heirfaus

Hi everyone,

I've made so much progress in my bike setup due to the help of this forum. Thanks to everyone who has contributed.

Today my question is about chainring selection. I just put on a FSA Energy compact with a 50/34 (shimano 9 in the rear). I've noticed now after about 30 miles of commuting I am not using my smaller cogs in the rear. On my small chainring I use the first 5 when taking off and then shift to the large chainring because the chain rubs on the large chain ring if I try to use 34/15(6th rear gear) combination. I find after shifting the front I still never touch the last four rear cogs. In order to make use of the whole range I am going to get a smaller large chain ring.

Is a 48 sufficient to move my cog use or do I need to use a 46?

Thanks,
Chris

FBinNY 

I don't think you'll see any real change, and a quick reading of your post tells me that you'd be happier with a much smaller outer ring, most likely in the range of 40 to 44t.

Do the math and divide the current outer ring by the smallest sprocket you use, then multiply by the smallest sprocket you have to see what size ring would give you an equivalent gear. ie, 50/16 x 12 = 37.5. That's probably too extreme and you wnat to leave some upside on high gear for those gentle downslopes or tailwinds.

If math isn't your forte, use a gear chart like this one, to see the big picture of your gearing and choices.

Chris_W

The 46 tooth is just under 10% smaller than the 50 tooth. The difference between most of the cogs in your cassette is probably about 10%. Therefore, switching to a 46 tooth will result in you using one cog smaller on the cassette for the same speed and cadence as with the 50 tooth. The 48 tooth would put you about halfway towards using one cog smaller.

I find that having a 50 tooth ring is too large for my style, which involves using a high cadence and not having the fitness of a professional rider. I've therefore got a 46 or 48 tooth big ring on my racing bikes, and find that this gives a better chainline and requires to shift between the large and small ring far less often. My cassette is a 12-28, and I can still pedal the 48-12 gear at up to over 70 kph (45 mph). Your riding style may warrant a different solution.

fietsbob

44:11 and 48:12 is the same gear as 52:13, just arrived at by a different combintion, it's still 4:1

dabac

For a high mileage bike you might consider looking for a cassette with a bigger smallest sprocket instead. Basically more teeth equals better durability. Use the gear calculator of your choice and play with the numbers.

Looigi

Basically, you only use the big ring and small cogs when you're going really fast, usually on a down grade, or a short maximal effort on the level. That's what they are there for. It's up to you to use them for that purpose.

BCRider

Welcome to the world of "riding reality". While it's true that racers will use their 53/12 combo on enough occasions to justify carrying these sprockets around I think it's safe to say that a lot of day to day riders will never use that combo of gearing. In my case if I'm on a downhill where it would be suitable to go even faster by shifting to the 53/12 I'm more than content to sit back and let Mother Nature and Grandpa Gravity do the work for me while I gander about enjoying the passing scenery and begin to worry about stopping at the bottom before I rush out into cross traffic

This bit of human energy reality may explain why even my "road" bikes both have MTB cranksets with 44/32/22 ring and 12-28 cassetes. I end up using the smaller sprockets and get a better chainline yet the 44/12 combo is still used generally only when I've got a strong tail wind. The rest of the time I'm two steps up on the 14t. For us older and "trying to stay in shape" codgers I'm finding that it's a nice setup.

So all in all if you find that you're not using the smaller rear sprockets then there really is no shame in switching to smaller rings on the front in order to both improve the chainline and to gain a wider range of USEABLE gearing options.

As for shifting with each stop that's something you want to get past. Bicycles aren't like cars where you need to spin at the best speed to get the power. Instead we are more like trains where there's one gearing and it's more normal to just put the pressure on the pedals and to ease back up to speed. Having said this I will also admit to gearing down as I approach some intersections so that I can make a snappier crossing and expose myself to traffic for a shorter time. Generally I prefer to do that with a quicker double shift of the rear derailleur. I find that the rear shifts are quicker to do. I reserve shifts of the front setup for times when I approach big hills where I know I'll be on the smaller front ring for a while.

