toomyus

my rd is rubbing on the biggest rear cog and ive the b screw fully adjusted. the specialized website specs say, my tarmac pro should have a 12-23t. im guessing this is why ive rub. anybody have any say on this? if its true , is there any chance of specialized giving me a new cassette with 12-23?
thanks guys and girls

sydney

Your RD should work with that 27 cog.

toomyus

you are right , it should work. so i dont get why it doesnt. ive three specialized bikes, all bought from the same store with all the same issue, two mountain bikes one a highish end roadie. the bikes come pretty much made in a box, they just throw the wheels on and handlebars. its not like they messed with it. im clueless. any answers is warmly appreciated. thanks syd, ur awesome

Ed Holland

Is the cable housing to the rear derailleur too short? This condition can restrict the movement of the derailleur pivot at the mounting bolt, nullifying the effect of adjusting the "B" screw. The newer gear cable housing is much less compliant than the old spiral wound housing that was much more like brake cable housing. This will cause problems if cut too short. Unfortunately, I can't give you the correct length for your bike.

Cheers,

Ed

sydney

Another guy had a big cog rub problem,and it turned out the casing section at the RD was too long. some folks have had problems with 34 cogs and mtb RDs that should have been ok acording to spec.Never had the problem myself with parts that were in spec, so duno.

jimmythefly

They most certainly did, or at least should have. Any reputable shop will essentially re-build a bike of this caliber when they build it. Making sure a bike shifts and that the quick-releases are snug is only scratching the surface. Housing length, the amount of cable left sticking out of the brake caliper, bar wrapping, BB shell facing, derailleur-hanger trueing, wheel trueing, etc.

Was the shop unable to stop the rubbing? If they can't go someplace else.

toomyus

i picked up the bike for cheap. i bought it for 2817 out the door and not 3500 plus tax. i reckon they can give these discounts because they dont have high end mechanics, only kids working there and stuff. ive three bikes, all bought for good value, and all have the same rd rubbing on the rear biggest cog. its getting old, im nowhere near the shop i bought them and the only good bike shop from here is far far away. i plan on making a trip there soon, but man, its gonna be costly id say. and thanks ed for your efforts. im not too sure the cable is too short, but the adjusting screw , fully adjusted in ,seems to be on the gears and if i loosen it, its really on the gears then. im quite mind boggled. it is almost like there is so much spring force in the rd that nothing can stop it from going in to the cogs.anyways thanks for the advice fellas

af895

FWIW, I have a 30tooth rear cog and the little wheels in the derailleur DO "mesh" with the cog.

BIG hint: I added a stem riser and taller handlebars which effectively "stretches" the shifting cables. I already replaced the brake cables and housings because they were too short.

I SUSPECT, as others have mentioned, this problem is one of too short shifter cables/housings. (at least in my case)

rmfnla

Casing as in cable housing? How can that effect the way the RD interacts with the cluster?

sydney

^^^...Try it sometime.