>If automakers were that serious about drag reduction, we’d see many more EVs riding on smaller wheels.
Has nothing to do with drag. EVs are heavy, and need big brakes to stop in an emergency. Wheels go over the brakes. Therefore, the wheels need to be big to fit the brakes. Smaller wheels mean longer braking distances. Nobody wants that.
EVs rarely use brakes, and larger wheels reduce the efficiency of regen braking. But we are optimizing for the worst case where braking is needed, so a larger wheels reduce size is useful.
You physically can't fit smaller wheels on the car and pass safety tests. A 14" wheel on a Tesla or Kia EV means downsizing the brake rotor and caliper to an unsafe stopping distance.
I don’t think it’s that the radius of the wheels makes it possible (or not) to fit brakes. You can make very strong brakes with relatively small discs for example. You can see on a sportscar that the discs are nowhere near the radius of the wheers (like they are probably 1/2 the radius).
All the forces for acceleration, braking and cornering for a vehicle are limited by the contact surface of the tyres on the road. This is drummed into you quite viscerally when you ride a motorcycle and have 100+ bhp engine and you find yourself leaned over having gone into a corner too fast. If you try to brake now that you are leaned over, your bike will skid out because you only have a contact patch about the size of the palm of your hand and your braking will use up some of the friction that would otherwise get you round the corner.[1]
Bigger tyres mean more contact with the road so you have more friction available for braking (or acceleration).
[1] on a bike your best option in this scenario is to keep your head up, look where you want to go, keep your speed constant and trust that your tyres will hold you and you’ll have a little bit of luck and not meet a patch of spilled diesel, sand, paint etc and slip out.
Are engineers not tweaking the durability-performance-feel tradeoff, in favour of brakes with more stopping power in smaller tires, but which happen to be rarely used?
I just find them so unnecessary. If you need them for fuel efficiency, is your battery / motor / whatever really properly designed? It just comes off as desperate.
The fuel efficiency claims are nonsense. Golf balls would like to have a word with these engineers.
They do it because it looks cool and futuristic. Just like replacing all of the physical switches with non-tactile touch-based things. Overall just reduces the vehicle's safety and increases the cost to repair. Door handles, by law should be mandated to be physical things. If you want a button that can automatically actuate the physical linkage that's fine but the handle itself should be a physical linkage to the latch.
> The flush Hyundai and Kia handles are motorized and retractable, but they can also be opened entirely mechanically without power. They are little more awkward to use when unpowered but it's entirely doable if you know how. You just push the front side in which pops out the rear grab handle part. This also how Chevy has done their Equinox EV handles which is powered on the higher trims but unpowered for the base model I believe.
So, as long as they fail safe, I think they’re fine from a form and function perspective. It’s the failing unsafely (Tesla) that’s the problem. If they do not work without power, they should fail safety testing.
I largely agree, although in an emergency bystanders/emergency workers shouldn't be trying to figure out how a door handle works at all. As a general non-driver, I find it kinda disturbing how auto manufacturers are constantly making these cosmetic adjust that impact safety - excessively bright headlights, distracting animated turn signals, weird ass handles. Not all features are innovations, some are just bad ideas.
That’s fair. I would also support pyrotechnic bolts or other systems similar to seat belt tensioners that cause doors to fail open upon impact. The primitives already exist to support isolating the high voltage battery pack in a crash event (triggered by airbag deployment) using a pyrotechnic switch. When Bad Thing happens, the vehicle should be designed to maximize occupant survival odds, including minimizing time to occupant extraction.
I feel the same way about door windows that don't have crank handles. Like, suddenly I have to place a lot of trust in the electrical system in all conditions.
>If automakers were that serious about drag reduction, we’d see many more EVs riding on smaller wheels.
Has nothing to do with drag. EVs are heavy, and need big brakes to stop in an emergency. Wheels go over the brakes. Therefore, the wheels need to be big to fit the brakes. Smaller wheels mean longer braking distances. Nobody wants that.
EVs rarely use brakes, and larger wheels reduce the efficiency of regen braking. But we are optimizing for the worst case where braking is needed, so a larger wheels reduce size is useful.
You physically can't fit smaller wheels on the car and pass safety tests. A 14" wheel on a Tesla or Kia EV means downsizing the brake rotor and caliper to an unsafe stopping distance.
Share the details of your calculations with us, please.
https://www.fhwa.dot.gov/programadmin/images/y2kgb27.gif
I don’t think it’s that the radius of the wheels makes it possible (or not) to fit brakes. You can make very strong brakes with relatively small discs for example. You can see on a sportscar that the discs are nowhere near the radius of the wheers (like they are probably 1/2 the radius).
All the forces for acceleration, braking and cornering for a vehicle are limited by the contact surface of the tyres on the road. This is drummed into you quite viscerally when you ride a motorcycle and have 100+ bhp engine and you find yourself leaned over having gone into a corner too fast. If you try to brake now that you are leaned over, your bike will skid out because you only have a contact patch about the size of the palm of your hand and your braking will use up some of the friction that would otherwise get you round the corner.[1]
Bigger tyres mean more contact with the road so you have more friction available for braking (or acceleration).
[1] on a bike your best option in this scenario is to keep your head up, look where you want to go, keep your speed constant and trust that your tyres will hold you and you’ll have a little bit of luck and not meet a patch of spilled diesel, sand, paint etc and slip out.
Are engineers not tweaking the durability-performance-feel tradeoff, in favour of brakes with more stopping power in smaller tires, but which happen to be rarely used?
It seems like a lot of brands will put the biggest wheels on the top trim, even if the performance is the same as other trim levels
I just find them so unnecessary. If you need them for fuel efficiency, is your battery / motor / whatever really properly designed? It just comes off as desperate.
The fuel efficiency claims are nonsense. Golf balls would like to have a word with these engineers.
They do it because it looks cool and futuristic. Just like replacing all of the physical switches with non-tactile touch-based things. Overall just reduces the vehicle's safety and increases the cost to repair. Door handles, by law should be mandated to be physical things. If you want a button that can automatically actuate the physical linkage that's fine but the handle itself should be a physical linkage to the latch.
From a comment:
> The flush Hyundai and Kia handles are motorized and retractable, but they can also be opened entirely mechanically without power. They are little more awkward to use when unpowered but it's entirely doable if you know how. You just push the front side in which pops out the rear grab handle part. This also how Chevy has done their Equinox EV handles which is powered on the higher trims but unpowered for the base model I believe.
So, as long as they fail safe, I think they’re fine from a form and function perspective. It’s the failing unsafely (Tesla) that’s the problem. If they do not work without power, they should fail safety testing.
I largely agree, although in an emergency bystanders/emergency workers shouldn't be trying to figure out how a door handle works at all. As a general non-driver, I find it kinda disturbing how auto manufacturers are constantly making these cosmetic adjust that impact safety - excessively bright headlights, distracting animated turn signals, weird ass handles. Not all features are innovations, some are just bad ideas.
That’s fair. I would also support pyrotechnic bolts or other systems similar to seat belt tensioners that cause doors to fail open upon impact. The primitives already exist to support isolating the high voltage battery pack in a crash event (triggered by airbag deployment) using a pyrotechnic switch. When Bad Thing happens, the vehicle should be designed to maximize occupant survival odds, including minimizing time to occupant extraction.
https://xray.greyb.com/ev-battery/tesla-crash-protection-tec...
I have a Hyundai and the handles are fine except when you forget to lock the car or they freeze shut
I feel the same way about door windows that don't have crank handles. Like, suddenly I have to place a lot of trust in the electrical system in all conditions.
But I guess I'm just, um, cranky.