RS-4 on 18x10 - do I want 285/35 or 295/40

[Duane Black]

It is tire time for me! I mainly just run HPDE4 and autocross with friends when I can. I’ve deduced I want some RS-4, but now the question is which tire size?

My gearing means my car is out of ideas at 123 mph on 285/30/18 but data at roebling shows power band was tapped out earlier and i was at 129 on a taller tire (275/40/19). The correct answer obviously is switch back to 3:27 gear, but I digress.

So I’m also concerned about width and sidewall height. Shorter sidewalls generally mean stiffer, correct? So should I go 285/35/18 or go 295/40/18 for better sidewall height that should save 4th gear to 130 mph? In my v6 auto, it’s out if ideas at 5th gear when it goes to 4200 rpm.

So my pros of each right now are...

285/35
-$50 a corner cheaper
-maybe a stiffer sidewall?
-less risk of fender rub (my v6 leans a lot)

295/40/18
-better top speed on straights at Road Atlanta, VIR, etc
-and thats it...


I’d appreciate feedback!

 

[Bill Pemberton]

295s way too tall ---you need the tire to be in the 25 inch diameter range.

Not a big fan of the Hankooks, the need a warm day to work. Dropped you a PM.

 

[Duane Black]

I do live in the south so a warm day isnt usually an issue. I’ll keep an eye on my inbox

 

[Bill Pemberton]

Oh, I do understand, but by cool I mean in the 60s. PMs here are under the heading conversation --click on your name and they are listed below.

 

[VoodooBoss]

Don’t forget to use the TMO Tire Rack link at the top of the page which is the link below.

https://www.tirerack.com/landing/fr...1770&cjevent=2d759484226b11e982dc01f60a1c0e0f

 

[Grant 302]

I'd have the tendency to prefer the shorter 285. And to change to a taller gear.

 

[Norm Peterson]

So I’m also concerned about width and sidewall height. Shorter sidewalls generally mean stiffer, correct? So should I go 285/35/18 or go 295/40/18 for better sidewall height that should save 4th gear to 130 mph? In my v6 auto, it’s out if ideas at 5th gear when it goes to 4200 rpm.

Your sixxer probably makes about the same power as my 4.6L, so I think high 120's, possibly as much as 130 or 131 on a really long straight or downhill, is about the most you can expect no matter what you do with axle gears and tire sizes. And 285/35-18's will give that to you with 3.55's in the axle and a 6R80's 5th gear. Unless the torque converter is allowed to unlock, rpms should be very close to what they are now with the 285/30-18 tires at 123 mph.

That's separate from the 285/35 being a much better choice for 10" wide wheels than any 295/40.


Norm

 

[Duane Black]

I did get to 145 at daytona with 3:27 gears and 275/40/19 tires. Of course, the right way to fix this is gearing. Its above ideal rpm by 110 so acceleration data shows it was actually better with 3:55 and the 19’s just because it was in the power band from 100-125. At the time I anticipated that I’d track on 19 inch tires and save my 18’s for autocross. But, no need to argue about how I got here, this is where I am. Either fix it with tires, fix it with gear, or live with it. Thanks for the input!

 

[Apex Wheels]

285/35-18 is a much better fit for 10" wide wheels compared to the 295/40-18. A local friend of mine ran the 295/40 RS4s on his 18x10" and they bulge considerably.





Here is a snapshot of the actual measurements between the tires. If you need the extra gearing, no issue achieving that through taller tires. The 295/40-18 is a perfect fit on an 18x11" wheel, you could join the Group Buy, save a bunch of money, and get the tire you want. Just a thought



- Cory

 

[Duane Black]

Wow, that’s more bulge than I thought.

On recommendation, I called tirerack. The tipping point was both cost and availability. The 295/40 is “special order”. The guy told me it was basically a matter of whenever Hankook fills the container, they’ll ship it. Hevsaid that could even be May. I got a corded re71r and need tires in march. 285/35 are on the way!

 

[Grant 302]

Yeah, forget waiting for backorder/special order items.

Wow, that’s more bulge than I thought.

Oh, don't bait me like that!

