k24madness

iTrader: (6)

Tran

I made a car performance calculator a while ago, while it does have some limitations, it is probably quite useful for this. I'll preface this by saying my launch model isn't very good and in my elapsed time on straightaway calculations, I can't get it to account for shift times (so I'll keep same number of shifts for both cars). Also, it was some time since I wrote it, so I hope I've not made any glaring errors with my data input....

I used the numbers above, with 18sqft frontal area to create 2 cars,
Car A, Cd=0.376, CdA= 0.63 standard top, closed windows
Car B, Cd=0.462, CdA= 0.77 convertible top, windows down

I assumed 2400# weight (with driver), 6 speed with 4.77 and a 140whp dyno that was used as an example for an S1 Supermiata power graph (this might not be exact, I ought to use data in tabulated form rather than reading off a graph). As a sanity check on the data, I calculate car A to have a trap speed of 95mph in the standing 1/4. Does that tie up with anything people have measured?

Both cars were calculated to be able to reach the gearing max of 118mph, but the graph below shows that there main difference is available acceleration at higher speeds. (the higher drag car is the solid lines)



At 60mph, car A has 3.0m/s/s of acceleration available and car B also has 3.0m/s/s available.
At 100mph, however, car A has 1.2m/s/s of acceleration available but car B only has 1.0m/s/s of acceleration available.

Trying to put this into context, assuming both cars having an exit speed of 60mph onto a straight with 500m before the braking zone,
Car A will travel that 500m in 13.07s, arriving at 105.6mph
Car B will travel that 500m in 13.18s, arriving at 103.8mph

If I made Car B1, which is car B but lightened to the extent to take the same elapsed time on the straight, I'd have to remove 52kg(115lb)!!! to get the time down to 13.07s. This car would arrive at 104.8mph. This probably isn't representative of a kind of parity weight though, while they'd spend the same time on the straight, the 52kg lighter car would make time everywhere else and on all straights with a lower top speed. If I make the straight only 200m long, then the equal elapsed time weight reduces to 30kg (66lb)

These results are quite interesting and while it does suggest that there is performance to be gained from lower drag, it does need to be considered if adding parts, eg a fastback, whether the weight gain for the drag improvement is worthwhile. The information I am lacking is how much time would be lost everywhere else from increased mass. Does anyone have this?

I can run more tests through the calculator. Is there anything anyone would like me to try?

Occam’s Racer