Ask the expert: Liz Colebrook answers your tech questions on bike mechanics

Ask the expert: Bike mechanics
Liz Colebrook
Liz Colebrook
Anna Glowinski's picture

Ask the expert: Liz Colebrook answers your tech questions on bike mechanics

An experienced mechanic and frame builder, Liz Colebrook is here to help you with your technical issues, no matter how big or small.

How do I know when wheel bearings need replacing? Is it possible/worth it to replace them myself, and if so, how skilled do I need to be? Leigh

Dear Leigh,

The wheel bearings enable the wheel to rotate around the axle at the centre of the wheel. The axle should be securely fixed to your frame via wheel nuts or some kind of quick release system. 

The word ‘bearings’ is short for ball bearings, which are round stainless steel balls packed into a sealed cartridge and pressed into position or snuggly nestled in grease and adjusted into position – sealed or non-sealed, the bearings sit in what’s called the hub. 

With the advent of sealed bearing cartridges, wheel bearings stay correctly adjusted for much longer, as the cartridge acts like a barrier to water and mud etc. You tend to find better quality wheels use sealed systems. 

The more traditional ‘open’ system involves 'Goldilocks' She needs to make an exact adjustment locking up the cone nut against the locknut - not too tight so the axle is difficult to turn, but not too loose resulting in a wiggle factor known as ‘play’. It must be just right. To see this in action, I recommend watching Park Tool's ‘how to service a hub’ online. 

The best way to tell if your bearings need servicing is to remove the wheel, hold the axle between thumb and finger, turn it and then wiggle it. It should turn smoothly and should not wiggle. 

My suggestion is to do an assessment, then take your wheel(s) to a bike shop if one or both do not pass the Goldilocks test. 

Liz

What advice would you give on cleaning an e-bike motor, given the need to avoid getting it wet? Thanks, Karen

Dear Karen,

It's ok to just brush away the loose mud/dirt with a damp cloth and a used toothbrush perhaps if there is mud stuck in grooves. Do not disassemble. E-bike motors are factory sealed and any bolts are there for factory assembly. The only people who disassemble these are trained e-bike specialist mechanics. 

When you clean any part of your bike, you are looking closely at the detail consciously and sub-consciously.  Just 15 minutes of zen cleaning every week can bring enlightenment. 

An example of this is the sudden awareness that the little metal cap has come off the end of a bear cable and the cable has unravelled and looks prickly.  (Re-twist and/or put some insulation tape round the sharp ends if you notice this). 


The ZEN of woven cables
The ZEN of woven cables

Another example would be spotting any damage to the cables on your e-bike or any loose nuts or bolts. 

Use hot soapy water for removing mud and a proprietary solvent or degreaser for other grime. A stash of clean rags, old toothbrushes, string and even pipe-cleaners can come in useful.  

Don’t touch the discs (rotors) of the disc brakes, or spray any lubricant near them!

Liz

Mini pumps: do you get what you pay for or do budget mini pumps just work the same? I’m not strong so I'm worried I will struggle using a bike pump. How much is reasonable to spend on one? Thanks in advance, Emma.

Dear Emma.

Yes, you get what you pay for. The first time you use a home pump (track pump/floor pump), it can be a bit of an effort but here’s a tip: Bring the valve to the 12 noon position so it’s easier to reach.

Once you’ve attached the pump head, use both hands and have both feet on the stirrups.

Bring the handle right up and push it right down with your upper body leaning over the pump – it’s that last couple of inches of “push” when the handle meets the pump that puts the pressure in. 

You don’t have to do it fast, just do the full stroke, watch the gauge and keep an eye on the tyre. 



Left: Pump fully extended. Right: Pump fully depressed

Having your tyres to the correct pressure (see side wall of tyre in good light as it’s not obvious) means you’re less likely to get a puncture.

When you do travel, I suggest a quality pump as a) they last and, b) they work (mine’s a Topeak Road Morph). 

Cheap pumps will work but the stroke is so short, you’ll be truly exhausted just getting enough pressure in to limp home.

Liz

I just bought a second hand road bike. I’ve been out a few times, but every time I’m out the tyres just get flatter and flatter even if I stop to pump them up. Why does this keep happening? Thanks, Holly

Dear Holly,

I can only assume that the valves are leaking because the small top section of the slim (presta) valve has been bent or it’s not been screwed down to the ‘closed’ position after pumping - or both. You can carefully straighten a bent valve core with small pliers, but be careful. 

As it’s a second hand bike, it may have had a puncture before you took ownership and the patch is leaking – highly likely if the valves are ok. 

Have a good look at the tyres and check they look free from cuts and cracks. If you need new tyres, chances are the inner tubes will be worn inside, so fit new tubes too. 

Finally, check the rim tapes, which are strips of strong, thin material that protect the inner tubes from the harsh edges of the spoke nipple heads or the holes to access the spoke nipples. You can replace these too if they are perished or damaged. 

Liz

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