My biggest complaint is that the car sometimes (but not always?) pushes badly when I am on throttle. Like, the sensation of front grip drops away.
I assume that's the diff working, plus weight coming off the front of the car (especially when I am going fast enough for the wing to work), assuming I am not actually hitting the bump stops.
The problem isn't the understeer itself so much as that I don't know exactly

That is the rear diff working along with rear toe in.

First thing to check is static rear toe in.
I have always run 0 rear toe and after switching to OS Giken diff I have the opposite problem where the rear always wants to scribe a wider arc than the front on exit. Which I like, but doesnt work that great on narrow cone lined courses. I will be adding 1/8" total toe in rear.

Next check for things that could cause dynamic toe in on accel. The stock rear upper control arm bushes are sliding toe bushes that toe in on accel. Poly will toe in on accel (much less than stock).
You need spherical bushes on Front/Rear upper arms to eliminate the stock driver aids. Adding them to the transverse lower pick up points is more risky as bumping curbing will bend things easier.

However, I would go with aftermarket on the lateral rear trailing arm to get spherical bushing there.

 

I have spherical bushings on the lower front arms and the rear toe links, and everything else is Black series Powerflex urethane, which is rock hard.

I think I have fairly minimal rear toe, but not exactly zero.

Wait, no, rear toe is exactly zero.

I also have rear wheels with 7 mm less offset, since I don’t own two matching pairs, and 7 mm is as close as I can get without going to long studs in the front. I can switch them back and forth, though…

 

lots of good back and forth on this thread... on my favorite subject... suspension tuning.

if the posts in this thread were all by actual racers TIRE TEMPERATURES would be in every post. then pressure, then camber, then spring rates. if you are at all interested in going fast while at the same time making your car easier to drive buy a Pyrometer. the end of the Suspension Section on my site explains exactly how to use it. you are BLIND without tire temps.

SUSPENSION

properly set up your car will have different camber and pressure settings on all four corners. it will be more than 2 seconds faster than what you are running and will be easier to drive.



i will be revisiting the coil over system on my car shortly and will share some helpful info.

 

I understand why having different cambers and pressures on all four corners would make a car faster, but it was my understanding that road racers typically use symmetrical setups (or a compromise between perfectly symmetrical and ideal) because it's somewhat unpleasant to drive a car that only turns well in one direction on a road course.

I will make a point to record my temps next time. It's just a bit of a faff when you're both the driver and the head engineer. Haha.
Hopefully I can get them recorded before the tires cool off too much...

On another note, I still don't quite grok why wedge increases understeer on ovals...

 

"I understand why having different cambers and pressures on all four corners would make a car faster, but it was my understanding that road racers typically use symmetrical setups (or a compromise between perfectly symmetrical and ideal) because it's somewhat unpleasant to drive a car that only turns well in one direction on a road course."

it wasn't so much that you end up differently at each corner but more that you are adjusting so that the tire can deliver properly... by reading temps. temperatures give you, among other things, the correct tire pressure. one or two pounds of tire pressure in a tire can make a huge difference. a nice digital tire pressure gauge and pyrometer are your best friends.

i remember dynoing my first shock. i was astounded. prior to reading the printout it was just an inanimate object a black cylinder that fits on the car. the graph showed the low and high speed resistance curves. it is the same w tire temps. they will astound you and let you get tuning. once you make the changes you will then be astounded as to how different the car drives. temps tell you almost everything.

actually almost all NA road courses are clockwise so if you are wanting to win a race or set a lap record you go for inside weight. i had over 50 pounds of lead in my right rocker. but for the other 99.99% of us a 50 50 L/R weight is great. rear weight is wonderful. my FD is almost 52% rear weight. FD rear weight helps in every aspect.

 

"I will make a point to record my temps next time."

do temps first. post your tire temps and pressures after 3 laps. then we will do some tuning in this thread.

 

The "blueing" on the outer shoulder of the tire really doesn't tell you much. As Howard said, it's the tire temps that will give you objective data on what to do with springs, bars, tire pressure, camber, cross weights, etc...

