Front mechs, arghhhhh!

MTB Nut

Jesus H Christ, front mechs drive me around the proverbial bend. The degree of accuracy required to successfully configure a fully functional three chain ring, 9 speed set up seems to require the hand dexterity of a god with extreme patience and a knack for not kicking the cat when he/she gets pissed.

Is it even possible to set up a 9 speed cassette with 3 chain rings and not have front mech chain rub at one extremity of the cassette or another? I have tw4tted on for ages trying to get the positioning just rights so I get no chain rub under full crank load in the outer and inner chain rings, to no avail. Then when I introduce the granny ring , grind grind grind.


I have a fulll deorre XT transmission except for the chain which is a SRAM 991 and I'm now getting to "watch out cat irritated." :evil:


Any suggestions?
Any suggestions or answers?

gonga

I gave up on a totally quiet front set up after hours of adjusting.
you must have to get it smack on to stop it rubbing!

chedabob

You can't get extremes on the casette in anything other than the middle ring. Granny works with the lower 4/5, and big ring the top 4/5. Anything else and it will rub and put a lot of stress on the chain.

stumpyjon

It'll probably rub in extremes. Is it a full suss you're setting up. COmpressing the suspension can have an effect on the chain line so that it's fine in the workstand but rubs badly when riding.

doggegg

I work on granny = top 4 sprockets, outer = lower 4 sprockets, and only try to get middle chainring with no rub in any sprocket but even then I usually fail to some extent.

If anyone can get all 27 gears in action without rubbing the mech I'd like to see....but you shouldn't be hitting those extreme gear combos anyways

Neily03

MTB Nut wrote:

Is it even possible to set up a 9 speed cassette with 3 chain rings and not have front mech chain rub at one extremity of the cassette or another?

Nope, you can't even do it on a 2x9 setup.

Chunkers1980

That's not correct is it really.

I run 3x9 and can get it to NOT rub on 22x11t-32t, 32x11t-32t and from 44x11t-28t of which you defo should not be using the 32 on the rear and poss not the 30t either.

If I removed my front 44t I could setup the gears so there was no rubbing.

I admit they are a complete PITA - but it is possible, you need the perfect angle and height.

I would suggest if you can't, you've either got a bent mech cage, poor chainline or bent rings/axel crankset.

konadawg

Chunkers1980 wrote:

That's not correct is it really.

I run 3x9 and can get it to NOT rub on 22x11t-32t, 32x11t-32t and from 44x11t-28t of which you defo should not be using the 32 on the rear and poss not the 30t either.

If I removed my front 44t I could setup the gears so there was no rubbing.

I admit they are a complete PITA - but it is possible, you need the perfect angle and height.

I would suggest if you can't, you've either got a bent mech cage, poor chainline or bent rings/axel crankset.

Agree.

The Rookie

Carrera Vulcan -3x9- with LX front mech, XT rear, LX cranks (square taper, triple - 42,32,22) Shimano cassette and chain, no rub ever.

Not saying every frame/component combo is possible to set to zero rub, but mine took 20mins to setup from fresh build and no rub, getting the front chainline right makes it a lot easier, many modern MTB's seem to shift the chainwheels out and that makes the chain slant more when using the largest cogs at the rear, also setting the height of front mech to match the 'step' on the inner plate to where it moves chainwheel helps, this may not always be at the normal clearance height for the largest ring, but in the past I've found rubs are more likely where the mech is set to high.

Simon

cobba

MTB Nut wrote:

Is it even possible to set up a 9 speed cassette with 3 chain rings and not have front mech chain rub at one extremity of the cassette or another?

Probably not, what you want to do is called cross-chaining and shouldn't really be done.
Cross-chaining will wear out your chain, chain rings, cassette and derailleurs much quicker.
You might have 27 gears but that doesn't mean you have to use them all or you should be using them all.
Of the 27 gear ratios there's probably a few that are exactly the same and there's even more that are so close in ratio that you probably won't notice the difference between them.

Gear Calculator: http://www.sheldonbrown.com/gears/

Tune your gears so you can at least get the big chain ring to use the 5 smallest sprockets on the cassette, the middle chain ring to use the middle 5 sprockets on the cassette and the small chain ring to use the biggest 5 sprockets on the cassette.

Cross-chaining: http://www.ehow.co.uk/video_5774031_fix-cross-chaining-bicycles.html

Chunkers1980

cobba wrote:

MTB Nut wrote:

Tune your gears so you can at least get the big chain ring to use the 5 smallest sprockets on the cassette, the middle chain ring to use the middle 5 sprockets on the cassette and the small chain ring to use the biggest 5 sprockets on the cassette.
Cross-chaining: http://www.ehow.co.uk/video_5774031_fix-cross-chaining-bicycles.html

You were doing well till you got to the bold.

Middle ring you can and should be able to use all 9.

Small ring, you can and should be able to use all 9. The only thing I would say for the small ring is when you get down to the 11t you tend to get a slacker chain (worse with cheaper mechs) if you've got the correct chainline, chain length and setup the only gear defo not to use is big/big and perhaps big/1or2 down from big.

underdog

Why would you want to use all the casset on the small or big ring? That's the bit I don't get. I ride 90% of the time in the middle ring, if I am using small or big ring then I will probably use 3 or 4 of the casset at most, any more than that then I prefer to shift at the front.

biff55

underdog wrote:

I ride 90% of the time in the middle ring.

so do i , hence the discision to dump the front mech and 2 chain rings in the bin.
no chain rub.
ever 8)

MTB Nut

Hey guys thanks for all your replies. All very useful and informative. It's not that I actually want to use all the gears, it was just a curiosity thing. My logic was, well, if they're available why can't it be done? My ignorance as to what was possible was breeding frustration.

At least I know what I should be aiming for. Many Thanks



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