51 replies to this topic

[vik]

How come my 17 year old Cousin can run faster than my 86 year old Nan?

Are they running similar power/weight ratios?

[minimarco]

The nan probably had her sub-frame solid mounted at some point.

And she stopped leaking oil ages ago.

[Wil_h]

What we seem to be missing here is any actual facts. We are supposed to be comparing a mini with a specific bhp/ton and a modern car with a specific bhp/ton.

So, My 998 turbo had 100bhp weighed 750kgs and got to 60 in 8.5 seconds, bhp/ton = 133

typically a 998 with 60bhp and 750kgs would get to 60 in 12 seconds, bhp/ton = 80

So all we need now is a moden comparison.

Ford Fiesta 1.4 (2005) 80bhp and 1100kgs 60 in 13.2 seconds, bhp/ton = 72

So, the reality is that the original hypothesis was wrong, feel fee to scour the net for futher examples. The 0-60 of the turbo was timed with GPS, the other is an approximation, but typical.

[oltonlad]

the reason a mini is not as quick 0 - 60 is simple its called evolution of technology and aerodynamics and old age.

You ever tried to run as fast as you used to? I have and i cant. A few horses have certainly left my stable.

i can hardly walk never mind run !!!!

hahahaha.............

[mini93]

text

Finaly, some common sence... as usual from wil_h. These topics always make me laugh though. I suppose the OP's Q was reffering to standard spec engines.
There's too much to vary in target markets for what was a budget car back then. space constraints etc. the mini only having 4 gears meant the gearing had to be made suitable for reasonable acceleration and reasonable top end. if you only wanted accel we would all be running round with diff ratio's over 4:1
the engines running on points and carbs. probably running low overlap cams. running electronics you can run a much more exotic spec and have it behave in a predictable way. better mpg, better power/torque... and the only way to make better power/torque/mpg and thus 0-60 is by increasing the burn efficiency... hence turbo's win hands down here and the creaton of the previously mentioned eco-boost

[Ethel]

The number of gears doesn't matter so much, it still takes less torque to accelerate the lighter Mini so, with the same power, it'd accelerate quicker in any particular ratio.

You'd have to compare the engines power bands along with the all the gear ratios you'd use to get to 60 fastest, it's not likely any car will use all its gears sprinting to 60 unless it's purpose built to do it. A production Mini can afford more favourable ratios because its top speed will be nearer to 60 than a more powerful, but bigger, rival. It can also afford to run a taller first gear, as it needs less power to set it rolling.

E.G.

Car A has 50hp to push 500kg - Car B has 100hp to push 1000kg

Everything else being equal they accelerate the same. But they have to accelerate through the air & if it takes 5hp to push them both at 30mph then A has 45 geegee's left over to accelerate it and B has 95. When they get to 60 (two times the speed) it'd need 2 X 2 X 2 times the power = 40hp so now has only 10hp spare for acceleration and B has 60hp, at double the weight it now has 3 times the power to weight ratio.

Of course if we're building cars for performance we look from the other end of the telescope: if two cars have equal power and the same top speed but one is half the weight it'll be twice as fast off the line but the fatty will close the gap exponentially as they speed up. (Yes, actually the rate the gap increases will reduce exponentially, but that isn't as catchy a way to put it!)

[Wil_h]

I like your thinking, but I think you typically need less than 20bhp to travel at 70bhp. But your maths make the point nicely.

Edit: Just to add to this, There is an extra bit of maths that you missed Ethel. At your predicted power consumption at 60 mph, you have a remaining power. But as we are accelerating we need to consider what we are accelerating. Therefore, the lighter car has 20bhp/ton remaining and the heavier car 30bhp/ton remaining, so not as large a differential between the two as initailly it looks.

Edited by Wil_h, 13 May 2012 - 04:53 PM.