Top Speed Physics

CLowndes888

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fubbletrouble888
As Special Stage Route X has arrived, it is now possible to reach the top speed of any car. Problem is, the speeds aren't 100% percent accurate to the real life top speeds. I tested the Veyron, the McLaren F1 and the Ferrari F40 to see if they could reach their claimed real-life speeds. With the Veyron, the highest speed I could reach was 403 KM/H, but that was going downhill. On the back straight it only achieved 396 KM/H, 11 off it's real life speed. Dumbfounded, I tested the McLaren F1; yet that was even worse. I managed to do 362 KM/H coming off the banking but couldn't go past 355 KM/H on the flat back straight. That's a full 31 KM/H slower than the 386 KM/H top speed. I then chose the F40 thinking that it could reach 322 KM/H and sure enough, the speed was achieved. But it kept going and ended up hitting 342 KM/H, 20 KM/H faster than the actual speed. All of this was done on Sports Soft to ensure a level field. So I want to know - what's causing this to happen? What aspect of the game's physics determine how fast a vehicle goes? Why can one vehicle go past it's real life top speed, whereas the other one struggles? Is the gravity too low? Are the aerodynamic properties working incorrectly? I'm bamboozled.
 

ARTAsean

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If I'm not mistaken that McLaren F1 top speed was set with the rev-limit increased. The in-game one is closer to the real deal.

I think the F40 top speed was set at the Nardo Ring which is an inherently flawed test as it's a humongous turn.

No clue about the Bugatti because it's a wanker-mobile.
 
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From what I understand...some top speeds are assisted by tailwind which gives them a little push towards the maximum velocity. I'm not too sure about the elements factor in GT Sport that contributed to this for top speed runs.

As for the McLaren F1 top speed, the official maximum speed quoted is 372 km/h. The record setting car actually had it's rev limiter increased in order to hit 386 km/h. We also have to factor in numerous element changes that may affect engine performance, and hence top speeds (i.e. temperature, humidity, air pressure, altitude, etc.)
 
3,058
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Dumbfounded, I tested the McLaren F1; yet that was even worse. I managed to do 362 KM/H coming off the banking but couldn't go past 355 KM/H on the flat back straight. That's a full 31 KM/H slower than the 386 KM/H top speed.
Try fitting the custom gearbox and set it to 380-390 km/h.
If I'm not mistaken that McLaren F1 top speed was set with the rev-limit increased. The in-game one is closer to the real deal.
The McLaren F1 in Gran Turismo is a massively flawed model with completely wrong gearing and exaggerated aerodynamic drag.
It's been that way since it debuted in GT5. 3rd gear in game can reach ~250 km/h. 4th gear IRL can reach ~240 km/h.
If you squeeze every bit of rpm out of 5th gear it stalls in 6th. The real car would pull hard into the rpm limiter in 6th gear.
 
697
Germany
Germany
As Special Stage Route X has arrived, it is now possible to reach the top speed of any car. Problem is, the speeds aren't 100% percent accurate to the real life top speeds. I tested the Veyron, the McLaren F1 and the Ferrari F40 to see if they could reach their claimed real-life speeds. With the Veyron, the highest speed I could reach was 403 KM/H, but that was going downhill. On the back straight it only achieved 396 KM/H, 11 off it's real life speed. Dumbfounded, I tested the McLaren F1; yet that was even worse. I managed to do 362 KM/H coming off the banking but couldn't go past 355 KM/H on the flat back straight. That's a full 31 KM/H slower than the 386 KM/H top speed. I then chose the F40 thinking that it could reach 322 KM/H and sure enough, the speed was achieved. But it kept going and ended up hitting 342 KM/H, 20 KM/H faster than the actual speed. All of this was done on Sports Soft to ensure a level field. So I want to know - what's causing this to happen? What aspect of the game's physics determine how fast a vehicle goes? Why can one vehicle go past it's real life top speed, whereas the other one struggles? Is the gravity too low? Are the aerodynamic properties working incorrectly? I'm bamboozled.

