[cwebster]

My current DRs [MT Street S/S ] are near or at the end of their life. I want to move to a street slick if possible with a shorter sidewall (lower profile) to reduce rotational mass and increase leverage to improve my 60-ft times. I've outlined my options and posed some questions below.

Here's my existing DRs. Facing the camera is the side with the most wear. The center treads are no longer visible. The opposite side has about 1/32" to 1/16" of visible tread. I've notice the same trend on my stock tires.



Here's the other side of one tire with melted rubber scraped out of the groove.



[Tire Wear]

How many more passes do these have in them? I'm thinking maybe 3 if I only do one 5-sec line-lock burnout and the other 2 rolling burnouts.

Unfortunately, tire wear has not been even. Each tire has worn pretty evenly across the tread from side-to-side but rotationally they've worn more on one side than 180 degrees away. To me this calls the wheel balancing job into question. I'm assuming that GM has balanced the rotors and I know they've worn evenly.

Where to you guys get your wheels/tires mounted and balanced? First, they have to have equipment that won't damage painted wheels. Second, they have to be able to simulate over 150 MPH on the balancer. Would you bring them to a dealer service center, local auto repair shop, or a speed shop? I'm leaning toward a speed shop, although there isn't one I trust within 50 miles.

Left side tire always wears out before the right. This seems to indicate that the eLSD is favoring the right side for power during wheel spin. It seems to me that an eLSD should be capable of tuning this bias. I doubt whether a dealership service dept. is equipped to do this, though. Even if a speed shop tech/tuner was able to do it I'm sure this type of 3rd party adjustment is a warrany buster. Dare I ask if anyone else has tuned the eLSD?

A workaround would be to rotate tires from left to right sides periodically to even out the wear. This would require unmounting the tires and swapping wheels so the inboard sidewall faces out. This way they'll rotate in the same direction. This might work with the DRs since the tread pattern is symmetrical. I doubt this would work on the stock Goodyear tires since the tread is decidedly asymmetrical.

[Tire Fitment]

I need a shorter DR that will fit on my 18x12 inch wheels and still offer good traction. The shortest MT is a Street S/S in P305/35R18. At 26.6" dia it's over an inch shorter but the tread is only 11.2" wide. I'm worried it won't have enough meat to slip and grip at the tree.

The only 18" MT Street R that fits is the P325/35R18 with 27.0" dia and 12.0" tread width. Although it is nearly an inch shorter, I'm worried the 12" wide slick tread will stick too well and not allow that minimal slip I need on the launch.

Both of the MT's are 5 lbs lighter than my current tire (P345/35R18). I'm not sure about the Hoosiers - never used them before.

Prospective MT 18" Replacements

Street S/S:
(current tire in bold type)

                                SECT.   TREAD                   APX.
TIRE SIZE /    MEAS RIM  O.D.   WIDTH   WIDTH                   WT.
EQUIV. SIZE    (+- 1")   IN.    IN.     IN.     CIRC.    COMPND LBS.   MATL #      PART #     

P305/35R18
26X12.50R18     11.0     26.6   12.2    11.2    83.6     R2     33     90000024570 3480
P345/35R18
28X13.50R18     12.0     27.8   13.5    12.4    87.3     R2     38     90000024573 3483

Street R:

                                SECT.   TREAD                   APX.
TIRE SIZE /    MEAS RIM  O.D.   WIDTH   WIDTH                   WT.
EQUIV. SIZE    (+- 1")   IN.    IN.     IN.     CIRC.    COMPND LBS.   MATL #      PART # 

P325/35R18
27X13.50R18     11.0     27.0   13.1    12.1    84.8     R2     33     90000028455 3581

Possible Hoosier 18" Candidates

Hoosier DR2 (PDF)

Item        Tire          Tread   Approx  Approx  Meas  Sec
Number      Size          Width   Dia     Circ    Rim   Width   Compound
17342DR2    P315/30R18    11.0    26.0    81.5    11    12.5    DR2
17345DR2    P335/30R18    12.2    25.9    81.3    12    13.4    DR2

I think I'm going to go with the MT Street S/S P305/35R18. This will give me the shorter, lighter tire and hopefully get rid of some of that tail wagging that's been freaking me out mid-track. I wish they made a 305 slick I could use. If I didn't have to worry about the bog I'd definitely go with the P325/35R18 slick.

