J4CKO

iTrader: (1)

A mate of mine with a Scoob has been using maths to prove why his car is faster than mine, it probably is, New age plus PPP vs a Saab 9-3 Aero plus BSR remap, the butt dyno suggests its a bit quicker but its also noisier which adds to the impression, I don't however reckon it will pull 8 car lengths ! Not bothered either way and he isn't, just a bit of fun and banter, he was pretty good at maths at school but I am not sure his working out is spot on and I suspect based on previous Math Debates on here that there are far better mathematicians.

Anyway, there is only really one way to settle it but he is in Southampton so its a little impractical seeing as I am oop North.

He reckons that from thirty to seventy he will pull 8 car lengths, heres his working out. The thirty to 70 figures are examples, might be out but I am interested in emailing him tomorrow with plausible (real or not) arguments as to why his calculations are off the mark.


say i do 30-70 in 5 seconds, and you do 30-70 in 6 seconds

30mph = 13.4112 metres per second (m/s)
70mph = 31.2928 m/s

distance covered = [final velocity + (initial velocity / 2)] x time taken

Scoob : [31.2928 + (13.4112 / 2)] x 5 = 190 metres
Saab : [31.2928 + (13.4112 / 2)] x 6 = 228 metres

difference on a 30-70 is 38 metres
average car length is 4.5 metres

So thats 38 / 4.5 = 8 car lengths.

The Chief

8 car lengths from 30+ not a hope in hell - maybe 1 or two but i doubt even that. I had a rolling start once from the lights in my 260bhp classic against a Honda ITR which are about 187bhp (although lighter) and by 80mph i was only at most 1/2 to a car length in front.

he'd need at least an extra 100-150bhp to make a big difference

LG John

8 car lengths is massive - I don't care what the maths say that isn't going to happen. I'd be surprised if a M3 CLS could haul 8 car lengths on your saab over that increment!

dnc

Got my brain in overdrive here (or completely muddled ). For an increment of 30-70, if he does it quicker he will actually travel a shorter distance than you, so you can't really compare this as described i.e. pulling ahead as it is not a measure of performance. Also any simple maths will have to assume accelaration is linear which obviously is not the case. Also not sure where this distance = {final velocity + (initial velocity)/2} x time comes from - should be (initial + final)/2 x time ??? - but as said it assumes linear accelaration between 30-70 for both cars.

Have a think about the increment idea; the slower accelarating car will actually travel the further distance to attain the 30-70 increment so you could claim to pull ahead of him. In your case above the slower car taking 6 secs to cover the increment travels 22.3 x 6 = 135 m approx whereas the quicker 5 second car travels 22.3 x 5 = 112 m approx

As chief says there is no way on this earth either of you will be 8 lengths quicker so there is a major flaw in this somewhere. The pulling ahead distance will be defined by distance each car travels in a set time rather than set increment. I'll see if I can work it out from the info given

dnc

dnc

dnc

last bit of sad gittiness for the day. In the example above using accelaration figures calculated from above a=(v-u)/t and assuming this is then constant, if the 2 cars above raced from 30 mph the distance between them after six seconds would be approx 11 m or 2 and a bit car lengths. A 1 second difference for that increment is actually a significant performance advantage.

This uses s=ut + 1/2a(tsquared). sorry cant do a superscript for the squared bit

Hope that gives you a bit of ammo

j4ckos mate

You failed to take into account j4ckos famine provision which would slow all but most cars down with the exception of thrust ssc

J4CKO

iTrader: (1)

Firstly "Famine Provision" was my designation for stored adipose tissue, and is trademarked and secondly I suspect I weight a few "ounces less" than you !

I am, granted, Heavier than Reedy though and its him doing the maths.

J4CKO

iTrader: (1)

He has re-assessed his figures and we are currently working on 2 car lengths, its almost worth spending a couple of grand on further tuning just to get him doubting his maths skills.


Interested in one of those performance analysers that work on GPS, is there a device that will record the time taken to get from 30-70, i.e. start a timre as you hit thirty and stop it as you pass seventy, the magazine must use something like that ?

New_scooby_04

iTrader: (4)

Go to performance calculator, let someon else do the math for you

LetsTorqueBHP - Home

Ns04

vindaloo

In order to do a proper job, you'd have to model the performance by increments, IMO.

Just get him on the drag strip and laugh at his 60' time

J4CKO

iTrader: (1)

Its me with the Saab, and indeed it is rubbish in first gear, fwd, 288 lbs/ft limited in first and traction controlled.

NotoriousREV

http://www.cartestsoftware.com/cartest4.5/index.html