Valkyrie

We talking about Calsonic GT-R levels? lol

Well, luckily dual wishbone cars don't need that much.

Now if only I had got my hands on a set of four 9" rims before I had ordered my new tires, I'd also be able to rotate them. But I have that option next time since I bought them anyway...

BLUE TII

iTrader: (9)

Exactly. Luckily FD has pretty good rear camber curve so we don't have to run much static rear camber.



I looked up Pettit "long track" alignment and I am . How did you run as little rear negative camber as they recommend? Shorter adjustable rear lower arms?



This shows that for your 17" wheels Pettit recommends -0.5 deg rear negative camber on the "long track" alignment.

I am at 25.5" at the rear and taking out as much rear camber as possible I can only get to -1.2 deg rear camber.

Stock alignment spec is -1.15 deg rear camber +/- 0.45 deg. This is much more negative camber than Pettit "long track" -0.5 degrees recommended for 17" wheels.

If you were on Pettit "long track" alignment on 17s you were running

Front
1/16" toe in (4/64")
-0.9 deg camber
6 deg caster

Rear
0 toe in
-0.5 deg camber

Stock alignment is-

Front
2.5/64" to 9.5/64" toe in
-0.05 to -0.50 deg camber
6.05 to 7.05 deg caster

Rear
5/64" to 12/64" toe in
-1.13 deg to -1.58 deg camber

Valkyrie

There's probably a reason Pettitt doesn't have this on their site anymore...


Also, the whole idea of using tire pressure or camber to increase or decrease under/oversteer is a completely absurd. Either the tires are optimized for grip or they're not.

In fact, the idea of using more/less sway bar to cure oversteer/understeer is actually wrong. In some cases, you can actually decrease understeer by using MORE front bar IF excessive roll is causing crazy amounts of positive camber.

There are no absolutes in suspension tuning.

BLUE TII

iTrader: (9)

Sometimes it is better to tune overall balance instead of having ultimate grip.

Sometimes it is better to tune for ultimate grip and drive under the limit so balance doesn't come into play.

Sometimes a driver prefers one of the above over the other.

Right, faster lap time is faster lap time no matter how you achieve it.

Valkyrie

Using tire pressure to change balance is a band-aid solution. Really, it should be bars and springs. And aero, if you've got it. And maybe a bit of rake.

Also, ultimate lap time isn't necessarily an absolute, either. What works for qualifying might not work for a race.

ZDan

Heh, the Pettit alignment specs are pretty out to lunch! As seen above in BlueTII's and Valkyrie's posts ^^^ Camber settings = ridic...

Even worse! Stock front camber spec is NOT appropriate for the track. You may feel more confident on the street, but with factory-spec slight POSITIVE front camber, your front tires are not doing all they could be, and will live a very short life on the track until the outer edges are corded...

Even on the street, zero or slight positive front camber is a bad idea. You might *need* that front cornering grip one day! I would want at least -1° front camber even for a street-only car. Which is actually an indication that I could/should run more negative camber...

Factory spec makes the Pettit specs almost look reasonable (aside from the ridiculousness of very different settings for different wheel diameters!).

Worth mentioning that "factory spec" is not a specific alignment, it is a broad range. Here it is: http://wright-here.net/files/manuals...suspension.pdf
Without going into every detail, here's the factory front camber spec:
front camber: *POSITIVE* 0° 5' +/- 45'
That's +0.08° +/-0.75°, a range from +0.83° to -0.67°

The only way this is happening is if you are beginning to go sorta fast and LIFT off the gas mid-corner. A big no-no... Unless you're trying to point the car IN more.

For the love of God, do NOT!

I guarantee that front camber spec is specifically to keep people who don't know how to drive out of the weeds. Totally inappropriate for the track! Or even for the street, IMO. No good reason to have zero or slight positive front camber.

