Kolia

iTrader: (2)

I’ve been thinking of my recent track event at MidOhio with a bad taste in my mouth. First time on r-compound tires, I was expecting to see an appreciable improvement of my lap times. It didn’t quite go like that…

The new surface at MidOhio might be accountable for the 1 second I ended up loosing. Best lap time was 1:53.00 vs last years best of 1:52.00. But then I was running on street tires (Falken Azenis 235/40R18 – 255/40R18). My first session was incredibly slow at 2:06.00 !!!

So, what happened? Simply put, I was distracted and uncomfortable with the car’s behavior. The car felt totally different. Pushing my boundaries in these conditions was not something I was willing to do.

Here’s my car’s setup:
’05 350Z Track
Cobalt Friction Spec VR brake pads all around
Toyo RA1 on 5Zigens wheels. 255/40R17 on 17x9.0 +30 (front)
275/40R17 on 17x10.0 +30 (rear)

Here are my findings:

Electronics
These wheels are under driven ~4% front and rear with a 2.5% stagger. I thought the electronics would be happy with that. Turns out that NO, the ABS was having a fit any time I tried to trailbrake. Basically, any steering input while trailing the brakes would set off the ABS on the front inner wheel. Upsetting the car’s balance terribly, generating massive understeer. Any bump would do the same. It was no fun at all and pretty scary. The natural reaction to that was to go easier on the brakes, which of course just made things worst.
It took me a while to convince myself to take the whole ABS/TCS/VDC unit off line and drive on my own. I took it really easy on the next session with no electronics, and lap time dropped a full 4 seconds.

Suspension/Handling
The car was doing some pretty nerve racking stuff on corner exit. Once past the apex, straightening the steering and getting back on power the car felt camped in a set. Once I got the steering pointing straight ahead, the car brought the weight transfer farter and would suddenly dart toward the outside curb. This was most evident in turn 1 where you have to cross back across the track to prepare for turn 2.

What I think is happening (input on that is welcomed) is I’m getting too much suspension travel and not enough rebound damping. Combined with a good amount of bump steer, the car basically turns out on exit. The fact that the tire combination keeps the car biased towards understeer, meaning more steering input for a given turn radius, didn’t help.

I was probably choking the exit too. Forcing the car back across the track in an “unnatural” way.

As for the overall balance of the car, it was definitely understeering. I had to really provoque it and throw the car into a corner in order to carry descent speed. Not very elegant! Not being able to adjust the front camber only compounded the issue. The outside of the front left tire took the brunt of the weight of the car as it rolled onto it.

In conclusion, I found that running 255/40R17 and 275/40R17 tires made for tons of understeer, rolling of the outside front tire’s side wall and worst of all, a bouncy car that darts left and right and can’t use ABS.

I have some ideas as to how I might address these issues. But I’d like to have a little brain storming session as to the possible causes and solutions you guys might have.

first350

iTrader: (24)

Wow...I have a very similar set-up and absolutley loved it. The main difference is that I also have suspension mods...

car: '05 Enthusiast
mods:
-Hotckis TVS 1 (springs / sways)
-Enkei 17X9.5 (+35mm) w/ 255 front, 275 rear Toyo RA-1's
-Raybestos st 41/43 pads
-intake/exhaust

I found that the car handled very well (neutral) and I never had a problem with the ABS kicking in...but I try to get all of my braking done before my turn-in.

what tire pressures were you running? (I start around 30 cold, and they get to 40 after a track session)

-Peter

christoc

iTrader: (2)

Peter, there's a pretty big difference in brake setups there, from an 05 track to an 05 enthusiast. That could make a difference with the ABS troubles, but from my experience I would think that the enthusiast would have more brake issues than the track.

daveh

iTrader: (9)

I can speak to this since tires were the first thing I threw on the car. Once you step up to an R tire, you uncover all kinds of deficiencies with the stock shocks. Take a trip to 350evo and have them fix you up with sways control arms and konis. You will have a different car.
In terms of the ABS, do you think it was kicking in because you were pushing harder and actually locking up wheels? R compounds have different braking characteristics than a street tire. My ABS will also kick in if I am too aggressive with trail braking. If I am smooth, it will usually be ok. I've got same sized tires all around but one wouldn't think that would make a difference since my diameters are also different than stock.
Seriously though the stock shocks are your biggest hinderance. Most street racer type folks will say that sways will change the car the most, but if you are truly driving at 10/10ths, I felt like the shocks played the biggest part in my at the limit handling.

