Panic braking

PhilH said:

I'd always assumed (with no evidence whatever) that the tyre diameter and width reduced rolling resistance.

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Rolling resistance is more a tire carcass construction, tread design, and rubber compound relationship verses the width or diameter. Low rolling resistance can be added to any tire width/diameter...but, cd is totally a function of width in the airstream. Combining low rolling resistance and a low cd were, I think, the reason they were used on the i3. Tire pressure helps, too, by preventing deflection. It takes energy to deflect the tire which generates heat which is wasted. Some of that heat comes from tread squirm, and the compound and shape of the tread blocks affect that. That energy comes from somewhere...it's not free. Bridgestone talks about it on their website. Nokian does as well on theirs and claims a 30% improvement over 'conventional' tires. There are some tradeoffs, as with most things. The narrow tires/wheels on the i3 decrease some of the barn door effect - you don't have to push as much through the air but allow enough tire patch to provide adequate traction. But, the bottom line is, it has a decent tire patch and thus can hold its own.

Replying to old post but so far, I haven't seen "even though the i3 stops really well, what happens to the car behind it??" - *Smashhh is the experience I got...

Snowie said:

Replying to old post but so far, I haven't seen "even though the i3 stops really well, what happens to the car behind it??" - *Smashhh is the experience I got...

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I've had two accidents where I stopped and the person behind me didn't...both were in slippery winter conditions. Too many people do not pay proper attention to adjust for the conditions. Outside of the US, BMW enables a set of flashing rear lights when deceleration exceeds a certain point. I think the US rules on flashing red lights prohibits that (as if a stopping car's flashing lights would be confused with an emergency vehicle under those conditions!).

jadnashuanh said:

...Outside of the US, BMW enables a set of flashing rear lights when deceleration exceeds a certain point. I think the US rules on flashing red lights prohibits that (as if a stopping car's flashing lights would be confused with an emergency vehicle under those conditions!).

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They call 'em Dynamic Brake Lights and I believe can be enabled. Had something similar in my Audi. I don't get the US regs, allowing red turn signals that use the brake light, but not something like this that has a modest influence preventing rear-end collisions.

US laws with headlights, dynamic brake lights, rear fog lights, side repeater signal lights are all screwed up and are in the stone age! They're actually BEHIND the rest of the world... they're still dealing with counting maximum watts allowed for headlight and front fog lights (hence not allowing front fogs to be on when high beams are on) when Europe is already playing with laser headlights.