i3 BEV tire size comparsion

[nismowu]

The base Mega BEV comes with 155/70R19 tires on all 4 wheels.
The Giga and Tera BEV comes with 155/70R19 tires on the front and 175/60R/19 on the rear.

Anyone test drive both of these before? Or can provide test data?
Which one accelerates faster? The 155 because it has less drag or the 175 because it provides more friction?
How about the handling?

 

[alohart]

I had a Mega BEV for an extended test drive and purchased a Giga BEV. I have not been able to detect any difference in handling, efficiency, etc., due to the different rear tire sizes.

Some i3 owners are reporting faster rear tire wear compared with their front tires, so I would think that wider rear tires would wear less rapidly. However, the ability to do a proper tire rotation with all tires being the same size should improve tire wear, in general. I would prefer all tires being the same size and was disappointed when I learned that our Giga BEV had different tire sizes front and rear for no apparent reason. It is understandable that a REx version might need wider rear tires due to its heavier rear weight.

 

[jadnashuanh]

The actual rolling diameter of the two tires is as close to identical as possible, which is why the wider wheel has a wider cross-section tire. So, from that viewpoint, there is absolutely no gearing difference that might occur from a wheel/tire combination that was larger or smaller than the narrower version. There is a slight increase in wheel/tire weight along with the increased inertia, but I'd be surprised if the average person would notice, or you'd be able to measure it in real life reliably.

FWIW, should you opt for the winter tire package, it is 'square', IOW, all of the wheels/tires are the same, and match that of the front of the vehicle, regardless of the configuration. Note, you will damage the tire if you put one of the wider tire/wheels onto the front of the car...there is not enough clearance, and you'll rub on things.

 

[nismowu]

The actual rolling diameter of the two tires is as close to identical as possible, which is why the wider wheel has a wider cross-section tire. So, from that viewpoint, there is absolutely no gearing difference that might occur from a wheel/tire combination that was larger or smaller than the narrower version. There is a slight increase in wheel/tire weight along with the increased inertia, but I'd be surprised if the average person would notice, or you'd be able to measure it in real life reliably.

FWIW, should you opt for the winter tire package, it is 'square', IOW, all of the wheels/tires are the same, and match that of the front of the vehicle, regardless of the configuration. Note, you will damage the tire if you put one of the wider tire/wheels onto the front of the car...there is not enough clearance, and you'll rub on things.

The overall diameter is close but the real difference is the contact surfaces since one is wider than another.
Obviously either tire can handle the instant torque coming from the motor so BMW limits the motor power with the traction control that you can't truly disable it.
What I would like to know is if the traction control is programmed to limit the power enough for the 155 to handle? Or the 175?
If it's programmed for 175 then the 155 models would probably have more tire spin during hard acceleration and could be slower.
If it's programmed for 155 then the 175 models are probably a little under powered and don't accelerate as hard as it could.

I think the difference would be significant as the BEV is so light.....or not, like Aloha mentioned.

 

[jadnashuanh]

The amount of traction available will depend on the surface, but the car only needs to see the relative speed of the unpowered wheels and the powered ones to decide if it needs to limit the torque being applied. IOW, while the wider tire might have slightly bigger footprint, neither one will exhibit wheelspin because of the computer sensing the relatively rotation of both the front and rear tires will dial back when it begins to detect any slip, only backing off enough to stop it, regardless of the surface and the tire involved. There is a stated difference in acceleration between the BEV and the REx because the REx is about 300+ pounds heavier. I've not seen anything listing a difference on the BEV which might have either a square setup or a staggered one regarding acceleration. If there is one, it's very small.

 

[nismowu]

The amount of traction available will depend on the surface, but the car only needs to see the relative speed of the unpowered wheels and the powered ones to decide if it needs to limit the torque being applied. IOW, while the wider tire might have slightly bigger footprint, neither one will exhibit wheelspin because of the computer sensing the relatively rotation of both the front and rear tires will dial back when it begins to detect any slip, only backing off enough to stop it, regardless of the surface and the tire involved. There is a stated difference in acceleration between the BEV and the REx because the REx is about 300+ pounds heavier. I've not seen anything listing a difference on the BEV which might have either a square setup or a staggered one regarding acceleration. If there is one, it's very small.

I thought about that too, but that's with the traction control on.
With traction control off, it no longer detects the wheel spin (or it no longer cares...) but the software still limits the power and increases gradually as the speed picks up - I believe that part is hard-coded.

Even though REx is 300 lbs more but with all that weight on the traction wheels, wider tires, and the instant torque from the electric motor should have plenty of power to compensate the additional load, but then like you said.....there's a stated difference in acceleration.
It feels more like both BEV and REx are running with the same power limitation and the REx is just much heavier.