Kolia

iTrader: (2)

Cold tire pressure was:
FL: 40 FR:38
RL:38 RR:38

Which is much higher than what you’re running!

Below that pressure I would roll badly on the front left and the tires would overheat and get greasy. I left a couple of big tire marks powering out of turns to keep the car turning…

daveh

iTrader: (9)

Toyo suggests low 40's hot. Sounds like you need way more front camber. When I upgraded to the evo control arms, I was actually oversteering with my newly found front grip.

You are at a crossroads my friend. You are asking the stock bits to do more than they were intended. I was there a year and half ago.

Rob Hines

iTrader: (3)

The first thing that I would do is to reduce your tire pressure. I suspect that 30-32 would be a good cold starting point for the Toyos. The construction of the Toyos is different than the Kumho V710s that I run on my Z, but as a point of reference, I typically start the Kumhos at around 22 cold and aim for 37-38 hot.

If you are thinking of upgrading your suspension, I'd suggest that you look at some good shocks first and then consider springs / bars. I am using TC Kline's DA Konis and have been very happy with them. Now that bump canisters are allowed in T2, I am considering upgrading to JRZs or Motons. $$$.

You mentioned lack of negative camber - that is an issue on these cars since there is no stock way to adjust front camber. If you choose to go with shorter springs, one of the results is that you will gain negative camber. You could also buy one of the camber adjustment kits on the market too.

Hope this helps somewhat...

-Rob

drumma022

iTrader: (4)

SCC found similar results back on their project 350z. Ive bookmarked this link since it has some great info.

http://www.sportcompactcarweb.com/pr...n_350z_part_2/

Similar findings on the understeer issue and they decided to run 275 all around to help out. It is a great article to reference to.

With my current setup and some decreasing radius turn testing, I have found that even with a simple off throttle turn-in the ABS will freak out. It is more forceful when trail braking like you had mentioned. I find that when you keep even the smallest amount of throttle in, it is MUCH better. (Even if the car is still decelerating)

**I have an enthusiast and street tires -- I am soon mounting 255/40 and 275/40 for the next track event and I suspect similar results**

zillinois

iTrader: (6)

The stock suspension sucks tookus in the corners and bumps. Eats outer front tires for breakfast. Lots more g's on the R's. No solution to the stock suspension other than to get rid of it.

Although, you could run a couple psi higher pressure in the rear tires than the front.

Aftermarket sways would likely reduce some of the exit problems you were experiencing, but it will also, if you keep it, likely make the ABS problems worse.

Kolia

iTrader: (2)

New dampers is the next upgrade in line. The TCKline’s DA Konis look great but are a bit too expensive for now. Plus I have a hard time having them return my calls. I want to keep the same ride height for now since I use the car on the street a lot. I might go for the SA that 350Evo offers. Or some other adjustable ones. I was hoping to postpone that purchase until later this year… Damn!

Tire pressure is another puzzle. I started lapping at about 34psi all around and it didn’t feel right. More air helped. I’ll try going the other direction next time.

Thanks for the inputs guys

undercat

do you check your tire pressure after lapping to see what you're running hot? also do you check your tire temps across the width to see where you're heating up more?

i looked up that Toyo recommends (as daveh said)

Dry Conditions
Front Drive - Starting minimum 24 psi.
Rear Drive - Starting minimum 18 psi.
Goal - 41 to 43 psi (hot)

I think you need more camber too.

