Have the rules changed or motors improved in regards to kv/voltage/rpm/erpm/heat/efficiency and all that?
I always followed the radium suggestions
Which has worked well for me so far but now we have guys like @zero_ads pushing a tonne of amps @21s through 205kv making a whole bunch of power at seemingly stable motor temps.
Is it as simple as 4wd spreading the load?
Not really. @zero_ads rear 6384’s see more amps than most people’s 2wd setups.
That table from radium is just a guide. It’s worth noting that Jimmy and Poast run way higher rpm than these motors are rated for. Anything over 12k rpm is generally not recommended.
Generally speaking higher kv motors can handle more amps because they have thicker gauge copper windings. That said, the he high rpm’s these motors reach result in a lot of iron losses. So efficiency tanks as performance increases. It’s not uncommon for Jimmy and Poast to push 40, 50, 60 wh/mile when they are pushing the race boards.
I run 151kv at 21s and generally see 28wh/mile, but I also don’t rip like Jimmy and Poast.
Long way of saying, go high voltage and choose a motor kv that works with your gearing and desired top speed. There’s a lot of flexibility here and you probably won’t be unhappy with whatever you choose from 150kv to 200kv
Yeah efficiency loss is the big one, and on the hardest of days on the track I start getting close to 100 wh/mi.
BUT on the track it’s go BIG or go home sooooooo lol
As long as your board isn’t your way to get home 
and don’t overheat and get forced home. 
In colder weather you can run higher rpms without issue. But there is a bit of a runaway effect after usually 25-30C ambient where you can get overheating with higher rpm setups.
There was a phase where magnets were curved N45 as I was thinking stronger magnets = more torque but that worsened operating temperatures. Now the magnets are thinner N45 and the back iron is thicker, so the effective strength is similar to N42 which did reduce torque very slightly but the motors also run a bit cooler now and are slightly cheaper to manufacture.
The fan is also around 1mm thicker so that may contribute to improved cooling. These changes were made from our batch 6 onward.
At the end of the day it really depends on your setup, riding style and climate. Some people can overheat 205kv 12S in summer and others are running 245kv with no issues. So there’s a bit of “find out and see”
What gear ratio you thinking?
12-67 on brp’s I think maybe 11 for t-race
It’s a good KV die tons of torque at 11 and 12 not a lot of top end for the bigger tracks. On BRPs. I’ve only run 205 and above at 21 so it’ll be interesting to see your temp experiences.
In the winter it doesn’t seem bad. If you’re riding in summer in hot temps that’s probably not ideal. All depends what you’re using the board for.
I would not run that setup on anything other than Radium/reacher/SKP modors. Everything else has lower quality bearings.
Then again, I’m about to run little maytech 170kv on 20s and 5.5 gear ratio… so I guess do what sparks joy and deal with it later if it doesn’t work out. 
Just t-race and short track. They’re reacher 55’s and 85’s. I did notice on a hot day they would get to 80 degrees pretty easily in 2wd but I haven’t had any issues at all since going 4wd.
I should need less amps with 175’s id be happy if I could get around 110-120 into them maybe.
Hmm I would assume you’d want more amps on 175 due to loss of torque in the wheel size.
I’m running 110 @16s on the rears at the moment. 14-67 on the brp’s. Would be an extra 2kw at 21s and more gear reduction. I dunno I would have thought it’d go pretty well.
What kv are you running right now 175?
Oh I think I misread this as 175mm wheels in a way to compensate for top end.
I was saying that at 11/12 67 gear ratio you might not have enough top speed. But if you’re just doing short track stuff you should be fine.
Yeah 175kv. For best brakes and acceleration I don’t really gear for much over 55 km/hr. For t-race anyway
Fuck around and find out😁
