When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I wanted to post up my impressions of the Hoosier R7, but more specifically this tire size combination on track. I've run this setup for three track days now across two different weekends and finally have a feel for them. Both events were on Summit Point Main.
I had these wheels and fresh R7s around from the C6Z so I thought I'd give them a try on my C7Z. The tires are the following sizes on CCW C10 rims:
315/30-18 Front on 18x11 rim
345/35-18 Rear on 18x13 rim
My car is a 2015 non-Z07 (FE6 suspension) car with the M7 trans. It is stock other than the wheels/tires, stage 3 aero pieces, and AP Racing front brakes. Testing was done in Track Mode and in PTM Sport 1, 2, and Race. Frankly I didn't notice much difference between the modes and the lap times were all similar.
First, I want to share that there is only very limited additional rubbing. With the stock wheels and tire sizes (both PSS and MPSC2) I've always had rubbing where the front "spat" meets the fender as well as some rubbing in the front and rear fender liners. With the bigger wheels and tires the fronts also rub the brake air deflectors and have worn a triangle shaped groove in them now. Frankly, I was surprised there wasn't more rubbing but that's good news.
I won't spend much time talking about the overall grip of the tire as I'm sure anyone that has run R7s know that there is a phenomenal amount of grip. In fact, the first day I ran them I really couldn't find the limits of grip for the car. I kept going in to corners too slow, braking too much, and with as much traffic as there was it was like being superman just driving around everyone else on track wherever and whenever you wanted. It was interesting but kind of boring.
I also wasn't able to get close to my previous best of 1:17.4 that first day. It really wasn't until last weekend that I found the limits and was able to get a feel for the car again which is what I really want to share.
I should probably start though with my impressions of the FE6 handling on stock size tires. Other than ultimate grip, I didn't feel much of difference between the MPSC2 and PSS tires on track and when warmed up a new set of PSS could give a worm set of MPSC2 a run for their money. As I posted in my Z06 vs Z07 comparison the Z06 definitely has a slower turn in and more understeer than the Z07. I had experimented with the Z07 sway bar bushings to try and dial in a little less understeer but that resulted in some nasty snap oversteer so I only ran those for one day and switched back to the FE6 bushings.
However, I found that with sufficient trail-braking you could make the FE6 suspension work very well on track and combined with PTM you could trail brake right down to the apex and then immediately get on the gas and let PTM manage the power out of the turn. Once you mastered this is was an incredibly easy car to drive fast until the tires finally wore out. In my case I always corded the fronts first and when you got near that no amount of trail-braking would turn the car in.
As you'll notice the front tires with the Hoosier setup are 30 mm wider and the rears are 10mm wider. The diameters are pretty darn close to stock and my hope was that this would dial in a little less understeer and require less trail-braking to turn the car in. That it did. In fact, it is a very different car with these tires even if you ignore the grip.
The 315/345 combo resulted in a car that tended towards oversteer although it is very manageable. If you like a slightly loose car then this is the setup you want. I quickly learned not to trailbrake but rather to brake and then toss the car in to the turns hard. There was so much front grip I never got them to break away. In this state the car was neutral to slight oversteer and on at least one occasion I did this in T1 at Summit (a long 180) a little too fast and the car basically slid in a perfect 4-wheel drift.
As you went back to throttle you have to be more careful as the car would step out easily but it was also very easy to control with small steering inputs. In slow speed turns like the carousel I could easily hang the tail out around the corner under throttle. While the PTM still seemed to work when you only had a little bit of steering input I found that in the tighter corners it basically did nothing and you could throttle steer your way around the track. I did try playing with the rear aero as well going from the wicker at its lowest position to its highest. In the higher position it did seem to help balance the car and I plan on leaving it there.
So to sum this up, the car went from trail-brake and then mash the gas to throw it in the turn off the brakes and then steer with the throttle. Is it faster? Yes, but I'm not sure how much of that is just the added stick of the tires. Is it easier to drive fast? Not really as you have to be on top of and ready to catch the oversteer. Is it more entertaining to drive? Definitely so.
I managed a 1:16.8 (0.6 off my previous best) but most of my laps were in the 1:18 range. I was feeling pretty good about that until Gary Church laid down a 1:16.2 in his A8 Z07 with a fresh set of MPSC2. He's a better driver for sure but I did notice that in the carousel he would pull away from me under power using the PTM to figure it out while I was trying to manage the rear end of my car.
In summary, I really like the new tire setup on my car. I'm curious to see what this would be like on an FE7 car as I suspect it would be a handful given that it already has less understeer. I know that ESVA beat my best at VIR on this setup though so it's definitely working for him.
