Q. about gearing, and some more questions

[Aero]

Hi RC monster and happy new year! start with a question is that okey ?

when people write their gearing xx/xx , what does it refer to? mean in rel. to total gearing. assuming rest of gearing is the same ? i'd assume there's gear differences in trucks and 'vehicles'. are diffs in general same gear ratio? so the xx/xx is obviously a hint to more or less gearing, but how to put that into ones individual calc/setup, relate to ir etc. ? when talking motors, isnt it the total gearing that matter, and not some count of whatever teeth ?

I am trying to catch a drift, with the gearing jargon, and believe noone has the same rc, or at least far from everyone. I can see how 'add or lose a tooth on pinion/spur' would make sense in a gearing/motor/battery/esc matter, as it tells the direction (up/down) of gearing change. Just don't get how some pinion/spur count would matter, if its individual in many cases.

as for gearing, how do i find the good range, or the outer limit? is any change in gearing a motor at all, a sure downturn in efficiency ? How to determine for a motor ? as overgearing and undergearing (i prefer to say 'more' and 'less', its making more at-once sense) does stress the motor otherwise off than standard, the temp rise from either going too fast, or going too tough ?

Right, some reading i have done along the sideline here in some years, but hope to be more active here in this year ;) BrianG's calculator is very neat, I need (sorry for rhyming) to figure out what gearing is meant with xx/xx.

im used to metric system, but do know imperial. the usual short numbers alone doesnt always compute. the switch of ',' and '.' is a bugger. if one doesnt know what data it is..32p 48p mod1 or checking diameters mm/" etc.

i would like to get at least one 44mm motor, any good bets on which ones are cheap ? l-cans and more ;) fastened endbells, can-wire-exit, no-ribs, and so on. well i would like some that has interchangeable endbells, if there's some of those ?

mainly want to switch motors from 36mm to 44mm and beyond.
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If knowing total gearing, weight of truck, and weight of wheels, can a kv-rating be calculated for a given battery voltage. ? Can BrianG maybe comment on this ?

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and a theor. q. : can you guys comment on POV: 4 x 2s1p 30c vs 1 x 8s1p 30c. goods and bads ? Disregarding wiring resistance and not thermal matters, amps, and runtime. I have this idea that 4 packs are more logic than 1 pack and would like to get low on that one..
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There must be some where to get 6mm mod1 pinions nearby europe ? do rcm sell this ?
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can rcm-shop please post high detail images, and specifications of the slipperential ?