[DFW1LE]

Originally Posted by cwebster

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

Cal, can you post a copy of this GM document?

[cwebster]

Originally Posted by mlee

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.

That makes sense and it's encouraging that you didn't get any ECM intervention with the 26.4" tires. I'm not sure what size rims you have but I'm guessing 18x11. Assuming you went with 305/35R18x11, your new tires would be 8/10 inch shorter. That would explain the tendency to spin the wheels - they'd effectively increase your gear ratio, putting more torque (higher wheel RPM) to the pavement for roughly the same size contact patch. The 305/40R18x11 would work the opposite way, providing less torque and keeping the tires from spinning so much.

Size            Dia (height)    Difference from stock
305/30R20x11    27.2" (691mm)   stock
305/35R18x11    26.4" (670.7mm) -0.8" (-20.3mm)
305/40R18x11    27.6" (701.2mm) +0.4" (+10.4mm)

I'm trying to do the opposite, increase the effective gear ratio to increase power to the pavement, but I'm going with a wider tread to increase the contact patch and minimize wheel spin. I know from my MT P345/35R18 DRs and 18x12 (43mm offset) rims that the wider tread will fit so my only concern going to a 26" tire is whether the automated systems will muck with my engine timing as some have suggested. If the 12" tread spins I'll just add fuel for weight and/or heat them up more.

Brand           Size            Dia (height)    Difference from stock
Goodyear        305/30R20x11    27.2" (691mm)   stock
Mickey Thompson 345/35R18x12    27.5" (698.7mm) +0.3" (+7.7mm)
Mickey Thompson 325/35R18x11    27.0" (684.7mm) -0.2" (-6.3mm)
Hoosier         335/30R18x12    25.9" (658.2mm) -1.3" (-32.8mm)

I'd really like to get the Hoosier slicks (bottom row). If it's likely the 26" tires will cause problems I'll have to go with the slightly shorter but narrower MT 325/35R18x11. Now if I can find another M6 ZL1 driver that's used 26" tires without ECM intervention I'll feel more comfortable pulling the trigger.

--Cal

[cwebster]

Originally Posted by DFW1LE

Cal, can you post a copy of this GM document?

Sure it's in my original fuse-pull thread: ABS Fuse Pull on 6th Gen ZL1 [Post #6]

--Cal

[Fraxum]

Watch out for more than one inch height difference. My experience is Stabilitrac will get sick. Not sure exactly where that kicks in. I was running a 3/4" F/R difference last year for a while with no problems. Leave some room for burnout wear.

[KonigWolf]

Originally Posted by Fraxum

Watch out for more than one inch height difference. My experience is Stabilitrac will get sick. Not sure exactly where that kicks in. I was running a 3/4" F/R difference last year for a while with no problems. Leave some room for burnout wear.

That's what I am curious about, is how much difference between the front an rear before the Stabilitrac goes bonkers. 0.75 is a good reference point that I'll keep in mind not to go beyond that if possible.

[cwebster]

Originally Posted by Fraxum

Watch out for more than one inch height difference. My experience is Stabilitrac will get sick. Not sure exactly where that kicks in. I was running a 3/4" F/R difference last year for a while with no problems. Leave some room for burnout wear.

Thanks for chiming in. What symptoms have you seen when it gets sick? Does it just get dizzy (handling issues) or does it cough up blood (ECM intervention)?

Okay, but if I turn off Stabilitrak and Traction Control by holding down the Traction Control button for 8-sec or more (like I always do at the drag strip) it should have no effect. I gave up on these "nannies" early last year after only a few weeks at the drag strip. If these are turned off then only unpublished, always-on "protections" are active like the infamous "Manual Transmission Protection" (aka Torque Management).

Up to now I've only compared tire height on rear wheels between stock and drag radials. Here's a comparison of front to rear looking at stock GY Eagles, my current MT DRs, and my best candidate for replacement - Hoosier DOT slick. Front never changes 'cause I'm keeping the Eagle F1 G3 tires.

                              Size
Brand         Front         Rear            Difference F/R
Goodyear      285/30R20x10  305/30R20x11    
(stock F/R)   26.7" (679mm) 27.2" (691mm)   +0.5" (+12mm)
-             -             -               -
Goodyear /    285/30R20x10  345/35R18x12
MT (Current)  26.7" (679mm) 27.5" (698.7mm) +0.8" (+19.7mm)
-             -             -               -
Goodyear /    285/30R20x10  335/30R18x12
Hoosier (New) 26.7" (679mm) 25.9" (658.2mm) -0.8" (-20.8mm)

Right off the bat I see that the stock rear tires are 1/2" taller than the front. The MT DRs I've been using are 8/10" taller, which at least partially explains why my times have actually been worse with the DRs. These new Hoosiers I've been looking at are 8/10" shorter so I should be good. If there were no intervention with taller tires I wouldn't expect any issues going an equal amount shorter.

