4 ms·

Do you really need a 0-60mph time of 3.0 seconds in a mommymobile?

by Animats 9mo ago

nomel 9mo ago
How much of that performance comes for free, from optimizing for range/efficiency? What's the obvious "that could be less" in the system that wouldn't negatively impact efficiency?
- actionfromafar 9mo ago
  None of it. It the motor is smaller, it pulls less current. If it pull less current, you can use batteries which aren't specced for high amps. If use use less amps, you can use thinner cabling and split the batteries up i various compartments. That means heat is more distributed. Less active cooling, if any, is needed, of both batteries and motors. All of the above can translate to less weight, which mean better range.
  - mortos 9mo ago
    Weight has nearly no effect on range of an EV. The YouTube channel Aging Wheels has two good videos on this. Here he talks about towing, and he demonstrates loading the truck to max capacity makes nearly no difference: https://youtu.be/UmKf8smvGsA https://youtu.be/UmKf8smvGsA He also covered an attempted Cannonball run where they stuffed two extra battery packs into a Rivian R1T: https://youtu.be/yfgkh4Fgw98 https://youtu.be/yfgkh4Fgw98 Real differences makers are smaller wheels and aerodynamics
    - nomel 9mo ago
      > are smaller wheels Looks like rolling resistance decreases with diameter [1]. So, is it from the increased drag from higher stance? Would lowering the car the same work better? [1] https://www.tirereview.com/science-behind-rolling-resistance-passenger-tires/ https://www.tirereview.com/science-behind-rolling-resistance...
      - mortos 9mo ago
        I think it's mostly from aerodynamics. Lowering the car could help but even just smaller rims, with the same overall diameter (rim + tire), can have a 15% impact on range. This Engineering Explained[1] video does an okay job with some of the math but he clarifies it well with a comment: > CLARIFICATION! Why do bigger wheels mean worse efficiency, when the overall tire diameter remains the same? This comes down to aerodynamics. A 20" wheel will cause more of a disruption in airflow than an 18" wheel. That's why Tesla (and others) uses aero covers on their wheels (Car & Driver testing showed it gives about a 3% efficiency bonus at speed). The smaller the wheel, the more of the side profile of the wheel & tire is perfectly flat (the tire is flat, the wheel open: more tire = more flat area, less open area). Ideally, you'd have just a plain, solid sheet for the wheel, but obviously that's not idea for brake cooling. Wheel covers are today's common compromise as they have some airflow, but minimal. [1] https://youtu.be/NYvKxsYFqO8 https://youtu.be/NYvKxsYFqO8
        nomel 9mo ago
        > solid sheet for the wheel, but obviously that's not idea for brake cooling So, temperature driven radial louvers!? :D
    - Animats 9mo ago
      That's interesting. It demonstrates that regenerative braking really works. The energy you expend going uphill, you mostly get back going downhill. The energy you expend speeding up, you mostly get back slowing down. His tests were a round trip, so start and end altitude are the same. And he kept a fixed speed on a freeway, so there wasn't much acceleration energy expenditure or energy loss into friction brakes. You don't get drag or rolling resistance back, so that apparently dominates. Those don't vary too much with load. Nice result.
    - actionfromafar 9mo ago
      It has an effect on the range of the tires.
  - nomel 9mo ago
    > from optimizing for range/efficiency? I meant for normal highway driving, not drag racing. Optimal highway driving is still lowest resistance and losses. Cold weather driving is what mostly results in a battery capable of the high performance, from what I understand. Is a "small" motors more efficient than a large one? I suspect no, with the assumption that everything is sized so the "drag race" operating range would be well into the peak, rather than sustained, operating range.
AHASIC 9mo ago
Having driven a very slow acceleration car, yes, yes you do, trust me. Nothing worse than merging into dense traffic with high-speed trucks next to you and not being able to come up to speed before the ramp ceases.
cucumber3732842 9mo ago
In my observation the primary purpose of this performance seems to be to be able to round on-ramps at really slow speeds and then floor it and merge leaving slower vehicles behind you with a crap situation.
1970-01-01 9mo ago
That's like asking if mommy needs a razor sharp knife in the kitchen or if we should keep it dull for legacy reasons.
- wpm 9mo ago
  Uhhh, what? No it isn't. Having a sharp knife is safer than a dull one. Having a massive heavy steel box that weighs thousands of kilos that can accelerate that quick, that you can operate in public with little to no useful training is not safer. I'm sorry, no car outside of a race track needs to accelerate that quick. It's absurd.
  - 1970-01-01 9mo ago
    The analogy fits perfectly. A slow car is also unsafe, that's why low speed plates exist along with minimum speed limits. There's no such thing as a vehicle with too much acceleration and never will be.
    - wpm 9mo ago
      Yeah what qualifies as a "slow car"? An Amish dude on a horse and buggy? I have driven plenty of "slow" cars with less than 100 horsepower without issue. If you can't figure out how to merge that's a skill issue, another prime reason not to be giving people cars with former F1 car levels of acceleration. You don't need 0-60 in 3 seconds to fucking merge, get real!

