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It helps that it weighs 4,600 pounds. (More than a thousand pounds heavier than the Volvo S60 they compare it to.) Heavier vehicles always do better-- which is

It helps that it weighs 4,600 pounds. (More than a thousand pounds heavier than the Volvo S60 they compare it to.) Heavier vehicles always do better-- which is why SUVs survive crashes so well.

guynamedloren 13y ago
I don't know much about the mechanics or engineering of the Model S, but I'm going to take a gander and say that much of that extra weight comes from the battery pack (and other parts of the non-traditional drivetrain), which isn't a (huge?) factor in a crash test (though I could be wrong). Just checked - yep - the battery weighs an estimated ~ 545kg or 1200 lbs [1]. I'd expect the structural components to actually be lighter than competitors, given that they're fabricated with aluminum vs steel. [1] http://www.teslamotors.com/fr_CA/forum/forums/model-s-battery-0 http://www.teslamotors.com/fr_CA/forum/forums/model-s-batter...
- mikeash 13y ago
  How much does the gas tank, motor, radiator, transmission, etc. in a normal car weigh? Have to subtract that out of the 1,200lbs to see how much extra is added.
  - akira2501 13y ago
    Mid-Range Estimates: Engine: 300 to 450 pounds Transmission: 120 to 140 pounds Gas Tank: 20 to 25 pounds Radiator: 20 to 30 pounds So, roughly 460 to 645 pounds. Add 110 pounds for 15 gallons of gas. The comparison is a little more difficult than this though, because the batteries just store energy. The Model S still has a (416hp) motor, there are a few other differences (regenerative vs standard brakes) and equivalencies (inverter vs alternator).
    - mikeash 13y ago
      Yep, it gets a bit tough, but that 460-645lbs range seems like a decent stab at it. I don't get the impression that the Model S's motors are all that heavy compared to the rest of this stuff, but I could be wrong. I'd also wager that the Model S needs a full set of mechanical brakes for emergency purposes, since it still needs to be able to stop safely even if all the electronics suddenly quit while going down the highway at 70MPH. And then there's the question of whether you compare against a 416hp motor, or a less powerful gas motor that would be more typical for a car that size....
      - akira2501 13y ago
        A Chevy 383 can make about 400hp+ in about 620 pounds. If we choose all our numbers for comparable cars that are highly in favor of the Tesla, we're still only likely going to match the weight of the Tesla's battery pack alone. The Model S curb weight is 4,647 pounds. A Cadillac STS, which is 5" narrower but very nearly the same in every other dimension as the Model S is only 3,922 pounds. That leaves the Model S 725 pounds heavier, still quite a bit of difference.
        ssmoot 13y ago
        It's in the ball-park though. Your assessment seems pretty fair. I've seen some call the Tesla's weight "insane" though. My old (still current gen) Volvo S80 T6 weighed 4,400lbs IIRC. I assume that's "dry" weight. Since a Model S is always "dry" aside from a gallon of wiper fluid or the like they probably weigh just about the same on the road. And the Model S is a bigger, faster car. My Jeep Grand Cherokee (with the panoramic sunroof option I didn't actually have) weighed 5,500lbs. Again, I assume like motorcycle manufacturers that car manufacturers are listing the "dry" weight. So that baby is probably over 3 tons wet when optioned up. The Cadillac seems on the light side for it's class. Even so, "wet" the difference in weight is probably one passenger. Despite it being a smaller car (5" actually seems pretty significant IMO, that's 5" less wiggle room to stay in your lane!). That's (I assume) the worst-case-scenario highest capacity Tesla. Performance is far in excess of most cars on the road already. Capacity with smaller battery packs will surely improve. It seems like weight can only go down from here, and it's not out of line with it's competition as is.
  - ssmoot 13y ago
    The 20+ gallon tank in my old Jeep Grand Cherokee would add over 300lb to the "wet weight". It also took (IIRC) an insane 7L of oil. So that stuff adds up.
corresation 13y ago
What is the calculated correlation between NHTSA vehicle safety score and vehicle weight. I don't know this, but suspect that it is a less significant factor than you imply. Add that the Tesla is 1000lbs+ of battery. Safety is engineering and materials. More materials help, of course, but more materials without the engineering simply equals more kinetic energy. There are vehicles from big SUVs to tiny SMART cars doing superbly on crash tests now.
- chemmail 13y ago
  Weight has a small impact, but you have to remember the low of geometric scaling.
- sbierwagen 13y ago
