Has anyone swapped out their chainring for a non-oem?

Kell

Über Member
Next time I need to change my chainring, I might look at something a little smaller than the 50T I currently have.

Tried the 44T in the past and it wasn't right. So looking at a 46 or 48 if I can find the right thing.

Why? After almost a year and a half of not using my Brompton, I was in at work for a week last week and noticed how much my cadence has changed since riding a road bike in that time. Whereas I was quite happy in the past sitting in 5th a 70rpm, I've been more used to 90rpm on my other bikes.

Changing down to 4th at the same speed meant my legs were going too fast for the Brompton as it bobs a bit, so I'd like to up the cadence (a bit) so that 5th at +/- 16mph is more comfortable. I was thinking of a 48t as it wouldn't change things too drastically.

Anyone done it? Can you recommend a particular chainring? Or is is a case of any old 5 arm PCD130 will fit?

Thanks in advance.
 
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I changed the outer chainring on my Tiagra crankset (50) for a Spa Cycles Zicral alloy (48). Absolutely no problems, and imo looks even better than the original, although that bit is subjective and others might not agree.
 

Sharky

Guru
Location
Kent
Before you replace the chainring, bear in mind that the chain and cassette wear quicker and will need replacing from time to time. From what you describe, the teeth difference between your 5th and 4th sprockets is too great. Might be worth considering alternative cassette sizes.
 
OP
Kell

Kell

Über Member
Thanks all.
Before you replace the chainring, bear in mind that the chain and cassette wear quicker and will need replacing from time to time. From what you describe, the teeth difference between your 5th and 4th sprockets is too great. Might be worth considering alternative cassette sizes.
I normally replace the whole drivetrain every six months.

Chainring, chain and sprockets.

Long story, but after a couple of snapped chains I no longer leave it to chance.

It’s overkill, I know it’s overkill, but I broke my coccyx last time and do not want to repeat that.
 
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rogerzilla

Legendary Member
I have a 52T TA on one bike and a 52T SR on the other (I use 110BCD cranks on them).

Gotchas: you may need to tweak chain length and the chainguard probably won't fit. Aftermarket chainguards are hard to find in some sizes and can be super-heavy. I do without one.
 

rogerzilla

Legendary Member
Before you replace the chainring, bear in mind that the chain and cassette wear quicker and will need replacing from time to time. From what you describe, the teeth difference between your 5th and 4th sprockets is too great. Might be worth considering alternative cassette sizes.
I'm guessing this is a Brompton 6-speed, so the "cassette" is two sprockets. You can't change their sizes without screwing up the gear progression - they fill the gaps between the hub gear ratios.

The old SRAM/Sachs 6 speed had far closer ratios.
 
OP
Kell

Kell

Über Member
I'm guessing this is a Brompton 6-speed, so the "cassette" is two sprockets. You can't change their sizes without screwing up the gear progression - they fill the gaps between the hub gear ratios.

The old SRAM/Sachs 6 speed had far closer ratios.
Yes - it is a 6-speed with BWR hub.

I did once try the 2-speed cogs (12/16 instead of 13/16), which sort of did exactly what I want to achieve here by making 4th a bit taller (and 2nd and 6th). But as it didn't affect the odd gears, as you say it messed up the ratios something chronic.

I think I've worked out that changing gears on the standard 6-speed adds or subtracts about 12-15 RPM with each change. That's quite a big difference compared to my old Dahon which had 27 gears and covered a similar spread. By switching to the 2-speed sprockets it made that better and worse at the same time.

I didn't have a cadence sensor at the time, so didn't conduct any sort of 'experiment' but it made switching from 5th to 6th comically wide.
 
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