Here's another encouraging note... I went to the dealer service dept. today to order a replacement vacuum line. While I was there I got in touch with their most experienced service manager - over 35 yrs. He says there should be no intervention whatsoever from Stabilitrak, Traction Control, or ECM going with rear tires 1" to 1 1/2" shorter than the front for drag racing.

I'm going ahead with the Hoosier DOT slicks. With the slick tread and extra 1" width I should have plenty of meat to control the extra power. Maybe I'll finally see some 1.7 60-ft times. With any luck I'll have them for the next race weekend.

Thanks to all for your insights and anecdotes guys. This forum rocks!

--Cal

[Fraxum]

Originally Posted by cwebster

Thanks for chiming in. What symptoms have you seen when it gets sick? Does it just get dizzy (handling issues) or does it cough up blood (ECM intervention)?

Okay, but if I turn off Stabilitrak and Traction Control by holding down the Traction Control button for 8-sec or more (like I always do at the drag strip) it should have no effect. I gave up on these "nannies" early last year after only a few weeks at the drag strip. If these are turned off then only unpublished, always-on "protections" are active like the infamous "Manual Transmission Protection" (aka Torque Management).

Up to now I've only compared tire height on rear wheels between stock and drag radials. Here's a comparison of front to rear looking at stock GY Eagles, my current MT DRs, and my best candidate for replacement - Hoosier DOT slick. Front never changes 'cause I'm keeping the Eagle F1 G3 tires.

                              Size
Brand         Front         Rear            Difference F/R
Goodyear      285/30R20x10  305/30R20x11    
(stock F/R)   26.7" (679mm) 27.2" (691mm)   +0.5" (+12mm)
-             -             -               -
Goodyear /    285/30R20x10  345/35R18x12
MT (Current)  26.7" (679mm) 27.5" (698.7mm) +0.8" (+19.7mm)
-             -             -               -
Goodyear /    285/30R20x10  335/30R18x12
Hoosier (New) 26.7" (679mm) 25.9" (658.2mm) -0.8" (-20.8mm)

Right off the bat I see that the stock rear tires are 1/2" taller than the front. The MT DRs I've been using are 8/10" taller, which at least partially explains why my times have actually been worse with the DRs. These new Hoosiers I've been looking at are 8/10" shorter so I should be good. If there were no intervention with taller tires I wouldn't expect any issues going an equal amount shorter.

Here's another encouraging note... I went to the dealer service dept. today to order a replacement vacuum line. While I was there I got in touch with their most experienced service manager - over 35 yrs. He says there should be no intervention whatsoever from Stabilitrak, Traction Control, or ECM going with rear tires 1" to 1 1/2" shorter than the front for drag racing.

I'm going ahead with the Hoosier DOT slicks. With the slick tread and extra 1" width I should have plenty of meat to control the extra power. Maybe I'll finally see some 1.7 60-ft times. With any luck I'll have them for the next race weekend.

Thanks to all for your insights and anecdotes guys. This forum rocks!

--Cal

The symptom was the Stabilitrac light came on (Was there a chime?) and 15 second ETs will be as good as it gets. Stabilitrac has alot of tricks I think. On my 5th gen ZL1 Stabilitrac started warning me verbally with a chime on all right hand sharp curves that my steering was failing.

Then GM decided they wanted that ZL1 back. So Stabilitrac moved me into a 2016 SS. I do wish it would have waited a while so I could have picked up a CA6 M6 ZL1. But now that I own my '16 SS I don't want to flush $25K down the toilet. The SS will have to do. Maybe a Paxton in the spring so I can turn my SS into a 3/4 ZL1. But I will be getting some hairy eyeballs at home. Oh, the price we pay to be gear heads.

[cwebster]

Originally Posted by Fraxum

The symptom was the Stabilitrac light came on (Was there a chime?) and 15 second ETs will be as good as it gets. Stabilitrac has alot of tricks I think. On my 5th gen ZL1 Stabilitrac started warning me verbally with a chime on all right hand sharp curves that my steering was failing.

Oh man! I can imagine how frustrating that must have been. I'd be livid! That was with just a 3/4" height diff? That doesn't sound like normal behavior at all.

Originally Posted by Fraxum

Then GM decided they wanted that ZL1 back. So Stabilitrac moved me into a 2016 SS. I do wish it would have waited a while so I could have picked up a CA6 M6 ZL1. But now that I own my '16 SS I don't want to flush $25K down the toilet. The SS will have to do. Maybe a Paxton in the spring so I can turn my SS into a 3/4 ZL1. But I will be getting some hairy eyeballs at home. Oh, the price we pay to be gear heads.