Nominal factory toe-in specs of 0.1° front, 0.17° rear are workable, very close to what I'm running right now.
Nominal rear camber spec of -1.2° is fine, could go higher though... Interestingly enough this spec is not dissimilar from the Pettit spec for "long track event" for 16" wheels (DAMN those different specs for 16" 17" 18" are silly!).

I'll take a pics of my nearly used-up old track tires tomorrow and post them up. I run -3° front and -2° rear camber and wear pattern is very even, even with a lot of street miles. Which would indicate that I could/should run more negative camber...

TL/DR version: Running "factory" positive front camber at the track is a bad idea, don't do it...

BLUE TII

iTrader: (9)

The reason more negative camber is required for higher profile tires (smaller wheel diameter) is the the more tire sidewall there is the more the tire's outer sidewall rolls under the car on the outside of the vehicle inducing positive camber in relation to the straight sidewall of the inside of the same tire.

It is a real effect and if you race on 16s, 17s and 18s I am sure you have noticed you need more camber on the 50 series sidewall than the 40 series or 30 series sidewall.

On my FC it liked -2.5 to -2.75 degrees on 35 and 40 series 17s and -5 to -5.5 on 50 series 16s. I never ran 18s on the FC.

I wouldn't want to be the guy to put an exact number on the camber difference required, but it is there.

ZDan

Optimal camber differences between different makes/models/construction tires are far greater than differences between 16", 17", and 18" which are going to be very small.


In my experience, 240z with 14" wheels and 50-series tires, S2000 on 16" wheels and 45/50-series, and FD on 17" and 18" wheels and 35-40 series tires all want a lot more camber than the goofy Pettit specs for any diameter anyway... I wound up at -2° rear camber for all of the above. It could be that optimum for the Z on 14" was 2.1° and optimum for the 18" rears on the FD is -1.9°, but I wouldn't bet on them being any more different than that. And anyway, it's going to be more a function of whether you're on something like a Hoosier A7 vs. Nitto NT01 vs. whatever...

The difference between optimal rear camber for the FD sure isn't what Pettit lists: -1.5° for 16", -.5° for 17", and -0.2° for 18". Ludicrous!

Also I question the differences for AutoX vs. Short Track vs. Long Track. I've heard of some autoX-ers sacrificing some front camber for improved initial turn-in response over sustained cornering grip.

IMO best to totally ignore the Pettit camber numbers...

Fritz Flynn

iTrader: (263)

Pettit info isn't bad for a novice or intermediate driver in a mostly stock FD running performance street tires which is the audience I believe they were aiming for.

I run 1/16 total front toe
2.4 front and rear camber
5 caster
Zero rear toe

780 springs 275 40 17 hankook c51 or hoosier r7s. I tend to hurt the outer edges both front and rear and the middle inside will eventually cord. I also should run a wider wheel which would help me get more out of my tires. I'm on 17 x 9.5 and really could use a 10 or 10.5.

Adj swaybars are designed to quickly change spring rates or change how the car behaves going into a corner. Raising or lowering tire pressure also effectively changes spring rates or changes how your car behaves.

An experienced driver can basically make any car push and any car oversteer with their brake and throttle control or in other words how you drive makes a big difference in how you should align your car.

If I was aligning an FD for both street and road racing with decent rubber say 275 to 285 R compound street tires and 500 pounds or more springs with your typical upgraded sways I'd set it like this.

Front camber 2 caster 6
rear camber 1.8 with zero toe

TomU

iTrader: (11)

Give me a good suspension thread over a HP thread any day

I just had my alignment done by a shop that preps spec Miatas and they set up -2 camber in the front and -1.6 in the rear (all other specs are near Pettit's) running 17" 255's RE-11s with 500 front springs and 400 rears and 290 rwhp. First day out i seemed to have overstear, but it was a damp track. Need more track time to see if i need to make any adjustments.

ZDan

But is an FD on 245/35-18s running -.8° front and -0.2° rear camber *really* equivalent the same car on 245/45-16s with -1.5° front and -1.3° rear???

The 18" Pettit camber numbers are woefully low for track work, even for a novice. The 16" camber figures are getting there, still low but workable.

