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Will the all-glass roof make the Model 3 top-heavy, affecting its low Center of Gravity?

Will the all-glass roof make the Model 3 top-heavy, affecting its low Center of Gravity?

I know in the Model S having a pano roof adds at least 50(?) lbs at top due to heavy glass. I wonder how the all-glass roof will affect the low CG (and no body roll), what Tesla is known for due to the low battery sled. I hope a heavy all-glass roof is not another "hubris" feature. Maybe Gorilla Glass or Corning Glass can reduce the weight.

TeslaTap.com | 2016年5月10日

Not an issue when you have a 1,000 lb battery at the bottom of your car. In its size class it will likely have the lowest CG of any comparable car, including lightweight sports cars. Might even be lower than the Model S, the current champ of low CG.

TeslaTap.com | 2016年5月10日

I should also point out that steel roofs are not that much lighter. Really not an issue.

jordanrichard | 2016年5月10日

If anything, the pano roof on the MS weights relatively more. The only difference between the roofs is that the MS has a support across the back, to support the hatch.

CraigW | 2016年5月10日

Keep in mind that the panels are aluminum, but the frame is largely steel. Projections put the weight of the Model 3 at over 4000 lbs, not that much less than an S70. Much of this weight is around wheel height. Physics says the roll factor of the Model 3 will more closely approach the Model S than it will other ICE cars.

Badbot | 2016年5月10日

S curb weight 4650.

If anyone knows the weight of the modules they can correct me.

ballpark 1000 pounds for the model S 16 modules.
ballpark 500 pounds for the model 3 16 modules.
save 500
say 10% weight savings for a 20% smaller car 450 pounds.
save 450
3700 curb weight for dual drive.

Badbot | 2016年5月10日

P.S. your mileage or weight may very!

Sparky | 2016年5月10日

How tall are you? The CG will not only be extremely low but the heavy battery pack is slung below the axle centres so the effective body roll due to lateral G will be almost zero.

Red Sage ca us | 2016年5月10日

OP: Uh... NO.

Son of a Gunn | 2016年5月10日

Uh, cool, thanks, that was really valuable.

Son of a Gunn | 2016年5月10日

@TeslaTap, any idea how much the pano roof glass weighs?

PaceyWhitter | 2016年5月10日

Yeah, I read that in the Motor Trend article also.

georgehawley.fl.us | 2016年5月10日

@ed: Nice work! My S85 has a battery pack that weighs 1250 pounds, 750 pounds of that is battery cells.
Guessing that the base capacity of the M≡ pack is 55 kWh, the cells should weigh about 485 pounds. The case and plumbing will probably weigh 20% or so less than for the S or maybe 400 pounds, total something like maybe 850 to 900 pounds. My guess is that the total weight will come in at about 3800 pounds for the RWD version.

I think we are in the same ballpark. Center of gravity for the S is 18" off the ground. My guess for the M≡ is 1/6 higher or 21 inches, still pretty low. The BMW 328i is about 21 inches for reference purposes.

jordanrichard | 2016年5月10日

At one time I asked my service center how much the pack weighed in my S85 and was told 1600 lbs.

JayInJapan | 2016年5月10日

Is the extra pano weight from the glass or the motor/support structure? I would guess the glass in M3 wouldn't weigh more than steel.

carlk | 2016年5月11日

Huh? Density of common glass: 2.4-2.8. Density of aluminum: 2.7. Density of steel: 7.8.

I guess this is how FUD is spread.

Son of a Gunn | 2016年5月11日

Goodness, carl.

A glass roof on a car is several factors thicker than a metal roof. A regular car window is thicker than the aluminum body panel.

carlk | 2016年5月11日

3 will be using mostly steel.

Chunky Jr. | 2016年5月11日

Imagine a 5 foot seesaw in perfect balance with 1500 lbs on the left side, and 100 lbs on the right. If you added 50 lbs to the right side, how far do you think you'd have to move the fulcrum to keep it balanced? My guess is no more than an inch. I'm sure there is an online calculator to figure this out, but there are so many unknowns I'm not sure if its possible to get more than a wild guess.

EVino | 2016年5月11日

The center of gravity height on a Porsche Cayman is ~18.5". Model S is ~18", less when air suspension is on Low (awesome). A Corvette is ~17.5". Exotic cars have CG height less than 17". The BMW i3, oh maybe 5 feet (j/k).

Center of gravity height test method:
http://www.caranddriver.com/features/new-car-and-driver-center-of-gravit...

jordanrichard | 2016年5月11日

I thought the center of gravity was 17 inches?

cephellow | 2016年5月11日

@Son of a Gunn,
Tempered automotive glass is generally available in 3, 4 and 5 mm thicknesses. (St. Gobain), in this fixed panel application the 3mm is most likely. Automotive steel panels are about .6 mm thick, so about 1/5 the thickness of glass. However steel is 7700KG/M3 where glass is 2500Kg/M3, so The math says that a steel panel is about 60% of the weight of a glass panel. However, the steel needs a headliner, sound dampening material, paint, as well as a join area for some kind of glass panel anyway (still have to see out the back), so it is probably the same or less weight overall than steel in the finished assembly.
Tesla chose glass because it looks great, adds headroom, has a lower total installed cost over a painted panel with little or no weight penalty.

jordanrichard | 2016年5月11日

It is also faster to literally glue in a glass roof than weld a panel in place.

Haggy | 2016年5月11日

In real life, center of gravity and T/2H had little real world correlation with actual rollovers. I haven't analyzed data personally or worked on any related project since electronic stability control became standard, and I suspect that will be a big factor. Real life rollover factors were so skewed toward driver demographics that factoring in a vehicle's inherent propensity to roll based on wheel base and center of gravity didn't tell you anything meaningful.

I'd expect that rollovers due to overcorrecting will be less likely. Tripping by slamming the wheels into a curb at high speed and having the momentum carry you over might be less likely due to the fact that you'd be less likely to lose control and the fact that the battery pack is so massive and low, but if you drive a Model 3 off a cliff, I wouldn't expect you to fare any better than with any other car.

The Model S rates so well on roof crush tests that nobody would claim that the panoramic roof it a negative. Immunity from roof crush isn't a predictor of fatality rates for vehicles when you look at it as a sole factor, and when you account for relevant factors, roof crush no longer factors into the likelihood of getting killed.

It is faster to have a glass roof put on the car than to have a steel one welded in place, and it would also be faster to replace a glass roof than to have a steel one refinished. But on the other hand, I had my glass replaced on the roof of the Model S and never needed to have the roof redone on any other car.

Son of a Gunn | 2016年5月11日

I think the concern has more to do with handling than rollover. We all agree that rollover's not a big concern. Back to handling, Center of Gravity height is a big factor in body lean. It also affects steering load during braking. A lower center of gravity is a principal performance advantage of sports cars. Let's hope the Model 3 is on par with the Model S.

Red Sage ca us | 2016年5月13日

The difference is that the Model S, Model X, and Model ☰ have a center of gravity that is 17 inches... below the ground.

adoh2010 | 2016年5月13日

Sparky: the pivoting point that the weight of the car rolls around is at the ground not the axles. That's why cog is measured from the ground.