Cycling with a compact chainset

[CharlesF]

My Genesis CdF has a Shimano Sora FC-3550 Compact Chainset 50/34T and a 9 Speed Cassette Shimano CS-HG50 11-30T.

My previous bike had a Triple Chainset and, for commuting, I stayed on the centre ring. With the Compact, I am not sure what to do; I find for commuting the big chainring is fine as I usually stay in the middle of the cassette.

I’m not near my bike at present, but I thinks these are the correct ratios plugged into Sheldon Brown’s gear calculator:

50 47.1 % 34

11 9.1 6.2

9.1 %

12 8.3 5.7

8.3 %

13 7.7 5.2

15.4 %

15 6.7 4.5

13.3 %

17 5.9 4.0

11.8 %

19 5.3 3.6

21.1 %

23 4.3 3.0

8.7 %

25 4.0 2.7

20.0 %

30 3.3 2.3

If I am looking for a low gear and change midpoint on the cassette (at 17/50) there is a huge drop down to a much lower gear at 17/34.

Is it OK to stay on the big chainring throughout the cassette?

 

[StuAff]

Short answer: No.
Yes, you could ride in 50x30, but it's not a good idea. You want to keep the chainline as straight as possible- last two or three cogs on the cassette with the big ring will mean it's anything but. It causes more wear to your drivetrain, more strain on the chain in particular because it's at an angle, and it's less efficient. There'll be a crossover point in the middle of the cassette where you have two or three gears that are fine on either ring. That's when and where you want to shift rings.

 

[R600]

when changing down from the big ring to the small ring change the rear gear a couple or three clicks. this will stop the huge gear difrence

 

[CharlesF]

Short answer: No.
Yes, you could ride in 50x30, but it's not a good idea. You want to keep the chainline as straight as possible- last two or three cogs on the cassette with the big ring will mean it's anything but. It causes more wear to your drivetrain, more strain on the chain in particular because it's at an angle, and it's less efficient. There'll be a crossover point in the middle of the cassette where you have two or three gears that are fine on either ring. That's when and where you want to shift rings.

Thanks, I'll give it a try, I'm just worried that shift to the small ring will see me spinning like mad and not going anywhere, then, if I shift to a higher gear I am crossing the chain in the other direction.

 

[cyberknight]

Do you use the bigger gears on the cassette?
If you dont need the easier gears you could change to a closer range cassette , i use a 12-25 on a comapct with no issues.I generally change to the small on the front and go up 1 gear at the front when changing .

 

[Cubist]

If you're slick with the shifters you can hit both at the same time and then maybe only need one mender after that.

 

[CharlesF]

Do you use the bigger gears on the cassette?
If you dont need the easier gears you could change to a closer range cassette , i use a 12-25 on a comapct with no issues.I generally change to the small on the front and go up 1 gear at the front when changing .

I don't generally need them, but I like the insurance of knowing I have that little bit extra for hills, which I hate

 

[CharlesF]

If you're slick with the shifters you can hit both at the same time and then maybe only need one mender after that.

Cubist, not sure what a mender is!

 

[Venod]

I use a 50/34 compact, with a 12-30 cassette, I just use the 34 ring as a hill climbing gear, I try not to use 50-30 and 50-27 because of the chain line,( I have used them occasionally) the other 8 are all used with the 50 with no problems, on some rides I never use the 34 ring but I am glad its there when I venture into the big hills.

 

[CharlesF]

I use a 50/34 compact, with a 12-30 cassette, I just use the 34 ring as a hill climbing gear, I try not to use 50-30 and 50-27 because of the chain line,( I have used them occasionally) the other 8 are all used with the 50 with no problems, on some rides I never use the 34 ring but I am glad its there when I venture into the big hills.

That sounds like a practical solution, and one that would work, thanks

 

[cyberknight]

I use a 50/34 compact, with a 12-30 cassette, I just use the 34 ring as a hill climbing gear, I try not to use 50-30 and 50-27 because of the chain line,( I have used them occasionally) the other 8 are all used with the 50 with no problems, on some rides I never use the 34 ring but I am glad its there when I venture into the big hills.

Sounds like how i ride as well with 10 and 8 speed i can get away with all on the big apart from the last 2.

 

[park1]

I currently have a compact with a 12-27 cassette.

I was thinking about changing the big ring to a 48t and the cassette to an 11-25. The 48-11 gives a higher gear ratio than the 50-12 (just) and would give a smaller gap when changing down. It would give a slightly lower gear higher up the cassette so less front gear changes.

Just a thought.

 

[TheDoctor]

Cubist, not sure what a mender is!

Probably an Autocorrect fail for 'amendment'?

 

[Cubist]

Probably an Autocorrect fail for 'amendment'?

no, a mender is the extra shift required to get you back where you were in the gearing. I may have made the term up.

 

[CharlesF]

no, a mender is the extra shift required to get you back where you were in the gearing. I may have made the term up.

Ah, that makes sense