set up for 2x9 gears

[02GF74]

Should it be possible for all 9 rear gears be usable with both front chains rings on?

ultegra - 53/39 front with 23-13(?) rear 9 speed.

asking as I got chain rub when on large ring on front and top 3 or 4 sprockets - I didn't adjust the front mech..... but I have since and get no rub, as on my prevous road bikes but these were 6 or 7 or 8 speed.

So just wondering if that is ok - I reckon it is, and yes, I know about chain angle being bad but it is only 2 rings on front, not 3 like on a moutainous bike.

 

[nuovo_record]

thin what you really need to avoid is "big-big" and "small-small".
i just trim the front mech if it starts to rub

 

[PpPete]

Should it be possible for all 9 rear gears be usable with both front chains rings on?

.

Why would you want to? "big-big" and "small-small" will be overlap gears anyway, apart from distorting your chain and making it wear out faster.

Work out your gear inches for all your possible combinations see which are simply not worth using. Chances are that 2 x 9 = 14 useful gears at best.

My 3 x 9 has only 21 useful gears and even then there is some overlap.

 

[ASC1951]

Should it be possible for all 9 rear gears be usable with both front chains rings on?

No. The chain will be too long if you can do that, and you will get less smooth changes.

 

[andy_wrx]

Why would you want to? "big-big" and "small-small" will be overlap gears anyway, apart from distorting your chain and making it wear out faster.

Work out your gear inches for all your possible combinations see which are simply not worth using. Chances are that 2 x 9 = 14 useful gears at best.

My 3 x 9 has only 21 useful gears and even then there is some overlap.

But in order to get to some of those equivalent gears you would have to double-change, i.e. change up with one ring and down with the other or vv.

And frankly that's sometimes a faff. Why should you be forced to change chainrings, why not stay in that ring and use all 9 cogs in sequence ?

Hence it's not 14 'useable' gears but 14 'unique' gears, of which all 18 or 16 if you don't use big-big and small-small are 'useable'.