JRP3
Hyperactive Member
They had to make a higher roof line for the Model 3 because of a single layer of the taller cells, and couldn't make it a hatch back. I'd think doubling the pack height would have to impact the seating height of the Roadster.
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Shocked by the new Roadster rolling out of the Tesla Semi!
- Thread starter rudholm
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- Roadster 2020
How are you factoring in the seating position? Sedans seems to be more upright, whereas the Roadster is more laid back. Heck, the front of the seat looked WAY higher than the rear. Looked like their heads were in front of the roof cross beam also.
Where does this information come from?
The only reason it's not a hatchback is the massive rear glass - which I thought was a production efficiency decision since it allowed them to use robots to load things into the cabin easily (though I do remember reading that it also added to rear seat headroom.)
I hadn't read anything about making the car taller because of the cells, and given that the difference between the 18650 and 2170 is less than 1/4", I find it highly dubious - especially since Tesla has been patenting ways to make the pack overhead thinner as well.
If indeed for instance 100kWh at double the outputs of 100kWh Teslas on sale, then the battery would need to be significantly heavier at the cell level than now used commercially by them. A 600kg pack become 700-800kg even before factoring in volume. Of course though, in the Roadster you would expect lighter packaging.
A 60-70kWh pack with externally sourced higher C rate cells might do the job. Aren't people already using Chevy Volt packs to build very, VERY punchy track cars? 130kg in cells, 16kWh, and I believe I read 300kW peak output. 3-4x that may well already do the trick for a demonstrator car that does many 0-70 launches.
Building a 200kWh pack that fits the Roadster may be possible at Tesla's "current" commercialized battery performance ball park, and it would offer plenty of peak power, but the Roadster would unlikely be a sub-2000kg car. I strongly suggest they are promising performance numbers for a 2020 car based off laboratory results of chemistry that's not quite a manufacturing success.
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JRP3
Hyperactive Member
Thanks for tracking down that image!Good points
Not much space between your butt and the floor.
Battery pack is the seat warmer?
Why the wide door sill, is that a cooling channel? Radiators in the rear fender?
JRP3
Hyperactive Member
Could be, but the rear headroom in the S has been a concern for some, so to mitigate that issue with the newer, taller cells they needed to increase the roof height and move the cross bar further back.
S rear headroom is definitely limited for us tall people, like a lot of cars in that class with the swooping roofline. More headroom will be great.
Not buying that the 5 mm increase in cell height drove all of that, though. They could probably have let the pack extend down another 1/4" instead if it came to that.
SomeJoe7777
Marginally-Known Member
I did some calculations that may help in estimating the battery pack size.
Given that we have the 0-60 time (1.9 seconds), and the total wheel torque (10,000 Nm) provided by Tesla, and we have the tire sizes provided in the pictures above, we should be able to make some reasonable assumptions and calculate the weight of the vehicle.
Given information:
Tires are Michelin Pilot Sport Cup 2, sizes are 265/35R20 front (diameter 27.3 in), 325/35R21 rear (diameter 28.7 in).
Total Torque at the wheel hubs: 10,000 Nm
0-60 MPH time: 1.9 sec
Tire diameters: Front 0.69342 m, Rear 0.72898 m
Let's assume power distribution is 33% front axle, 67% rear axle during max acceleration.
Let's also assume that the acceleration is linear from 0-60, which is probably close to correct given that the torque is held constant at maximum by the inverter.
Let's assume that the system is powerful enough to maintain maximum torque all the way to 60 MPH. (It may not. If it doesn't, then the vehicle will have to be lighter than this calculation will show, thus this calculation is an upper bound on the vehicle weight).
Let's calculate acceleration in m/sec^2:
Vf = at + V0
Vf = 60 MPH = 26.8224 m/sec
V0 = 0 MPH = 0 m/sec
t = 1.9 sec
a = 14.117 m/sec^2 (1.44 G !)
Let's calculate the force on the vehicle given the torque, tire diameters and power distribution:
F = Torque / distance
F = Torque / (% Power Dist front * (Tire diameter front / 2) + % Power Dist rear * (Tire diameter rear / 2) )
F = (10000 Nm) / (0.3333 * (0.69342 / 2) + 0.6667 * (0.72898 / 2) )
F = 27,889.07 N
Compute mass of the vehicle:
F = ma
m = (F/a)
m = (27889.07 / 14.117)
m = 1975.56 kg
m = 4355.4 lbs
I believe that's enough mass to hold a 200 kWh battery and a light vehicle structure.
Given that we have the 0-60 time (1.9 seconds), and the total wheel torque (10,000 Nm) provided by Tesla, and we have the tire sizes provided in the pictures above, we should be able to make some reasonable assumptions and calculate the weight of the vehicle.
Given information:
Tires are Michelin Pilot Sport Cup 2, sizes are 265/35R20 front (diameter 27.3 in), 325/35R21 rear (diameter 28.7 in).