But mainly it's the big difference between camber recommended for 16" vs. for 18" wheels, I find it laughable!

Ha, I thought I was the only guy running 5° caster!
We're not too far apart overall, considering our cars are very different...

Legit (natch!)

Fritz Flynn

iTrader: (263)

Yep I didn't pay any attention to the wheel sizes and only looked at the 16 inch wheel size settings.

Typically the wider the wheel the less camber you will need so possibly that's why his 17 and 18 inch wheel #s very. Also the stiffer the side wall the less camber.

You can go really deep with all this stuff but what's totally crazy to me is a 245 45 16 tire will have the same contact patch as a 285 30 18 tire. The big difference is one contact is longer than the other from side to side and the smaller tire is longer front to back. Apparently the longer side to side contact patch works better

All this stuff makes a difference and the best way to align your car is to go out and drive it and check the tire temps. I just feel them and look at them, I also don't use a torque wrench LOL.

I've heard of people using massive camber #s. You just have to go with what's working for your setup. Again with that said the pettit #s are a good start for a stock car with good street tires.

BLUE TII

iTrader: (9)

Long contact patch from tall skinny tire provides more "vertical grip" (acceleration and braking) and wide contact patch from short wide tire provides more "horizontal grip" (cornering).

That is the theory anyways.

Applied, there are many ways to skin a cat and someone may want more traction accelerating out of the corner and think of that as cornering traction but really it would actually be mostly "vertical grip".

If you want to see the affects of cornering on sidewalls (and why taller sidewalls need more camber) and you haven't worked the corners on a course check out this video.

BMW M5 "ultimate driving machine" on test rig.
Look at around 0:35sec when the tires start squealing a bit. That sidewall!

Fritz Flynn

iTrader: (263)

Yep

It all starts with matching things to the tire you use.

Valkyrie

I kind of suspect that it's bunk. Given the same downward pressure, a rectangular contact patch should produce the same grip in every direction when you ignore things like sidewall flex. Push a rectangular rubber eraser into your desk with a constant amount of force and push it sideways laterally and longitudinally. I suspect it has the same amount of resistance in every direction.


That is straight-up suspension torture ****.

Dat slip angle.

j9fd3s

iTrader: (3)

i was wondering the other day why with a race car we always go with a fat tire, but the OEM's, like Mazda always go with a bigger diameter.

i was looking at my miata, a 92 and a new one. mine was 185/60/14 and the new one is like 195/60/17 or something.

TomU

iTrader: (11)

It's form over function. People like the looks of the larger diameter wheel and a skinny tire gets better gas mileage.

adam c

iTrader: (2)

Also, a skinny tire is cheaper, and has a more comfortable ride than a tire with a short sidewall.

ptrhahn

iTrader: (9)

For OEMs, the tire/wheel diameter thing is also a function of modern designs. In part due to safety refs. Hip lines and hood lines keep getting higher, cars are taller, so larger wheels are necessary due to proportions. 19 and 20" wheels aren't uncommon now, but they won't even really fit on our cars much less not look ridiculous.

All that talk of contact patch shape to me is a bit silly. I've never heard of any racing series not limiting tire width, and certainly never heard of anyone running less than mandated tire width (though I'm sure somebody can pull some instance out of their ***). So within reason and other things being equal, wider is better, unless it ultimately is an aero drag or rolling resistance issue on a low powered car.

Fritz Flynn

iTrader: (263)

LOL

YEP

Sometimes physics doesn't make sense. If you want to go fast always run as much tire as you possibly can BUT I'll repeat you will have to change everything else to match the tire.

ZDan

Pics, sorry they are crappy...
Here is the left-side 275/35-18 rear NT01 on the car now (right-side similar). These have seen 4 track days (2 at Mosport which is CW and 2 at Palmer MA which is CCW) and about 2000 street miles. Rear camber -2°, rear toe = 0.15° (1/16") total. Wear is pretty much even across the tread.