I'm anxious to hear what you guys are using and what you think of my choices.

--Cal

[Shorty45]

A shorter diameter tire will get you a better rear end ratio, 3:73 to maybe 4:10? Maybe not your intention but anything between .5-1” overall height difference? I don’t know these new cars. I did try this 30+ yrs ago, with my 82 Z28, going from 3:23 to about 3:73 back then. Kind of curious if anyone has tried this with an eLSD.
Hope you get it figured out, Cal. I’m running NT05 on stock.

[cwebster]

Originally Posted by Shorty45

A shorter diameter tire will get you a better rear end ratio, 3:73 to maybe 4:10? Maybe not your intention but anything between .5-1” overall height difference? I don’t know these new cars. I did try this 30+ yrs ago, with my 82 Z28, going from 3:23 to about 3:73 back then. Kind of curious if anyone has tried this with an eLSD.
Hope you get it figured out, Cal. I’m running NT05 on stock.

Yeah, that's what I'm thinking. With that tall 1st gear there's no torque when it hooks @ low RPM. Should get more pull on the low-end as long as I've got the meat to keep the extra energy under control. I just noticed that Hoosier P335/30R18 is like 2" shorter and has the 12" tread width to control it. I might even have to shift to 5th gear in the 1/4 mile with that one.

Since it's an eLSD it has to already have some kind of bias built-in. I'm not sure if all the stability control logic is in the ECM or some other control module. I don't think the M6 has a TCM. The eLSD control box sits behind a cross-member just rear of the diff itself but I don't know if it can be accessed directly. Be nice to know if it can be tuned.

[KonigWolf]

I'm currently in the same boat as you on deciding which tire to get in a sense. Radials or bias-ply.
ET Street SS or ET Street R.
Make my 18x11 rims work, or sell them.
Buy a set of 17x9.5 or 17x11.
Keep as close to 27.6 as I can for minor tune adjustments, or drop to a 26" and pull fuses and fuss with my shift points/tune.

Dig race they said, get on A list they said, it'll be Easy they said.



How much sidewall is too much? Or stops having a positive effect on the launch?
My brother has a set of 28x10R17s on his 2018 A10 mustang, they're a bit tall and made his 2k launch a bit sluggish, but he hooks, so now I've Got to find a tire that will Hold all the LT1 torque and Not hurt my overall gear ratio so I can get out the hole Better than him.

[parish8]

I always take the mt dr’s down to the cords. On many sets it seems like once the tread is gone they are only about 1/2 done. They work well right up until the cords show.

[mlee]

I tried the 35's and didn't like them. Too short so I sold.

Wish I had gone 40's which at the time I was unaware they had that size.

[cwebster]

Originally Posted by parish8

I always take the mt dr’s down to the cords. On many sets it seems like once the tread is gone they are only about 1/2 done. They work well right up until the cords show.

Oh, good. At least I can get a few more passes out of them. I was just worried about a sharp stone pushing through the soft rubber and piercing the cords. It would be annoying to get a blowout at 130 mph.

Do you get your DRs mounted and balanced at a speed shop or what? I don't trust any local repair shops and not sure if the dealer even knows how important high-speed balance is for this car.

--Cal

[cwebster]

Originally Posted by KonigWolf

I'm currently in the same boat as you on deciding which tire to get in a sense. Radials or bias-ply.
ET Street SS or ET Street R.
Make my 18x11 rims work, or sell them.
Buy a set of 17x9.5 or 17x11.
Keep as close to 27.6 as I can for minor tune adjustments, or drop to a 26" and pull fuses and fuss with my shift points/tune.

First, I would definitely NOT recommend pulling the ABS fuses. I tried it on a few passes to get rid of the 4000 RPM idle limit and remove the bog and it did not behave as I expected. Very unstable, too unpredictable and dangerous! See this thread for my trial and error: ABS Fuse Pull on 6th Gen ZL1

I was leaning toward the 26"x12" Hoosiers for the leverage and traction I needed. They're like 12 lbs lighter than my MTs too. Now I'm worried whether stabilitrak will pull timing even with the "nannies off", as wnta1ss described in your thread "Tire size question: Stock fronts with 26" rear. [Post #2]". I always race with the nannies off. I really don't want to cripple myself out of the gate like that. I need to confirm this with other ZL1 owners.