  Amusing that you mention the Smart Fortwo. http://www.iihs.org/news/rss/pr041409.html http://www.iihs.org/news/rss/pr041409.html ARLINGTON, VA — Three front-to-front crash tests, each involving a microcar or minicar into a midsize model from the same manufacturer, show how extra vehicle size and weight enhance occupant protection in collisions. These Insurance Institute for Highway Safety tests are about the physics of car crashes, which dictate that very small cars generally can't protect people in crashes as well as bigger, heavier models. "There are good reasons people buy minicars," says Institute president Adrian Lund. "They're more affordable, and they use less gas. But the safety trade-offs are clear from our new tests. Equally clear are the implications when it comes to fuel economy. If automakers downsize cars so their fleets use less fuel, occupant safety will be compromised. However, there are ways to serve fuel economy and safety at the same time." http://www-nrd.nhtsa.dot.gov/Pubs/808569.pdf‎ http://www-nrd.nhtsa.dot.gov/Pubs/808569.pdf‎ Large vehicles have historically been more stable and provided more protection for their own occupants than small ones, but they presented a greater hazard to other road users. Between 1985 and 1993, the population of light trucks - pickups, sport utility vehicles (SUV) and vans - increased by 50 percent in the United States. Since the major downsizing of passenger cars during 1975-82, light trucks have had a substantial and growing weight advantage over cars. By 1992, the number of fatalities in collisions between cars and light trucks exceeded the number in car-to-car collisions In car-light truck collisions, 80 percent of the fatalities are occupants of the cars. That raises the question whether the growth in the number and weight of light trucks is having an adverse impact on the safety of passenger car occupants and other road users, possibly exceeding any safety benefits of the vehicle-weight increases for the occupants of the trucks. Vehicle safety is complicated, obviously, and vehicle weight isn't the only variable of merit, obviously. (See http://energy.lbl.gov/ea/teepa/pdf/aps-ppt-wenzel.pdf‎ http://energy.lbl.gov/ea/teepa/pdf/aps-ppt-wenzel.pdf‎ ) But all things being equal, in a head on collision between two identical vehicles, save that one weighs a thousand pounds more than the other, the heavier car is going to win.
pkulak 13y ago
I don't think that test wall moved more because of the weight of the Tesla.
dredmorbius 13y ago
First: SUVs don't survive crashes particularly well -- they're very prone to rollover, which generally makes for a bad day for the occupant. I've witnessed multiple large-SUV vs. Camry (mid-sized sedan) accidents where the Toyota fared far better (walk away vs. ambulance or worse). Weight can be a factor, especially in multiple-vehicle accidents, where the heavier vehicle simply has more momentum and kinetic energy. In a multiple-vehicle accident, the larger vehicle experiences lower g-forces, and the occupants lower forces. Collisions with a stationary object (the basis for the NHTSA tests) largely takes this factor out of the equation. More mass can _still_ result in better survivability if it means more material around the driver, but here the choice of materials and engineering matter far more. Look at the comparison tests of classic (1950s/1960s) and modern (post 1980 and more recent) vehicles: http://www.youtube.com/watch?v=joMK1WZjP7g http://www.youtube.com/watch?v=joMK1WZjP7g I don't know the GVW of the Bel Aire, but I suspect it's rather higher than that of the Malibu. Of course, modern vehicles with poor engineering and materials can also fare badly: http://www.youtube.com/watch?v=g5SRyG6UR2A http://www.youtube.com/watch?v=g5SRyG6UR2A
- stevewilber 13y ago
  First: SUVs don't survive crashes particularly well This is outdated information, SUVs are now far safer than cars. Death rate (per 1M vehicle years) for 4WD midsize SUV: 23. Midsize Sedan: 51 [1] [1] http://www.iihs.org/externaldata/srdata/docs/sr4605.pdf http://www.iihs.org/externaldata/srdata/docs/sr4605.pdf
  - chockablock 13y ago
    Great link. What is the rationale for reporting death rates in terms of vehicle-years, rather than rate per mile traveled? What if SUVs just get driven less (due to poor mileage, only being taken out in the snow...)
    - duskwuff 13y ago
      > What is the rationale for reporting death rates in terms of vehicle-years, rather than rate per mile traveled? Vehicle-years can be determined directly from vehicle registration data. Miles traveled would require a lot more guesswork.
mrb 13y ago
"Heavier vehicles always do better" You are wrong. At least in the perspective of crash tests. In a crash test against a wall (equal amount of kinetic energy transferred to the wall and to the vehicle), a lightweight vehicle does better than an otherwise identical but heavier vehicle. This is because its mass is less, therefore there is less kinetic energy to dissipate. However in road crashes, heavy vehicles fare better because the heavy vehicle transfers more kinetic energy to the more lightweight vehicle. NHTSA crash ratings are well known to not reflect this difference. But the point remain that heavy vehicles are disadvantaged compared to lightweight vehicle, and the fact the Model S does so well despite its weight is a testament to its good crash resistance.
jcromartie 13y ago
But it's not the heaviest car ever made. So they're doing something exceptionally well other than making it heavy. I'd imagine much of that weight is in the batteries and electric motors.

