Thursday, July 18, 2013

BMW i3 Wheels: Efficient & Effective or Skinny & Skidding?

You get a better view of just how tall and thin the tires on the i3 without the body in place.
One of the features on the i3 that have had many BMW loyalists cringe when see them is the tires. They are tall and thin, and look more like you would expect them on a Toyota econo-box, than from the engineers in M√ľnchen.  The standard rubber on the i3 will be custom made for the car, low-rolling resistance 19-inch Bridgestone Ecopia tires, sized 155/70 R19. They are mounted on  featherweight 19" x 5" wheels, weighing only 15lbs. There will also be a 20" wheel option, but BMW hasn't disclosed the exact size of that wheel of the tires that they will mount on them. 

The stock 19" wheels
I suspect many potential i3 buyers will get past the thin, underwhelming look of the tires as long as they perform admirably. After all, they only look bad from the from or rear; when looking at them from the side it's difficult to see how thin they actually are. But what do I mean by perform admirably? That may be different for different people. Low rolling resistance tires typically aren't good for the "ultimate driving experience" the rubber is hard and doesn't usually offer premium grip for cornering. Sticky high performance tires usually deliver bad fuel economy because the rolling resistance is high. I suspect many i3 buyers will be most concerned with efficiency and range in which they would probably favor efficiency slightly over performance. But let's face it they still expect it to perform like a true BMW, and that's something BMW has promised will be the case with the i3. 

What may be the 20" optional wheels
When discussing the tall, narrow tires with Georg Kacher of Car Magazine, Ulrich Kranz of BMW said "It’s not rocket science. All that matters is the size of the contact patch. The 19-inch tires may be skinny, but their tall height generates the same contact patch as a low-section 16-inch MINI tire"  Kacher then went for a ride in a pre-production i3 and wrote this about the handling: "This is extraordinary. The i3’s most awesome dynamic talent is its incredible grip. The made to measure tires are about as narrow as those of a 125cc motorbike, yet they hang on almost as tenaciously as BMW’s latest DTM racer... The car zooms towards the apex, kisses the cobbles and flies out onto the short straight. There is very little lean considering the considerable pace, and I don’t recollect more than a faint trace of front end pitch and no yaw at all. This i3 appears to handle like the best BMWs."
The original i3 concept wheels
Then Michael Specht from the Automotive News wrote this after driving an i3 a couple days ago: 
"BMW's i3 electric car looks set to be a winner. I drove it recently and I can only say: Wow! Whoever drives this car will want one immediately. I can't remember when I was more surprised by a car's driving dynamics. One of BMW's marketing slogans is "sheer driving pleasure." BMW was keen that this should apply to the automaker's new electric vehicles sold under the "i" subbrand and the company has succeeded with the i3."

The i3 concept coupe's 20" wheels
However Autoblog had less than total praise for the i3's handling: "The test cars were fitted with skinny, rock-hard and low-rolling resistance 19-inch Bridgestone Ecopia tires, sized 155/70 R19. After just a single spirited lap of the set course in 93-mph v-max Comfort mode, it was clear that we were driving the i3 in a style for which it was never designed. If you try to make the i3 live up to the well-honed definition of "Ultimate Driving Machine," you are categorically missing the entire point of the i3." That's not what the majority of potential i3 buyers want to hear - me included. Don't tell me I'm missing the point if I buy a BMW and expect it to handle like a real BMW! I don't care what type of fuel it uses or whether it's a hatchback or sedan, it's a BMW!  However this is the only article I've seen that criticizes the handling and I've probably read about a dozen that have said they were impressed. The final verdict for me will be when I get behind the wheel of on myself and I urge everyone else to do the same thing. It's nice to see car reviews but let yourself be the judge when you are purchasing a car. After all, it's your money and you'll be driving it!

BMW has done everything they reasonably could to cut the weight of the i3. This allowed them to use a smaller battery and still get their tareted range of 80 to 100 miles with the i3.With the battery being the most expensive component of an EV by far, it's not surprising they are so obsessed with weight savings. However what is the perfect balance of efficiency and performance? No doubt the car would handle even better with wider, stickier tires on there which would need wider wheels, which would then weigh considerably more. Finding the perfect balance was BMW's task, it's just up to us to drive and enjoy the car. I hope they got this one right because the i3 won't be the Ultimate Driving EV if it isn't fun.


  1. Those are some wimpy looking tires Tom. I hope they offer an upgrade with some more rubber. I don't mind sacrificing a few miles to look good

  2. you are entitled to your ignorance re: skinny tyres!

    Low rolling resistance is only part of the deal - the faster you go the more frontal area your wide boy tyres have and more drag hence significant range loss.

    1. Yes you are correct to a point. Range loss because of the drag is certainly measurable, but significant, certainly not. If the tires were 185/60 R19 instead of 155/70 R19 or thereabout, you would have a car that looks significantly better visually, and much better handling. The range loss would be nearly unmeasurable at low speeds (perhaps 1 mile per full charge) and maybe as much as 2 - 3 miles at highway speeds.

    2. As the owner of an Audi A2 1.2 TDI (93 MPG Imp) for over 11 years and 185,000 miles I can assure you even a change from 145R14 to 165R14 makes a significant. even sticking with same section Bridgestone 145 going from Ecopia in summer to Blizzak version in winter consumes 10% more fuel.

      Tyre PSI is also much higher than normal car tyres - around 38 to 44 psi

      Looks are not everything.

  3. Road and Track isn't impressed with the handling of this car either. Complaining of lot of body roll, understeering (even though it's a RWD car),etc.
    I wish you could put in 185 width tires on it without rubbing the mud guards but that might not be possible.

    Guess it's the Chevy Volt for me then since I believe it uses 215 wide tires.

    1. If tire width for looks is what's important for you than I agree but I can assure you the Volt would lose an any race with the i3; either in straight line or on a track. Next week BMW will have hundreds of journalists in Amsterdam for thorough test drives. Personally I like the Volt, and recommend it to many people, but it doesn't perform nearly as well as the i3 does on the track.

    2. I thought wider tires usually mean more g-forces around corners. Yeah the i3 is quicker in a straight line that the Volt but you can hack the Volt to get a 6 second 0-60 time and people are trying to put a rear sway bar on it.

  4. Novices don't understand CONTAC PATCH is not wholly dependent on width dimensions. A taller wheel tire has a longer contact patch. I had a whole writeup but it didn't register,not going to do it again.