2 less teeth up front?
 

i’m slower these days, and for medical reasons not trying to get faster. I do like climbing, though, and there are lots of hills around here.

the steepest climbs i regularly seek out average around 8% over sustained distances (let’s say at least 5 minutes worth) and my average cadence is consistently around 65rpm in such situations. At 6%, cadence looks to average more like 75rpm. I’m not a spinner, but 80rpm is probably my natural comfortable tempo cruise, per many many flat uninterrupted segment records. I keep my HR to 110 average or so during climbs, 100-130 absolute max.

i love my current road bike, no desire to change much, and it’s 12 speed dura ace di2, currently with 52/36 up front and 11-34 in the back. Chainrings have around 15k miles on them, seem fine, but I’m swapping the crank out for one with a different power meter as soon as it gets back from 4iiiiiiiiii in Canada. So, for the brain trust, given regular climbs that have me at 65rpm and no desire to push it harder, any advantage to going 50/34 up front? I love bombing descents at the same power levels or higher than i go up them, but it’s not like 52-50 is a huge difference. 36-34 is all of 6% steeper than 34-34, so i suppose one could simply say my cadence for the same effort and power would be 69rpm instead of 65. Seems almost significant. I DO enjoy climbing 6% more than 8%, but most of the nice rides have 8% sustained stretches.

I think 2 teeth is not enough to make a material (significant) difference.

I was also thinking of swapping out my new bike’s 52-36 for a 50-34, which is what I have on the old bike.

But the new bike’s low gear is 36/34, versus old bike’s 34/28, so I’m already getting a 13% lower low gear.

I guess it comes down to what cadences you can tolerate. Today, I in-the-saddle mashed up a grade that was 14-20%, barely staying above 5mph. Cadence was in the 50s, which seemed ok for a few minutes.

I assume you meant insignificant? I think you’d notice it.

On climbs I noticed the difference between the 36 and 34 front rings, but I'm not all that strong and on hills I use every bit of assistance I can reasonably afford (except a motor).

34/36 (assuming 700c wheel, 28mm tire) = 28 gear inches where 34/34 = 27 so not much change but at least in the right direction.

Doing the opposite (add four teeth in back, where possible) would be more effective = 25; adding just two (36/36) = 27.

You should notice a difference when on the 34-34 combo and climbing hills. On whether or not it's significant, it's subjective in my opinion.

Since you already plan on changing your chainrings, try it!

GRX FC-RX820 crankset with 48 | 31 chain rings?

The change from 52/36 to 50/34 is not going to be life changing. But in the low gear it’s a difference of about 5 rpm, for a given speed.

Going up a hard hill, I think you will definitely notice the difference between a cadence of 65 rpm and 70rpm

On the top end the small difference between a 50/11, and a 52/11 is not going to hold you back, unless you plan to get your UCI license.

Given that the change costs nothing, in that you’re going to change cranksets anyway, it seems a pretty easy decision to go with the 50/34.

This ‘might’ be an issue…but maybe not. A few years ago I wanted to change one of my bikes from the usual 52-42 chainring setup to a 54-38 combination. I got everything reassembled and discovered that now with a larger circumference big ring and smaller circumference small ring, that the geometric angle of the chain from the small ring back to the cassette smaller two or three gears caused the chain to catch on the larger ring. I couldn’t get it to work and had to change back to the original setup. Here’s a crude drawing of what I mean.

https://cimg9.ibsrv.net/gimg/bikefor...af185a069.jpeg


Dan

I changed to 50's on everything. I use more of the cassette and it works just fine for me.
FWIW of course YMMV

Soon to be 72 here. I'm trying very hard to keep ALL my front teeth for as long as possible! ) (But I am backing off to 50 on my bikes. All are triples. Most have 24 tooth inside rings. FWs and cassettes up to 28 teeth.)

That's one of the reason why you usually change both IMO when you decide to upsize or downsize one of the two. Also, you're not supposed to cross-chain #stopthechainsuffering.

If 36x34 is low enough for your steepest climbs, then changing rings isn't going to accomplish anything.

seems like consensus is that it’s worth the difference. it’s a relatively inexpensive but not free change, in that i already have a spare DA crankset with the 52/36 on it from a big sale a while back. but picking up the 50/34 rings and selling the 52/36 won’t be a big investment.

and one reputable dissenting opinion!

If you're not thinking about going faster, I don't think of fewer teeth up front as a way to limit cadence: cadence in your situation is a red herring. Cadence isn't your limiter, it sounds like HR is your limiter. A smaller chainring is a way to allow you to go slower while still balancing. Depending on your medical condition, you're trying to keep your HR below 130 max -- how close do you come to this on those sustained 8% climbs? Since a lower gear allows you to go more slowly, you'll gain a little margin of error (about 5%) in keeping your HR lower. That 5% difference is *roughly* like getting another rear cog that's a couple of teeth larger (and sort of making your smallest cog the equivalent of about half a tooth larger). If you're *not* bumping up against your max HR, then there's not much to be gained (or to be lost) from switching, but the decision isn't about the *average* effect (which is kinda small) but at the margin (where it can be more important).

not looking to go faster, because as you note that would require more power (regardless of the gearing) and thus a higher HR.

i don’t really bump up against the limit at 6%, at 8%, approach it at times and the ability to go a bit slower (balance is fine) without cadence dropping uncomfortably low (50rpm?) would be nice. let’s just say it takes 200w at 120BPM to comfortably climb a grade, i believe the 6% lower low gear might allow an equally comfortable climb at 190w. same cadence, climbing slower, lower HR. or, alternately, higher cadence, same speed, same HR.

Saw the post title and thought "Howths your Shpeech ?".

https://cimg8.ibsrv.net/gimg/bikefor...ee14acf396.gif

So are you talking about this happening in your 36x34, or in other gears?

I had the same thought before I bothered to get deeper than the title.

Ditto.

When I went 2X on my 20" folder, I chose 50/34 because I needed more low than I needed high. 34T is the smallest I can go on 110mm BCD. That said, if the BCDs are compatible, if you go 50/34 and miss the 52, you might try putting that on (I'd recommend leaving the chain a couple links longer than you need on 50T at first to allow this possibility) and see if the FD works fine. While modern setups max at 16T difference, there are tons of folks on here that have run 20T difference and shifted fine, and that was with vintage flat rings with no shift pins or ramps on the large ring. What does need to be compatible if swapping out is maintaining the same offset in the ring, whether it is totally flat, or dished to offset the teeth further outboard than the mounts at the spider.

it definitely occurred to me to try 52/34. Many say it works despite not being officially supported.

I’m pretty much always in 36x34 when climbing anything over 6%, which is fairly often. The last time i looked at the shimano eTube app or golden cheetah i think it was my second most used gear after 52x14.