GTP Cool Wall : XJ220

[Venom800tt]

959?

Heh, everyone forgets the Countach also...

Also I always heard the XJ220 had respectable handling (not as good as the F40, but not bad either), but had crappy brakes...

 

[dylansan]

*Famine wonders if the joke with me saying everything looks good in purple was a bit too subtle*

What are you talking about? The only color I can relate to you is indigo.

 

[Stevisiov]

To within a couple of miles per hour or so. Weight is a factor, just not much of one.

My fag-packet calculation says that, at 217mph, an extra tonne requires about 30hp - or, if it were a tonne lighter, the XJ220 could do 219mph.

I will agree that weight is a factor but as far as I could tell it is fairly negligible at 542bhp like many other factors which affect top speed.

You couldn't show your fag packet calculations could you, I am rather intrigued. As far as I can tell weight has no affect on aero dynamical drag which for a supercar is the primary resistance factor affecting top speed. I had a quick scout around to find some possible answers. The rolling resistance between the tyres and the road will increase with additional weight but since this isn't exponential and generally stays the same in motion the additional effects of this should be negligible. The extra weight can also increase drivetrain losses slightly which seems the most likely candidate for capping top speed, how does this work and how did you calculate the 2mph?

 

[niky]

Dear God... never ask Famine to show you his calculations... it'll take the rest of us hours to read them and try to understand them...

 

[Jim Prower]

Hey, it cant' be THAT bad. for an Enginerd like me.

 

[BlackedoutRX7LM]

I laughed at the OP and how inaccurate it was, glad you guys caught it right away.

I voted cool because the car has a striking appearance and isn't all that similar to other super cars. But as Famine has said, the car failed in so many facets that it's no where near sub zero. Im also not really a fan of throwing on big turbos and cutting the number of cylinders in half, imagined if Ferrari did that with the Enzo

 

[Famine]

I will agree that weight is a factor but as far as I could tell it is fairly negligible at 542bhp like many other factors which affect top speed.

You couldn't show your fag packet calculations could you, I am rather intrigued. As far as I can tell weight has no affect on aero dynamical drag which for a supercar is the primary resistance factor affecting top speed. I had a quick scout around to find some possible answers. The rolling resistance between the tyres and the road will increase with additional weight but since this isn't exponential and generally stays the same in motion the additional effects of this should be negligible. The extra weight can also increase drivetrain losses slightly which seems the most likely candidate for capping top speed, how does this work and how did you calculate the 2mph?

You're pretty spot on with rolling resistance - it's essentially (though not technically) a constant, but it does depend on the weight of the car. Ballpark figures are about 1.3% of a vehicle's mass is rolling resistance at any speed, including "additional" weight from aerodynamics (or lack of).

So, imagine (a) car is clipping along at 217mph with about 850lb of aero drag (just to guesstimate - it'll be here or thereabouts) and weighs a flat metric tonne. It has about another 30lb of rolling resistance - 1.3% of its weight - for 880lb total drag which, at 217mph, requires about 510hp to overcome.

Now (b) car is clipping along at 217mph with about 850lb of aero drag, but weighs a flat two metric tonnes (it's towing an identical car behind it ). It has about another 60lb of rolling resistance - 1.3% of its weight - for 910lb total drag which, at 217mph, requires about 525hp to overcome.


Assuming (b) car has 525hp, its top speed is 217mph. Give or take.

The reverse calculation is tricky and I haven't worked out a decent formula to get top speed out of it, but by repeatedly punching numbers back in you get something between 219mph (522hp) and 220mph (529hp) as its new top speed.

The calculation I did earlier used the real numbers for the Jaguar and I got a 23hp difference between it and car a tonne lighter, and a 2.3mph improved top speed. But I forgot what those numbers are now...


Aero Drag: Speed * Speed * Drag Coefficient * Frontal Cross-sectional area (square feet) * 0.00256
Rolling Resistance: Weight (lbs) * 0.0135
Total Resistance: Aero Drag + Rolling Resistance
Power Required: Total Resistance * Speed/375