 

[jadnashuanh]

Except in maybe deep snow or sand, IOW, strange situations for most of us most of the time, why would you want to turn the traction control off? Do you like wearing out the tires faster, or what?

Everything that I've read implies the differences in 0-60 times between the BEV and the REx is totally because of the extra 10% dead load it has to carry around all of the time. All BEV's with the Giga or Terra trim have the same tires as the REx, and only the Mega BEV has a square set as standard.

 

[stumbledotcom]

You presumably can measure a performance difference on a skidpad. I'm guessing a BEV with 175 rears will generate fractionally higher cornering force. I doubt it would be noticeable anywhere off track. The only real world difference is likely a higher threshold before the traction control activates.

For what it's worth, BMW routinely fits staggered tire sizes in higher-spec vehicles across the line. I'm sure the engineers can produce charts and graphs showing improved performance at the extremes. But it's probably also just as much about marketing.

 

[i3Alan]

...the wider tire might have slightly bigger footprint...

With the same air pressure set, both the narrow and the wider tire will have the same size footprint. The contact area is the weight on the tire divided by the pressure in the tire. Pounds divided by pounds per square inch gives you the square inches. The shape of the contact patch will be different, but not the area.

 

[ASUN]

Which one accelerates faster? The 155 because it has less drag or the 175 because it provides more friction? How about the handling?

I am sorry, but this is a practical, city car...if you want performance, look to the i8, P1, 918, Model S etc...

 

[nismowu]

Which one accelerates faster? The 155 because it has less drag or the 175 because it provides more friction? How about the handling?

I am sorry, but this is a practical, city car...if you want performance, look to the i8, P1, 918, Model S etc...

I am sorry, that you misinterpreted that I'm trying to understand the difference of the performance between the tires, not between the cars. Nor was I trying to pick the fastest i3 on the market.

 

[jadnashuanh]

IMHO, the difference in drag between the 155 and 175mm width tires is so in the noise, I doubt you'd ever notice. Both designs are low-rolling resistance and holding up the same weight. The 5.5" wheel is slightly heavier along with the tire, but again, it might make a subtle difference in ride and lateral grip, but is really a small difference. The slightly longer grip of the narrower tire probably would help verses the wider tire patch on straight-line acceleration. BMW does not indicate any differences except between the REx and the BEV, and I think you'd be hard-pressed to find it differing with tires. The car does not have enough torque or power to spin the wheels with the added computer control unless the surface is much less than ideal, and even then, not for long before computer intervention.

 

[nismowu]

Thanks for all the feedback, good to know!

 

[UKi3BEV]

The base Mega BEV comes with 155/70R19 tires on all 4 wheels.
The Giga and Tera BEV comes with 155/70R19 tires on the front and 175/60R/19 on the rear.

Anyone test drive both of these before? Or can provide test data?
Which one accelerates faster? The 155 because it has less drag or the 175 because it provides more friction?
How about the handling?

I've driven both a rex with rear tyres, and a bev with wider rears and a bev with all 4 narrows.

(When I mean driven, I mean serious amount of daily miles - my current Bev i3 is the highest mileage in the UK according to the dealer).

Result: The BEV with all 4 narrows has the fastest acceleration of all i3's. Period.
I can assure you it IS VERY noticeable.

If you have a rex and want that faster feeling, swap your rears for narrows next time (when changing for winter season). You'll feel a grin inducing difference

 

[I33t]

Result: The BEV with all 4 narrows has the fastest acceleration of all i3's. Period.
I can assure you it IS VERY noticeable.

So how many tenths of a second does it make 0-100kph?

All i3's here in Australia have the staggered wheel setup, rex or not.

 

[UKi3BEV]

Result: The BEV with all 4 narrows has the fastest acceleration of all i3's. Period.
I can assure you it IS VERY noticeable.

So how many tenths of a second does it make 0-100kph?

All i3's here in Australia have the staggered wheel setup, rex or not.

I don't have the equipment for that, all I'm going on is my experience, with one car right after the other on the same road and conditions. I'm about to swap rear 175's back to 155 on current car, (I have had access to several).. if you could suggest a tool or phone app to get this definitive data, i think it would be pretty cool to do this properly.

Re: Australia market difference - wasn't aware of that. I wonder why its so different there?

 

[janner]

Get the BMW Laptimer App from the iTunes Store. It will record 0-62 as well as lap times.

 

[jadnashuanh]

The long/narrow footprint of the narrower tires is better for acceleration while the wider ones, for cornering. Depending on the road surface, it may not make much difference at all. I have the OEM winter setup and the staggered OEM setup I use the rest of the year...don't really notice much difference except I think the narrower tires are more affected by wind and road conditions. The difference in weight is not really all that much. The factory spec only shows a difference in acceleration between the BEV and the REx, almost entirely because of the extra weight, but the cd is slightly worse on the REx as well.