Jim’s Tech Talk
By Jim Langley
In case you read about my new Trek Checkpoint SL 5 Gravel Bike in this space back in February, I want to share that I’ve changed my mind on the bike’s stock gearing.
What I wrote in that review was this:
“Due to a parts shortage my bike came with a Praxis Alba 48/32 crankset instead of the GRX’s 46/30. I still get a nice low gear that’s working fine.”
By “GRX’s,” I am referring to Shimano’s GRX crankset. And I should also explain that the Checkpoint comes with an 11-34 11-speed cassette.
Figuring Out What Gearing Is Right For You
In the weeks since I purchased the SL 5 I’ve climbed a ton on it including up Mt. Lemmon in Tucson, which I wrote about here: https://www.roadbikerider.com/climbing-mt-lemmon-tucson-arizona/. But back here in Santa Cruz, California I’ve been taking it up some famous local climbs that are far steeper than Mt. Lemmon such as Jamison Creek Road and Zayante Road. Zayante has a few spots that are 16%. Jamison tops 13% at times.
The rule I recommend following for choosing gearing or dialing in gearing that doesn’t feel right is to get easy enough gears so that even on the steepest climbs you might ride and even when you’re very tired you can still keep climbing.
That means that you shouldn’t have to push super hard on the pedals while pedaling seated or have to stomp on the pedals when standing while wrestling with the handlebars. And though it’s fine to do it if needed, zig zagging across the road shouldn’t be the ONLY way you can make it up the steepest pitches you ride.
With these rules in mind, I decided that I was wrong and the “nice low gear” the Checkpoint came with, a 32-tooth front chainring with a 34-tooth cassette cog (a gear of 25 inches), simply wasn’t low enough. It was just too difficult getting up the steeps on my local hills.
I could muscle it up them standing and sitting and even zig zagging a bit but it wasn’t enjoyable and it used up too much energy and also hurt my knees.
When lowering gearing you can replace the cassette, replace the chainrings or do both. For my Checkpoint, since I knew I needed to significantly lower the gearing, I decided to do both. And this required getting a new crankset because the Praxis Alba that the bike came with already had the smallest chainrings available for it.
So I purchased a Shimano GRX crankset with 30/46 gearing. And, for the cassette, I bought a Shimano 11-speed 11-40 cassette.
According to Shimano’s tech specifications on its GRX rear derailleur, the maximum cassette cog size you can run is 34 teeth. But, it turns out that it will shift perfectly fine across the 11-40 cassette. You just have to turn in the derailleur B screw a couple of turns to get the top derailleur pulley to clear the cog. That’s all it takes.
NOTE that you also must be sure to never try to shift onto the 40 when you are on your large chainring! If you do that you could damage the drivetrain.
Comparing the Drivetrains
When you’re looking for better gearing options, you can do it by making a little table like the one below that shows my before and after gearing. To get the “gear inch” numbers you divide the front chainring tooth count by the rear cog tooth count and multiply by 27. So for example, my lowest gear was a 32 tooth chainring divided by the 34 tooth cog times 27, which equals 25 gear inches.
Crankset gearing 32/48
Cassette gearing 11-13-15-17-19-21-23-25-27-30-34
Gear inches on 32 chainring:
79, 66, 58, 51, 45, 41, 38, 35, 32, 29, 25
On 48 chainring
118, 100, 86, 76, 68, 62, 56, 52, 48, 43, 38
Gear inches on 30 chainring:
74, 62, 54, 48, 43, 39, 34, 30, 26, 23, 20
On 46 chainring:
113, 96, 83, 73, 65, 59, 52, 46, 40, 35, 31 (cannot use this gear)
Looking at the lowest gear combinations with the new crankset and cassette, you can see that the two easiest gears are both lower than what I had before. Before it was 25 and now there’s a 20 and 23.
It might seem silly to spend $70 for a new cassette and $150 for a new crankset to basically just get two lower gears, but it’s making a huge difference for me – basically the difference between surviving the climbs and enjoying them. So to me it’s money well spent.
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.
David Frost says
Your note about not shifting to the 4oT cog when on the big ring could very likely be resolved by using a slightly longer chain. Not that you’d ever NEED that big-big combination, but why risk damage due to an accidental shift, at night for instance when you can’t see the chain position easily?
My wife’s bike has gearing similar to your new combination (11-40 11-speed rear, 34/46 front), and a longer chain results in continued excellent shifts (mechanical) throughout all possibilities. Her rear derailleur, which predates GRX, is a long cage Ultegra on a Wolftooth extender.
As a volunteer mechanic rebuilding literally hundreds of donated bikes for our large local non-profit, bikeworks.org, it would be irresponsible to put out a bike that could be seriously damaged in normal use, such as shifting to the big-big combination. I ALWAYS size chain length using the “big-big + 1 inch” rule to preclude such damage.
