Change to clutch pack LSD or not

[CSG Mike]

Originally Posted by Icecreamtruk

Alignment specs are dialed in using pyro measurements, so im not doubting those, except maybe the toe. Its -4.7 camber up front, 0 toe, -2.8 camber rear and a pinch of toe-in (0.05 I think). Stiffer springs were added to allow me to run the car with the splitter closer to the ground without scrapping all the time. Its a compromise to gain aero dependant grip, giving up some mechanical compliance in the process. I will lower the rear to see if it helps.

That's a strong indicator that your car is too low.

I run a very "normal" amount of camber in the front of my car, and remember, I'm on a 6kg main spring, with an extended air dam and hood louvers.

[Icecreamtruk]

Originally Posted by CSG Mike

That's a strong indicator that your car is too low.

I run a very "normal" amount of camber in the front of my car, and remember, I'm on a 6kg main spring, with an extended air dam and hood louvers.

Could be, but I wouldnt be so sure. I will take exact measurements when I readjust the rear ride height, but I doubt its too low. I think its not even 20mm lower than stock heigh at the moment.

The splitter is not directly stuck into the bumper, its 2.5" lower with an airdamn covering the gap, and said splitter is around 2" from the ground at the edge, so it "looks low" but isnt as much really.

I did try a higher ride height at the front, at the beginning of the season but the car pushed a lot at the front, it was understeer from corner entry to exit. After I added more camber and lowered the front .5" more the car suddenly had tons of front grip.

If I had to choose between less grip at the front but a stable rear or how the car is right now, I'd rather keep the front grip and manhandle the rear. The stopwatch also shows im faster with more grip at the front, regardless of how wild and crazy corner exits can get (its harder to get a good lap in tho).



Notice how much lower the splitter is than the actual bumper. This is mid corner at around 40-50% throthle and feeding more in, its a long left hander. Thats as high as the splitter gets while accelerating, while braking and turning it goes low enough to lightly scrape on the ground.

[JeremyR]

alignment specs seem good.

is there anyone local you can swap suspension with? maybe test out some different dampers and see if that makes any difference? what psi are you running? what are the tire temps after a hot lap?

[CSG Mike]

Originally Posted by Icecreamtruk

Could be, but I wouldnt be so sure. I will take exact measurements when I readjust the rear ride height, but I doubt its too low. I think its not even 20mm lower than stock heigh at the moment.

The splitter is not directly stuck into the bumper, its 2.5" lower with an airdamn covering the gap, and said splitter is around 2" from the ground at the edge, so it "looks low" but isnt as much really.

I did try a higher ride height at the front, at the beginning of the season but the car pushed a lot at the front, it was understeer from corner entry to exit. After I added more camber and lowered the front .5" more the car suddenly had tons of front grip.

If I had to choose between less grip at the front but a stable rear or how the car is right now, I'd rather keep the front grip and manhandle the rear. The stopwatch also shows im faster with more grip at the front, regardless of how wild and crazy corner exits can get (its harder to get a good lap in tho).



Notice how much lower the splitter is than the actual bumper. This is mid corner at around 40-50% throthle and feeding more in, its a long left hander. Thats as high as the splitter gets while accelerating, while braking and turning it goes low enough to lightly scrape on the ground.

Have you considered that your suspension and aero setup is largely pushed biased, and you may be over-scrubbing your tires, leading to tainted pyro data?

I see both you and William dialing in more steering than should be needed with this quick of a rack, and then that state of push snapping into unwanted rotation which then needs correction.

As a grounds for comparison, re-watch my video, and you'll notice I don't ever give the wheel as much input as either of you in my car, in any steady-state corner that is grip limited.

Food for thought.

[strat61caster]

I like this thread

[Leveq]

Hey, it's Will here, finally got my registration accepted lol.

So first of, trust me I wasnt steering into scrubbing the front, if I did that without noticing I'd just hang my helmet right now. If you watch the video properly I barely turn any more than you Mike, and that's considering grippier tyres (NT01s vs 300tw Michelins) and more aero. FOV is also a bit high on my camera, corners are tighter than they appear on video. Hairpins I had more trouble with but I'll get to why in a minute.

Now for the setup, Vic's car might be a tad on the stiff side and a bit underdamped. But mainly I think there's an imbalanced due to the fact that he's rocking the OE anti-rollbars still, and the rear being WAY too high. He's fixing both of these so we'll see then. I think he also has single springs, so maybe it's struggling to keep the tyres on the ground at times. And no roll center correction kit, but I'm less knowledgeable about strut cars and I dont know how bad it really is on his car.