You should give P1 GTR a go. That bloody thing easily hits 420+ km/h on Mulsanne straight full stock! I can't even imagine how fast it can go when tuned and on the arrow-straight SSRX (I should try it myself too, actually)

There's also LaFerrari which accelerates way faster than the real thing does
 

CLowndes888

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You should give P1 GTR a go. That bloody thing easily hits 420+ km/h on Mulsanne straight full stock! I can't even imagine how fast it can go when tuned and on the arrow-straight SSRX (I should try it myself too, actually)

There's also LaFerrari which accelerates way faster than the real thing does
Yeah I'm going to, and I presume that it will be faster than the Veyron.
 
12,580
Antarctica
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What aspect of the game's physics determine how fast a vehicle goes? Why can one vehicle go past it's real life top speed, whereas the other one struggles?
Gearing (this includes tire diameter), maximum engine rpm, drag, probably some other resisting forces that I can't recall off the top of my head.

Is the gravity too low? Are the aerodynamic properties working incorrectly? I'm bamboozled.
Assuming that the cars are hitting the rev limiter, no.
 
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eran0004

Premium
9,690
Sweden
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eran0004
As Special Stage Route X has arrived, it is now possible to reach the top speed of any car. Problem is, the speeds aren't 100% percent accurate to the real life top speeds. I tested the Veyron, the McLaren F1 and the Ferrari F40 to see if they could reach their claimed real-life speeds. With the Veyron, the highest speed I could reach was 403 KM/H, but that was going downhill. On the back straight it only achieved 396 KM/H, 11 off it's real life speed. Dumbfounded, I tested the McLaren F1; yet that was even worse. I managed to do 362 KM/H coming off the banking but couldn't go past 355 KM/H on the flat back straight. That's a full 31 KM/H slower than the 386 KM/H top speed. I then chose the F40 thinking that it could reach 322 KM/H and sure enough, the speed was achieved. But it kept going and ended up hitting 342 KM/H, 20 KM/H faster than the actual speed. All of this was done on Sports Soft to ensure a level field. So I want to know - what's causing this to happen? What aspect of the game's physics determine how fast a vehicle goes? Why can one vehicle go past it's real life top speed, whereas the other one struggles? Is the gravity too low? Are the aerodynamic properties working incorrectly? I'm bamboozled.

Top speed is a force equilibrium: what stops you from accelerating further is that the sum of all forces acting on the car is exactly zero. Making all the variables of a car come together to produce the equilibrium at the exact right spot is incredibly difficult. Top speed is the end result of a lot of variables, some of which are squared, so a lot of tiny input inaccuracies can blow up to become a pretty substantial output inaccuracy.

If top speed accuracy is important, you (as a software developer) can calculate the difference between achieved top speed and desired top speed and then perform an arbitrary change to the aero drag (pretending that it’s the aero drag that is wrong when really you don’t know) so that the top speed becomes accurate. That might lead to other inaccuracies though, such as too high/low frictional losses, too much/little downforce, too much/little grip. But those inaccuracies are harder for the player to detect.

Ideally you would try to isolate and test each of these factors first, and when all of them turns out to be correct, then aerodynamic drag must be the culprit and you can perform your arbitrary changes with relatively high level of confidence.
 
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I've read that the Veryon requires to be configured in Top Speed mode (i.e. low drag, no wing deployed, lower ride height) in order to hit 407km/h. The regular mode hits about 380km/h according to a magazine which I couldn't remember. It's said that beyond 380km/h the rear wing would rip off due to structural limits.

But either way, environmental variables do contribute to the adjusted top speeds.
 

MatskiMonk

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Top speed is the result of an equation whose variables.. vary...

