GRX - advice on how to make gearing lower (easier)

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Sparky56
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GRX - advice on how to make gearing lower (easier)

Post by Sparky56 »

I’d like some advice on how I might adapt the gearing on my gravel bike to make it easier — I’m planning some bikepacking trips in hilly areas this year (GB Divide the main objective after something gentle with my son)

The bike’s running a shimano GRX 600 groupset on a 1x set up. & I’ve already modified it a bit….

The front chain ring is 36t (Wolftooth) - which I understand (perhaps incorrectly) is the smallest chainring that the 1x GRX can take.

The back cassette is a shimano 11-46, 11 speed

I have found that this set up works well, smooth gear changes etc,

This set up is ‘so much better’ than what I had originally (40t/ 11-42) but I can see that some easier gears will be really useful when fully loaded on off road tracks.

So my questions are

1) are there any manufacturers that make a smaller front chain ring for GRX 1x please? (It’s 110 BCD, 4 bolts). I can’t find any. Wolftooth told me that this is the smallest possible for GRX.

2) What are the implications of changing the crankset to something that takes a smaller front chain ring? I.e. is this possible? Would it require new bottom bracket ? Currently I don;t find I’m spinning out on the flats but clearly there will be a limit at some point

3) Alternatively I could change the cassette to something bigger (e.g. Garbaruk, Sunrace) - but that would mean new derailleur cage extender etc etc & some of the reports I’ve seen about these components aren;t glowing about the quality compared with Shimano.

Thanks ever so much
Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

Does the crankset have the inner ring or is it 1x specific. If it 1x specific you could swap it out for the 2x version and use the inner ring 80BCD for a smaller chainring. Few factors to consider, but it should work. Probably least problomatic.

Give you the options to convert to 2x if you ever wanted to...

I think it possible to get a 34t chainring on the 110BCD, but finding one is another matter...
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Chris Jeggo
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Re: GRX - advice on how to make gearing lower (easier)

Post by Chris Jeggo »

Jupestar wrote: 16 Dec 2022, 3:09pm .....

I think it possible to get a 34t chainring on the 110BCD, but finding one is another matter...
Smallest possible on 110BCD is 33t, but the spider is Shimano asymmetric, i.e. arms are not at 90 degrees, so you're stuck with Shimano.
Valbrona
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Re: GRX - advice on how to make gearing lower (easier)

Post by Valbrona »

Switching to a smaller BCD, MTB crankset is one option, thus allowing the fitting of a smaller chainring. But caution is required as it may come with greater stance width, and I have always found MTB cranksets to be too wide when used for road riding/with road shoes.
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Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

Valbrona wrote: 16 Dec 2022, 4:23pm MTB cranksets to be too wide when used for road riding/with road shoes.
I agree it feels weird, although you can get narrower ones, plus presumably the BB would need to come out and be shimmed 5mm, and probably need a larger sleeve. At which point you could just as well change the lot...
zenitb
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Re: GRX - advice on how to make gearing lower (easier)

Post by zenitb »

Jupestar wrote: 16 Dec 2022, 8:47pm
Valbrona wrote: 16 Dec 2022, 4:23pm MTB cranksets to be too wide when used for road riding/with road shoes.
I agree it feels weird, although you can get narrower ones, plus presumably the BB would need to come out and be shimmed 5mm, and probably need a larger sleeve. At which point you could just as well change the lot...
I thought GRX bottom brackets had already been widenened to the MTB standard width ? Heres a quote from Shimano "Shimano GRX cranksets feature a +2.5mm outboard chainline, which improves rear tire clearance, making room for wide gravel tires. This also means that the GRX crank’s Q-Factor is +2.5mm wider on each side compared to Shimano road cranks" (from https://bike.shimano.com/en-US/informat ... ompon.html)

So given thats the case could you not just slap on an MTB 30 tooth crankest like this ?
Deore 1x
Deore 1x
EDIT .. here is an "offically" 11 speed one
11 speed "one by" chainset
11 speed "one by" chainset
You would still have the old crankset and could swap back for times when you were not Bikepacking ?
cycle tramp
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Re: GRX - advice on how to make gearing lower (easier)

Post by cycle tramp »

If you're using something like a 29 inch wheel size then even with a 46 tooth sprocket on your freehub you're going to need a chainring of under 30 teeth to get anywhere close to a 18" climbing gear (I think that the moment your works out at 23 inches)

Which explains why alot of people on this forum stick with a triple chainset. However the alternative as championed by Chris Juden is the apline chainset which uses a larger chain ring for most riding conditions but carries a smaller chainring for climbing. If you go down this route I suspect you'll need a front changer, new bottom bracket and new cranks

Personally I really won't be that worried. If you do have an 18 inch climbing gear the chances are you'll be pedalling up a hill at the same speed as if you'd be walking it....
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andy74
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Re: GRX - advice on how to make gearing lower (easier)

