Quote: Originally Posted by
CAMPYBOB . ...
For pulling trucks back onto the road, get that SRAM 42T pie platter and some carbide-studded ice racing tires ...
Hi CAMPYBOB, interesting ...
Let's have a look at the gearing ratios of say a SRAM XX1 10-42T cassette with a 46T single crankring and an 11-28T cassette with a 34-50T dual crankring.
Specifically 42/46 and 10/46, and 28/34 and 11/50 ...
Formula is ... Drive wheel diameter (26.5") x front crankring divided by rear sprocket
SRAM XX1 10-42T cassette with a 46T single crankring ...
- 42/46 - (26.5 x 46)/42 = 29.02
- 10/46 - (26.5 x 46)/10 = 121.9
11-28T cassette with a 34-50T dual crankring
- 28/34 - (26.5 x 34)/28 = 32.18 ... a 31/34 - (26.5 x 34)/31 = 29.06 ... a 32/34 - (26.5 x 34)/32 = 28.16
- 11/50 - (26.5 x 50)/11 = 120.45
As you can see from the above calculations that the SRAM XX1 10-42T cassette with a 46T single crankring setup is very similar to an 11-31T cassette with a 34-50T dual crankring setup. The benefits of the single crankring are
- Better Q or at least easier to obtain a better Q
- less complexity
- left lever is a brake lever
- no issues with chain drop due to mech over shifting
- the rear derailleur has been optimised for the 10-42T cassette
- one less cable to deal with
- the XX1 groupset is lighter than the SRAM Red groupset (I believe that it is 20gms lighter)
- the crankring has been optimised for single setup, especially as there are no ramping and pinning requirements
- and there are probably other benefits
thanks KL