It helps that it weighs 4,600 pounds. (More than a thousand pounds heavier than the Volvo S60 they compare it to.) Heavier vehicles always do better-- which is why SUVs survive crashes so well.

guynamedloren 13y ago

I don't know much about the mechanics or engineering of the Model S, but I'm going to take a gander and say that much of that extra weight comes from the battery pack (and other parts of the non-traditional drivetrain), which isn't a (huge?) factor in a crash test (though I could be wrong). Just checked - yep - the battery weighs an estimated ~ 545kg or 1200 lbs [1]. I'd expect the structural components to actually be lighter than competitors, given that they're fabricated with aluminum vs steel. [1] http://www.teslamotors.com/fr_CA/forum/forums/model-s-battery-0 http://www.teslamotors.com/fr_CA/forum/forums/model-s-batter...

mikeash 13y ago
How much does the gas tank, motor, radiator, transmission, etc. in a normal car weigh? Have to subtract that out of the 1,200lbs to see how much extra is added.
- akira2501 13y ago
  Mid-Range Estimates: Engine: 300 to 450 pounds Transmission: 120 to 140 pounds Gas Tank: 20 to 25 pounds Radiator: 20 to 30 pounds So, roughly 460 to 645 pounds. Add 110 pounds for 15 gallons of gas. The comparison is a little more difficult than this though, because the batteries just store energy. The Model S still has a (416hp) motor, there are a few other differences (regenerative vs standard brakes) and equivalencies (inverter vs alternator).
  - mikeash 13y ago
    Yep, it gets a bit tough, but that 460-645lbs range seems like a decent stab at it. I don't get the impression that the Model S's motors are all that heavy compared to the rest of this stuff, but I could be wrong. I'd also wager that the Model S needs a full set of mechanical brakes for emergency purposes, since it still needs to be able to stop safely even if all the electronics suddenly quit while going down the highway at 70MPH. And then there's the question of whether you compare against a 416hp motor, or a less powerful gas motor that would be more typical for a car that size....
    - akira2501 13y ago
      A Chevy 383 can make about 400hp+ in about 620 pounds. If we choose all our numbers for comparable cars that are highly in favor of the Tesla, we're still only likely going to match the weight of the Tesla's battery pack alone. The Model S curb weight is 4,647 pounds. A Cadillac STS, which is 5" narrower but very nearly the same in every other dimension as the Model S is only 3,922 pounds. That leaves the Model S 725 pounds heavier, still quite a bit of difference.
      - ssmoot 13y ago
        It's in the ball-park though. Your assessment seems pretty fair. I've seen some call the Tesla's weight "insane" though. My old (still current gen) Volvo S80 T6 weighed 4,400lbs IIRC. I assume that's "dry" weight. Since a Model S is always "dry" aside from a gallon of wiper fluid or the like they probably weigh just about the same on the road. And the Model S is a bigger, faster car. My Jeep Grand Cherokee (with the panoramic sunroof option I didn't actually have) weighed 5,500lbs. Again, I assume like motorcycle manufacturers that car manufacturers are listing the "dry" weight. So that baby is probably over 3 tons wet when optioned up. The Cadillac seems on the light side for it's class. Even so, "wet" the difference in weight is probably one passenger. Despite it being a smaller car (5" actually seems pretty significant IMO, that's 5" less wiggle room to stay in your lane!). That's (I assume) the worst-case-scenario highest capacity Tesla. Performance is far in excess of most cars on the road already. Capacity with smaller battery packs will surely improve. It seems like weight can only go down from here, and it's not out of line with it's competition as is.
- ssmoot 13y ago
  The 20+ gallon tank in my old Jeep Grand Cherokee would add over 300lb to the "wet weight". It also took (IIRC) an insane 7L of oil. So that stuff adds up.

corresation 13y ago

What is the calculated correlation between NHTSA vehicle safety score and vehicle weight. I don't know this, but suspect that it is a less significant factor than you imply. Add that the Tesla is 1000lbs+ of battery. Safety is engineering and materials. More materials help, of course, but more materials without the engineering simply equals more kinetic energy. There are vehicles from big SUVs to tiny SMART cars doing superbly on crash tests now.