Nice write up! I'm wondering if the PTM is specific to not just the FE6/FE7 versions, but also for the specific tyres that come on those versions also. Meaning that with a markedly different tyre, the R7, the PTM doesn't work as well as it isn't calibrated for it. Honestly I'd expect the R7, especially in those sizes, to be 2-3 seconds per lap faster than the OEM tyres.
Bish
I believe it's been stated that the Z07 is tuned to the MPSC2 and the Z06 to the PSS. Based on the description in the Ask Tadge write-up on PTM I would have expected the PTM to pull power early on a tire with more grip but I suspect the wider fronts and different balance are messing up its calculations. Of course, I'm just guessing.
I really wouldn't expect the R7 to be 2-3 seconds a lap faster than the MPSC2 but I'm sure a better driver could get this car down in to the 1:15's. Of course, by the time I came to grips with the setup the R7s have ~5 hours of track time on them so fresh ones would have been faster.
The other thing that's interesting about this car is that the fast laps for me are almost always on lap 2 or 3 of the session. After that it feels like you're driving just as hard but the times fall off a second or so and then remain consistent. I don't if it's the car pulling power or the tires just get hot quickly with the weight of the car. I'll dig in to the vmax data but it doesn't seem to be changing much based on a quick glance at the HUD
I noticed some similar trends - lots of rotation when trail-braking in comparison to stock PSS tires. I'm probably wrong, but I was crediting some of that to softer side-walls. When threshold-braking, the rear would get a bit wobbly on me.
I was considering running more front camber, but now that I'm thinking about it, that might increase over-steer.
What are your thoughts on running front FE7 bushings, but rear FE6 bushings. I think that would decrease oversteer a bit.
I noticed some similar trends - lots of rotation when trail-braking in comparison to stock PSS tires. I'm probably wrong, but I was crediting some of that to softer side-walls. When threshold-braking, the rear would get a bit wobbly on me.
I was considering running more front camber, but now that I'm thinking about it, that might increase over-steer.
What are your thoughts on running front FE7 bushings, but rear FE6 bushings. I think that would decrease oversteer a bit.
Get as much negative camber as you can both front and rear, and be very careful mixing FE6/FE7 components would be my recommendations.
Get as much negative camber as you can both front and rear, and be very careful mixing FE6/FE7 components would be my recommendations.
YMMV,
Bish
I really want to get a pyrometer and someone to take some tire temps. Just from looking at the tires I have a suspicion that the rear could actually benefit from a little less camber.
It'll also be interesting to see how these tires wear. On my C6Z even with -2.8 camber front it would eventually cord the outside edges. At least on the MPSC2 and PSS the C7Z seems to just delaminate a tread block in from the outside.
I really want to get a pyrometer and someone to take some tire temps. Just from looking at the tires I have a suspicion that the rear could actually benefit from a little less camber.
It'll also be interesting to see how these tires wear. On my C6Z even with -2.8 camber front it would eventually cord the outside edges. At least on the MPSC2 and PSS the C7Z seems to just delaminate a tread block in from the outside.
What alignment settings were you running with the cup 2's and how was the tire wear?
I run the exact same set up in my Z07 except I run A7s vs your Rs. In the front, are you running the 4mm spacer?
No spacer. The APR Racing brakes seem to fit under the 18" CCW C10 without a problem. I think you have the AP Racing setup too, don't you? How come you needed a spacer?
Originally Posted by Robert R1
What alignment settings were you running with the cup 2's and how was the tire wear?
Factory recommended track settings. -2.0 F/R camber etc.
Honestly it's too soon to really tell on the wear. What I found interesting was that if you drove the car off track and through some dirt it only looks like the inner 1/2 of the tire was touching.
For those interested I posted one of the sessions was last weekend. The second lap was my fast lap.
Very hard to tell conclusively by the videos but your car does seem to oversteer more than mine. Lateral G's are high but not extreme, and longitudinal is the same. Seemed like you were rolling onto the throttle and not stabbing it and it's not like you were WOT.
Im still in shock you can get a 315 on the front. My stock tires rubbed a hole in to the carpeting lining. my 285 slicks only made it worse. Im thinking of ordering the 305 slicks this next time since you have proven the 315's work up front.
Im still in shock you can get a 315 on the front. My stock tires rubbed a hole in to the carpeting lining. my 285 slicks only made it worse. Im thinking of ordering the 305 slicks this next time since you have proven the 315's work up front.
I'm shocked as well and my stock tires also rubbed through the wheel well liner. Have you ever noticed that where the liner gets rubbed there are ridges like it's designed to wear through.
