19" or 20" wheels?

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tiburonh

Well-known member
Joined
Jan 1, 2014
Messages
206
Location
Tiburon, CA
Has anyone had a chance yet to drive on both the 20" and the 19" wheels? If so, could you please share your thoughts on what the difference is in ride quality between the two?

Normally I like to go with a vehicle's standard wheel size because the tires, by having more sidewall, usually provide a more forgiving ride than the tires on the bigger (bling) wheels. I wonder if the super skinniness of the tires on the i3 has any impact on this. I suppose it could mean that going to a bigger wheel means going to an even harsher ride than on other cars, but maybe there is some law of tire dynamics that says the opposite in this case?
 
I'd stick with 19 " - ride better with higher profiles and replacement or Winter tyres also cheaper!
 
I'd prefer 19" wheels for ride quality and tire longevity, but unfortunately BMW has decided to make all 3 19" options pretty ugly, and my normally frugal wife will opt for the additional expense of 20" wheels for the sake of appearance. What most of us probably do not realize is that the attractive 20" wheels are not actually the simple 5 x double spoke wheels they appear to be, but are actually a pretty brilliant aerodynamic shape with black paint used to disguise the trailing edge fairings of each "double spoke" fiction.

I'm hoping to talk her into the goofball Style 427 wheels that come standard with USA's awkwardly labeled "Tera" package in order to save the $1,300 upgrade, but anyone on this forum who is married will understand the futility of that effort...
 
What we really need is some back to back comparisons of ride and handling between the options:

1) 427 in 5J x 19 front and rear.
2) 427/428/429 in 5J x 19 front, 5.5 x 19 rear
4) 430 in 5J x 20 front, 5.5 x 20 rear

Having the actual assembled wheel and tyre weights between the options would be very helpful. Generally, larger wheels weigh more as tyres are lighter than alloy, and lighter unsprung weight is better from a ride and performance perspective IMO so the 19's should be the pick if you can stomach the styling.

Other than that, perhaps stay with standard and wait for aftermarket wheels to appear.
 
I have driven both wheels. The 19 inch with winter tyres are just fine but by heavy wind you should make steering correctings. The 20 inch drivers more smoothly
 
ultra turtle said:
…What most of us probably do not realize is that the attractive 20" wheels are not actually the simple 5 x double spoke wheels they appear to be, but are actually a pretty brilliant aerodynamic shape with black paint used to disguise the trailing edge fairings of each "double spoke" fiction...

In person, I found the painted black wedges on the 20" wheels quite apparent and off-putting. Just personal aesthetics. Still, make the effort to actually see them and not rely on just photos before ordering.
 
stumbledotcom said:
In person, I found the painted black wedges on the 20" wheels quite apparent and off-putting. Just personal aesthetics. Still, make the effort to actually see them and not rely on just photos before ordering.
I saw them up close on my test drive and was very impressed. IMO, BMW's biggest challenge in successfully rolling out what I believe to be the smartest travel solution for the vast majority of us is to explain the intricacies of the multitude of smart decisions that resulted in the final design to luddites such as you and I. This one I get. Having personally raced thousands of miles of Ironman triathlon and longer endurance cycling events, and invested many thousands in race wheels, I can tell you with a fair amount of experience that there is not a cyclist on the planet that will intelligently argue against the use of a large diameter, skinny, lenticular disk wheel as being the most efficient aerodynamic shape to move a vehicle forward (crosswinds influence other tactical wheel choices on a bike, but don't really apply to a car). The base wheel approaches a pure lenticular disk shape, and is the smartest (yet ugliest) design for anyone who truly thinks the problem through. Consider that the top of the wheel is travelling forward into the airstream at twice the velocity (therefore 4 times the drag) of the vehicle itself, and you may start to grasp the importance of an aerodynamically sound wheel design. Openings for brake cooling? Fine, but who in their right mind would exceed regenerative braking on a regular basis, and engage the calipers? My current plug-in EV has extremely mild regen capability, yet I can count the times I exceeded it's capability on one hand for the two years I've been driving it - all in response to unpredictable behavior of drivers ahead.

