Review: Xiaomi DZN4006GL Mi Pump Air Compressor

Xiaomi compressor inflating my Brompton's rear tyre

I was lucky enough to receive the Xiaomi DZN4006GL Mi Pump Air Compressor as a Christmas present.

And, since I now have a blog, I am going to review it.

Bet you're feeling glad you click on this.

But if you're happy to stick around, read on for a review of something which has exceeded my expectations so far.


A useful compact device, which exceeded my expectations, and is priced reasonably at £35ish. But a bit too heavy to be chucked into a saddle bag and forgotten about.

What it is

It's a small(ish), battery powered air compressor, designed for inflating tyres.

I think it's intended for use with an electric scooter (you know, the kind you can't ride lawfully almost anywhere other than your own garden).

It comes with a drag-string bag, and I'd have welcomed something in heavier-duty, wipe-clean fabric, rather than the quite nice black fabric they've used.

It also comes with a very short micro-USB charging cable, and adapters for different nozzles. I haven't tried them. There is a small pocket in the bag, which velcros shut, to hold these, which is a nice touch, but they don't fit in the pocket in the bag I received. Oh well.


It's great! I was hoping it would be good, given the numerous positive reviews, but I'm very impressed.

I went on an inflating spree, checking the pressures on everything I could find: two bikes, and two cars.

The cars were not too bad, as I had done those recently, but my bikes were way under. I was amazed, as I had pumped them both up with a foot pump not too long again.

Perhaps I was just not quick enough getting the pump connector off last time, but:

  • my Brompton tyres should be around 100 psi, and they were 25-ish
  • my Elephant bike types should be around 60 psi, and they 22-ish

I hadn't realised they were so far under!

Speed-wise, the numbers just speed up, which was pretty impressive.

The convenience of the unit will also mean I'm more likely to check the pressures more regularly, and inflate them to whatever is needed, so a definite win there.


It's a compact unit, and fits easily in my hand.

It's not heavy, but it's still a bit bigger and heavier than I could stick in my saddle bag and forget about.


The circular controls remind me of a classic iPod, although it doesn't have a scroll wheel.

It's easy to use, and — good news right now — can be used with gloves on.

It has a number of different categories — including bike, car, and motorbike — and those are basically presets / memory slots, as they store the last pressure you set for that particular slot. I'll probably use one for my Brompton, one for my Elephant Bike, and one for cars.

Setting the pressure you want is very easy, if you want to deviate from one of your presets.

The screen is bright, and clear.

Battery life

So far, so good.

I've nothing to measure it against, but it had no problem doing eight car tyres (increasing by about 3 bar per tyre), and four bike tyres (increasing each by a lot — between 40 and 70 psi).

I imagine that, if I was trying to inflate a tyre — particularly a car tyre — from flat, it would consume a lot more power.

It charges off a mini-USB connector, so it's pretty convenient (although I would have preferred USB-C).


Not too bad, and a bit quieter than the mains-powered compressor which came with one of our cars.

It's definitely not silent (which would be an unreasonable expectation), so no complaints there either.

Changing my Brompton's front mudguard

The Brompton I bought from eBay was in good condition overall, but it had a cracked mudguard at the front.

My guess is that it was caused by someone folding the bike poorly and, while it was not causing any obvious problems, it didn't look good, and it annoyed me.

So I fixed it.

The longest part of the job was waiting for the part to arrive, since it was seemingly held hostage by Hermes for a couple of weeks.

It arrived today, and it took about 10 minutes to remove the old mudguard and fit the new one. It was much easier than replacing the rear mudguard as part of the addition of the rack, which entailed removing the rear wheel.

So that is, I think, the last job I "need" to do. What I really need to do now is build up my stamina when actually cycling the thing, as some of the hills around here — steep, but short — are challenging me at the moment.

Although a telescopic seat post is still tempting me. Aaargh.

The EZ Clamp Spring: keep your clamps in position

This post combines three things I like: 3D printing, cycling, and Creative Commons licences.

One of the joys of a Brompton folding bike is the folding bit. And the clamp system is both clever and robust.

But the clamps have a nasty habit of spinning on the bolt, which makes them that bit more difficult than is ideal when it comes to unfolding the bike.

