Actually, not too wierd at all. I have developed more comfort in braking than I do with handling power oversteer conditions. I can steer with my throttle while approaching the apex, but haven't quite got the power oversteer down yet. That is an area of car control I know I need some work on.

Also, are you running a staggered set up? I suspect, to some degree, that 245/275 setup contributes to more scrubbing at the front. I see 1g in braking and cornering while only half of that in acceleration. If I don't drift my rear out, wouldn't that cause my fronts to wear out before the rears?

 

Me too. My rears are completely worn out while the fronts still have some tread left. If the fronts are going too quickly, that means he's getting a lot of push. He's probably going into the turns too slow and accelerating out too early. That, or his car is not set up right. (would be my guess)

 

Actually, I usually have more of a problem going in too fast than too slow, and a lot of times, I have to lift a bit mid-turn to rotate the car enough to make the apex. I don't get much push on exit...mostly on entry, which to me, means I'm entering the turn too hot. I believe most cars, even those set up properly will push if the turn is entered too hot.

On the other hand, I went off course on the last track day when my rear end came around on exit. Instructors suggested to me that I must have lifted, but I'm pretty sure that I gave it too much gas too early in the turn, and power oversteered the sucker into the weeds..

My current set up feels much better than with the stock setup, which IMO, is amazingly crappy at limit!!! I would experience push on entry AND exit like you described, and that car was not very responsive to throttle-induced rotation. The front OEM tires looked butchered up compared to the rears, which barely looked scrubbed.

After this set burns out, I'll be trying 255 up front instead of 245. It may allow more equal wear.

 

I'm writting a big reply...

Be back in a few minutes...

 

Yeah, going into turns too hot will make you push in entry, because you're trying to brake and turn at the same time, overloading the front tires. Instead of upping the front tire size so much, you should consider braking earlier before the turn to get the car slowed enough so that when you turn the steering wheel, you're not going to overload the grip of the fronts too quickly. You can trail brake a bit to maintain weight on the front tires, but it's not a good idea to dive into the turns.

Try it out next time to see if it helps with your understeer problem. I have the stock size up front, and don't experience very much understeer exept for the entry of really tight hairpins.

One problem of running too much width up front is upsetting the brake balance, making the rear lock too easily--but this isn't too much of an issue on our cars because VDC doesn't go off for braking unless you remove the yaw sensor.

 

I’m also staggered at 235 and 255.

275 is very wide. Is your car pretty much stock? Except for that red sway bar? Is it an adjustable one? My guess is your car has too much grip on the rear. And the solution might not be to increase width of the front tires but to reduce the rears.

With so much grip at the rear, the car probably has a huge tendency to understeer. You have to work harder the front ones to match the rear. Thus, the extra wear of the fronts.

You are right, excessive speed at the corner entry is often the cause of initial understeer. Trail braking should solve that. In your case, it might not work, again because of lots of rear grip. Does it get “twitchy” on threshold braking? I’m guessing your car is very stable under braking (1g is a LOT for a street car) but will loose front grip easily with steering input? Mine is dancing under heavy braking (from 100+ mph). No problem turning in!

You hint at mid-corner understeer also. This should not happen. Try your front sway bar at a lower setting. Or increase the rear tire pressure, but be careful with your use of the gas pedal is you do the later.

Wide tires do not allow as much slip angle than slimmer ones. They will snap when you go over the limit. Might explain your surprise oversteer?

Getting the rear end semi-loose is the whole point of going to the race track. But it’s something we have to build up to gradually. Increasing the overall grip level of the car will mean you will go a lot faster before you can explore the “brink of loosing it” state of driving. With wide tires, the margin for error is smaller (less slip angle).

Since we’re not racing, I prefer to have less grip but to spend more time on the edge (and on a wider edge!). I learned to drive on a track in Italy. Plenty of race tracks with really fast corners (flat out, lift and you spin!) with crazy instructors. So I quickly became comfortable with a slipping car at speed. It’s sooo much fun!


Order this little book:
http://www.sae.org/servlets/productD...&PROD_CD=B-789

Kind of a cheat book for track guys!

edited a bit my post...

 

I've been away on vacation in Maine and Quebec, so couldn't respond sooner. Besides the wheels, hotchkis springs and adjustible sways, the car is pretty much stock. I started with a popular size 245/275, but it did seem like too much stagger, and that's why I've got 255 to go on up front the the next set of tires. I would consider reducing the rears, but my rim is 10.5 wide, which practically necessitates a 275 minimum. I tend to overdo a few things here and there and "grow into the shoe" as opposed to the other way around.