Do you really need a 0-60mph time of 3.0 seconds in a mommymobile?

by Animats 9mo ago

Do you really need a 0-60mph time of 3.0 seconds in a mommymobile?

nomel 9mo ago

How much of that performance comes for free, from optimizing for range/efficiency? What's the obvious "that could be less" in the system that wouldn't negatively impact efficiency?

actionfromafar 9mo ago
None of it. It the motor is smaller, it pulls less current. If it pull less current, you can use batteries which aren't specced for high amps. If use use less amps, you can use thinner cabling and split the batteries up i various compartments. That means heat is more distributed. Less active cooling, if any, is needed, of both batteries and motors. All of the above can translate to less weight, which mean better range.
- mortos 9mo ago
  Weight has nearly no effect on range of an EV. The YouTube channel Aging Wheels has two good videos on this. Here he talks about towing, and he demonstrates loading the truck to max capacity makes nearly no difference: https://youtu.be/UmKf8smvGsA https://youtu.be/UmKf8smvGsA He also covered an attempted Cannonball run where they stuffed two extra battery packs into a Rivian R1T: https://youtu.be/yfgkh4Fgw98 https://youtu.be/yfgkh4Fgw98 Real differences makers are smaller wheels and aerodynamics
  - nomel 9mo ago
    > are smaller wheels Looks like rolling resistance decreases with diameter [1]. So, is it from the increased drag from higher stance? Would lowering the car the same work better? [1] https://www.tirereview.com/science-behind-rolling-resistance-passenger-tires/ https://www.tirereview.com/science-behind-rolling-resistance...
    - mortos 9mo ago
      I think it's mostly from aerodynamics. Lowering the car could help but even just smaller rims, with the same overall diameter (rim + tire), can have a 15% impact on range. This Engineering Explained[1] video does an okay job with some of the math but he clarifies it well with a comment: > CLARIFICATION! Why do bigger wheels mean worse efficiency, when the overall tire diameter remains the same? This comes down to aerodynamics. A 20" wheel will cause more of a disruption in airflow than an 18" wheel. That's why Tesla (and others) uses aero covers on their wheels (Car & Driver testing showed it gives about a 3% efficiency bonus at speed). The smaller the wheel, the more of the side profile of the wheel & tire is perfectly flat (the tire is flat, the wheel open: more tire = more flat area, less open area). Ideally, you'd have just a plain, solid sheet for the wheel, but obviously that's not idea for brake cooling. Wheel covers are today's common compromise as they have some airflow, but minimal. [1] https://youtu.be/NYvKxsYFqO8 https://youtu.be/NYvKxsYFqO8
      - nomel 9mo ago
        > solid sheet for the wheel, but obviously that's not idea for brake cooling So, temperature driven radial louvers!? :D
  - Animats 9mo ago
    That's interesting. It demonstrates that regenerative braking really works. The energy you expend going uphill, you mostly get back going downhill. The energy you expend speeding up, you mostly get back slowing down. His tests were a round trip, so start and end altitude are the same. And he kept a fixed speed on a freeway, so there wasn't much acceleration energy expenditure or energy loss into friction brakes. You don't get drag or rolling resistance back, so that apparently dominates. Those don't vary too much with load. Nice result.
  - actionfromafar 9mo ago
    It has an effect on the range of the tires.
- nomel 9mo ago
  > from optimizing for range/efficiency? I meant for normal highway driving, not drag racing. Optimal highway driving is still lowest resistance and losses. Cold weather driving is what mostly results in a battery capable of the high performance, from what I understand. Is a "small" motors more efficient than a large one? I suspect no, with the assumption that everything is sized so the "drag race" operating range would be well into the peak, rather than sustained, operating range.

AHASIC 9mo ago

Having driven a very slow acceleration car, yes, yes you do, trust me. Nothing worse than merging into dense traffic with high-speed trucks next to you and not being able to come up to speed before the ramp ceases.

cucumber3732842 9mo ago

In my observation the primary purpose of this performance seems to be to be able to round on-ramps at really slow speeds and then floor it and merge leaving slower vehicles behind you with a crap situation.

1970-01-01 9mo ago

That's like asking if mommy needs a razor sharp knife in the kitchen or if we should keep it dull for legacy reasons.

wpm 9mo ago
Uhhh, what? No it isn't. Having a sharp knife is safer than a dull one. Having a massive heavy steel box that weighs thousands of kilos that can accelerate that quick, that you can operate in public with little to no useful training is not safer. I'm sorry, no car outside of a race track needs to accelerate that quick. It's absurd.
- 1970-01-01 9mo ago
  The analogy fits perfectly. A slow car is also unsafe, that's why low speed plates exist along with minimum speed limits. There's no such thing as a vehicle with too much acceleration and never will be.
  - wpm 9mo ago
    Yeah what qualifies as a "slow car"? An Amish dude on a horse and buggy? I have driven plenty of "slow" cars with less than 100 horsepower without issue. If you can't figure out how to merge that's a skill issue, another prime reason not to be giving people cars with former F1 car levels of acceleration. You don't need 0-60 in 3 seconds to fucking merge, get real!