The EZ Clamp Spring

I was pondering what I could do about it, and looking around to see what others have done, and a chap called Steve Wood (Gyrobot) has solved it with a very simple 3D printable widget: the EZ Clamp Spring.

It exerts pressure on the clamp, keeping it in the right orientation.

It's a perfect solution to the problem.

Print or buy: it's up to you

You can either print it yourself, or buy a pre-printed version ready to install.

Normally, I'd print a model myself, but the creator suggests a particular type of filament, which is more flexible than the filament I have to hand (and I'm not sure my printer would cope with it anyway), so I bought a couple.

Shipping times are obviously not under their control (especially at the moment), but mine arrived very quickly.

If you want to print it yourself, you can download the files from Thingiverse.

Installation could not be easier

Dead easy — about a minute per clamp.

You simply remove the clamp and bolt, thread the EZ Clamp Spring onto the bolt, and then screw it back in place. That’s it.

Once you've installed it, you can see the benefit of it immediately: when up undo the clamp, it stays in exactly the right place, ready to be tightened.

A surprising choice of licence?

The 3D printing files are licensed under a Creative Commons licence (great!), but not the one I would have expected.

The inclusion of the "NC" — non-commercial — restriction is not unexpected, but the "ND" — a prohibition on tweaking the file — surprised me.

I'd have thought that improvements would have been welcome, but I'm not the copyright owner, so it's not my choice!

Nice rack!

I spent an enjoyable hour-and-a-bit today, fitting a rear rack to my Brompton. I haven't bothered with a photo: it looks like a standard Brompton with a standard Brompton rack attached to it.

In hindsight, I'm not sure why I didn't buy one with a rack already fitted, but oh well. Aside from it being a way of thinking about Something Other Than Work for a bit, the process of installing it taught me some quite a lot about the bike, which is undoubtedly going to be useful from a maintenance perspective.

What I did

I worked out how to do it by following a number of videos on YouTube, and referring to the supplied instructions.

As far as I can tell, there's nothing detailing the end to end process, so it was a bit of guesswork, and trial-and-error.

Edit: someone has suggested it would help if I said what bike it is. It's a 3-speed.

I did things in the following order:

  1. Remove the rear wheel
  2. Remove the rear mudguard
  3. Put on the rack and new mudguard
  4. Put the rear wheel back on
  5. Replace the old front rollers with the new, larger, ones which came with the rack
  6. Fold the bike and put on the new seat post bung. (I say "new"; I didn't have an old one to remove.)

All in all, it took me about 1.5 hours. This included a fair amount of time re-watching bits of videos, to make sure I had understood, and intentionally taking it slowly to try to lessen the risk of messing it up — there was no rush. If I were to do it again, I'm pretty sure I would at least halve that.

Removing and replacing the rear wheel: what I wish I'd known

There are a few videos about this, all pretty similar.

There are a couple of things which I wish I had known upfront, which I didn't see covered in any of the videos I had watched:

  • The first step is to remove the indicator chain — the bit which goes into the hub to make your gearing work. It's easy to do, but I would take extra care not to move the nut, or to move it as little as I could. When it came to putting the bike back together, and making sure the gears were working, I spent a lot longer working on this that would have been the case had I left the nut in roughly the right place at this step.
  • How to deal with the brakes. I guessed that, rather than attempting to take them apart, the simplest approach would be to deflate the tyre and squeeze it through. Even then, it was a tight fit, but it work.
  • The "tab washers" — the bits which help keep the wheel attached to the frame have a top and a bottom.
    • Again, after the event, the official instructions do say this. Perhaps my biggest learning is to rely less on YouTube, and more on the official instructions!

I'm glad I've learned these lessons now since, when it comes to fixing the inevitable puncture, I'll be able to do it a lot faster.

Is it worth it?

Time will tell but, as with most things Brompton, this was an expensive bit of metal.

I have immediately noticed how much easier it is to roll the bike around when folded down. I had a real challenge with this at the station, as the small wheel on the old mudguard seized up every few metres, making a horrible noise and rendering the bike immoveable.

