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Milage range at track speeds?

I am very interested in the Roadster sport. But, I am also a fan of BMW CCA performance driving schools. The speed and acceleration of the roadster is perfect. However co-workers tell me, that when you push the car (peddle to the metal) the range DROPS! Like it might be hard to do 4 15-20 min. track sessions at VIR on one charge.

Can anyone tell me how much a heavy foot decreases range?

Thanks,
Dale

You'll want to see the range-versus-speed chart at http://www.teslamotors.com/blog/roadster-efficiency-and-range.

Of course, in addition to speed, acceleration takes a huge hit. (Some of which you may get back by regen; depends on how you're braking). I don't think I've seen any numbers for that, though.

I've never taken mine to the track, so here's where somebody who has can step in with a real-life experience.

No real-life experience about Roadster, but I have driven some track laps with other cars.

"Like it might be hard to do 4 15-20 min. track sessions at VIR on one charge."

You are quite correct. In track you need more serious braking than what Roadster regen can give, which means regen doesn't help much and you will be pushing the accelerator at max in every single straight using ~200kW of power. That amount of power drains the battery in 15 minutes, maybe 45min tops in twisty track. Can't do 4 15 minute track sessions unless you have fast charger in place and you have enough time to charge something like 25% of battery between sessions (bit less than hour).

Roadster is not race-car, with more power in regen (preferably in front wheels) you could extend that time _a lot_, but as it is now your track time would be rather limited.

SpeedVentures has run a one-day event named REFUEL in July the past two years at Laguna Seca for alternative fuel vehicles, of which Tesla Roadsters were the majority participants. The day consisted of 3 sessions, a 1-lap time trial, and a final session, interleaved with sessions for two or three different groups of ICE vehicles. Each session was about 15 minutes (5 laps or so). Between sessions we were able to charge with 40-amp charge cables, but it was not enough time to get all the way back to full.

Besides charge depletion, another limiting factor is hitting temperature limits in the motor and PEM.

hmm, that chart of range vs speed practically screams for some sort of gearbox to make the engine run at lower rpms during high speeds. even if you are going 90 on a highway, thats still a 125mile range, but if that could just even be doubled, thatd be all the more impressive. hopefuly someone can design a gearbox that is up to snuff for future tesla models.

Gearbox doesn't help one bit at that. I don't even understand how could it. What is your reasoning behind that gearbox could give you more range?

Total power stored in the battery pack is around 53 Kwh,

now if you use 53 Kw of power it will last for 60 min,

53 + 53 = 106 will last for 30 minutes

212 Kw (close to max power of motor itself, 215 Kw) = will last for 15 minutes..........!!!!!!!!!!!!!

_______________________________________________________________

PROVIDED,

if you are ready to neglect the extra power required for accessories, AC, Music system, and God knows what.....on top of that battery is operated at room temperature........:-)

@bhp, your analysis is appropriate as a back-of-the-envelope measure, but it omits the consideration that when you draw out the energy at a faster rate, the total you get is reduced. For lead-acid batteries, the effect is pronounced, and is named the Peukert effect after the scientist who studied it. Other battery chemistries have different behavior, but I believe all of them suffer some reduction.

Yes,

I'm aware about Peukert effect: I^n X t = C

Where I is the discharge current in A,
“t” is the duration of the discharge in hours
n = Peukert no.
C = theoretical capacity of the battery.
__________________________________________________________________
Moreover my answer was basically based on,

SOC % = (1 - (amps*time)/Ah*3600)*100

and i have not considered any kind of irreversible capacity losses....:-).......which i know LiCoO2 has !

One positive aspect of lithium batteries is that there is virtually no Peukert effect. I know with lead batteries if you have a 100 amp-hr battery and pull 5 amps out it will last 20 hours for a total of 100 amp hrs. But if you pull say 100 amps, the battery will last about 20 minutes for an effective capacity of about 33 amp-hrs. With the same capacity lithium at 100 amp draw it will last about an hour. Lithium does not care if you pull the current out fast or slow. At least that is the case over a very wide range of current draws.

I took my Roadster to the Autobahn track near Chicago in October 2009, on a trailer. It was a cool day in the 50s, and the car was able to complete 4 15 minute sessions, with only a little reserve at the end (I did not recharge). I had a professional driver drive the first round and then he accompanied me as the passenger/coach, he loved it. It was fun but I could not compete with track cars driven by experienced drivers. The biggest problem was reduced power due to temperature limits after about 10 minutes. If I was to do it again, I would pack the trunk with ice in a garbage bag.

Seems to be that overheating the engine is a main problem for Roadster in any track sessions. I think that is the reason why they chose to use liquid cooling for Model S. Maybe also Roadster 3.0 or 4.0 which is build using same basic principle as Model S will use that too.

I believe the current Roadster already uses liquid cooling.

AFAIK it still is air-cooled. IIRC "eberhart" told us that his car engine was overheating because air blower had broken and his car was version 2.5.

@Timo: I am pretty sure that blower is forcing air onto a heat exchanger. The blowers are in the front of the car while the engine and battery are in the back.

My understanding is that the PEM and battery pack are liquid cooled, but the motor is air cooled.

Greg.

In the Roadster, it's just the battery that's liquid cooled, the rest are all air cooled.

You're correct. Sorry, I misread that as referring to the battery. Thanks.

I had my 2.0 Roadster on a 1.5 mile road course near Detroit MI. I started with 190 ideal miles on a performance charge. I drove 15 miles to the track. Track time during the afternoon consisted of four, 5 lap sessions. I then drove back the 15 miles back and arrived at my charge point with 85 ideal miles. Estimated miles was down around 35, due to my "non-green" driving on track. Sorry my numbers aren't more precise this took place 6 months ago.


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