Question on 2006 C6 tire size for auto-x
10-25-2011, 10:17 PM
#1
Instructor
Thread Starter
Question on 2006 C6 tire size for auto-x
I have a 2006 Z51 that I am planning on competing in Super Stock. I auto-x'd for about 6 years straight in the late 1980s and early 1990s then family life changed my priorities. Now I'm looking to get back into competing again. I plan on keeping the car in SS for a while so I am limited to the stock size wheels. Hoosier A6s look to be the only game in town, but there are a few possible sizes. Fronts are available in stock 245-35-18 size as well as 255-35-18 (would be slightly pinched on the 8.5" rim) Rears the obvious choice would be the 295-30-19 or a really pinched 315-30-19. So what sizes are people running on their non-Z06 cars in SS?
Steve
Steve
10-26-2011, 04:20 PM
#2
Burning Brakes
Steve -
Doesn't look like anyone else is going to offer any advise, so here goes...
With the construction of modern R-compound tires, the name of the autocross game is maximizing and maintaining CONTACT PATCH! The more, the better. Also very important is being able to put all that rear-drive power to the ground on corner exit.
With that in mind, I used 285-18 Hoosier A6's in front and 315-19's in the rear on an '08 Z51 coupe using OEM 'Gumby' forged wheels. Here's a picture of the 285 front tire on this wheel in case you don't believe they would fit - - they do, and they worked REALLY well. I have other pics I can post, too.
Actually, if I hadn't been forced to sell the car, I would probably have bought 295 Hoosiers next for the front. The 295's are NO wider, but have a much higher load rating and are a bit taller, so they would probably last longer and not overheat as quickly on hot auto-x days. The trade-off is they may not offer quite as quick turn-in as the (shorter but otherwise identical) 285's. The nationally-competitive Shelby Mustang guys in F-Stock run these 295's quite successfully on even narrower 8-inch wheels, and they are carrying a bunch of weight on the front of those cars.
BTW - those forged OEM wheels, Carbotech autocross brake pads, Pfadt adjustable shocks and a Super-stock specific Pfadt front swaybar are for sale. PM me if interested ...
I can also share alignment settings with you, if you'd like...
.
Doesn't look like anyone else is going to offer any advise, so here goes...
With the construction of modern R-compound tires, the name of the autocross game is maximizing and maintaining CONTACT PATCH! The more, the better. Also very important is being able to put all that rear-drive power to the ground on corner exit.
With that in mind, I used 285-18 Hoosier A6's in front and 315-19's in the rear on an '08 Z51 coupe using OEM 'Gumby' forged wheels. Here's a picture of the 285 front tire on this wheel in case you don't believe they would fit - - they do, and they worked REALLY well. I have other pics I can post, too.
Actually, if I hadn't been forced to sell the car, I would probably have bought 295 Hoosiers next for the front. The 295's are NO wider, but have a much higher load rating and are a bit taller, so they would probably last longer and not overheat as quickly on hot auto-x days. The trade-off is they may not offer quite as quick turn-in as the (shorter but otherwise identical) 285's. The nationally-competitive Shelby Mustang guys in F-Stock run these 295's quite successfully on even narrower 8-inch wheels, and they are carrying a bunch of weight on the front of those cars.
BTW - those forged OEM wheels, Carbotech autocross brake pads, Pfadt adjustable shocks and a Super-stock specific Pfadt front swaybar are for sale. PM me if interested ...
I can also share alignment settings with you, if you'd like...
.
Last edited by EvilBoffin; 10-26-2011 at 05:07 PM.
10-27-2011, 12:07 AM
#3
Instructor
Thread Starter
WOW! I would never have thought the 285s would fit the 8.5, and a 295 on an 8 is even more amazing. Any alignment tips you have I would greatly appreciate. Right now I'm going to stick with the stock shocks and go with a bigger front bar. Eventually though I will do shocks.
Looks like there might have been some rubbing on the inside edge?
Looks like there might have been some rubbing on the inside edge?
Last edited by SteveC68; 10-27-2011 at 12:15 AM.
10-27-2011, 05:12 AM
#4
Burning Brakes
First - remember that the 295 Hoosier A6 is NO wider then the 285 - their only measurable difference is sidewall height and load rating (the 285 A6 is very short). I spent lots of time researching sizes on the A6 specs pages of the Hoosier & TireRack websites. I had NO issues w/rubbing on either inside or outside edges with the 285's - here's a pic of this tire on the car:
As for the Alignment --
After getting my Z51 corner-balanced by the notable Corvette expert, Mr. David Farmer (DavidFarmerStuff.com), here's what we did :
Front--
2.0 - 2.2 degrees negative camber
1/16th - 1/8th inch total toe-OUT
Max caster
Rear--
0.9 - 1.1 degrees negative camber
1/4th - 3/8th inch total toe-IN
This was a completely comfortable and drivable setup on the street, though I didn't have the car long enough to really tell how long my street tires would last with that much toe dialed in.
