tmak26b

I never said I was the fastest driver, but then I know enough to know what works and what doesn't. If you don't think the tire pressure works, don't use it. I do have moderate success to backup what I said. If you feel like you can do better, go right ahead. Even if you don't, post anyway. It is only wrong if someone proves you wrong. If you feel like you are so good, do bring up something to backup what you said. I never post what I said to blow myself up, I simply want to tell the new guys you don't have to blow the tires up to get grip. I think I have done enough to backup what I said, now prove me wrong if you can. I am not asking about how to get rid of a nasty understeer.

The national tour isnt the goal for everybody. I have no intention to drive 1500 miles for a few silly runs against cars that are hardly stock. I would have done the regional tour if my car wasn't broken! I am perfectly fine with a car that I can drive to work, to run errands, autox, hillclimbs and track events in. If it means I am .5 sec slower than a car that is all decked out, so be it.

PedalFaster

I've trophied twice at Nationals, won a National Tour, and have around a dozen trophies at both Tours and Pros. I'm also a former member of the SCCA's Stock Advisory Committee. I have a regional championship to my name, and am usually in the top ten or fifteen in raw time in an A Stock car out of 150+ cars in a region with several current and former national champions. Despite the above, I don't feel like I'm "so good", nor would I claim to run with the big boys at the national level, because I'm not as fast as the big boys are. That's why I called you out on your statement of same.

Anyway, no need to respond. I just felt that you were talking the talk, and wanted to see if you would walk the walk.

tmak26b

That's very good for you, now prove how I am wrong about my tire pressure selection. I am not backing up my talk? The last time I checked I was racing my car. You enjoy driving around the country doing your three minutes. I enjoy driving close by to put in my miles with different events. I do okay keeping up, I would love to see you come and embarass me. I am always ready for a good challenge. The last time I got embarassed was finishing almost three seconds behind Daddio in a 30 sec course, but then I was having my first run in a brand new car with 245 miles on it. I am not going to complaint about a second overall finish on my first drive in a new car that is not mine.

PDX_Racer

iTrader: (2)

So I guess that you won't be in Topeka then, backing up your claims either on the Solo pad or the track.

tmak26b

The track? My times are listed on the web, feel free to bring your car there and compare it. I have no desire to autox around the country, it just doesn't do it for me.

rednezz

iTrader: (1)

I am running the 350Evo adjustable camber arms so I wouldn't have that problem. If you don't have adjustable arms I would still runmore than the minimum allowable of -1.3 if you are running non staggered setup. This can allow you to rotate you tires to get more life out of them.

PedalFaster

tmak26: I think you misunderstood how getting called out works. You're the one who says he's "running with the big boys in a bone stock BS car." You're the one who said "I am still slightly ahead of a former national champ in BS this year on my "underflated" RA1". If you claim to be king of the world, the onus is on you to prove it, not on the doubters to disprove it. That's got nothing to do with me -- I explicitly stated earlier in one of the threads that I'm not one of the big boys. I shouldn't have to prove that I'm as slow as I claim.

Anyway, again, I wasn't trying to pick a fight -- I was just trying to (initially) politely point out that your talk output was exceeding your results output by a large enough margin to be notable. It's up to you whether you care, but continuing to argue by doing things like challenging people to come 3000 miles from Seattle to Connecticut to show you up in your local parking lot just adds to the impression that you've got more mouth than speed.

Back to the original subject: by definition, increasing tire pressures above optimal doesn't improve grip, otherwise "optimal" wouldn't be optimal. Test to see what's optimal for your car; other people telling you what works with a different tire model is pointless since different tires require different pressures. Once you've determined pressures which provide optimal grip, you can tune the car's handling by changing pressures on the end that has too much grip (the back end of an understeering car). Note, however, that (a) this is a terrible hack, and if you have adjustments other than tire pressure, you should use them first, and (b) I should reiterate the consensus opinion of most on this thread that the problem here is likely overdriving rather than the car.

tmak26b

I never said I was the king of the world, all I said was I can keep up using tires that are "deemed" to under inflated. The whole purpose of this tread was to how to get rid of understeer and optimum tire pressure. I can backup what I said about the undeflated tires, so how are you embarassing me? I am less important because I run with five people rather than run a big event with 150 people? People have different priorities, I have no plans to drive across the country to autox.

