excessive Chain rub

kenniff

On a bianchi varone 7 compact 18 gear
Rubs in 9 when on the small back ring (even when adjusted)
Rubs in 10/11/12/13 Cant be adjusted not to.
The big front sprocket has lots of rub marks on the inside rim,will try and post a pick.
Is this normal for the viron,cos its been back in for a service and new bb and came out the same
cheers
ken

paulbox

Are you saying that you are using the small front ring and smallest rear? If so, I don't think it is physically possible to do that without rubbing on the big front ring due to the angle. You should really try & use the big front and drop down on the rear to achieve a similar ratio.

kenniff

Cheers
unfortunately a similar ratio is the big cog and the big rear mech which as i say also rubs.
Think my next bike will have a road rather than a compact setup

amaferanga

I'm having difficulty working out exactly what you mean. If you were to call the front rings 'chainrings' and the rear rings 'sprockets' it might make a bit more sense.

Anyway, whether you have a compact or standard chainset, big-big or small-small combinations should be avoided. With 10-speed cassettes you will (almost) always get rubbing on the big chainring if you try to use the small chainring with the smallest sprocket. But then you should never use that combination. As a general rule you should avoid using the two smallest sprockets when using the small chainring and the two biggest sprockets when using the large chainring.

kenniff

Thanks for the addy

unfortunately a similar ratio is the big chain ring and the big rear sprocket which as i say also rubs.
Think my next bike will have a road rather than a compact setup
So generaly the gears im in most are these and they rub,annoying,expensive

John.T

What size cassette and rings are you using. It is most unlikely that the small/small and big/big combinations give the same gear ratio. For instance 34/13 and 50/19 give the same ratio. So is you are using 50/34 and 12/23 you will not need to use 34/12 or 50/21 or 23.
http://sheldonbrown.com/gears/
Put your rings and cassette on here and you will see which gears are duplicated.

kenniff

Gear chart using Gain Ratios
For 27 inch (nominal) tire with 170 mm cranks
With 9-speed 12-13-14-15-17-19-21-23-25 Cassette
50 47.1 % 34
12 8.4 5.7
8.3 %
13 7.8 5.3
7.7 %
14 7.2 4.9
7.1 %
15 6.7 4.6
13.3 %
17 5.9 4.0
11.8 %
19 5.3 3.6
10.5 %
21 4.8 3.3
9.5 %
23 4.4 3.0
8.7 %
25 4.0 2.7


This small version of the chart can be printed, cut out, and taped to your bicycle for reference.


8.4 5.7
7.8 5.3
7.2 4.9
6.7 4.6
5.9 4.0
5.3 3.6
4.8 3.3
4.4 3.0
4.0 2.7

John.T

So your big/big gear is the same as the one right in the middle of the cassette on the 34 so no need to use it. Likewise small/small is near enough the one right in the middle of the cassette when using the big ring. Work with this chart and you will find that you can avoid almost all rub.
You should not get any rub on the 34/14 and very little on the 34/13. I don't.
Any rub on the big ring is on the mech cage and can be eliminated by using the trim facility.

1stGenRex

maybe this video will help, maybe not.

http://www.youtube.com/watch?v=_05Eic7KgcA

kenniff

Many thanks
GREAT advice and very helpfull i will work with it....
cheers

kenniff

John.T wrote:

So your big/big gear is the same as the one right in the middle of the cassette on the 34 so no need to use it. Likewise small/small is near enough the one right in the middle of the cassette when using the big ring. Work with this chart and you will find that you can avoid almost all rub.
You should not get any rub on the 34/14 and very little on the 34/13. I don't.
Any rub on the big ring is on the mech cage and can be eliminated by using the trim facility.

Excellent,i have improved my shifting considerably and have all but elliminated chain rub apart from the odd occation.Thanks JohnT.That makes this forum all the more worthwhile for me

John.T

kenniff wrote:

John.T wrote:

So your big/big gear is the same as the one right in the middle of the cassette on the 34 so no need to use it. Likewise small/small is near enough the one right in the middle of the cassette when using the big ring. Work with this chart and you will find that you can avoid almost all rub.
You should not get any rub on the 34/14 and very little on the 34/13. I don't.
Any rub on the big ring is on the mech cage and can be eliminated by using the trim facility.

Excellent,i have improved my shifting considerably and have all but elliminated chain rub apart from the odd occation.Thanks JohnT.That makes this forum all the more worthwhile for me

Happy to help. Getting to understand and use the gears correctly greatly enhances riding enjoyment and speed. Using the extremes not only wears things out faster but you end up stuck out on a limb. I have quite often followed a rider up to the bottom of a climb, him hanging on to the big ring, me on the small one. I watch him keep changing down until he is on the next to big sprocket. That is when I start to give him plenty of room as I know any minute he will hit the big sprocket and then realise he has nowhere else to go. The next move is often a dropped chain as he goes for the small ring. If he makes it he is now spinning his legs off. Knowledge and anticipation make life a lot easier.

Garz

Unless John he stays in the big ring and leaves you for dust!

John.T

Garz wrote:

Unless John he stays in the big ring and leaves you for dust!

The ones that can leave me on the big ring are not grovelling on the big sprockets.