10

I recently bought a trek procaliber 9.6 and the rear cassette is lasting about 200 miles/320 km on the smallest cog.

I have a roughly 6 mile/10 km flattish ride to the trails and stay in the smallest cog all the way pretty much on the way their as it is pretty level or downhill.

Trek dealership are now saying that I will have to drive to the trails or accept the drive train will wear out that quickly. My issue is I have two other bikes that don't do this.

Has anyone come across this? Not really sure what to do as I now have a bike that can't really be used.

https://www.trekbikes.com/us/en_US/bikes/mountain-bikes/cross-country-mountain-bikes/procaliber/procaliber-9-6/p/33260/

  • Stock cassette is 10-51 Shimano SLX M7100 in 12 speed.

  • Chain is Shimano Deore M6100, 12 speed

  • Crank Shimano MT611, 30T steel ring, alloy spider, 52mm chainline

3
  • 7
    Welcome to the site - 200 miles/320 km is ridiculously short life for a cassette. Can you add any photos of your worn cassette? How's the chain? how dirty is the bike when you're riding home - is it caked in mud? Can you add photo of the front chainring teeth as well. edit lets you modify your own post.
    – Criggie
    Nov 11, 2022 at 1:54
  • Is the bike more noisy or clattery in the little 10T cog compared to any other gear ?
    – Criggie
    Nov 11, 2022 at 1:57
  • 1
    What are your two other bikes and what drivetrains do they have?
    – MaplePanda
    Nov 11, 2022 at 7:53

3 Answers 3

13

The highest/hardest gear is 10T which is not a lot of teeth-chain contact. If you're riding home with a very dirty bike that could grind into the 4~5 teeth that are meshed with your chain. If so, rinse your bike transmission of mud and dirt before riding on the road.

10T is also right on the edge of the cassette so the chain has to flex sideways the most to get over there. It could be that your indexing is slightly off allowing the chain to torque sideways on each tooth as it leaves. However I'd expect that to remove the finish from the side of the tooth, not metal from the curve of the tooth

It is possible to buy replacements for the high gear cheaper than an entire cassette, but still not "cheap" Search around locally and find something like this: https://www.thehubcyclecentre.co.nz/collections/mountain-cassettes/products/shimanocs-m91001012treplacementsprocketunits which is the 10 and 12T gears only.


One longer-term fix option is to increase the chainring size. The specs at https://www.trekbikes.com/us/en_US/bikes/mountain-bikes/cross-country-mountain-bikes/procaliber/procaliber-9-6/p/33260/ say that the bike has a 30T chainring, and can go as high as 36T.

By adding 6 more teeth, the chainring is 20% larger, so riding in 30:10 will feel the same as 36:12. This looses you some of the ultra-low gearing, because 36:51 will feel about like you're in 30:40. Do you ever use the 51 and ~44 tooth rear gears ? If not, no loss.

You'll need a longer chain too, best to replace the whole thing.

5
  • 2
    I'm waiting for a photo of the worn cassette - I anticipate visual wear but not mechanical wear.
    – Criggie
    Nov 11, 2022 at 2:11
  • 1
    Note that the price given for the sprocket seems frankly on the high side (Ok, the dollars are the NZ ones, and I imagine there is an "island tax"). Around 20€/USD seems more reasonable: r2-bike.com/…
    – Renaud
    Nov 11, 2022 at 6:23
  • 1
    A 36T chainring on a 1x MTB will be too big for most riders. That's a gear typically used by elite men, even elite women are typically only running a 34T. I'd say this is only an appropriate change if the OP is riding somewhere very flat
    – Andy P
    Nov 11, 2022 at 8:52
  • @Renaud yeah - that's why I didn't mention a price here. The cassette is $220 NZD so the two little cogs are about 25% the cost of the whole thing. Still seems like a lot given its 18% of the gears and probably around 8% of the overall mass.
    – Criggie
    Nov 11, 2022 at 9:48
  • 1
    @AndyP fair call - I used 36 cos its the biggest chainring size supported by that bike frame.
    – Criggie
    Nov 11, 2022 at 9:49
9

If you are pretty much exclusively using the 10t sprocket I’m not very surprised that it’s only lasting 320km in a mountainbike context with lots of dirt and sand.

