Maybe info of little interest, sitting at the keyboard on a rainy day, but there is more going on with e-car tires than is commonly known. To back up in time, a little bit, here is an interesting story (at least it was to me).
When California made a rule (I think it was around 1990 or so) that all major manufacturers had to sell 10% of their new cars as "electric", by year 2000, all the car companies got busy on the study. At the time, the GM EV-1 was on the road (lease only). Toyota management told their top engineers to study the best plan for an EV, and bring a logical solution. When the engineers showed their idea, management was shocked.
Basically, the car they recommended was shaped about like a Model A sedan, with similar ground clearance and tall skinny wheels, and upright windows. What in the world were they thinking!!??
It was explained to me that there were some key factors:
1. Tire size (actual rolling diameter) was important. Anyone who has ever worked for a rock and gravel yard knows the rule: Never load more than 1/2 weight in solid rocks, versus sand/gravel mix. Heavy solid mass puts too much shock load into axles, bearings, and tires because it lacks the elasticity of looser material.
The EV was going to have a very heavy (like 1000 lbs), very solid mass hanging under the center of the car. The tires needed large diameter to reduce impact force angles during regular driving.
2. Ground clearance. The battery had to hang under the car, in a position that it could be removed for maintenance or repair. It needed to be high enough off the ground to clear the concrete parking dividers that people like to goof....and drive over.
3. Window and windshield angles. The biggest constant draw, driving in sunny hot California, was going to be the air conditioning load demanded by drivers and passengers. Extreme sloped front and back glass (like EV-1) was the wrong choice. You don't need much aero improvement to sit in freeway traffic jams for hours.
4. Proper geometry for good ABS function (and more tire issues here). EVs can NEVER be operated without big brakes, effective ABS, all tied to very smart motor control. Those electric motors are solidly locked to the wheels. If you ever get them stopped, during a panic stop, they will NOT start rolling easily when you come off the brake pedal. The motor has to actually ADD power during emergency braking to prevent that uncontrolled skid.
Remember the little toy flywheel cars we had as kids? You pushed them a couple times on the kitchen floor and they'd go zooming across the room. If you tried to hit the floor too fast, the flywheel couldn't spin up and the tires just slipped. Now you know....
I remember the first EV I ever drove (a prototype) that was a simple little van, filled with lead-acid batteries, and the electric motor connect to a 3-speed column shift manual trans (yes...with a clutch pedal). During the session indoctrination, we were all told that if we EVER failed to push in the clutch before using the brakes, we were out of the program. No questions, no argument....OUT!! After stopping, we left the trans in 3rd gear, let out the clutch, and could then apply throttle to drive away.
Anyway, my story gets a little off track, but.... the final solution for initial design led to the launch of the first RAV4. Tall skinny wheels, high ground clearance, upright windows...and a "mini SUV" aimed at getting customers back into that style vehicle (instead of streamlined, pretty sedans and coupes.) That was the strange start of the compact SUV market....all aimed at getting ready for a year 2000 rule that quietly disappeared.
As Paul Harvey used to say, ".....the rest of the story." This one I know, because I was there, folks!
