Crankset compatibility

[jimmy156]

Hello all,

Back in feb took my first foray into a drop bar bike and bought a gravel bike (which I love!) but with what I use the bike for, which is plenty of road riding, actual gravel trails and the odd bit of bridleway or more technical off road (very rare) I am finding that I am regularly using "the smallest cog on the cassette, even when riding on a flat (this is becoming more regular as my strength improves), and spin out very easily on road descents.

The bike had Shimano GRX400 10 speed bits on it, with the GRX RX600 30/46 crankset.

Staying within the GRX family, there is the GRXRX810 crankset, which is 31/48 so I have two questions.

Will going from 46 to 48 on the big ring make a noticeable difference?

Will I be able to use the 810 crankset (which is designed for use with an 11 speed system) with my 10 speed stuff (think tiagra 10sp vs ultegra 11sp) or will it require the rest of the drivetrain being "upgraded" too.

TIA!

Edited by jimmy156 on Monday 10th August 15:32

[Paul Drawmer]

I think the GRX crankset has a greater offset than 'normal' road bike cranksets, so I suspect that your best option to raise the gearing would be to go for a bigger ring to replace the existing large one. I suspect you'll need a 50 tooth one.

You'll need to find out the PCD of your set up, and buy a replacement ring with the same PCD.

[jimmy156]

Thanks for your response! Would changing the big ring affect the shifting on the front? I thought the chain rings and derailleur are designed to go between particular chain ring sizes. Would I get away with just swapping the big one to a 50?

[BrundanBianchi]

jimmy156 said:

Thanks for your response! Would changing the big ring affect the shifting on the front? I thought the chain rings and derailleur are designed to go between particular chain ring sizes. Would I get away with just swapping the big one to a 50?

Strictly speaking the spacing between rings on an 11 speed chainset and a 10 speed are different. However, it’s just a chainset, and both will be interchangeable with no show stopping big issues ( possibly a bit of extra noise ). I agree that you’d probably be best off just sticking a larger ring on, to up gear. Make sure that the front mech is clear ( vertically ) of any up sized ring though.

[frisbee]

The front chain rings are usually already at the limits of what the derrailler will handle.

46x11 is 30mph at 90rpm. Even if you switch to a 52x11 that’s only going to be 34 at 90 rpm.

[TwilightJohnny]

frisbee said:

46x11 is 30mph at 90rpm. Even if you switch to a 52x11 that’s only going to be 34 at 90 rpm.

I'd say that's a huge difference but forget being able to shift cleanly from the 30t ring to a 52 or even a 50t.

OP, it doesn't sound like you need the lowest gears available from the GRX crankset. Pretty much any Shimano Hollowtech compact 34/50 would probably suit your needs. Road chainrings may fit the GRX, I'm not sure, but it can be cheaper to buy a complete crankset than just new rings anyway! You may need a different front derailleur but they are not particularly expensive.

By the way, I think the GRX600 crankset is designed for 11 speed so your actual question is already answered there.

[PomBstard]

I’d agree with the previous post. I’ve got 105 group set with 2x11 (50/34T and 11-34) on my gravel bike and it suits riding road, gravel and the odd bit of techie singletrack fine with just about enough gearing to cover steep rocky climbs off road and keep up with roadies on road.

Have never felt I need lower or higher gearing. More grip, stronger legs and better technique perhaps, but not different gearing

[mikecassie]

I don't think just putting a 50t chainring on to replace your 46t chainring will work. The jump between chainrings will be too big, I think 16t is the biggest it can cope with.

[bigdom]

jimmy156 said:

Hello all,

Back in feb took my first foray into a drop bar bike and bought a gravel bike (which I love!) but with what I use the bike for, which is plenty of road riding, actual gravel trails and the odd bit of bridleway or more technical off road (very rare) I am finding that I am regularly using "the smallest cog on the cassette, even when riding on a flat (this is becoming more regular as my strength improves), and spin out very easily on road descents.

