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Tire Size

6K views 17 replies 4 participants last post by  X3forlife 
#1 ·
So the 28i will have 17 inch tires while the 35i will have 18 inch tires.

Could one of you car geniuses please explain in English what effect tire size has on driving? Is bigger better?

Thanks
 
#2 ·
No, bigger wheel size is not necessarily better, especially in winter driving where you want a tall tire sidewall (profile). Bigger wheels do tend to look better however as they better fill the wheel wells. So, it really depends on your climate and intended use.
 
#6 ·
Tire and wheel size

In my E86 X3's I have had both 17 and 18 inch diameter wheels with different tyre sizes. The 17's were 235X55 and the 18's were 235X50 Scorpions. The rolling diameter was 27.2" for the 17's and 27.3" for the 18's. These diameters are almost identical and considered interchangable as long as all 4 wheels are identical. I suspect the new F X3 will have similar sized tyres.
 
#7 ·
Everytime it crosses my mind that the 18" wheels/tires on the 35i might make for stiffer ride and might not be good in the snow, I have to remind myself that all of this talk is theoretical hocus pocus and BMW has likely adjusted for all of this.

For one, they are not likely to ignore the dynamics on their higher end model of the two.

Secondly, and most importantly, the X5 comes standard with 18s and nobody is worried about how that handles in the snow or if the ride on the X5 will be too stiff. They have made their adjustments and know what they are doing.
 
#9 · (Edited)
It should be fine for most I would think. Again, the most powerful argument in my mind is that those are the wheels/tires that are standard on the X5. If the 17s were so much better in snow or comfort, they would find away to get it on the X5. That is their flagship (for the X series).

It's probably true that given the same suspension...but they just adjust the suspension for it.
 
#10 ·
So...I just watched a video of the X6 in the snow and it looked good to me...and that has 20" tires.

So i think this tires size only matters if the car cannot adjust suspension and handling to account for it. If it is thought about ahead of time and BMW adjusts handling, suspension, the X-drive, Dynamic dampening etc. to that particular tire (while testing ride quality), it probably doesn't matter.

Their mother of all flagships the 760Li has 19 inch tires yet is comfortable and probably handles well in the snow (I watched a video but I'm not sure how much spinning the driver is trying to do on purpose). They just need to adjust things.
 
#11 ·
Wheel size = aesthetics. Tire size =performance. A wide tire with a big contact patch spreads the weight of the car over more road surface. This is great in the dry and (depending on tread compound and pattern) wet, bad in the snow. A skinny tire with a smaller contact patch won't handle as well in non-winter conditions, but it will be better in the snow (and maybe in standing water that could cause hydroplaning). A low-profile tire (say, aspect ratio of 40 or 35) may affect the car's ride by providing less cushioning over the road surface, and may expose wheels and suspension parts to damage from potholes, as well as exposing wheel rims to "curb rash" because there isn't enough tire there to protect the wheel from curb contact. A low profile tire may also produce more road noise, higher rolling resistance (and inferior fuel economy as a result) and some handling problems like "tramlining" and pulling to the outside on crowned roads. Of course, on a given car, there are limitations for the circumference of the mounted tire, for the combined diameter of the mounted tire and wheel combination, and for the width of the tire.
 
#12 ·
Interesting...sounds like you are saying we should be focused on the width (and thickness) of the tire when considering weather. I haven't been paying much attention to the width but again, if the higher end cars can handle it, then an X3 should be able to handle it too.

So it sounds like the two components of the tire are the width and the "thickness" of the tire (I don't want to say radius or diameter since that will depend on the wheel size).

I wonder if most people even know these numbers. I'll try to pay attention next time I look.
 
#14 · (Edited)
So looking at it the tires on the X3

28i = 245 mm wide, 134.75mm tire thickness

35i = 245 mm wide, 122.5 mm tire thickness

So for the X3, the width is not adjusted, only the tire thickness. I'm sure they will adjust the suspension to account for this as far as ride. How would tire thickness affect snow/ice?

By comparison, the 18" tires on the X5 are wider and thicker than both of these.

255 mm wide, 140.25 mm thickness
 
#18 ·
No. They're different cars.
Even thought they have all the same X-drive and stability systems, i guess one could argue that weight, wheel axle length anfd other factors make a difference.

All in all it seems like the cars they have been testing the most are the 35i and 20d. I have not seen any reviews of the 28i or seen it out being tested anywhere.

I can't wait until somebody compares the 2 cars. I just didn't want to give up snow handling for looks.
 
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