Power to weight ratios.
Discussion
Off the line...differences in gearing, grip levels, torque/weight ratio will help the Beemer get off the line and transmit the power to the road more effectively.
At the top end of the speedo...the lower BHP of the BX will limit top speed as the power needed to cut through the air at higher speeds increases the faster you go, so 160bhp is never going to crack the 150mph barrier in the BX whereas the extra horses in the Beemer let it stretch its legs to 155-ish.
There's also the fact the BMW driver will be better able to concentrate whereas the Citroen driver will be distracted by trying to hold on to the various bits of trim rattling and falling off as you nail it (speaking as a previous Xantia owner)
At the top end of the speedo...the lower BHP of the BX will limit top speed as the power needed to cut through the air at higher speeds increases the faster you go, so 160bhp is never going to crack the 150mph barrier in the BX whereas the extra horses in the Beemer let it stretch its legs to 155-ish.
There's also the fact the BMW driver will be better able to concentrate whereas the Citroen driver will be distracted by trying to hold on to the various bits of trim rattling and falling off as you nail it (speaking as a previous Xantia owner)
Personally I'd put the difference down to every 330i BM engine producing more or less 230bhp all day long, whereas Citroen's figure was probably a notional ambition...
Seriously though, save any silly gear ratios on either part, up to 60 it'll be traction that causes the difference, beyond that Aero takes over from weight for that sort of power output.
If the BM 'feels' a lot quicker at lower speeds it's probably more down to better engine torque spread.
ETA - I'd also be fairly surprised if a BX actually weighed 50% less than the BM like for like
Seriously though, save any silly gear ratios on either part, up to 60 it'll be traction that causes the difference, beyond that Aero takes over from weight for that sort of power output.
If the BM 'feels' a lot quicker at lower speeds it's probably more down to better engine torque spread.
ETA - I'd also be fairly surprised if a BX actually weighed 50% less than the BM like for like
Edited by The Wookie on Friday 25th February 09:54
There are basically two things that a car must overcome to accelerate: weight and aerodynamic drag.
Weight is the main issue at low speeds and you can overcome that with a high power to weight ratio.
But drag becomes increasingly important as the speeds go up (to the point where it becomes more significant than accelerating the mass) and this - for given drag characteristics - can only be overcome with power.
So a car that gets 300bhp/ton from 600bhp and two tons will accelerate quicker than one with the same drag profile that has 150bhp and weighs half a ton.
Weight is the main issue at low speeds and you can overcome that with a high power to weight ratio.
But drag becomes increasingly important as the speeds go up (to the point where it becomes more significant than accelerating the mass) and this - for given drag characteristics - can only be overcome with power.
So a car that gets 300bhp/ton from 600bhp and two tons will accelerate quicker than one with the same drag profile that has 150bhp and weighs half a ton.
B Huey said:
I've been looking into the BMW 330ci recently, it struck me the power to weight ratio is very similar to my old Citroen BX 16 Valve.
The performance figures for the BMW are pretty much in a different league to the Citroen.
What performance figures are you using to compare them? 0-60 is obviously going to be biased towards a RWD car, especially if it has favourable gear ratios for that test. What other performance stats do you have?The performance figures for the BMW are pretty much in a different league to the Citroen.
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