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

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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, 7:33pm buy a Shimano MTB spec bottom bracket (that matches the cranks)
If you change the BB, or even shim it there are loads of options, but OP was trying to keep the BB. I assume to keep it as simple as possible..
scottg wrote: 17 Dec 2022, 7:48pm 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
GRX 1x for GRX 2x seems like a the least problematic swap. Axle length will be the same and you can use the inner ring. No messing around with the BB. Although I'm sure other cranks could do the same. Chainline maybe not be spot on but I doubt it will matter much. Unlikely to be any clearance issues. Could put a chain guard on the outer (if you could find one). Or two single speed chain rings and manually swap (Chain length permitting)
Sparky56
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Joined: 26 Nov 2022, 6:27am

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

Post by Sparky56 »

Thanks all for your help — it’s given me some useful leads for internet searches.

This is what I’ve found so far

1) The Shimano GRX 1x Derailleur (theoretical max 42t) is _designed_ for 1x but there seem to be various reports on forums that 2x will work fine with it. A 2x set up with 28/44 up front would give 16.92 gear inches at the lowest gear (with 46t at the back) and 111.20 gear inches on the highest — so if that works it would be super attractive (perhaps a big ‘if’). Stock GRX 2x is 30/46 but can get lower here:

https://specialites-ta.com/double/440-1 ... ure,44-dts

2) I contacted the company that makes the bottom bracket on my bike (https://sn-vitae.bike/), & for £25 they sell an adapter (for that bottom bracket) that allows SRAM GXP 22/24 spindle to be fitted. This opens up potential for lower geared SRAM 1x cranksets (e.g. 30-34t)
cycle tramp
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Re: GRX - advice on how to make gearing lower (easier)

Post by cycle tramp »

Option one sounds really exciting and gives you a great range of gears... if a front changer and associated cabling and shifter malarkey isn't for you, would you consider running a double front chainring and shifting the chain with your fingers? If you go for the front changer (with or without the other bits)- please write up about how the fitting went and your views on how it operates with a couple of photos, please :-D

Choice two is a bit more of a compromise- with a 30 tooth chainring you will gain a really nice crawler gear, but a 30 tooth chain ring, a 11 tooth sprocket and a 29 inch wheel only gives you a top gear of 80 inches - limiting your ability to pedal down hill or make full use of any tail wind...
Sparky56
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Re: GRX - advice on how to make gearing lower (easier)

Post by Sparky56 »

cycle tramp wrote: 18 Dec 2022, 3:34pm Option one sounds really exciting and gives you a great range of gears... if a front changer and associated cabling and shifter malarkey isn't for you, would you consider running a double front chainring and shifting the chain with your fingers? If you go for the front changer (with or without the other bits)- please write up about how the fitting went and your views on how it operates with a couple of photos, please :-D
Yes I agree if it worked it would be fabulous— I’m still considering options but will report back my eventual solution.

This video is helpful and encouraging although I’d dearly love to stick with the 46t cassette….

https://bikepacking.com/gear/wide-range-grx-2x11/


PS, slight tangent, I run a 3x on my town bike (12 years old tatty hybrid, weighs 16kg+) - 22 cogs on the front small chain ring, 34 on the back largest = 17.58 gear inches! All shimano Altus —- very happy with this gearing and I do use the smallest gear on some of the steep alleyways. I upgraded the cassette from 32 to 34 when hill training and it seemed the new bike wouldn’t arrive…. So it was very strange when the new gravel bike arrived with initial 40 front/ 42 at the back …(26 gear inches minimum)… I suppose that kind of explains why I started this thread… (perhaps should take the town bike on my bikepacking adventures…at least I’d not worry about it getting stolen.
Sparky56
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Joined: 26 Nov 2022, 6:27am

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

Post by Sparky56 »

Sparky56 wrote: 18 Dec 2022, 4:04pm
cycle tramp wrote: 18 Dec 2022, 3:34pm Option one sounds really exciting and gives you a great range of gears... if a front changer and associated cabling and shifter malarkey isn't for you, would you consider running a double front chainring and shifting the chain with your fingers? If you go for the front changer (with or without the other bits)- please write up about how the fitting went and your views on how it operates with a couple of photos, please :-D
Yes I agree if it worked it would be fabulous— I’m still considering options but will report back my eventual solution.