Front notes -
Get as much negative camber as is possible on both sides equally. If you find that the max available camber is very different between the left and right sides, have your subframe (thrust angle) aligned, then re-align the suspension.
I settled on 2.0-2.2 negative camber as an aggressive street/auto-x compromise, though my particular Coupe could get as much as -2.5 stock, from what I remember. If my car was not also street driven, I would've gone further.
A little Toe-OUT up front aids initial turn-in and transitions. But don't take it too far, or you may induce mid-corner understeer (the outside tire will be scrubbing horizontally during the steady-state part of the turn).
Rear notes -
You don't want much negative camber in the rear - keeping the tire upright will help maintain contact patch back there. At least 1 degree less negative then the front seems to be a good place to start for the rear.
Significant Toe-IN (1/4 inch or more) in the rear helps reduce oversteer on corner exit, allowing you to get back on the power earlier. Lots of toe-IN is not good for tire life, but I liked the results too much to reduce it.
General notes -
The stock Z51 shocks and swaybar combination are not very well balanced, and are known to make this car pretty nervous. I found the Pfadt Super-Stock adjustable front swaybar, set on 2-of-3 or 3-of-3 (stiffest), really helped plant the nose under braking and reduce rollover onto the front tires. It matches the big stock rear bar very well.
The Pfadt shocks noticeably reduced the nervousness, even though I didn't have enough time to get them properly adjusted before selling the car.
Let me know if you're interested in the Pfadt swaybar, those wheels or the other stuff mentioned above...
Hope that helps!!
.
As for the Alignment --
After getting my Z51 corner-balanced by the notable Corvette expert, Mr. David Farmer (DavidFarmerStuff.com), here's what we did :
Front--
2.0 - 2.2 degrees negative camber
1/16th - 1/8th inch total toe-OUT
Max caster
Rear--
0.9 - 1.1 degrees negative camber
1/4th - 3/8th inch total toe-IN
This was a completely comfortable and drivable setup on the street, though I didn't have the car long enough to really tell how long my street tires would last with that much toe dialed in.
Front notes -
Get as much negative camber as is possible on both sides equally. If you find that the max available camber is very different between the left and right sides, have your subframe (thrust angle) aligned, then re-align the suspension.
I settled on 2.0-2.2 negative camber as an aggressive street/auto-x compromise, though my particular Coupe could get as much as -2.5 stock, from what I remember. If my car was not also street driven, I would've gone further.
A little Toe-OUT up front aids initial turn-in and transitions. But don't take it too far, or you may induce mid-corner understeer (the outside tire will be scrubbing horizontally during the steady-state part of the turn).
Rear notes -
You don't want much negative camber in the rear - keeping the tire upright will help maintain contact patch back there. At least 1 degree less negative then the front seems to be a good place to start for the rear.
Significant Toe-IN (1/4 inch or more) in the rear helps reduce oversteer on corner exit, allowing you to get back on the power earlier. Lots of toe-IN is not good for tire life, but I liked the results too much to reduce it.
General notes -
The stock Z51 shocks and swaybar combination are not very well balanced, and are known to make this car pretty nervous. I found the Pfadt Super-Stock adjustable front swaybar, set on 2-of-3 or 3-of-3 (stiffest), really helped plant the nose under braking and reduce rollover onto the front tires. It matches the big stock rear bar very well.
The Pfadt shocks noticeably reduced the nervousness, even though I didn't have enough time to get them properly adjusted before selling the car.
Let me know if you're interested in the Pfadt swaybar, those wheels or the other stuff mentioned above...
Hope that helps!!
.
Last edited by EvilBoffin; 10-28-2011 at 04:03 AM.
10-28-2011, 03:56 AM
#6
Burning Brakes
This is a very odd-ball range of sizes from Hoosier, so you're doing the right thing by analyzing the detailed specs carefully for each size. You just can't go by the information printed on the side of the tire when trying to decide how it will work on your car.
Heck, Miata and RX-8 guys have been known to run 255 or BIGGER Hoosiers on 6.5 to 7.5-inch wide wheels!!
Last edited by EvilBoffin; 10-28-2011 at 04:15 AM.
