Chainring advice

[gf1959]

I have a Giant road bike with compact gearing,too low for me,i'm thinking
of changing the inner ring from 34 to 39,or getting someone else to do it
more like.
How much should i spend? It's Shimano but what spec i don't know,nothing
on the ring itself. I've seen them for £10 up to £50,i don't want something
cheap and flimsy but no point in going overboard either,maybe someone's
done the same conversion?
34,just way too spinny.

 

[jimboalee]

1/ Most of your riding should be on the 50T ring.
2/ The 34T ring is for climbing and battling a +20 mph headwind.

Chart the ratios and draw a 'gear progression' table. You will find the 4 or 5 larger sprockets couple with the 34T ring and all but 3 sprockets couple with the 50T ring.

 

[mickle]

Learn to spin.

 

[HLaB]

I've never done the conversion 34-39 but my ramblings fwiw:

I think a 39, while OK 90% of the time would be too high for the odd get me home occaisions or steep hills and IMO if you put too large a small chainring on (contradiction ) you need to go with the expense of a larger large chainring.

I quite like the campag compact gearing on my Bianchi for hills, they do a larger 12-25 cassette with a 36/50 chainring. I've found my self spinning out a fair bit on downhills and occaisional flats with the club so I specced my new bike with a 39/53 with a 12-25 cassette, however to get it ready in time the lbs fitted a 38/52 (they had that in stock). They offered to change it when a 39/53 came in but I quite like it and will probably stick with that.

 

[onlyhuman]

1/ Most of your riding should be on the 50T ring.
2/ The 34T ring is for climbing and battling a +20 mph headwind.

That's more or less the opposite of what I've been reading recently, where I was told that most of my riding should be on the smaller ring, that neophytes make the mistake of thinking they should always be trying to get on the bigger ring. I was told that spinning is better for the joints, and that it will develop souplesse, that coaches sometimes disable rider's larger rings during the training season, or advise that they should not be used.

Comments Jimbo?

 

[MichaelM]

1/ Most of your riding should be on the 50T ring.
2/ The 34T ring is for climbing and battling a +20 mph headwind.

I agree with the op. I've got a compact on my old (now winter) bike, and tbh it gets on my tits. The gap between 34 and 50 is just too much. I'll probably replace the 34 with a 38.

FSA 36, 38, 39 Compact chainring £22.99

£19.34 for 36 or 39

 

[Will1985]

Jimbo is right - imagine the riders on a club run...those with doubles might spend their time in the small ring and maybe three middle sprockets at the back which could be gears of around 64" and 74".

The same gear lengths on a compact could be achieved using the inner ring and the smallest three sprockets....the chainline here is very bad. The alternative is the big ring plus perhaps the 3rd,4th and 5th largest sprockets which gives a slightly better chainline.

If you ride compact on your own you might not be bothered, but it is noticeable in a group unless you spin really fast. I don't need to drop to my 36t inner unless there is a proper incline.

 

[jimboalee]

That's more or less the opposite of what I've been reading recently, where I was told that most of my riding should be on the smaller ring, that neophytes make the mistake of thinking they should always be trying to get on the bigger ring. I was told that spinning is better for the joints, and that it will develop souplesse, that coaches sometimes disable rider's larger rings during the training season, or advise that they should not be used.

Comments Jimbo?

50/34 x 12 – 25 10 speed.

34 x 25 = 37", 34 x 23 = 40", 34 x 21 = 44", 34 x 19 = 48", 34 x 17 = 54"

50 x 23 = 59", 50 x 21 = 64", 50 x 19 = 71", 50 x 17 = 79", 50 x 16 = 84", 50 x 15 = 90", 50 x 14 = 96", 50 x 13 = 104" & 50 x 12 = 113".


5 largest sprockets with the 34T ring. All but 1 sprocket with the 50T ring.

50 x 25 = same as 34 x 17, but no-one uses ALL 10 sprockets with the 50T ring.

I'd spend most of my riding on 50 x 17 at 80 cadence at 30 kmh. 160ish Watts.
On 50 x 19, the same speed can be maintained ( for the same power ) at 90 cadence. This is where the pros might ride IF they used a Compact, but they don't, they use 53/39. No, sorry, they'd be riding on a gear higher than 90" most of the time.

PS. The gear arangement I describe is suitable for an 18lb bike with a bottle of water; and a PRK under the seat.

 

[Seamab]

50 x 25 = same as 34 x 17, but no-one uses ALL 10 sprockets with the 50T ring.

I do! I've just replaced my 50T ring as it was worn out whereas the 34T is still going strong.
I'm a bit of a grinder and usually don't change ring unless something pretty steep is coming along. Other riders can hear me coming with my 50 x 25 rattle.

Whats the point of having a bike equipped with 20 gears if you are only ever going to use less than half of them?

I've never heard of anyone complaining about chainline when they are struggling up a steep slope in the granny gear. "Oh dear, i mustn't use that gear the chainline is just so terrible you know - i'll just walk instead..."

To the OP - don't bank on getting a Shimano chainring - they are scarce at the moment

 

[4F]

Whats the point of having a bike equipped with 20 gears if you are only ever going to use less than half of them?

The point is that your chain will wear out a lot quicker and cost you a lot more in the long run.

 

[mickle]

If your rings are wearing out you're doing it wrong.

 

[gbb]

A few differing opinions above...here's my take
Campag 50/34...as most say, way way too spinney for the average rider in average terrain.
Changed mine to a 40...perfect for round here.
As my fitness has increased, i spend about 50% of the time between the 50 and 40.
For club / serious etc riders, you probably should spend more time on the 50, but i spent a long time mostly on the 40, just for comfort, but i'm an average rider...no more.
That said, i now switch to the 50 far more frequently.

It's a quite easy job OP....i can switch mine in about 15 mins with the appropriate allen key and a broad screwdriver. Sometimes you dont even need the screwdriver....

I did see a reply re chainline. Does anyone notice the same on a Campag cpmpact setup ?....small ring to 25....the chainlines awful.

 

[addictfreak]

I was out and about in the North Pennines yesterday, and my 34 was a life saver on the climbs.
My two mates who are not only twenty years younger, but also tri athletes managed no problems with there 39. The only place I really noticed the difference was on the downhills when they would get away from me pushing the 53

 

[gf1959]

Thanks guys for the great input and the product links,i can see there are many valid opinions as to the correct way to go. For me i'm not bothered about the big ring,i can quite happily stay on the small one and apply my real effort to the hills and tend to think a 39 would cover all bases for me.
I never use the 25 first gear now,with a 39 inner ring i think i would and it would be very similar to now,but it would also be less spinny in higher gears.
That FSA 39 looks nice and i assume would fit,nice to read all your views.

 

[onlyhuman]

Jimbo is right - imagine the riders on a club run...those with doubles might spend their time in the small ring and maybe three middle sprockets at the back which could be gears of around 64" and 74".

The same gear lengths on a compact could be achieved using the inner ring and the smallest three sprockets....the chainline here is very bad. The alternative is the big ring plus perhaps the 3rd,4th and 5th largest sprockets which gives a slightly better chainline.

If you ride compact on your own you might not be bothered, but it is noticeable in a group unless you spin really fast. I don't need to drop to my 36t inner unless there is a proper incline.

Hi Will,

I can't easily imagine the riders on a club run, partly because I've never been on a club run. I don't understand why it would make any difference to the other riders if one of them used different gears.