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This may be a stupid and uncommon (definitely seems so) question. Also forgive me for potential etiquette violations, as this is my first one on bike stackexchange.

I'm thinking about buying a gravel bike (nukeproof digger comp 2020) which has the Shimano GRX 1x11 drivetrain. Having almost no experience with gravel bikes, I'm just trying to understand, whether it would at all be possible in the future to "upgrade" to 2x11 - should the need arise.

So consider this a thought experiment: what would be necessary for such a conversion and what are the potential problems/showstoppers?

Thanks!

p.s.

The rather scarce relevant posts here (see below) did not help me definitively. Also there are might be some GRX specifics

I've also read several articles on extending 1x11 range with aftermarket cassettes and hardware, such as this excellent one on bikepacking.com and understand that something like that might very well be the (significantly easier if more limited) solution too

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3 Answers 3

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It depends. For most gravel bikes it will be an easy, yet expensive, swap. A couple of gravel bikes frames are built in a way that makes shipping a front derailleur as good as impossible. There may not be enough room for the chain stays to clear a second chain ring. What is more, some frames lack mounting positions and the shape or material of the seat tube does not allow clamping. A minor obstacle might be cable routing.

Many gravel bikes come in 1x and 2x configurations. Only the group is different while the frame is identical. Migrating on these bikes from 1x to 2x is easy to do. The costs involved are substantial though. You will need to replace crank-set, brifters, rear derailleur, chain, bar tape.

Unless you use SRAM's wireless group you also need to rout a cable. As before, gravel bikes that come in a 2x configuration make this easy. Bear in mind though, for internal cable routing you might have to remove the bottom bracket. Cable routing can be substantial and frustrating work, and may be expensive in a shop.

With so many components to replace, a good way to estimate component costs is to look at the price of a group set. It is typically at about 1/3 to 1/2 of the complete bike's price. Together with small parts and finishing kit you can expect the cost of modification to exceed the value of the bike after a year of riding.

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    Nuke Proof's specifications page is annoyingly unclear if the bike is compatible with a front derailer. No 2x versions of the bike exist. There's no specific mention on the page if it takes an FD. I'd suggest that the OP call a Nuke Proof dealer to confirm if he is set on possibly converting to 2x, but I agree these conversions tend to be uneconomical relative to buying a different (new or used) bike. Of course, sometimes frames take on a lot of sentimental value.
    – Weiwen Ng
    Aug 4, 2020 at 12:45
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    Al frame with roud tubes, clamping should not be an issue. Cable routing will be an ugly bodge with hose clamps, unless one goes wireless. But it's one of the newest fad of old school MTB geometry with drop bars and super wide tyres. I should not be surprised if a double will not clear the chainstays. correction just saw pic of '19 digger from the left. It has FD cable routing ports.
    – gschenk
    Aug 4, 2020 at 13:10
  • Many thanks for an extensive answer! Just FYI, as I pointed out in a comment to the post below, there is limited evidence that the specific rear derailleur rx812 works with a 2x setup
    – Dima
    Aug 4, 2020 at 13:26
  • It wasn't 100% clear that the seat tube was round where the clamping location was just from the current model year spec page. If the 2019 Digger had an FD routing port, then it's more likely that the 2020 model can take an FD. @Dima I have heard that on the 812 RD, the arc in which the derailer travels is more optimized for the MTB cassette and its bigger cogs. That said, I acknowledge the experience of the CX Mag writer who said it worked well enough with an 11-34 cassette in practice.
    – Weiwen Ng
    Aug 4, 2020 at 13:53
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gshenk's post is excellent general answer, here's the specific answer for the setup on the Digger Comp.

The Digger comes with an RX-600 40t crank, RD-RX812 derailleur and CS-M7000 11-42 cassette. The RD-812 derailleur is compatible with wide-range mountain bike 11 speed cassettes (which have different spacing that 11 speed road cassettes). It's not designed to be used with a double crank.

This of course means that converting the bike to 2x would involve replacing the entire drivetrain.

You can compare the RX-810 2x and RX-812 1x components and see which other components they are intended to be used with on this Shimano component line-up page. Note that the 812 setup with a 42 tooth crank gives you 0.9 - 3.6 ratio spread and the 2x 810 with a 11-34 cassette gives 0.9 - 4.3, with smaller gaps between ratios. The 1x drivetrain sacrifices gear ratios for simplicity and chain retention and control.

Think what you want to do with a gravel bike. If you want to ride rougher off-road trials exclusively a 1x bike may be better. If you want more flexibility and to use the bike on road as well as off a 2x bike would be better.

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  • just FYI: I have seen a small number of posts saying that RD812 works with 2x (even though being officially uncompatible), e.g. here: "Of course, there’s a difference between what’s recommended and what actually works. Due to a mix-up, our test bike arrived with a GRX 2x RX810 crankset, front derailleur and front and rear shifters, but with a 1x RX812 rear derailleur. It did the job without complaint or issue ...."
    – Dima
    Aug 4, 2020 at 13:18
  • many thanks for the specifics! I assume that with Digger running a 40 crank, the range is rather 1:0.95 - 3.63:1, isn't it?
    – Dima
    Aug 4, 2020 at 13:38
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    @Dima you are right, somehow I used 42 teeth for the crank in my calculation
    – Argenti Apparatus
    Aug 4, 2020 at 14:40
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I can't speak to GRX specifically, but one of the Old Saws of cycling is "Buy the bike you want" which means to avoid buying a bike with the immediate intention of upgrading/replacing parts.

Generally speaking, a new bike will work well together - by swapping things about, that new-bike feel may diminish.

Unless your LBS is really nice and credits you for take-off parts, the cost penalty of buying the bike with bits you don't want and additionally buying more parts at retail will soon add up. If you intend to swap the parts yourself then this may make any warranty claims later problematic.

However all this goes out the window if you're talking about a used bike, where there are no warranties and parts come pre-bedded-in (or worn out)

Upshot, Buy the bike you want to ride, in the spec you want.

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    This doesn't answer the OPs question (though I agree with the sentiment)
    – brendan
    Aug 7 at 13:04
  • @brendan you're right - it doesn't answer about changing an existing bike from GRX single to double chainring but it does address OP's need. They were buying a new bike and it is easier to buy the bike as-desired rather than buying it and immediately making substantial changes. Warranty, and overall cost minimisation are the main drivers in this answer.
    – Criggie ♦
    Aug 7 at 18:45

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