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Discussion Starter #1 (Edited)
Current wheels and tires: (staggered)
Style 193: 18x8 ET34 and 18x8.5 ET37
Dunlop LM703: 225/40R18 and 235/40R18

Looking to replace with: (squared)
Style 360: 16x7 ET31
Hankook Ventus V12 Evo: 225/50ZR16

Car is generally stock.

I know I will be gaining MPG's, which is a good thing, and the tires for 16's are much cheaper - performance summer 16" tires are cheaper than touring summer 18" tires. However, the track width in the front is reduced by 10mm per side (calculated on Turner's website), which I believe means a slight decrease in handling (although a 20mm decrease in total track width may not be noticeable, would it?). And the sidewall height is increased by 22.5mm, which could induce more sidewall flex. However, the taller sidewall should also make the tires absorb road imperfections better. Furthermore, although the 16" performance tires are directional, they can be rotated front and back on the same side, but the tires I have on now in the staggered setup can be rotated left and right due to non-directionality but cannot be rotated front to back due to different rim widths and tire sizes.

The main question is, would I lose a noticeable amount of performance - especially in cornering, because I will be gaining MPG, value, comfort. and the ability to rotate tires front and back.
 

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Ironman
01 330iT 6MT, 98 M Roadster
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Your question is impossible to answer without testing. There are far too many variables. You cannot make assumptions about ride based upon the height of the sidewall. It's a common myth that people keep repeating, but I've gone to same width, but lower profile tires (larger wheel size) multiple times and have been quite surprised. In fact, I just switched from 17" wheels/tires (45 aspect ratio) to 18" wheels/tires (40 aspect ratio) and the 18" set is FAR more comfortable to drive on, even though they are a much higher performance tire.

The mass of your wheel/tire combo will have a performance effect on both straight-line, and cornering (on all but the smoothest of surfaces).

In the end, IMHO, you have to ask yourself what your objective is. Unless you are wheel to wheel racing on a track or doing time trials, I wouldn't worry too much about the performance of one vs the other. In general, lower mass is better, and for tires, read the reviews (Tire Rack has some pretty good reviews), and guess. For absolute knowledge, only testing will give you your answer.

Despite what I wrote about mass, I seldom choose wheels for my road car based solely upon mass. I won't buy anything TOO heavy, but it's a road car. They wheels have to survive poor roads. Other than that, I'm not too terribly concerned about performance. I don't race my car. If I did, my choices would be limited based upon rules, so that opens up a whole different Pandora's box.

So, what's your objective?
 

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There are MANY variables to what you want. Generally speaking overall lightness on a low HP car like yours is a good thing, if you can get Under 40 lbs that would be great. Since the sidewall is taller, a higher speed rating (V, Z, W, & Y) will help with turn-in/handling. Also a lower wear rating (UTQG) should typically mean more grip.



Rob43
 

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Discussion Starter #4
Thanks for the feedback guys.

I guess my main objectives are daily-driving and some spirited inertial-driving on rough-ish roads (since my engine is so small), hence I would want to conserve as much speed through turns as possible.

Initially I wanted to go with 17" rims, however I couldn't find one available for purchase that was lighter than 9.8kg per wheel (Style 165: 17x8 ET24), and had almost decided on buying that already. But the 16" Style 360 wheels weigh in at an astonishing 8kg per wheel, and it is an original BMW wheel, so I predicted it to be tougher than most aftermarket lightweight wheels (e.g. Kosei).
 

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Thanks for the feedback guys.

I guess my main objectives are daily-driving and some spirited inertial-driving on rough-ish roads (since my engine is so small), hence I would want to conserve as much speed through turns as possible.

Initially I wanted to go with 17" rims, however I couldn't find one available for purchase that was lighter than 9.8kg per wheel (Style 165: 17x8 ET24), and had almost decided on buying that already. But the 16" Style 360 wheels weigh in at an astonishing 8kg per wheel, and it is an original BMW wheel, so I predicted it to be tougher than most aftermarket lightweight wheels (e.g. Kosei).

You'll weigh in at ~40 lbs which will feel very good. There's one last thing I want you to consider, look at a 215/50-16 tire. The reason for this is they measure 24.5" vs the 225/50-16 that measures 24.9". This slight 2% difference will give you a gearing advantage which will be beneficial, everything else will remain the same.

So when you compare all this to your old tire & wheel weight, you're down 10 lbs per W/T; this is a whooping ~25% difference !

If you went with the 215/50-16 tire, the gearing difference between old & new becomes ~4%. This ~4% difference is like starting with a 3.07 diff & going up to a ~3.19 diff ratio.




Rob43
 

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Discussion Starter #6
You'll weigh in at ~40 lbs which will feel very good. There's one last thing I want you to consider, look at a 215/50-16 tire. The reason for this is they measure 24.5" vs the 225/50-16 that measures 24.9". This slight 2% difference will give you a gearing advantage which will be beneficial, everything else will remain the same.

So when you compare all this to your old tire & wheel weight, you're down 10 lbs per W/T; this is a whooping ~25% difference !

If you went with the 215/50-16 tire, the gearing difference between old & new becomes ~4%. This ~4% difference is like starting with a 3.07 diff & going up to a ~3.19 diff ratio.




Rob43
And 215's will have less rolling resistance than 225's too (smaller contact patch)! Yup, I will definitely look into getting the 215/50-16.

Also, I found a set of light 16" rims that has a good amount of offset as well - Style 134: 16x7 ET20. Plus, it also weighs in at only 8kgs as well - same as the Style 360's. The 134's will stick out by 1mm when compared to the 193's I have on as well, which basically keeps the track width intact. :thumbsup:

Thanks again guys! :bow:
 

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Discussion Starter #7 (Edited)
You'll weigh in at ~40 lbs which will feel very good. There's one last thing I want you to consider, look at a 215/50-16 tire. The reason for this is they measure 24.5" vs the 225/50-16 that measures 24.9". This slight 2% difference will give you a gearing advantage which will be beneficial, everything else will remain the same.

So when you compare all this to your old tire & wheel weight, you're down 10 lbs per W/T; this is a whooping ~25% difference !

If you went with the 215/50-16 tire, the gearing difference between old & new becomes ~4%. This ~4% difference is like starting with a 3.07 diff & going up to a ~3.19 diff ratio.




Rob43
Hi again! :)

Although I may have said that I was going to go for 16" rims with 215/50R16 tires, the only performance-oriented tire available where I live is the Dunlop Direzza DZ102, which is only a V-rating tire. A good set of tires, e.g. Conti Extremecontact DW is only available in 225/50R16 and comes with a W-rated sidewall. However, the overall diameter will be 24.86", which is a -2.14% difference from the 235/40R18's rear tires I have on now, so I guess the final ratio will be affected slightly. The total weight of wheel/tire combo (with Conti Extremecontact DW's) is 38.6 lbs - a very attractive number indeed.

However, if I move up to 17" rims with 215/45R17 tires, I could still get the Conti Extremecontact DW's, and the overall wheel diamter will be 24.62", which is a -3.08% difference, so I should be able to notice more gain in the acceleration. But the total wheel/tire combo will weigh 41.8 lbs, which is heavier than the 16" combo but still not too much. Although I guess I would gain the benefit of a stiffer sidewall due to its shorter height than the 225/50R16's sidewall.

If you guys were me, and you were given these two choices, which one would you choose?

[Note: Aesthetically speaking, personally, I do like the design of the style 233 17" rims more than the style 134 16" rims.]
 
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