121 replies to this topic

[mcerqueira]

Everytime a new super-duper-hyper car arrives it promptly "lives a Formula 1 in the dust bla bla bla...". This time is the Bugatti Veyron. Been reading the article on Car magazine and the performance figures of 2.5 0-100kph (0-62 mph) and stating that it beats a F1 to 200 mph...

Now I know the massive downforce an F1 has and that ultimate top speed is of course not the issue but even so I think an F1 will only start to loose from 200 mph on, after all it has almost the same power and wheighs a quarter, that would surely give it a huge initial advantage.

Does the trick DSG seven speed box and 4wd of the Veyron give it sufficient advantage to offset the huge power/weight ratio diffence?

Did several searches but couldn't find current acceleration figures, anyone as some data to share?

[McGuire]

These sort of comparisons don't do a lot for me. For cars with significant power/weight ratios, acceleration is mostly a function of available grip. If the tires and suspension are optimized for longitudinal acceleration (in other words, set up the thing like for drag racing) lots of cars can produce numbers that can make exotic supercars or F1 racers look pretty lame. So what does all this mean? Not much to me.

How do the Bugatti Veryon and the F1 car compare in interior cabin volume? That stat is far more important to me. Maybe you can pick up chicks with the F1 car, but where are you going to put them?

[mcerqueira]

...that was my point, sort of not the chick part though...

Actually It was a starting point to see current performance figures, the 0-62 time is also interesting to see were the F1 looses it's huge p/w advantage (presuming worst traction?). I'd imagine it won't be much faster than 2.5 secs?

[Greg Locock]

Since 0-60 in 2.5 seconds is only just over 1g there is no reason why the tyres would struggle at that acceleration, therefore the reason would be elsewhere.

The rotating inertia of the engine driveline and wheels is probably dominant at that sort of acceleration.

[Bill Sherwood]

Originally posted by McGuire
THow do the Bugatti Veryon and the F1 car compare in interior cabin volume? That stat is far more important to me. Maybe you can pick up chicks with the F1 car, but where are you going to put them?

And FFS can people please spell 'lose' correctly?

[McGuire]

Originally posted by Greg Locock
Since 0-60 in 2.5 seconds is only just over 1g there is no reason why the tyres would struggle at that acceleration, therefore the reason would be elsewhere.

The devil you say. An F1 car (or the Veyron) can put 100% of its power down from a standing start?

Engineers say the darnedest things.

[Greg Locock]

No,I didn't say that at all.

I measured the longitudinal grip available from a bog standard street tire. For 10 seconds at a time it was delivering 1.2 g on normal asphalt, in a normal event, in a controllable fashion.

The limitation is elsewhere in the system.

Or have I been trolled?

[Ross Stonefeld]

I recall reading/hearing an F3 car car can out-accel an F1 car 0-60mph?

[MclarenF1]

I recall seeing a video of a British SBK, an F1 car and an offshore powerboat race. I'm not 100% certain, but I think the bike was ahead for maybe 60 ft and then the F1 car pulled it. Does anyone else remember this?

F1 car power/weight assume 1,323 lbs and 900 hp, approx 1.47 lbs/hp (.67 kg/hp)

While a superbike is about 500 lbs with the rider (350 + 150 seem reasonable?) and produces about 200 hp which equates to 2.5 lbs/hp (1.13 kg/hp)

Could the higher CG of the bike allow higher initial acceleration?

Assume wheelbase and CG heights of:
F1
WB = 122 in (3,100 mm)
CG = 10 in (254 mm)
accel factor for 100% weight transfer = 12.20g

SBK
WB = 55 in (1,397 mm)
CG = 40 in (1,016 mm) w/rider (just a guess)
accel factor for 100% weight transfer = 1.37g

so it is fairly obvious that the motorcycle is going to be wheelie limited and the F1 car is going to be traction limited. Does anyone else want to continue? I have to get back to work....

