Adding an extra gear to a 4-speed

[Kell]

A friend of mine has got one of the 4-speed bikes and is finding the range of gears a bit limiting.

He asked me if I know anyone that can add an extra gear. At the minute I'm not sure what that means exactly, but it could mean one more gear, or it could mean several more.

While I try and find out, has anyone seen this done on these new bikes in any form?

I'm not aware of it being done, but I've not been looking out for it.

 

[Kell]

OK, so he's spinning out a bit too easily at the top end, but wants to retain the low end for hills.

 

[Nibor]

we would need what type of gears the existing bike has is it a hub gear or .......?

 

[T4tomo]

OK, so he's spinning out a bit too easily at the top end, but wants to retain the low end for hills.

he need to improve his high cadence pedalling, as i suspect he isnt actually spinning out.

@Nibor nailed on 4 speed means one of new 4 speed bromptons.

as its proprietary changer / derailleur, no hope of just adding a rear cog.

dirty finger change on a double chainring is a possibility.

 

[Kell]

I'd say he could quite easily be spinning out as the 4-speed has a lower top end than the three speed and I found that I span out on that.

Compared to my road bike, maintaning anything over 80RPM is much more difficult on a Brompton in my experience.

 

[12boy]

Assuming he has a P or T line he could increase his range fairly cheaply by replacing the front chainrings with a 58 and adding a 38. This would require a stop and manual shift. However, the high gear on the 58 would be 84.7 gear inches and the low 33.9. I bought a P line in mid December and the weather here has only allowed for about 30 miles of riding. The stock gearing seems ok for now with a 54 tooth chainring and I will want to get more miles in before I go the 58/38 route. I have another Brompton with the 58/38 set up so I may just keep them as they are.

 

[Schwinnsta]

Larger chainring.

 

[Kell]

Larger chainring.

OK, so he's spinning out a bit too easily at the top end, but wants to retain the low end for hills.

 

[Tenkaykev]

There's a chap on YouTube who has a few Bromptons and posted a video about changing gears on his 4 speed Brompton.

View: https://www.youtube.com/watch?v=qnzixSTXY-Q

 

[Schwinnsta]

If it were me, I would start with a larger chain ring, then change out the cogs as in the video. I would prefer that to trying to go to a smaller cog.

 

[berlinonaut]

As far as I know P- and T-Line come with a 50t chainring from factory. This means the spinning out issue could this be solved easily. Maintaining the low gear at the same time would however not be possible.

 

[Kell]

Thanks all for the tips.

When googling this morning I came across someone that had fitted a 7-speed derailleur and a Schlumpf system. But it was all in Indonesian and he had a very heavily modified CHPT3 bike with carbon wheels, so it would be impossible to say if that fitted on a normal 4-speed wheel.

View: https://www.youtube.com/watch?v=l56kth0OUKM&t=2s

 

[MichaelW2]

I have seen Schlumpf on a UK Brompton. It seems to work OK for a small weight penalty

 

[berlinonaut]

A Schlumpf can be fitted w/o issues as can an Efneo, both replace the bottom bracket. Both do however add a relevant amount of weight. If you bought a P-Line for saving on weight you'd thus work agains your intentions and goals. What you can do w/o too much weight penalty is (as usual) use a second chainring.
The guy who did Lejog in a record time on a Brompton did this based on a 4-speed including a front derailleur, you can see it in the advertising video despite not uncovering the clamp that was used:

View: https://youtu.be/iMgi0UXJ9Z8?t=148

 

[Kell]

The guy in question with the 4-speed was the guy whose handlebar stem snapped on his brand new Brompton.

Brompton were going to replace his with a brand new SL 6-speed, but he didn't like the colours that were availalble at the time

By the time he decided to go ahead, they were no longer making that SL and so he was given the 4-speed as his replacement bike.

So he didn't have a huge amount of choice in the gearing he was offered.

I know at the time I had a conversation with him about limited range on the 4-speed.