Thursday, March 25, 2010
(image credit: http://aroundtheedges.wordpress.com/)
Nope i'm not going to tell you how Sir Chris Hoy rampaged in the keirin tonight. 10th world championship! Awesome power - watching him kick then kick again to come round for the lead and then power on the gas for the win got me pretty damn goose pimply, i can tell you...
Anyway: 6 speeds...i've been reading around what folk have tried and it all seems pretty system dependent. We dont know how the 17-34 cassette is going to go on the back of the Vertigo just yet. the spacing has some leeway i would imagine because the spokes are so highly angled, the modded cassette can be moved in towards the middle of the wheel as well. The further away from the derailleur it is, the teeth it can cope with. This seems to be the stumbling block for some set ups. It also means you have to use lots of b-tension (which changes the arc of the top pulley compared to the cassette). Unfortunately, the more b-tension, the less smooth the shifts. There is also a minor matter of the limit screws being longer so the range of throw can be kept in check.
I want to use a saint mech, because they are tough. They are also shadow style mechs, which means they are tucked under the cassette further out of harms way but critically, closer to the cassette, decreasing their ability to cope with a 6 speed/large range set up. It is possible it aint going to like the 34 tooth low gear. Options: spacing the deraileur out from the drop out, sometimes by as little as 2mm can be useful apparently. Im not sure what i think about that...yet!
I could also drop the 17-34 modified cassette. The reason i am using that spread is primarily because it comes on an alloy carrier. The singlespeed cassette body of DT hubs is aluminium and individual thin steel cogs will chew it up for breakfast.
Other options. Use 18-32 xt cassette part. i drop a gear ratio, and get less useable range, but the 32 low gear may work. The xtr cassettes come on carriers and could give a similar range, but no real benefit over xt there.
I could also use a road cassette: in looking at the older style 9 speed ultegra 6700 i can use the two low gear parts - 21-24-27 on an alloy carrier and 17-19 pinned together. Then, because the pinned together bits dont have a spacer attached, (see the tech docs) a chris king cog should nudge up along side very nicely, maybe with a judicious 1mm spacer, to give me 15-27 6 speed. With the large range widget in place on the saint mech i reckon if the 17-34 doesnt work, this will. Only issue - the teeth on the 15 tooth king are likely to be a little taller, so the shifting onto and off may not be hugely crisp, we'll see if it is needed.
In that scenario, the gear development would change only very slightly if i use a 36 tooth ring. It is possible that this would allow me to put the ring in the middle position also - which MAY be better for chainline...we'll see.
With 36 tooth c'ring and 15-27 i get 121.5 to 218.7 development versus
with 40 tooth c'ring and 17-34 i get 107.2 to 214.4.
I could also use 35 or 34 if i needed more climbing gear.
Given the gear i run on the singlespeed (33-19) gives a development of 158.2 im pretty happy with this range.
Damn. My brain might have just cramped.
So once again, here is Hoy, on the BBC winning his 10th (!) world title...