The CdA value can be fixed according manufacturer data, but air density/pressure/humidity and effective speed through it (i.e. accounting for head/tail wind) vary, and do make a difference to drag. They also would make a small difference to the engine power available to overcome that drag. IIRC a Veyron is using something like 800+hp to overcome aero drag at top speed.... loosing 1hp means you are not going to reach the same top speed - a 5mph head wind on dry air, versus a 5mph tail wind in humid air will mean you are not going to achieve the same speed. Tyre deformation also changes the rolling radius which effectively alters gearing, and then there's just the rolling resistance on the tyre - even if PD make an allowance for those things, they might not be quite the same as those values that were present when the real cars are top speed tested. As eran points out, things in this equation are multiplied by each other, and the effective speed through the air is squared... small changes add up. To get it "accurate" compared to a test on real world tyre, in a real world location, with real world weather, with real world drivetrain losses, would simply require PD to fudge the figures. IMHO this is no better than having it be "inaccurate".
 

CLowndes888

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Top speed is a force equilibrium: what stops you from accelerating further is that the sum of all forces acting on the car is exactly zero. Making all the variables of a car come together to produce the equilibrium at the exact right spot is incredibly difficult. Top speed is the end result of a lot of variables, some of which are squared, so a lot of tiny input inaccuracies can blow up to become a pretty substantial output inaccuracy.

If top speed accuracy is important, you (as a software developer) can calculate the difference between achieved top speed and desired top speed and then perform an arbitrary change to the aero drag (pretending that it’s the aero drag that is wrong when really you don’t know) so that the top speed becomes accurate. That might lead to other inaccuracies though, such as too high/low frictional losses, too much/little downforce, too much/little grip. But those inaccuracies are harder for the player to detect.

Ideally you would try to isolate and test each of these factors first, and when all of them turns out to be correct, then aerodynamic drag must be the culprit and you can perform your arbitrary changes with relatively high level of confidence.
It's not as straight forward as I thought...

I've done some more tests to try and understand the physics; this time with the P1 GTR. It was a rather curious experiment because the speeds were quite inconsistent, as if there was either a fierce headwind or tailwind acting on the car. I started my first lap and before going over the bridge, I got up to 435KM/H, and hit about 442KM/H going downwards. I got back to level ground and the car slowed dramatically, right down to 400KM/H before hitting the first banked corner. On the back straight, the car couldn't go any faster. When I started my second lap, the car was still going 400KM/H and my ghost data sped by, as if I'd picked up a vicious headwind. I couldn't even get to 410KM/H when going downwards. After the first corner, I proceeded to hit the brakes and stop the car. I accelerated again and hit 435KM/H, as if I'd picked up a tailwind. However, I don't think wind speed in simulated in GT Sport, so how can this happen? Why would there be a 35KM/H difference in speed? It wasn't the case with the Veyron or the McLaren F1, so I gather that downforce plays a role somehow.
 

K32

434
Australia
Australia
It's not as straight forward as I thought...

I've done some more tests to try and understand the physics; this time with the P1 GTR. It was a rather curious experiment because the speeds were quite inconsistent, as if there was either a fierce headwind or tailwind acting on the car. I started my first lap and before going over the bridge, I got up to 435KM/H, and hit about 442KM/H going downwards. I got back to level ground and the car slowed dramatically, right down to 400KM/H before hitting the first banked corner. On the back straight, the car couldn't go any faster. When I started my second lap, the car was still going 400KM/H and my ghost data sped by, as if I'd picked up a vicious headwind. I couldn't even get to 410KM/H when going downwards. After the first corner, I proceeded to hit the brakes and stop the car. I accelerated again and hit 435KM/H, as if I'd picked up a tailwind. However, I don't think wind speed in simulated in GT Sport, so how can this happen? Why would there be a 35KM/H difference in speed? It wasn't the case with the Veyron or the McLaren F1, so I gather that downforce plays a role somehow.

That'd be the hybrid system finally running out of power. The P1 goes on a sort of low boost mode after reaching 7th (which is why you are able to maintain ~430 km/h) , but after a while the energy is eventually spent and the car relies entirely on pure horsepower to keep going (the reason why you can barely stay above 400 km/h) .

As you slowed down the brakes generated heat, which is recovered as energy by the McLaren's ERS system, thus giving you that boost to once again reach the same top speed after accelerating anew.