On a more personal level, I couldn't manage the ABS really, it felt awful. Held the car back massively on trailbraking, kicking super early and aggressively and it would make the car push noticeably. Nothing too surprising tho, street car ABS just isn't good enough on a car with that level of "because race car". I basically had to guess how much grip the car would give me in the transition from brake to throttle. The latter not being linear (DBW and I think it's set-up wonky in the tune) gave me some trouble being precise enough too, it was too aggressive on the initial input.

Anyhow, that's kinda how I feel about it. Still worth keeping in mind that I had no experience prior in his car, so kinda going by feel really. Here's my lap without the split screen:
[ame]https://www.youtube.com/watch?v=YPNncgP_5pI[/ame]

[ZDan]

2 cents...
1. I haven't perused the whole thread, but it's worth noting that a "square" spring setup gives a big front wheel-rate stiffness bias due to not-very-much-leveraged front struts and very-much-more-leveraged rear multilink. 12kg/mm spring rates all around should give ~10.8 kg/mm front wheel rates and ~6.8 kg/mm rear wheel rates (assuming 0.95 and 0.75 front and rear motion ratios, which is an educated guess on my part). I would definitely be trying out more rear-biased spring rates to get front/rear wheel rates more in line with front/rear weight distribution.

2. For this kind of suspension stiffness I would think a clutch-type diff would be the way to go for consistent and predictable handling, as with stiff suspension any small perturbations will have a significant effect on relative loading/unloading of the rear wheels, which the Torsen diff isn't going to deal with as well as a good progressive Salisbury clutch-type diff.

[CSG Mike]

Originally Posted by Leveq

Hey, it's Will here, finally got my registration accepted lol.

So first of, trust me I wasnt steering into scrubbing the front, if I did that without noticing I'd just hang my helmet right now. If you watch the video properly I barely turn any more than you Mike, and that's considering grippier tyres (NT01s vs 300tw Michelins) and more aero. FOV is also a bit high on my camera, corners are tighter than they appear on video. Hairpins I had more trouble with but I'll get to why in a minute.

Now for the setup, Vic's car might be a tad on the stiff side and a bit underdamped. But mainly I think there's an imbalanced due to the fact that he's rocking the OE anti-rollbars still, and the rear being WAY too high. He's fixing both of these so we'll see then. I think he also has single springs, so maybe it's struggling to keep the tyres on the ground at times. And no roll center correction kit, but I'm less knowledgeable about strut cars and I dont know how bad it really is on his car.

On a more personal level, I couldn't manage the ABS really, it felt awful. Held the car back massively on trailbraking, kicking super early and aggressively and it would make the car push noticeably. Nothing too surprising tho, street car ABS just isn't good enough on a car with that level of "because race car". I basically had to guess how much grip the car would give me in the transition from brake to throttle. The latter not being linear (DBW and I think it's set-up wonky in the tune) gave me some trouble being precise enough too, it was too aggressive on the initial input.

Anyhow, that's kinda how I feel about it. Still worth keeping in mind that I had no experience prior in his car, so kinda going by feel really. Here's my lap without the split screen:

[ame]https://www.youtube.com/watch?v=9Jw0yeTx0Ig&t=45s[/ame]

Here's another video that will better represent the difference. This car is on the same coilovers and sways I am (17 rear), but on cycled A052 and a stock engine. Ignore the second through fourth turns, where the input is exaggerated due to exploitation in elevation change. In particular, you want to watch the high speed right, followed by the right over the crest, followed by the right hairpin. Specifically, the right hairpin is perfectly flat on this track (by design). The high speed right is slightly banked.

You are indeed, scrubbing the front in the video, just ever so slightly; you rarely stay in a state of scrub for long, and its not much scrub at all. For example, watch the turn at 1:38 on your video. You initially over-input the front because the front end of the car is not responding, which then leads to a snap rotation when the dampers catch up which you immediately correct out, and then sustain less input, which then brings the car back to a front-limited state. This is in stark contrast to the corner at 1:10, where you never exceed 90 degrees, and never scrub the tires.

I make the exact same scrubbing error you did at 1:38 in the first right hander in the video I linked. There's a small dip leading into a crest, that I attempt to exploit for extra compression grip, but hold the steering too long, turning it into an initial scrub, and then unwanted over-rotation. The same error is made on the third right hander on the course going over the crest, where my steering input is smaller, but still too much for the available grip, immediately resulting in a snap into unwanted rotation.

