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Discussion Starter #1
Looks like Nate is going to make it possible for me to finally own my dream wheels. Fikse MachV's. The sizes are standard Z06 17X9.5 Front and 18X10.5 Rear. My queston is what size Hoosier R Compound Track Tires. I was thinking 275/40-17 front and 305/30-18 rear. My car is lowered and I don't want to take a chance on fender rub. I need some help here
David
 

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David,
Never driven on that combo, but the sizes sound right for the wheels and the combo should have a good balance.
I have run the stock F1s on two track days, 275/40-17 Kumho Ecsta MX in front with stock F1s in the rear for one track day, several races with Hoosier 275/40-17 front, 315/35-17 rear and several races with Kumhos of the same size, and finally one race with 315/35-17 all around. All of these were okay. The car is very forgiving.
I am guessing your setup will give you slightly more understeer and a slightly better ability to put power down as compared to stock (especially with Hoosiers mounted), but not quite the outright grip as the bigger 315s on 17s all around.
Many guys are even running 315s front and 335s rear in SCCA T1 now. Verdict is still out as to whether this is faster. The 335s are definitely wearing the tub though. Not for the every day street car.
Good luck. Enjoy the new wheels.
:cheers:
 

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Discussion Starter #3
Do you have to reprogram with the 315/35-17's. It looks like you are using a smaller rim size to get the wider tire in?
thanks/Dave
 

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If your going to spend that kind of money why dont you get larger rims, say 18x10.5 width and a 11.5x18 in back. With these sizes you could go with a 295x18 fr and a 315 or 335 r these sizes will fit with the proper offset and no rubbing. If you go with the Hoosier tire you will not be able to drive it on the street, the fibreglass will puncture to easy thus making them dangerous. Michelin Sport Cup, Toyo actualy has 18x275 and 18x335 it will work.
 

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Subdriver said:
David,
Never driven on that combo, but the sizes sound right for the wheels and the combo should have a good balance.
I have run the stock F1s on two track days, 275/40-17 Kumho Ecsta MX in front with stock F1s in the rear for one track day, several races with Hoosier 275/40-17 front, 315/35-17 rear and several races with Kumhos of the same size, and finally one race with 315/35-17 all around. All of these were okay. The car is very forgiving.
I am guessing your setup will give you slightly more understeer and a slightly better ability to put power down as compared to stock (especially with Hoosiers mounted), but not quite the outright grip as the bigger 315s on 17s all around.
Many guys are even running 315s front and 335s rear in SCCA T1 now. Verdict is still out as to whether this is faster. The 335s are definitely wearing the tub though. Not for the every day street car.
Good luck. Enjoy the new wheels.
:cheers:
Normally it is a nono to mix different tire brands. Did the combo of front Kumho's and rear GY stock tires cause you any problems?
 

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Discussion Starter #6 (Edited)
G Stamatakos said:
If your going to spend that kind of money why dont you get larger rims, say 18x10.5 width and a 11.5x18 in back. With these sizes you could go with a 295x18 fr and a 315 or 335 r these sizes will fit with the proper offset and no rubbing. If you go with the Hoosier tire you will not be able to drive it on the street, the fibreglass will puncture to easy thus making them dangerous. Michelin Sport Cup, Toyo actualy has 18x275 and 18x335 it will work.
These will be for track tires only. I will be switching back to stock for street. With these different size tires and rims, will I need to reset the PCM for any reason? Also, aren't the 335's rubbing the fenders on the lowered cars?
I really appreciate the imput guys.
Dave
 

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Do you have to reprogram with the 315/35-17's. It looks like you are using a smaller rim size to get the wider tire in?
Dave,
Contrary to what many have said on this forum, no reprogram is required, and AH/TC work just fine with both 275/40-17 front, 315/35-17 rear and 315/35-17 all around. Driven on the track many times with these combos with AH/TC fully on - no problems, and in Comp Mode - no problems.
The SCCA T1 rules for the Z06 allow either stock wheel sizes or 17x10 front and 17x11 rear. Everyone runs the 17s. So yes, the 315s on the front are on a narrower wheel, but still fit fine.

Normally it is a nono to mix different tire brands. Did the combo of front Kumho's and rear GY stock tires cause you any problems?
I have read many times that mixing tires is a no no. I personally disagree as long as you aren't an idiot about it. I am not mixing tires side to side, but front to back. All this is going to do is very slightly change the balance front to rear, i.e. more or less understeer/oversteer.
The 265 F1s and the 275 Kumho's are very comparable and the car was well balanced with either. As I did not do a back to back comparison, I can't give concrete results, but my seat of the pants feeling was that the Kumho's, though a little wider, had a little less grip than the F1s (but at about 60% of the cost), leading to very slightly more static understeer.
I have done one race with 275 Kumho Ecsta 700 in front and 315 Kumho Victoracer 700 in the rear - no problem. Due to a puncture, I was forced to change the rears to 315 Hoosiers at the next race at the last minute and ended up running 275 Kumho Ecsta 700s front with 315 Hoosiers in the rear - no problem (I won over a Z06 with Hoosiers all around).
With that said, every combo I have run the tires were very very comparable. It would be bad for example to run 315 Hoosiers in front and 295 F1s in the rear.
Common sense applies. If you put on a set of better tires in front you are going to get less understeer, worse tires more understeer. If you put better tires in the rear you are going to get less oversteer (or more understeer), worse tires in the rear leads to more oversteer (or less understeer).
Final comment, overall diameter of all of my tire combos has been within 3% of stock. By picking tires that aren't stock, the tire diameter needs to be considered. However, within the sizes I have tried, I have had no problems.
:cheers:
 

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Running the smaller 275/40x17 on the front for the track and larger width rears will give the car poor turn in and static understeer in mid corner. This holds true for both track and AutoX, high or low speed. The only time the 275/40x17 is desirable is in the rain with rain tires on.

