Upgrading cassette on GRX-600 Gravel Bike?
 

Hey everyone,

So I recently got into gravel riding and I freaking love it. My bike is Scott Speedster Gravel 30 - I do wish I had spent a little more and gotten something a bit lighter (I didn't know I would like it this much) but it is very much serviceable.

The bike comes with a GRX 2x10 drivetrain - 46/30 and 11-34. This is already a pretty big range, but I live in a rather hilly area and some of the trails around here have grades north of 20% for short sections. I almost always end up having to dismount halfway up these really really steep parts and I'd like to be able to clean them without getting off.

I'd like to upgrade the cassette to something with a few bigger cogs, but according to what I've found online, the most people have fit on the GRX-600 RD is an 11-36. I don't really want to spend the money on a new cassette for 2 teeth, so would there be a way to get an 11-40 or so on there? I do have a spare Wolf Tooth RoadLink (this one) laying around - would that work for what I'm trying to do? Any other suggestions?

Thanks!

I'd like to tell you that you can work with your 46/30 and the 11-34 cassette, but my experience tells me that you need a minimum of 12 more teeth on the largest cassette cog than on your smallest front chain ring. Truth be told, I run 1x (30T) and a 11-46 cassette. On forest service roads, I never miss higher gears. It's the low gears that get me up the uphills, and brakes that let me survive the down hills. Even in the 30-46 low climbing gear, there are grades that make me walk, especially if I have luggage.

On my paved road bike, I have a 46/30 and a 10-42 cassette. I have toured on that bike with a 26-42 low gear, with luggage. A 6% or steeper grade that is five miles long can require a low gear if you want to avoid walking.

So you would recommend something like an 11-42 or greater?

Yes, but I had to replace my handlebars, shifters, levers and rear derailleur. Oh yeah, I had to replace the crankset and whole rear wheel and hub, because SRAM required it. You might want to go 1x and get an "e-Thirteen" 9-46 cassette. Not sure what hub it may require. Large cassettes usually don't work with 2x cranks.

You really should look at sheldon brown's gear calculator. You can plug in different values for cassettes and chain rings, tire sizes. Low gears are important when pedaling uphills with a load of luggage, like when you're touring. For that, I recommend a "Gear Inch" low gear of 17. Lower if you are heavy, maybe 18-19 if you are lighter. Forest service roads tend to be rather steep, in my experience.

I apologise for throwing so much crap into the decision process. Most gravel bikes, in my opinion, are seriously over geared. A 42/26 crankset for off pavement makes much more sense to me, than a 46/30, especially if you have a 11-34 cassette. If you're trying to do both pavement and gravel with one gear setup, let me know if you figure it out.

Won't work...at least not with a GRX/double drivetrain. Take a look at the derailleur spec/capacity on Shimano's site.

I have an Ultegra setup that can handle 46/30T on the front and 11-36T cassette with no drama (and a little bit of a B-screw tweak). This can get me up a 17.5% grade. The Ultegra derailleur that I have is spec-ed at 32T max cassette. I bet you could get an 11-40T or 11-42T on there with a GRX derrailleur without a problem. Try it. If it doesn't work, then use the Wolf tooth extension or an XT long cage derailleur or Box derailleur.

Your bike has the gearing that I wish mine had

I don't suppose anyone is making a small chain ring with less than 30 teeth for a GRX crank just yet?

An expensive option for not much gain but if you ever upgrade wheels a 27.5 inch wheel slightly improves the low gearing.

I have lower gearing on my drop-bar mountain bike, but frankly 30T in the front and 36T in the back is so low that I think I would fall over if it went much lower.

You'd be right at the capacity limit of an XT SGS. No road or gravel derailleur will handle a big cassette like that combined w/ a double in the front.

I was thinking of doing this with my touring bike, but with an XT derailleur. I might borrow a cassette from an 11-speed mountain bike and test the hypothesis.

Hi! did you try this? Im thinking of doing the same upgrade, currently riding with 10 speed 30/46 in the front and 11/34 cassette. thanks!

There is also a better way of knowing by just checking the specs of the derailleur first. No need to guess or listen to people who have shifting issues because of cheap knock-off derailleurs that aren't having problems and are perfect in every way. Shimano kind of does this for a living and has for a couple years now (I think 100 now) so a good way to just know. Doubles can be tough with larger cassettes but with todays 11-13 speed drivetrains you can do a 1x pretty easily and still have a lot of the gears.

It is well known that Shimano's specs are conservative. So strictly following their specs will eliminate an option(or two) that are very much possible

This, 100%.