[wegmann]

I thought F1 cars got up to 100mph in 4 seconds or so, so why couldn't they do 62 in 2.5?

Like McGuire said, let's set up the F1 car for maximum acceleration and see what happens. Ballast all the way in the rear. No brake ducts. Max engine power (hey, we're not going to use the two-race engine rule, are we?) And how long is the race? If it's short we want high-downforce to get grip early, if it's long we want low-downforce for maximum top speed.

I'm not convinced the Veyron would come close to the F1 car in any performance comparison, but unless someone lets me test both, I can't really say for sure. The two cars are designed for completely different purposes, with two completely different sets of rules about what is allowed (one being the F1 Technical Regulations, the other being some country's environmental and vehicle safety rules).

[J. Edlund]

A F1 car do 0-100 km/h in slightly above 2.5 seconds. However, 100-200 km/h is done in about the same time.

A F1 car is grip limited up to around 150 km/h which results in pretty bad acceleration 0-100 km/h. The reason for the bad grip is the low cog, the tires required by the regulations and the weight distribution the tire sizes call for. Since the rear tire isn't that much wider than the front (compared to earlier F1 cars) much weight must be at the front.

Bugatti Veyron is all wheel driven and should not be that dependant of weight transfer.

[McGuire]

Originally posted by Greg Locock
No,I didn't say that at all.

I measured the longitudinal grip available from a bog standard street tire. For 10 seconds at a time it was delivering 1.2 g on normal asphalt, in a normal event, in a controllable fashion.

The limitation is elsewhere in the system.

Or have I been trolled?

No, I am not trolling. I thought maybe you were kidding. These cars are both profoundly traction-limited, especially at 0-60 or anything involving a standing start.

[Engineguy]

Claimed acceleration:
0-100km/h 2.5sec
0-200km/h 7.3sec
0-300km/h 16.7sec

Anybody have standing start F1 timings?


Wheels: 20-inch alloys (front), 21-inch alloys (rear)
Tyres: Michelin Pilot Sport PAX, 265/680 (front), 365/710 (rear)

engine and gearbox weight 650kg (1430 lbs)

kerb weight 1888kg (4154 lbs)

Add driver:
test weight 1956kg (4304 lbs)

1956/605= 3.23 times F1 weight

1001/930= 1.08 times F1 HP

1956/1001 = 1.96 kg/hp Veyron
0605 / 930 = 0.65 kg/hp F1

A few points:
The same higher CoG that helps Veyron rear wheel traction reduces Veyron front wheel traction.
Even 2005 F1 tires would be much softer compound than road tires, I assume?
Much higher inertia in drivetrain, wheels, tires.

[Nathan]

I would have to think at some point drag becomes a big factor in things. I could believe a Veyron would beat a F-1 car to 200mph due to this, even if you trimmed the F-1 car. But I do have a hard time believing Bugatti's number's are with road tires.

[F1Champion]

No way, the F1 car would always win. Past 200mph is maybe another matter but I can't imagine with the amount of weight the Bugatti has its going to put the power down and outdrag an F1 car.

I remember watching TV programme on the F1 car vs. Superbike vs. Powerboat. At the start the Superbike pulled away but once the F1 car reached a certain speed the downforce and grip came together and propelled it past the Superbike. If an F1 car can outdrag a Superbike then I have a hard time thinking that the Bugatti will out do a Superbike.

[McGuire]

Originally posted by Engineguy
Anybody have standing start F1 timings?

Any stats you can find will not mean very much. As you know, these cars do not use "standard" gearing... and from a standing start they can smoke the tires hard with any gearset in the truck anyway.

[McGuire]

For those who are into these apples vs. oranges vs. pork chops comparisons, here is one Road & Track did recently on one-mile standing start with an interesting variety of vehicles...


http://www.roadandtr...article_id=2572

[Ross Stonefeld]

apples and pork chops sounds good

[Greg Locock]

OK, the question I was getting at is why, if a very ordinary standard tire can give mu=1.2 longitudinally, did the 4wd only achieve less than 1.1g on reasonably expensive tires?

