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BMW i3 I01 (2014 - Current)
The BMW i3 and BMW i8 are the first two cars launch under BMW's new sub brand BMW i. The i3 is an all carbon fiber, all electric vehicle meant for urban mobility.

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  #1  
Old 02-15-2015, 01:31 PM
BHi3 BHi3 is offline
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i3 Tire and Wheel Fitments

I'm interested in i3 tire and wheel fitments.

To start with I'll suggest:

Front, 215/45-18, 25.61" diameter, 3.81" sidewall height, 18 x 7 wheel
Rear, 225/45-18, 25.97" diameter, 3.99" sidewall height, 18 x 7.5 wheel

Then I'll increase wheel offset over OEM by up to 30mm but I need to work out the minimum increase in wheel offset that makes the inner clearance. As for the outer clearance, the fender can be cut and a fender flare bolted on. Of course the wheels can be custom built after the wheel offset is worked out. (See, the wider wheel with OEM wheel offset might have enough inner clearance even as it is less inner clearance. But if it is not enough inner clearance then the wheel offset should be more outward the least amount that is necessary.)

I'm also looking for other tire size suggestions since these tire sidewalls are a little tall. Well, a 225/40-19 rear is available but there's no pairing to a 215/40-19 front.

My shop doesn't yet have the car but looking at photos I think the 18" wheels will clear things like suspension arms and knuckles. However, a 19" wheel would be safer. So that calls for a 225/40-19 tire front and rear on an 8" wide wheel. So now the wheel is wider and that doesn't help. But note the 3.54" tire sidewall height. Well, both setups need to be tried. A 225/40-19 setup front and rear could run something like 30 psi in the front tires and 35 psi in the rear tires.

Front, 225/40-19, 26.09 diameter, 3.54 sidewall height, 19 x 8 wheel, 30psi in the tire
Rear, 225/40-19, 26.09 diameter, 3.54 sidewall height, 19 x 8 wheel, 35psi in the tire

Okay, there's also a 225/45-19 but now the tire sidewall is tall again. However this setup is closer to OEM tire diameter:

Front, 225/45-19, 26.97" diameter, 3.99" sidewall height, 19 x 7.5 wheel, 30psi in the tire
Rear, 225/45-19, 26.97" diameter, 3.99" sidewall height, 19 x 7.5 wheel, 35psi in the tire


Really, various developments are likely to choose from these three setups
.

Last edited by BHi3; 02-16-2015 at 10:52 AM.
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  #2  
Old 02-16-2015, 07:35 PM
NoMoreGas NoMoreGas is offline
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Without being obnoxious, might I ask why?
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  #3  
Old 02-17-2015, 10:41 AM
BHi3 BHi3 is offline
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Quote:
Originally Posted by NoMoreGas View Post
Without being obnoxious, might I ask why?
Why should an electric vehicle not have good lateral traction ?

It's just a mistake for electric vehicles to pursue minimum rolling resistance at the expense of roadholding.

And this is a car near 3000 pounds weight. The tires on this car are too narrow.

Basically, sports car racers can fix your car.


Now some vehicles are high-center-of-gravity-vehicles and then put on narrow tires so that the low amount of traction will be less risk of a roll-over. But that just makes a vehicle that easily runs wide off the road and then if it hits anything it rolls over anyway. These high-center-of-gravity-vehicles just don't do well statistically but are allowed.

Now, I don't think that the i3 is a high-center-of-gravity-vehicle and that because the batteries are in the floor. But if it is, then what is needed is increased wheel offset. So even though I am looking for the minimum outward increase in wheel offset that makes the fitment, really the outward increase in wheel offset should be at least 5mm.


Still not convinced that car maker polices can be wrong ? Suppose someone wants to run the i3 in autocrosses. Can't they have wider tires ?

In any case, a 225 tire for a car near 3000 pounds is not too much tire
.

Last edited by BHi3; 02-17-2015 at 10:51 AM.
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  #4  
Old 02-17-2015, 10:55 AM
NoMoreGas NoMoreGas is offline
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So my other car is 2015 Subaru STi with front mount and protune which I have autorxed and prior to this I had a 2012 STi which was 407 hp at the wheel. There is no way on gods earth that this vehicle's handling dynamics could be improved to the point that there will be a noticeable difference. In addition, the cost in efficiency and in driving comfort is questionable at best. I think the benefit of these skinny tires with the largish sidewall is that the lightweight is concentrated over a relatively small contact patch which means less aquaplaning and better snow slush traction. I would be scared to drive this car with wider tires in anything except dry. Good luck.
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  #5  
Old 02-17-2015, 11:06 AM
BHi3 BHi3 is offline
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I have autocross experience with 2400 pound cars running 235 size tires. The tires work very well but note the tire sidewall height of about 3.6". Also, the tires are on the correct width wheel.

A 215 size tire for a sedan near 3000 pounds would be okay but it's the 225 size tires that are available and that's not too much tire. I'm okay with a tire sidewall height up to 4".


I found a skid pad number for the i3 and it's 0.78G. That's okay compared to the average econobox. I would guess the wider tires at 0.85G and the wider tires with a sport suspension at 0.90G. Make the wider tires the Star Spec autocross tire and that's 1.0G.


