Larger chainrings and larger cogs are more efficient and save watts.
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I spend most of my time on singlespeeds. I recently switched from 32 to 34, which also required a larger cog to get the equivalent gearing. I don’t know if there is any measurable difference, but it feels slightly smoother. The downsides are a slight loss in ground clearance and a very small weight penalty.
I’ve always ran a 30t with a 10-42 cassette.
I recently expected to keep the eagle that came on a new bike, so I ordered a 32t ring instead. I ended up hating the eagle and going back to 11sp 10-42.
I’m really enjoying the 32t and haven’t ran out of gear on a climb yet.
Does anyone have the data on how many watts are saved between 32T to 34T to 36T assuming the remainder of the set up is the same?
I’ve seen some broader discussion regarding running in the small vs large chainring up front on a road bike, but that is a much larger difference in number of teeth.
There was also some discussion about SRAM 10t rear cog on the 12 speed AXS groups losing efficiency due to the very small size and tight bend of the chain so some teams have gone away from it. But a small 10t is really at the pointy end of the spectrum.
It would be really interesting to know what the watts difference is at for the mtb rings.
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I wasn’t able to find anything on MTB specifically but the two links below compare gear ratios in a 2x setup and the second link looks at a 1x set up (more road/gravel gearing though).
I think the biggest gains aren’t from less chain wrap at the front but rather by a better chainline or bigger gear in the rear. Based on that second link there is much more friction in the small side of the cassette than the large side in a 1x setup. 48x21 costs you about 10 watts while a 48x10 costs you 18. So going bigger in the front will probably save you 0.5-1W from the front and then maybe 2W from using a larger cog in the rear.
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I did the exact same.
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What did you end up hating about eagle?
30t Oval with 10-42 11 speed.
Like others I would probably go a larger chain ring if I had a wider range cassette available. Looked at the Sunrace cassette but was put of by the reviews.
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It was very very finicky to setup. It was just gx though so it’s well known for that.
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I wouldn’t think you ever would as the difference between a 30/42 and a 32/42 is minimal. It’s on the other end 30/10 vs. 32/10 where the difference is more noticeable/meaningful.
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Based on this chart and making some hopefully reasonable assumptions, you are probably looking at around 1-2w depending on the chainline between a 32t and a 36t
A 2.0 ratio corresponds to a 36t/18, 34t/17 or 32t/16 which is going to be close to the middle of the chainline for mtb.
Which isn’t bad tbh. An extra watt or two average over the course of an XC race is probably ~5 seconds.
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So when talking about chain wrap or chainline friction losses. How does that scale to either RPMs or chain tension?
E.g. say that 2 watt gap between the 11 and 10 tooth cogs in that graph at 100 RPM and 250 watts. Does it scale linearly with both? So at 110 RPM is it 2.2? Or in an all out sprint to the line at 1500 watts and 115 RPM is it now 10+ watts?
I run a 28t and may go to a 30t with the 52t cassette. However full disclosure. I am old 60yrs and have 277ftp done outdoors this July using the TR 8 Minute Test Outdoors. I live in the second most mountains region in the Spain loaded with Cat 2 climbs and one HC. And while we are on the coast if you want to do any serious cycling road or MTB you have to embrace the climb.
I only do two races a year a UCI S1 MTB 4 day Stage race 5700m climbing and a MTB Ultra 3 day stage race 340km 8000m climbing both races end on the beach but you must first climb a massive moutain to get there with 100+kms on your legs at the start of the climb its tough.
I recently switched to the 28t with the Eagle50t cassete. For the 3 day Ultra it helped me immensely with the 8000m of climbing.
I felt undergeared on two occasions in the flats of the UCI MTB 4 day stage race but I was good on all climbs. Well minus one 20min techincal climb.
TR has helped as well and post quarantine this summer I did SSBII and Sustain Power all Outdoor workouts and it was great!
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I’ll preface my response with this fact. I’m a much bigger dude than @Jonathan. I’m 6’2" and race weight is ~187 lbs.
My race bike is wearing a 34T front ring with 10-50 out back. I’ve tried 32T and while ground clearance is improved I didn’t feel I needed to go that low for any climbs that I would encounter in normal riding. I’ve raced in Southern Mo. in the Ozarks where it gets pretty climby and the 34 has served me well. For short races or reasonably flat ones (less than 6K ft.) I’d stick with the 34T. If I were doing more sustained climbs (leadville) I’d drop back to 32. I can’t see the need to go to a 36. Too much risk of hitting a tooth on a log or rock with such little benefit. Even on a fire road or gravel I’ve seldom used 34-10.
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What size cassette do you run day to day? 10-52?
I’m very interested in the thoughts and experiences here. I’ve just gone from a 32 to a 30T, but I run 11-42 10 speed rear. I never ran out of gears previously but I did use all my gears a few times. I have a much lower speed capability on the flat now.
My A race is a 100km XCM. I’ve got a bunch of XCO races over summer lined up after so I might experiment with a 32 and 34.
Get a 34 oval and have both!
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Some qualification - almost all of my riding is on short punchy hills (let’s say 200 feet in elevation gain/drop). I very seldom have long downhills, and it is always in the woods and somewhat twisty so pedaling isn’t relevant as it is hard enough to just stay off the brakes. I don’t think I’ve ever used the 2-3 smallest cogs in the back. That said, 30 up front and 11-42 in the back is just about perfect. It is just missing the complete bailout for when my legs are fried. I have another bike with 32 up front and 10-50 in the back. I’m not sure I’ve ever needed the 50 tooth cog. I suppose I could bump that bike up to a 34 or 36 and be okay, but I don’t need any more top end anyway.
I have been eyeing up oval. Would 34T be the spec to choose? Any experience with chain ring wear? One comment that slowed me from installing an oval instead of the 30T round was that it would wear the chain ring more quickly and become noisy. I’m not sure how valid that is or not, I see a heap of racers online using them, but no-one I’ve met face to face has one on yet for me to eyeball.
Good topic.
I run a 32, because it seems to be the best of both worlds, I don’t spin out ever and have almost enough gears uphill. I tried a 30, I did NOT like it because I actually found some instances on trails where I wanted a taller gear, admittedly that was rare to spin out, but for PR level efforts I did not enjoy it. I’ve also used a 34 and liked it although I found that it was a little tall for most of the tougher single track climbs.
Another aspect of this decision is pedaling efficiency with regards to full suspension bikes. At sag, most bikes are optimized for a 32-34 chain ring - I suspect. Some smaller chain rings may have a noticeable affect on pedaling on certain suspension layouts. This was most obvious to me when I ran the 30t chain ring on a Horst Link bike, it seemed to bob more than with the 32t ring. In other words the gear combination, especially the chain ring has a direct relation to the affects of a bikes anti-squat.