Determining factor of 18's not fitting?

[Misterkris]

I have a tendency to be long winded so I'll try to be exact. I'm looking for an 18" winter setup and feel like I'm missing something. With an 18x8 square set with a slightly higher (or lower) than stock offset, what causes the vast majority of these wheels to be instantly considered too small for the caliper? Is it the spokes or the internal barrel diameter? If it's not the barrel I would think that unless the spokes are super deep or the offsets are weird there should be enough room with adequate spacers to fit them over the front caliper. I've spoken to dealers,private sellers and read too many forum posts to know that only specific 18's are deemed to fit. If it's the internal diameter does anyone know what that minimum is? Sorry if I'm missing something but there seems to be something magic that people instantly know about a wheel besides it's diameter and offset that makes a wheel obviously not fit. How can I also instantly dismiss certain 18x8 wheels that otherwise have usable offsets just by looking at pictures of them. Thanks!

[andrey_gta]

my winters are 17x8 et40 on 225 tires - it fits over 135i calipers.

Some 17's may not fit over 335i brakes ( or very rarely even 135i brakes) because of lacking some kind of barrel groove/angle depression near the spokes. 18's are fine in all cases.
In the diagram below, see where near the wheel spoke that bump is at its maximum than levels off


Spokes them selves only affect real BBK kits that are truly wide and need the spoke to be thinner as it leaves the center.

An 18 inch wheel will not fit the caliper if the spokes touch it, this is usually done if offset is too High - makign spoke too flat & caliper contact.
On a very low offset wheel - fitment issues will arise if the spokes are not concave & more straight/flat thus causing the caliper to touch them

[Misterkris]

Thanks for the help. In relation to the dismissal of such a high rate of 18s not fitting on the 1M I'm thinking that it might have something to do with the 'barrel groove/angle depression near the spokes'. With the right offset you can fit 10's in the front. But you can't make most 8s fit that have a similar ratio or more advantageous offset, even though you could stuff a large spacer in there. I know an inch or two isn't a lot. According to tire rack the only 18x8 wheel they stock that fits is the sport edition a7. I don't really believe that but what is special about the design of that wheel that no other wheel in their inventory has?

[andrey_gta]

My bad - didnt see that this is a 1m section.
What i said applies to 135i more

[M3 Adjuster]

Originally Posted by Misterkris

Thanks for the help. In relation to the dismissal of such a high rate of 18s not fitting on the 1M I'm thinking that it might have something to do with the 'barrel groove/angle depression near the spokes'. With the right offset you can fit 10's in the front. But you can't make most 8s fit that have a similar ratio or more advantageous offset, even though you could stuff a large spacer in there. I know an inch or two isn't a lot. According to tire rack the only 18x8 wheel they stock that fits is the sport edition a7. I don't really believe that but what is special about the design of that wheel that no other wheel in their inventory has?

an " inch or two isn't a lot " is a RELATIVE statement. (That's what SHE said !) LOL. Before this conversation hits the gutter....What gta said and what you deduced is correct. Spoke design.



Keep In mind that many of the 10" wide wheels that fit in front are specially designed to allow such a wide wheel up front. This is the reason that companies like Apex can carve a niche in the aftermarket wheel market.


Whereas many buyers will clamor (and pay) for a wider wheel up front, such that it's worth the time for a company to engineer a wide wheel with the correct offset, not many buyers are willing to pay a premium price for a wheel that is narrower than stock fitment and only used for part of the year, like a winter wheel.




So. What happens is that no one spends time designing a wheel for the purpose you are looking for and It becomes simply random luck to find an option that works. There is no way to " eyeball" this kind of fit and don't underestimate the time that the Tire Rack has taken to test fit all the wheels in their catalog to the vehicle to test fit for you. I'm not employed by them so I don't know for sure that they physically fit them all. For example it very well may be that they know the exact measurements needed for the car and have the data you are looking for. If so, I would bet that is info that they probably would not release to you as it is proprietary from their own research!


Are there other wheels that will fit? Sure, but they are going to be wheel brands that are not sold by Tire Rack. That means either a custom wheel or more than likely a lower quality aftermarket wheel. Assuming you find a good aftermarket wheel brand sold by a vendor other than the Tire Rack. (That is certainly possible... They don't sell all the available wheels on the market! ) you will then have to confirm that the wheel fits either through that vendor's testing, another owner that has confirmed the wheel works in your application , or through your own trial and error.

" Good luck with that!!!! " if you choose to go that route !

In other words. Quit disbelieving the fact that few 18x 8 wheels fit over the calipers , and rejoice in the fact that even one wheel option is actually available.


Furthermore, I believe this exact same wheel is the only wheel that fits over the calipers on an e36m3, allowing those owners the * only * 16" winter wheel option on a vehicle that comes with 17" wheels stock.