Front Mech - its a black art - help needed.

JD_76

Just completed a new build and am struging to get the front mech set up right.

On the middle ring should I be able to access all 9 gears?
Im finding I can get the top 8 or bottom 7 before the chain drags on the front mech.

Also I understand there are Low and High screws but what happens in the middle if I need to adjust?

Any tips on setup gratefully received... :?

delcol

is the mech lined up with chainring,, and have you got the correct chainline....

front mech

front mech

nicklouse

no.
you adjust the top and bottom positions.

Or really the bottom and the tension.

read the set up info on Parktools and the topic on using gears in the FAQs.

JD_76

delcol wrote:

is the mech lined up with chainring,, and have you got the correct chainline....

front mech

front mech

Thanks for the links, I think Ive got the mech lined up ok, but chainline not sure?

The BB is 73mm so I fitted the Hope BB with just one spacer on the drive side, how do I check & adjust the chainline?

Thanks Nick, ill have a butchers.

delcol

sheldon

good info on sheldons website about chain line..

nicklouse

JD_76 wrote:

The BB is 73mm so I fitted the Hope BB with just one spacer on the drive side,

may be right or wrong depending on the cranks.

JD_76

Thanks chaps, ill have a measure up tomorrow as see what comes out.

Reading the instructions, it seems I can adjust the front mech setting on the middle ring with the barrell adjuster.
Winner.

cooldad

JD_76 wrote:

Reading the instructions....

nicklouse

JD_76 wrote:

Thanks chaps, ill have a measure up tomorrow as see what comes out.

Reading the instructions, it seems I can adjust the front mech setting on the middle ring with the barrell adjuster.
Winner.

No, the barrel adjuster adjusts the tension.

try reading the instructions.

JD_76

cooldad wrote:

JD_76 wrote:

Reading the instructions....

Sorry I forgot, dont ask for help an advice on a public forum as there will always be one joker who says, "Try using the search function" or "Read the instructions"

The point of the post is so I dont have to read through pages and pages of instructions, instead I choose to ask other subject matter experts who have so I get to the information I want quickly, plus any other tips that are often excluded from said instructions.

Do me a favour.

JD_76

nicklouse wrote:

JD_76 wrote:

Thanks chaps, ill have a measure up tomorrow as see what comes out.

Reading the instructions, it seems I can adjust the front mech setting on the middle ring with the barrell adjuster.
Winner.

No, the barrel adjuster adjusts the tension.

try reading the instructions.

I did

Shift the front derailleur to the middle gear, and run through the entire range of rear sprockets to make sure the chain does not rub on either side of the front derailleur cage. If it does rub, you can adjust the trim by tweaking the barrel adjuster on your front shift lever. If you have an older friction shifter, often you will have to manually adjust the trim while riding.

cooldad

JD_76 wrote:

cooldad wrote:

JD_76 wrote:

Reading the instructions....

Sorry I forgot, dont ask for help an advice on a public forum as there will always be one joker who says, "Try using the search function" or "Read the instructions"

The point of the post is so I dont have to read through pages and pages of instructions, instead I choose to ask other subject matter experts who have so I get to the information I want quickly, plus any other tips that are often excluded from said instructions.

Do me a favour.

People are, by replying, but if you don't get the irony....

Shackster

In essence it boils down to:

1) set low limit screw so that chain just clears mech on granny ring/largest sprocket. Connect cable with moderate tension applied by hand.
2) Attempt to shift to middle ring - if it won't shift up you need more tension in the cable - screw the barrel adjuster out at the shifter. If it shifts up but then the chain rubs on the inside of the mech (while still in largest sprocket) you need less tension, basically because the mech is moving too far with one shift.

When you have done this, and you shift to the smallest sprockets (smallest 2 probably), you will get the chain rubbing on the other side of the front mech. You can't get away from this, it's up to you to decide whether you'd rather have access to middle/largest or middle/small without rub. You can get the same gear ratios (as middle/smallest) by shifting to the big ring (assuming you've got 3) and a larger sprocket.

You will never reach a condition where you don't get the chain rubbing on the mech at one or other side of the cassette. Unless you have a front shifter like the good old gripshift where you can tweak the front mech position whilst riding.

Hopefully, once you've done this you will also not have any chain rub when you are in the big ring and smallest sprocket. If you do you can increase the tension very slightly so it just misses.

supersonic

Park Tools has the best guide.

http://www.parktool.com/blog/repair-hel ... djustments

JD_76

Thanks Shackster, I will settle for not being able to go down to the 11t on the middle ring, ill give it another go at seting up tomorrow. - It is a triple 22/32/44 & 11-32 Cassette.

I find the middle ring 32t and largest rear sprocket also 32t is a good combo for climbing when the going gets a little tough.

P.S. Ill have a read of that also supersonic.

Is it me or is the whole front mech system a bit limited, I think it could be improved with a bit of clever engineering.

supersonic

There has been differential plate front mechs in the past (XTR), but a well adjusted standard cage does the job nicely. They can just takr a lot of tweeking!

Make sure the cages aren't bent.

JD_76

supersonic wrote:

There has been differential plate front mechs in the past (XTR), but a well adjusted standard cage does the job nicely. They can just takr a lot of tweeking!

Make sure the cages aren't bent.

Good point , this is a standard XT one and it looks ok but has been well used in the past.

I know what will happen, ill get it set up just nice then the new cables will stretch a little and it will need further tweaking.....

nicklouse

JD_76 wrote:

supersonic wrote:

There has been differential plate front mechs in the past (XTR), but a well adjusted standard cage does the job nicely. They can just takr a lot of tweeking!

Make sure the cages aren't bent.

Good point , this is a standard XT one and it looks ok but has been well used in the past.

I know what will happen, ill get it set up just nice then the new cables will stretch a little and it will need further tweaking.....

If it is set up it will need no tweaking other than adding a touch more tension. If you have o do anything else ou have added too much tension or you did not set it up correctly in the first place.

JD_76

Thanks Nick, thats good to know.

Just been reading about the B screw adjustment on the rear derailer as well, something else to check tomorrow...

nicklouse

JD_76 wrote:

Thanks Nick, thats good to know.

Just been reading about the B screw adjustment on the rear derailer as well, something else to check tomorrow...

Why? Does the rear not work well?

JD_76

nicklouse wrote:

JD_76 wrote:

Thanks Nick, thats good to know.

Just been reading about the B screw adjustment on the rear derailer as well, something else to check tomorrow...

Why? Does the rear not work well?

Not really set it up yet, its a bike ive just finished building and I cant get past the front mech setup, the rear index ok but could be better and will need tweaking.

I was just having a butchers on the parktool website and came accross the rear derailler setup, didnt even know what the B screw was for until now -