1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

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Mountgrove
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Joined: 8 May 2018, 12:35pm

1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by Mountgrove »

Hi,
Current setup of my spare/commuting-backup/holiday bike.
1x11 drivetrain (SRAM Apex Derailleur) (SRAM 11-42t PG-1130 Cassette).
SRAM 11 speed shifter.
Connex chain / quick-link . 112 links.
Chainring 130BCD (5 bolts). allows me to use a chainring of between 38T to 44T .

I want to choose a suitable new crank-set that will allow me to have options of between 30T and 38T chainring. (Direct mount to make removal easy as possible).
Preference would also be 1x .
(IF there is a 2x and its compatible I would go for that option.)

Most of the time when commuting I use another bike and this is a spare for two purposes :
1. Spare bike for winter commuting (where I normally use 54 gear inches 95% of the time). So I use the 38T chainring with the 19t sprocket. This gets me to work and back without having to change gear. I could probably use a single-speed bike but in the summer I can use higher gears.
2. Holiday/Weekend cycling. This is the main reason I want the climbing gear of 20 inches.


So I want a crank-set that allows me to be able to switch between the 38T and install the 30T chainring. (Direct mount) This then covers me for any winter commuting, holiday cycling and anything in between.

Question A. Can this be done with a 110 BCD (direct mount) or do I need even smaller?
Question B. What would be the drawbacks (chainline, slipping etc?).
cycle tramp
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Joined: 5 Aug 2009, 7:22pm

Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by cycle tramp »

Hello There

Due to the size of the chain rings a 38 tooth chainring would have a BCD of 110 mm, whereas the 30 tooth chainring (due to its small size) would have a BCD of 74 mm.

Thus if you got the chain line correct for one ring, it would be wrong for the other ring, if you were using a 110/74 BCD chainset (although you could mount the two rings together on the 110/74 chain set permanently and just move the chain across with you fingers or just fit a front mech, when you wanted to change chainring sizes).

If you are very sure you only want the one chainring and the choice of using either 38 tooth or 30 tooth chainring, then you are probably better using a dedicated 1 x chainset with a much smaller BCD than 110
It's time to go :-)
UpWrong
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Location: Portsmouth, Hampshire

Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by UpWrong »

You can fit a 33T ring to a 110 BCD crankset. That gets you down to around 22" which might be good enough.
Mountgrove
Posts: 12
Joined: 8 May 2018, 12:35pm

Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by Mountgrove »

Thanks both,
I am emailing a vendor with regard to their Raptor Chainring 104BCD - Narrow Wide as it is advertised as between 30T & 38T.
So hopefully I can purchase a new crankset compatible with my SRAM Apex 11 speed 1x (11-42t). These are £35 each.

The 2x route sounds interesting as well. When I read the suggestion about switching over by hand - I made an audible "Duh" (why did I not think of that lol!).
There is a SHIMANO XT M8000 Double 38/28 11 Speed Chainset, (the vendor reduced price from £200 to £100 - sounds like a bargain but not sure if it is compatible).
The crank arms are Forged HollowTech II The chainrings have "spike pins" ,170mm.
This does not look like direct mount so I guess it means replacing the entire crankset if the teeth develop an issue ? (perhaps that is why it is reduced?). I would probably purchase 2 for £200 just in case.

Now I have got my head around the fact I do not need a front derailleur and can just buy a Double Chainset & switch by hand - that opens up so many options ! I have realised I can also keep a specific chain for each chainring. I will use quicklinks to make life easier.
When I think about it neither the 30T or the 38T chainring would ever be used with the whole cassette :-(11,13,15,17,19,22,25,28,32,36,42). (Realistically only 9 with each would ever be needed) . I am going to disregard chain stretch because I rotate chains and I will specifically keep a chain for each chainring .
Why the heck did I buy a 1x in the first place ?? :oops:
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cycleruk
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Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by cycleruk »

The SHIMANO XT M8000 Double 38/28 11 Speed Chainset does have removable chainrings.
It is a HollowTech 11 so will require suitable BBs.
The specification says "for use with 11 speed HG-X MTB chains only" ??
https://www.wiggle.co.uk/shimano-deore- ... e-chainset

Will you need a "specific chain for each chain ring" as the rear derailleur should take up the slack. ?
Presuming that the RD will accommodate the 11/42 cassette plus the double chainset.
You'll never know if you don't try it.
pq
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Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by pq »

My gravel bike has a SRAM Force 1 crankset which can be used with direct mount chainrings. I currently have a 26 fitted and sometimes use a 30 and a 32. Swapping direct mount chainrings isn't quite as straightforward as a conventional set-up with a spider, but it's no problem and for me is justified by the smaller chainrings I can use (and the lower weight is nice).
One link to your website is enough. G
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Mick F
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Re: 1x drivetrain 11 speed. How to change from 38T 130 BCD to smaller chainring. for 20 gear inches climbing gear.

Post by Mick F »

This is yet another question asked by someone with an 11t small sprocket.
If you use the 11t quite a bit, it will wear out faster than any other of the cluster.
The smaller the sprocket, the faster it wears.

Replace the whole cassette?
Can you buy a separate 11t for your cassette?

If you want lower gears, buy a bigger cassette. If you can't, go back to Plan A and fit smaller chainrings, but better still, ditch the 11t cassette.

That's what I did.
I got through four(?) 11t sprockets before swapping the cassette for a bigger one.
I bought a "job lot" of them before I saw the light.
https://www.bike-discount.de/en/shimano ... m771-10-bl?
Mick F. Cornwall
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