MoodDude

Kolia,
I hope my first experience on my new track tires isn't the same, in a week and a half. I ended up with the cups with 265 front and 295 rear. Yet, none of my suspension is stock (coilovers, A-Arms, brakes, ...)
Let us know your solution.

Nano

iTrader: (1)

imho, same tires all around should definitely be a more ballanced setup (on stock suspension).

staggered wheels + staggered tires might prove too much.

daveh

iTrader: (9)

I actually think a staggered setup is ideal once everything else is sorted out. The only reason I am running the same size all around is so I can rotate them and save some money since I do so many track days a year.

Nano

iTrader: (1)

But shouldn't one upgrade tires and wheels first, and then sort out suspension?

Kolia

iTrader: (2)

Then you shouldn’t have any problem getting the correct camber. I’m curious to hear about the Michelin Cups

Do you have a baseline setup for your suspension? GRM of May has a neat article about damper adjustment, including a “recipe” detailing steps to get a good damping setting. I can scan it if you don’t have it.

Staggered with same width all around sound like a perfect combo. Steven (?) is running that in his Z and has no ABS issue, despite being pretty brutal on the brake pedal! His suspension is all tricked out too.

undercat, I did take the tire pressure after each session. But I don’t have it in my notes. I think it was near 46-48psi. A needle pyrometer is on my wish tool list.

I do need more negative camber up front. I think I won’t be able to run a lower tire pressure before this is fixed, as the tire just rolls on it’s side wall.

I’m trying to weight which parts to change first. Correct the damping or alignment?

Has anybody tried to shim the steering to correct/change the bump steer?

EnthuZ

iTrader: (2)

Kolia, are you still running OEM sway bars? I would address them ASAP. They will keep the tire tread a lot flatter & allow you to dial out understeer. I like my Hodgekis bars, which work well with the stock suspension &/or with stiffer springs.

I'll be trying my full tread RA1's the same sizes as you have tomorrow at Road America. A hoped for big step up from my non-staggered RT-615's. Weather looks awful, but I hope to put a couple heat cycles in them.

My enthusiast doesn't have VDC, but I do have TCS, which I always turn off at the track.

Kolia

iTrader: (2)

If you’re running on full thread RA1, have no fear of the rain. As long as you can channel the water though the grooves, they’ll stick very wheel. Much better than the RT-615 in fact!

I was amazed by the grip they offered at MidOhio in relatively heavy rain. Still didn’t push faster than 70 mph, but very stable still.

I’ve always been against playing with roll-bars as a first suspension fix. Pig headed certainly, but I don’t like linking the left and right wheels. It’s really bad on the street when the ride gets bumpy. My impression is that if damping is currently insufficient, augmenting the “virtual” spring rate of the suspension would compound the problem. I don’t know if the reduction in the front outside tire’s loading would be beneficial enough to compensate the lack of damping/camber.

MoodDude

Wow - someone else on this forum actually reads GRM? I have that article, great write up. Makes you relize just how much time it takes to set a suspension correctly!!! I have set up the suspension now for a perfect 50/50 cross, 50/50 left/right, and 51/49 front/back. I have -1.5 camber all the way around with zero toe. I am waiting for my evo A-Arms to play with my front camber. Since my coilovers are just dampening and rebound in the same adjustment - I run them really stiff in front and about 1/2 stiffness in the rear.
I won't be able to take tiretemps next week due to how the event is handled, yet two weeks after I will be at a private track event and hope to tune the suspension.

Kolia - I don't know if you want to drive down to Alabama - but I will be at the CHIN event at Barber Motorsports Park, then you can see the Cups in action.

EnthuZ

iTrader: (2)

Stiffer sways are not the best solution, but they work!

I just went for my 1st drive in the rain on the RA1's to the bookstore to find the GRM May issue. D*mn, the June issue is out. Could you please scan the shock article for me and send to: EnthuZ@BCRLtd.net I need help getting my DA Truechoice coilovers dialed in.

The RA1's seemed pretty good on the brief drive.