The bike had Shimano GRX400 10 speed bits on it, with the GRX RX600 30/46 crankset.

Staying within the GRX family, there is the GRXRX810 crankset, which is 31/48 so I have two questions.

Will going from 46 to 48 on the big ring make a noticeable difference?

No, have a look at a bike gear calculator. Also depends on what you're running on your cassette.

jimmy156 said:

Will I be able to use the 810 crankset (which is designed for use with an 11 speed system) with my 10 speed stuff (think tiagra 10sp vs ultegra 11sp) or will it require the rest of the drivetrain being "upgraded" too.

Technically the crankset will be fine, I believe the GRX 10 speed front derailleur has a maximum range of 16T, so that's an issue. You can mix components a bit, although shifting accuracy becomes compromised. There's limits to what you can make work. You would need new a new freehub to but an 11 speed cassette on the rear. It definitely becomes a cost/upgrade question

Last year I geared down Triggers broom, or as Genesis called it when I bought it Croix De Fer, from 50/34 to 46/30 (Shimano 11 to Rotor crankset), changing the cassette to 11-30. Loses 1 on the top, and provides better spread across the cassette, with same low gear as before on 11-34. It quite often has panniers or tows a trailer, so works for me. It does spin out downhill but thats at around 40mph anyway.

[jimmy156]

Thanks for all the responses everyone! Seems like a mix of opinions!

The rear cassette is 11-34, so I have a big spread of gears, but rarely use the bigger cogs on the cassette in either ring (I don’t think I have ever been in the 34 cog!)

Hmm reading all the responses, perhaps I would be better waiting until some bits wear out and then man mathsing an upgrade to a different drivetrain set up...

That website that works out gearing etc looks very useful.

[flight147z]

frisbee said:

The front chain rings are usually already at the limits of what the derrailler will handle.

46x11 is 30mph at 90rpm. Even if you switch to a 52x11 that’s only going to be 34 at 90 rpm.

Based on this I would say that you are cycling at too low cadence

I'm guessing you are not doing the above but are doing something like 20mph at 60rpm (unless you really are riding around on the flat at 30mph in your top gear which would be pretty impressive!)

Try increasing your cadence in a lower gear which is a more efficient way to ride

I have a top ratio of 52x11 on my road bike and I rarely use that combination unless I am going downhill

[jimmy156]

flight147z said:

Based on this I would say that you are cycling at too low cadence

I'm guessing you are not doing the above but are doing something like 20mph at 60rpm (unless you really are riding around on the flat at 30mph in your top gear which would be pretty impressive!)

Try increasing your cadence in a lower gear which is a more efficient way to ride

I have a top ratio of 52x11 on my road bike and I rarely use that combination unless I am going downhill

Makes sense, just checked a recent 2.3km flat segment (it’s a 0.2% 10m incline, so almost totally flat!) and my average speed was 22mph.

I tried riding a gear or 2 down on where I normally would and despite it feeling unnatural and I thought I was going slower, I was actually pretty pleased with my average speed over the ride. Feels like hard work though!

So maybe “pedal faster” is the answer

[flight147z]

jimmy156 said:

Makes sense, just checked a recent 2.3km flat segment (it’s a 0.2% 10m incline, so almost totally flat!) and my average speed was 22mph.

I tried riding a gear or 2 down on where I normally would and despite it feeling unnatural and I thought I was going slower, I was actually pretty pleased with my average speed over the ride. Feels like hard work though!

So maybe “pedal faster” is the answer

Larger gears probably isn't the right answer then, I think you need to work on increasing cadence and lowering your gears. I've just checked a recent ride I did in the lakes and I didn't drop to 60rpm until I hit a 20% incline. If you can cycle with higher cadence in a lower gear and maintain the same speed you should be more efficient and reduce fatigue (albeit I am not an expert on the science!)