Bottom line is that fairing the leading and trailing edge of the spokes on the 20" wheel is a deliberate and smart move by BMW to give us an efficient and attractive wheel, and I'm in favor of the approach.
 
ultraturtle said:
stumbledotcom said:
In person, I found the painted black wedges on the 20" wheels quite apparent and off-putting. Just personal aesthetics. Still, make the effort to actually see them and not rely on just photos before ordering.
I saw them up close on my test drive and was very impressed. IMO, BMW's biggest challenge in successfully rolling out what I believe to be the smartest travel solution for the vast majority of us is to explain the intricacies of the multitude of smart decisions that resulted in the final design to luddites such as you and I. This one I get. Having personally raced thousands of miles of Ironman triathlon and longer endurance cycling events, and invested many thousands in race wheels, I can tell you with a fair amount of experience that there is not a cyclist on the planet that will intelligently argue against the use of a large diameter, skinny, lenticular disk wheel as being the most efficient aerodynamic shape to move a vehicle forward (crosswinds influence other tactical wheel choices on a bike, but don't really apply to a car). The base wheel approaches a pure lenticular disk shape, and is the smartest (yet ugliest) design for anyone who truly thinks the problem through. Consider that the top of the wheel is travelling forward into the airstream at twice the velocity (therefore 4 times the drag) of the vehicle itself, and you may start to grasp the importance of an aerodynamically sound wheel design. Openings for brake cooling? Fine, but who in their right mind would exceed regenerative braking on a regular basis, and engage the calipers? My current plug-in EV has extremely mild regen capability, yet I can count the times I exceeded it's capability on one hand for the two years I've been driving it - all in response to unpredictable behavior of drivers ahead.

Bottom line is that fairing the leading and trailing edge of the 20" spokes is a deliberate and smart move by BMW to give us an efficient and attractive wheel, and I'm in favor of the approach.

Hi ultraturtle-

Love the explanation of the science behind the wheels, but could you clarify for me please whether or not you have a preference between the two sizes. Are you saying that the base wheels (the 19"s) are the best for aerodynamics but the 20"s are still OK, just more attractive than the 19"s? Or am I misreading that?

Thanks.
 
tiburonh said:
...could you clarify for me please whether or not you have a preference between the two sizes. Are you saying that the base wheels (the 19"s) are the best for aerodynamics but the 20"s are still OK, just more attractive than the 19"s? Or am I misreading that?

Thanks.
Bearing in mind that a very fit human being can only generate about 1/4 hp (about 1/680th of the i3) for short bursts, one might think the comparison a bit frivoulous, until he or she considers that automobiles operate at roughly 4 times the speed of a human on a bicycle, and the top of that wheel will now be looking at a factor of 16 times the drag that would be experienced at cycling speeds, so yeah, aerodynamics do matter somewhat.

Still, BMW has apparently put a lot of work into ensuring that all 4 wheel choices are very aerodynamically efficient, and I would recommend making the choice based on personal taste, as I am confident that any difference would equate to a small fraction of a mile's worth of range over the battery bank's total capacity. In theory, the base wheels look to be (by the tiniest of fractions) more aerodynamically efficient than other choices, but I seriously doubt the difference would be measurable. The purpose of my post was to point out that the disguised fairing were a smart idea, and that without them, a pure spoked wheel would create enough drag to significantly reduce the overall vehicles aerodynamic efficiency, likely dropping significantly more range per charge.
 
ultraturtle said:
tiburonh said:
...could you clarify for me please whether or not you have a preference between the two sizes. Are you saying that the base wheels (the 19"s) are the best for aerodynamics but the 20"s are still OK, just more attractive than the 19"s? Or am I misreading that?

Thanks.
Bearing in mind that a very fit human being can only generate about 1/4 hp (about 1/680th of the i3) for short bursts, one might think the comparison a bit frivoulous, until he or she considers that automobiles operate at roughly 4 times the speed of a human on a bicycle, and the top of that wheel will now be looking at a factor of 16 times the drag that would be experienced at cycling speeds, so yeah, aerodynamics do matter somewhat.

Still, BMW has apparently put a lot of work into ensuring that all 4 wheel choices are very aerodynamically efficient, and I would recommend making the choice based on personal taste, as I am confident that any difference would equate to a small fraction of a mile's worth of range over the battery bank's total capacity. In theory, the base wheels look to be (by the tiniest of fractions) more aerodynamically efficient than other choices, but I seriously doubt the difference would be measurable. The purpose of my post was to point out that the disguised fairing were a smart idea, and that without them, a pure spoked wheel would create enough drag to significantly reduce the overall vehicles aerodynamic efficiency, likely dropping significantly more range per charge.

Cool. Understood, and appreciated. Can we look forward to a video of you racing on your bike against a friend driving your i3?