[bobqzzi]

I'd imagine that aero-drag is the dominant factor. The Veyron will also have much greater power under the curve.

[McGuire]

Originally posted by Greg Locock
OK, the question I was getting at is why, if a very ordinary standard tire can give mu=1.2 longitudinally, did the 4wd only achieve less than 1.1g on reasonably expensive tires?

Wheelspin.

[Lukin]

Greg, with what vertical load did the tyres reach mu=1.2? It's have to be a 1.3g load or so (assuming Fz~Fy^.7) wouldn't it. Is that approximation roughly valid for all tyres?

Im guessing the 1.2g was either on a tyre testing machine or in braking?

In initial take off, before any weight transfer happens, both tyres can only have a maximum of 1g vertical load if they are starting on a flat surface. So until the load transfer begins they won't be able to generate the 1.2g longitudinal load your talking about.

By the time they do have the vertical load to achieve 1.2g (or whatever your aiming to do) Im guessing the engine can't produce the forward thrust required anyway.

I think it's a case of when the engine can do it, the tyres can't. And then the roles get reversed. Under braking it's no worries, but going backwards is always easier than going forwards.

I guess no one is privy to a time/distance plot for longitudinal acceleration of a F1 car or a rocket propelled tank.

Also, what happens when 1956kg of overpriced scrap metal tries to take turn 1 at Barcelona at 190 odd km/h?

[Greg Locock]

It was under braking. I see no reason why the braking load should be different conceptually to an accelerating load, so far as the tire goes. This was the instantaneous mu, ie Fx/Fz, so weight transfer is accounted for (and not very important in the context of an accelerating AWD such as the Bug).

I'm in the process of researching that 0.7 exponent, it seems to work better for lateral than longitudinal loads. In lapsim he uses the equation

Fy(max)=Fz*(mu0-dmu*Fz)

where mu0 is around 1.75 (or more) for an F1 tyre, and dmu is .05/1000N

Which is quite a different shape to

Fy(max)=muref*Fz^0.7/Fref^0.7*Fref

which seems to work OK for that Avon F3000 data

Measured mu long seems to be greater than measured mu lat, generally. That makes sense to me, does that agree with other people's experience?

Back to the Bug - at 100 kph the aero drag is about 70 lb, say 4% of the accelerating force, and rolling resistance is about 2%... so if the Bug's tyres were only as good as those of a cheap SUVs then 1.1 g accel to 60 could be explained away as a result of those loads. But I put it to you that at lower speeds the aero drag is less, and the tyres must be better, so we are still left with a puzzle.

If the tyres are good for mu>=1.4 (WAG), and it is all wheel drive so weight transfer is fairly unimportant, and the acceleration is traction limted, why is the average acceleration to 60 mph only 1.1g? 1.2g would be 2.35 seconds, by the way.

[Admiral Thrawn]

These figures are estimates for an F1 car of around 2004, so in the low 900 horsepower range, with medium downforce.

0-100kmph : 2.6s

0-150kmph: 3.9s

0-160kmph: 4.1s

0-200kmph: 5.0s

0-250kmph: 6.5s

0-300kmph: 9.9s

So, obviously much quicker than the Veyron, which is to be expected, except to 100kmph (where the F1 car is traction limited).

[MclarenF1]

here is an interesting thread from a few years ago discussing CoF.

http://forums.autosp...?threadid=39295

[Engineguy]

Interesting plot I pulled together from various sources. Solid lines based on data, the dashed line extensions are my quicky estimates based on the aerodynamics and horsepower... for example the Champ Car hits a brick wall at about 185 mph, I assume the F1 car does too. Many magazines only give time-to-speed data up to 130 or 150 mph.

Keep in mind that the Bugatti trace crossing the Champ Car trace at about 18 seconds doesn't mean the Bugatti is passing the Champ Car... it just means that at the 18 second mark they're both traveling the same speed... the Champ Car is way ahead... and the F1 car is out o' sight.