Simple.

Hope this clears that up for you.
 
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CLowndes888

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K32
That'd be the hybrid system finally running out of power. The P1 goes on a sort of low boost mode after reaching 7th (which is why you are able to maintain ~430 km/h) , but after a while the energy is eventually spent and the car relies entirety on pure horsepower to keep going (the reason why you can barely stay above 400 km/h) .

As you slowed down the brakes generated heat, which is recovered as energy by the McLaren's ERS system, thus giving you that boost to once again reach the same top speed after accelerating anew.

Hope this clears that up for you.
Oh I completely forgot about that. I'm soo used to driving on regular circuit that I always expect to have it. I feel so dumb now:lol:
 

LeGeNd-1

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GTP_LeGeNd-1
As Special Stage Route X has arrived, it is now possible to reach the top speed of any car. Problem is, the speeds aren't 100% percent accurate to the real life top speeds. I tested the Veyron, the McLaren F1 and the Ferrari F40 to see if they could reach their claimed real-life speeds. With the Veyron, the highest speed I could reach was 403 KM/H, but that was going downhill. On the back straight it only achieved 396 KM/H, 11 off it's real life speed. Dumbfounded, I tested the McLaren F1; yet that was even worse. I managed to do 362 KM/H coming off the banking but couldn't go past 355 KM/H on the flat back straight. That's a full 31 KM/H slower than the 386 KM/H top speed. I then chose the F40 thinking that it could reach 322 KM/H and sure enough, the speed was achieved. But it kept going and ended up hitting 342 KM/H, 20 KM/H faster than the actual speed. All of this was done on Sports Soft to ensure a level field. So I want to know - what's causing this to happen? What aspect of the game's physics determine how fast a vehicle goes? Why can one vehicle go past it's real life top speed, whereas the other one struggles? Is the gravity too low? Are the aerodynamic properties working incorrectly? I'm bamboozled.

Top speeds have never been accurate in GT land because of how inherently flawed the aero and downforce modelling is. PD doesn't model underbody downforce from diffusers/venturi tunnels (or not enough of it by itself) so for cars that rely a lot on underbody downforce they has to fudge the numbers by giving it a lot more upper body downforce (wings/splitters) in game.

The Mac F1 generates most of its downforce from the underbody fans in real life, but if you look at the settings screen in GT it has way more downforce than even some race cars. So its top speed is going to be limited as upper body downforce generates a lot more drag than underbody.

The F40 is the opposite - it doesn't have any downforce in game and aero drag modelling in GT land is significantly lower than real life if a car has no downforce values - hence the higher top speed.

The Veyron is an interesting one. People who say it doesn't enter top speed mode in game is only half correct. If you drive in rear view you see that the spoiler goes up at 220 km/h, and actually goes DOWN at 370 km/h to simulate the top speed mode. However, top speed mode in real life also LOWERS the car's ride height to minimise frontal area drag. GT forgots to do this, and the car actually GOES UP when the spoiler goes down because of the loss of downforce (you can feel this easily when driving on bumper cam, the view would "bounce upwards" at 370 km/h), so the frontal area drag is actually increased. Also, the Veyron has something like 100 rear downforce which further adds drag like the Mac F1.

Remember also the wheelie glitch in previous games? It's because PD only modelled the downforce as a force vector perpendicular to the car. So when you rake the car forwards (front high, rear low), the downforce vector is now pushing the car forwards and gives exponentially higher top speeds with more speed. Like so F \ <-- R

TLDR, don't use Gran Turismo for verifying top speeds of cars :lol:
 
520
United Kingdom
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K32
That'd be the hybrid system finally running out of power. The P1 goes on a sort of low boost mode after reaching 7th (which is why you are able to maintain ~430 km/h) , but after a while the energy is eventually spent and the car relies entirely on pure horsepower to keep going (the reason why you can barely stay above 400 km/h) .

