Do you skip gears?

fullerand

Hi,

I'll start with my usual preface: this may be a dumb question but...

I have a pretty new 24-speed bike (Trek 7.1fx). When in the following gear combinations (front-back) I can hear the chain rubbing against the front derailler:

1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8
                    ***  ***  ***  ***
2-1, 2-2, 2-3, 2-4, 2-5, 2-6, 2-7, 2-8
***  ***                           ***
3-1, 3-2, 3-3, 3-4, 3-5, 3-6, 3-7, 3-8
***  ***  ***  ***

It sounds pretty awful, and feels like I'm between gears. I was just about to tweak them, but my friend reckons this is normal behaviour. I suppose it makes sense: when the front derailler is far in and the back derailler is far out, the chain is slightly twisted across the gearsets... and vice versa.

So is it normal to skip these gears, and jump straight to combinations in which the front and back deraillers are about the same positions?

Thanks

Thomas_S_Hunterson

From what I understand, that's normal enough behaviour. Chain's by their nature are meant to be run perfectly straight and there's only so much bend that the deraillers can give.

Chips Lovell

Yes, it's totally normal. There is cross over in some gears available, so you can get near enough the same gear using different combinations. "Cross chaining" is what causes the noise. Avoid big ring/big cog and small ring/small cog combos.

Freddy687

Fullerand
The main reason you are hearing the chain on the front derailleur is that you are riding a Triple front chainring setup.
With a triple you may be able to select any one of the 24 combinations, but you are not supposed to use them all. There is a group of gears that triple is not meant to use.
These combinations would be smallest chain ring (30) with 3 smallest rear sprockets and largest chain ring with largest (50-52) 3 rear sprockets.
To put in the method you used 1-6 to 1-8 and 3-1 to 3-3.
This would explain the majority of the noise you are hearing.
The reason is that the side movement of the chain is to much and will shorten the life of the chain. Also the front derailleur is not wide enough to allow you to use these gears and still be able to change the front ring.
You can use all rear sprockets with the middle chain ring.
To stop clicking on the middle chain ring wit the top and bottom sprocket is a achieved with a lot of patience and minor tweaks to the cable tension and the stop positions for the derailleur. Even the information from Shimano will admit to needing some trimming( slight shift of the lever to move the derailleur but not enough to shift the chain the next chain ring) of the derailleur when on the middle chainring.
Also there is no need to use these combinations as these ratios can be achieved on the middle front chain ring.
1-8 would be almost the same as 2-6 and 3-1 would be very close to 2-3.

beans

^^ sound advice

In this regard, my downtube friction-shifters work well with my triple - little trims here and there are easy-peasy.

Could you even achieve this with an indexed system?

daymobrew

beans wrote: »

In this regard, my downtube friction-shifters work well with my triple - little trims here and there are easy-peasy.

You are just "hiding" the chain rubbing against the derailleur - it's essentially warning you that your chain is not running in a straight line.

blorg

Rubbing in the crossover combinations is normal although it does sound like you have an extreme case of it, your front derailleur may need adjustment.

I have a triple myself and there are really only two gear positions that rub, e.g. 52-27 and 30-12. I'm not even 100% sure if they do rub but I would avoid them anyway. AFAIK the general advice from Shimano is that it is only these two that you need to avoid although I wouldn't often be in the ones close to that either.

Shimano STI (road bike levers) has front derailleur trim, you have two positions for each gear on the front. I do need to trim to avoid rubbing though.

I doubt your bike is a Trek 1.4, I don't think there was ever a bike with that designation. Is it a road bike/MTB/hybrid?

fullerand

blorg wrote: »

I doubt your bike is a Trek 1.4, I don't think there was ever a bike with that designation. Is it a road bike/MTB/hybrid?

You're right, it's a 7.1fx. Don't know what I was thinking.