285/40r18 vs 285/35r19 square setup

[WildHorse]

Which setup would you guys pick? I'm kinda leaning towards the 40r18 as I feel the taller sidewall will give more bite into and out of the corners. Thoughts?
MT82/3.31 gear if that makes a difference. Thanks.

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[gearhead2685]

18s based on cost alone lol

 

[Norm Peterson]

What wheel width and what kind(s) of use?

Shorter sidewall tires generally turn in better and corner a little more precisely, and you shouldn't be shocking the tires with sudden power applications at either of those times. Or even on corner exit, for that matter.

From a pure function-over-form standpoint, with 3.31's you could even consider 285/35-18's unless you'd then absolutely need to be grabbing 3rd gear at autocross or briefly using 6th gear on a fast road course.


Norm

 

[wildcatgoal]

What makes you think a taller profile tire will net you "more bite" in corners?

Personally, I'd only use a 40 profile tire on an 18 or 19 wheel in an attempt to compensate for the fact I have 3.73 gears. You have 3.31 gears... 285/35-19 all day long, IMHO. I use that same size, with 3.73 gears, on road courses. I run out of 5th gear sometimes. I should probably try a 40 sidewall on those 19" wheels but it looks terrible, haha.

 

[EFI]

I agree. More sidewall is 1) not really going to gain you that much traction out of corners (it's not like launching from a dead stop) and 2) that's going to be worse in 99% of the remainder of the track compared to the shorter sidewall.

I'd go with the shorter sidewall tires especially with your tall gears.

What makes you think a taller profile tire will net you "more bite" in corners?

Personally, I'd only use a 40 profile tire on an 18 or 19 wheel in an attempt to compensate for the fact I have 3.73 gears. You have 3.31 gears... 285/35-19 all day long, IMHO. I use that same size, with 3.73 gears, on road courses. I run out of 5th gear sometimes. I should probably try a 40 sidewall on those 19" wheels but it looks terrible, haha.

 

[WildHorse]

What makes you think a taller profile tire will net you "more bite" in corners?

How it was explained to me is that the deflection in the taller sidewall will keep the contact patch square to the road, whereas shorter sidewall will tend to lift the corners of the tread effectively making the contact patch smaller.

 

[BmacIL]

How it was explained to me is that the deflection in the taller sidewall will keep the contact patch square to the road, whereas shorter sidewall will tend to lift the corners of the tread effectively making the contact patch smaller.

Yeah...it doesn't really work like that. A stiffer sidewall will help do that. Generally, lower profile will have be stiffer.

I'd go 285/35R19 on tire selection alone. There's not much for 285/40R18. The 19" also is about 0.3-.04" wider tread width.

 

[Norm Peterson]

How it was explained to me is that the deflection in the taller sidewall will keep the contact patch square to the road, whereas shorter sidewall will tend to lift the corners of the tread effectively making the contact patch smaller.

That's probably an argument better used for needing slightly greater roll stiffness.


Norm

 

[WildHorse]

Well I do have BMR front/rear swaybar & diff bushing to buy. Should stiffen the roll rate a tad.

 

[Norm Peterson]

That will probably depend on bushing details. But I wouldn't intentionally use any suspension bushings for increasing roll stiffness as it would generally indicate that I'd have added more 'bind' than desirable.

Diff bushings won't do anything for roll stiffness, but should increase driveline stiffness against torque reactions, though.


Norm

 

[Grintch]

I'd go 285/35R19 on tire selection alone. There's not much for 285/40R18.

While in theory I would prefer the 18's, take a hard look at the differences in both wheel & tire selection.

 

[S550GTCS]

While in theory I would prefer the 18's, take a hard look at the differences in both wheel & tire selection.

This. I've been looking to buy new wheels and was initially interested in an 18x11 square setup but the tire choice for 305+ section tires in 18s is pretty bad.

 

[WildHorse]

Nitto NT01 are available in:

305/35ZR18 101W
315/30ZR18 98W
335/30ZR18 102W

 

[BmacIL]

Nitto NT01 are available in:

305/35ZR18 101W
315/30ZR18 98W
335/30ZR18 102W

All of those require between an 11-12" wide wheel to fit properly for handling (I assume that since you're posting here, that's the priority for you). They're available but also hard to come by. I'd be hesitant to pigeonhole yourself into a single tire. Also, all those tires are definitely too small diameter, the 305 being the only one somewhat close.

 

[F0J]

Something that was recommended to me was to have two sets of cheaper wheels+tires instead of going all out for maximum grip. That way you can compare different tires and see which ones you prefer.

The asphalt at Gimli is a little rough around the edges. Some guys get their tires at Costco or Canadian Tire though I haven't looked. I personally bought 265/45R18 Potenza 71 (on APEX 18x9) from TireRack as no one else in Winnipeg could source that size. Has close to OEM tire diameter and a very high load rating (stiffer) though the patch is a "little" big for a 9" wide wheel. An other consideration is that Winnipeg can have some funky weather (snow in August) so if you plan on buying something that might crack in cold weather be prepared to swap tires at 6AM to go out on your daily commute. My next tire will probably be a narrower and shorter Potenza 11 (and then later buy a bigger set of wheels with full slicks).

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