Bigger sprockets last much longer. I think there is an exponential relationship between sprocket size and wear somewhere. Chainrings bigger than ~28t are almost all made out of aluminium and still last a looong time. On expensive cassettes the bigger sprockets are made out of aluminium or titanium because wear on them is not much of an issue.

In your 10t sprocket you should be reaching a speed of around 40km/h at 95rpm pedaling cadence. I find it hard to believe that somebody would spend considerable time on an MTB doing 40km/h (while pedaling with force). So consider using your 12t (~33km/h) and 14t (~28km/h) sprockets and raise your cadence to the typical 90–100rpm. It will spread the wear and a 14t sprocket should already wear much slower than the 10t.

Cassettes usually last around 10 000km (~4 chains) but it depends on a lot of factors like which sprockets you are using, lubrication, sand/dirt/mud/water and your power output. Usually the smallest sprocket will see the least amount of use and all others around ~1000km (ideally more of it on the bigger sprockets). So it’s conceivable that riding 320km on a 10t sprocket could be enough to wear it down.

1
  • 2
    Hypothesis: larger cogs have both less force applied (due to constant torque and longer lever arm) and more surface area to spread wear over. This is imperfect because force is not applied over the entire section of engaged chain (thus contact area does not scale with tooth count as much as one may expect), but does roughly point to the non-linear relationship you describe.
    – MaplePanda
    Nov 11, 2022 at 7:57
7

I often rant against 1× drive trains for how unsatisfactory they are for road+MTB use, and particularly those 10-teeth sprockets are simply a bit rubbish.
But they're definitely not that bad either. The 10-50t SRAM GX cassette on my enduro bike lasted perhaps 1500 km, a lot of it in the small sprockets, no problem. (I would probably have kept it a lot longer still if I hadn't replaced the entire rear wheel.) And I don't think Shimano SLX is much worse, 320 km really should be nothing for it.

So if that sprocket is in fact worn out already, there must be something else wrong. As the other answers said, riding with a very dirty chain is an obvious explanation – but that's actually something I'm also often guilty of, and again it hasn't shortened the life of my cassette like that.

What I'd strongly suspect instead is that the cassette is not dead yet, or at least wasnt killed purely by the distance of road riding. You didn't say in the question how you've came to the conclusion that it's worn out, but presumably you mean it doesn't properly shift into that gear and/or keeps skipping when riding in it? Well, that can have multiple reasons other than being worn out.

  • A dirty, rusty or worn chain will always shift worse and be more prone to skipping. And a 10-tooth sprocket makes it particular hard because the chain needs to bend around such a tight radius, so even if the other gears still work it can still be all the fault of the chain.
  • A slightly misaligned or stuck derailleur can obviously cause these problems easily too, and again it is common that this surfaces first in bad performance on the outermost sprockets.
  • As I said, 10-tooth sprockets are generally a bit rubbish. Even in prime condition they aren't really suitable for putting a lot of power down, but only as a “highway gear” for cruising along or for gaining a little extra speed on a down slope. If you regularly used this gear for out-of-the-saddle sprints, then I'm not surprised you would get chain skip.

Even if one of these were the original problem, then it is very possible that repeated skipping and/or bad shifts have by now destroyed the cassette. So one takeaway is: heed the symptoms early on – don't punish a drivetrain that starts to behave badly with brute force, instead get down to the underlying cause immediately and treat it.

And generally treat a cassette as the delicate thing that it is. I often hear MTB riders mercilessly crunching through gear shifts to the point that I almost feel bodily pain. Don't do that. Decent quality sprockets can withstand big power and last a long time if you treat them well. Always reduce the load under upshifts or multi-gear downshifts (single gear downshifts on a steep climb are ok under full load). And if you ride at strong power, use big enough cogs, at least 12 teeth. Yes, if you want to keep that riding style then that may mean you need a bigger chainring, but I'm not sure it really makes sense to ride this way.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.