Can any ZL1 owners confirm this problem with tire-size mismatch pulling timing? At what point does it become a problem? 1/2" - 1" - 2" shorter?

I like how you've laid out your choices in a spreadsheet. With all your power mods you want to get meat to make use of all that muscle. You've probably already tuned out the torque management bog so your problem is a bit different than mine. You want to dead hook at the tree and keep it planted through like 6 gears?

Originally Posted by KonigWolf

I'm currently in the same boat as you on deciding Dig race they said, get on A list they said, it'll be Easy they said.

HaHa! What fun would that be, though? Who ever got any great degree of satisfaction from doing something easy?!

Originally Posted by KonigWolf

I'm currently in the same boat as you on deciding Dig How much sidewall is too much? Or stops having a positive effect on the launch?
My brother has a set of 28x10R17s on his 2018 A10 mustang, they're a bit tall and made his 2k launch a bit sluggish, but he hooks, so now I've Got to find a tire that will Hold all the LT1 torque and Not hurt my overall gear ratio so I can get out the hole Better than him.

Good luck! I'll be interested to see what you go with...

--Cal

[parish8]

I just goto a local(not chain) tire shop and get a mount and balance. Not sure what equipment hey use. The chain places seem to have a lot of reasons why they can’t do what you want them to do.

[cwebster]

Originally Posted by mlee

I tried the 35's and didn't like them. Too short so I sold.

Wish I had gone 40's which at the time I was unaware they had that size.

Can you elaborate? Were these 35R18? Why didn't you like them? Was the ECM pulling timing or did you just get a lot of wheel spin?

Do you let the dealer balance your DRs?

Do you get uneven wear on one side more than the other?

--Cal

[cwebster]

Originally Posted by parish8

I just goto a local(not chain) tire shop and get a mount and balance. Not sure what equipment hey use. The chain places seem to have a lot of reasons why they can’t do what you want them to do.

Hmm... Well, I'm going to be sure that whomever mounts this next set can spin them up to speed and perfectly balance them. I guess I'll call around. Any vibration can be amplified at the natural resonant frequency of the suspension. If that happens at 40 or 50 MPH no big deal but at 120 MPH it could cause problems. At the very least it could cause premature tire wear or suspension issues.

I don't trust anyone to properly torque the lugs, though. Even the dealer service dept admitted they do not put a torque wrench on the lugs. I always re-torque whenever the wheels come off for anything.

--Cal

[KonigWolf]

Originally Posted by cwebster

First, I would definitely NOT recommend pulling the ABS fuses. I tried it on a few passes to get rid of the 4000 RPM idle limit and remove the bog and it did not behave as I expected. Very unstable, too unpredictable and dangerous! See this thread for my trial and error: ABS Fuse Pull on 6th Gen ZL1

I didn't have any issues with my car when I pulled the fuses. It was actually your post that I found when searching for which ones to pull. I drove my car for about three weeks with the 26s on the rear and fuses in the center console. I data logged the car several times tweaking the tune/shift points, never experience any timing being pulled for issues related to tires.

[cwebster]

Originally Posted by KonigWolf

I didn't have any issues with my car when I pulled the fuses. It was actually your post that I found when searching for which ones to pull. I drove my car for about three weeks with the 26s on the rear and fuses in the center console. I data logged the car several times tweaking the tune/shift points, never experience any timing being pulled for issues related to tires.

Well, that would make sense if you're driving the A8. This confirms that the torque management nose dive or "bog" is a direct result of the "Manual Transmission Protection feature" described in GM Doc ID 4733151. That's so unfair to the M6 guys - can't even use the fuse-pull to work around it.

I really need to find out whether any ZL1's (especially M6) have had timing pulled with a shorter tire. I don't want to be the first to try and waste $600 on tires I can't use.

--Cal

[mlee]

Originally Posted by cwebster

Can you elaborate? Were these 35R18? Why didn't you like them? Was the ECM pulling timing or did you just get a lot of wheel spin?

Do you let the dealer balance your DRs?

Do you get uneven wear on one side more than the other?

--Cal

I was having issues getting squirly (unstable) on the rear end and putting the smaller tires on increased that quite a bit.
Most will probably be fine with 35's but 40 seemed to be the perfect fit for these cars. However they cost a little more.