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# Hub Dyno mathematics

### Tech Articles

If it's not really about tuning or wiring. Then it belongs in here.

Hi all.

We are currently building our own dyno as stated in previous forum posts.

We have received our KLAM-CFK550 With rated max cold brk TQ 4660@650Axle RPM and it's scaling down from there with a max sustainable Axle RPM of 6000RPM .

However i associate who does not really believe in my idea that this will be able to dyno High powered Drag cars -.-

He is still in the age of Inertia based dynos that rollers are the "Only" option Or Engine dynos .

Yeah i know that Eddy-current brakes loose efficiency when getting hot.

But i had the calculations in my head before but i need to double check.

Is it Engine RPM / Transmissions Ratio = Prop shaft RPM / Final drive ratio = Car Driven Axle RPM?

Yes, gearbox ratios are the number of input revolutions for 1 output. Some get confused with overdive top gears, but that's because it's less than one input for one out - math still is the same. Same principle for differential - it's input revolutions to one out.

They're actually more useful for 'drag' cars as most can be programmed to simulate the acceleration rate for the vehicle's weight, which is useful for things like figuring out how and when boost comes in, torque converters, shift points, chassis tuning, etc. Another advantage is if it uses bolt on hubs, rather than being driven by the tyres, tyre slippage on the rollers cannot occur.

Attached is the specs for the brake. I've got 4 of them and we are designing it to be "modular" with the ability to couple 2+2 together for the high powered cars when needed but also retain the AWD capability for most of the time.

You have the same arguments i use and what my knowledge and experience tells me. But yeah doubters and knowitalls will always exist. even in a small town like Trelleborg, Sweden with its 35.000 residents

We usually reply within 12hrs (often sooner)

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