Hey Everyone,

After doing some searches, I believe I have figured out that switching from 17-inch wheels to 18-inch wheel will not reduce wheel gap, but would like to verify this.

My initial thoughts were as follows (dont laugh too hard, I'm not very mechanically inclined ):

I will have 1/2'' (I am switching from 17's to 18's) less wheel gap, but will be 1/2'' higher off the ground, therefore there will be no change in the distance between the "arch" and the wheel.

However, I am moving to a 215/35/18 tire, from a 205/45/17, which means I will have less sidewall (~0.66 inches = 17mm less side wall, which means 0.66 inches [17mm] more wheel gap, I believe?

If someone could verify this for me it would be highly appreciated!

Thanks in advance,

Bill

 

You are correct. Whether you run 15", 16", 17". or 18" wheels, the aspect ratio of the corresponding tires will be lower as wheel size increases - ie., the bigger the wheel, the shorter the tire sidewall and vice versa. The bottom line is that the overall outside diameter of the wheel/tire combination will be practically the same regardless of what size rim you select. Choosing a bigger rim will not reduce your wheel gap, but rather will only give you a heavier wheel/tire unit which will hinder handling. Many believe that 16" wheels are optimum for the MINI.

 

Although what diploman is sorta true about the wheel size, it's only true if you are able to keep the tire sizing exact. Your size selection are slightly different so they will change things a bit, but not much.

You will be increasing the wheel gap slightly and lowering the height of the car slightly. You can't compare the sidewall heights. An 18 will have less sidewall because the wheel is bigger. Your gap will only increase .17" not .66"

The radius is:

215/35/18: 11.96"

205/45/17: 12.13"

 

I would go with a 215/40/18... 215/35/18 was too thin for my tastes on my R53.

 

Thanks for the help Rally, Diploman, and Wake! it makes a lot more sense now (had to draw it out, but I see how it works now !) As for the 18'' rims, they are lighter than the current S-Lites (6.2 pounds lighter per wheel/tire, still heavy, but an improvement ).

Thanks again,

Bill

 

Wheel gap is related to your tire choice, but the outside diameter of an 18" rim will always be 1/2" closer to the arch than a 17" rim.

Not exactly. The height off the ground has nothing to do with the distance from the center of the wheel (or from the rim) to the arch. It is still 1/2" closer to the arch with the 18" wheel. The only way to change that is to modify the suspension - lowering springs, coilovers, etc.

Below are the calculations to figure your wheel gap. First find the sidewall height by multipling the tire width by the aspect ratio. Notice this has nothing to do with rim size. Then add the radius of the wheel to the sidewall height. This will give the radius from the center of the wheel/tire to the outside of the tire.

215/35/18 = 75.25 sidewall ht + 228.6 (9") = 303.85
205/45/17 = 92.25 sidewall ht + 215.9 (8.5") = 308.15

The results show a 4.3mm larger wheel gap with the selected 18" wheel/tire combination. Your vehicle will also sit 4.3mm closer to the ground. Let's see how that changes with a (1)taller and (2)wider 18" tire:

(1) 215 x 0.45 = 96.75 sidewall ht
(2) 225 x 0.45 = 101.25 sidewall ht

Notice that these two tires have the same aspect ratio (i.e. 45), but because (2) is wider than (1) the sidewall ht increases. Now add 1/2 the dia of the rim and compare:

96.75 + 228.6 = 325.35
101.25 + 228.6 = 329.85

Both of these choices will result in less wheel gap. Compare center of wheel to outside of tire distances:

205/45/17" = 308.15
215/45/18" = 325.35
225/45/18" = 329.85

The difference between the 17" and the largest 18" is:

329.85 - 308.15 = 21.7mm less wheel gap, but 21.7mm higher (from the ground) than the 17s.

There is a tradeoff and most people try to go to a lower aspect ratio on a larger rim dia in order to maintain the same centerline of wheel height as with the stock rims.

Hope this clarifies.

 

my used 05 MCS came with 215 45 17 and the wheel gap didn't seem as bad, now not nearly as bad with lowring springs, ( see gallery)
but if you go 18s go 215 or even 225 40 18 and the wheel gap won't be as apparent.
cheers
boxcars