I found a source that says that the i3 went to a very tall tire so as to increase tire contact patch. Well, most racers know that the width of the tire contact patch is more important than the area of the tire contact patch but here I am pushed towards the taller diameter setup and the third setup. It would be helpful if the tire makers would make a 215/45-19 front tire to go with a 225/45-19 rear tire. (In fact they could make that 215/45-19 front tire more like a 215/46-19 for just the right amount of stagger.) In fact, it might be roll center design that makes a long tire contact patch work but again I am pushed towards the taller diameter tire setup
.

Last edited by BHi3; 02-17-2015 at 12:48 PM.
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  #6  
Old 02-17-2015, 12:17 PM
shaunatl shaunatl is offline
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What are you planning to do to address the camber up front?
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  #7  
Old 02-17-2015, 12:37 PM
BHi3 BHi3 is offline
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Quote:
Originally Posted by shaunatl View Post
What are you planning to do to address the camber up front?
I would normally be inclined to lower the car 1/4" to 1" with shorter springs or with a shorter shock body length.

But I'm now thinking that the car has a suspension roll center design that makes a long tire contract patch work. So I might stiffen the suspension without lowering and use the tire setup near 27" diameter
.

Last edited by BHi3; 02-17-2015 at 12:40 PM.
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  #8  
Old 02-17-2015, 12:46 PM
shaunatl shaunatl is offline
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Quote:
Originally Posted by BHi3 View Post
I would normally be inclined to lower the car 1/4" to 1" with shorter springs or with a shorter shock body length.

But I'm now thinking that the car has a suspension roll center design that makes a long tire contract patch work. So I might stiffen the suspension without lowering and use the tire setup near 27" diameter
.
Several of us have lowered our car by ~1" and found that camber up front is still at around -0.5.

There are alternate swivel bearings available to help with this, but it would still only provide around -1 negative total.
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  #9  
Old 02-17-2015, 12:53 PM
BHi3 BHi3 is offline
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Yeah, start thinking in terms of roll center design. One type of roll center design pushes laterally on the tire when in a curve but another type pushes down on the tire.

The i3 with these tall tires on the small car has done something different.

Well, I'm thinking that the i3 has a roll center height design that is critical to the tire diameter. So if the car is not lowered it should have the 27" tire diameter setup. But if the car is lowered then we don't know what the tire diameter should be. Basically, just go research roll center heights. (The 1967 book "Racing and Sports Car Chassis Design" discusses both high and low roll centers but it's only a couple of paragraphs.)


Well, I don't see any problem with increasing negative camber with the wider tires. The OEM setup just didn't want to tilt the narrow tires off the road. Of course, negative camber improves cornering but is less tire contact when driving straight
.

Last edited by BHi3; 06-04-2017 at 07:10 PM.
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  #10  
Old 02-17-2015, 12:59 PM
shaunatl shaunatl is offline
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I'm just looking to correct the shoulder wear I'm getting on the front tires at this point
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  #11  
Old 02-18-2015, 12:23 AM
eldy eldy is offline
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Anyone know what the stock 19" giga wheels and the 20" optional wheels weigh?
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  #12  
Old 01-09-2016, 11:09 AM
worelteam worelteam is offline
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Somebody 225/45-19 tires on I3? please some photos..
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  #13  
Old 01-09-2016, 05:49 PM
jadnashuanh jadnashuanh is offline
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FWIW, someone had the shop make an error when fitting their winter tires on their car and installed the wider ones on the front. Ruined the tires in short order as there was not enough clearance. That was only with 0.5" wider wheel.
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  #14  
Old 06-02-2017, 07:07 PM
BHi3 BHi3 is offline
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I found some very neat new tire setups in 215/225 but the tire sidewall heights went over 4". I'm going to drop the first setup that I posted because I now see the OEM tire diameters as taller in the front. I'm not going to worry about shorter tire diameters overall because the outward wheel offset is probably going to increase and then change the roll-center height.

Front, 225/45-18, 25.97" diameter, 3.99" sidewall height, 18 x 7.5 wheel
Rear, 225/45-18, 25.97" diameter, 3.99" sidewall height, 18 x 7.5 wheel

Front, 225/40-19, 26.09 diameter, 3.54 sidewall height, 19 x 8 wheel
Rear, 225/40-19, 26.09 diameter, 3.54 sidewall height, 19 x 8 wheel

Front, 225/45-19, 26.97" diameter, 3.99" sidewall height, 19 x 7.5 wheel
Rear, 225/45-19, 26.97" diameter, 3.99" sidewall height, 19 x 7.5 wheel


I found wheels at TR under the 2000 Audi A4 at 35mm to 37mm wheel offset. Of course wheel sizes available are 18 x 7.5 and 19 x 8. One 18 x 7.5 wheel would have to be bought just to see if it would fit around the suspension. Of course a 35mm wheel offset with a 7mm spacer would represent at 28mm wheel offset. It might be easier to convert the lug bolts to lug studs. So one wheel needs to be bought and have a tire installed on it just to work out the required wheel offset.

