Power-to-weight ratio law and bikes

**AIkonNZ** · 12th September 2008, 17:07

Hi all,
New member here - Currently saving for a bike after recently getting started on my license (On [L]arry license at the moment - sigh).

I hear of a law change looming in regards to cc ratings being pushed aside for power to weight ratio values.

So being useless at maths, conversions and pretty much everything else I thought a thread could be useful for myself and fellow n00bs, where bike power to weight ratios could be posted for easy lookup.

I had been looking at a Hyosung GT250R: After panicking that my future bike would be ripped from my fingers by Mr. Plod I decided to work out the p2w ratio to double check it was still an option.

Hyosung GT250R
Bike weight = 171 kg dry (to be on the safe side)
Bike power = 29ps:10,000rpm (I am told this unit is a 1:1 with the HP rating)
29ps:10,000 = 29 HP (Close enough anyways)

So first i converted the HP in to KW:
29 HP = 21.63 KW (I used a online calc, but you roughly multiply the HP by 0.77 to get the KW rating)

Now we know our bikes KW rating (If you didnt already), we can use this formula to work out p2W ratio:

Power to weight ratio = (power divided by the weight) x 1000

So (21.63 KW divided by 171 kg) x 1000 = 126 KW power per tonnes weight

And if we add the "90 KG rider + fuel" bit into the total weight we are going to be even lower.

So Hyosung GT250R is still sweet option for [L]arrys under the new law.

Lets do a 2008 Kawasaki Ninja 250R (The rough method)

Bike power: 31PS:11,000rpm
Bike weight: 152 kg dry

31PS = 31 HP (1:1)

31 HP multiplied by 0.77 = 23.87 KW

(23.87 Kw divided by weight of 152 Kg) x 1000 = 157KW power per tonnes weight!!

OH NOES!!...Illegal!?? but wait.... if the new law follows Aussies standard (Which i havent bothered checking) then the 90 KG rider and fuel weight is added to the calculation so that will bring you back under the 150 KW per tonne legal limit.

(23.87 Kw divided by real weight of [152kg bike +80kg rider + 10kg fuel]) x1000 = 99KW power per tonne.

So sweeeet as!

Well thats my examples: Im no mathmagician so please point out any rediculous mistakes or such. I will be surprised if theres none

Please feel free to post more examples too! Be interesting to see a bike that would actually not be legal with the new law.

**James Deuce** · 12th September 2008, 17:13

THis will give you an idea. The power to weight ratio INCLUDES a 90kg rider, as you said. Stop hyper-ventilating. Find a paper bag and breathe into it. Remove paper bag before you pass out.

http://www.rta.nsw.gov.au/licensing/...iceriders.html

**AIkonNZ** · 12th September 2008, 17:16

Cheers dude, that site is gold

Oh and re: "Remove paper bag before you pass out." - Why isn't that half the fun??

**MaxCannon** · 12th September 2008, 22:50

I predict a resurgence in the 400cc market.
Mine calculates to 138KW / ton (including the 90KG for rider)

I think it's a pretty sensible limit really. It's around the point where the bike will still perform well and isn't stuck at 80kph up a hill like some gutless 250s but it's not so powerful that a touch too much throttle will get you in trouble before you know what is going on.

**fridsy** · 14th September 2008, 01:43

What if your 190kg rider?... can I get an even more powerful bike?....lol

**chester** · 14th September 2008, 22:00

no Hornet 250 on the list!!!!!

**lostinflyz** · 14th September 2008, 23:03

whats the go gonna be with guys who been on restricted for years and owning NSR250's and the like.

i wonder if they will follow the trend of allowing those who have been under the old laws to continue under them as they have in the past on occasions or force upon us the will of the people.

anyone got a date for the new laws??? roughly

**Junkers** · 15th September 2008, 00:05

Are they banning 2 strokes over here?

I've always wanted an RGV..

**breakaway** · 15th September 2008, 01:12

They aren't banning anything. Right now, it's perfectly legal for a learner to jump onto a RS250 right after passing his BHS and scratchies. A RS250 is more powerful than any 400cc 4 stroke. But with these new laws, that won't be possible. It's not limited by engine size, it's the amount of power produced by the engine.

**MarkH** · 15th September 2008, 07:20

Originally Posted by fridsy

What if your 190kg rider?... can I get an even more powerful bike?....lol

High performance bike mod - eat less pies and get some exercise (I said LESS pies, walking to the pie shop is the WRONG exercise) you lazy fat bum!

This is cheaper than buying light weight parts that save a KG or 2.

**MarkH** · 15th September 2008, 07:21

Originally Posted by lostinflyz

whats the go gonna be with guys who been on restricted for years and owning NSR250's and the like.

Resticed for years? My guess is that those guys will finally go and get their full.

**fridsy** · 15th September 2008, 12:40

Originally Posted by MarkH

High performance bike mod - eat less pies and get some exercise (I said LESS pies, walking to the pie shop is the WRONG exercise) you lazy fat bum!

This is cheaper than buying light weight parts that save a KG or 2.

Thanks for the personal insult.... fell better?