I guess a shiny new SS would be irresistible bait after the pain you went through with the ZL1. A new supercharger could help scratch that itch too. Who could blame you? ...well, I guess whoever owns those hairy eyeballs could, huh?

Hopefully I'll have better luck than that. If mine gets sick maybe I'll just trade her in for a boat and go fishing... a really really fast boat.

[Fraxum]

Originally Posted by cwebster

Oh man! I can imagine how frustrating that must have been. I'd be livid! That was with just a 3/4" height diff? That doesn't sound like normal behavior at all.

I guess a shiny new SS would be irresistible bait after the pain you went through with the ZL1. A new supercharger could help scratch that itch too. Who could blame you? ...well, I guess whoever owns those hairy eyeballs could, huh?

Hopefully I'll have better luck than that. If mine gets sick maybe I'll just trade her in for a boat and go fishing... a really really fast boat.

Don't worry GM will stand behind your car during the warranty. They did for me and others.

No sorry, I was not clear in that post. The 3/4" height difference was fine. My problems with the ZL1 were on stock tires and rims. I think there was a short somewhere that Chevy could not find after replacing all the computers and possible cables in the car. The even sent an engineer to look things over. In the end it probably ended up as somebody's parts car or maybe they crushed the poor thing. It was my favorite modern car I have owned. I was not a fan of the 5th gen Recaros.

Boats can be a PIA and even bigger money pits than cars but nothing like being in the water close to a whale more that twice as long as your boat. Awe inspiring. One of my happiest days was picking up the boat and taking it out on my training voyage, and another one the day I sold it. Motorcycles, boats all gone. Only the Camaro SS left. It is a great consolation prize.

[laynlo15]

Do you drive your car to the track? Install Dr's once you get there or trailer?

[cwebster]

Originally Posted by laynlo15

Do you drive your car to the track? Install Dr's once you get there or trailer?

I drive to/from the track, usually on the stock wheels. I don't have a trailer. Had a 20' enclosed priced out but first I need a 3/4 ton truck to haul it (2500's are pricey). Gotta watch my spending now, though...

I usually try to get one of my daughters or grandson to follow me with my Colorado. It carries the fuel jugs, DRs, jack, air, etc. That's where most of the 5,300 miles comes from. I've driven it 20-50 miles to a few car shows and a date but it mostly sits under the car cover between track days when I'm not cleaning, waxing, changing oil, plugs or whatever.

I did drive on the DR's several times right after I got them. Then I went a several trips with half my passes stock and half DRs. Haven't run the DRs since I think mid-Oct.

With my now Hoosier DOT slicks I don't think I'll be driving 50 miles to the track on them.

--Cal

[cwebster]

Originally Posted by Fraxum

Don't worry GM will stand behind your car during the warranty. They did for me and others.

No sorry, I was not clear in that post. The 3/4" height difference was fine. My problems with the ZL1 were on stock tires and rims. I think there was a short somewhere that Chevy could not find after replacing all the computers and possible cables in the car. The even sent an engineer to look things over. In the end it probably ended up as somebody's parts car or maybe they crushed the poor thing. It was my favorite modern car I have owned. I was not a fan of the 5th gen Recaros.

Boats can be a PIA and even bigger money pits than cars but nothing like being in the water close to a whale more that twice as long as your boat. Awe inspiring. One of my happiest days was picking up the boat and taking it out on my training voyage, and another one the day I sold it. Motorcycles, boats all gone. Only the Camaro SS left. It is a great consolation prize.

Gotcha... you just happened to get one of those hair-ball problems that no one can cough up a solution for.

Yeah, I've heard that about boats. I live in a coastal community and know several "boat people". I'm a pretty fair mechanic so at least I could avoid most of the ridiculous labor costs.

--Cal

[laynlo15]

I run a non dod hoosier slick, that's what I would recommend for a manual.

[cwebster]

Originally Posted by laynlo15

I run a non dod hoosier slick, that's what I would recommend for a manual.

I had to go with what would fit on my BC Forged 18x12 wheels, sized to offer the leverage I need to pounce out of the starting gate without bogging. According to their product list, the only 18" tires are the DOT slicks. My P335/30R18 Hoosier DOT Slicks arrive tomorrow so they'll be ready for race day on the 18th. Jegs really came through for me. I ordered them yesterday and they shipped them 2-day via FedEx from Ohio for free. They had the best prices too at $254 ea. Now I just have to choose a shop to mount and balance them. No speed shops close by but I want to ensure they wear evenly and I don't pick up vibrations over 130 MPH.

I'm excited to see what they'll do. Looks like the weather is shaping up to be warmer that ideal but I'll take it if it's dry.

--Cal