EDIT: My extension of the Corvette Z06 trace is probably wildly optimistic since it has only 500 HP to the Ford GT's 550 HP.

[desmo]

Interesting I wonder what Top Fuel cars might do with no restrictions whatsoever, they almost seem to operating by a different set of physical laws as it is!

[Admiral Thrawn]

That graph isn't quite accurate because F1 cars were hitting 370kmph (230mph) on the Monza circuit during testing this year, and 330kmph at several other circuits, and have been in that ballpark for the last several years.

They only 'hit a wall' above 300kmph (186mph) at high downforce circuits (e.g. Monaco).

[Wuzak]

A test was run at Suzuka using the MP4/4 at the end of the 1988 season. Due to the limited space they were allowed to use they could not do a standing 1/4 mile/400m.

Standing Start Distance elapsed
km/h in metres time (s)
0-10 0.7m 0.5s
0-20 2.3m 0.8s
0-30 4.1m 1.0s
0-40 6.6m 1.3s
0-50 10.0m 1.5s
0-60 14.3m 1.8s
0-70 19.5m 2.0s
0-80 25.3m 2.3s
0-90 31.5m 2.6s
0-100 38.9m 2.8s
0-120 52.6m 3.3s
0-140 77.7m 3.9s
0-150 86.4m 4.2s
0-160 98.8m 4.4s
0-180 125.2m 5.0s
0-200 159.4m 5.6s

The car was equipped with a 5th wheel, and the (rather large) data logger placed on the sidepod of the car. The car was still in Suzuka spec.

[Engineguy]

Originally posted by Admiral Thrawn
That graph isn't quite accurate because F1 cars were hitting 370kmph (230mph) on the Monza circuit during testing this year, and 330kmph at several other circuits, and have been in that ballpark for the last several years. They only 'hit a wall' above 300kmph (186mph) at high downforce circuits (e.g. Monaco).

That is consistant with my graph... by "hit a wall" I don't mean actual top speed, but where the trace takes a hard turn toward horizontal.
Not trying to create the definitive graph (impossible... which of many aero/gearing configurations "defines" what an F1 car is?), just an interesting comparison of a variety of cars.

[Powersteer]

Nice work Engineguy.

Easy on praising the top fueler or Ratliff shall return ;)

Comparison really splits the men from the boys. Champ car leads the pack to 100 miles an hour, is it because of the torque factor or slick tyres when comparing to the F1 car? Is the F1 car under launch control? I guess the Veyron only does what its suppose to do, beat the great McLaren F1.

[McGuire]

Originally posted by Greg Locock
If the tyres are good for mu>=1.4 (WAG), and it is all wheel drive so weight transfer is fairly unimportant, and the acceleration is traction limted, why is the average acceleration to 60 mph only 1.1g? 1.2g would be 2.35 seconds, by the way.

So a tire is good for 1.4 g of longitudinal grip, resulting in a potential acceleration of 1.4 g...that is, provided 1.4 g worth of rotational force is supplied at the wheel hub, of course. But what if there is more torque than that? The tire will spin on the pavement, won't it? What is the acceleration rate now?

[Greg Locock]

Why do they have to drive at full throttle?

Or more likely, change up early

Or even more likely, use TC

These people are drivers, they should be driving the car to get maximum performance, not applying step input controls.

After all, if they are trying to establish the optimum braking they don't just jump on the brake pedal as hard as they can.

[Lukin]

Originally posted by Greg Locock
It was under braking. I see no reason why the braking load should be different conceptually to an accelerating load, so far as the tire goes. This was the instantaneous mu, ie Fx/Fz, so weight transfer is accounted for (and not very important in the context of an accelerating AWD such as the Bug).

If the tyres are good for mu>=1.4 (WAG), and it is all wheel drive so weight transfer is fairly unimportant, and the acceleration is traction limted, why is the average acceleration to 60 mph only 1.1g? 1.2g would be 2.35 seconds, by the way.