Getting called out is if you can't backup what you said, I have results to backup what I said. You might be a great driver, but I doubt you can do circles around me. Since autox changes every event, let's compare some lap times if we ever get a chance to. I am sure my times will hold up ok. If you ever do laps here in the east coast, do share the times and I would love to see you embarass me in a similar car. Yes I am more mouth than speed, I just get lucky with a few wins here and there.

Racer86

Before I get flamed here,,,, 35 years in SCCA, Nascar, Imsa, Nasa.
1. get a tire pyrometer and get tire temps as fast as possible after a run. Do the inside edge, middle, outside edge of each tire. Most Radials like to see about 15 degree's across the tire. inner should be the hottest. The middle should be the average of the inner/ outer temps. If the center is hotter than the inner/outer, you have too much pressure, lower it for the next run. if the center temp is low, add air pressure. if the outer is too cold, you have too much neg camber, if the outer is too hot, you don't have enough neg camber. Don't try to tune your car with air pressure until you get all the other items working first. Tires usually will tell you what they want with their temp readings. Get your tire temps corrected so that you know your tires are happy with the camber settings. might have to change camber when you see how the tires are with the temp readings.
Now, Swaybars,,, antiroll bars,,,, If you have the tires working and camber is working with the tires, and tire pressures are corrected to help the temp readings,, Remember the really old racing rule. STIFF end slides first. If you have understeer, increase the rear bar rate (stiffer rear bar) Or lower the front rate, then you get to do your tire temps again to see what the tires want. Also, a tire is a big spring, lower pressures are the same as a softer spring. That is why people change the tire pressure to correct handling problems, (remember the stiff end slides first deal?) but unless you know what the tires are doing, you are really detuning the car so it may feel better, but its slower. OK, puting on my Nomex suit, let the flames begin the key to a fast car is to understand the car and what it wants. This "stuff" is not guess work, you have to do the work to find out the answers. Or just continue to plow around corners and wonder

Jrb300z

Racer86, I am by no means an expert, but your post is exactly the way I understood how to tune a car. So no flaming from me!

Fluid1

iTrader: (19)

What's your real name?

Racer86

JRB, thanks for not starting the fire on, as this site would call me, a noob.
Just trying to help a car guy with his question.
Fluid1. I thought this discussion was about tuning suspension, but if you must know, the name is Bob! What soes this have to do with camber/ caster, sway bars, tire pressure, and having fun with your car?

Fluid1

iTrader: (19)

Because I live in Charlotte and would think I'd know you if you were involved with the SCCA.

PDX_Racer

iTrader: (2)

When you have the ability (such as road racing) to "fix" suspension deficiencies, what Racer86 says is absolutely true. However, the OP was asking about AutoX, which has a much more restrictive set of rules.

When you're running stock suspension (which is required in Solo II for B Stock and B Street Prepared), you have to adjust what you can, and on the Z that is the tires (you can barely change the suspension, and even the things you can change have severe limits on what you can't do). For example, MR-2s have an upper strut mount that can be installed in two orientations, but all those who had them installed in the non-stock orientation (which gave more camber) were disqualified, even though they were the stock part installed in the stock location, but not in the stock orientation.

Quite a few of us have done the homework and have found the answers for street tires and DOT-R tires. DOT-R tires are the variable -- each brand works well in its own range of tire pressures. Street tires, on the other hand, all seem to like a very similar range of tire pressures.

And tmak26b, getting called out is backing up what you say in a known environment against competition that is running their best equipment. Even in a highly-competitive region, the best people often run year-old tires on heavier wheels with less-than-optimum suspension settings and with "stuff" still in (and on) their car. Show up at a National Tour or at the National Championships, and I'll guarantee that you'll see new (or just scrubbed-in) tires on the lightest wheels money can buy with perfect suspension settings and lightened as much as the rules allow.

How do I know this? I run in one of those regions that has the #1 driver in the nation last year, many multi-time national champions, and multiple national-level instructors (all of which have national championships or ProSolo championships in their resume), and I'll guarantee that even though they are all competitive, they all have their "national" set of parts that they only use at national-level events. As an example, our last event had rain and while several of the competitors had rain tires available on site, they chose not to run them, since they were not convenient to get to, and they may need them for a national event later this year.

