I have had a 39T chainring on my Bromptons for years. I have always thought that Bromptons are overgeared for anything other than short commutes in flat cities, even with the 44T option. Thye really should offer this as an option (with chainguard) instead of just messing about with different colours and pretending that this gives more choice.

Eight years ago when I got my Brompton it had a 50 tooth chain ring, a couple of years later I went to a 44 tooth, this year I put a 40 tooth chain ring on. My chain rings are getting younger and I'm getting older.

My Brompton had the 50t chainring, yuck for climbing up the hill back home. So I replaced it with 44t chainring, now thinking of dropping it down to the 39 teggies chainring as I'm sure that hill is getting steeper. (BCD) Bolt Circle Diameter of 130 mm. Thanks for this video and stick with the 50t if your legs are borrowed from Chris Boardman.,

I might do this. Even with a 44T chainring, I rarely use 3 high or 3 low.

To sad that Brompton doesn’t offer a chain guard for the 39T chainring. Nice presentation as always 💐

My Brompton was a 2Sp, which I converted to 6sp, and subsequently replaced the dinner plate sized 54T chainring with a 39T one: This absolutely revolutionised the bike, and made it SO much more capable. It spins out on descents at about 45kph, but at any faster than that I'd rather be freewheeling anyway! I think the minimum size that can be fitted is 38T? On the subject of the lack of the chainguard on the non-standard chainrings, one of my first 3D printer projects was to design one of these. It simply fits on with a set of M5 bolts that go through the middle of the chainring bolts themselves.

I changed from the default 50T to the 44T back in the day when my Brompton was named M6L. I wanted to order with the 44 from the start but the vendor at the bike shop looked at me like I had just asked to be shot in the face or something, and somehow convinced me that lowering the gearing would "make me feel like a hamster on a spinning wheel". I listened to him because, why not? He's got the experience and I had never ridden a Brompton before. He was wrong of course. And the default 50T made me feel all kinds of discomfort. I'm a very short woman (I'm 5ft). With very short legs on top of that. And the 50T was completely inadequate for my type of cycling, my cadence, my fitness, EVERYTHING!! So much so, that I was NOT enjoying my bike rides at all, and kept wondering what was going on that felt so wrong 😓The 4th gearing always felt too loose and the 5th too hard. I didn't even try the 6th. Well. Maybe once. Just to see how it felt like. Changing to the 44T has been THE BEST modification I made to my beloved Brompton. I use consistently ALL of the gears and my cadence improved a ton. Yes you lose some speed on your highest gear but, how fast do I want to ride anyway? Having a lower first is more important to me

Fitted a 39t in the summer to get around the Cotswolds. It makes a huge improvement. The 44t was seemingly for velodromes, and the 50t for Chris Hoy.

Very helpful video. I am suprised there wern't more bloopers mind you! Love your channel 🙂

sharing my implementation here, i've gone to the limit of 38T. the chain just comes into contact with the spider arms but I haven't had any problems. for the chain guard, I fashioned one out of a 2mm kitchen cutting board (kitchen boards are oil/acid resistant by design - available at my local $2 store). attached it on to the 4 chainring bolt hexagonal holes using "rubber mushroom plugs" (don't know the proper name). they attach snugly when the round tails (of mushroom plugs) are squeezed into the hexagonal allen bolt holes. been riding it so for a year, 2 bikes, haven't fallen off.

On my electric Brompton I put a larger chainring on as I was forever spinning out. My S6R has been kept at 50 tooth. I hadn’t realised that more modern bikes have a 52 tooth chainring. Thanks as always for your film.

Since I have my S6L-X, I’ve changed the front chainring for a 39T. It’s a real game changer for those who live in hilly areas. I’ve done another great change: adding a third sprocket and converted my 6 speeds Brompton to a 9 speeds one. It’s even better now.

Been using 39t for few years. Previously not really using the 3+ gearing when I was with 44t or 50t but now I am able to use 3+ to get 35-40km/h plus I am able to get up hilly road where I am staying ❤

I’m running an H&H 40T chainring on a BWR six-speed, with rear sprockets of 13t and 18t. Lowest gear is 23.6 gear inches. The intervals between gears are not even, but you get used to that. I’ve had two dozen Bromptons since the 90s, and still can’t understand why Brompton over-gear their bikes so much.