As you slowed down the brakes generated heat, which is recovered as energy by the McLaren's ERS system, thus giving you that boost to once again reach the same top speed after accelerating anew.

Simple.

Hope this clears that up for you.

The system does not generate the energy to charge the battery from heat!! It generates it by converting the kinetic energy of the cars movement into electrical energy using electric motors linked to the drive shafts. This energy charged the batteries in the car. Then, when needed, the batteries drive the electric motors which turn the drivr shafts as well as the petrol engine to make the car go faster.

CJ (owner of two hybrid cars)
 
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[QUOTE="MatskiMonk, post: 12611923 Tyre deformation also changes the rolling radius which effectively alters gearing, and then there's just the rolling resistance on the tyre - even if PD make an allowance for those things, they might not be quite the same as those values that were present when the real cars are top speed tested. [/QUOTE]

Are you sure about the tire deformation thing? I am no engineer or physicist but I am extremely familiar with drag race tires, no other racing tire that I can think of changes shape quite like they do. At the end of the day even though the diameter may change from load the tread still has the same rollout (or circumference), regardless of loaded diameter which is what really determines the tire RPM vs gearing. Thinking of drag race tires, I have always wondered if drive tire rolling resistance really affects speed, rolling resistance is usually thought of how much effort it takes to roll the tire but does that change when the tire is propelling or accelerating the car compared to tires on the non drive axle?
 
6,232
Canada
Canada
@LeGeNd-1 nailed it...GT physics are far too inaccurate, especially at the extreme ends of speed (play around with cars at really really low speeds, you’ll notice lots of weird things too), to try to find anything logical regarding top speeds of various cars.

Another thing to keep in mind about Route X, going back to GT5 and GT6, it had different physics than other circuits in the game. In any car, you could accelerate quicker and have a higher top speed on Route X than any other track in the game. I haven’t tested it in GT sport yet, but it wouldn’t surprise me if it’s the same as it was before.
 
1,208
Serbia
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Warlock__SRB
...it's not, it has same physics as any other track as far as I can see.

Regarding physics alone, if you push cars to the limit, you will see problem with tire model a lot. It is specially seen in FF cars, they simply don't act as they should. Also there are problems here and there with AWD/4WD cars too, for example R34 is basically RWD car with some controllers that in certain situations make it AWD. Also Veyron has really complex AWD system, by the way it looks in GTS it is simple all wheel permanent on.
Also aero is totally off on some of the cars, for example Group C cars never had that much of downforce, then there are RSR and LMS that basically have a bit different aero vs GT3 cars, and also all GT3 cars don't have same aero properties, not to mention notorious Gr3s lol...

There are many many more examples...

Cheers...
 

Scaff

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Are you sure about the tire deformation thing? I am no engineer or physicist but I am extremely familiar with drag race tires, no other racing tire that I can think of changes shape quite like they do. At the end of the day even though the diameter may change from load the tread still has the same rollout (or circumference), regardless of loaded diameter which is what really determines the tire RPM vs gearing. Thinking of drag race tires, I have always wondered if drive tire rolling resistance really affects speed, rolling resistance is usually thought of how much effort it takes to roll the tire but does that change when the tire is propelling or accelerating the car compared to tires on the non drive axle?


Yes it does still apply when the cars in motion, it just doesn't apply as much.

More force is required to change a body's state (Newtons first law), so it requires more force to over come rolling resistance to move from a body at rest to a body in motion. Once in motion less force is required to keep overcoming the rolling resistance, but it doesn't suddenly zero. Aero also plays a factor here, as aero load increases, the rolling resistance will also increase.
 
697
Germany
Germany
Top speeds have never been accurate in GT land because of how inherently flawed the aero and downforce modelling is. PD doesn't model underbody downforce from diffusers/venturi tunnels (or not enough of it by itself) so for cars that rely a lot on underbody downforce they has to fudge the numbers by giving it a lot more upper body downforce (wings/splitters) in game.