This video is helpful and encouraging although I’d dearly love to stick with the 46t cassette….

https://bikepacking.com/gear/wide-range-grx-2x11/


PS, slight tangent, I run a 3x on my town bike (12 years old tatty hybrid, weighs 16kg+) - 22 cogs on the front small chain ring, 34 on the back largest = 17.58 gear inches! All shimano Altus —- very happy with this gearing and I do use the smallest gear on some of the steep alleyways. I upgraded the cassette from 32 to 34 when hill training and it seemed the new bike wouldn’t arrive…. So it was very strange when the new gravel bike arrived with initial 40 front/ 42 at the back …(26 gear inches minimum)… I suppose that kind of explains why I started this thread… (perhaps should take the town bike on my bikepacking adventures…at least I’d not worry about it getting stolen. (So to get same low gear on my gravel bike I’ll need 28/30 up front & 46 on back……. )
Sparky56
Posts: 175
Joined: 26 Nov 2022, 6:27am

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

Post by Sparky56 »

cycle tramp wrote: 18 Dec 2022, 3:34pm Option one sounds really exciting and gives you a great range of gears... if a front changer and associated cabling and shifter malarkey isn't for you, would you consider running a double front chainring and shifting the chain with your fingers? If you go for the front changer (with or without the other bits)- please write up about how the fitting went and your views on how it operates with a couple of photos, please :-D
Yes I agree if it worked it would be fabulous— I’m still considering options but will report back my eventual solution.

This video is helpful and encouraging although I’d dearly love to stick with the 46t cassette….

https://bikepacking.com/gear/wide-range-grx-2x11/


PS, slight tangent, I run a 3x on my town bike (12 years old tatty hybrid, weighs 16kg+) - 22 cogs on the front small chain ring, 34 on the back largest = 17.58 gear inches! All shimano Altus —- very happy with this gearing and I do use the smallest gear on some of the steep alleyways. I upgraded the cassette from 32 to 34 when hill training and it seemed the new bike wouldn’t arrive…. So it was very strange when the new gravel bike arrived with initial 40 front/ 42 at the back …(26 gear inches minimum)… I suppose that kind of explains why I started this thread… (perhaps should take the town bike on my bikepacking adventures…at least I’d not worry about it getting stolen. (So to get same low gear on my gravel bike I’ll need 28/30 up front & 46 on back……. )
Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

Sparky56 wrote: 18 Dec 2022, 2:12pm for £25 they sell an adapter (for that bottom bracket) that allows SRAM GXP 22/24 spindle to be fitted.
You can get ones of these adaptors for less than a fiver in alot for places - just look for a hollowtech to GXP adaptor.

I would not recommend them though, IMO they encourage premature and uneven wear on the bearings. I tried it once it did not last long.... Maybe a more expensive one is better.

If your moving to SRAM GXP you can buy a GXP BB for £25. I find GXP BBs wear unevenly as well. I use them anyway, but service the bearings.....
Sparky56
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Re: GRX - advice on how to make gearing lower (easier)

Post by Sparky56 »

Thanks @jupestar.

The more I read into this the more comfortable i feel with staying with shimano and trying a 2x set up. Seems like 2x with 11-42 is a reasonably standard modification

E.g. from this website (by the way i have no intent/interest/ability to race but I would dearly love to bike pack the route of the Atlas mountain race).


https://bikepacking.com/bikes/2020-atla ... race-rigs/
2F79B453-25DE-414B-BB94-FEFFF635E138.png

And a few more modified GRX 2x (and 1x) here

https://bikepacking.com/bikes/2022-tour ... gs-part-2/
Last edited by Sparky56 on 19 Dec 2022, 7:47am, edited 1 time in total.
Nearholmer
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Re: GRX - advice on how to make gearing lower (easier)

Post by Nearholmer »

If you do go the 2x with 11-42 route, is there any possibility that you could post a ‘blow by blow’ account of how you do it?