Learning how to properly use a PROBE type pyrometer is also crucial for accurate data. You want to stab the tire 2-3 times before taking your first measurement, and then measuring outside, then middle, then inside tire temps. It's also crucial to NOT do a cool down lap and bring the car in hot, and then measure the temps as quickly as possible. Cool down laps will greatly affect the results.

It's amazing how some professional race engineers subscribe to the symmetrical alignment idea. However if you followed your tire temps to maximize the distribution of heat/load, you'll never end up with a symmetrical alignment or a 50/50 cross weight. Tracks are not symmetrical and there will always be a bias of loading in one direction or another, requiring different cambers and crossweights to optimize grip over the entire track.

In regards to your on throttle understeer. What LSD do you have? IMO, all Japanese LSD brands (OSG, Kaaz, Cusco, Carbonetic, etc...) are WAY too tight and act like spools. I prefer to deactivate nearly half (or more) of the clutch discs to allow for more wheel speed differential between the inside and outside tires. I'm sure you installed the diff right out of the box, which would result in more on throttle understeer in the car that you would need to adjust your setup around.

 

Right, I always preheat the probe before measuring tire temps. I probably do let them cool off too much before I am able to measure them, though.

It's a used KAAZ 1.5 way. I think it was shimmed before it went in.
I'm trying to think whether the car understeered on throttle in this particular corner before the LSD....

 

we do an asymmetrical setup at Sonoma/Infineon/Sears Point, its all right turns, so it helps to set the car up for right turns.
some of the other tracks are less sided, but there is usually a turn that helps to optimize for, and hopefully one that doesn't matter as much.

my friend and i have a really dumb process at this point, we basically just try all of the adjustments. one to find out what is best, but second to find out what does what.
its a lot of work, but when you're having some mid corner thing its nice to know you can change the rear ride height like a quarter turn (rear ride height effects camber AND toe, so its sensitive)

 

I just noticed that the protuberances in the rear arms somehow managed to punch holes in my shocks in both sides. I can’t even imagine how these two parts touched.

 

It touched from full compression of the suspension, it's not too hard to imagine the arm articulating up towards the damper body as the shocks compresses. I would grind away at the lower damper mount to make clearance for the nub on the upper control arm. Or grind down the UCA.

 

I know how it hit, I just wouldn’t have thought it could move that far before hitting the bump stops or the wheel well.

 

I'm more surprised that HKS messed up and didn't allow for more fork clearance.

 

Here are the last readings I took from my track day the other day.

FL 127 141 155 FR 153 155 147

RL 135 148 153 RR 164 169 162

Cold pressures are 25 PSI, hot around 30 PSI.

This was at a small left-turning circuit.

I still need want more front grip and response.

I think my tire temperature reading technique is bad, since I got wildly different numbers every time. I think I also got the readings backwards a few times.
A few seconds here or there makes several degrees difference.

I wonder if maybe the Kaaz diff isn't working a bit too hard, since I get a lot of understeer under power. It makes quite a bit of chatter when turning at slow speeds.

Part of the issue may simply be that the rear track width is too wide versus the front, since the offset is about 7 mm lower on each side.

 

thanks for posting your data. initially i was scratching my head but then noted your track is primarily left turns.

you car is mildly oversteering/loose. that's what i prefer. average front temp 146.3, average rear 155.1

the car is way undercambered on the important (since you are turning L) right side. you should have had not a lot of grip.

LF camber good, pressure good.

RF add 1.5 degrees additional neg camber. remove 2 pounds air

LR camber good, remove 2 pounds air

RR add 1.5 degrees additional neg camber remove 1 pound of air

.

 

Thanks.

The strange thing is that I'm not sure if I would describe it as loose.
But I don't think I ever really understand what's going on with the suspension to begin with...

I will have to see about offset bushings, because I'm right at the limit of camber you can get with the stock suspension.


I think every time I took temps, I did it in a different order, which probably skews the temperatures somewhat.
I am also a bit inconsistent in terms of readings as well.
I really need to refine my technique...

 

practice, practice, practice...

 

Just looking at my alignment specs again, and I noticed the caster was five degrees, which is below the stock specs.
This is because I've got the camber maxed at out a bit over 2.4 degrees.

I wonder if another degree or two of caster would give me the feel in the front I am looking for.