On a side note, I've always wondered about the merits of the trend to "bling" wheels (i.e, larger, fatter, etc.). Your analysis confirms my suspicion that such wheels are actually WORSE for driving on many levels.
 
tiburonh said:
On a side note, I've always wondered about the merits of the trend to "bling" wheels (i.e, larger, fatter, etc.). Your analysis confirms my suspicion that such wheels are actually WORSE for driving on many levels.

I wouldn't go quite that far...

From an economy point of view, and possibly the risk of hydroplaning, narrower than accepted 'normal' wheels/tyres have benefits. On almost every other parameter sensibly wider deliver roadholding and driving benefits up to a point.

All the wheels available are spoked with air gaps. The economy benefits of the sizing would be from the width of the tyre not the style of the wheel and the mixed size options would have the largest wind resistance and therefore the most impact on range. All the options are basically the same overall height, and it is only the bottom part of the wheel/tyre that is in direct airflow, unlike the situation on a bicycle.

The wheel arches would have more impact on economy than wheel style and size. It's not an option on the i3 due to the outboard wheel placement, but wheel arch covers can reduce drag significantly - up to 1/6 of total drag is down to the air turbulence in wheel arches. The i3 is already making headway in the drag department, the underbody is quite smooth.

All told, most of the i3's will be doing city running, I expect there will be negligible range impact from wheel choice. Most won't be travelling fast enough for long enough to make a noticeable difference.

Edit: Found this post describing the effect of tyre size on drag: Ecomodder: Tyre Width vs Drag (Cd)

Basically confirms BMW's decision to go skinny. :)
 
tiburonh said:
I saw them up close on my test drive and was very impressed…

Apologies tiburonh, I obviously didn't make myself clear. My not impressed comment referred strictly to the aesthetic decision of hiding the aerodynamic structures with black paint in order to mimic currently stylish thin spokes. I understand the principles you explained and prefer all of the 19" designs because their forms more closely follow function. Even though I (hopefully) ordered the Giga package and its standard wheels, I would take the base disc-style wheels if offered as a stand alone option. Reminds me of the wheel covers on the car I came of age with as a driver--the delightfully weird Saab 99 3-door, née Combi Coupe.

http://saabblog.tumblr.com/post/67585042449/vaerktoj-saab-99-combi-coupe

Mine was even the same odd orange, which Saab officially labeled Yellow 97.
 
I am only leasing the car for 3 or 4 years I don’t see much point in paying for lots of extras so I have kept to the standard wheels (and most of the other standard items). Did opt for the comfort access as I have had this on my Z4 for 4 years and have got use to not using my keys!
 
:mrgreen: I really appreciate nice wheels on a car. I thinks it's neat that BMW gave us four options on wheels. After considerable thought, I decided I liked the Mega World wheels the best. They look neat, look like they belong on a electric car, and will be the easiest of the four to clean. My second choice would have been the 20" wheels. The Mega World wheels look more basic, while the 20" wheels look more high class. Cost wasn't and issue, and in the end, I got exactly what I thought looked the best on my Ionic Silver i3.
 
One operational thing to consider...the tires that come on the 20" wheels are SUMMER tires, NOT all-season rubber/tread. So, if it gets either cold or snowy, you're either going to have to park your i3, or opt for winter tire package, and those are now only available in 19", and in the USA, you only get the 427 wheel. You can buy the wheel, center cap, TPMS, and winter tire package from BMW for less than the 427 wheel costs as a replacement on its own, so it's a good deal. TIreRack has a wheel that will fit the i3 (due in late October), but when you price it out, the BMW OEM winter tire package is cheaper.
 
I33t is more accurate re: aero effect of these wheels than other posts here.

Skinny tyres offer far less frontal area and a more longitudinal contact patch than a low profile tyre. This is beneficial in wet conditions but less so for all out dry cornering speeds.

It would be great if someone could weigh the wheel tyre combos for the i3 range.

Larger diameter wheels require more weight and this weight is distributed more at the outer edges where it will have the greatest impact on gyroscopics eg: when turning a corner. The bending moments across the hub are also higher for a given turning speed requiring extra rigidity in their hub design (usually more weight).

The extra weight will require more energy to accelerate and greater stiffness in the tyre walls (lower profile needed to match original wheel diameters else get large gearing effect).