And before anyone jumps on the use of MTB gearing for a road bike I'll mention that I can easily get up to around 55 to 58 kph or around 35 mph using the top gear setting. I've done so for giggles on a slight downhill while pedalling like a madman. And I'm still not over spinning at that speed. But I hit the "wall" with the wind. Obviously a racer would laugh at me. But I find there's more folks like me than there are racers or extra strong riders that can actually USE the top gear settings frequently. So I really don't see that setting up a bike with gearing that the rider can fully us is such a styling faux pas.

scruggle

Hi Chris, similar boat here.

At risk of repetition, 50x12 is very close to 46x11.

If you currently never touch your four rear cogs while in the big ring I am not sure you'll find a cassette to solve that, unless you are jumping from a 11-[whatever] to a junior cassette. Sounds to me like you would be fine getting the smaller ring up front (I say go 46T) and after riding with that for a while deciding if you want a different cassette, or even a few just for varying terrain.

I understand from manufacturer docs that some chainrings are designed to play nice together. Also, the front derailleur/frame/chainring all need to cooperate. I'm not sure how sensitive you or your setup will be to those considerations.

I am surprised you get chain rubbing in 34x15 since '6th gear position' is only one off from the middle cog. I doubt this has to do with the size of your large chainring but a better description of the setup is the first step.

bobonker

Sounds like you might be happy with a 46/38 cyclocross crank. It's something I've been toying with. With the 50/34, there is a lot of rear D movement each time you move to the front D (to maintain or come close to maintaining the current speed).

Bob

fietsbob

46/34 is a reasonable 12 tooth difference , Spinners benefit from a bit easier gear
wider range cassette , Mtb derailleur 12-34
something close to the 34:15 [2.26] is 20~21 on the 46

Drew Eckhardt 

Some FSA "9 and 10 speed compatible" cranks have an unusually small distance between the rings.

I spaced mine back to Campagnolo 9 speed dimensions using thin spacers made for the purpose by Wheels Manufacturing and Le Tour so that I'd have one overlapping gear between rings instead of noise or a hole between them.

Branford Bike sells the .6mm spacers.

Looigi

Oops forgot to mention this nifty graphical gearing calculator that lets you compare gearing:

https://www.gear-calculator.com/#KB=2...F=2099&SL=2.15

Al1943

Be sure that you can move your front derailleur low enough before buying smaller chainrings.

oldbobcat

Right. Today I just built a Madone 5.2 with a tab-mount front derailleur and 50-34 compact gearing. The front derailleur was at the very bottom of the mounting tab.

Chris_W

I have a 2007 Madone that I did this on. Since the hole in the FD mounting plate didn't extend far enough down, I bought a replacement plate (get them from your local Trek dealer) and filed the hole down a few mm further. It works fine with a 48 tooth, and is just about low enough for a 46. No problems in over 2 years of running this setup so far.

Sixty Fiver

You should not be having issues with chain rub if your bike is set up properly although it is always more efficient to maintain the straightest chain line possible for a specific gear.

By swapping to a 48 your top gear will still be 115 gear inches which is something the average rider is not going to push anywhere except down a hill for any distance... humans have a narrow power band and fairly fit humans can use gearings between 50-100 gear inches quite efficiently while lower gearing is good for hills and taller gears are best used in a paceline or on descents.

When you watch a guy like Contador doing a time trial he does not have his bike maxed out at 53:11 as that is 126 gear inches and you will see that he is most often running down a few steps in his range and probably living in that 90-100 gear inch range and spinning at a higher rpm which is far more efficient than trying to hammer a big gear.

