[Thomaswhite99]

Hi all,

I have a 800whp 2023 ZL1 (Non 1LE.) struggling for traction so my plan was to switch from the 20 inch wheels to the 1LE sized wheels. Going from stock 305/285 setup to a 345/305 setup… Besides moving the wiring harness, do I need to worry about rubbing or anything? Also, will the magnetize/traction control get confused about the different setup? I know that the stock systems are designed for the stock setups.

I don’t want to go to a weld setup since I do still like to take some corners when I can (and I don’t like how it looks.) Though the car is mainly for straight line.

Thanks!

[CamaroDreams76]

I know this doesnt answer your question but have you thought about a Nitto NT555RII? Its a "drag radial" but has a stiffer sidewall compared to a MT ET Sreet Or ET Street R. Does pretty good in corners and had good traction too. I run a 305 NT555RII on the rear of my car and it hooks pretty well.

[Midlife ZL1]

How many options are in the 345/305 range? I only found one tire that runs both those sizes. Even just 345 in the back there is only a few options that look street legal. I only ask because I'm in the process of figuring that out as well. I'm going to try 345's in the 555RII's to see how the traction is at 889whp. But if I was doing a matching set I am going to do 325's in the back like the 1LE and 305's in the front.

Besides the wire harness in the driver side rear I think your good with stock suspension but from what I have read you might have to either use a spacer on the front or grind the suspension down in a specific spot once your add some camber or lower the car.. I could be wrong but I believe it's something along those lines.

[arpad_m]

The 305/345 setup you're planning should work.

The front to rear ratio difference vs stock is +1.4%, which is well within the tire size difference range that the ECM can automatically compensate for. Those 345 rears will be almost an inch taller than stock, which will help with launches. Your speedo will read 2 mph lower than actual at 60 mph unless you recalibrate it in the tune.

Indeed you may need spacers to avoid rubbing the wheel well liner or hitting the suspension, I've never tried to fit a 345/30/19 tire.

Also, that 555RII tire has a W speed rating, so its max speed is only 168 mph. Just something to keep in mind if you want to do, say, a max speed run and hit 200 mph, because it won't be safe to attempt on these tires.

[Thomaswhite99]

Thank you for the response! I was thinking of getting those R2s in the 345. Wgat power level are you running? At 800whp now I want to make sure it’s usable Yknow? Shoot it’d be cheaper to get a 305 if that would work!

[Thomaswhite99]

Originally Posted by arpad_m

The 305/345 setup you're planning should work.

The front to rear ratio difference vs stock is +1.4%, which is well within the tire size difference range that the ECM can automatically compensate for. Those 345 rears will be almost an inch taller than stock, which will help with launches. Your speedo will read 2 mph lower than actual at 60 mph unless you recalibrate it in the tune.

Indeed you may need spacers to avoid rubbing the wheel well liner or hitting the suspension, I've never tried to fit a 345/30/19 tire.

Also, that 555RII tire has a W speed rating, so its max speed is only 168 mph. Just something to keep in mind if you want to do, say, a max speed run and hit 200 mph, because it won't be safe to attempt on these tires.

Thank you for the response! Good to know about the slight difference on the Speedo… I’m aware of the speed rating, I would love to run the car in 1/2 events at some point. However I’m more concerned about how the car will hook on the street. The NT555R2 seems to be the most popular tire that is “street able.” Though if theres a better option I’d def look into that!

[Thomaswhite99]

Originally Posted by Midlife ZL1

How many options are in the 345/305 range? I only found one tire that runs both those sizes. Even just 345 in the back there is only a few options that look street legal. I only ask because I'm in the process of figuring that out as well. I'm going to try 345's in the 555RII's to see how the traction is at 889whp. But if I was doing a matching set I am going to do 325's in the back like the 1LE and 305's in the front.

Besides the wire harness in the driver side rear I think your good with stock suspension but from what I have read you might have to either use a spacer on the front or grind the suspension down in a specific spot once your add some camber or lower the car.. I could be wrong but I believe it's something along those lines.

There’s not a ton of options like you said. I was planning on the NT555R2 as well. Seems like the most street usable tire out there for high power. It was also recommended by my tuner. I would prefer the 325/305 like the ZLE, however idk if that’s enough to not die on the street lol. I haven’t hear about the spacer/grinding situation. I’ll have to look into that, I hope that’s not the case. Though I am on lowering springs so maybe that clears it?

[CamaroDreams76]

Originally Posted by Thomaswhite99

Thank you for the response! I was thinking of getting those R2s in the 345. Wgat power level are you running? At 800whp now I want to make sure it’s usable Yknow? Shoot it’d be cheaper to get a 305 if that would work!

801/779 on a dynojet and 803/704 on a hub. 1st spins bad. 2nd depends on temperature. 3rd never had a problem even brake boosting.

Only thing I would say is keep in mind my car is a twin turbo setup. I dont have that instant shock or torque a PD blower makes. My car makes peak torque at 4400/4500rpm and take about a second to spool depending on RPM and gear.

As far as speed rating good friend of mine asked me this question....... why would you be doing over 168mph on the street. Followed by the statement of, you wont hit that in the quarter either.

[TransamGTA350]

I run a 305/30R19 square setup on 19x11 wheels on my SS1LE. So, no experience on the wider rears you want to run, but yes to the 305's on the front and can share my experience with that.

You didn't say if you were planning to run 19 or 20" wheels.

With 305's on 19"x11" in the front, you will get a lot of poke, especially with stock alignment. The poke is so much I would be concerned with the tire hitting the fender. With 3 degrees of negative camber, the top of the tire still pokes a little bit, but it's minor and no rubbing on the fender. To get that much negative camber, you will need to grind the mounting ears on the struts for clearance and adjust the knuckle into the strut as far as it will go. That will get to about -2 camber and adjustable camber plates will then get it to -3.

-3 camber is good for road course, but not really so great for street driving. If it's going to be primarily street driven, I would not do the 305's and stay with 285's in the front and a more conservative alignment.