Mate… there’s a thing called “max chainwrap capacity”. The maximum difference between the largest gear combo (big big) and smallest (small small) a derailleur can handle. Grx is rated for 48/31 with 11-34. Going to 11-40 means it literally can’t make up the difference in length. Either small small combos will leave you with a floppy chain or large large combos will overextend and damage the derailleur. Since big-big should never happen anyway most people cut chain on shorter side to keep tension on derailleur more in normal gears and prevent chain slap.
I use the GRX 46-30 crank with an 11-42 XT 11 speed cassette by adding the wolf tooth roadlink DM. I use a Shimano 11 speed chain with 116 links. Shifts perfectly in all combinations.
Bike Fitness Coach says
What’s more important than this topic is to get the correct crank lengths for your inseam length.
Jeff vdD says
Looks like the “chain wrap” capacity of the GRX rear mech is 40 teeth. The needed chain wrap for 46-30/11-40 is 45 teeth, so I’m not surprised you can’t get the big-big combo to work. Even the 46f/35r combination puts you slightly outside the capacity of the rear derailleur, but only by 1 tooth. More impressive is that derailleur’s ability to accommodate the 40t cog with only an adjustment of the B screw.
For really steep climbing needs, I ran 46-30/11-40 on an 11-speed gravel setup, and plan to try 46-30/11-39 on 12-speed this summer, both with the Wolf Tooth RoadLink. That’s on SRAM AXS, which has a 36 tooth chain wrap, so I was over by 9. Rather than avoid the big ring-big cog combo, I size my chain to allow for it (but still try to avoid shifting into it).
The compromise is that the chain gets really slack in the small-small combos. My experience has been that this doesn’t really matter. First, I try to avoid those combos. Second, if I get into them, I notice it by sound and can shift out.
My overall goal is to get wide range on a gravel bike. I don’t care too much about large jumps. My travel gravel bike uses a SRAM AXS 1x mullet setup: 46t chain ring paired with 11-51 SunRace cassette (I went with this cassette because my different wheel sets all use HG freehub bodies). That gives me almost as much range as the 46-30/11-34 I usually ride with, but doesn’t come close to the 46-30/11-34 I want when things REALLY get steep (Leadville).
So if you need to go into ‘overdrive’ gearing, then why go up these hills at all, so you can say that you’ve ‘accomplished’ something?? (30×34 is ridiculous) I felt like a wimp doing the Zoncolan and Mortirolo (steady 18 to 24%) with a compact front (50/34) and 27 in the rear.. In the past, there was no such thing and all riders huffed up the climbs with 53/39 and 11/23 or 25 at most.. You can always create a gearing that will let you pedal 100 revs while going 2 km/hr but what’s the point?? Get an electric bike if it’s for the view at the top.
Paul Schack says
I agree. Derailleurs weren’t allowed on the Tour De France until 1937. Why should anyone need more than one gear combo?
Brian Nystrom says
In all the years I’ve been on RBR, it’s always been a bastion of civility. Like-minded riders come here to seek and/or offer helpful advice, not to pound their chests or criticize each other. There are plenty of other places online where that’s tolerated, but it’s not welcome here. We may have different opinions, but we have chosen to be respectful of each other. Let’s keep it that way, shall we?
Jeff vdD says
Along with no good gearing, we also used to have no reliable food supply, no indoor plumbing, and no vaccines! That’s not an argument for going back to those days. [grin]
Grinding up steep grades on too-tall gearing isn’t a misery we need to endure any more. MTBs are already geared far lower than what we’re talking about. But the use case for gravel includes a larger gearing range than what MTBs offer.
No one is talking about 100 rpm to go 2 kph. But 50-60 rpm for 5 kph is more comfortably and healthily (for the knees) done by mortal on gearing lower than 34f/27r.
…and guess what? People do still cycle into their 70’s and 80’s and lower gearing allows you to keep riding. Not everyone who rides is a 20 year old. Give us an update in 50 years and let us know how that race ready gearing is working for you on those 5 mile climbs @ 7%. 😂
Jerry Brick says
My Cx/gravel bike came equipped with a 50×34 crankset with a 32×11 cassette. I had trouble and would just tire out on long hilly rides. So I installed a 42×28 crankset years ago and have never regretted it. My climbing has improved as well as my endurance and I don’t really notice A substantial loss of top end,I’m A spinner not a grinder,and now considering lowering the gearing on my road bikes as well. Probably not as low though.
Matthew Albert says
I’ll be doing the exact same thing on my Diverge with GRX for bikepacking.
Jeff vdD says
While I totally agree that big-big should never happen, the consequences of it happening with too short a chain simply aren’t worth the risk. I’d much rather have a slack chain in small-small.
Common sense is uncommon. I’m actually toying with going smaller up front on my 1x now as my knees are starting to complain
Bike manufacturers should get this message too.
Fortunately, Specialized has on the bike I’ve chosen, and it’s worth looking at.
I’’m 71 and buying a gravel bike that I had plan the hills nearby.
I had to nix many models to find one w decent gearing for me. The bike I just chose, a 2023 Sirrus 5.0 X fit the gearing need 38, front, and 51 back., new frame design, carbon, w flat bar at a very reasonable price.