 

[Duane Black]

@APEXRaceParts , do you have any photos of 275/40r18 hankooks on those 18x10? I see they're the recommended tire on your fitment guide, I'm running 285 and its fitting without a spacer with -2.5 camber and a pinky widtg nearlu between the struts and the tire.

Also, can anyone whose experimented with different widths on the same wheel testify to if outrighr grip via a wider tire is better or sidewall strength and proper fitment is better for pointing and shooting?

I know contact patch is impacted by wheel. I noticed my new 285 hankooks on an apex wheel have more contact thsn my old sve wheels. The stack of tires side by side was a half inch taller with apex wheels.

Anywho. I'm really torn, i think i could use a little more gearing at certain tracks with the 275/40, I just wonder if I'll wish i had 295 if i buy them

 

[Mad Hatter]

I liked 295/30-18 R7 or Dunlop Dz03 tires on my old 18x10 Drifts. It did bulge a little (Dont tell Grant). But they worked out well and had some great results. 295/40-18 would be way too tall with your rear end... (the cars I mean).

Our cars like meaty tires!!!

 

[Duane Black]

I mighy want to argue with you... the height is 27.1 vs 27 with my street continentals (255/40/19) and they achieve similar straightaway speed. Im running the 6r80 auto with 3.55 rear gears

I picksd 3 land marks on vir back stretch. On my 255/40r19, im exiting oak tree at 35 mph, 106 at the emd of south paddock pitlane, 116 at Madison ave, and 120 cresting the hill. Thats wet

On the hankooks, im 44 exiting oak tree, im 113, 120, and 127. In the dry, I'm roughly the same straightaway speed, maybe 1-2 mph slower on continental in rhe dry, but nothing i cant attribute to faster corner exit.

I found a dry lap on 275/40r19 michelins where i was 42 exit, 110 at soith pit, 118, and 123 at crest. Ultimately, my fastest laps i saved data for show me being 3-4 mph faster on hankook 285/35r18 vs 255/40r19.

I know therss a diminishing point and i expect theres experts here better thsn me. I know damned good and well tge answer isnt to put 22" wheels on the car


In conclusion, after a few edits, and checking my old data and videi, i may have affirmed @Mad Hatter , I'm probably optimally tired for my gear, maybe 275/40 at.7 inch taller than my 285 but .6 shorter than my 255/40r19 is optimal... I'd like a little more, like 7 more mph out of 3rd gear at road atlanta. Coming down tge esses and going into t6 its just a little short.... data supports upshifting for 6 mph is worth it tho.

 

[Mad Hatter]

I mighy want to argue with you... the height is 27.1 vs 27 with my street continentals (255/40/19) and they achieve similar straightaway speed. Im running the 6r80 auto with 3.55 rear gears

I picksd 3 land marks on vir back stretch. On my 255/40r19, im exiting oak tree at 35 mph, 106 at the emd of south paddock pitlane, 116 at Madison ave, and 120 cresting the hill. Thats wet

On the hankooks, im 44 exiting oak tree, im 113, 120, and 127. In the dry, I'm roughly the same straightaway speed, maybe 1-2 mph slower on continental in rhe dry, but nothing i cant attribute to faster corner exit.

I know therss a diminishing point and i expect theres experts here better thsn me. I know damned good and well tge answer isnt to put 22" wheels on the car

True, I had not digested that you have the 3.55 with your auto. Most of our automatics down here are on 3.15 nose bleed gears!

 

[Duane Black]

Just to note, i edited while you were typing that i think

 

[Duane Black]

@Mad Hatter , have you run narrower tires on those same wheels?

 

[Mad Hatter]

@Mad Hatter , have you run narrower tires on those same wheels?

No, I jumped from 275/35-19 Dunlop DZ02 (similer to the RE71) down to 295/30-18 Dz03 semislicks.. Was good for a 2 sec drop in lap times. Three with R7s in the same size

 

[Apex Wheels]

@APEXRaceParts , do you have any photos of 275/40r18 hankooks on those 18x10?

Not an RS-4, but 275/40-18 RE11. You'll still want at least -2.5* camber for optimal performance.

 

[Bill Pemberton]

Mad , can't you go to a 315 tire and stay in your Class ? Apex 18x11s and 315s R7s or BFG gforce R1Ss and you might drop 4 seconds!!