Post by andy74 »

zenitb wrote:
Jupestar wrote: 16 Dec 2022, 8:47pm
Valbrona wrote: 16 Dec 2022, 4:23pm MTB cranksets to be too wide when used for road riding/with road shoes.
I agree it feels weird, although you can get narrower ones, plus presumably the BB would need to come out and be shimmed 5mm, and probably need a larger sleeve. At which point you could just as well change the lot...
I thought GRX bottom brackets had already been widenened to the MTB standard width ? Heres a quote from Shimano "Shimano GRX cranksets feature a +2.5mm outboard chainline, which improves rear tire clearance, making room for wide gravel tires. This also means that the GRX crank’s Q-Factor is +2.5mm wider on each side compared to Shimano road cranks" (from https://bike.shimano.com/en-US/informat ... ompon.html)

So given thats the case could you not just slap on an MTB 30 tooth crankest like this ?
deore 1x.JPG
EDIT .. here is an "offically" 11 speed one
11 spd version.JPG
You would still have the old crankset and could swap back for times when you were not Bikepacking ?
Yes, it's true that GRX has a wider q factor and chainline. It still uses a standard road Hollowtech 2 bottom bracket. So to use an MTB crankset, you would need an mtb bottom bracket too

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Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

zenitb wrote: 17 Dec 2022, 2:42pm GRX bottom brackets had already been widenened to the MTB standard width ?
I thought GRX axles where for a road bike BB... I.e 68mm shell. So for a MTB designed for a 73mm shell. You would either need to shim the BB between the frame and then BB by 5mm. Or put an 5mm spacer on the outside and have the bearings on a different part of the axle.

I could be wrong about the GRX being designed for a 68mm shell.
Valbrona
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Re: GRX - advice on how to make gearing lower (easier)

Post by Valbrona »

The chainline difference between a GRX crankset and an MTB crankset will be either non-existent or not different enough to matter in the case of bikes running just one front chainring.

But I wager that stance width will be different.
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Sparky56
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Re: GRX - advice on how to make gearing lower (easier)

Post by Sparky56 »

Thanks for the replies so far - I;m watching with interest…

If it would be possible to swap the crankset without needing to do anything to the bottom bracket, that would be ideal.
Nearholmer
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Re: GRX - advice on how to make gearing lower (easier)

Post by Nearholmer »

I’m not super knowledgable on all this stuff, but I’ve read people talking about using GRX 2x, with a 42T largest cog at the back, which is outside the theoretical range, but apparently can be made to work. With 30/46 at the front, that gets you down to something like 19 gear inches, assuming 40mm tyres, and avoids being driven insane by lack of top gears on the easy stretches.

Worth a thought?

If 2x is a step too far, and/or you want an even lower gear, keep the 46 cassette at the back, and remove the 46 ring from the set at the front as Jupestar says (I’ll buy it from you for when mine wears out!).
zenitb
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Re: GRX - advice on how to make gearing lower (easier)

Post by zenitb »

Jupestar wrote: 17 Dec 2022, 5:02pm
zenitb wrote: 17 Dec 2022, 2:42pm GRX bottom brackets had already been widenened to the MTB standard width ?
I thought GRX axles where for a road bike BB... I.e 68mm shell. So for a MTB designed for a 73mm shell. You would either need to shim the BB between the frame and then BB by 5mm. Or put an 5mm spacer on the outside and have the bearings on a different part of the axle.

I could be wrong about the GRX being designed for a 68mm shell.
I think you are probably right on this Jupestar - looks like I oversimplied. So a potential route for Sparky would be to
a) buy the Deore 30t crankset

b) buy a Shimano MTB spec bottom bracket (that matches the cranks) designed for a 73mm bottom bracket shell rather than the 68mm shell he probably has

c) buy a couple of 2.5mm spacers to fill the gap .. like these ?
2.5mm spacers from SJSC
2.5mm spacers from SJSC
This is pushing the price up to around £70 now. Do you think this is workable though ? Given SJSC sell the adapter I guess Sparky could give them a ring before buying ?
scottg
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Re: GRX - advice on how to make gearing lower (easier)

Post by scottg »

Jupestar wrote: 17 Dec 2022, 5:02pm[snip]
I could be wrong about the GRX being designed for a 68mm shell.
I've a GRX double, used a Ultegra BB, bike has a 68mm shell, 135mm rear spacing.
Used the GRX front mech, chainline is fine with the 135 rear.
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Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

Nearholmer wrote: 17 Dec 2022, 7:18pm using GRX 2x, with a 42T largest cog at the back,
I'd probably go down the 2x route. But RD capacity is 31. You would need a LH shifter of some description a smaller cassette, and to see how you get the FD fitted, on a bike that may not be designed for an FD. It's not a simple swap.
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