Sorry guys for another "max width tire" thread but I legit searched for over 2 hours and so far I'm more confused.
I have a 2020 track edition stock height.
My goal is to get:
(in order of importance)
1st. Maximum straight line traction (best drag times)
2nd. Lightest wheel
3rd. Smallest diameter wheel

I've read over 30 different threads on wheel and tire sizes and offsets and did not find quite what I'm looking for.
I am going to be running 18" wheels in the rear.
With stock height and an 18" wheel, couldn't I go​​​​​ 325/35R18? Or wider? Would I even need wider than 325 on a "just bolt ons" rcf?
I saw someone else did a 345/25R20 but a 20" wheel is the opposite of what I need and what does 25 aspect ratio even mean on a 345 tire for drag racing???
For the sake of argument, let treat it as if I am %100 sure that I can fit an 18" wheel on the rear.
Do I go 325/35R18? Wider? Would 35 AR rub? I know for drag times you want more tire and less wheel so what would the optimal 18s set up even look like.

I have made a deal with a wheel manufacturer for a custom set of rears, identical face and composition to my factory wheels (15lb for 18s x11.5-12) and need to be giving the dimensions and offsets soon and I am just STUCK. I know that there will be a point (of width) that going wider will simply not do anything, so I am not trying to go crazy like 365 and end up with alot of future headaches for zero benefit. If anyone has any insight, or can point me in the right direction I will forever be grateful.
Thanks in advance everyone!

 

I will give my two cents on this.

I personally would not go over 305 since it is not like we make tons of low end torque. If you are running drag radials, it will hook up well with 305s. Besides, having too much grip in the rear could potentially blow up the diff because of the level of mechanical grip. You also need to consider, with more rubber comes more weight. If you do something like 315 or 325 then it will be a few pounds more per corner and due to rotational inertia, it ends up having a compounding effect as the tire rotates faster. Also, the fronts don't need to be much wider than stock because the rear wheels are driving it and the front wheels are really to steer. In the case of a drag strip, you are only driving straight so your focus really should be on the rear tire.

 

305 would be ideal for 11.5". I have 305's on 11.5" wide rears with +34 offset and that's cutting it really close to the fenders that 325's will rub. I personally think 12" isn't necessary.

 

Rolla is right, anything above 305 will probably be more of a hindrance instead of a benefit. Go with a +35 through +40 offset setup and it should work just fine. According to tiresize.com, a 305/35/18 wheel/tire setup has a diameter of 26.4 inches, where as the OEM 275/35/19 has a diameter of 26.6. The main thing you have to worry about when running an 18 inch wheel is hitting the calipers. Sometimes wheel manufacturers make the wheel diameter smaller the farther in it goes (like, on the outside it's 18 inches but on the very inside it's 17.5 or something of the sort). I wouldn't go absolutely crazy over it, remember that more weight can potentially slow you down. If you don't feel safe then just go with an already proven setup, there isn't much need to go into the unknown. With a good set of even 295 tires you would probably get the grip you need without increasing the grip too much.

 

Thank you Rolla, yeah my main concern is only over the rear wheels, the "custom" order is only for the rears. The fronts I was actually thinking to go as small as possible for weight reduction.
I do agree with you about the weight, but track edition has carbon ceramic rotors and some other weight reduction and I'm simply spinning waaay more than average rcf. I've watched plenty of vids, and haven't seen anyone on full stock set up have traction issues all the way through the whole 2nd gear like I am. Even on days with 90°+ weather, where traction should be a bit better and power slightly reduced I am still having traction issues.
The whole, full/better grip=damaging rear dif thing I have not considered. It does make sense though if there's absolutely no wheel spin and you're getting full mechanical "lock up" at launch that it will put more stress on the diff. I just figured if Lexus felt confident putting "launch control" on their cars, where the act of using it is putting maximum tension on the diff due to brakes and throttle being applied at the same time, that I would be ok. But it is a good point.

Yeah part of the "deal" is that it will %100 clear the caliper/rotor. So, what do you think, could I get away with a taller tire then? 305/40r18? Maybe even 305/45r18? Wouldn't that extra sidewall help with the launch?

