Power to Weight ratio..... A Fools economy??

[GTI POLO]

Hi,

Ive read a few threads on an chipped Polo Gti Vs all sorts of other cars.. Mazda3 MPS is the most recent.

Now despite a chipped Polo having a similar Power to weight ratio as many of the cars considered...

Doesnt weight matter less and less as speeds rise?

So does a car with say 300kw and a Power to weight the same as a chipped Polo still have the advantage as speeds rise?? say from 100km/h to 200km/h

If weight matters less and less and then there is 300kw as opposed to say 152kw from our Polos...... Doesnt the 300kw car start to stretch its legs on us...

[GTI_jim]

are you talking about about economy (thread title) or performance???
I dare say a 300kw car will beat a chipped polo GTI most of the time anyway...

[Grant]

weight only effects acceleration, not top speed. generally acceleration tapers off when approaching the top speed of a car.
so correct me if i'm wrong...
a 300kw car will have a greater top speed than 150kw car. meaning that the faster your traveling, the slower the Polo's acceleration will be relative to the 300kw car.
does my jabbering make sense?

[GoLfMan]

it has a number of factors, those numbers are "ideal" numbers in that they are flywheel power.

so drivetrain loss comes into it so do gear ratios, power curves etc.

power to weight is a very misleading indication of a cars actualy speed in some senses, but its a good guide as to how quick your car may be..... ill stop my rambling

[JCM308]

From what I've read on various posts regarding chipped Polo's most people only talk about low accelleration (0-100, 80-120 etc) which makes sense. If you take on a powerful V8 you'll probably have it until about 140 and then you're gone (expirienced this many times with previous cars). Of course these sort of tests will only be done at the track

[Guy_H]

I Think Grant is spot on the money in this case!

[dubbed]

Well I'm no doctor of Physics so this could be completely wrong, but think about the following. (Just to make the numbers easy to understand I've chosen a motorbike with 1/3 of the power of a big V8 sedan). Again, I could be totally wrong as this is a wild hypothetical guess; but think about this:

You're going to have a very hard time catching a 110kw Ducati 999R in a 300kw VE GTS. The 999R has a power-to-weight ratio of approximately 100kw:160kg whilst the GTS has something like 100kw:400kg, these are rough estimates mind you.

A 999R will cover 0-400 metres in 10.3~ seconds going at over 215km/h whilst the GTS will be lucky to be hitting 175km/h and covering the same distance in (if it's lucky) less than 13.5 seconds. Now if you think about how much ground they will both cover after the 400 metre point one will have a clear advantage and already have a few seconds head start. Even if the Ducati maxes out at 260km/h (just to make a point) and the GTS could hit a top speed of 300+km/h (again all very hypothetical) the Ducati would be kilometres in front taking a hell of a long time for the GTS to gain that lost ground that the 999R has already coverd.

There's a lot more to power-to-weight to factor too - power curve and delivery, gearbox ratios, final drive ratio etc.

So what's my point? A Polo with a better power to weight ratio will get to one point quicker than another car with less power-to-weight even if it has more total power. Sure the other car will eventually catch up given enough road, but that all depends how far they're racing in a straight line...

Instead of all the rambling I could've just posted this:
http://www.youtube.com/watch?v=g2DBtNo2ipc

(Imagine the Polo is the bike and the 911 is a Mazda3 MPS lol!) So yes you're right, but the top speeds we can get on our roads means a chipped Polo has a very good advantage

[GTI POLO]

Not the clearest answers...

Im talking about two cars with the SAME power to weight ratio but one car has 300kw and the other has 150kw...

Im asking as speeds rise, does this power to weight thing mean less and less and the more powerful car will come over the top..

[Timbo]

In summary, E=MC^2

[VW GTI]

Not the clearest answers...

Im talking about two cars with the SAME power to weight ratio but one car has 300kw and the other has 150kw...

Im asking as speeds rise, does this power to weight thing mean less and less and the more powerful car will come over the top..

What gear ratios are they running?

The answer is not really simple.