# Forum

Unisciti allacomunità

How far will the Model S go at interstate speed??

I want to know what the actual distance these cars will go at 75mph on the interstate? For the 40kwh, the 60kwh, and the 85kwh. I do not think that it is logical to say that people will go 55mph on the interstate.

This is the exact question I've had as well, I wish I knew the calculation to determine.

Look at the Roadster chart at

Model S CdA is approx same as Roadsters, so aerodynamic drag is same Roadster is about as aerodynamic as a brick, Model S is larger (A) but much better in Cd. However rolling resistance ("tires" in the chart) is higher because it is heavier car. That's pretty constant at any speed.

Roadster uses about 230Wh/mile at 55mph, we know that Model S 85kWh battery should last 300 miles at 55mph. That gives us 283Wh/mile.

Difference is 53Wh. Roadster uses about 330Wh/mile at 75mph, so Model S should use 383Wh/mile at 75mph. 85kWh/383Wh/mile = 222 miles.

Estimation, but should not be far from truth.

I can't be sure, so maybe someone who knows about this will chime in. But I think they listed "55" to show the average between city and highway driving. Maybe when it's closer to delivery there will be more specific information about different speeds. I know there's a good deal of detail on the Nissan Leaf page about what causes different levels of strain on the battery (heater on/off, speed, incline, etc.,). I would hope Tesla will provide this level of detail as well, but just needs more time to gather the data.

@Timo,
Awesome! I always estimated a 25% penalty for realistic highway driving. Virtually all my driving is highway. This fact should weigh heavily on the battery size decision for anybody doing a lot of highway driving. Looks like your math is almost dead on with my guestimate.

Thats an excellent question! You know when computers first came out I always wanted the biggest memory, etc.. but realized it is unnecessary if you do not use all the computing power.

Its the same with the battery but the unknown of highway distance, battery degradation over time and cold weather effects on distance makes me weary to not get the 300 mile battery. I would save \$10,000.00 if I really do not need the 300 mile pack(going with 230) but the comfort level would be much higher with the 300.

I did some calculations and it matches Timo's value (75mph=225miles)