Gus90

I've seen some previous posts regarding this but I am still confused.

If most of my riding is going to be on bike trails that are relatively flat with some rolling hills or bridges over roadways, would I be better off putting a compact crank on with a 50/34 set up or stick with the 46/36 that the bike came with? I could see myself participating in a cx race some day but for now it's not an issue.

I looked at Sheldon Brown's website. At any given RPM the speed difference is about 2-3 mph difference in each cog between the 50 vs the 46 crank. I have been riding a compact on my current CX and I do notice a pretty big gap when shifting from the 50 to the 34 ring when climbing. According to Sheldon, it's a 47.1% gap. At 90RPM the 50/11 gives a speed of 33.1mph. The 46/36 has a 27.8% gap between the rings and the top speed at 90RPM in 46/11 is 30.4mph.

I'm just trying to decide if I'd prefer a little faster speeds or I guess smoother or more efficient transitions when climbing and shifting between the rings. My cassette is an 11-speed 11-28. Or am I way off and it's just that my climbing skills when it comes to how to properly shift when approaching a climb need a lot more work.

FBinNY 

Only you can know the answer.

If the current high gear is stisfactory to your needs, then stay with it. If you find yourself riding in high and wishing for one more shift higher (about one step is all your going to get from a change from 46 to 50t) then make the change. Ofhand I'd say you shouldn't need it, but only your hairdresser knows for sure.

Gus90

Thanks for the advice. I just noticed a recent post by someone else that basically asked the same question. I should have caught that earlier. Now I feel stupid for starting another thread.

krobinson103

Try this. The next big downhill don't shift all the way down the cassette and see how it feels. If it doesn't bother you then the chain ring swap will probably be worth it.

thisisbenji

I personally use a compact.

The reason being that a frequently take my cyclocross bike on group rides out on the road and I'v been known to show up to a crit. or two on my cyclocross bike.

If I strictly rode the thing on gravel trails I'm sure I would be fine with cyclocross gearing.

Barrettscv 

If you are using a 11-2X cassette and can hold a fast cadence, the bigger chainring is not needed. A 90 rpm cadence should not be used as a maximum rpm, unless you stay below that cadence speed 99% of the time.

Use this gear calculator: Mike Sherman's Bicycle Gear Calculator


It allows you to put in a range, I use 87-100 rpm as a cadence range.

It also displays a bar graph, this is a better display of data than using numbers.

I also use this calculator when comparing two divetrains: kstoerz.com | visual drivetrain comparison tool

DirtRoadRunner

A 46 front is really nice for a non-racing gravel bike. I have a 46/34 crank and 11-36 cassette on my gravel bike. With the 46, I only spin it out at 30+ mph, which is pretty fast for a gravel road. On faster, paved descents, I'll hit 45+, in which case I'd be spinning out a 50/11 anyway, so there is really very little (if any) speed advantage to running a 50t big ring, unless are a pretty strong rider.

The other nice thing with the 46 is that I can stay in it until my ground speed drops to about 10 mph, before dropping into the 34. So you effectivley can ride, at a decent cadeance (~75-100), from 10 mph to 30 mph in the same chainring. This really reduces the amount of front shifting.

For flatter rides, a 36t small ring is probably fine, but it is not OK for hilly areas unless you are a great climber. We have a lot of 20+% sustained grades on the gravel I ride, which is hard for me to even push a 34/36 combo up when I'm getting tired. I finally bit the bullet and ordered a Sugino OX801D with the 46/30 gearing, which I think should be perfect for a hilly gravel bike.

Gus90

Excellent, this is both great information and helps a lot. Thank you.

fietsbob

I fit a Triple, like my touring bike .

Andy_K 

This would be the deciding factor for me. I find that with a 50-34 I'm wanting to make the transition between the big ring and the small ring pretty frequently in any urban setting, and while I haven't used a 50-34 offroad, I would expect it to be even more common. I've got a 46-34 on the bike that I use for gravel grinding and CX racing. For gravel grinding, 46-34 is just about perfect. I expected to want to put the 36T ring back on for racing, but it turns out that in most situations I can race in the big ring and leaving the 34T on there gives me an even lower bailout gear when I need one for a long, steep hill.

The other factor to consider here is that you already have the 46-36 crankset, and new 50T rings are generally pretty expensive. You might be able to find one cheap at a co-op, but as previously discussed the gain is minimal at best and negative at worst. On the other hand, you can get a 34T ring for less than $15 so that's a more reasonable investment if you want to make your crankset better suited to all-around riding.