For reference, my specs are:

Front
Camber -2'43 degrees
Camber 5 degrees
Toe -1 mm

Rear
Camber -1'58" degrees
Toe 0 mm

 

I'm surprised Howard would recommend such an extreme camber change with such little information.

Your tire temps seem very low and out of the window of operation for most street tires.

Before making changes to your alignment, what was your process to measure the tire temps?

- Did you do a cool down lap or bring the car in "hot" (you can brake early and don't have to accelerate hard on straights, but cornering at 100% on the cool down lap will keep the tire temps accurate).

- How soon after coming into the pits are you measuring your temps? Are you driving around a big paddock slowly back to your area, grabbing some water to drink before measuring the temps or are you quickly jumping out and measuring them?

- You said you use a PROBE type pyrometer and preheat the needle, do you measure outside-middle-inside, or do you measure inside-middle-outside?

- how far from the edge do you take your inner and outer readings?

The smallest difference in processes make a huge difference in readings. Even at a professional level, I commonly see mistakes from mechanics that lead to drastically different temps and spreads. Even one mechanic to another can see 20*F variances in peak temp and spread. Ensuring good practices will ensure good data and good decision making.

 

The highest temperatures I recorded were 180 degrees or so on the right rear. That's probably more reflective of what the actual temperatures were, at least on the hottest tire.
I didn't mention the first two readings I did because I'm pretty sure they were basically junk data.
I tried brought it in hot-ish but not flaming hot. I wasn't cornering at 100 percent.
I jumped out of the car and tried to record them as quickly as possible, but trying to record the temps in my iphone was a somewhat frustrating process, so the whole ordeal took twice as long as it should at times.
I would say I was wildly inconsistent. After a few tries I would try to record in whatever order would allow me to type the numbers in order. On the left, it's outside-in. On the right, it's inside-out.
Occasionally I would realize I was doing it in the wrong order.
Somewhere between one and two inches. Like I said, my inconsistency was very inconsistent. There is no rubber on the exact middle of this particular tire, so it was offset to one side or another by about an inch.

 

Thanks for the feedback. It would be good to get in the habit of cornering at 100% on a cool down if you intend on measuring temps, and then measuring them as quick as possible. Every 30 seconds makes a difference.

What pyrometer are you using?

Get in the habit of measuring outside first, then middle then inside, and measure as far away from the edge of the tread block as possible, right in the middle of tread blocks. Make sure to stick the needle in ALL of the way, and preferably at a 45* angle into the tire (rather than straight down).

I wouldn't make any changes until you get a little more proficient and consistent with your measuring. Make a log book where you record all of your temps and pressures.

 

It’s a basic Longacre pyrometer circa 2014(?).

My air pressure gauge is also a Longacre unit I bought at VIR in 2008, back when $35 seemed like a lot of money.

Everyone who sees them here is immediately confused because they don’t understand Fahrenheit and PSI. Hahaha.

 

there is no way your RF is only 6 degrees hotter with 2.5 degrees neg camber. maybe if you were just cruising but your video looked like you were on the gas.

there's no magic in doing tire temps. do 3 laps at race pace. exit the car promptly, do temps first then pressures. make sure the probe penetrates. on race tires you get to the cords. street tires have more tread so you may not hit the cord. that's fine.

i like your stated camber F and R for an initial track setting. your inner RF reading should be close to 20 degrees hotter than the outside.

 

my friend and i have a method where if something is adjustable, we try all of the settings. partly to see what the optimum is, but also to see what each adjustment does.
its a ton of work, but later when you're having some issue, you know what to adjust to fix it. its forever ago, but we had the integra dialed in such that we'd change rear ride height by quarter turns (it does camber and toe together) to do what we wanted.
our approach is pretty dumb, you can waste a lot of time measuring stuff you aren't going to change, like the suspension geometry.

or if you like, race cars are simple. all we care about is the lap time. so you make a change, and see if it went faster or slower. not much in life is this straight forward
you also want to keep track of why, what happened. and you just work through all of the adjustments.

for example, the last car we started from scratch on was someone's daily driver miata. step one was just to lower it until it stopped going faster. then we added spring rate until it stopped going faster. ad Infinium....
we have 5 national level trophies with that car

 

I wasn’t able to get readings after the session in the video. The readings were from a practice session.