Total Torque at the wheel hubs: 10,000 Nm
0-60 MPH time: 1.9 sec
Tire diameters: Front 0.69342 m, Rear 0.72898 m
Let's assume power distribution is 33% front axle, 67% rear axle during max acceleration.
Let's also assume that the acceleration is linear from 0-60, which is probably close to correct given that the torque is held constant at maximum by the inverter.
Let's assume that the system is powerful enough to maintain maximum torque all the way to 60 MPH. (It may not. If it doesn't, then the vehicle will have to be lighter than this calculation will show, thus this calculation is an upper bound on the vehicle weight).
Let's calculate acceleration in m/sec^2:
Vf = at + V0
Vf = 60 MPH = 26.8224 m/sec
V0 = 0 MPH = 0 m/sec
t = 1.9 sec
a = 14.117 m/sec^2 (1.44 G !)
Let's calculate the force on the vehicle given the torque, tire diameters and power distribution:
F = Torque / distance
F = Torque / (% Power Dist front * (Tire diameter front / 2) + % Power Dist rear * (Tire diameter rear / 2) )
F = (10000 Nm) / (0.3333 * (0.69342 / 2) + 0.6667 * (0.72898 / 2) )
F = 27,889.07 N
Compute mass of the vehicle:
F = ma
m = (F/a)
m = (27889.07 / 14.117)
m = 1975.56 kg
m = 4355.4 lbs
I believe that's enough mass to hold a 200 kWh battery and a light vehicle structure.
Not bad. This assumes that the car is using all the torque the motors can put out (an assumption you had to make to do the math.)
Given that we heard a lot of tire spinning during all the launch videos, that isn't the case, so the car is likely somewhat lighter than your math shows, but it's hard to say for sure and we don't have any better numbers to use.
Esme Es Mejor
Member
They covered that already— the Performance Model 3 will have Corvette level 0-60 and sticker price. And it’s coming a lot sooner than the Roadster. Tesla isn’t wiping out the Lambo market instead of the Corvette market— they’re wiping out both.
JRP3
Hyperactive Member
True though considering previous incidents with pack impacts in the S and the solution of raising ride height they may have not been comfortable with a lower pack. To me the Model 3 roof line is higher than it should be from an aerodynamics, (and IMO styling), perspective and I feel there must be some reasoning behind it.
JRP3
Hyperactive Member
This got me thinking so I looked at some videos trying to get a better perspective as to the floor height of the Roadster. It's actually higher than I realized and the distance between the floor and the bottom of the car is greater than I would have imagined. Definitely enough room for a double stack pack though I still suspect it's under 200kWh at this point in time. I think it would have to be to keep it within the wheelbase.
In this pic Franz has not yet lifted his foot off the floor.
I’m hoping this could indicate this car could very well be able to handle the conditions on a race track.In that video at -0:57 driver says:
"Car's been doing this all night, 67% SoC, started at like 92% I think it was" ... "and it's repeating the same times"
Considering a diagonal line through the bottom of the seat, perpendicular to the wheel axles, I think the seat is actually quite low after all. It's a real seat, not a thin pad on a monocoq.
No volumous pack seems to be hiding in that car. At least a doubling of energy density is needed to put 200kWh in there and have good amounts of storage space left. Remember Model 3 only had room for 75kWh and 100kWh was totally undoable? It got a bit over 80kWh and with cells. Roadster needs to house an extra motor, and each seems quite strong.
Imagining the motors still do 16,000 rpm or so, and 3500rpm or so to make 250mph, a reduction of at least 4.5x seems needed to drive the wheels. That brings the total motor torque down to 2222 NM. Individual to 740 NM. Does that make any sense?
AMPd
Well-Known Member
Why are people questioning teslas ability to fit 200 kWh worth of battery in the roadster?
They have always come through on their advertised battery capacities.
Having said that, one of the main reasons I’ll be buying this car is for the range. So they better deliver.
They have always come through on their advertised battery capacities.
Having said that, one of the main reasons I’ll be buying this car is for the range. So they better deliver.
Could be. The seat bottom is well below the door opening though, which in turn is not hugely high.
I can't imagine a double layered pack after, then the world begged for a 100kWh Model 3, they could only fit 75kWh. In road cars, a higher floor is a trend, not a problem, right? A Roadster with (att least) 500kg extra in batteries, on top of the already biggest one on the market? Tesla must be promising 2020 because the tech is simply not ready. At best, I think the show cars had laboratory made batteries from something new.
I'm questioning whether the 200kWh is in there NOW. And whether it's using cell tech used today, or something still under development. For S&X Elon couldn't see the needd for more than 100kWh even when whole countries with huge markets really, really wanted it, and to pay for it. Roadster, just do nearly triple the Model 3? Makes no sense unless there has been a breakthrough. Same breakthrough may be instrumental to squeeze 500 miles of range into a sleek semi tractor, also for 2020.
