How good is the physics - Spec Miata tune - thought experiment

[mekilljoydammit]

All right, so as one of the bigger roadrace classes in the US, and the fact that the suspension and modifications are limited, Spec Miata makes it possible to have a very good idea how the race cars are actually set up. And Laguna Seca both has a Spec Miata lap record, and is in GT5.

First the car
'89 Eunos Roadster
Sports air filter, exhaust manifold, cat converter, and exhaust
This gives us, for mine off the showroom floor, 137hp, which is about right.
Stock transmission, driveline, etc.
Sports soft tires
No weight reduction
Chassis reinforcement

Suspension
Ride Height: -10 / -10 (free to modify)
Spring Rate: 12.5 / 5.8 (restricted by rules)
Extension: 6/4 (resticted by rules, but questionable accuracy at best)
Compression: 6/4 (see above)
Anti-roll Bars: 4/2 (restricted by rules)
Camber: -2.0 / -2.0 (free to modify within stock suspension limits - maybe another half degree available)
Toe: 0.00 / 0.00
Braking 7/5 (free)

Spring rates and bar rates should be about right; the alignment is a baseline used by the Spec Miata community and is described as pretty neutral. It feels that way to me too, but I may not be that great a driver.

Try it out and fiddle the available options if you want. The Laguna Seca lap record in the class is 1:46.7, and I'm curious to see if anyone can get to that or beat it within the limitations of the class. I'm in the 1:50s so far, and the car *feels* right...

Thoughts? Input? Flames on how I'm not that great a driver?

 

[Schadenfreude13]

Just looking at those real world spring rate/anti-roll bar settings, it raises some interesting questions about the game's modeling of suspensions.

I recently spent a lot of time with Leonidae's tune for the NC MX-5, and was having some minor issues with understeer. His springs are set to 6/6 front/rear. Based on the Spec Miata settings you've posted with the rear being relatively very soft compared to the front, I can imagine some horrific understeer issues in-game.

There is one key difference between your setup and his, however. His car is an 07 (NC) tuned to 352HP. Yours is the old NA tuned to 137HP.

Link to the Mad Finn Tuners MX-5: https://www.gtplanet.net/forum/showthread.php?p=4442110#post4442110
Link to my review of said tune: https://www.gtplanet.net/forum/showthread.php?t=196255

If I have time, I'll try your setup out tonight (on the NA version you specced) and give you some more feedback.

 

[mekilljoydammit]

In this case, it's a matter of motion ratios... NA Miata has the coilover in the front going to about halfway along the lower wishbone, while the one in the rear goes closer to the hub, so the leverage is different between the front and rear. NC's completely different, suspension geometry-wise.

 

[budious]

This game doesn't actually implement suspension differences, it's pretty rudimentary in its approach. Just approach both ends of the car from a linear travel perspective because that's how it is implemented for all cars, even the exotics, and formula cars.

 

[Motor City Hami]

Spec Miata

Have you seen the Spec Miata racing series in the online community on this forum. Your suspension settings look like what they used in the series. Season two is about to start with pre-season race this weekend. Now called the Flying Miata Super Cup.

https://www.gtplanet.net/forum/showthread.php?t=191385

Are you a full scale Spec Miata racer? 700 lb front springs, 350 rear springs. about 4.75" of ride height. I can stand next to my Spec Miata and push down on the trunk with one hand and easily bottom out to the shock bump stop. Even that softly sprung, the car can achieve alot of oversteer. The Miatas in GT5 don't come anywhere close to handling like Spec Miatas. The real world cars sort of dance through the corner between oversteer and on the limit. In GT5, most of the Miatas push using near same spring rates. Tune the LSD and you can get it closer to feeling real worldish, but not really close.

 

[mekilljoydammit]

Nah, hadn't seen that... I've yet to talk myself into getting into the online racing side of things. And no, don't run Spec Miata in real life, though have friends who do. As an engineer, I'm putoff by any class where you can't tune things sufficiently, so I run a 1st gen RX-7 in basically SCCA E-Prod.

But nooooo, they couldn't put a 1st gen RX-7 in this game...

 

[BrianJ129]

I know, Im digging up an old thread here, but its pretty perfect for what im asking.

