Kickass ratio for comparison

BenBenBen

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Jun 18, 2022
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Hello All,

I'm still designing my drivetrain theory for my YZF 250 conversion.

It's a bit hard sometimes to compare specs between all the e-bikes arround, so I tried to create a parameter that allows me to compare the "acceleration capacity @ low speed", which I'll call "Kick ass ratio".

To calculate it, I try to get enough public informations to get (or retro calculate) the torque @rear wheel, and the size of this wheel which gives me a linear thrust force. Then I divide it by the weight of the bike + a 75kg rider on it, and it gives me a figure that I can use for comparison. I think that figure is verry interesting, especialy for dirt bikes projects where max speed is not so much the point.

Here what I've found for the moment. There probably some aproximation, or maybe even mistakes, but it's seems like a good starting point.

Do not hesitate to give me the figures I miss, or correct me if I'm wrong somewhere. Or even give me your own built figures so I can add it in the comparison, just like I did with my project.
 

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  • kickass Ratio V2.jpg
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  • Motorcycles Setup Comparison.xlsx
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never heard about the "kick-ass ratio" as you calcoulate it. In the automotive industry there are extensive enginering documentation about simulating vehicle dinamics -

you can try to simulate the accelaration, but using more complex models than you did

https://x-engineer.org/vehicle-acceleration-maximum-speed-modeling-simulation/

But I can anticipate that you need a very detailed tyre and road data (Pacejka files) to get accurate results. On road Vs off road slip coefficients are completly different too... For this kind of bikes, as soon as you reach an acceptable torque spec @ rear wheel (>500Nm) any further analysis is just a waste of time. It's all about how you put such torque on the ground that means working on weight, suspensions geometry and tyre specs.
 
Glancing at it I think there is one slight error in the spreadsheet, you calculated thrust as torque divided by wheel diameter when I believe it should be by wheel radius. I have a similar spreadsheet and I was comparing my numbers and wondering why they were different by a factor of 2.

In reference to what BigBlock said while I don't have the source I have a note in my data sheet of the traction limit for bikes in dirt (I can't recall if this was dirt bikes or mountain bikes, probably calculated with mountain bikes in max braking conditions?) to generally be around 0.5-1g of acceleration which I've been using to calculate some things. But you get the idea you can find some rough numbers for acceleration (or deceleration) in your conditions to see if you're roughly at usable amounts of torque.
 
Right for the factor 2, sorry! But at is is only a "grade scale" ratio, it doesn't change anything for the comparison purpose. I'll update the formula for next rev and I'll add bikes.

And Yes, this is definitly not science! But just a quick way to compare 2 bikes taking in account:

- Rear wheel torque
- Rear wheel size
- weight to push

And for example, it's interesting to compare the KTM, the Storm Bee, and my YZF project. They are similar kind of bikes and I would equip them with same tires. So we can imagine that my bikes is supposed to perform more or less like a Storm Bee, and push a bit harder than the KTM. But definitely not like a Alta or A Stark that are a totally different category.

It's more like a benchmark view, to cross with riding "expenrience and feeling" than any acceleration capacity calculation.
 
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