Squidly

Hi,

I had a gravel biking trip at the weekend and ran out of gears quite often. Looking to get some easier gearing so I can get up climbs easier.

Current setup is
RD-RX817 di2 long cage derailleur
11-42t XT M8000 Cassette
42t shimano chainring up front.

I am trying to work out what my options are here and get some advice.

1. Change rear cassette to an 11-50t, not sure this would be enough. Would I need to change the Rx817? it only has a 31t range according to shimano. What about if I installed a new cage and pulley from garbaruk?

2. Go 2x. For this I believe I would need the GRX di2 front derailleur and cranks (30-46). But would I also need the Rx815 derailleur? As I am not sure if you can setup Rx817 in a 2x configuration. Also if I went this route would I have to move to a smaller cassette or could I get that working with the 815 or 817?

With these new setups would I need a new chain as well?


If someone could help me with my questions or provide alternatives I might be missing that would be appreciated.

I really want to be able to spin up hills and still have the same top end gear for flats and roads as I use the 11t frequently on the current setup.

Thanks

sovende

That 42/42 combo is pretty low. You need stronger legs . Keep riding, your legs will get there!

Iride01 

People always flame me for saying this, but if you aren't in the best of cycling shape already, then riding more often might strengthen your legs up pretty quick and a lower gear ratio will be useless to you.

Also, I think you'll be going outside the specs for your current rear DR and while everyone agrees Shimano specs are conservative, you might not exceed those without some other stuff besides just a new cassette and chain.

More sprockets on the front will give you the most range of gearing over anything you can put on the rear. However that also will be an expensive upgrade.

I'd probably just opt for a smaller ring on the front for the near future and see what that does. Depending on the crank, that might be the cheaper option and more effective at getting you up hills comfortably. Your high end will suffer some, but probably not as much as you think since it is unlikely you always ride in the 11 cog and at your maximum speed!

Maybe you need another bike.

Welcome to BF.

Squidly

I have a 305 FTP and can and have pushed 3.4w/kg for an hour. I would have thought that would have been ok? Or am I well below the average cyclist?
​​​​​​
I believe my current setup is in range of the Shimano spec but right at the limit which is why I wanted to upgrade the pulley if moving to an 11-50. But just not sure if that will give me enough range of gears for what I am after. Basically I want to be able to spin up very hard climbs. On my 42t at the weekend up really steep gravel and single track climbs I was doing about 40-50rpm at 350ish watts and any slower rpm I would have stopped dead. I would like to be able to spin at a higher rpm and not have to put that power out and go slower up the climb.

ThermionicScott 

Amazing how far things have come. My first bike needed a triple to achieve that range.

DaveSSS 

It will take a new crank, FD, RD and cassette just to get a 30/34 low gear that's 12% or one shift lower. A 50T large sprocket would be 16% lower, but require an MTB rear derailleur.

https://gravel.shimano.com/US/produc...el/components/

HTupolev

The RX812 and RX817 do not have longer cages than the RX810 and RX815, they're geometrically optimized for 1x.

If you want to go down this route, one option would be to try it out, and then get the new cage if it isn't working well. You'll want to have spare or reusable master links on hand for this, though.

I've heard of people setting up a Di2 drivetrain with a 2x-oriented derailleur connected, and then swapping in the RX817. But I don't think the software will allow you to do the configuration while the RX817 is attached.

Several of my friends are using RX400 or RX810 (similar geometry to RD-RX815) derailleurs on 2x drivetrains with 16-tooth front differences and cassettes larger than spec. 11-40 or 11-42 is very doable, although in some cases you may need to a Roadlink DM to achieve well-behaved clearance. Do expect the chain to get fairly slack if you're riding in the small-small region of the drivetrain.

You're going to want to make sure that your chain is appropriately-sized for whatever new drivetrain arrangement you come to. The possibilities you're proposing will all merit a longer chain.

Iride01 

​​​​Well you are much better than I in the power department. Maybe it's just your technique though and not your gearing. If you have a narrow range of cadence, then that will, IMO, be one strike against you for keeping up with your peers or your aspirations of what you imagine you should be doing. Do you ride with others that do better than you? What gearing do they have on their bikes?​​ Or what do they do different?

Yes a 48 tooth low is the max tooth for that DR. So anything bigger will be a experiment and might require other stuff.

edit... Actually it's 42 teeth for the max low sprocket.... https://bike.shimano.com/en-EU/produ.../RD-RX817.html (hit the chevron to open all the spec's)

It's what I'd recommend. Though I don't do gravel or off road stuff. Since I started spinning 80 rpm as my comfort rpm and higher for times I'm accelerating or doing a hard climb, my cycling numbers have improved. I only spin slower when I'm resting or just completely worn out.