And here are the 275/40-17 NT01 rears that I ran a couple of years ago (outside of tread is up for both). 8 track days, ~2500 street miles. Same rear camber, a smidge less rear toe-in at 0.10° total. Again, wear is very even across the tread, you can make out the ghosts of the treadwear indicating divots at the top and bottom of the bottom tire.


I am probably running a little overinflated (37-38psi hot at the track, 30-32psi cold on the street). My impressions from the even wear is that for optimal track performance I could probably use more negative camber. But I'm fine with wearing the tires evenly for overall usage...

Anyway, the 35 AR tires on 18" appear to me to be wearing in exactly the same across the tread as the 40 AR tires on 17".

*Theoretically*, perhaps lower-profile tires on larger-diameter wheels should need less camber. But in my experience on 14", 15", 16", 17", and 18" tires with aspect ratios from 35 to 55 I've never found this to be true to any significant degree (pun!). Difference is going to be on the scale of a tenth or two of a degree, IMO.

But Pettit spec doesn't mention aspect ratios or widths at all, it just blanketly prescribes -1.5° for 16" wheels, -0.5° for 17" and -0.2° for 18" for rear camber, "short track event". Those numbers are low, the 18" figure is ridiculously so, even for street-only usage.

So I'm still calling B.S. on those camber numbers. For general starting-point recommended camber at the track, I would say to start somewhere in the -2° camber range all around and know that you will likely need more than that at one or both ends of the car once you begin carrying some corner speed. -2° up to 3° can be used for street/track setup without undue uneven tire wear. In my experience...

j9fd3s

iTrader: (3)

when i built my peripheral port, i put the jets in the carb that the book said, and it ran like poop. it took a while to realize that how I wanted to tune it didn't matter, the engine told me what it wanted, and once i listened to it, and started making it happy, it runs really nicely.

the tires are the same way. 38psi looks high, but it might just look that way and be fine.

we've learned with the race car that if you make the tires happy, not only does wear improve, but the tire will give you max grip longer too. we used to do 2-3 laps and then a cool down, but with happy tire, it'll go the whole session

Valkyrie

Proper race cars are designed around a given tire.

But the average tuner car or track car.... not so much.


My next set of tires are going to be 255 all around (or whatever I can fit on 9J rims without pinching them and still fit in the fenders AND afford), so even if I dial in this setup (stock 17" size) I'll inevitably have to redo the settings.

ZDan

Generally, yes, but I also think that the actual lateral grip benefits of wider tires are often overstated, especially for street-only usage. For sure a 2800 lb. sports car doesn't *need* 285-width tires all around!

Tires do behave differently in lateral grip/slip vs. longitudinal grip/slip for a lot of reasons, including:
1. The outer sidewall influences load/contact pressure distribution and contact patch shape during cornering due to increased stiffness and change in geometry at the edge/shoulder of the tread. Under hard braking or acceleration, the highly loaded forward/aft edges of the contact patch don't see the same locally increased stiffness or local change in geometry.
2. The tire is rolling in the longitudinal direction, no relative motion relative to ground laterally until you start cornering. Change in rotational slip under braking or acceleration isn't exactly the same as change in slip angle under cornering.
3. The tire's carcass/structure has different stiffness properties in the fore/aft direction vs. left/right direction.

With a narrow tire, the load at the edge of the contact patch during cornering will be greater vs. a wider tire. During cornering the contact patch goes from being somewhat elliptical to a rounded triangle, with the outside edge being relatively overloaded. This is particularly true if you aren't running much negative camber. This effect is reduced with a wider contact patch.

Valkyrie

Track day today... It turns out my rear rode height was too high. Dropping it 10 mm took two seconds off my time.

I was short-shifting at 6000 rpms but shifting at 7000 made my car MUCH more stable. And faster in the straits, of course. I think I drove faster than I've ever driven today.... haha (127 mph). I ended up going another two seconds faster.

All in all, I beat the time I did at this track with R-comps (using street tires).