I’ve been trying to source a 42/26 for several months now, but with no luck. I think I’m likely to convert a MTB triple to get there.

People always say that. But in reality you would just pedal with a a more normal cadence, rather than grinding up a steep climb at sub 60 rpm. Not quite the same thing, but my mtb trail bike has a 30T front and 10-50 cassette and I don't fall over riding in the lowest gear. Even on a steep road climb I don't often spin it out. My road bike has a 50/34 front and 11-34 rear. For my weight (75 kg) I need to put out 300W to climb a 15% slope at 8 kph. That's only 62 rpm cadence in my lowest 34/34 gear. If I was riding on steep gravel climbs I would want a much lower gear.

Not sure what the difference is between a GRX RX-810 & GRX RX-600. My Revolt comes with rx-810 and it works well with the 11-40 cassette.

My Giant revolt adv 2 comes with

Crankset Praxis Albe 2D, 32/48
Rear Derailleur Shimano GRX RX-810
Cassette Shimano 105, 11-speed, 11x34
https://www.giant-bicycles.com/us/revolt-advanced-2

Since it has a GRX RX-810 I was able to install a 11-40 cassette. 32 front and rear 40 should be deep enough of gears for most things.


I never shift big to big now. It shifts ever so slighty worse than a smaller cassette. TBH I can't tell the
difference. Might just be in my head.



Gravel Cyclist: Shimano GRX 2x with 11-40T Cassette
by Jeff Whitfield on November 7th, 2019
https://velonut.com/blog/shimano-grx...1-40t-cassette



https://cimg1.ibsrv.net/gimg/bikefor...1613940ee7.jpg

:lol:
https://cimg6.ibsrv.net/gimg/bikefor...acff8a54eb.png

It only takes a few minutes at the shimano website to figure out that there are no options to gain more low gearing unless you change to 1x and lose a significant amount of top gear. A 30/34 is as low as shimano offers.

I can setup my sram axs drivetrain with a grx 46/30 and 10-36, but that's not much lower. It works for speeds in the 3.5-5 mph range on pavement. The problem with riding steep gravel is usually a lack of traction, requiring an extra low gear combined with a relatively high cadence. I'd expect to get off and walk on really steep gravel.

https://bike.shimano.com/en-EU/produ...-11-speed.html

Again- that is their official capacity, which has been shown to be conservative. There are options to gain more low gearing.

How about working on the other end, the FD? Two teeth larger on your cassette is ~6%, two teeth on the chainring is ~7%. If you went to a 24 tooth chainring, that would be about 20% lower ratio.

This video might be helpful:

Every RD has to have some extra capacity due to variations in chain stay length. Some bikes may have a length that corresponds to a chain length of almost exactly 54,55, 56... inches, while others can fall anywhere in between. If you can find a cassette that works properly with a cassette that has a few more teeth, it may work without increasing chain length. 4T more sprocket size requires 1 inch more chain length. Adding that extra inch may result in the chain hanging loose in the small ring and one or more of the smallest sprockets. That's no a big deal, as long as you don't use them.

I have a SRAM AXS setup with the standard RD that is supposedly limited to a 13T difference at the crank with a 10-33 cassette, which is a 36T wrap. I can just barely get it to clear a 36T sprocket by turning the B screw nearly all the way in and use it with a GRX 48/31 crank, for a total of 43T of wrap, but with AXS, you can't shift into the little ring and 10T sprocket, so it's really 42T of wrap. With my 415mm chain stay length, the 11T with the 31T little ring is a bit too loose, but nothing bad happens if it's used. The clearance between the upper jockey pulley needs to be reduced from the recommended 5mm to only around 3mm. If that's not done, then problems may occur with the 10-11 shift from the big ring, due to insufficient wrap around the sprocket.

It can be done. Inspired by that bikepacking.com video posted right above my post, and with the 46/30 GRX 600 crank on my steel gravel bike, i went from an 11-34 Shimano cassette to a Sunrace CSMX8 11-42 cassette, same chain. I'm using the GRX 810 RD. I had to really adjust the b-screw, but it worked fine. I took it to my LBS to have them doublecheck and the mechanic said Just don't ever cross chain! I never do. I wished i had watched to see if he adjusted anything, but i was too busy chatting with the shop owner.

I do have a Wolftooth Goatlink for 10-speed (as in the video) to help insure the B-screw is sitting flat against the stop, but have yet to install it.

eric
fresno,ca.

OOOOPS! i just saw the original date of this thread. lol