ccwebb

I've been thinking about and researching various wheel / tire widths for a long while now and I'm about to commit so I was hoping to get some insight from those here who are running wider aftermarket wheel / tire set-ups.

I don't track or autocross my car but living in SoCal I am constantly driving through twisting hilly roads which place constant demands my car's grip through turns. In a fun way...thanks to PS2's and Super Sports on my stock width wheels.

I understand that tire selection is also a major factor in all of this, that said I've considered square set-ups with aftermarket wheels ranging from 9" to 10.5" and while I am tempted to go as wide as possible my concerns with that are:

1. How a 10" or 10.5" set-up truly feels for non-track, street driving, i.e. any excessive tramlining and/or NVH concerns, effects on steering response.

2. Whether I want/need more than 9" or 9.5" for a car that realistically will not be tracked.

3. Then of course there is tire cost but I'll leave that out of the equation for now.


Thanks in advance for any insights.

Norm Peterson

My "normal street" setup is 265/40's on 18x9.5 and my "track setup" is 285/35's on 18x11. Both tires are MPSS. Even the track setup is fine in normal street driving, just that I'd rather not use up or risk damage to the track set in mundane street driving.

1. The track setup is more responsive at 0.9g than the street setup is at 0.8g in the same corner (the g's were datalogged in both cases). There is little (if any) tramlining with either set. The track set does ride a little firmer, which you'd expect with about 0.3" less sidewall height and max-width vs measuring width on the wheels. But ride harshness is way more a function of shock/strut damping than the difference between those tire setups (or the 255/45 GY's on 18x9.5's before that) - setting my Koni yellows anywhere near track damping levels can get pretty rough over uneven expansion joints with any of the tire sets I've ever used. Including OE.

2. and 3. You need to put tire size (cost, availability) and wheel width together.

For "enthusiastic" corner-carving that's still short of track pace, I'd make 265/40's on 9.5" and 255/45's on 9" the points above which you should start seriously considering wider rims. Steering response and precision are the important things here, and having wheels at or slightly above "measuring width" tend to give you that.

10" for 275/40's or 285/xx, 10.5" for 295's.


Happy Thanksgiving.


Norm

ccwebb

Thanks Norm, this is extremely helpful.

For your 11" track set-up how do the 285's compare to the measuring width of the wheel? Slightly narrow? I ask because I have never been able to wrap my head around the formula of tire width / sidewall height / wheel width. I actually miscalculated my current MPSS tires which resulted in my tire width being a tad more narrow than it should be for the wheel even when considering a set-up that favors steering response.

Interesting how Michelin seems to be abandoning the 18" wheel in their 4S and SC2 tires...I guess they're just following suit with the industry trend for cars to have 19" and 20" factory wheels. That said, the MPSS are fantastic tires and are still available in the sizes I am considering.

Also, just out of curiosity, are your 11" wheels the Forge Stars that Vorshlag was offering? I see that Apex offers their Mustang centric EC-7 in 11" now but I haven't read any feedback on how they fit.

I think the 10" 275/40 MPSS will be my next set-up.

Thanks again for your help.

Norm Peterson

Since it's a "max-width" wheel for that size, it does look slightly 'stretched'.




It's most apparent when looking directly in the plane of the wheel




Strut-side clearance is really, really tight. Like barely more than 1.1 mm. Although it wasn't rubbing at that much clearance I've since added 3mm spacers and 3" long ARP studs for a little more peace of mind.


Tires are measured on wheels of that size's "measuring width (duh!). When you either stretch or shrink the wheel width from there, it's the beads that stretch or shrink by the amount of wheel width change. About midway up the sidewall, the change there is only about 40% of the change at the beads.


More like annoying.


Yes, I got my Forgestars through Vorshlag. I don't think I've heard enough specific information about the Apex 11" wheels to even guess, though I think I may have participated in a survey for them and I do receive email notices from them on occasion.


Norm

ccwebb

Those 11's look like a natural fit. I've never see any pics that illustrate it this well. These pics also do a great job of showing the tire fit relative to the wheel. Thanks for posting these pics. Again, a big help.

The part that confuses me about the tire size, wheel relationship is how the sidewall height effects the position of the edge of the tread relative to the edge of the wheel. I use the term " tread edge" knowing that it may not be the correct term.

Case in point. The correct tire size for my stock wheel is 235/50/18 but the last time I ordered 235/45/18 which seemed to affect the edge of the tread aligning with the width of the wheel. With the 50 sidewall the edge or tread was in line with the wheel width but with the 45 the tread seemed to be more inboard and the tire seemed stretched a bit. Someone told me that with a 45 I should have ordered a slightly wider tire. That said my steering response was much more precise...someone attributed that more to the fast that my previous tires were PS2's and my new set were PSS's. Still seems like the lower sidewall and stretched effect of lower sidewall also helped steering response.

Anyway, it's the sidewall's relationship to the fitment that I don't know how to calculate this despite reading up on it. I can't seem to find that answer.

But thanks to you, 18x10's with 275/40's seem like my solution.

Norm Peterson

Tread width can vary quite a bit even among tires of the same size and category. Never mind the fact that identifying just where the "edges" of the tread are seems to be somewhat fuzzy judgment call.

For instance, Michelin claims the same 10.2" tread width for both their 265/40-18 and 285/35-18 MPSS tires. The claimed MPSS 275/35-18 tread width is slightly narrower than either of those at 10".


Norm

ccwebb

OK I've been agonizing for the past week over an 18' vs a 19" wheel. I have always assumed that I would stick with an 18" wheel due to its weight advantage over 19s.
For example...

• Forgestar F14 18x10= 20lbs.
• Apex EC-7 19x10= 24lbs.

I know that in street driving the weight difference isn't a massive performance factor but I'm loath to add 4 lbs per corner based on sheer principle.

But the reviews of the 4S have me seriously considering that tire...which would require 19"wheels.

If so, would a 275/40 still be the correct size tire a 19x10 wheel or would a 275/35 or even 275/30 be a better fit?

Thanks again!

Norm Peterson

First off, that additional 4 lbs/corner in wheel weight is going to be partially compensated for by the tires being anywhere from 2 to 6 lbs lighter (looking only at Michelin MPSS and PS4S).

275/35-19 is going to be a better diameter match for your original 18" setup and is very close to the same diameter as the 275/40-18.

275/30-19 is a lot shorter, something like 25.6" compared to about 27" (18" OE). That's probably too short for most peoples' appearance preferences, about like what a 275/35-18 would be (and 0.3" shorter than my track tires).


I'm also hoping that the PS4S will eventually show up in a few more 18" sizes.


Norm

ccwebb

Great point on the tire weight vs. wheel weight as well as the total height. With that in mind I'm going with the Apex EC-7 19x10 275/35-19 combo.


Thanks again for all of your help with my questions!

AuburnFalcon

Hmm, now you have me second guessing myself. I too am going with EC-7 19x10's in a square setup but I was looking towards 285/35's. My reseach says it's more of a better fit for the wheel size.
Well, at least I have till the end of winter to figure it out.