Fitment Wizards Please! 315/35r18?

[DeTh]

Trying to figure out the feasibility of me running a 315/35r18 on the rear.
Im at the limit now of the 295/30r19 R888r I'm currently running, and want to put a daily tire back on my 19s and get a drag pack.
I see a lot of people running 305/35's, and some people running 315/30's, but I havent seen anyone run a 315/35.
Would ideally be looking to do 18x12 (welds), and am curious about what offset I would need (or if its even possible to do). I've looked all over the place and have tried to do all the math but cant find any results with certainty.

Thanks!

[M3SQRD]

Originally Posted by DeTh

Trying to figure out the feasibility of me running a 315/35r18 on the rear.
Im at the limit now of the 295/30r19 R888r I'm currently running, and want to put a daily tire back on my 19s and get a drag pack.
I see a lot of people running 305/35's, and some people running 315/30's, but I havent seen anyone run a 315/35.
Would ideally be looking to do 18x12 (welds), and am curious about what offset I would need (or if its even possible to do). I've looked all over the place and have tried to do all the math but cant find any results with certainty.

Thanks!

For a 315/35, the tire sidewall is too tall for the f8x. Also, there aren’t many tires offered in the 315/35 size. Tire Rack has only one tire in this size - Hoosier R7 competition tire.

There’s a guy running HRE R101 19x11.5et47 with 315/30-19 tires. Also, there’s a guy running HRE RC100 19x12et50 with 325/30-19 tires. Additionally, although not optimal, there are quite a few people running 19x11et42-44 wheels with 315/30-19 tires.

[DeTh]

Originally Posted by M3SQRD

For a 315/35, the tire sidewall is too tall for the f8x. Also, there aren’t many tires offered in the 315/35 size. Tire Rack has only one tire in this size - Hoosier R7 competition tire.

There’s a guy running HRE R101 19x11.5et47 with 315/30-19 tires. Also, there’s a guy running HRE RC100 19x12et50 with 325/30-19 tires. Additionally, although not optimal, there are quite a few people running 19x11et42-44 wheels with 315/30-19 tires.

To clarify here, Im looking for 315/35r18
The diameter very close (.1in) to the 325/30r19.
I'm looking to run the Toyo TQ. Can you link me to the HRE RC100 fitment please?

[M3SQRD]

Originally Posted by DeTh

To clarify here, Im looking for 315/35r18
The diameter very close (.1in) to the 325/30r19.
I'm looking to run the Toyo TQ. Can you link me to the HRE RC100 fitment please?

Oops…read the 18x12 as 19x12.

I’ll have to search for the thread. It was from 2016-2018.

[DeTh]

I did some thinking and I think this would be doable on an 18x11et44. They're rated for a 10.5-12.5 so the contact patch shouldn't be super pinched (although 18x12 would be better I agree, but the 11in would bring the overall inflated width in just slightly, which youll see why this might benefit me below)

It has an overall inflated width of half an inch less than the 325/30r19 r888r (and only .2 more than 305/35r18 r888r, which we know fits without question).
This (and the fact that Signature Wheels has said that 325/30 on 19x11 can have a 6mm flex in offset of et38 to et44 depending on tire shoulder) would make me think this would be ok (for outboard clearance)

On apex test fitment guide here:
https://f80.bimmerpost.com/forums/sh...p?t=1182475%22
It looks like Apex said that 18x11 et 46 would be too close, which brings the 305/35 2mm more inboard. The 315/35 based on sectional width (measured on an 11.5) would be 2.5mm more inboard (.5mm more inboard than the 305/35 on et46).
I could always counteract this with a small 3mm spacer just to ensure nothing rubs, but Im hoping that the slightly smaller wheel width of an 11in compared to its measured width on an 11.5 would bring the inflated width down just slightly.
325/30r19 is 5mm more outboard than 315/35r18, so I should have room to spare there for the 3mm spacer

Please let me know if any of this doesnt make sense lol

[M3SQRD]

You need to adjust the section width by 0.2” as you change wheel width. For example, if the ideal rim width 9.5” results in a 10.2” section width then a 10” rim would result in a 10.4” section width.

Just because a tire of a certain size fits on a range of widths, the two extremes do not produce the same level of grip as the mid-range wheel width. I definitely would not run a 325 on an 11” wheel. The 305, and maybe the 315, would have more useable grip than the much wider 325 & 11” combo. An 11” wheel cannot provide sufficient support for the 325. Also, the pinched 325 will have very different (abrupt) breakaway characteristics at max grip (high slip angles). Wider is not always better.

[DeTh]

Originally Posted by M3SQRD

You need to adjust the section width by 0.2” as you change wheel width. For example, if the ideal rim width 9.5” results in a 10.2” section width then a 10” rim would result in a 10.4” section width.

Just because a tire of a certain size fits on a range of widths, the two extremes do not produce the same level of grip as the mid-range wheel width. I definitely would not run a 325 on an 11” wheel. The 305, and maybe the 315, would have more useable grip than the much wider 325 & 11” combo. An 11” wheel cannot provide sufficient support for the 325. Also, the pinched 325 will have very different (abrupt) breakaway characteristics at max grip (high slip angles). Wider is not always better.

Im still talking about 315's here...
Im simply using the 325 on 19x11et44 for measurement purposes because we know that people run them without rubbing.

To clarify my previous post,
315/35r18 on an 18x11et44. With the decrease of .2 in sectional width like you mentioned, based on the information that Im reading online and extrapolating fitment clearances based on known "fitting without rubbing" sizes, Im thinking 315/35r18 would fit without rubbing on an 18x11et44. I get my drag pack in about a month or so.

[M3SQRD]

Originally Posted by DeTh

Im still talking about 315's here...
Im simply using the 325 on 19x11et44 for measurement purposes because we know that people run them without rubbing.

To clarify my previous post,
315/35r18 on an 18x11et44. With the decrease of .2 in sectional width like you mentioned, based on the information that Im reading online and extrapolating fitment clearances based on known "fitting without rubbing" sizes, Im thinking 315/35r18 would fit without rubbing on an 18x11et44. I get my drag pack in about a month or so.

Most 315s (extreme performance and track may be too wide in certain cases) will fit on an 11et44 wheel. I’m certain a 315 would fit on my HRE R101LW 19x11et42 with minimal rear camber (< 2 deg negative camber).