So, while it's possible to beat someone at a regional event, if you never compete against them at a national event, you're simply deluding yourself.

betamotorsports

iTrader: (1)

I delude myself all the time! Here in SoCal we have many multi-time national champions spread across SS, AS, BS, CS, DS, BSP, CSP, DSP, ESP, BP, FP, and more. Sometimes my times get pretty close at regional events and I start thinking, "Hey, I might be getting good at this." Then I run a NT and these same guys that I was within "X" seconds of, suddenly put me "X * 3" seconds behinds...

PedalFaster

Let's leave tmak26b alone -- I think everyone has the data they need to form their opinions.

NGZ

iTrader: (1)

Thanks for the explanation, Racer86. But now I'm confused. It seems that there are 2 conflicting points of view about tire pressures.

I was looking at the 3 links pasted earlier:
http://www.tirerack.com/tires/tirete....jsp?techid=58
http://www.wtrscca.org/tech.htm
https://www.rsracing.com/tech-tire.htm
and I concluded from those pages that tire pressure works in the unintuitive way (at least to me), compared to springs.

With springs, it seems logical: softer front to decrease understeer or increase oversteer. But for tire pressure, the 3 links say that if tire temps are optimum, increase front tire pressure to decrease understeer or increase oversteer. So it conflicts with your "tires are like springs" analogy.

Which is the correct answer for tire pressures?

Chishifu asked about this a few posts back:
Anyone know the physics behind increasing tire pressure = increasing oversteer (all else being optimum)?

Racer86

Ngz, all good info on your links. We have to assume that your tires were working well before you can say a pressure change will do what you want it to. If the tire is at street level pressures,with understeer, and you raise the pressure and it still understeers, the tire were not at the right starting pressure. tires work in a window of pressure, outside the pressure window, the tire will not work correctly. Its too far off to work. Per your links, go to the SCCA one and read more about tire temps and how they work. I understand about the SoloII rules, but tire temps are still a great way to dial the car to the track. I think it is the first thing I would do to help tune a car with limited mod's allowed.
"Tire as a spring test." Drop a mounted tire off a 6 foot ladder with 25 lbs of air and watch it bounce. Let all the air out of the tire and do the same drop off the ladder, its not going to bounce. Different spring rate! Just for fun from my old notes on Indy lites cars with Firestone tires,,,, Front tire with 15lbs pressure =970 spring rate. with 25 psi= 1370 spring rate. we needed to know that to set the ride height with ground effects and Aero loads. how much would the tire deflect and lower the car.
Fluid 1, Sorry about My answer to your question,but noob's on this site seem to get flamed for no reason. SCCA member since 1968 San Francisco Region. retired and moved near Charlotte, NC. Don't follow Scca much any more. but, I am currently rebuilding a Radical SR-3

gunslinger

Simply:

Inertia acts through the center of gravity of the car which is above the ground. Inertia affect the weight transfer. Adhesion acts through the tires which are on the ground.

There are lift forces exerted by the ground on the tires. The size of these forces determine the ability of the tire to adhere. An imbalance between the front and rear forces coupled with the inertia of the car can cause understeer of oversteer.

Now, if you increase the rear spring rate or decrease the front spring rate you transfer more weight to the front which helps tire adhesion. Therefore it follows that lowering the front tire pressure or raising the rear will reduce understeer.

Conversely, if you are in an understeer condition you can lift and cause the tire to adhere again. I'll let you think about that one. Also think about why a lower car handles better.

I'm not a national champ, but I am a physicist.

betamotorsports

iTrader: (1)

And your logic is in error if it assumes the above is always (or even most of the time) true. Stiffer springs often increase grip at the end of the car they are added to by controlling roll and camber change. The VW Golf is a prime example: Adding a huge front anti-roll bar makes the car quicker and reduces understeer. A 350Z with a high lockup LSD will have less oversteer at the limit if rear roll stiffness is increased - up to a point.

Nope. Tires ARE springs. They are air springs with a typical rate around 1,200 lb.in.