Best Chainring Size for XC Racing

I’ve typically used a 32 tooth chainring on my cross-country bike, but this year I switched to a 34 tooth and found the additional speed really helpful for Outside Workouts when I’ve “ran out of climb” on a route and had to hold power over a flat or downhill section.

More recently I’ve been riding a 36t chainring, and I’m really liking it! The added speed is a big help for TrainerRoad Outside Workouts, I haven’t come across too many instances where I’m out of gears, and the inner nerd in me is excited that I am experiencing less drivetrain friction since my chain doesn’t have to bend around as tight of an arc (I’m just telling myself that’s at least a watt… :wink:)

My FTP is around 310 and most of the terrain in our region is at or below 10% with very steep sections only being very occasional and brief, so it actually seems like something I could get used to using for local riding and most races.

So I guess my point is, I never ran a larger chainring before, but I actually like it. What size chainring do you run, why, and have you tried a larger size?

  • 28 tooth
  • 30 tooth
  • 32 tooth
  • 34 tooth
  • 36 tooth
  • 38 tooth

0 voters

Full transparency: Expect me to run the smallest chainring I can find at Singletrack 6 in 2021 if we go straight up those darn ski hills again :joy:

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This should generate some good discussion. The advent of the 10-52 rear cassette really opens up the option of moving to a bigger ring up front as well knowing the bailout is still there.

When I’ve gone back and forth between a 32 and a 34t up front on the same local trails, I am faster on the 34t. However I did find I’m working harder so have to have the fitness to back it up.

The efficiency argument is interesting. For endurance events it will again be a decision about trade offs, more efficient front ring from a chain wrap stand point vs a more efficient cadence on the long climbs…

For Leadville I ran the popular 32t with a 10-50 Eagle rear cassette. It seemed fine but come Powerline it might be nice to be able to go lower. The question becomes whether to stay at 32t with a 10-52 cassette or jump up to 34t since it might be more efficient…

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Great point on the rear gearing. I am running a 10-50 rear cassette.

In terms of gearing for Leadville, Powerline is just SO hard. Even a 28 would feel like not enough, and that’s coming from somebody who rode Powerline in reportedly the best condition it has ever been.

I think a 10-52 or 10-51 could be good for Leadville. I was in my 50 for the steep part of columbine where it turns to a Jeep Trail, and all of Powerline, but other than that, I bet the vast majority of my day in terms of time was spent in my smallest 4 cogs.

Another thing to consider is clearance of frame and obstacles. Assuming your frame can clear it and that’s no issue, if you are on a rocky course, a bigger chainring could mean you smash a rock or log when you otherwise wouldn’t. On my SB130 I have a OneUp chainguide / bashguard combo that works well with a 34t, but I’ve heard of pro enduro racers judging their chainring size entirely off of whether or not they need a bit more clearance to not smash their bashguard and lose momentum in a critical section.

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As cassette sizes have gone up, I’ve increased my chainring size accordingly. Currently I’m on a 34t on the Chameleon, because a 36t doesn’t clear the chainstay and I regularly spin out on even modest -1% grades.

I agree that for something like Leadville, the benefit of having a 28t or 30t up front far out weighs any drawbacks given how much time is spent on those two climbs.

Otherwise, I’m planning on a 36t or 38t ring on the 2021 race bike that I’ll be getting eventually. Even the steepest sustained climbs in my area of 13-15% are still sub-threshold in the lowest gear for those ratios (either 51t or 52t in the back)

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I train & race on a 34t chainring but I’ve also wondered about sizing up to a 36. On the road you soon run out of gears if your pushing on and it’s only of the steepest of climbs I might wish for a 34 again.
I did wonder how a 36t paired with a 10-52 cassette might ride like as that could be perfect.

I guess if you’re not climbing up super steep stuff and with your fitness a 36 or 38 shouldn’t be a problem.

I use a 34t chainring and have just reluctantly upgraded my xc hardtail with an eagle 11-50 cassette. Im not convinced that having a “bailout” gear for racing is necessary or practical (a 10 tooth jump from the 42 is enormous) but an 11 speed upgrade was the same price as the 12, so i went for the eagle.

With the huge jump between 42 and 50 (or now 52) in mind, im not convinced that changing chainring size BECAUSE of that wider range cassette makes any sense.

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Looking at the AXS data from the one race of the year:

I was briefly in the 34x36, but mostly used 34x32 as the lowest gear, with the 34x19 as my favorite gear.

This matches a lot of my recent intervals as well.

