Gearing on a new bike, what should you expect?

[Clydesider]

I've just bought a Btwin fit 300 road bike with shimano 21 speed gears, on delivery the gears were rattling on the second biggest cog, I took it into Decathlon Breahead, after some tinkering by the bike tech, I took it away only to return 5mins later as things were worse.
To cut a long story short it now rattles on all three cogs depending on which back cog you select.
"try to keep the chain straight" was the advice from the young bike tech.

Should you not be able to select any gear on any cog and expect it not to rattle?

 

[vickster]

I've just bought a Btwin fit 300 road bike with shimano 21 speed gears, on delivery the gears were rattling on the second biggest cog, I took it into Decathlon Breahead, after some tinkering by the bike tech, I took it away only to return 5mins later as things were worse.
To cut a long story short it now rattles on all three cogs depending on which back cog you select.
"try to keep the chain straight" was the advice from the young bike tech.

Should you not be able to select any gear on any cog and expect it not to rattle?

Best to avoid small-small; large-large...those will rattle. What is the deraileur?

 

[Clydesider]

Best to avoid small-small; large-large...those will rattle. What is the deraileur?

Shimano SRAM 3.0

 

[KneesUp]

I also have 7 x 3 gearing on my bike (i.e. 7 cogs at the back,3 wheels at the front)

I get some rub on the front derailleur if the chain isn't totally straight. In my case it's because the derailleur isn't on quite straight (because I put it on a bit wonky after taking it off to clean it) and I keep forgetting to straighten it up. My front changer isn't indexed though, so I can 'trim' the position of the front mech as I ride.

Anyway, it might be worth checking that the front derailleur runs totally parallel to the chain.

 

[vickster]

SRAM and Shimano are different makes?

 

[KneesUp]

It's SRAM 3.0 I'm not sure what make the mech is makes a difference though?

If it's rubbing in most gears it's something needs adjusting, and if it's rubbing when the chain is at a big angle (e.g. smallest-smallest or biggest-biggest) then it's just one of those things.

 

[Paulus]

It is not advisable to use the biggest chainring and the largest cog, or visa versa the smallest and smallest, but if the chain is rubbing on the front derailleur then some fine adjustment is needed as there should not be any chain rub, even on those acute angles.

 

[Racing roadkill]

Try having the hanger on the rear mech aligned, I had a bit of a rattle when the chain was at an angle on my Btwin Riverside. I did a rear hanger alignment and it ran much smoother.

 

[Apollonius]

I suspect that when you took the front changer off, you put it back with too big a gap between the chain-ring and the curved guide of the derailleur. It needs to be very close to the ring - about 1mm clearance. Not easily spotted by the shop, as they would not expect it to be disturbed.

 

[Clydesider]

Thanks for the responses, sorry about the Shimano SRAM thing you can tell i'm no expert! I will try and adjust things myself then and maybe consult a youtube video or two, I certainly have no desire to go back to Decathlon Braehead, the young french guy in the bike dept was a bit arrogant for my liking and had a very blasé attitude.

 

[Mobytek]

If you have the largest cog (rear) and smallest Chainring (front) then everything is in line. Same for smallest cog and largest CR.

On the smallest CR you should be able to get 1 to 4 without rubbing on your front. 5 - 7 will, but then they are doubled up when you move to middle ring.
Middle ring should have 2/3 to 5/6 with a rub top and bottom.
Largest CR you'll have 4 - 7 with rubbing at the largest end.

The angle of the chain causes it so the keeping it straight will work, but requires you to know and understand your gears to avoid the extremes and recognise the overlap of gear ratio-ing.

For a 7 speed you are looking at

Gear ratio overlapping
S M L
1 2 3
L----S
1
2
3
4 1
5 2
6 3
7 4 1
. 5 2
. 6 3
. 7 4
. . 5
. . 6
. . 7

If you want someone to talk you through it drop me a line . All you'll need is a cross head screwdriver .

 

[glasgowcyclist]

the young french guy in the bike dept was a bit arrogant for my liking and had a very blasé attitude.

Quelle surprise!

GC