Great video. Love the way you use the fold mechanism to insert the chain into the tensioner. Until now I linked the chain under tension which is not great-

I changed to a Thorn 39T when I did the C2C a couple of years ago. 6 speed bike, so it helped. Still have a fairly hilly commute to work, so I've left it on.

First mod i did to my 6 spd brompton was to install an old nos durace crankset i'd had lying around for years. Depending where im riding i manually switch between the large and small chainrings. Works a treat.

I changed to 44t about 4 years ago (hilly area ) I left a review on the Brompton website and because it was the first, Brompton sent me two free inner tubes !! I still use it but mainly level 1 assist on my e brommie theses days

Very well explained! Thanks you

Excellent video! Thank you for this. It’s very helpful.

Congratulations. You are a great brompton mechanic

Very informative again.👍

Very informative video .....thank you 😊

Great timing, this has been on my to do list for over a year 😂 I can't believe how long the stock gearing is. Waaaay over the top for 99% of us.

Nice. Did this last week 😉 But because of the bad weather, I haven't been able to do a test drive on some of our local hills yet 🤷‍♂

Lefty Lucy is a new one to me, never heard that before. I'm getting old and I'm going to have to do this to my Brommie soon. Getting old sucks.

I have a 39 tooth chainring on my Brompton. I use it around town and on the occasional bike camping trip. I have been tempted to file the ends of the spider just a bit so I could use a 38 tooth. After I put the 39 on, I had a bit of problem with the chain coming off. So I switched to a chainring with wide-narrow teeth and it has never come off after that

Brilliant!

I used a T39 (an old Shimano 105 chairing) during my last journey in England

This is great... nice video. 2 questions... what is the percentage reduction in gearing from 50->39T on a 6 speed and how did you know to remove 4 links from the chain?

Stronglight chainsets (£31 from Spa cycles) are a direct swap for older non spider bikes. I have a 44T and a 38T I use here in hilly Bradford. Much cheaper than Brompton OE.

I use a 53 / 39t dual front. The 39 is a backup ring for overseas for manually changing with my foot lol

Hello. Great video and the change seems straightforward. But I do have one question. You change from a 50t to a 39t and remove 4 links on the chain. How do you determine how many links to remove (or add) when changing to a smaller chainring (or larger)? I currently have the 50t and am thinking of trying the 44t.

Hi, can you talk about changing to a s-handle bars or straight bars from a h - handle bars, this is something I am looking to do, I know you have to change the stem also 👍🏾 great content as always 💯

Yes. A-Line has 44-15 B75 has 44/39 double and 25. Expedited 6 speed has 44/39 and std. P-Line has 46 and 21,19 first and second gear. I live at the top of the highest hill in town!

I just did one!

I would ignore the comment about not re-using quick links, I have re-used them dozens of times !

"Just do one!" 😂😂😂 Love it. 😂

As an owner of a 2019 SuperlightM6LXBrompton (Presently, below 9 kilo, original mudguards and still falling, with a little more work!) I did at first wonder for what use I had the low gears, of 6, till I met a steep serpentine road going up and I had to walk on top! I have seen a double chainring for being mounted in front, but honestly, I hardly think I have any use for more - low gears. Finn. Denmark

Great video, lovely and clear guidance. One question, what is the formula for working out how many links to remove from the chain?

Looks like the chain rubs the rear triangle when folded. I guess it doesn't do that with bigger ring? Anyway I would add some protection tape on the frame.

I replaced my old chainring bolts with Ti ones, as the old ones were rusting.

Great video. I love your videos and clear explanations! I also changed mine to a 39T but did not shorten the chain. I don't see any problems for the moment. Is it really necessary to shorten the chain? Thanks!

Thank you for this. I have previously changed to a 44" but had to resort to trial and error for how much chain to remove. Is there a formula or a look-up chart you could share which shows how many links for how many teeth?

I love my new chainring ❤ I live on a very steep hill so this video was a godsend. Also looks sick! However, my chain slips when I back pedal - did I do something wrong there?

I find with my 6 speed the gaps between gears are too big and even as a roadie I rarely use top gear as it’s too high

Heresy! Sheldon Brown bicycle gear calculator is the go to calculator!

