kwhiteside

Suffered for two days with understeer pushing thru turns, and/or not being able to whip the car around. I went to Barber which is a turn crazy track last weekend. One month ago at Road Atlanta, I did not have this issue.

C5 Z06
V710 335/30/17 on ZR1 17X11 50mm offset on rears. Same both events

V710 275/40/17 on stock 17X9.5 fronts
Road Atlanta - new tires, groove lines on inside
Barber - Diff set 75% tread left, groove lines mounted on outside.
Temp was 30+ degrees cooler at Barber this weekend
I adjust my rake by raising the back 3/8 as I was running 4" front and back with my slicks on.

The people I asked seem to think the 275's on the front were the issue, but since I didn't have the problem at RA, and I can't go wider on those wheels, I'm looking for more thoughts.

I did not mess with tire pressure as nobody seemed to think that could be the problem.

I have to wonder about
--tire pressure?
--new rubber vs used rubber?
--mounting the two grooves the v710 has on the outside edge where the tires are hitting hardest?
--Could the increased rake put more pressure on the front?

Educate me a bit please.

drivinhard

I have run 9.5/10.5 and square on both. the C5Z likes to be square to be neutral.

swaybar, springs and shocks stock? how much camber in the front?

Jason

335 rear/275 front is a big difference

wtknght1

It could be a lot of things you mentioned including pressures, etc, but in T1, we ran 315s all around and it was pretty neutral. I know when I did some testing with the 335s on back, it pushed, so anything smaller than that on front will definitely be worse.

And the 2d rule of racing is "Don't chase bad tires." To do proper testing, you need to be on fresh rubber...all the way around...and make 1 change at a time.

kwhiteside

I had this alignment setup done, would have to check my exact sheet when I get home to my files.

Aggressive
FrontCamber-1.6deg
Caster5 to 8deg
Toe0.0in
RearCamber-1.1deg
Toe - 1/8in

Since I had it aligned, I have put on Bilstien Sport Shocks. I have put on a DRM brake duct kit too. So I've had things apart and maybe have lost/altered some settings.

Sways are Stock

shifter77

Kwhiteside.

larryfs

you can get 295's on the front rims, no problem.

0Randy@DRM

I have ran 275-315 on the front of my car and they do make a difference. But went the fastest on the 275's The only time I really felt a big push was in the gear oil of a VW.

Randy

sperkins

Understeer was worse where? Corner entry, middle or exit?

kwhiteside

I noticed it all the time on long sweeping turns (Barber turn 3) pinching the pushing front left tire as try to get into the inside of turn. (middle turn)

Also the sharp left at turn 5. No way could I whip it in there. This turn should be similar style to turn 7 at road atlanta where I was able to park it and almost do a 90 if I wanted to go deep.
(start of turn)

kwhiteside

I was putting my tires away tonight and found my front left to look very odd. Please expand the pic and notice the two grooves how there is cuping around the grooves. I've never ran with the grooves on the outside and was unconfortable with it because that is where the tires are pushing the most. When you are pushing the rubber around out there, having that ravine has to weaken things. The rubber will naturally move more at the groove. Path of least resistance I would think. Hence the cuping.

I'm not expert, but it seems to make sense to me that when we move rubber around like we do, having that groove is just going to give the rubber a natural place to go.

Tell me I'm wrong, but explain it if you do.

sperkins

T5 at Barber really isn't like T7 at Road Atlanta at all - big difference in entry speed and corner radius. I think that the massive meats you had on the rear made the understeer much worse than if you had a better size match or square set up. I wouldn't start worrying too much about what may be wrong with the car just for that reason. Remember that C5's are engineered to understeer from the factory (with smaller tires up front) and you simply exagerated that with the sizes you ran.
Did you have the TC/AH fully on?

kwhiteside

Competitive Mode

Jason

Flipping 710's won't make any appreciable difference.
Big on back, small on rear will make you push.
Comp mode will make you push.

kwhiteside

Can you explain how the Comp mode makes you push?

Please look at this pic and notice the cuping at the grooves. The tire is no longer flat across the surface. Are you sure flipping and putting the grooves on the outside "pushing surface" wont make any difference after seeing what happened to this tire that was on my front left.

drivinhard

that "cuping" is normal. they all do that.

looking at the edges, you could use more camber, but the car may still be a street car so...

sperkins

The YAW sensors for AH are still active limiting your ability to achieve ideal slip angles for R compounds and throttle steer.

kwhiteside

Thanks guys,

I'll make a couple tweaks before Roebling Road next month.

Let me ask this. If you see your lefts wearing more than the rights after a full day, would it be wise to swap left and right tires before day 2? My right front was like new compared to that one in the pic. My day Sunday seemed to handle worse as it went on. Of course I was getting much faster too. But it seems like some fresh tread from the other side might have helped.

Really looking forward to Roebling Road where I first started out. I've had 5 days at Road Atlanta and 2 at Barber since I've been there. That track seems like a piece of cake compared to the others. It will be fun to go fast again. Might even see 150 on the Roebling straight

sperkins

Who are you running with at Roebling? I'd like to tag along if I don't kill the new car at CMP.

Oh yeah....it's always a good idea to cross rotate the tires. I usually do it every other session if time allows.

kwhiteside

Chin

Events coming soon...


Nov 1-2VIR (Full course)Nov 21-22Roebling RoadNov 28-29Road Atlanta