I have just finished reading "Speed Secrets" by Ross Bentley. I really liked it. What I got out of it is that I should be trail braking into turns, as you have hinted. I haven't been trail braking as I've been only tracking for the past year, and am working on a few other fundamentals such as smooth braking, steering, and throttle input, as well as heel-toeing technique. Adding trail braking into the equation so early on would probably hinder my progress elsewhere. Before the Z, I had been driving a 110hp front wheel drive sentra on the street for 10 years, so there has been quite a bit of learning and adaptation.

I do not get twitchiness under braking. The car is quite stable. My brake balance is pushed forward from the poor combination of Cobalt VR Spec front and Hawk HPS rear. The hawks are nearly nonexistant in its contribution to braking. Still, I get around 1g in braking and cornering, not including some instantaneous spikes into 1.2g. The Gtech unit I have seems pretty accurate, as I've done a few basic tests to confirm its accuracy.

I can control the oversteer at lower speeds, but it's the 70+mph turns that I haven't got down pat. It's defintely a 'comfort' thing. I've gone back to stock tires for a track day to increase my slip angle and margin for error, but I ended up pushing the car all over the place. Balance was so poor, that I ended up not enjoying the day at all. For some reason, the car didn't seem responsive to throttle steering.

I'm going to decrease my front air pressure because the cold pressures of 40psi(f)/37psi(r) I use is purely based on load capacity, and not maximum grip or balance. The high front pressure certainly does not help with the overall balance and understeer, but I can rotate the car with the throttle. I have yet to use a pyrometer to determine optimal pressure, but will someday when I get a hold of one.

I'm slowly getting more comfortable with getting to the edge with this setup. I'm starting to look into getting RA-1's, but plan to do half a dozen more track days with street tires before moving onto tires that don't chunk up so much. Also, I just ordered the Carroll Shelby book...thanks for the link

What I found interesting in my reading is that I was carrying too much speed without trail braking. Supposedly, I should still be on the brakes when I turn in, and quickly, but smoothly taper that brake pressure off before going into pure cornering grip, and then gradually tapering on the throttle as soon as possible. I had the impression that all braking had to be done before turn-in so that maximum cornering grip would be available for turn-in...well, that's not so.

 

it is all about alignment, and more specifically, toe. Lot's of places "say" they do it properly, and will even give you a printout saying they did it properly. I have found out the hardway, after dropping $400, yes $400 on 4 alignements from 4 different places (1 place did it twice) to find out all of them were using machines that were woefully out of spec. What's worse, is that all the machines were Hunter's that are at most 4-5 years old. Lots of places are just plain LAZY, and will literally fudge the numbers to tell you it is "in spec", and when you complain about tire wear or the car not tracking straight, blame it on your "lowered" suspension.

Before my latest round of suspension mods earlier this year (a arms and rear toe arms/camber arms), we had done an alignment at the shop, without a rack, using the same method we use on the race care (we run BMW's) at the track - good old string and a level Since camber was not adjustable on my car, we were merely setting toe and rideheight. At the end of the day, I got 31k out of my T1S's via this method, and those that know me, know I do not baby the car at all. The trick, as I said, is getting toe spot on and making sure rideheight is even side to side (easy to do with coilovers, impossible with springs). These cars have a VERY stiff chassis....changes you make to the front in terms of height impact the back in a big way, and the more you lower them, the more out of spec things become.

So, I called up a friends shop in CT - yep, a whole different state, to get my alignment done. Cost me $75 to take the ferry there, and drove the car home (1.5 hours), but it was well worth it. Despite my "lowered" car, everything on it is adjustable now - from front camber, to rear camber and toe with my mods below. The first thing we did was baseline measure the car to see where we were starting off with. Despite the previous shop "realigning" the car the day before, the baseline at my friends shop was no where near any of the printouts I had received from previous alignments. In other words, everyone up to this point was totally full of sh&t. I knew the car had not felt "right", and this confirmed it. Now, my friends shop is a high end dealership in CT (Ferrari and Maserati), but they also happent o run in the 360 Challenge Cup, and service several Challenge car drivers. As such, their equiment is top notch, and they maintain it very regularly. My car was on the rack for 2 hours to get everything perfect, and perfect was the net result.