There are a number of solutions:

1. the T1 alternate to stock set up is fine. 10x17 wheels in the front and 11x17 in the rear with 315/35x17's all the way around. These are SCCA legal. for T1

2. If your not bound by SCCA T1 rules you can do even better.
My personal preference is to run Hoosier 305/30x18 on 11x18" wheels in the front. I like the 315/35x17 on either 11 or 11.5x17" for the rear. The reason I like this combination is:
- the tire contact patch is almost equal F to R.
- this reduces the static and mid corner understeer and makes the car as neutral as possible.
- the 30 aspect ratio on 18" in the front reduce the side wall flex and allow crisp turn in with hardly any flex
- this also reduces dive under heavy braking
- the larger contact patch in the front besides reducing understeer and flex also increases front grip and allows higher cornering speeds
- the 35 aspect in the rear allows more side wall flex in the rear than the front and allows better F>R weight transfer under hard acceleration this allows quicker straight line trap speeds and higher corner exit speeds
- there is also more grip and tire contact patch in the rear which aids traction.

3.I have been toying with the idea of going to 335's in the rear but you either need to be tubbed or with more positive offset which allows them to stick out. also I fear that a 305/335 commbination would regress the car to the understeer condition.

4. the 315/335 F/R combination might be an alternative though.

The is no need to reprogram and the nice thing is all of these tire combinations have 25.5" diameters
 

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DJ,
Concur. I'd like to try the 18x10 or 11 front with 305s, but constrained by rules.
In my one track day with 315/35-17 on 17x10 front and 15/35-17 on 17x11 rear, I found the car to handle much the same as with 275s in front. I believe this is because with the 315s on a 10 inch wheel they bulge significantly, causing a loss of contact patch. I looked at my tires after rolling into the pits and I am losing near an inch each side in static conditions. Now in corners under load, I probably get some of this back, but the gain was nowhere near as signifcant as I thought it would be.
In fact, I have heard that 275s up front is faster on high speed tracks due to less aerodynamic and rolling drag.
As I have no back to back comparisons, most of this is just my seat of the pants observation.
 

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I just purchased the Hoosier 275/305 R combination and mounted them on a stock set of Z06 wheels. I tried to scrub them a bit this past weekend (before track use) but did not have a great deal of success...just could not get enough heat into the tires.

I plan on using them this weekend at Beaverun, but Mother Nature may have differnent plans for me. I will let ya'll know how they work out.

Fitment is fine.

DMP
 

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Discussion Starter #11
More help here guys. If I decide to run 18X10 Fronts and 18X11.5 Rears. 285/35Fronts and 335/30Rears, Will the tires rub the fenders or transverse spring on a lowered car? (lowered as much as factory bolts will allow. Is there a 315/30 you could run on the rear?
Dave.
 

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Are you fixed on Hoosiers?

If not then you could try the Michelin Pilot Sport Cup tires. Their sticky and have a treadwear rating of 80.

I have 285/30-18 mounted on 18x10 front and 315/30-18 mounted on 18x11 rears

First track event is this coming weekend at Texas Motor Speedway. I beleive P51 Aviator is also running this setup.


 

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Like a dummy I bought a duplicate set of factory wheels, so I am stuck with a limited selection of tires. The Sport Cups do not come in sizes that work for the Z, if my memory hasn't failed me.

DMP
 

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18" drag radials available ????????

Has anyone got any info on BFG drag radials or equal tires availability yet?

Thanks
:guiness:
 

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David,

Try the Goodyear F1 GS-CS r-compound tires. They come in the exact right stock sizes (I too bought an extra set of stock wheels before checking out competition tire sizes - stock wheels are an incredible bargain) and are cheaper than the Hoosiers or Michelins. They also wear decently. I've run them at two different events and have been very happy with them. Don't think you'll regret it.

Jim
 

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I have the pilot sports on stock size wheels (CCWs) 255/40/17 front and 295/30/18 rear. the car is balanced and work as well if not better then the Hoosier's in there 275/40/17 and 305/30/18. No traction control problems and they can be driven to an from events, I have over 2k on them and about 50 laps with only 2/32 of wear so far. In fact I won a American Auto X event Yesterday, (SS class) and place 5th an the National Tour at Atwater.
 

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How did the Michelin Pilot Sport Cup tires work for you at the track? I am wondering about tire pressure. What did your optimal tire pressure end up being? I want to start close to the ideal pressure. Thanks!
 
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