mm wrench like this one:
And one of these!
Preparing to change the flat
Josh here has a bike stand which can hold the Brompton off the ground and, in general, this makes working on any bike easier. However, if like most of us you don’t own a fancy mechanic stand, just find a stable place to lean your bike so you can work on the rear wheel without the bike moving around on you. Then get your 15 mm wrench ready, we’re about to go to work.
Step 1: Detach the shifter chain
At the axle of your rear wheel there is a large nut. At the center of this nut there is a small chain which goes into the rear hub itself. This chain connects at the other end with your shifters, and it is responsible for shifting your gears. The first thing you want to do is detach this chain by loosening the small cylinder at the base of the chain:
Then detach the chain entirely by loosening this cylinder looking thing.
Once the chain is detached it will be hanging freely out of the axle nut like a piece of noodle.
Step 2: Remove the axle nut!
Use your 15mm wrench to loosen the axle nut, pull it off the chain, and remove the washer behind it:
Once the bolt and washer are removed, remove the shifter chain itself by twisting it counterclockwise and pulling it right out of the hub! Make sure to set nut, washer and chain aside in the order you removed them. When you put these parts back on the bike, you’ll screw the chain back in the hub first, then thread the washer back on, and then screw on the nut, so it’s helpful to set them aside in this order.
Step 3: Pull off the chain tensioner and loosen the nut behind it!
There is now nothing holding the rear derailleur in place so you can go ahead and remove it from the from the frame.
Once you have the chain tensioner removed, you will see a second nut behind it. Loosen this nut with your wrench. You can remove it entirely or just loosen it half way like Josh did here:
You’ll notice above that there is a strangely shaped washer behind this nut. This washer has two little wings which nestle into the frame and can be a little tricky to wiggle free. The easiest way is to pry it off using your wrench like this:
Step 4: Remove the rear wheel and extract the tube!
Once you have loosened this nut and washer on both sides of the axle you are ready to remove the wheel from the frame and change out the tube. Just lift the frame of the Brompton off the wheel, squeezing the flat tire with your fingers to allow it to pass through the brake calipers.
Once the wheel is free you want to use your tire levers to pop the tire off of the rim. Here’s how you do it. Take one tire lever and insert the curved end (not the hook end) underneath the lip of the tire. Use the lever to pry the tire over the edge of the rim. This will bend the rubber of the tire and create tension, so you’ll want to hook the other end of the lever around one of the spokes, holding the tire in place and preventing it from snapping back into place. If the lever is hooked around the spoke properly, you should be able to remove your hand and let this lever bear the tension of the tire all on its own. With this lever jammed up underneath the tire, you should have enough room to insert the other lever under the exposed tire lip and begin to bring the rest of the tire over the rim, by pulling your lever counter clockwise around its circumference. Below you can see Josh begin to do this:
Step 5: Replace the tube, and reinstall the rear wheel
Once you have the tire brought over the lip of the rim, you can remove the bad tube per usual. This is standard tube changing stuff, but I’ll try to describe it in some detail for any first timers.
Start by finding the valve, pulling it down through the hole in the rim and clear from the tire. Holding this section of the tube in your hand you will be able to pull the rest of the tube free from the tire, like a snake from its rubbery den. Here you will want to carefully run your hand along the inside of the empty tire to make sure there is no dirt or glass stuck in there that could cause another flat. Be very careful while doing this so you don’t cut yourself.
Here Josh chose to remove the entire tire from the rim although it should be noted the tube can be removed and the tire checked with one side of the tire still inside the rim. If you did remove the entire tire from the rim, you’ll want to put one side back around the rim before installing the new tube.
To install the new tube, fill it with tiny bit of air so that it isn’t so flat, and then push the tube inside the tire under the lip that has been brought over the rim. You’ll want to start with the valve. Bend the tire back a little so that the hole in the rim is exposed, shove the valve down into it, and bring the tire back OVER the valve. From here you should be able to push the rest of the tube up underneath the tire, moving around its circumference. Just pull the loose edge of the tire away from the rim and tuck the tube inside it. Once the tube is evenly distributed, bring the tube filled tire back over the rim.
Bringing the loose edge of the tire back over over rim with the tube inside can take a little practice. You should be able to bring 3 quarters of the circumference of the tire back over with no problem, but once you run out of slack, you will need your trusty tire levers to pry the remaining tire back over the rim and allow it to snap back in place.
Once the new tube is inside the tire and the tire is back on the rim, replace the front wheel onto the frame, placing the two prongs of the fork back on the bolts on either side of the front hub, threading the still flat tire back through the brake calipers, making sure that the bike chain is threaded around the teeth of the hub sprocket.
Once the wheel has nestled itself back in place with the chain around the sprocket, push the funky washers back flush with the frame, making sure the top of the washer says “TOP” on it, and then re-tighten the nuts using your wrench.
Now you are ready to replace the chain tensioner!
Step 6: Replacing the chain tensioner
One of the things that makes it a little more complicated to change out a flat on a Brompton bike is that you have to remove and replace the chain tensioner. As we saw, removing it is no big deal, you just unscrew the nut, and it pulls right off. But putting it back on takes a little more technique. Here’s how you do it.
First place the tensioner back over the axle nut so that it looks like this:
You can see the long arm of the chain tensioner is pointing up while the short end is pointing down. Here you want to make sure that when you place the tensioner on the bike that the chain goes UP and OVER the teeth on the shorter arm like this:
Next, replace the small shifter chain, by sticking it straight into the axle and twisting it clockwise. Twist it until it won’t twist any more and then go back two spins counter clockwise. This creates a little slack which you will need later when you reconnect this shifter chain to the shifter cables. When this is done, replace the washer and the larger axle nut like so.
Next, take the longer arm of the chain tensionser, rotate it counterclockwise, past the shorter arm of the tensioner, and set it ON TOP of the bike bike chain like this:
Now you’re pretty much all done! To finish off, screw the shifter chain back onto the shifter cable, by twisting the thin cylinder thing as shown below.
There should be a little slack in the chain to allow the Brompton to shift to all three speeds in the internal hub.
Then pump up your tires and you’re DONE!!!!!
I hope this was helpful. Follow these steps closely and you’ll be fixing flats on you brompton folding bike in no time!