I swapped to S03's this spring when we did the other suspension mods (a arms up front and camber arms/toe arms in the rear), and now with around 9k since that time, tire wear is perfectly even side to side (checked it in detail yesterday). This despite the fact that I am running below the factory tire pressure specs. I should be running 35 front/rear (or a slight variation thereof), but am running 32 and 31 psi front to back, as the S03's are just WAY too harsh over bumps at anything higher.

 

Had Toyo T1S proxis on my old suby, best 10,000Kms of driving I ever did with her, but damn, those tires dont last long at all!

 

It’s Caroll Smith, not Shelby! ;-)

Trail braking is the key to going fast with a street based race car. I was surprised by the extreme cautions with which instructors in Canada and the States approach that concept. It was one of the first things, after seating position, the Italian instructors told us. “Stay a bit on the brakes for your turn-in, otherwise you’ll go straight!”

The sad truth to that is that the average North American driver is a complete noob to car control… Europeans drive fast all the time. Hence the different approach.

I really like Ross Bentley also. I learned there is a fourth book in his Speed Secret series. I’ll order that today. I like his psychological approach to the whole thing.

Keith Codes is also a good author. His is for motorcycle racing, but the concepts he explains on track/road reading and “brain power” resource management in The Soft Science of Road Racing Motorcycle are helpful.

But the single best resource I’ve found so far, is discussing driving experience with fellow drivers (much like one we’re having now). New ideas and new concepts emerge that way and we all benefit from it. Regardless of how fast everybody is, we all miss some things when we drive on a track. Having a former rally driver and a test driver for Maseratti amongst your friends also help…

OT: Where did you go in Quebec ?

Z1 Perf, nice comment. I'll check that out !

 

Yeah, practically every instructor I drove with kept emphasizing "get all your braking done during the straight". It's understandable, however, because it's very easy to get yourself into trouble if you don't know what you're doing with trail braking. I'd wager that most people new to the concept would overbrake into the turns and plow into whatever is in front of them.

Once you do start understanding the process, however, it's cool just how quickly the car reacts when there's just the right amount of weight over the front.

 

After the last alignment was performed on my car (I've had two done so far), I found the lock nuts on my rear camber arms completely loose! This was at a Les Schwab center. I've considered, on several occasions, purchasing Smart Strings for around $400, and doing some of the alignment myself, but since very few on these boards have experience with this unit, I am hesitant to purchase the system. Camber is quite easy to measure and adjust, but toe and caster takes a bit more effort.

If I can get 22k miles and 6 track days on these tires, I'd say these tires are awesome, and wouldn't hesitate to recommend them (along with a proper alignment).

 

It is understandable. If I was an instructor, I wouldn't want to show a newbie how to trail brake because of the high probability to apply too much trail braking, and subsequently causing the tail end to come around.

There are turns that are more suited for trail braking, and a high speed sweeper is probably not one I'll be learning on.

 

check my new sticky thread to avoid this problem...

https://my350z.com/forum/brakes-and-suspension-diy/137762-how-to-rotate-staggered-directional-tires.html

 

My Falkens are asymmetrical. I just swap the wheels left to right.

 

unfortunatly that will NOT help inner tire wear...

 

It will help a bit, by changing the leading edge of the thread blocks.

Not by much, but every bit helps !

 

Funny how my "backwards" alignment has gotten me to 23K so far on my stock tires and still climbing. I've got the reverse of what Nissan recommends, toe-out in the front and toe-in in the rear. Mr rears are nearing their end (having too much fun with the nismo lsd) and my fronts should take me up to 30K miles. No feathering what so ever and fairly even tire wear up front. My rears are wearing a little faster on the inside but not enough to lessen their life.

I totally agree with the fact that you need to get an alignment from a reputable place who frequently calibrate their machines. When my car was aligned at unitech racing (the old fashioned way but with lasers instead of strings) I was amazed at how stable and straight my car felt. They even rolled the car back and forth between each adjustment make sure everthing was settled. I wish I had my own pit crew..

 

caster is not adjustable on the car so no need to worry about it...it ends up where it ends up. Despite my rideheight, caster is still within spec

 

I have the T1-S w/ about 10,000 miles on them. Filled 35 cold front/rear for normal driving. That wear looks spot on when compared to mine.