I wasn't doubting that it wouldn't be able to generate that load under acceleration (drag cars do it), more thinking along the lines of the few occasions when there is both the vertical load and the accelerating load from the engine at the same time.

Had slight brain fade there sorry. If the tyres are good for mu=1.4 @ 1g vertical load then it must be a problem with the power delivery to the contact patch.

[Lukin]

Does the rate of change of acceleration forces (Fx) at the contact patch effect the overall traction. Guess that does come back to wheelspin a little.

[Greg Locock]

Well, maybe, according to the big bang bikies. Unfortunately this is so far removed from any tire model I've had to play with that the answer is a definite maybe.

[Lukin]

Big bang bikies?

It could be simulated on a tyre testing machine couldn't it?

[McGuire]

Originally posted by Greg Locock
Why do they have to drive at full throttle?

Or more likely, change up early

Or even more likely, use TC

These people are drivers, they should be driving the car to get maximum performance, not applying step input controls.

After all, if they are trying to establish the optimum braking they don't just jump on the brake pedal as hard as they can.

Full throttle is not required to break the tires loose on cars like these.

Drag Racing 101: with any car capable of wheelspin, too much or not enough throttle will harm the acceleration times. The more overpowered the car the more sensitive it will be. If the chassis doesn't work very well here or the torque curve is tricky, it will be even more difficult.

I don't know where we got the idea that just because a tire can do 1.4 longitudinal g, the car will just drive away from a standing start at 1.4 g like a train leaving the station. Does it work that way for lateral grip? No. Just because the tires are capable of 1.4 g lat, that doesn't mean the chassis is, or that the driver can find it. Longitudinal grip, same thing. Acceleration or braking. If it were as easy as tires, why would anyone bother with chassis tuning?

You will find that high-powered road cars often turn better standing-start acceleration times with the TC shut off. The calibration usually won't be optimized for maximum straightline acceleration but for safety and handling. If this time was turned with the TC on, well there ya go.

[McGuire]

Originally posted by Greg Locock
If the tyres are good for mu>=1.4 (WAG), and it is all wheel drive so weight transfer is fairly unimportant

No, due to weight transfer AWD is relatively unimportant...at least in straightline acceleration from a standing start on normal pavement. As Engineguy noted, AWD is a limited-sum game for this purpose. To whatever extent the chassis loads one tire pair, it will unload the opposite pair -- laterally, longitudinally, diagonally. When any tire pair is loaded unevenly, the total grip of the pair is reduced. Drag racers have no use for AWD; this is why.

[McGuire]

Originally posted by Lukin
Does the rate of change of acceleration forces (Fx) at the contact patch effect the overall traction. Guess that does come back to wheelspin a little.

Wheelspin and wheel speed. Take a look at the acceleration rate of the TF car. Does any tire in the world have a rolling CF like that? So how does the car DO that? From a standing start it can't be aero downforce eh.

[Canuck]

Barrels of VHT super-sticky stuff. Not that 8000hp can't overwhelm any traction we can throw out.

[Lukin]

I am going to buy the Haney book and did a quick search on here for posts about it.

Found this relevant post from Ben.

The Chuck Hallum paper referenced in the thesis desmo linked to has a fairly good theory in my opinion. He explains that the 4-5g accelerations are a result of the transfer of tread momentum in the contact patch. He appears to suggest that the friction coefficient itself is around 1.5-2 but that the normal load is increased by the momentum transfer.

Bear in mind as well that the load sensitivity of mu is a based on steady-state conditions, instantaneous load transfer and the temperature changes that occur cloud this picture considerably and would certainly be relavent in the case of a dragster.

Ben

[McGuire]

Originally posted by Admiral Thrawn
That graph isn't quite accurate because F1 cars were hitting 370kmph (230mph) on the Monza circuit during testing this year, and 330kmph at several other circuits, and have been in that ballpark for the last several years.