46:11 is still 110 gear inches... if you can spin that gearing out you will have to be in great shape but it will be a nice gear for coming down those hills you have in Portland... which I have ridden up and down to excess.

markjenn

Is a 48 tooth chain ring readily available for the 110mm BCD compact cranks? I have a standard 50-34 and the gearing is Okay, but my RD is slightly short of capacity with my ultra-wide 11-36 rear cluster - if I size the chain for the 50-36, it goes slack on the 34-11 and 34-12. I hardly ever use the 11 and 12 tooth cogs on the big ring, so I wouldn't mind losing a little on the top end to be able to use all my gears on the small ring.

- Mark

markjenn

Answering my own question, it appears this is a reasonably-priced and readily available option. While my shifters and FD are SRAM, my crank is an ultegra compact with 34t and 50t Shimano chainrings....does anyone see any problem running this FSA outer chainring on my Ultegra crank with an Ultegra inner chainring?

https://www.amazon.com/FSA-Road-chain.../dp/B0028MVJ76

- Mark

Sixty Fiver

Nope... if the chain ring is 110 bcd it will fit and should not cause any issues.

markjenn

I know it has been touched upon in other threads, but I'm pretty confused about this note that appears in most of the listings for FSA chainrings:

Some are designed to work in specific tooth combinations; see specific compatibility at individual part number bullet point
S10 is compatible with Shimano, SRAM and Campagnolo Ultra Narrow 10-Speed
S9/C10 is compatible with Shimano 9 speed and Campagnolo C10 10-Speed
N10 is compatible with Shimano, SRAM and Campagnolo Ultra narrow 9 and 10-Speed

From this, I would assume that I want an S10 version, but the listings for the parts don't say anything about S10, S9/C10, etc. or how to order the different versions.

https://aebike.com/product/fsa-48t-pr...r3952-qc30.htm

FSA's web site has almost no technical information whatsoever.

- Mark

Al1943

When I replaced the 52-42-30 on my wife's bike with 49-39-28 I ground down the slot in the FD with a Dremel tool to get the FD low enough. This seems to be a common problem with people wanting smaller chainrings.

heirfaus

Thanks for the link very informative and great to see how I can accomplish similar output with different gear combos.

I love your advice because it lacks the macho side of things that we often see in cycling. This is exactly what I'm trying to achieve, more useable gears and a better chainline.

To be honest I'm not sure if it was 34x15 or 34x14 but it was there. I looked at the crankset manual it even says that there may be chain rub on the small chainring and 7th, 8th, and 9th cog. I took it too the LBS and he confirmed it was setup correctly and working perfect, it's just the way it functions.

I'll keep this in mind for the future. I'm 139lbs soaking wet thus I'm not a powerhouse and rely on a higher rate of spinning.

I actually seriously considered this but with the hills here I need the lower gearing. As it is, the 34 is pushing it with some of the hills I commute on. I go down a hill at 40-45 mph and have to come back up that beast on the way home!

Like I said up above in this post it does rub just like the manual says. I chalk it up to the design of the crankset...

and good points on gear inches. I hadn't considered this before. I'll have to keep this in mind as I continue to experiment with my gearing.

heirfaus

And to wrap up the question at this point, I bought a 46t and have put about 40 miles on it. It's MUCH better than the 50 as far as functionality of gear use, at least for my body.

Again, thank you all SO much for the advice, it has helped me get to a place where I'm enjoying my ride more!

barturtle

I've got my main bike set up with 46/34 and a 13-30 9sp. Gives me 95-30 gear inches. That covers everything from commuting to fairy hilly centuries. Only time I make any changes are flat club centuries where I know I'll be pacelining a lot, then I switch to a 11-26 (112-35 GI). My MTB, used as a winter commuter, grocery bike and gravel grinder is 42/32/22 with a 11-28 8sp (95-19 GI).

I think going to something like the 13-30 cassette I run (a Harris Cyclery custom) would be a best first change, but going to a 44 or 46 with it, will really make for a great combo.


EDIT: Must read entire thread before posting...glad you like the 46.

heirfaus

Oh and one more note. On my way home from school today I realized I can now use 34x13 (8th position) without any rubbing with the smaller 46, but it still rubs on 34x12 (but I will never use that combo let alone 34x13).