this post was submitted on 13 Jan 2025
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Experiences with different gearing on a 6-speed Brompton? (lemmy.ml)
submitted 5 days ago by [email protected] to c/[email protected]
4 comments fedilink hide all child comments
 

So I let the chain wear down too much in the past two years and the rear sprockets appear to be worn out and will need to be replaced. The stock 50T chain ring is also showing signs of wear but appears to still be good for a few years.

I wanted to use this opportunity to see whether I could switch the gearing up a little.

The 13-16 gearing has been surprisingly capable but I need just a little more hill climbing ability; the lowest gear (2.64m) is just barely enough sometimes. I'd like it a tad lower I think.

On the high end, I usually ride in the upper two gears on flat ground. The highest gear (7.98m) feels just a tad too much sometimes though and I then fall back to one lower (6.49m) but that feels a good bit too low. That doesn't bother me a lot but it'd still be nicer to have a gear that's just right.

On a downhill, the highest gear is always sufficient for me; feels pretty much exactly right. I wouldn't mind slightly more metres of development but, honestly, I don't care very much when I'm already going way past 30km/h and I don't ride downhill for very long usually. I'm unsure whether reducing the highest gear slightly would make me pedal uncomfortably quickly down hill though.

Stock and current config:

Hub 64% 100% 157%
Low sprocket 2.64 4.14 6.49
High sprocket 3.25 5.10 7.98

I'm currently thinking about a 44T chain ring with 12-17:

Hub 64% 100% 157%
Low sprocket 2.19 3.43 5.37
High sprocket 3.10 4.86 7.61

or 12-16:

Hub 64% 100% 157%
Low sprocket 2.33 3.64 5.71
High sprocket 3.10 4.86 7.61

The lower gears being lower and closer together sounds very nice.

In the higher gears, my hope is that the slightly lower highest gear would allow me to use it the majority of the time on flat ground because I suspect the second highest gear would feel quite a bit too low as a fall-back.

I could see 12-15 being an option perhaps but that also gets the lowest gear much closer to 13-16 again:

Hub 64% 100% 157%
Low sprocket 2.48 3.89 6.09
High sprocket 3.10 4.86 7.61

But obviously the lowest gear gets very close to the previous config again.

Where I have a hard time is imagining how significant the difference between 2.64m, 2.19m, 2.33m and 2.48m are in an uphill scenario. The jump between the lower gears in 13-16 (3.25m to 2.64m) in practice feels significant but not that large either and we're talking about a much lower absolute drop being gained in the low end by switching gearing. I don't know whether the practical effect of this is linear though and I suspect it might not be.

I'd really appreciate practical experience here. Have you changed gearing on your Brompton? From what to what and how significant were the differences?

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[–] j4k3 1 points 5 days ago (1 children)

The only time I rode with close gearing was crit racing. I rode standard 53/39 11-28 through the 8-11 speed eras on road most of the time. That worked well for pretty much everywhere for me. I can get away with never using my inner ring so long as the slopes stay below 6 degrees. When I first started commuting hardcore, I rode a 55/39 with a dura ace triple FD and a range of everything from 11-21 - 11/23 - 11/25 - 11/28.

You need to know your rear derailleur capacity to know what will potentially fit.

Unless you're trying to improve your times on a 66 mile round trip daily commute to work, or racing where the differences between riders is miniscule and the perfect gear to sit on a wheel might make of break your race, I would go for the widest possible range your FD/RD can handle. You'll never regret having the extra easier or harder gear to pedal in. If you are never pedaling down hill or in a tailwind, skip the hardest end. If you never see a climb skip the easier. If you like to explore and go wherever life takes you, keep your range as wide as possible. If you do not have the ideal comfortable gear, spin the lighter one faster and consider it cadence training. If you keep at it, within a few weeks you will begin to have a faster average cadence. This is part of race training as higher cadences are more efficient overall. Some people train on a fixed gear or single speed at times to push themselves to higher cadences in unique ways.

[–] [email protected] 1 points 4 days ago (1 children)

Right but I do like to ride fast when possible. It's not for competitive edge or anything; it's just comfortable.

The main thing I want answered is whether the difference in metres of development in the low end actually makes a difference and how significant they are in practice.

[–] j4k3 1 points 4 days ago (1 children)

I tried to relate the limited niche where having closer together gearing makes a noticeable difference. Unless you are operating in a very small margin, you will never notice having close together gearing. I only ever noticed the difference with racing where I'm on the edge of blowing up throughout the entire race and happen to feel like I'm on a knife's edge and spinning a little too fast or slow to hang on for more than a few minutes, and comparing times on a given route and pulling a few minutes out of an hours long route. In all other instances, having more range has been better for me. So I prefer to have as wide as my drivetrain supports. If I have any choice, I prefer a tighter set of low gears and a bailout final cassette cog.

Sorry if the abstraction is hard to ground in your understanding. Broadly speaking, this is how I setup any bike. I wouldn't worry about the total, and would start with the widest cassette that will work with your current setup. Then I would only change the front chainring if you still feel a lack of top speed. In my experience, only the standard combinations and matched group sets shift really well at a racing or top performance level. The more unconventional setups can be made to work reliably but shift speed and shifting under load become lower quality in ways that are not worth the compromise. There are subtle elements like how the front derailleur cable is routed that are designed for a specific combination. While it may seem trivial, in practice I have seen issues from moving a derailleur up or down significantly beyond normalcy, or changing a chain line, or even tooth profiles between models of chainrings.

Back in the days before indexed shifting, people often played a lot more with gearing, but the issues are different with friction shifting, as are the shifting performance and expectations. This is why people do not generally alter gearing in the same way any more.

[–] [email protected] 2 points 3 days ago

I tried to relate the limited niche where having closer together gearing makes a noticeable difference

You appear to be misunderstanding. This isn't about making gearing be closer together, this is about increasing the range of the gearing by making the low end lower and only reducing the high end by a little.

If anything, the configurations I wrote about would make gear spacing less even as the default is quite nicely spaced.

What I need to know is whether the change in the low end is actually noticeable in an uphill scenario and by how much.

So I prefer to have as wide as my drivetrain supports. If I have any choice, I prefer a tighter set of low gears and a bailout final cassette cog.

It's the same for me I think. I'd prefer some variety of low gears for uphills and some variety for relatively flat ground. I don't very much care what's in between as long as it's not too far apart.

When I start riding, I usually use one of the lower gears for half a turn and then immediately switch the hub from 64% to 100% (skipping the gear in between) which is a jump from 2.64m to 4.14m or 3.25m to 5.10m and then usually up to 5th gear (6.49m) for a bit and then the 6th gear when conditions allow.

I wouldn’t worry about the total, and would start with the widest cassette that will work with your current setup. Then I would only change the front chainring if you still feel a lack of top speed.

This again appears to be a misunderstanding: This is a 6-speed Brompton.

6-speed here means 6 gears total, including the hub.

The gearing is as follows:

  • Hub with 3 fixed ratios (64%, 100%, 157%)
  • Derailleur between two sprockets that can be equipped with a maximum of 17 teeth due to size constraints
  • One chainring (no derailleur)

I get to choose the two sprockets and the chainring. That's it; there is no wider cassette that physically fits this frame.

The reason for changing the chainring is merely to shift the gearing down which isn't possible by changing the sprockets because a sprocket larger than about 17T will physically not fit. Again, this is a Brompton with tiny 16" wheels that folds down to suitcase size.