Sat-Sun was my first real competitive event this year (Autocross) and I got a real surprise going from an NT-01 to Z214 C71 compound. The weather was not the best and I had a lot of trouble getting any heat in the rears and keeping the car controllable, this kind of surprised me coming from a tire that is supposed to require a lot more heat. The only change in suspension from last year on the nittos was an additional degree of negative camber in the rear (now 2.5) to fit my street tires, but I would have expected the opposite especially with my setup.

Camber challenged EK front 1.5 deg
Rear camber 2.5
Toe 0 front and rear
12k fronts
10k rear
Stock EX front bar
ASR rear bar full soft
225/45/15 z214 c71 compound on 949 8" rims

By all aspects the car "should" understeer more than be as tail happy as it is now.

 

Just at a glance it looks like your rear camber could be a lower than it is now... it's possible you're not using all of the contact patch and simply losing rear grip.. which will also impact your tire temps a little bit. Do you have access to a pyrometer to check tire temps between runs?

If youre temps are somewhat stable... then maybe a little bit of toe-in in the rear? I'm just thinking alignment settings not so much changing hardware.

 

I plan to address the camber issue this week if possible and get re-aligned, it's mainly that way to keep my street tires off the fenders.

 

Tire pressures? Shock setting? Bushing condition?

 

I had the same experience going from 17 in. RA1 to BFG R1 but on a Honda Challenge car with a very different setup than you OP(16K/20K),was like driving a rear wheel drive car, learned alot though, but the tire has a stiffer sidewall and carcass so it is spring rate remember that so maybe need to be less agro with the rear setup. Possibly in an auto-x enviro where you need quick heat,Toe in a tad and let the tire slide so it will stablize the rear and also build heat.just my $.02

 

remember also that the 214 has way more grip and if you don't have the spring rate to match the tire you are going to have a lot of body roll and lose grip.
I think your springs are way to soft for those tires.

 

Springs may be a bit soft in the front, I was told I was once again picking up a rear around a good portion of the track. I have a pair of 14k's I can give a shot to see if there is any improvement.

Tire pressures ended up 31 front 26 rears on my final run. The autocross events I participate in most tend to be a bit abnormal and carry a bit more speed which may be why my setup is a little different from the norm.

This is a typical layout, I attend smaller courses as well but tend to focus and enjoy this location the most.

 

I dont know if Hankook has a similar "booklet" for the Z214, but I reference this for my R1's and it seems to be accurate from what I've tried
http://www.tirerack.com/images/tires...ce_R1_care.pdf

 

I just don't think that a 40 second run would be enough to get any heath in the tires for them to work properly. I'm not familiar with autocross since I have never even seen one event.
At a l race track it takes about 2-3 laps of going really fast to get them to operate properly. I don't see how you can do the same in a parking lot.
Plus the spring rates we have are way stiffer and the camber way more agressive.
I know guys that run 12 and 10 in their street cars.
I would think with those rates and r compound you would have a lot of body roll when the tire is at working temps.
your 26psi in the rear just proves that you are not getting it hot.

My 2 cents

 

If I could get a 40 second run on the track I posted I certainly wouldn't be complaining.

The c71 compound hankooks are intended for autocross use.

 

ok 1 min or 2 I really don't think that 214 and parking lots are in the same bucket but whatever.
The numbers you are posting are not adding. And you are loose. Just my opinion.

 

The Z214 C71 IS an Autocross tire, made for short runs. But like you said your not familiar with any of this.

 

It's not. I race with Midwestern Council, which runs a high speed autocross on the same track most weekends. There are many autocrossers using the autocross tires (Hankook C71, Hoosier A, even the V710 leans more toward autocross). They are not able to get the tires to optimal temperature like the race cars. However, they are able to get them to enough temperature (combined with the gripper rubber) that they are significantly faster than the hot street tires.

I believe the V710 was originally designed for the autocrossers, and now is a pretty good race tire. As Natural Aspirations noticed, the C71 and Hoosier A are both autocross tires (C51 and R sister race tires), however, both are used very commonly by the racers for qualifying and cool/cold weather races. I also think there are a lot of other variables to consider. I know it takes a little while to get my rears up to temp, but I assume a rear wheel drive car might have an easier time heating them up on a pace lap.

What were the starting cold pressures? For reference, my V710's (sorry, I have no direct experience with the Hankooks, only the Hoosiers, but I use the Kumho's now) start at 28 psi front / 30 psi rear and end about 38-40 psi after a race session. Unless you are starting out very low cold, I think this shows that you are able to get some of the heat in them (and you will benifit from this extra grip over a soft street tire), but not enough to get to the optimum working temp for the rubber. For the V710's this is about 180-220 deg F.

 

Looks as if I was adjusting my tire pressures incorrectly for the type of tire.

 

I'm curious to see how many runs you get out of Z214s in the C71 compound. Corded a set in 3 events, about 30 runs with rotating them every event. Corded all along the outside and beginning to show cords on the inside. I'm back on the NT01s now, can't afford to race running anything else.

 

C71's are super soft but really sticky. Try some C91's.

 

I've got 17 runs on them so far I'll keep count. They still have grooves

 

26psi sounds pretty low for rear pressure. Keep in mind that any pressure away from ideal, in the positive OR negative direction, will result in decreased grip. Too-low pressures can feel loose just as much (but in a different way...) as too-high pressures.

 

Without adjusting toe in the rear going less negative camber will increase toe out correct?

IE adding washers behind the rear UCA will reduce my negative camber AND result in a little toe out.

Correct?

 

yes

 

I have pro-c coilovers and found out today I've been running around with 2 shocks (front/back) in the wrong end.

Ugh.... Well got that fixed and went 14k/12k

 

**** my *** with a rusty pitchfork.... It's worse...

The car is perfectly stable on the street but I cannot get the rear to stick at all with the kooks. I can feel the rear let out mid-turn, doing my best to counter steer and/or throttle on to plant the rear (which does work if I don't outer shoot the next turn)

I'm really discouraged, I'm going to drop the rear spring back down to a 10k tonight and see if my rear bar goes any softer.

The tires are rolling to the middle of the arrows at 41f/36r, started off at 40/40 and worked my way down. Shocks were set to the middle and ended up with almost full stiff in the front and almost full soft in the rear.

I have another event tomorrow I'm going to look into a different alignment if this doesn't work out.

 

Are you doing a lot of lifting on the throttle in those corners, or is it all corners? Not trying to accuse driver error but just asking.

Why not unbolt the endlinks on the rear sway one run to see if maybe there is something else thats causing the car to act funny in corners?

 

I may be lifting some in the corners, I do my best to avoid upsetting it but it's become much much touchier.

 

Dropped the rear springs to 10k's and found I had ~ 3/8" preload in the rear bar.

Try again tomorrow....