Workshop: How to fix punctures on a hub gear bike
By George Ramelkamp, Cycling Plus | Wednesday, August 4, 2010 8.00am
The popularity of folding bikes with hub gears has skyrocketed over the past few years, but what happens when you get a puncture? Here, we explain how to fix flats on one of the most popular bikes of this type, the Brompton, as well as machines with Shimano Nexus hubs.
- Adjustable spanner
- 15mm spanner
- Tyre levers, pump, patch kit
- Allen keys or multi-tool
1 Tip it up
Here’s a tip to start: make sure that you carry a spare inner tube and adjustable spanner, patch kit and multi-tool, and don’t forget the pump! Working by the side of the road in the rain, trying to prop up a bike while the wheel is removed or installed can be doubly daunting. Fortunately, the folding design of the Brompton allows for a clever bit of positioning. Having swung the rear wheel under the bike, drop the saddle down about halfway, then tip the other half of the bike backwards, bringing the back of the saddle to rest as pictured. You’ll now have easy access to the important part of the bike, with both hands free. Laying the bike down on its left side will do if there’s nowhere level enough to place the bike.
2 Remove indicator
Both SRAM-equipped and Sturmey Archer-equipped Bromptons use small shifter rod indicator chains for shifting duties. These are quite fragile, so treat with great care. To prevent damage while removing the tension arm retaining nut, ﬁrst shift into third or ﬁfth gear to remove tension on the cable. Unwind the adjuster barrel, after having unlocked the adjuster lockring just a nudge. Keep the lockring in its original position and use it as a quick adjustment reference when re-setting the gears. Now, carefully unwind the rod and withdraw it from the axle. Having removed the indicator rod and chain, loosen the 15mm nut holding the tension arm. Note the light torque required for removal of the tension arm nut.
3 Remove tension arm
With the bike upside down and thus partially folded, the chain tension arm can be released fairly easily. You can choose to ﬁrst lift and drop the chain away from the crank – this will give you plenty of slack with which to manipulate the arm. You can also bring the two guide wheels together, which should allow you to slip the chain out from the lower guide pulley (that’ll be the one closest to you, because the bike is upside down), making sure to hold on to it securely, otherwise it will ﬂing open and could pinch a ﬁnger. Notice the chain routing: above the top pulley which sits between the metal shifter fork, then around and below the lower spring loaded pulley, which opens against the chain, keeping it tensioned.
4 Remove wheel, fix flat
Now you need to loosen the two 15mm axle nuts. Five-speed Bromptons will have a further plastic indicator guide that needs to be removed. Note the position of its retaining washer, paying particular attention to the placement of the anti-spin washers, which are gold coloured on recent models, and are marked with the word TOP. This bent tab needs to ﬁt into the slot provided for it in the dropout, and will help orientate the axle, which features two ﬂats meant to slot into the dropouts. While repairing the tyre – if you don't know how to do this, check out part two of our Beginner's Guide to Mountain Biking – ensure the rim strip is correctly positioned over the spoke nipples, with no damage around the valve hole. Make sure you ﬁnd and remove the cause of the puncture. Refer to step 8 for further tips.
5 Reverse order, adjust
Re-install the wheel by reversing steps 2, 3 and 4. With three-speed Sturmey, set the shifter into second gear, then adjust the cable barrel until the square shoulder of the indicator rod is level with the edge of the axle (note: it’s set slightly too far in on the photo to better illustrate the shoulder). With five-speed, align the red (or blue) band on the rod level with the edge of the axle when in second. Test and re-lock the locknut. With a SRAM/Sachs three-speed, once the indicator rod has been carefully screwed back in without forcing, slide the Clic Box back onto the indicator chain shaft, and set with a bit of slack in third gear. When ﬁrst gear is engaged, the indicator rod should pull out to its maximum travel limit exactly, without forcing!
6 Removing a Nexus wheel
Once again, turning the bike upside own is a viable option with internally geared hubs. Be careful not to damage your controls. Lights and computers will get scratched, so remove them ﬁrst, along with any accessories clipped to the bar. Similarly to Brompton wheels, the Shimano Nexus hubs need the axle to be prevented from spinning in the frame under high pedalling loads, as well as having to withstand braking loads on wheels with hub brakes. Using a 15mm or adjustable spanner, loosen the axle nuts, noting how ﬁrmly they were done up. Remove the torque arm retaining bolt if applicable. Pay attention to the order and orientation of the anti-spin washers, along with any other washer on the axle. Do not lose them.
7 Removing the cable carrier
Remove the shifter plate assembly by turning the retaining plate with the yellow dots anti-clockwise, as pictured below. Rear roller brake torque arms on Nexus systems can make life even more challenging, so make sure you remove the retaining nut and bolt from the frame bracket. It’s usually a 10mm nut with 6mm thread. Some frames also incorporate a shifter cable guide stop on the right chainstay. This means you’ll have to unload cable tension in the shifter plate in order to slip the cable out of the guide slot. With Nexus, place the shifter into ﬁrst gear, which will release the tension, allowing easier removal from any cable guide ﬁxed to the frame. A plate incorporating a cable guide, as pictured, will be easier to deal with.
8 Tips for tough tyres
Urban debris accumulating on roadsides has made manufacturers respond with some very tough tyres, suited to severe conditions. Tyres like the Schwalbe Ultra Marathons and Specialized Armadillos have such rigid sidewalls that removal and installation becomes very difﬁcult. With a bit of manipulation, you can take advantage of the rim's smaller central circumference, and gain a few extra millimetres of play to help remove the tyre. Before attempting to pry with your tyre lever and risk breaking it, squeeze any remaining air out of the inner tube. Now manipulate the bead and move it to the middle of the rim by pinching it around its circumference as shown. You’ll gain extra slack, and might even be able to remove the tyre by hand.
9 Re-install wheel and adjust tyre
Re-install the actuator plate, then the wheel, by reversing the order of disassembly. Make sure the gear selector is in ﬁrst, and that all cable slack is pulled up. Match up the red dots on the main plate and hub, and then the large yellow lockring dots. Turn the lockring clockwise, while keeping the plate pushed against the hub, lining up the second yellow dot to lock it. Select fourth gear. Shimano have conveniently put adjuster viewing lines on both the top and the bottom of the actuator plate. The lines need to be even with each other, as pictured. Work through the gears a few times, then re-check alignment of the yellow lines. Turn the barrel adjuster in whichever direction brings them even with each other when in fourth.
10 Chain tension adjuster
Adjusting the chain is done either with a set of adjuster screws at the dropouts – acting on the wheel position – or by moving the distance of the cranks via an eccentric bottom bracket. The latter should be a fairly simple operation, as long as the eccentric shell was carefully ﬁtted and is free of burrs and notches. Loosen the two main bottom bracket clamp bolts, then jam a screwdriver, long Allen key or other suitable tool into one of the pin openings. Rest a crank arm against this bar as pictured, and use as a lever to shift the eccentric BB. Adjust the chain until it is snug without being too tight (about 1-2cm deﬂection in the middle), keeping the bottom bracket centred in the shell. Re-tighten the clamp bolts ﬁrmly.
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