The amount of steering necessary on the car in my video is dictated by how the corner is entered; any gradual entry will be greatly throttle assisted steering, versus purely steering with the front wheels.

If the car has a Solo 2 DL, you'd be able to corroborate the steering input versus wheel speed vs scrub and slip angle, vs lateral g.

The 13-16 OE sways have an inherent front load bias, as does the spring rate setup on the car, as well as the aero (i think).

You're 100% correct on the trail braking; the car has a heavy mechanical biasing issue with the brakes, rather than an ABS issue. Additionally, you're 100% correct in that most tunes are very bottom-loaded with the throttle response.

Do you spend the majority of your time in double wishbone cars, rather than strut? I'd love to see you drive @Icecreamtruk's car after it gets dialed in properly! Totally solid driving for a car you've never been in.

[Leveq]

Maybe you're right with the scrub, but then again, hairpins as I mentioned I struggled with haha. It'll be interesting to see how the car drives after the changes. Cheers.

And yeah, suppose I have. Mostly my stock-power Miata... I do use my 3rd gen Mazda3 in autocross this year tho, but not really the same.

Same track in the Miata, but better weather:
[ame]https://www.youtube.com/watch?v=e-_lGugJX_o[/ame]

[CSG Mike]

Originally Posted by Leveq

Maybe you're right with the scrub, but then again, hairpins as I mentioned I struggled with haha. It'll be interesting to see how the car drives after the changes. Cheers.

And yeah, suppose I have. Mostly my stock-power Miata... I do use my 3rd gen Mazda3 in autocross this year tho, but not really the same.

Same track in the Miata, but better weather:

That miata looks pretty planted with a hint of rotation What happens if you brake a little earlier with that last left hairpin?

If you slow down your hands just a tad to accommodate the struts in the 86, you'll become deadly quick in it The same will carry over to BMW/Porsche/Evo/STi, as opposed to S2000/Ferrari/Lamborghini/Mclaren.

[Leveq]

Originally Posted by CSG Mike

That miata looks pretty planted with a hint of rotation What happens if you brake a little earlier with that last left hairpin?

If you slow down your hands just a tad to accommodate the struts in the 86, you'll become deadly quick in it The same will carry over to BMW/Porsche/Evo/STi, as opposed to S2000/Ferrari/Lamborghini/Mclaren.

Don't think it was that late but it's a very hard braking zone to get right, it's right over a hump haha. It doesnt feel like I lost over a tenth and some on video tho so not all that bad I think.

And yeah car is alright. Underdamped tho, just some Koni Yellows with too much spring rates haha, and it's still too soft ! Extended lower balljoints for camber (-3.5) and swaybars. DIY hardware store aero, splitter and lexan spoiler. Rest is bone stock really, even the exhaust is OE ! It's taking a break this year, gotta find a 6 speed (5 speed has a dead 3rd synchro hence the double-clutching on video), that'll make the gearing much shorter and will avoid me touching the final drive. Couple other things, ducting and exhaust really. Should be well into the 46's after that.

[Icecreamtruk]

So, bringing this back a bit from the dead ( well not really) to update on the situation. I did some changes based on some of the suggestions thrown around by people here and by William. The car is much better, and faster than before I think, it is much more predictable and easier to drive after sway bar changes (both changed, front is stiffer than rear relative to previous stock values) and after lowering the back (rake is down to 10mm now).

Now, the saucy part, I had data logging working for a session, before getting into and impact with another car in practice and spending the day repairing the damn thing to get a timed lap before the end of the day, but I managed to capture my problem on it. Yellow line is wheel speed, green line is GPS speed (tires have bigger diameter than stock, hency why green is always a bit higher than yellow):



You can see, in all of the turns except for the carousel (long double apex) that is banked, at the exit, there's a spike on yellow line. There was no oversteeering at all whatsoever here, it was a very uneventful lap, except for that, so no it was not both wheels spinning, just one. I forgot to put the camera on but you could clearly hear the car engine going off high. After the bustop (big chicane on the right side of the track), I could see the speedo climb up to 85-88km/h while the wheel was spinning before going down to 60km/h again. I also heard some weird diff noises (like gear grinding noise) on some of the biggest wheel spins during the day.

Some more changes suggested by a couple of people would be to go back to OEM rear bar, but im not sure, the car understeers ever so slightly now, I really like it where it is, I certainly do not want any more understeer tho. Thoughs?

[CSG Mike]

A diff customized to your car will help lock down th ose wheels of single wheel spin.

Verify with wheel speed traces; you can see individual wheels.