I read some of the very summarised accounts of people doing it, and I’m afraid that some of what they say goes straight over my head.
Sparky56
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Re: GRX - advice on how to make gearing lower (easier)

Post by Sparky56 »

Nearholmer wrote: 19 Dec 2022, 6:49am If you do go the 2x with 11-42 route, is there any possibility that you could post a ‘blow by blow’ account of how you do it?

I read some of the very summarised accounts of people doing it, and I’m afraid that some of what they say goes straight over my head.
Yes of course I’ll post as much information as I can provide

— however I’m a hopeless mechanic so will get the bike shop to do it (but I’ll get as much info as possible from them and post it here).
Nearholmer
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Re: GRX - advice on how to make gearing lower (easier)

Post by Nearholmer »

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

Post by Jupestar »

Sparky56 wrote: 19 Dec 2022, 6:14am
The more I read into this the more comfortable i feel with staying with shimano and trying a 2x set up. Seems like 2x with 11-42 is a reasonably standard modification

E.g. from this website (by the way i have no intent/interest/ability to race but I would dearly love to bike pack the route of the Atlas mountain race).

https://bikepacking.com/bikes/2020-atla ... race-rigs/
I was surprised by the number of setups in that link, who are simply running standard 1x over 1145kms through the Altas Mountains. A few 2x and (although I didn't look at them all) I saw no 3x... I see people on my daily commute with a wider gear ranges....

In terms of getting 2x with 42t rear. I guess it's a combination of pushing the design spec, and lowering the RD so it can take a larger capacity..
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cycleruk
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Re: GRX - advice on how to make gearing lower (easier)

Post by cycleruk »

Jupestar wrote: 19 Dec 2022, 10:48am In terms of getting 2x with 42t rear. I guess it's a combination of pushing the design spec, and lowering the RD so it can take a larger capacity..
If your RD currently goes to 42T cassette then it will not require any changes to it. (no lowering needed)
If you decide to go 2x on the chainset then the FD needs to match the chainrings difference and sizes.
The FD has also to have the matching chainline so probably a GRX one.
(Be wary that an FD will only go down so far before it catches the chainstay.)

I do know of someone who did have a set up of manually changing the chain over from one chainring to the other. (no FD)
With this though there is a chance if you cross chain on big to big the chain can unship from big ring to small on its own.
Not too bad a problem but on one of my bikes it would unship sometimes onto the BB. :(
With a 2 ring set up the chain has to be long enough to wrap around big ring to big sprocket plus a link. This may require an extra long chain ?
You'll never know if you don't try it.
Jupestar
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Re: GRX - advice on how to make gearing lower (easier)

Post by Jupestar »

cycleruk wrote: 19 Dec 2022, 2:27pm If your RD currently goes to 42T cassette then it will not require any changes to it. (no lowering needed)
I believe the GRX 1x RD is max 42t cassette, with total capacity of 31t. OP has it on a 11-46t which is already out of it's designed range. The GRX 2x is max 34t with 42t total capacity. The OP doesn't actually say which one he has (there is no GRX 600series RD). But he's 11 speed which implies he had the 800 series RD and probably the 1x.

I assume the limits can be stretched, as the OP has seen in other threads. but never tested it.
cycleruk wrote: 19 Dec 2022, 2:27pm With a 2 ring set up the chain has to be long enough to wrap around big ring to big sprocket plus a link. This may require an extra long chain ?
Which is then possibly be too long a chain for small-small.... I believe that is why there is a total capacity for the RD.
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