They only 'hit a wall' above 300kmph (186mph) at high downforce circuits (e.g. Monaco).

It's not that the graph is not accurate. Modern race cars are nearly infinitely adjustable in chassis setup, aero and gearing. At Monaco and Monza you may as well be talking about two different cars. Their performance characteristics and stats will be as different as any two road cars you select ...one more reason these road car vs. race car comparisons are fun but meaningless. Allow the race car guys to adjust their stuff for and on the same test venue the road car will lose every time. Road cars aren't adjustable.

[Greg Locock]

Mcguire wrote

quote:
--------------------------------------------------------------------------------
Originally posted by Greg Locock
If the tyres are good for mu>=1.4 (WAG), and it is all wheel drive so weight transfer is fairly unimportant
--------------------------------------------------------------------------------



No, due to weight transfer AWD is relatively unimportant


end quote

que?

[Ben]

Originally posted by Greg Locock
It was under braking. I see no reason why the braking load should be different conceptually to an accelerating load, so far as the tire goes. This was the instantaneous mu, ie Fx/Fz, so weight transfer is accounted for (and not very important in the context of an accelerating AWD such as the Bug).

I'm in the process of researching that 0.7 exponent, it seems to work better for lateral than longitudinal loads. In lapsim he uses the equation

Fy(max)=Fz*(mu0-dmu*Fz)

where mu0 is around 1.75 (or more) for an F1 tyre, and dmu is .05/1000N

Which is quite a different shape to

Fy(max)=muref*Fz^0.7/Fref^0.7*Fref

Where did you find the details of the equation in lapsim?

Also where does the 0.7 come from?

Ben

[Paul Ranson]

This is taken from the data logger on our single seater hillclimb car, the track this was logged at is more or less straight but not level. About 540kg with driver, 620BHP. It would be fun to go to a drag strip (or better a clean tarmac runway...) and see what happened... The numbers here sort of line up with the claims for CART and F1.



Lower chart is throttle, the flat bit is fully open regardless of the scale on the left. The upper is wheel speed measured on one of the front wheels and shown in km/h. The x-axis is time in seconds.

Paul

[Lukin]

That's a slip ratio of about .0875 at 160 km/h! Awesome work! Do you have a long g sensor?

For those of us without rear wheel speed sensors, could you be so kind as to generate an XY graph of slip ratio (RWS-FWS)/FWS against Longitudinal G.

[Greg Locock]

Ben asked "Where did you find the details of the equation in lapsim?

Also where does the 0.7 come from?"

It's in the tire setup page in lapsim.

The 0.7 is just an average for a rule of thumb I'd observed for several different tyres over the range 0.2 to 2 times the nominal wheel load

Fy(max) increases proportional to Fz^0.7

It's slightly confused because for real data the slip angle for maximum Fy tends to change with Fz, that is, the cornering stiffness changes as well.

Looking at the Pacejka formula he uses a quadratic (a1 Fz^2+a2 Fz) but does not really work very well for beyond the peak slip ratio.

[Ben]

Thanks Greg,

On motorcycle tyres the Pacejka slip stiffness equations are fairly poor to be honest. Having just fitted Pacejka to a load of F&M data I'm rapidly losing interest in it. To go into that much detail yet enforce a single vertical spring rate and have no thermal or surface effects amazes me.

Chris van Rutten's approach in LapSim is apparently a much reduced set of Pacejka equations and in my opinion that is far more appropriate for motorsport applications.

I certainly think that plotting slip ratio vs. longitudinal G from logged data is a very sensible thing to do. It's the closest you'll get to knowing what you actually want to optimise to achieve the best acceleration.

Ben

[McGuire]

Paul,
Thanks for posting the DA for your hill climb car, great stuff. Is this the Cosworth XB NA powered car?


...it's a totally divergent subject, but climbing a grade is fairly interesting dynamically, when you think about it...