Nice video, really informative, thanks! I think I might do this or something similar for a hilly ride I'm planning. My only concern is the lack of a chain guard on the 39T. H&H makes a 40T chainring that has an integrated chain guard and that will fit the Brompton. I wonder if anyone has tried it? I doubt it'll be much different from the 39 T except for the chain guard. Oh, and can anyone comment on what it's like to pedal on the flats with such a small chainring?

Exactly what I’ve been thinking about doing! Do you sell the SRAM 39T chainring? Another alternative is the FSA

I’ve referred to your informative video to install the 39 tooth sprocket to my Brompton. Would you identify the tool that holds the shoulder nut on 4 of the five fasteners? It fits the slots on the recessed nut(?). Thank you so much. Paul in Chicago

That was quick! I think I'll be doing this myself. I just can't understand why Brompton overhear their bikes!

Is there any way of changing to 39 from 44 on an old Brompton without changing the bottom bracket and going to a "spider"..? Thanks,,,I have the original non-spider type crank with the integrated crank/ring/chainguard.

I have a 38t on there, it does barely rub the spider so 39t is probably better

would any chainring work as long as its 130 bcd and 5 holes? I see options of 39T from inner chainrings for 2by cranksets. Do those work aswell? I still have the 50t installed but want to try 44 or even 39 since I almost never use the hardest gear event on flats in my commute but I have hills on my daily commute/rides. The 44t brompton chainring is quite expensive here in my area so I wanted to try a 44T or 39T first (from cheaper brands) before I commit.

I went other direction, 54T chainring and swapped 13T to 12T sprocket on BWR hub. Would love to go even bigger chainring but all in the market seems very “aliexpress special”.

How do I calculate how many links need removing from a standard A Line 44T down to the 39T in your video? Thank you in anticipation.

How did you know to take out 4 chain links? Is there some kind of link between the difference in teeth and the number of links removed?

Have you consider changing to a dual chain ring 53T/33T without deraileur? I am happy to stay at 33T for most of the terrain if possible. I am on Brompton A series 3 speed internal hub. Can I add three sprocket to the back?

Great video. Since my chainring, sprockets and chain are all lining-up (due to wear) to be replaced together, I have to decide to go to T39 or back to T50. My favourite 'flat' cruising Gear Inches was 81.3 (second to last hardest). I do miss that cruising gear everyday with my T44. But, on the T39, seems like the hardest gear is close to it (78.0 gear inches). Someone should 3D print a chain guard.

Han Solo, hey there, how does the 39 affect the higher gears when in use? Thanx, Laurie

I wish brompton 42T would be released

@brilliantbikes why don't you put a 17t sprocket on the rear to widen the ratio ?

So there is no chain catcher to interfere with, right? Might be trickier with new P line.

if you were to add a double chainring (with manual shifting ofcourse), from H&H, I guess the chainring comes with 50-39 double, I guess you do not shorten the chain. So in that sense, can you live without shortening the chain even with a single 39 chainring? What are the disadvantages if any in retaining the longer chain (that comes standard with the 50 tooth chainring)?

Trouser clips - not as good as a chain guard but definitely better than nothing!

Why no chain ring guard on the 39 tooth sprocket?

May i know the SRAM model/part number u used? Tnx!

Hi baby, thanks for this video.

What does the p line come with? Annoyingly I feel like I need a bit more either side 😂😂

Giving rise to that well-known saying “I would watch her remove links from a bike chain”😂

No need to change sprockets and chain?🤔

Has anyone 3D printed a chainguard for a 39T chainring?

Why not just add a charming on it make it 2by and install ah fd hanger and fd shifter then even the stock Chainring will never be change again just for hill climbing

I’d love to see this done on a pline. Maybe to 46?

It is interesting that the current-you is watching this comment about the video of your past-you talking to your past-current-you. Looking forward to the future-you click like to this comment.

Single 39? I think the H&H 33/50 or 33/54 are better. If you need speed, put on the bigger chain ring and for everything else the 33. Plus 1 ring that works with 1. Chain length that gives you 2 options. Oh and it got a ring guard as well for the clean ride.

39T is too slow for flat roads

Nearly a bike ,have a similar feeling regarding my humour = nearly a joke, thinking about hills wasn’t you going to do a comparison with the P - line against the six speed up that hill you have down other comparisons on ? People have often told me that I’m the missing link must be some kind of compliment, yes the song is here stop being impatient, song = Chain Reaction = Diana Ross.

Love your channel, but “Climb hills easier”?!!! “More easily”, please🙄😊