No spacer. The APR Racing brakes seem to fit under the 18" CCW C10 without a problem. I think you have the AP Racing setup too, don't you? How come you needed a spacer?
Factory recommended track settings. -2.0 F/R camber etc.
I think I can answer that question. This is a sad lesson I learned with my C6Z earlier this year. The C6Z Z07, the C6ZR1 and the C7 Z07 have the CCM brakes that have a dished in rotor hat. This works fine with stock wheels or stock sized repro wheels. However, the CCW wheels have a slightly larger diameter where they meet the rotor. The spacer permits use of the CCW wheel with that rotor hat. If not used the wheel rides on the radiused edge of the dished in area and doesn't tighten down properly even when torqued properly. That means the wheel is moving around on the hat when you are driving which leads to lug stud failure.
I found this out on my C6Z since I had a similar dished in Wilwood hat on my car. After 7 track days all 5 studs on my left front hub sheared off in Turn 1 at VIR letting the wheel take a trip to the fence while I rode into the grass on the rotor. I was lucky I was on a 2nd cool down lap and going slow when it happened. A couple of laps earlier I was in the 150+ range on the back straight and if it had happened there it could have been much worse.
When I sent my wheel back to CCW to have them check it for damage that is when they informed me of the issue with the CCM rotor hats. The spacer for the CCMs is different than the one required for the Wilwood hats so they made special ones for me and sent some extended thread lug nuts that provide more thread engagement.
This was my fault because I assumed that two different parts that worked well with GM parts would work with each other. Not necessarily so and it is the user's responsibility to make sure they will interface properly.
Bill
Last edited by Bill Dearborn; 10-05-2015 at 01:43 PM.
I think I can answer that question. This is a sad lesson I learned with my C6Z earlier this year. The C6Z Z07, the C6ZR1 and the C7 Z07 have the CCM brakes that have a dished in rotor hat. This works fine with stock wheels or stock sized repro wheels. However, the CCW wheels have a slightly larger diameter where they meet the rotor. The spacer permits use of the CCW wheel with that rotor hat. If not used the wheel rides on the radiused edge of the dished in area and doesn't tighten down properly even when torqued properly. That means the wheel is moving around on the hat when you are driving which leads to lug stud failure.
I found this out on my C6Z since I had a similar dished in Wilwood hat on my car. After 7 track days all 5 studs on my left front hub sheared off in Turn 1 at VIR letting the wheel take a trip to the fence while I rode into the grass on the rotor. I was lucky I was on a 2nd cool down lap and going slow when it happened. A couple of laps earlier I was in the 150+ range on the back straight and if it had happened there it could have been much worse.
When I sent my wheel back to CCW to have them check it for damage that is when they informed me of the issue with the CCM rotor hats. The spacer for the CCMs is different than the one required for the Wilwood hats so they made special ones for me and sent some extended thread lug nuts that provide more thread engagement.
This was my fault because I assumed that two different parts that worked well with GM parts would work with each other. Not necessarily so and it is the user's responsibility to make sure they will interface properly.
Bill
Hey Bill,
I'm glad you figured out the issue and didn't get hurt in the process. Here are a couple pictures I took of the malfunction. Question: is the wheel usable or did you just buy another one?
Hi Bill. I remember that and was paddocked across the row and down a bit from you. I have been monitoring this but to be honest I'm not 100% certain what to look for. Is the center part of the hat being dished in or dished out that causes a problem?
I have a steel brake car but I did notice that one even I picked up a bad high speed vibration and there is some scoring around the hub bore on one of the front wheels. The hats on that factory steel brakes are dished out and while the back of the CCW wheels are flat you can see where the center section of the wheel is larger than the dished out portion of the hat.
I've since gone to open lugs (Katech titanium ones) and now have the AP Racing front kit but your situation definitely has me concerned. I don't trust these C7 OEM lugs to being with and I'm hoping the someone can identify a suitable APR replacement.
Yes there is an outer 'dish' to this minimal offset hat. If the wheel pads is larger than the flat surface inside this dished area the wheel will appear tight but actually be seated (as shown by the silver line I see) against only the radius of the material. Not truly secured to the hat in the manner in which it should be.
*Best seen in the lower right corner where there are less lines on this drawing. The wheels pad base circle is too large for the dish diameter upon which it sits.
An option would be to fit a wheel spacer into the hat pocket that allows the wheel to sit fully against it and then the hat also. Of course it would push the tire out a tad and you'd need to check the stud length for proper nut engagement.
10-03-2015, 11:42 AM
Track Impressions: 315F/345R Hoosier R7