But I think you'll get the best info from looking at what others you ride with or see out there doing the same ride in the same conditions use. And that might well be a different bike. You'll pay a lot to get significantly lower gearing that won't affect your top end or leave you with big gaps in your lower ranges that just a rear cassette change will do.

base2 

For about $300 plus wheel build you have 2 options.
If not through axle but with disc: Sturmey Archer CS-RK3
If not through axle but rim brake: Sturmey Archer CS-RF3
You can operate either hub on road bars via a Paul 31.8 adaptor & SRAM triple mountain shifter. I have one bike set up this way. 20-140 gear inches using the 42 ring & 11 speed, 11-42 cassette you have already.

If not thru-axle & you'd like to spend about $450 plus wheel build instead, you can look on the used market for a second hand SRAM dual-drive. Repair parts are seldom, if ever available & my understanding is the 3 speed hub shifter is flat (straight mountain) handle bar only. But they work good.

If your bike is metal with a BSA bottom bracket & you've got about $900 floating around: Schlumpf mountain, speed-drive, or high-speed drive are options. It is not suitable for exceedingly filthy enviromnents. A speed-drive with a 34 tooth ring would give you about 0.75:1 & a top gear of 56-11 & still look like a 1x. You can get chainrings as small as 27 teeth with the "dash '08" varient. My Dahon has a speed-drive with a 34 ring mated to a Nexus 7 with a 17 cog. 24 to 97 gear inches.

If you are made of money & the above options don't tickle your fancy: Rohloff in any way you see fit. My touring bike has one. 17.5 to 93 gear inches. You can pair a Rohloff with a double crankset.

Or you could just go old school with an older model triple, 8 speed Claris, or 9 speed Sora or 10 speed 105 shifters with a 24(or28),38,48 triple & a 11-34 cassette. Road shifters, matching road triple front derailleur, & a long cage non-Dynasys mountain derailleur. That's how it was done back in the day.

Lots of ways to skin a cat.

BTW: 1:1 ~29-31 gear inches, is what road riders use locally for roads. For gravel here in the PNW, about 0.6-0.75:1 or ~16-20 gear inches is common. People who are not me seem to happily top out at about 18-25mph & be ok with it that way.

base2
(Who continues to be unimpressed by GRX, Di2, thru-axles, press-fit bottom brackets, or 1x.)

cpach

If this is what you really want, I'd probably just advise you to not take any shortcuts and do a 46/30 crank with an 11-36 cassette (just out of spec) with the correct derailleurs. Larger cassette than that may or may not work but I haven't had the chance to try it.

I'm pretty sure if you want you can also run a MTB Di2 RD 1x with road shifters, which officially max at 11-46 but would probably work OK with a 50t.

I'm all for 1x, but currently still not quite there for me for a bike that gets ridden on asphalt and gravel somewhat evenly.

sean.hwy

My Ibis MX grx came with
https://www.ibiscycles.com/bikes/hakka-mx
Rear Derailleur Shimano GRX RX812 Shadow Plus
Cassette Shimano XT 11-46

Most bike manufactures are conservative so you could probably put a 11-51 with that derailleur. How much top speed do you really "need" vs it would be nice to pedal at 30+ mph down a smooth road hill? I would drop the front chain ring down to 36 or 38 also. I always gear my bikes for what I need vs it would be nice to have.

EddyR

What were others on that weekend using?

Polaris OBark

I'm doing this, and make significant use of that lowest gear, especially off-road. Those who say a 1:1 ratio should be good enough probably ride different conditions.

I've heard, anecdotally, that you can keep your rear derailleur and cassette and add a GRX Di2 front derailleur and a GRX double crankset, and it will work as long as you don't need the sync shifting.

Kapusta

Assuming you crank can fit it, it seems like a smaller ring would be the cheapest and simplest route to go as long as you won’t miss the high gear.

stevel610 

1. Ride more (as has been suggested).
2. Get a single speed conversion for the cassette with a 17, 18, 19 tooth gear and learn to use momentum.
3. There is nothing wrong with walking a hill now and then . Seeing how much further you get up any given ride is a perfect measure of your improvement.

4. Go buy all the stuff suggested by others and see how much your fun/value changes for the positive.

HTupolev

Given that the OP has a >300W FTP, they probably will miss the top-end if this is being used in a mixed-surface capacity. There's even a fair chance that they have use for another gear or two higher.

There is if you want to go fast.

Yan 

Change your chainring to a 34 or 36t and be done with it. You don't need the highest speed gears. Next time you go for a ride pay attention to how much you actually use the smallest cogs in the back. I bet the answer is "about twice a year".

sean.hwy

Where did you get 300W FTP from?

People with 300W FTP can probably get away with 36F / 28R or even a fixie ha-ha


With bad knees from when car hit me while I was riding my motorcycle and I am in the 200 club I like 32F / 34R for road. for gravel I like 32F / 40R.

HTupolev

From the OP telling us in post #4 that their FTP is 305W.

Depends on their bike+rider weight and the climbs they're doing. We know that the OP is badly bottomed out even with a 1:1 low gear.