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I recently bought a folding electric bike for commuting by train, and braking has been a constant pain.

The shop has adjusted them most weeks, I've never had a bike need this much adjusting, but they won't even entertain the idea that they could be faulty.

Today, they've changed the brake pads, after less than 200 miles use, and when I've come test the bike, the front wheel doesn't come close to locking (nor does the rear of the bike raise off the ground), and the bike will casually come to a stop.

The mechanic has just argued that v brakes function like this and should not lock the front wheel, and he couldn't make them any more effective than they are, I explained that every bike I've ever owned with v brakes was able to lock the front wheel, but it just felt we weren't going to see eye to eye.

So, should v brakes be able to lock the front wheel?

Update To clarify, the bike has at times been able to stop much more sharply than it currently is, on delivery, the brakes were okay, and after each previous 'adjustment', so the weight is not the problem. It can 'endo', the claim by the mechanic is that it shouldn't be able to, and that configuring the brakes like this is fine.

A few details, which were requested in the comments: It has 20" wheels and weighs 18kg,

Here's a picture of it:

Photo of a bike

  • Yeah you should be able too – Ben Poulter Jan 28 '18 at 18:32
  • That is what I thought, but to have a cycle mechanic say things with such confidence made me doubt myself – ThomasRedstone Jan 28 '18 at 18:52
  • Yep, any normal brake setup should be able to lock the front wheel, at maximum lever force. (But note that you never should intentionally lock the front wheel, as this can be dangerous.) – Daniel R Hicks Jan 28 '18 at 19:09
  • For me, the comment box says "Avoid answering questions in comments" before I type into it. How is it for you? – ojs Jan 28 '18 at 19:10
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    Can you see the fork flexing when applying the front brake? If so, then it might be the fork that contributes to the weak braking feeling. Installing a booster for V brakes might make it somewhat better; however I have some questions to the manufacturer that chose to install such brakes on an electric bicycle. – Grigory Rechistov Jan 28 '18 at 20:21
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Regarding locking the front wheel, they are sort of correct: on paved surfaces and tires with decent grip the rear wheel should lift off the ground before front wheel locks.

However, it sounds like you can't lift the rear wheel either. A decent set of brake pads should last much longer than 200 miles and brakes should not be adjusted every week (unless you ride 2000 miles in a week), so it's probably best to switch to a different shop. It might also be that the brakes are just garbage and could be replaced with a better set. As mentioned in a comment, a brake booster arch might also help.

  • There may be a legal aspect: my state's law says that the brakes have to be able to make the bike skid/lock up. – compton Jan 28 '18 at 20:23
  • That goes probably for rear wheel. For the front the only ways to make it skid on asphalt are slippery front tire or chopper-style fork. On the other hand I have seen a couple of "modulator" kludges designed to limit front brake to prevent endos and wipeouts. – ojs Jan 28 '18 at 21:43
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    A locked front wheel is generally considered a non desirable occurence when riding because the consequence is quite dramatic. When stationary the brake should be able to somewhat lock the wheel in a way that it may be hard to push the bike forward if enough downforce is applied to the handlebars. – Carel Jan 28 '18 at 21:55
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    Brakes prevent the wheel rotating relative to the bike frame. They can't stop the wheel turning if the entire bike (and rider) rotates vertically forward. – bdsl Jan 28 '18 at 22:26
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    I think the attribute "braked" is the key here. My reading would be "there must be at least one brake, which may affect one or more wheels, which it must be able to skid", so it would be legal for example to have a tricycle which has one brake at the rear axle which brakes both rear wheels. – ojs Jan 29 '18 at 19:32
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Back wheels with hub motors weigh a lot. The battery will also add weight behind the front wheel. The whole bike sounds light for an electric model though (is that definitely the weight with the battery?) Combined, this will make lifting the back wheel much harder than it otherwise would be. While the wheelbase is short, your weight is also quite a lot way back.

I've my locked my front wheel twice in 40000km of riding. Both times were on wet leaves on tarmac. It's just not something you do, so it's not a good test.

I have ridden an e-bike with poor front (disc) brakes. A little more back brake than on a normal bike was the only adjustment needed, similar to riding with a rear child seat. In both cases the extra weight means that back doesn't skid.

But v brakes with good pads should be able to stop the bike as hard as you're prepared to risk in terms of not skidding the front or going over the bars. After all, they were standard on MTBs until discs became affordable. I've never seen good pads on v-brakes when the bike is shipped. I upgraded mine to XLC dual compound, with much more stopping power (quite cheap on ebay). I've since gone for some Kool Stop dual compound pads because the XLCs were wearing out too quickly.

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    Have an upvote for mentioning geometry relation to lifting the back wheel, because indeed that makes a difference. Just like 20" wheels vs bigger wheels, I assume. Actually if I get my physics correct, I think that given 2 brake systems with equal stopping power (let's say able to generate the equal amount of friction on the rims), the bike which does not lift the back wheel will be able to come to a stop sooner because none of the power applied to the lever gets lost in lifting the back wheel. But I might be wrong. – stijn Jan 29 '18 at 13:21
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    You are wrong. Rear wheel lift happens because of deceleration, not braking power. At maximum stable deceleration all weight is on front wheel. – ojs Jan 29 '18 at 19:42
  • @ojs Sorry I don't really understand. Take one normal bike, and one imaginary bike where the chainstay is 2 meters long (but, say, thinner so both bikes weigh the same), moving at the same velocity. If you take the amount of friction needed to lift the first bike's rear, and apply that to the second bike, it won't lift the rear. But do they still decelerate at the same rate and come to a stop after the same distance? Then where did the energy go needed to lift the first bikes' rear? – stijn Jan 30 '18 at 10:08
  • @stijn the energy to lift the rear comes from the kinetic energy of the bike moving forwards. The bike must be moving with a decent bit of forward speed to lift the back wheel, however hard you squeeze the brake (perhaps this is easier to test while walking the bike -- it's lighter so everything happens more slowly, and you can't go over the bars). So a tiny bit of the energy lost to braking is dissipated in the tyre/back suspension when the wheel drops back down, rather than in the front brake. – Chris H Jan 30 '18 at 10:26
  • The answer to the thought experiment is that the imaginary bike has its center of mass further back, so it can decelerate faster without tipping over. You aren't braking it at maximum. It is slightly counterintuitive, but a tandem bike be braked harder than a single bike and a touring bike with panniers in the back harder than a racing bike. – ojs Jan 30 '18 at 18:47

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