It's a trailbike with Shimano 12speed drivetrain.
I'd like to purchase the Wolf Tooth Powertrac chainring to have a go at oval chainring for the first time. At the same time I'm dropping from 175mm to 165mm crankarms(primarily for ground clearance).
Will both of these changes mean I can confidently go from a 32T to a 34T chainring and have no added issues when riding uphill?
I run an XT 10-51T cassette today and the 32T chainring has been more than sufficient for what I ride in terms of uphill, and I'd like to at least have the same capability uphill, yet also a slightly better speed on the straights and down.
I've never tried shorter cranks nor oval chainring, so for me so far this is just theory which is why I'm asking. I just don't want to end up with much less speed on straights and downhill, which is why I was thinking of upping to a 34T chainring(there's room for a 36T on my bike so no clearance issues, and yes I know an oval will need slightly more room)
Fresh sign on and asking big questions. I dig it. Short crank, oval ring proponent here. I went down to 155s from 170s and kept the same ring size as the stock round. DH, straight line, and climbing feel more efficient. Good reference is this lil vid from Absolute Black https://www.youtube.com/watch?v=5Ywg4Rd0jTM
There's some good intel to be had in that one. One bit someone will bring up is that generally speaking you want to go down a ring size when you drop crank length. Personally, I didn't find much of an issue back when I went down to 165s from 175s decades ago, and I see the point if going to 155 or less, but I found the oval in the same count to perform just fine for me. As always, YMMV though.
The video you linked only isolated chainring size specifically, so it won't help me with my theory.
This is what Wolf Tooth claims with their oval chainrings:
- A 34T oval chainring behaves like a 36T chainring when you want power, while behaving like a 32T chainring when you’re climbing.
This is what got me thinking because they clearly state an oval 34T will behave like a 32T when you're climbing. When it comes to crankarm length I see now how shorter would create less power so maybe a 32T oval ring with 165mm cranks will be somewhat similar uphill compared to 32T round ring and 175mm cranks(?)
I am adding a new cassette and chain into the equation as well, so it is a slight expense, which means I'd like to land on the best suited chainring on the first go.
Keep the same size ring, it effectively gears you up for a 1/3 of a rotation (as explained above). Although from experience - oval chainrings don’t really have a huge benefit in MTB, smoother pedalling in uphill tech is the main thing. I run rotor cranks on all my bikes (road/mtb) and have done for 10 years +. It’s a nice feeling, but not really ground breaking. 165mm cranks are brilliant though, clearance, less hip articulation Is a massive one for me.
A rule I try to live by on bike setup is changing one variable at a time. You could try the shorter cranks on their own, see what you learn, what's different, what's weird, etc and then add in an oval ring later. That way it's easier to parse what the benefit is, and what the problem is (if there is one).
Leave it to a robot to reply with logic.
I have used oval rings in the past and found that they smoothed out my pedal stroke a bit. It wasn't game changing by any means though. Switching back to round rings felt weird for about 2 minutes and then completely normal again.
I also tried 165mm cranks after using 175mm for basically forever. The ground clearance was nice as I'm on the East Coast and our trails require you to pedal through rocks and roots. BUT, one thing I wasn't anticipating was the effect of raising my seat height to compensate for the shorter cranks. This raised my center of gravity by a noticeable degree, causing me to feel "tippy" particularly in low speed tech. I tried the 165s for a full summer before deciding they weren't for me.
Ultimately, I ended up with 170mm and that's been a great compromise for me in my terrain.
Oh that is interesting about the balance issue. I have been wanting to switch to shorter cranks for a while, partly because it would allow me to run a 240 instead of a 210 dropper. But also I’m too cheep to just buy new cranks.
@Pedal Bob i have used oval rings before. Didn’t make a huge difference to me. Luckily it’s a cheep change to make and I really didn’t see any downsides of it either. I agree with Mr robot tho. I’d do cranks first and then after getting the feel of those then throw on the new ring.
Yeah, I’ve got pretty long legs so my saddle is already way up there.
I run an oval ring in the Enduro bike. I like it for the horrid steep spin out or loop out fire road climbs, as it makes them easier. I use the same size ring - I have temporarily swapped back to a round ring and didn't like it as much for the climbs (though I've not bothered changing the round ring on the trail bike). I'd say it's smoother pedaling but you lose some of that ability to power over steep ledges as in effect you're in a higher gear for that section of the stroke. I would certainly not go up a chainring size unless your climbs aren't that bad and you have gears spare. If you drop crank length, you're also in effect increasing your gearing, so for smaller cranks you need a smaller chain ring
I used oval rings for a while. They made sense since you are effectively using a smaller ring when you are weakest (top and bottom of the pedal stroke), and a larger ring when you are strongest. I felt like they helped most at really low cadences, like you might find on a mountain bike, or in a really low position with hip impingement, like on a TT bike. But the independent studies don't show any benefit. There is some magic going on with ankle flexion that mean an oval ring isn't discernibly better than round in terms of power production. Did they test at 50 rpm? I don't know.
Anyway, the studies showing oval rings are magic are all funded by companies that make oval rings.
The good news is that those same pesky scientists that ruined my oval vibe have also shown that crank length doesn't matter for power production as long as you stay within a reasonable range. So go shorter. As others have mentioned, drop your ring size. You have less torque with a shorter crank, but you make up for that with higher cadence at the same foot speed. Having said that, I definitely feel different riding 160s on the e-bike if the assist is off. Fortunately, there is a solution for that under my left thumb.
Raised center of gravity by a degree, does that mean more weight towards the front or back(you said low speed tech but did not mention if this was on the flat or uphill)?
My bodyweight is already too much back given the geo on my bike, so if my weight will be moved more forward that will actually help in the uphills given my bike has a light frontend (75.5 degree seat tube angle). It's got a flip chip so I can change geo by half a degree if I have to.
Maybe degree wasn't the right word choice here. I meant the increase in saddle height was enough to be noticeable and noticeable enough that I didn't like it.
Our trails here are techy going up, down, or flat, but the tippy sensation I referred to was most apparent on flatter, pedally sections of techy trail.
From that other crank thread: https://www.vitalmtb.com/forums/hub/mountain-bike-crank-length-discussion?page=1
""ideal crank arm length should be 20.5% of leg length or 41% of tibia length."
That matches what Canfield says. "Geared trail/AM/enduro bike: 20% to 20.5% of inseam length". https://canfieldbikes.com/pages/mtb-crank-chainring-faq-canfield-bikes
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With that theory I'm landing pretty much around 170mm and 175mm is currently on the bike. Just more info telling me not to go for 165mm, and now I'm not even sure I want to bother just for a 5mm change, because it does cost money as well.
Given crank length became a topic all of a sudden, must really just mean most people are shorter than me, thus having a valid need for something else. At 184cm tall I think I'm just going to put the whole crank thing on the backburner and just run with stock 175mm cranks.
Now it actually makes more sense to try an oval chainring though. An aid for all the techy uphills, as well as me being a flattie user.
I agree with this. My general thought is you don't need the same crank size as me at 168cm (5'6"). You're tall. My calculator told me you should probably have a 170. I doubt you'll notice much different in 5mm. Most of my tall friends like ~170 or 175.
That said I am selling an X0 transmission crankset (and a threaded BB ) at 170 that'll go online this spring if you're in the market.
I like the oval primarily as I find I get smoother traction on tech climbs. I'm also a flat pedal masher so it might help that. One of my fastest climbing partners didn't jive with an oval ring. Its not a mind blowing difference, but its fun to try new things. But at the end of the day we need to remember its all just riding a bike.
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