chemmail 13y ago
Weight has a small impact, but you have to remember the low of geometric scaling.
sbierwagen 13y ago
Amusing that you mention the Smart Fortwo. http://www.iihs.org/news/rss/pr041409.html http://www.iihs.org/news/rss/pr041409.html ARLINGTON, VA — Three front-to-front crash tests, each involving a microcar or minicar into a midsize model from the same manufacturer, show how extra vehicle size and weight enhance occupant protection in collisions. These Insurance Institute for Highway Safety tests are about the physics of car crashes, which dictate that very small cars generally can't protect people in crashes as well as bigger, heavier models. "There are good reasons people buy minicars," says Institute president Adrian Lund. "They're more affordable, and they use less gas. But the safety trade-offs are clear from our new tests. Equally clear are the implications when it comes to fuel economy. If automakers downsize cars so their fleets use less fuel, occupant safety will be compromised. However, there are ways to serve fuel economy and safety at the same time." http://www-nrd.nhtsa.dot.gov/Pubs/808569.pdf‎ http://www-nrd.nhtsa.dot.gov/Pubs/808569.pdf‎ Large vehicles have historically been more stable and provided more protection for their own occupants than small ones, but they presented a greater hazard to other road users. Between 1985 and 1993, the population of light trucks - pickups, sport utility vehicles (SUV) and vans - increased by 50 percent in the United States. Since the major downsizing of passenger cars during 1975-82, light trucks have had a substantial and growing weight advantage over cars. By 1992, the number of fatalities in collisions between cars and light trucks exceeded the number in car-to-car collisions In car-light truck collisions, 80 percent of the fatalities are occupants of the cars. That raises the question whether the growth in the number and weight of light trucks is having an adverse impact on the safety of passenger car occupants and other road users, possibly exceeding any safety benefits of the vehicle-weight increases for the occupants of the trucks. Vehicle safety is complicated, obviously, and vehicle weight isn't the only variable of merit, obviously. (See http://energy.lbl.gov/ea/teepa/pdf/aps-ppt-wenzel.pdf‎ http://energy.lbl.gov/ea/teepa/pdf/aps-ppt-wenzel.pdf‎ ) But all things being equal, in a head on collision between two identical vehicles, save that one weighs a thousand pounds more than the other, the heavier car is going to win.

pkulak 13y ago

I don't think that test wall moved more because of the weight of the Tesla.

dredmorbius 13y ago

First: SUVs don't survive crashes particularly well -- they're very prone to rollover, which generally makes for a bad day for the occupant. I've witnessed multiple large-SUV vs. Camry (mid-sized sedan) accidents where the Toyota fared far better (walk away vs. ambulance or worse). Weight can be a factor, especially in multiple-vehicle accidents, where the heavier vehicle simply has more momentum and kinetic energy. In a multiple-vehicle accident, the larger vehicle experiences lower g-forces, and the occupants lower forces. Collisions with a stationary object (the basis for the NHTSA tests) largely takes this factor out of the equation. More mass can _still_ result in better survivability if it means more material around the driver, but here the choice of materials and engineering matter far more. Look at the comparison tests of classic (1950s/1960s) and modern (post 1980 and more recent) vehicles: http://www.youtube.com/watch?v=joMK1WZjP7g http://www.youtube.com/watch?v=joMK1WZjP7g I don't know the GVW of the Bel Aire, but I suspect it's rather higher than that of the Malibu. Of course, modern vehicles with poor engineering and materials can also fare badly: http://www.youtube.com/watch?v=g5SRyG6UR2A http://www.youtube.com/watch?v=g5SRyG6UR2A

stevewilber 13y ago
First: SUVs don't survive crashes particularly well This is outdated information, SUVs are now far safer than cars. Death rate (per 1M vehicle years) for 4WD midsize SUV: 23. Midsize Sedan: 51 [1] [1] http://www.iihs.org/externaldata/srdata/docs/sr4605.pdf http://www.iihs.org/externaldata/srdata/docs/sr4605.pdf
- chockablock 13y ago
  Great link. What is the rationale for reporting death rates in terms of vehicle-years, rather than rate per mile traveled? What if SUVs just get driven less (due to poor mileage, only being taken out in the snow...)
  - duskwuff 13y ago
    > What is the rationale for reporting death rates in terms of vehicle-years, rather than rate per mile traveled? Vehicle-years can be determined directly from vehicle registration data. Miles traveled would require a lot more guesswork.

mrb 13y ago

"Heavier vehicles always do better" You are wrong. At least in the perspective of crash tests. In a crash test against a wall (equal amount of kinetic energy transferred to the wall and to the vehicle), a lightweight vehicle does better than an otherwise identical but heavier vehicle. This is because its mass is less, therefore there is less kinetic energy to dissipate. However in road crashes, heavy vehicles fare better because the heavy vehicle transfers more kinetic energy to the more lightweight vehicle. NHTSA crash ratings are well known to not reflect this difference. But the point remain that heavy vehicles are disadvantaged compared to lightweight vehicle, and the fact the Model S does so well despite its weight is a testament to its good crash resistance.

jcromartie 13y ago

But it's not the heaviest car ever made. So they're doing something exceptionally well other than making it heavy. I'd imagine much of that weight is in the batteries and electric motors.