Most Eco cars use smaller diameter wheels with skinny tyres than their regular street cousins:

e.g: BMW 116d ED has 16inch wheels where the standard 116d has 17" with 18" option on Sport models.
 
ecoangel said:
Larger diameter wheels require more weight and this weight is distributed more at the outer edges where it will have the greatest impact on gyroscopics eg: when turning a corner. The bending moments across the hub are also higher for a given turning speed requiring extra rigidity in their hub design (usually more weight).
The 19" and 20" i3 wheels+tires are exactly the same diameter. The 19" refers to the diameter of the wheel, and have 1" taller tires than the 20" wheels. The rubber is typically heavier than the wheel alloy "spoke" extensions, so the 20" should be a bit lighter than the 19". Given less massive rubber, the gyroscopic, which is not very great as the RPM of the wheel is not very fast, would then be less on the 20". The bending moments on the hub would be nearly identical, but the spokes do need to be stronger and more compliant because the shock absorption of the tires is less, imparting more stress on the wheel.
 
i3Alan said:
The rubber is typically heavier than the wheel alloy "spoke" extensions, so the 20" should be a bit lighter than the 19". Given less massive rubber, the gyroscopic, which is not very great as the RPM of the wheel is not very fast, would then be less on the 20". The bending moments on the hub would be nearly identical, but the spokes do need to be stronger and more compliant because the shock absorption of the tires is less, imparting more stress on the wheel.

In my experience, larger diameter wheels and tyres are heavier than smaller. The amount of rubber is less on a 20 inch wheel, so the tyre is marginally lighter for the same width. The extra weight does impact performance, and if the choices are well executed the handling and roadholding improve at the cost of altered ride and noise. For some cars and some owners, this can be an improvement in transmission of information through the chassis.

Here is a test run by Car and Driver in 2010 on a Golf: http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

effects-of-upsized-wheels-and-tires-tested-chart-678-photo-568637-s-original.jpg


For the i3, we really don't know the specifics until some owners of both 19 and 20 inch wheels take one off their car and weigh it!
 
I33t said:
Here is a test run by Car and Driver in 2010 on a Golf: ...

For the i3, we really don't know the specifics until some owners of both 19 and 20 inch wheels take one off their car and weigh it!

In this chart, only the 8" examples are comparable, so there is this one data point of the 18" being 3lb heavier than the 17". That is a fairly significant 6% difference, too. Could be the same situation on the i3 options as well. My guess is the narrower wheels on the i3, reduces, and possibly reverses the difference. That is because the tire weight difference is in the sidewall height difference, but the wheel difference is in the circumference times width of the rim plus the added length of the spokes. The circumference of the tread times the width of the tread is the same in all cases. Since the rim is narrower, the additional material in the larger rim will be less.

I would love to see the respective weights for the i3. I wouldn't put money on it either way!
 
i3Alan said:
I33t said:
Here is a test run by Car and Driver in 2010 on a Golf: ...

For the i3, we really don't know the specifics until some owners of both 19 and 20 inch wheels take one off their car and weigh it!

In this chart, only the 8" examples are comparable, so there is this one data point of the 18" being 3lb heavier than the 17". That is a fairly significant 6% difference, too. Could be the same situation on the i3 options as well. My guess is the narrower wheels on the i3, reduces, and possibly reverses the difference. That is because the tire weight difference is in the sidewall height difference, but the wheel difference is in the circumference times width of the rim plus the added length of the spokes. The circumference of the tread times the width of the tread is the same in all cases. Since the rim is narrower, the additional material in the larger rim will be less.

I would love to see the respective weights for the i3. I wouldn't put money on it either way!

You have one data point that supports the fact that larger wheels of the same width weigh more in combination with their tyres than smaller diameter wheels, yet you still think that the reverse is likely. Is this wishful thinking, or what? The 8" wheels in the article are the same width with just a one inch increase in diameter - that is the exact same scenario as the i3's wheels!

Your contention that the extra material is in the spokes only is incorrect: the circumference of the wheel rim is larger, even though the tyre circumference is close to the same: Circumference = π * D

3.14 * 19 = 59.66
3.14 * 20 = 62.80

Each spoke in the 20 inch rim is half an inch longer, and each rim is 3.14 inches longer. If you observe the wheels, you will notice that the spokes are widest close to the rim = more mass in the last half inch of spoke than anywhere else on the spoke.

I would suggest that the best we could hope for in the i3 is that BMW used lighter materials and processes to bring the 20's down to the same weight as the 19's. I'm doubtful, I think they would make some noise about it if this was the case.

I can see why you wouldn't put money on it. :mrgreen:
 
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