Some kind people on Twitter suggested that it is easier to pull a Brompton than to push one, but now it seems — on the basis of some very limited testing in the confines of our kitchen — to be better. A lot better.

While I love the idea of making the most of my new rack by heading off into the distance on a folding bike, tent and provisions strapped to the back, I'm realistic:

  • we're in a lockdown and, while this has got to be about as low risk as it's possible to get, I very much doubt it's consistent with the current rules. Whatever they might be.
  • even if we were not, I can find time to squeeze in the occasional two or three hour ride, but anything more than that is just wishful thinking.

Put it this way: I'm not going to be rushing out to buy luggage to hang off it.

Easy/Eazy wheels?


Well, not yet.

I was tempted, but I'm very aware just how much money I am pouring into a a bike when I am not sure just how much I'll use it.

Next job: front mudguard

I think I'm almost through my (Brompton-related) jobs list.

The only other bit I really want to replace is the front mudguard, as that is cracked; at a guess, from a previous owner not being careful enough when folding it, and smacking the rear wheel into the front wheel. It looks like a pretty simple thing to fix.

My first ride through a Tier 4 Newbury

Tonight, I went for my first cycle ride through a Tier 4 Newbury.

It wasn’t the longest ride – about 30 minutes – and I decided to go through the town centre.

I suppose I don’t really know what Newbury town centre is like early on a Sunday evening anyway but there’s only one word for it tonight: tumbleweed.

I think I went all the way from the clock tower at the top, to the other side of the railway line at the bottom, without seeing more than three people.

From a cycling point of view, it was great (although I do need to adjust my saddle a bit, as it has slipped backwards). But what does it mean for Newbury?

The future?

I do wonder what Newbury, and perhaps other similar small towns, are going to be like, once the pandemic is over.

It used to be a lovely High Street, although in recent years, it has become replete with the usual stores, charity shops, and generic coffee chains. With one or two notable exceptions, you could be in almost any town without realising it.

I suppose that I am part of the problem (if the decline of the traditional High Street is indeed a problem), as the bicycle I was riding, the accessories on it, and every stitch of clothing I was wearing except my shoes, were bought online.

Not a new trend, but the pandemic obviously is not helping either. Debenhams is closing down, and quite a few other shops are now vacant, adding to those which already lay empty.

Places of leisure?

Perhaps High Streets will become places of leisure rather than for shopping?

But then I’m in no rush to head back to a restaurant either.

There are some lovely independent, or at least small chain, places to eat in Newbury, but the many offer delivery, and all offer takeaway. Which suits me just fine.

So we really are down to the situation which I wish to meet someone somewhere other than at home, and that happens very, very rarely.

If not food and drink, then what?

My occasional, usually regretted, trip to the cinema (more hassle, more expensive, more people, and less pleasant than waiting and watching the film at home) isn’t going to prop up that. And I love the Corn Exchange in theory, but I last went perhaps seven years ago? Life gets in the way, and I often can’t be bothered to leave the house, especially if it involves mingling with other people.

So, for now, I guess that just leaves the town centre as a place through which I can pass on my bike on a quiet evening.

Fixing a very noisy Brompton

On my cycle back through Hyde Park earlier in the week, I noticed my Brompton was making some odd noises. "Odd" in the sense that it had not been making them before, and I hadn't heard other bikes making them, but potentially perfectly normal for a Brompton since I've only had one for a couple of weeks.

I popped it up on the stand yesterday to take a look, and to do some normal bike maintenance.

There were two noises — a rattling noise from the hub, and a rubbing noise from the front type.

Rattling noise from the hub

I'm not convinced I've fixed this, but oiling the chain, and hub, and cycling through the gears, seems to have made a difference. I only had time for a quick test ride, and it did seem quieter.

Looking online, the general consensus seems to be that, if it is changing gears smoothly then, even if it is making a noise, it's probably fine.

That worries me slightly, but, since I don't plan on taking the hub apart, I'll leave it for now and see what happens.

Rubbing noise

This was the noise I had heard most when cycling, and it was a simple one: the front mudguard had got clogged up with mud and other detritus from the wet road. Clearing that out made an immediate difference.

I finally cycled in London!