Or take measurements and calculate:

http://www.kbhscape.com/wheel.htm

Don't forget to use available space under the fender. In other words don't just put the wider wheel and tire at the same inside position as the OEM setup.

I would plan front and rear wheel offsets as the same but allow wider width wheels in the rear than in the front.

Here's a link to fender flares:

http://www.greencarreports.com/news/...mage=100484630


Well, here are the sizes that I dropped:

Front, 215/45-18, 25.61" diameter, 3.81" sidewall height, 18 x 7 wheel
Rear, 225/45-18, 25.97" diameter, 3.99" sidewall height, 18 x 7.5 wheel

Front, 215/55-18, 27.3" diameter, 4.7" sidewall height, 18 x 7 wheel
Rear, 225/50-18, 26.9" diameter, 4.4" sidewall height, 18 x 7 wheel

Front, 225/50-18, 26.9" diameter, 4.4" sidewall height, 18 x 7 wheel
Rear, 225/50-18, 26.9" diameter, 4.4" sidewall height, 18 x 7 wheel


Here is the Very Strange Setup:

Front, 195/50-20, 27.7" diameter, 3.8" sidewall height, limited stock, 20 x 6 wheel
Rear, 215/45-20, 27.6" diameter, 3.8" sidewall height, 20 x 7 wheel

SSR 3-piece wheels are available in 20 x 7 with three wheel offset choices. These tires are known to use 20 x 7 front and 20 x 7.5 rear. Just determine required wheel offset and whether or not fender flares are needed.
.

Last edited by BHi3; 06-06-2017 at 02:48 PM.
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  #15  
Old 06-04-2017, 04:16 PM
MGS9500 MGS9500 is offline
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Wow, almost 1 1/2 years between posts.

Anyway, I was kind of curious about your statement concerning patch width being more important than area.

The BMW i3 has a large area for linear and lateral handling.

You are taking a risk by changing the engineers who have evaluated the handling and tuned the cars to this tire.

And, for the record, the lateral width of the tire patch may improve lateral handling, but at the expense of linear acceleration. And, this occurs because a wide tire has a diminished area if not run at low pressure.

Physics is the same, friction is friction.

Look at this discussion and proceed at your own risk. Lots of time and money for perhaps a diminished performance.

From a physics forum
https://www.physicsforums.com/thread...debate.330790/
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  #16  
Old 06-04-2017, 04:43 PM
BHi3 BHi3 is offline
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Quote:
Originally Posted by MGS9500 View Post

Anyway, I was kind of curious about your statement concerning patch width being more important than area.
Yeah, I explained that. A low roll-center height pushes down on the tire while a high roll-center height pushes against the side of the tire. Pushing against the side of the tire calls for tire contact patch width.

But to to get wider tires on the car is going to require more outward wheel offset and that raises the roll-center height anyway. (Wheel width doesn't change roll-center height but only wheel offset.)

http://thecartech.com/subjects/auto_...oll_Center.htm .


When the 1967 book "Racing and Sports Car Chassis Design" discusses roll-center heights I think they are talking about the point in history where race cars began going from low roll-centers to high roll-centers. A high roll-center sounds bad but just means that the roll-center height is closer to the center-of-gravity height and then the center-of-gravity has less leverage on the roll-center. (At that point in time race cars were going from tall narrow tires to short wide tires.)

Last edited by BHi3; 06-04-2017 at 07:09 PM.
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  #17  
Old 06-04-2017, 05:35 PM
jadnashuanh jadnashuanh is offline
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I have high confidence that BMW engineers evaluated all sorts of tire/wheel/suspension combinations on the i3 during its development. They wouldn't have gone with a unique tire/wheel combination if it didn't meet their design goal. Now, if you don't agree with that goal, then, sure, you can change things around. You might really be surprised at the result when you change things around, maybe not for the better. But, if your driving is all in one mode (say on the track), you may not care.
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Old 06-04-2017, 06:35 PM
BHi3 BHi3 is offline
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Originally Posted by jadnashuanh View Post
I have high confidence that BMW engineers evaluated all sorts of tire/wheel/suspension combinations on the i3 during its development. They wouldn't have gone with a unique tire/wheel combination if it didn't meet their design goal. Now, if you don't agree with that goal, then, sure, you can change things around. You might really be surprised at the result when you change things around, maybe not for the better. But, if your driving is all in one mode (say on the track), you may not care.
Yeah, there is a technology for tall narrow tires and it's low roll-centers.

But how is the lateral traction of the i3 improved from the current levels ?

Of course I do have one wide-tire setup that maintains good tire diameter. (Actually there are four wide tire setups that maintain good tire diameter.)


Now to get wider wheels and tires on the i3 probably requires more outward wheel offset and that does increase steering kickback. So the increase in outward wheel offset could be minimized for nice steering or maximized for big fender flare look.

And more outward wheel offset changes roll-center heights.

Also, heavy wheels and tires are a big problem. The heavy wheel is more force bouncing off the road.

But a car with lower lateral traction drives a wider line and spends more time turning. That's true even at 30 MPH around town.

Last edited by BHi3; 06-06-2017 at 02:49 PM.
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