I really wish Shimano had manufactured the tight-range light-weight 10-45t 11speed cassette that they said they would here: https://bike.shimano.com/en-US/information/news/new-shimano-xtr-m9100-series-mountain-bike-components-debut-new-.html

funny you should mention this

Shimano do make a 12 speed 10-45 that I think would be the ultimate mtb cassette for 1x systems. Unfortunately I couldn’t justify the price involved with upgrading my wheels to a microspline freehub. Still hoping they might make a 11-45 cassette for normal freehubs (like sram did with the NX cassette that I have)

https://www.rosebikes.co.uk/shimano-xtr-cs-m9110-wide-flange-11-speed-cassette-2669181

A few places listing it but none in stock…and not cheap!

It’s never been in stock anywhere. I don’t know of a single person who has ever had one unfortunately.

I run a 34 almost always but did go to a 32 at Leadville. FTP is 340ish during race season.

I’ve read that Nino runs a 36/38 not necessarily for the bigger gears but to run a straighter chain line to his ideal gearing. Could be something to consider for those national level races you compete at when efficiency matters more than versatility for a particular course. (I’m sure other riders do other things but when you are the champ you get a lot of articles written about your gear so people like me can read about it, hence the Nino reference).

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Slow traffic week, so I’ll play.

I’ve still got a 2x on the front of my aluminum hardtail with base OEM fork. I live, generically, in the midwest. 36?x tiny up front, and whatever the SRAM 10spd OEM cassette is… I’ve spent so little time in the inner ring (even when the MTB was set up to pull two kids in the chariot on pavement) that the anodized surface is still about 95%.

This thread topic has too many variables to be discussed in a thread (words). It should be a multidimensional chart or table including geography (including altitude) , focus (XC Oly, XC Marathon, Leadville), rider fitness, rider weight etc. This requires some sort of mathematical formula that I wouldn’t be able to complete, anyway.

Reminds me of “gravel tires and tire pressure.” Ok, so you’re not running 25mms tubulars, but passed that, we know nothing. What someone mounts to ride Trans Iowa vs Kanza vs Colorado fire road vs someone else’s chipseal century vary so much. Oh, and throw in the fact that I’m damn near 200lbs (with hamfisted handling, according to my second favorite shopee) and Jonathan Lee looks like… [lightweight joke censored]… Throw in anyone who values comfort over speed, and all the calculations are turned sideways. Yeah, just put a google doc out there with about 15 variables.

I used to run a 34 with a 11-46 XT rear but that was when I had a 308 FTP…I raced that at Sea Otter, Tahoe Trail 100, and Carson Off Road. But those were my younger/stronger years. Now that I am 50+ I have 32 with 10-51 XT, literally feel like I could climb a wall in the 32/51 combo. I could see running a 34 or 36 on flatter courses to have more top end and straighter chainline.

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Usually 34t on my XC bike, and I prefer the 12s Shimano 10-45 cassette. Briefly used a 36t when I was at peak fitness this spring and chasing KOMs. My rides are often heavy on pavement and/or bike path (to/from).

The short cage XTR derailleur has been flawless for me, but my experiences with the longer cage XT derailleur and XT and SLX 10-51 cassettes have been pretty mediocre. Even dropped the coin last week to go to the short cage XTR on the enduro bike too (and 10-45). That ones also running a 34t.

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Switched to 36t (10-50) before this summer and I’ve loved it so far! Never going back, at least not until I’m facing a race with super steep hills or anything like that.

On my scott spark rc with quarq xx1 PM I have 32 and 36 oval chainrings(from garbaruk) with xo1 10-50cassete.
for majority of xco courses it’s ok 36 but for long mountain xcm, my pick it’s 32.

for training aswell I prefer 36 but this week i’ve discovered that I cannot swap the chainrings anymore because of SRAM…
I have to pull out the right crank but I cannot unscrew that f’king bolt !!! I tried with an alain key with long leverage but nothing :))

It’s worth bearing I’m mind your physiology also. I run 36 oval on a Spark (so 34/36) with a GX 10-50. I’m good at big gears on the flat, so the ability to run at 10/36 when I’ve topped a climb really speeds me up. I’ve not met anything in the UK yet I can’t climb up with this setup, but - with a big FTP increase this year - I did notice in a recent race I was pulling away from people on short steep and Rooty single track climbs and did wonder whether some additional strength plus higher gearing helped.

Switched from a 32 x 10-50 to a 34 x 10-52 this year. I like the 34 for training outside on gravel. I don’t need the 52 very often but it’s nice to have when I do. With the 34 up front the 52 is basically my old 50.

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Sounds like the bolt is seized a bit. Try spraying some WD-40 down there, let it sit for a couple minutes, then try again. Or take it to a bike shop.

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