sram cassette sizing

RB 24

Likes Dirt
Hi all,

Junior RB is off to ride the national hill climb at Mt Buffalo in April. However being a JM15 he can't block off gears and has to have the correct sizing of cassette to meet roll out of 6.0mt. He will use his 34 tooth chain ring and whichever cog to be on the max roll out..

Now the question is this:

Let's say he wants to spin like a demon up the hill, what is the most realistic range of cassette. He currently has a 12/26 however having a bit bigger cassette would be handy. A 1:1 ratio is not an option as I think his cadence would be too high to match roll out per rev. Can a cassette easily be customized with say portion of an ultegra top end an a sram bottom end? Will a big variance in cogs stuff up changing?

Bike is a caad10 sram red shifters force rd. FD is a red but is set up only for trimming as running a 1 x chain ring.

any help is really appreciated.
 
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