The Mac F1 generates most of its downforce from the underbody fans in real life, but if you look at the settings screen in GT it has way more downforce than even some race cars. So its top speed is going to be limited as upper body downforce generates a lot more drag than underbody.

The F40 is the opposite - it doesn't have any downforce in game and aero drag modelling in GT land is significantly lower than real life if a car has no downforce values - hence the higher top speed.

The Veyron is an interesting one. People who say it doesn't enter top speed mode in game is only half correct. If you drive in rear view you see that the spoiler goes up at 220 km/h, and actually goes DOWN at 370 km/h to simulate the top speed mode. However, top speed mode in real life also LOWERS the car's ride height to minimise frontal area drag. GT forgots to do this, and the car actually GOES UP when the spoiler goes down because of the loss of downforce (you can feel this easily when driving on bumper cam, the view would "bounce upwards" at 370 km/h), so the frontal area drag is actually increased. Also, the Veyron has something like 100 rear downforce which further adds drag like the Mac F1.

Remember also the wheelie glitch in previous games? It's because PD only modelled the downforce as a force vector perpendicular to the car. So when you rake the car forwards (front high, rear low), the downforce vector is now pushing the car forwards and gives exponentially higher top speeds with more speed. Like so F \ <-- R

TLDR, don't use Gran Turismo for verifying top speeds of cars :lol:

I mean, your post has valid points. I agree with most of them. But it still doesn't explain why Mac F1 has no torque whatsoever on 6th gear. When you reach the top end of 5th gear and switch to 6th, the car basically refuses to accelerate and even barely manages to hold the speed it already accumulated. As far as aerodynamics go, it shouldn't affect the engine performance that much (or should it?).

Comparing it to the Andy Wallace's VMax run, where F1 easily hits the limiter even on 6th gear and would probably easily handle the 7th gear too, GTS'es rendition of F1's power surely is confusing
 

Scaff

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I mean, your post has valid points. I agree with most of them. But it still doesn't explain why Mac F1 has no torque whatsoever on 6th gear. When you reach the top end of 5th gear and switch to 6th, the car basically refuses to accelerate and even barely manages to hold the speed it already accumulated. As far as aerodynamics go, it shouldn't affect the engine performance that much (or should it?).

Comparing it to the Andy Wallace's VMax run, where F1 easily hits the limiter even on 6th gear and would probably easily handle the 7th gear too, GTS'es rendition of F1's power surely is confusing
Yes if it results in excessive levels of drag in comparisons to the real car, but as has been said the GT F1 model is poor in many ways.
 
6,232
Canada
Canada
...it's not, it has same physics as any other track as far as I can see.

Regarding physics alone, if you push cars to the limit, you will see problem with tire model a lot. It is specially seen in FF cars, they simply don't act as they should. Also there are problems here and there with AWD/4WD cars too, for example R34 is basically RWD car with some controllers that in certain situations make it AWD. Also Veyron has really complex AWD system, by the way it looks in GTS it is simple all wheel permanent on.
Also aero is totally off on some of the cars, for example Group C cars never had that much of downforce, then there are RSR and LMS that basically have a bit different aero vs GT3 cars, and also all GT3 cars don't have same aero properties, not to mention notorious Gr3s lol...

There are many many more examples...

Cheers...
Have you done any actual tests?
 

LeGeNd-1

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I mean, your post has valid points. I agree with most of them. But it still doesn't explain why Mac F1 has no torque whatsoever on 6th gear. When you reach the top end of 5th gear and switch to 6th, the car basically refuses to accelerate and even barely manages to hold the speed it already accumulated. As far as aerodynamics go, it shouldn't affect the engine performance that much (or should it?).

Comparing it to the Andy Wallace's VMax run, where F1 easily hits the limiter even on 6th gear and would probably easily handle the 7th gear too, GTS'es rendition of F1's power surely is confusing

As Scaff said, it's not a lack of torque or power, but the Mac hits an aerodynamic drag wall basically. IIRC the default gear ratios are also wrong on the F1, and especially the 6th gear is much longer than the actual car which further compounds the problem.