Not to mention that, on a significant number of racetracks, the design of the track itself means that gearing for acceleration between the corners is often more important than gearing for top speed. Many tracks have far more curves and corners than long straights, and if you gear for a higher top speed on the long straights, you would end up losing out on the rest of the course.
These trade-offs are less of a problem with modern transmissions, which have more gears and much faster gear changes than older manual transmissions, but the fact remains that on many tracks it’s acceleration between the corners and speed around the corners that are more important than outright top speed.
And just to make this answer really explicit, “no ground friction” here means “jets don’t need friction between their tires and the ground to accelerate, because they accelerate by pushing back against the air that they shoot backward, not the ground”. It’s (mostly) not a question of e.g. the energy lost in that friction.
This is all well and good but I guess I am looking at cars that want to hold the title of “fastest road car in the world”. I think some street legal car recently eclipsed the Veyron but if not we can go with the Veyron. A $2.6 million car. And as noted above it will empty its gas tank in 12 minutes doing in and shred its tires.
Most super cars hover around 200 MPH top speed. Yes there are some well past it but +/- 20 off 200 MPH seems to be a sweet spot for most of them and breaking out of the high end seems to need considerable effort and cost.
Hence my question what is it that around 200 MPH for a road car seems so difficult and expensive to surpass?
Probably the whole diminishing returns thing on engine life, power curve, gas mileage, tire life, etc.
I do wonder how much wear is on the Veyron engine after 12 minutes at 267?
Fair enough. That question is less interesting to me, and probably not coincidentally, as a car buff i’ve always hated the Veyron.
It is, to be sure, an incredibly impressive piece of technology and engineering, but it leaves me completely cold. It seems to have been designed largely as a dick-measuring exercise for people who want the fastest and most expensive thing possible, but who aren’t actually that into cars. Also, while i recognize that aesthetics are rather subjective, i find it pretty ugly, both in photos and in person.
Lack of tire grip makes going around a low-bank corner faster than say, 150 MPH, VERY difficult. High-bank tracks like in NASCAR and very large corner radii like at Indy reduce the required side grip and speeds may get to 200-250.
If you want to go faster than 250 you need minimal cross-section area, adequate weight or downforce to achieve traction, and you go in a straight line. Like these guys:
The square of the speed means you design a given aerodynamic body and that is the limiting factor. There is no magic design that eclipses the next one when comparing cars in similar categories. They’re all pretty close. So while HP can vary the basic size of the car (frontal area) and the drag coefficient remain close. The limiting factor is the drag involved.
If you look at aircraft they have very little frontal area compared to a car. Take the same Lycoming 108 hp engine. Put it in a Piper Colt and it cruises at 100 mph with a top speed of 140. Pull it out and stick it in a Long-EZ and it cruises at 144 mph with a top speed of 185.
Here you can see that changing the frontal area and thus drag makes a tremendous difference.
To summarize my last post, sports cars are all going to be similar in frontal area and drag coefficient so there they will all be affected by the same limiting factors of drag.
Unless you want to drive in a tandem seat car that is half the width of a regular car then 200 mph is roughly the top speed you’re going to hit without adding considerable amounts of hp for each mph driven faster. And at that speed you also have to have enough down force on the drive wheels. High speeds will lift cars up taking away traction.
There is a rough terminal velocity for a given amount of total drag.
Also, I meant to add that if you add another 40 hp to a Piper Colt the increase in cruise speed does not approach that of the Long-EZ. You get better climb performance and maybe 10 mph of cruise speed. The plane is limited by it’s aerodynamics.
also keep in mind that cars designed to travel at those speeds have a lot of downforce because they’re meant to stay on the ground. Downforce adds drag but prevents the car from trying (unsuccessfully) to be an airplane.
There’s literally nowhere in the world you can drive a Veyron at 267 for 12 minutes. You’d need 60 miles straight and flat with no traffic or debris and an army of emergency responders to ensure reasonable response time when it blows up.
But it’s even worse than that. Drag force goes up as square of speed, but the power needed to maintain speed is force x speed (because work = force * distance, so work/time = force * distance/time). So the engine power needed to overcome drag goes up as cube of speed. Which means if you double the engine power without increasing weight or air resistance, you only increase top speed by 25%. (2^(1/3)=1.25)
as mentioned above it’s all a bit theoretical over 200mph - no-one is actually going to do this speed for more than a few seconds - maybe - on an Autobahn. Even most circuits you’d struggle to hit 200 on the longest straights.
One thing that no-one has mentioned is gearing. most sports cars are geared to accelerate very quickly at a little lower speed than we’re talking about. If you gear your top ratio to achieve a very high top speed, you may well be left with a very looong top gear at the expense of acceleration in that gear. In reality, that would mean that other gear ratios would probably be longer too.
Unless you stick a megaton of power in the engine, you’ll be left with a “relatively” slow sports car with a high top speed.
The Bugatti is a fantastic car, hugely expensive and it’s rumoured that VW lost $6M for every one sold. That’s what it takes in the 250mph market!
“no ground at all” … The grades and curves of the road surface would limit the speed of a jet plane that tried to go along like a car… its far easier if you are intending to go straight down a flat runway than to start doing turns AND go over grades!
“ground friction” is in a way wrong - The car goes faster when “ground friction” is higher. It can reduce the downforce surfaces…
Around 400 MPH your car is going to have a rudder … and probably on the fly adjustable downforce… (trim… a bit like pitch control )
People are correct in saying that drag increases approximately as the square of speed, but it’s perhaps of more interest to discuss the power requirement, which increases as the cube of speed. So if 500 horsepower gets you to 200 MPH, 1000 horsepower will get you to 252 MPH. That’s assuming no changes to the basic shape of the car - but the reality is that it’s hard to pack 1200 horsepower into a car without making it physically large, increasing its drag. The Veyron is a damn big car compared to slippery low-slung Lamborghinis and Ferraris.
Engineering is all about meeting specific goals. Supercars are not designed to set straight-line speed records, and therefore not optimized for it. Supercars are designed to look fantastic, go around corners fast, and accelerate quickly.
A car optimized for top speed would look something like this car, which set a 403 mph record. It’s fully enclosed, it’s twice the length of the Veyron, and barely has room for 1 person inside. It looks like it won’t generate much downforce at sane speeds, and appears to have a very narrow wheel track, so it probably won’t win any races that involves corners. And even if a street-legal variant could be made, there probably isn’t a market for it.
According to the Wikipedia article on the Blue Flame, they used custom-designed tires with an outside-diameter of about 35 inches. This is considerably larger than the typical street-car tire, which means lower RPM for a given speed (and therefore reduced centrifugal stresses). Also, they weren’t using the wheels for propulsion. That car hit 622 MPH.
The Thrust SSC, which hit 763 MPH, didn’t used tires at all - it used solid aluminum wheels. Like the Blue Flame, it didn’t rely on the wheels for propulsion, so fore/aft traction wasn’t a major concern - and at those speeds, I’m guessing lateral traction isn’t even a huge concern compared to aerodynamics.
I’ve always wondered what a suitably faired and geared turbo-era F1 car circa 1984 could do in a straight race.
Very light but with 1500bhp from a 1.5 litre engine you are looking at a small frontal area. must stand a chance of getting close to 500kph
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