This is the same issues that drifters have when entering a turn too hard or too late.... as a result, the tires are turned and your going too fast and suddenly, you decide to brake to compensate but instead you lock and slide forwards.. ie understeer.

Dont bake, just release the gas and correct. No mater the set up on your Z.. its roadtime that corrects understeer. Some cars have more than others... a good driver learns his car and compensates for error.

...Im still learning!

 

Wow, quite a debate...

Well, I did exactly what was suggested here (slow down) on the next day (there were 2 events: Saturday and Sunday) and my times dropped and my tires sure thanked me.

So, I will keep on working on the technique. On track, I find the car excellent and well-balanced as is. It's probably since I've been around the local track a few times. AutoX course was a different experience.

That said, I'm still hungry for grip, so now I'm off to searching threads with R-compound recommendations and some lightweight 17" wheels. That is if I can figure out how to stuff 4 of them into the Z. ...but I digress.

 

I have all 4 the same with understeer as well. I did not say that your understeer is 100% cured with 4 of the same tires. Come on.

The Z is a SIFO car. Find the straight line. heh

 

Just curious as to the reasoning behind running a higher front pressure than rear. I've always read/heard that running lower pressures will increase the contact patch, thus increasing grip, which would mean that the OP's idea of dropping front pressure makes sense.

However, is your reasoning, running a higher pressure in the front will prevent gaining camber throughout the corner due to the tightness of autox corners? Sidenote, pedalfaster's post was spot on and i'm talking about pressures relative to optimal.

 

Everything I've read in the last 20+ years of driving says otherwise. Of course we are talking within optimum psi range.

Here's a few I just quickly searched:

http://www.tirerack.com/tires/tirete....jsp?techid=58
http://www.wtrscca.org/tech.htm
https://www.rsracing.com/tech-tire.htm

 

Very informative links, thank you. Just printed some of that off to take to the track with me this coming weekend. We'll see how she responds.

 

Right, these articles are simply repeating what you guys said about how to cure certain handling characteristics. I'm wondering if someone could explain the physics behind this reasoning. I did a quick search on google using tire,pressure,physics, and handling and other combinations... but wasn't coming up with anything decent.

So basically, what's going on in my head is totally contrary to what i'm reading and I'm hoping to get that clarified. Why would increasing tire pressure relative to optimal give you more grip? Increasing tire pressure will create a kind of ballooning effect which will decrease the size of the contact patch. Thus wouldn't dropping the pressure increase the contact patch and grip? Or is this countered by the fact that with lower pressures, the tire basically gets softer and rolls over onto the sidewall?

Really hoping someone can explain the physics. Thanks in advance.

*edit: Just read that increasing tire pressure increases the load capacity of the tire, which is why you get better grip. Could someone explain what this is? I can it means that the tire will handle more load, but the weight of car is fixed... While a crisper turn in is possible, how can you get more grip?

 

It doesn't, that's why I use 33-34psi with great success. THe only drawback is that I wear the tires fast because I can lean on the sidewall. Sure it costed me a few tires, but I will take it if it means running with the big boys in a bone stock BS car.

 

Camber (-3 degrees in front and -2 in the rear), sways, coilovers, and same size tires help me get rid of alot of understeer. My car can still understeer (depending on my setup) if I over drive the car into a corner but the corner exit speeds are alot higher before I hit understeer.

 

Does that mean you're going to Nationals in Topeka this year?

 

I find the tire pressure recommandations for over/under steer on these sites to be very confusing and contrary to what I usually do...

 

OK guys, regarding tire pressures...

Within an optimum tire pressure range as determined through testing and taking tire temps, handling balance can be adjusted in subtle ways using tire pressures. Making gross changes in tire pressures (5 psi or more) means you're not in the optimum tire pressure range and you're scrambling to find something close.

A tire is a spring just like the coil springs in the suspension. Depending on the tire's construction, each psi of air is equal to 20 to 32 lb. in. of spring rate with bias play tires at the lower end of that number and radials with short sidewalls at the high end.

Assuming you're in the proper tire presure range, a change in 2 psi on typical tires for our 350Z works out to a spring rate change of 64 lb. in. A 5 psi change works out to 160 lb. in. and shows you why if you're making such large tire pressure changes you missed the setup at the start.

 

Not Topeka, but I can certainly attend the regional event if I want to. It's a matter of buying a set of new 710s to run autox or a set of other tires to do time trials. I value my TT wins more than autox wins, so I am not going to bend over backward just to get one competitive event in for the year. Last time I checked, I am still slightly ahead of a former national champ in BS this year on my "underflated" RA1 in autox this year. The lead is virtually nothing now, but the fight is still up in the air. After five events, if you add up the best run of all the events, the difference is .5 sec or something.

John nailed it on the spot. If you have to go nuts on the tire pressure, chances are that your setup is wrong to begin with.

 

Running non stagger is a HUGE improvement to getting more front bite.

Second most effective improvement is adding front camber. Good news is that adding more front camber allows an even wider non-stagger setup.

Personally, I preferred zero toe front & rear.

 

-lots of ppl say to stay away from R-comps if you're still relativley new...it developes better habits by using street tires.

-I've fit 4 275/40/17s in the Z...it's easy to do, but takes more time for loading/unloading, and also occupies the front passenger seat.

 

Your tires can only to 100% of one thing at a time. Remember everything about road course's and AutoX is weight transfer.

The above in the probably the best advice you can get...don't over drive the car. Remember, it's usually the indian, not the arrows. However, you can set your car up to handle better. Perhaps a camber adjustment would help, too?

 

Speaking of camber adjustment - what about those people who daily drive the Z. I haven't really seen anything mentioned about camber adjustments that are good for autocross and still streetable with respect to tire wear.

The factory specs for camber are Min -1.33º, Nom -0.58º, Max 0.17º. At my last alignment, I was at about -1º. I'd like to get closer to the min allowable (-1.3) but wonder what effect it's going to have on my daily driver tires. Anybody out there running < -1.5 who can comment on that?

 

The lazy guy here is still on -3.0 degrees and it's a killa' for the tires !!!

Drove it for a couple of hundred miles and the wear is visible. I'll straighten that for my ride to Montreal next week. Driving the Civic in the mean time.

 

1.7 seems to be the limit before they wear.

 

I don't want to come across as picking a fight here, but your comment about running with the "big boys" hit my virtual funny bone. Forgive me for saying so, but regional guys who say they can run with the best at the national level but won't actually come out to prove it are a dime a dozen (witness this guy).

Guys who won championships twenty two years ago aren't necessarily still fast; we have a "vintage" national champion in our region too, and he's usually several seconds behind the current national champions and contenders.

So: I'd suggest attending the Devens Tour to see how you stack up against today's national-level drivers. Otherwise you're just talking about being able to keep up. Or don't-- up to you whether you want to back up the talk.