Configuring gears for junior triathletes: 5.70m and 6.20m development

[ffox88]

Hi Guys'n'Gals,

my teenagers (13 + 15y.o.) are entering a triathlon race this summer where there are strict rules about the maximum "development" (length covered by bicycle with one complete pedal stroke). The maxima allowed are 5.70m and 6.20m, according to age groups. In this particular race, it is apparently not allowed to block chain rings with the set screws, like I have been doing so far. That means I might have to reconfigure their entire gear system. I have found a perfect combinations chainring--cassette--tyre that gets me just under the limits
32T -- 10/12-34 -- 25-622 = max devel. 5.68m
32T -- 10/11-34 -- 23-622 = max devel. 6.18m

The question is how do I get there? Both bikes currently have a shimano 105 3x10(11-32) system. Can I get away with switching the cassette in the back and going to 2 chainrings in the front? Could I then keep the left levers? I think the derailleurs can handle sprockets up to 34T.
The other question is: where do I even buy shimano-compatible cassettes that start at 12T?

Or for the creative types: how would you configure this?

thx in advance

Chris

 

[JonBuoy]

10 speed Shimano cassettes starting at 12T are available. For example: https://www.merlincycles.com/shimano-deore-hg500-10-speed-cassette-1-61919.html

 

[N0bodyOfTheGoat]

https://sheldonbrown.com/gear-calc.html is an oldie but goodie for gearing

At a super quick glance from the cassette choice window, SRAM do 10-speed 12-32, can't see 12-34 option.

I've got Shimano 12-36 9-speed on my '20 Marasa hybrid, with a 26-36-48 triple.