Brompton bike in front of The Walkie Talkie building in London

Well, today was a first for me: I cycled in London. And I didn't die.

I've been thinking about it for a while, but I've always been worried about it — roads in London are much busier than the roads I normally cycle in Newbury — and so I haven't done it.

But, since I didn't want to be on the tube today, nor spend the length of time it would take me to walk, today was the day to give it a go.

Perhaps today was just a "good" day, but I wish I had done it sooner.

Cycle superhighway CS3

Screenshot of cycle superhighway CS3

I went from Paddington to Westminster and, other than the very first bit and very last bit of the route, I was in segregated cycle lanes or in parks. It was very much a stressfree journey.

So much so that, when I arrived with some time to spare, I decided to explore a bit more, and ended up cycling along the "superhighway" CS3 up to Bank and back.

Dedicated, segregated cycle lanes make a huge difference. And I mean actually segregated lanes, not just a white line along a road. At no point in the ride did I feel uncomfortable or at risk.

I'd prefer cycle lanes to be segregated from pedestrians too (which is not the case on some of the route in Hyde Park) since that seems like the safer option for everyone.

Bits to fix

I had a bit of hanging around at Paddington due to a train cancellation, and pushing my folded Brompton around was not as easy as I had hoped. The small roller on the rear mudguard jammed every couple of minutes, and it certainly wasn't a smooth roll. So I bit the bullet and ordered a rack, to give me two wheels at the front (when folded).

Some odd noises coming from the front wheel as I was heading back, so that's something for me to investigate.


Overall, a hugely positive, fun, experience.

I wasn't the fastest cyclist, nor was I aiming to be. But I achieved my goals: I cycled in London without dying, and I got to where I needed to be faster than if I had walked, and without going on the tube.

I also scouted out some places where I could lock my bike, if needs be, as I doubt I'll always be able to take my bike inside with me. I'm not sure I'm a fan of that idea, even with a robust lock and thick cable, but I guess that's part of the reason for having bike insurance...

I (finally) bought a Brompton

After many months of not going to London for work, it looks like I might be going in at least a few times in the near future. And, since I don't fancy getting the tube at the moment, I have a good excuse for getting a Brompton.

After keeping an eye on eBay for a while, I bought a second hand 2017 model, and picked it up last week.

I've seen people making lots of upgrades and changes, but I'm loathe to do too much until I've used it in earnest, and worked out what is most important / worthwhile.

But I have made a few immediate changes:


I've added the same cheap set of LED lights that I use on my Elephant Bike.

These are in addition to the lights on my helmet, and they're cheap enough that, while I'd still be annoyed if someone took them, I'm not going to be too concerned.

The front light, mounted on the handlebars doesn't affect the folding, but I've not found a good place for the rear light yet.

At the moment, I've got it immediately under the saddle, but it stops the seat post from sliding fully into place. Not enough to stop the bike from locking, but enough to make the saddle a bit higher than it would otherwise be. I'll need to see whether it's still folded enough to fit in a train's luggage rack — if not, I'll either need to remove the light each time (which will be a pain), or come up with a better plan.

Phone mount

I know the way to the station well enough, and I think I have a reasonable idea of how to get around London, but I can see it might be helpful to have my phone available, in case I need mapping.

I'm aiming to avoid roads as much as possible, and stick to cycle paths, and I've yet to find anything which shows London's various cycle ways in a user-friendly manner which cycling.


The previous owner had looked after it well, overall, but one of the bar grips was a bit ragged.

I have replaced the thin foam grips with something a little more contoured and, hopefully, a little more comfortable.


I also replaced the pedals, since the ones on the bike were designed to be used with cycling shoes with clips, and that doesn’t suit me at all.

I bought a £35 set of metal folding pedals, which got reasonable reviews. I've only done a few miles on them but, so far, so good.

Seat height

I'm nervous about this, but hesitant about buying a replacement. My initial reaction is that, even pulled out to its fullest, the standard seat post is not quite long enough, as I can't fully extend my leg.

But, instead of buying a telescoping seat post, I've tried adjust ing the saddle. I've flipped the Pentaclip over, to give a bit of additional height, and I've moved the seat. So let's see. It might just be enough.