akmal's bike park

akmal's bike park

Saturday 23 January 2016

Tech: SRAM's 11 speed

SRAM has a lineup of groupsets featuring 11 speed cassette on the rear as below:
  • XX1 - single chainring with 11 speed cog; top of the range
  • X01 - X0 in single chainring with 11 speed flavour
  • X1 - single chainring with 11 speed cog; higher weight
  • GX - entry level 1x11 offering; available also as 2x11 (36/24 front) and 2x10 (36/22 front, 11-36 rear)
But why 11 speed? What are the advantages?

Personally, I'd like to analyse from gear ratio perspective; the performance side of it. Gear ratio is the tooth count ratio of front chainring over the cassette, e.g. gear ratio of 32T chainring and 10T of 10-42T cassette is: 32/10 = 3.2

SRAM's 11 speed is a bit special as it has the advantage of having the 10T gear on their cassette. This is made possible with the introduction of their new XD Driver body. Yes, another 'standard', but it makes sense and gives out performance advantage.

Compare these two parameters below, on a 29er with 2.1 tires spinning at 90 rpm and 175mm crank length:
1. 32T chainring with 11T gives out theoretical speed of 35.7 km/h (Fig. 1)
2. 32T chainring with 10T gives out theoretical speed of 39.3 km/h (Fig. 2)

1T more on the rear means 3.6 km/h faster, ceteris paribus.

Fig. 1 - 32/11 gear combo at 90 rpm with 29x2.1 tires gives 35.7 km/h
Fig. 2 - 32/10 gear combo at 90 rpm with 29x2.1 tires gives 39.3 km/h
For a racer, that is a lot and worthy the investment for upgrade/migration.
But is it for you? Only you can decide.

Now imagine if Shimano's Capreo system which include 9T on its cassette is introduced for MTB, that would be something big, at least for racers. And pretty attractive for those who are thinking of jumping into the 1x bandwagon.

Well, while Shimano is working on it and churned out their new 11s systems (under XT and XTR badges) with 11-40T and 11-42T cassettes, e*thirteen has spawned into production a 9-44T mega number - TRS+. That's massive on both ends! Requires SRAM XD Driver freehub.
*their 10s cassette is 9-42T.

Holding all other parameters the same as in above figures, 32T chainring with 9T gives out theoretical speed of 43.7 km/h! How about that.

Do visit and read further:

9T Extras:

Happy trails!

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