 

You can soften rear end if you have coils, that would help a lot also. You want the rear end to squat to maximize your set up. I'm running 305/19 and coils. There is a trade off when adjusting rear end for drag duty, it could induce body roll

 

Like Dean said, if you want straight line performance then the spin is mostly related to the rear not loading up under off-the-line acceleration due to stiffness preventing load transfer. I run 42 PSI in the rear and even with super sticky PS4S extra load tires, due to the stiffness of the rear end, there is almost no load transfer to the rear, which results in wheel spin. I can spin pretty easily, but since I don't do drag racing it off the line (with hard launches) and prefer rolling performance or turning, off-the-line launches is not a big deal for me.. You can simply reduce your rear tire pressure down to 26 PSI and soften the rear end with more load transfer under hard launches. With 305 section tires and 25 - 25 PSI, you should hook up really well.

 

stock suspension. The main reason I'm going with 18s is to have more sidewall, so the tire can "load up" and I get smoother launches. I'm not too crazy when it comes to racing, I'd rather get a slower time than be on the edge of damaging my car like Rolla said. So if I go with 305s on an 18" wheel, what do you think the optimal Aspect Ratio would be? The bigger the better? As long as it fits?

 

you are in the right frame of mind. I think 305/18/35 might work. The hard core drag guys bring their rear drag wheels to the track and change out there. That way, they weren’t dealing with air pressures and DR on the street. Good luck

 

IMO no F model needs anything wider than a 275 DR. Even boosted F's don't leave hard enough to need a wider tire. Just added weight.

 

With respect, have you seen anyone drag a track edition? Or try to "launch" for best 0-60? EL headers and exhaust and it won't hook the whole 2nd gear. The fact that I have 80 pounds less of rotation mass directly on the rear wheels is what's causing the extra slip imo, especially with a 35R19 run flat tire. I imagine if I were to do a tune and try to do a couple runs on a colder day with better air densities and lower friction coefficient and I'm probably going to spin even in 3rd gear. Now, like I said before, I'm no pro, so thats why I'm asking for advice. So far, even on 100°+ days, it doesn't hook without a burnout, doing pulls on the streets (hypothetically ofcourse) makes it really difficult to "prep" haha. But I do agree in principle, I think a DR 275 tire is going to make a tremendous difference already, so maybe I don't "need" that much.
I just figured, if I already paid for the wheels, and the price between 18" and 19" or 305vs275 is negligible, I might as well get the most I can get away with

 

OEM tire is not run flat. It is just a stiffer tire than normal summer tires for cornering. It is not a drag racing tire. That is the point you are missing. I put even more aggressive PS4S extra load variant tire (with stiffer sidewalls than the OEM tires) and it spins easily in the rear especially if I keep it around 42 PSI in the rear with 39 PSI front. Once you put drag radials on, you will realize they are as mushy as marshmallow figuratively. They squat down very hard off the line to dig into the pavement causing a lot of load transfer from front to back. It is apples to oranges with the OEM tires. Some cars can bog down off the line. Also, if you are going to drag strips, they have slick compound on them for additional traction. Anyway, it is your decision.

 

This is on 305/19/35 PS4S with lowered air pressure and softened rear end with coils. I did a slight walk out and I have Apex on red

 

I'm not sure where we're disagreeing, are you saying that for the same exact amount of money you wouldn't go 305 drag radial? That as long as it's drag radial tires Itll be fine with stock specs?
Yeah I definitely need to play around with air pressure for sure. And I've noticed I don't get as much spin on just Sport vs Sport+ (assuming because the susp. is smoothet) but the car is just a tad bit slower (0-60)



My intent wasn't to argue with anyone or prove any point, just to get as much information as I can, sorry if it seemed otherwise

 

I'll take the rcf out today and take a couple vids for you guys. I don't think you guys understand how bad the wheel spin is from a dig, on a track edition.

P.S. in order to use the Launch Control, you have to turn off the traction control for the "launch" to enable. If I don't turn off TC and just floor it from a regular stop, it'll blink a bit in 1st, and a little in 2nd right after the shift but not much different than regular rcf. But, at that point I'm getting 4.6-4.8 0-60 times and that's a tremendous difference from a 3.98 that'll definitely roll over into a bad QT mile time.
Thanks everyone for your time and responses, this platform is new to me and isn't like others I'm used to.