I always thought negative camber is increased with lower ride height resulting in better corner handling.
I actually raised the heights 10mm that was set by HKS out of the box.

 

Nothing of the sort. There's a balance and science to suspension, and lower /= better. This book would be worth a read. Dennis Grant has a bit more of a clue than most, including me by a far sight.
Suffice it to say, it's very likely your measured performance is far worse than stock at the drop you are running. The only way to know for sure is to test it, but doing the homework first will at least get you in the ballpark.

 

Funny, I almost raised the car a couple of days ago. Set everything up in the garage but then just put everything away again.
I think you've now convinced me to raise it maybe 10mm all around, I'll have to get it all re-aligned.

EDIT; Whats good alignment specs to maximize handling? I currently have toe at front neg -0.5mm and rear positive +0.9mm.

EDIT; Worked out my lower than OEM tire heights contribute to an extra 9mm lower, so in actual fact my coilovers are lower than OEM heights of 17mm front and 12mm rear, so maybe might increase 7mm all around.
tires are 265/30/19 & 235/35/19, 50% worn but l'm going to purchase 275/30 & either 255/35 or 245/35.

Here's what it looks like, there's plenty of fender clearances

 

I understand what your saying, but also wonder why all time attack and race cars seem to be lowered? Was the CCSR lowered or stock height? I’m guessing all time attack cars have fully adjustable suspension arms that allow them to alter their geometry? I say this not at all to debate, just as a confused bystander. The fastest ISFs that I follow are all very low.

 

The fastest Supras were all at stock ride height. It wasn't possible to make the car faster with a drop. There may be 10mm of drop available, but without measuring the chassis, it's impossible to be sure. I heard anecdotally Lexus raised the front 10mm to clear parking stops when the car was released. We were also told early promotional shots of the USB pre-production model in the desert had cut springs to lower the car. The whole problem comes down to a watch and a course. Once the roll center drops far enough, the roll couple is so long there is no practical spring rate strong enough to manage roll. Roll impacts camber, so you need to know where you are on the camber curve at normal ride height so you can calculate camber gain and instant centers. But Grant goes into all this stuff in detail. Also, ride height on the IS F is measured by taking a difference between where the lower knuckle is and where the chassis sits relative to the center bolt on the lower knuckle. This is the most accurate way to get ride height correct as it does not depend on the tire's height at all. Previous measurements (Supras for sure) just measured from the LCA pivot bolt in the front to the ground which doesn't account for the possibility of running different diameter tires. Keep in mind, at the highest levels of racing (F1, etc.) they sweat ride height down to the millimeter. Granted, those cars share nothing with our rubber bushed suspensions, but the importance of getting the ride height right can't be overstated.

Last but not least, the most important part in any car is the nut behind the wheel. A really determined driver can overcome lots of setup problems with sheer tenacity.

But, in general, arbitrarily lowering a car without understanding what happens to the camber curves is a recipe for going slower, and often much slower than the correct ride height.

Here's an even easier read than David Grant's book from Mike Kojima: https://motoiq.com/how-to-make-crappy-cars-handle-well/

Mike is also one of those guys who has forgot more than I'll ever know about setting up suspensions.

 

I've ordered PS4S 275/30 & and 255/35, as Lance recommended I'm going to adjust my HKS coilovers to 10mm lower than OEM.
With this set up Can someone recommend good alignment specs for decent handling without too much wear on tire edges. I've read with wider tires its best not to have too much toe.Whats better toe out or in front and rear and by how much?

 

When tire wear is your first consideration, the front with OEM bushings needs toe-in because it toes out dramatically on braking and kills the inside edges of the front tires. There's a long thread here about Reconsidering the Factory Alignment that goes into detail on this. If you put polyurethane rear LCA bushings on the front end like Figs or RR Racing sell, you can go to zero toe and get excellent wear. If you're like me and prefer the car turns in better, you can go toe-out 1/16" - 1/8" but you will have faster inside edge wear for sure.

In the rear, run the factory spec - 3mm toe-in. It shouldn't present any tire wear issues and the toe-in helps the car turn. If you have replaced rear links with polyurethane or solid bushings, you can experiment with other settings, but the factory settings work well for tire life and turn in both with the OEM bushings.

 

Fantastic thanks for your advice Lance.
I do have front superpro bushings which l believe are the same as figs.
1/8" is around 3mm
I'll do front 3.0mm toe out and back 3.0mm toe in.

What are good cold tire pressures with hard spirited driving, 36 to 38 front, 32 to 34 rear. I have removed everything in the trunk including spare wheel, so it's a bit lighter in the back.

​​​​​​I might even raise the height to OEM.Thanks again.

Cheers Jim

 

Any reason you'd want to go 4 psi lower at the rear? I'd say stick with 35-36psi cold all around and you'll be close to optimum for most street use scenarios. I understand that you're looking to maximize handling for spirited driving but IMO this is difficult to optimize as optimum pressures for handling will vary depending on model of tire, ambient temperature swing from where you park overnight to on the road, humidity, whether you use air or nitrogen in your tires, type of road, speeds, etc. A lot of these variables are constantly changing. You could try the chalk on sidewall method or take tire temps across the tread width to try and optimize for different conditions if you have the patience for it.

 

Thanks, yes I've done the chalk method before and I'll do this again. I've always found lower cold pressures work better, I'll aim for OEM pressures when they're hot. Tires should arrive in a couple of weeks. Looking forward to larger contact patch.

 

32 psi cold. 44 psi hot at the track. 36 psi cold on the street. Those work for me.

 

Hi Lance,
I raised the suspension 10mm front & rear, had MPS4S tires fitted today 255/35/19 Front & 275/30/19 rear. Heights are now just 4mm lower than OEM.
They maxed out the Toe, 1.9mm toe-out front and 3.1mm toe-in rear, no more toe adjustment. They said I'll be lucky to see 10,000km wear in the inside edges and recommended more neutral toe but I said I'd rather have happy 10k's than frustrating 30ks. So I went with your recommendations.
Car seems to handle much better, much more grip and no stability control lights flickering, happy days.

Many thanks Lance