Modding a Brompton B75

[DBrown67]

Picked up my new B75 today. After all this talk of mods I decided to buy the standard bike from Halfords to get the 10% discount. I will mod the bike in stages from now on. I mat still fot the 6 speed later I don't know. Might even go electric as I've discovered that I can get a cheap kit that uses my existing battery from my MTB.

Anyway... onto 1 issue I have. Or may not have, you guys can tell me. The white suspension block on my bike is fixed solidly to the rear frame. No issues there. But when the bike is unfolded to ride the rear frame isn't tight when it clips in. There's about 2-3mm play and I can gently bounce the back wheel up and down and the release clip wobbles back and forth as I do so and it rattles. Is this correct? I must stress I have not ridden the bike at all yet. I'm in the process of putting new mudguards on it.

 

[u_i]

The rattling is about normal. The suspension block has two settings reached by rotating it around, one where the rear triangle locks and one where it does not lock at all, with the top detaching from the rest of frame as you lift the bike. The loose nature of the connection is irrelevant for riding since the top of the triangle presses against the frame when you sit and ride, compressing the suspension block.

 

[DBrown67]

Thanks u_j... glad it's normal. Just been out on it for the first ride and deliberately went up the steep hill near me that I use as a gauge as it's basically the steepest I have to navigate regularly. The reduced gearing helped but still no cigar. Couldn't make it. I'm thinking of going 39t crank with a 15t sprocket as that's the lowest I can go on 3 speed without messing with anything else. That basically moves my gearing along where 1st becomes 2nd and 2nd becomes top and I gain a nice low down 1st I've yet to try.

Current B75 gearing: 42.0 56.0 74.7
39t crank x 15t sprocket: 32.3 43.00 57.4

I found with the B75 on my test tonight I was using 2nd on the flat comfortably but still not getting into 3rd, except on THAT downhill for a test (after I'd walked half way up) and I can tell you that was getting just a bit too spirited for me. I could lose that 3rd gear no problem and just spin out. I need to climb that damn hill!

 

[u_i]

Congratulations, obviously, belated, on the bike! I just wonder whether you might try riding the hill on some other bike, find out what gear you need and transcribe it onto the Brompton, so that you do not go through a hit and miss.

 

[DBrown67]

Congratulations, obviously, belated, on the bike! I just wonder whether you might try riding the hill on some other bike, find out what gear you need and transcribe it onto the Brompton, so that you do not go through a hit and miss.

Did that already on my electric MTB (with the power off). Being a different bike I wasn't too sure. I've tried that hill on that bike, a demo Brompton with std 3-speed and now my B75. I'll now try the limit I can go with 3-speed and if that doesn't work, then I'll seriously consider the electric kit.

 

[Tenkaykev]

Thanks u_j... glad it's normal. Just been out on it for the first ride and deliberately went up the steep hill near me that I use as a gauge as it's basically the steepest I have to navigate regularly. The reduced gearing helped but still no cigar. Couldn't make it. I'm thinking of going 39t crank with a 15t sprocket as that's the lowest I can go on 3 speed without messing with anything else. That basically moves my gearing along where 1st becomes 2nd and 2nd becomes top and I gain a nice low down 1st I've yet to try.

Current B75 gearing: 42.0 56.0 74.7
39t crank x 15t sprocket: 32.3 43.00 57.4

I found with the B75 on my test tonight I was using 2nd on the flat comfortably but still not getting into 3rd, except on THAT downhill for a test (after I'd walked half way up) and I can tell you that was getting just a bit too spirited for me. I could lose that 3rd gear no problem and just spin out. I need to climb that damn hill!

I'm a cautious rider and going downhill at speed on my Brompton can feel a bit unnerving, especially with the state of some of the roads hereabouts.
I've found it rides better with my basketbag fitted and loaded up.

Of course it's extra weight to get up the hill, but it works for me.

 

[12boy]

Re the rubber block....earlier Bromptons had no latch on the rubber block and would break in half when picked up. As far as the hill goes, have you tried standing up as you pedal?

 

[DBrown67]

Re the rubber block....earlier Bromptons had no latch on the rubber block and would break in half when picked up. As far as the hill goes, have you tried standing up as you pedal?

Standing up is never my style. Yes, I know I'm making it more difficult for myself.

Fitted a 39t chainring today which gave me a low of 37.2 It's better and I got further up the hill but still had to bail out. Next is to get the 15t rear sprocket as I'm still on the standard issue 13t. That will give me a low of 32.3. If that doesn't work then I could try the crank set off my Giant Escape 1. But I don't really want to take that apart if I don't have to. And besides, it might mess up the chain line. Is 15t the largest I can fit on a standard 3-speed hub?

The good thing is the 96 link chain as fitted to the B75 didn't need to be shortened. It rides and folds perfectly fine with the 39t chainring.

Another question I do have though.... been using Sheldon Brown's gear calculator and in the "Internal Hub" menu there are various choices for Sturmey Archer 3 speed hubs. Which is the correct one for 3 speeds fitted to current Bromptons? They all have different names/codes and I haven't a clue.

 

[12boy]

The 3 speed hub is a SRF3. The hub has a177% range...2nd is direct drive, 1rst is 25% less and 3rd is 33% more than 2nd. The 3 speed used in the 6 SPEED Bromptons has a 256% range.

 

[12boy]

An 18 tooth sprocket with a 50 tooth chain ring will be very close to the 39/15 tooth combo. Sprockets are much cheaper than chainrings.

 

[yoho oy]

Can shifter and brakes on B75 be replaced to match M3L? What part numbers are these? Can't seem to find it.

 

[Nibor]

Can shifter and brakes on B75 be replaced to match M3L? What part numbers are these? Can't seem to find it.

QBRLEVAL-LH[2] = left hand brake lever
QGSHIFTR3A = right hand brake lever and shifter

 

[yoho oy]

Thanks.

 

[yoho oy]

Picked up my new B75 today. After all this talk of mods I decided to buy the standard bike from Halfords to get the 10% discount. I will mod the bike in stages from now on. I mat still fot the 6 speed later I don't know. Might even go electric as I've discovered that I can get a cheap kit that uses my existing battery from my MTB.

Anyway... onto 1 issue I have. Or may not have, you guys can tell me. The white suspension block on my bike is fixed solidly to the rear frame. No issues there. But when the bike is unfolded to ride the rear frame isn't tight when it clips in. There's about 2-3mm play and I can gently bounce the back wheel up and down and the release clip wobbles back and forth as I do so and it rattles. Is this correct? I must stress I have not ridden the bike at all yet. I'm in the process of putting new mudguards on it.

Does B75 from Halfords include brompton pump? Also what are your impressions (I assume you already took it for a spin)? Have you tried higher in the range brompton model? Trying to figure out which brompton is for me...

 

[yoho oy]

There are a few hills near place I work and I see many riders with different bromptons (and all sorts of other bikes for that matter) zipping past all day long. It seems for some of them it is a bit of a challenge (they pedal leaning forward from a seat) but some of them are able to do it while seated. I am trying to see what is this related to - 6 speed broptons, higher fitness of the driver, moving inertia (just the right moment trough traffic lights) or anything else. One thing that I noticed is that it seems that B75 is not so common among the drivers. Or I would have seen it with it's distinctive color.