you cant really compare truck axle to motor shaft, even if they are the same dimension, they are 2 totally different animals. you would smash a motor shaft to bits if you did that sort of thing with it.
Dude? are you serious?
Why would 8mm stainless steel shafts smash to bits?
How is it possible that all the precision downhill trucks work without smashing to bits? Because they all have 8mm diameter stainless steel axles.
the only reason 15mm wide belts can be problematic is due to the arch coming off the hanger of a caliber truck, there is a point where the nice square & flat clamping area of the hanger begins to change shape - this means itās not good for clamping to anymore, the alignment of the motor mount when too close to the centre of the truck becomes very difficult because its not square/flat.
I have calculated that a maximum belt width of 12mm is compatible. Of course you could add extra washers onto the axle and push the wheel out further. Each speed washer is normally 0.8mm thick so you need another 4 of them to allow a 15mm wide belt. But even at this point you are clamping onto the edge of an area that is not perfectly flat & square, each truck is different also, I personally prefer to keep a few mm away from the angle change that occurs on the hanger.
I have never had an issue with 15mm belts on caliber trucks. Though Iāve always run single motor setups until this last week and Iām using a randall clone on that build.
Itās mount dependent, If your mount is very thick like the current enertion mount which is 17mm thick itās not a good idea to use 15mm belts. With the original enertion mounts, which were just 13mm thick, it would work easily because they offer more space because they are mounted closer to the wheel pulley.
Ahhh, I didnāt realize your new mount was so thick.
yes Iām serious. there are hundreds of different grades of stainless, all with different properties. none of which are used in the gap vid you posted because street skaters donāt use long board trucks.
stop using potatoes to prove salad.
@onloop
Your statement about increasing the length of the lever and thus the force is wrong.
Actually, the inverse is true: increasing the diameter will decrease the tangential force acting on the grub screw and/or key.
Torque = Force x Lever, so for a given Torque the force will decrease with longer levers, ie thicker shafts, which could be a benefit if you need to convey more torque.
But I get what youāre saying, if an 8mm axle is already OK for a given application, then a 10mm axle will not change anything.
I also agree there may be other more important weak points before a (good quality steel) 8mm shaft becomes an issue.
Maybe if I have some time over the weekend Iāll do some stress calculations for our typical setup to see in which ballpark weāre playing.
On a side note: I wouldnāt want to drop in on those precision trucks, they donāt have an axle in one piece. Failure mode would be losing a wheel instead of bending an axle 
. Those trucks are clearly designed for precision not for vert/park.
Also bear in mind that from a structural perspective, plain carbon steel is often a better choice than a lot of the common stainless steel grades.
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since Iām getting a free physics lesson I might as well ask some more questions.
So in terms of the lever & load concept.
Does it matter where the torsional load is coming from, from outside inwards vs inside outwardsā¦ when accelerating itās coming from the outside in, when braking itās coming from inside out.
Does this change anything?
So now that you are starting to understand the science behind increasing shaft size you can see why 8mm shafts are inadequate for driving larger drive pulley sizes under heavy load.
Of course all of this is irrelevant if you donāt have the battery pack to drive this amount of power. You can be using the best motors in the world and it would just be window dressing without the power to drive it.
Correct! Iām not a scientist, but I do have lots of experience building eboards.
I do know that the drive train is only as strong as the weakest link, I doubt many people will argue thatā¦
Over the last 3 years of investing hours & hours on forums & building many eboards I have never heard anyone say they have snapped an 8mm shaftā¦
I also sell motors, lots of themā¦ Never had one snapped shaft! Even the cheapest motors I could find in china never had a snapped shaft. Something else always gets destroyed before the shaft - normally the belt followed generally by things melting due to heatā¦
I also strongly value evidence & real world test dataā¦ you donāt need to be a scientist to gather data or learn from it.
For instance when I was curious about using 3mm pitch belts, I invested in various configurations and tested them to learn the facts. I realized anything under 15mm wide wonāt work. This is not just my opinion its knowledge gained from doing the testsā¦
There is a big difference between opinion vs facts, So letās make it clear as day - itās simply your opinion that 8mm shafts are not strong enough.
So until you can give us data or evidence you need to stop saying stuff like
Based on the evidence presented so far there is no reason to stop using 8mm shafts. However, I am willing to change my mind when you can provide some evidence that they fail under load.
The last thing we need is people reading this thread and starting to think that 8mm motors shaft are somehow a problem that need to be avoidedā¦ As a community, we need to promote facts and filter opinion.
The really isnāt a difference, either youāre accelerating and your motor is applying torque to the drive system, causing the wheels to exert a tangential force to the pavement or youāre braking in which case your motor is dragging (torque in the other direction), causing the wheels to exert a force in the other direction. In both cases there is torque on your motor shaft. But: as acceleration on an e-board is generally stronger than braking, acceleration torque will be larger than deceleration torque and will strain your shaft more.
Acceleration and deceleration are governed by Newtonās second law: Force equals mass times acceleration F = m x a. To accelerate an object with mass m, you need to apply force F.
Come to think of it, you could determine the actual max torque by measuring max acceleration = the time it takes to reach a certain speed when going full-out. You obviously know rider/board mass so you can then calculate the force F and thus the torque.
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If there are absolutely no examples of 8mm shafts failing under load, what is the issue? Sure 10mm shafts will be stronger, but for what reason? Heck, lets do a 12 mm shaft as that will be even stronger. The more standardisation of component dimensions the better it will be for us consumers, & just adding a whole new set of pulleys etc to match a new shaft diameter that wasnāt even needed seems a bit unnecessary.
This topic on motor shafts should have its own thread so people can find it easier. Verry interesting 
Iāve used both. This isnāt new tech. Having choices is a good thing. Standardization? Do you see alot of excitement coming from that camp? Doing things the same way all the time just for the sake of consumer comfort is basically boring.
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Iāve actually used all three sizes.Still have yet to snap any size shaft. I think the availability of the 10mm pulleys might be less than 6mm and 8mm, which would be my only concern. Although I now know of a source for 10mm pulleys, they only offer two tooth profiles that I would use.
I am also switching to a different belt type, one better suited to high torque applications. curvilinear vs trapezoidal. The drive I am building is not intended for conventional use either, not to say you couldnāt use it to cruise around 30mph or less.
The fact is, all the improvements I am making are out of necessity. We are looking to pull a large amount of wattage at some very high speeds. 8mm is just too close to the edge on tolerance to trust something wont go wrong. We are also machining the trucks so the wheel pulley will be riding on a third bearing and much larger shaft than 8mm.
Will the improvements I make be noticed at low speed? Most likely, yes. This drive should also work well for off-road use.
For the record, I do not recommend riding at any of the speeds I have mentioned. It is highly dangerous and death is only a moment away!
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Oh then Iām out! Haha
Have to post the disclaimer every now and then. 
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@chaka seriously broā¦ I hope you donāt die manā¦ thatās the last thing we need on the newsā¦
I can hear the news report now:
Man Killed by unidentified-high-speed-devil-board, Freinds of the man said he built it at home using 10mm bits of steelā¦ Today at 4 pm the tragedy occurred during a Police helicopter pursuit that went horribly wrong after chasing man on a custom made electric board doing 80mph through small town. A witness on the scene said he saw strange lights coming from under the board then the rider and board vapourised leaving two burning lines on the ground for 100m. The witness was taken to the hospital and treated for shock and burns to 50% of his bodyā¦the area has now been closed by the army hazmat team due to high levels of radiation being detected in the surrounding area. .
Ride safe people!
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