johnyguy

i got a synapse and when the chain is on the big cog on the front and on the small cog on the back the chain don't line up everything is working fine otherwise but the bike don't like to be in that setup everything is more smooth when the chain is on the 3rd cog from the smallest .

I guess its normal because soo many cogs in the back so this is unavoidable .?

JLopez149

you need to re-adjust the limit screw on the rear derailleur and also rest the cable tension. If you don't know how you LBS can do it for you.

johnyguy

no no i dont need to i meant when you look at the chain from the rear wheel its not a perfect straight line thats all im sure this is the way it is.

Carbonfiberboy 

Yes, that's correct. You'll get a little more chain noise there than 2 cogs in. It's normal. Partly I think it's because the small cog has fewer teeth and so the chain hits each tooth a little less favorably than if the cog were in the same position but larger and with more teeth. Check to make sure that the chain isn't touching anything in the dropout area.

rms13

First off, your eyes can play tricks on you so you need to measure distances with a ruler to determine chain line. Secondly, chainline on a multi geared bike is usually determined with the rear derailleur in one of the middle gears so you aren't going to have a perfect chainline in small cog

johnyguy

thanks thats what i thought

69chevy

On a bike with a 40cm chainstay (most are a bit longer) and the chainrings splitting center by 2.5mm (5mm apart)...

The Big/Small combo gives a chain angle of 2.72 degrees.

The Big/Big combo gives a chain angle of 3.43 degrees

The chainring center is ideally in the cassette center which is the 6th cog.

johnyguy

So I guess this is where the standard crank has an advantage because you don't have to shift down all the way to the smallest cog to get the speed ,mine is a compact.

69chevy

Multi speed bikes are full of compromises. The ideal setup is where you can ride your preferred cadence in the center of the cassette and travel at your average speed.

Needin to run a chain at an angle is a compromise, but a very small one.

johnyguy

Yes that's fine with me, I'm enjoying bike riding as more I ride and I think I'm getting use to my seat as well I'm kind of surprised about that.

gaucho777 

Doesn't not don't.

Don't confuse a comma for a period, or shy from using the latter.

Saddle, not seat.

"Front cogs" are chainrings.

Forgive any condescendscion, u doesn't want to seems...you get the idea.

Yellowbeard

A standard big ring (53 tooth) vs a compact (50 tooth) is only worth about one shift in the rear anyway.

andr0id

The actual chain line is from either:

The center of the middle ring on a triple at 45mm

OR

An imaginary line exactly between the two chain rings at 43.5mm

To

The center cog when the number is odd

OR

An imaginary line between the two center cogs when the number is even

The rear may vary 1 or 2 mm.

gregf83 

How many teeth on the smallest cassette cog? You shouldn't be spending much time in the smallest cog unless you're sprinting or going downhill or riding with a very low cadence. With a 12 tooth cog and 90RPM you'd still be riding close to 30mph with a compact crank.

johnyguy

You mean I should be on the small cog on the front most of the time? That's too slow for me

gregf83 

Not at all. Your comment was that a standard crank was an advantage because you didn't need to shift to the smallest cog in the rear. I was pointing out that you shouldn't be using the smallest cog in the rear regardless of whether you have a standard (53) or compact (50) chainring in the front.

johnyguy

On OK I got it but on the straight the smallest the fastest obviously ,anyway I use third one from the smallest usually.

Yellowbeard

The fastest gear is the one in which you generate the most power. That'll very rarely be the smallest.

Power = torque x RPM

Road Fan

That sounds about right, for a compact.

Dan333SP

Tony Martin runs a 58T chainring, not because he can spin out a 58x11, but because he can leave it in the 13 or 14T cogs and have a slightly straighter chainline for a tiny amount less drivetrain friction. 58x13 at 95 rpm is 33 mph, a typical TT pace, and that's probably the straightest chainline with that setup.

Point is, on most any 10 or 11 speed bike, a chain won't be perfectly straight when on the 11 or 12t cogs.