10-30-2011, 04:45 PM
#7
Burning Brakes
Steve -
I just realized why you were asking about rubbing on the inside edge - -
The 1st photo I posted above shows little rubber shards sticking out from the inside edge. That makes it look like there is significant rubbing on that one side.
That was not the case - they are simply leftover rubber pickup from driving through the pit area right after a run on very hot tires. I then drove home (26 miles) after the event on the same tires, which cleaned the pickup off the tread area, but didn't clean it off the sidewall edge.
.
I just realized why you were asking about rubbing on the inside edge - -
The 1st photo I posted above shows little rubber shards sticking out from the inside edge. That makes it look like there is significant rubbing on that one side.
That was not the case - they are simply leftover rubber pickup from driving through the pit area right after a run on very hot tires. I then drove home (26 miles) after the event on the same tires, which cleaned the pickup off the tread area, but didn't clean it off the sidewall edge.
.
Last edited by EvilBoffin; 10-30-2011 at 04:51 PM.
12-05-2011, 11:07 PM
#8
Instructor
Thread Starter
Where would you take the car to get the subframe (thrust angle) aligned? Got the wheel alignment done and I could only get 2.1 degrees negative on the drivers side front. The passenger side still had more adjustment available at the eccentrics so I had the guy just set them both to 2.1
12-09-2011, 12:47 PM
#9
AKA "The CLOWN"
Member Since: Feb 2010
Location: Chicago South Suburbs
Posts: 6,261
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Steve -
Doesn't look like anyone else is going to offer any advise, so here goes...
With the construction of modern R-compound tires, the name of the autocross game is maximizing and maintaining CONTACT PATCH! The more, the better. Also very important is being able to put all that rear-drive power to the ground on corner exit.
With that in mind, I used 285-18 Hoosier A6's in front and 315-19's in the rear on an '08 Z51 coupe using OEM 'Gumby' forged wheels. Here's a picture of the 285 front tire on this wheel in case you don't believe they would fit - - they do, and they worked REALLY well. I have other pics I can post, too.
Actually, if I hadn't been forced to sell the car, I would probably have bought 295 Hoosiers next for the front. The 295's are NO wider, but have a much higher load rating and are a bit taller, so they would probably last longer and not overheat as quickly on hot auto-x days. The trade-off is they may not offer quite as quick turn-in as the (shorter but otherwise identical) 285's. The nationally-competitive Shelby Mustang guys in F-Stock run these 295's quite successfully on even narrower 8-inch wheels, and they are carrying a bunch of weight on the front of those cars.
BTW - those forged OEM wheels, Carbotech autocross brake pads, Pfadt adjustable shocks and a Super-stock specific Pfadt front swaybar are for sale. PM me if interested ...
I can also share alignment settings with you, if you'd like...
.
Doesn't look like anyone else is going to offer any advise, so here goes...
With the construction of modern R-compound tires, the name of the autocross game is maximizing and maintaining CONTACT PATCH! The more, the better. Also very important is being able to put all that rear-drive power to the ground on corner exit.
With that in mind, I used 285-18 Hoosier A6's in front and 315-19's in the rear on an '08 Z51 coupe using OEM 'Gumby' forged wheels. Here's a picture of the 285 front tire on this wheel in case you don't believe they would fit - - they do, and they worked REALLY well. I have other pics I can post, too.
Actually, if I hadn't been forced to sell the car, I would probably have bought 295 Hoosiers next for the front. The 295's are NO wider, but have a much higher load rating and are a bit taller, so they would probably last longer and not overheat as quickly on hot auto-x days. The trade-off is they may not offer quite as quick turn-in as the (shorter but otherwise identical) 285's. The nationally-competitive Shelby Mustang guys in F-Stock run these 295's quite successfully on even narrower 8-inch wheels, and they are carrying a bunch of weight on the front of those cars.
BTW - those forged OEM wheels, Carbotech autocross brake pads, Pfadt adjustable shocks and a Super-stock specific Pfadt front swaybar are for sale. PM me if interested ...
I can also share alignment settings with you, if you'd like...
.
Could you please post some pics of your 315s. I have a C5 with 19x11 rims and I can't decide weather to go with 315/40 or a 325/30. I have 325/30/19 Invos now and they fit perfect. I just don't know if the Hoosier 325/30 is wider as I am maxed out as far as room!
Also does anyone have pics of 325/30/19s with Hoosiers???
12-09-2011, 07:43 PM
#10
Track Junky
Excellent post! I'm trying to learn to do my own alignment and this is seems to be a good starting point. Looks to me that getting the car up enough to reach the adjustment bolts could be tough. I may have to get creative with ramps.
