10 Speed combinations

[Dr Drey]

Does anybody know of any reason why they only offer 26/39 & 28/42 and not a 26/42?

I played around on a freinds Cannondale Flash 2 with a FSA SLK crank............he is very happy with the combo claiming he has the best of both worlds.

[Schnavel]

Normally it's because of the front derailleur. The FD can only shift 14 (not sure of exact number) teeth sizes bigger if I'm not mistaken. Hence the gap on a 26/42 is too large...

 

Maybe the new derailleurs have a new system?

[Tubeless]

it can shift 1.5

ie. 26 + 13 = 39

28 + 14 = 42

[Captain Fastbastard Mayhem]

Why do you want a 42? Unless you're riding on dirt roads (ie: not proper mtb) all the time, I find the 42 to not only compromise your clearance on the tech stuff, but to be too big to warrant it. A 36/11 should give you all the high end speed you need unless you're riding jeep track all the time

[NINER_boy]

With the bigger jump 26 / 42 the "hole" in between gears will be just too big.

 

In the one you will spin and the next you will need to upshift.

 

1x1.5 is the best combo for sizes in F shifting.

[petatodd]

it can shift 1.5 ie. 26 + 13 = 39 28 + 14 = 42

 

Not true.

 

SRAM worked out smoother shifting with more upshift points using 2/3rds ratios so they have 26/39 28/42. The 26/39 has 13 upshift points, the 28/42 has 14, most other brands have 4 to 6 upshift points.

 

Other manufactures have not yet followed this perfect ratio of upshift points on the chainring so still generally use unsymmetric ratios limited only by the maximum throw of the front dérailleur which is normally 14 for a 2 chainring system or 22 for a triple.

 

Shimano still use 28/40 30/42, RaceFace use 26/38 28/40 30/42.

[Dr Drey]

....so the only thing preventing a 26/42 combo should be the throw of the front derailleur?

[Captain Fastbastard Mayhem]

....so the only thing preventing a 26/42 combo should be the throw of the front derailleur?

 

And the chainrings. SRAM chainrings (as Petatodd pointed out) have "shifting pins" which "catch" the chain when attempting the shifts.