First - remember that the 295 Hoosier A6 is NO wider then the 285 - their only measurable difference is sidewall height and load rating (the 285 A6 is very short). I spent lots of time researching sizes on the A6 specs pages of the Hoosier & TireRack websites. I had NO issues w/rubbing on either inside or outside edges with the 285's - here's a pic of this tire on the car:
As for the Alignment --
After getting my Z51 corner-balanced by the notable Corvette expert, Mr. David Farmer (DavidFarmerStuff.com), here's what we did :
Front--
2.0 - 2.2 degrees negative camber
1/16th - 1/8th inch total toe-OUT
Max caster
Rear--
0.9 - 1.1 degrees negative camber
1/4th - 3/8th inch total toe-IN
This was a completely comfortable and drivable setup on the street, though I didn't have the car long enough to really tell how long my street tires would last with that much toe dialed in.
Front notes -
Get as much negative camber as is possible on both sides equally. If you find that the max available camber is very different between the left and right sides, have your subframe (thrust angle) aligned, then re-align the suspension.
I settled on 2.0-2.2 negative camber as an aggressive street/auto-x compromise, though my particular Coupe could get as much as -2.5 stock, from what I remember. If my car was not also street driven, I would've gone further.
A little Toe-OUT up front aids initial turn-in and transitions. But don't take it too far, or you may induce mid-corner understeer (the outside tire will be scrubbing horizontally during the steady-state part of the turn).
Rear notes -
You don't want much negative camber in the rear - keeping the tire upright will help maintain contact patch back there. At least 1 degree less negative then the front seems to be a good place to start for the rear.
Significant Toe-IN (1/4 inch or more) in the rear helps reduce oversteer on corner exit, allowing you to get back on the power earlier. Lots of toe-IN is not good for tire life, but I liked the results too much to reduce it.
General notes -
The stock Z51 shocks and swaybar combination are not very well balanced, and are known to make this car pretty nervous. I found the Pfadt Super-Stock adjustable front swaybar, set on 2-of-3 or 3-of-3 (stiffest), really helped plant the nose under braking and reduce rollover onto the front tires. It matches the big stock rear bar very well.
The Pfadt shocks noticeably reduced the nervousness, even though I didn't have enough time to get them properly adjusted before selling the car.
Let me know if you're interested in the Pfadt swaybar, those wheels or the other stuff mentioned above...
Hope that helps!!
.
As for the Alignment --
After getting my Z51 corner-balanced by the notable Corvette expert, Mr. David Farmer (DavidFarmerStuff.com), here's what we did :
Front--
2.0 - 2.2 degrees negative camber
1/16th - 1/8th inch total toe-OUT
Max caster
Rear--
0.9 - 1.1 degrees negative camber
1/4th - 3/8th inch total toe-IN
This was a completely comfortable and drivable setup on the street, though I didn't have the car long enough to really tell how long my street tires would last with that much toe dialed in.
Front notes -
Get as much negative camber as is possible on both sides equally. If you find that the max available camber is very different between the left and right sides, have your subframe (thrust angle) aligned, then re-align the suspension.
I settled on 2.0-2.2 negative camber as an aggressive street/auto-x compromise, though my particular Coupe could get as much as -2.5 stock, from what I remember. If my car was not also street driven, I would've gone further.
A little Toe-OUT up front aids initial turn-in and transitions. But don't take it too far, or you may induce mid-corner understeer (the outside tire will be scrubbing horizontally during the steady-state part of the turn).
Rear notes -
You don't want much negative camber in the rear - keeping the tire upright will help maintain contact patch back there. At least 1 degree less negative then the front seems to be a good place to start for the rear.
Significant Toe-IN (1/4 inch or more) in the rear helps reduce oversteer on corner exit, allowing you to get back on the power earlier. Lots of toe-IN is not good for tire life, but I liked the results too much to reduce it.
General notes -
The stock Z51 shocks and swaybar combination are not very well balanced, and are known to make this car pretty nervous. I found the Pfadt Super-Stock adjustable front swaybar, set on 2-of-3 or 3-of-3 (stiffest), really helped plant the nose under braking and reduce rollover onto the front tires. It matches the big stock rear bar very well.
The Pfadt shocks noticeably reduced the nervousness, even though I didn't have enough time to get them properly adjusted before selling the car.
Let me know if you're interested in the Pfadt swaybar, those wheels or the other stuff mentioned above...
Hope that helps!!
.