I have one of these I setup after seeing the existance of the series some time ago, and I wanted to try one of these cars.

my build:
'91 Eunos Roadster j-limited, yellow
Sports air filter, exhaust manifold, cat converter, and exhaust
This gives us, for mine off the showroom floor, 137hp, which is about right.
Stock transmission, driveline, etc.
Stage 2 weight reduction
Chassis reinforcement
Ride Height: -12 / -12
Spring Rate: 12.5 / 5.8
Extension: 6/4
Compression: 6/4
Anti-roll Bars: 4/2
Camber: -2.5 / -2.0
Toe: -0.07 / 0.10
Braking 7/5

now, I started this with comfort softs, as I found a video of someone lapping Laguna at a 1:53.7 , push push push, and I nailed that time (offline)

then I put the sports mediums on and nailed a 1:48.05x pretty close to the lap record in real life, and I had a little more to go. so I thought maybe I should try online.

now with the comfort softs on online this thing is almost stupid loose.
I have upped rear toe in to .22, put in an adjustable diff, and set that to 10/28/12 and have backed rear camber out to -1.8 just trying to get the back end to stick, but once it goes, its outa here folks, and the spin stops in a wall.

Im trying to get back to a 1:52.5 on comfort softs online, but still cant keep that back end in line. I used the motorcity tune as well, but it says it was offline, and I can tell.
I have a 1:54.7 now, but am lacking stability to run consistent times.

any tips are appriciated.

Also, on a side not, i know the Flying miata cup is still going, with the new roadster tc setup, but does anyone get a group of the old spec cars together and have fun anymore, or has that pretty much gone away?

Thanks,

 

[CSLACR]

Dumb question: How does 700lb front spring / 350lb rear spring translate to "12.5/5.8"?

700lb = 2x 350lb. Real-world car has the front 2X stiffer than the rear.

12.5/5.8 = Front 2.2X stiffer than rear.

11.6/5.8 = Front 2X stiffer than rear.

Despite this oddity, I'm quite interested in this. Can somebody link me or post all the actual real world parameters for this car?

His springs are set to 6/6 front/rear. Based on the Spec Miata settings you've posted with the rear being relatively very soft compared to the front, I can imagine some horrific understeer issues in-game.

If you're driving online, you're in for a surprise it sounds. If you're driving offline, there's a good chance you'll not be able to tell a difference in terms of rotation.

 

[Taz69]

Yea if your GT5 miata has 6/6 for springs lower the rear spring rate and the car will start to oversteer.. The games discription is wrong stiff front lower rear oversteer.. Soft front high rear spring wise understeer. So an even springed car like 6/6 if its pushing go 6.0/3.50 spring wise and see if it helps turn.. Just try it.

 

[Motor City Hami]

Can somebody link me or post all the actual real world parameters for this car?

Links to rule books below. Not sure how helpful these are. You will probably need more information about the specs of the Eibach suspension kit, the Biltien shock settings, the Hoosier and Toyo tire specs and some engine HP/torque numbers?

http://cms.scca.com/documents/Club Forms/2010 Tech Forms/sm-jan.pdf

http://www.nasaproracing.com/rules/spec_miata_rules.pdf

http://www.nasaproracing.com/rules/showroom_spec_miata_rules.pdf

HP numbers for front running cars, I have heard 125hp. Torque of 115 ft pounds.

Sway bars
Front 27mm Adjustable
Front 24mm Adjustable
Rear 15mm Adjustable

Link to shock dyno results... http://specmiataclassifieds.com/SMF/index.php?topic=146.0

 

[CSLACR]

Suspension alignments (camber, caster, toe) are unrestricted
within the limits of the unmodified factory adjustments.
Minimum ride height is unrestricted.

Do you know what the factory limits are?

Toyo Tires recommends the following general set-up guidelines for the Proxes RA1:
Operating Temperature: 160°F to 220°F
Hot Inflation Pressures: High 30s to Low 40s (psi)
Camber: -2.5° to -5.0°

Not sure it means anything, just thought it sounded like a lot of camber.

In itself the tire is a SM at best. For older year Miatas the tire size is increased over stock, but I didn't find any specs in any of the links to an '89, so it sounds like the '91 is a better fit, although you could use any year model you wanted it seems.
Since tire size brings into question whether it's really worth an extra tire grade, I would start by picking a Miata that comes with 205/50/15 wheels/tires stock.

It seems 2000-2004 have a 205 option , I didn't check them all. On any of those cars the tires should certainly be no more than SM. The tires description is clearly not that of the absolute top of the line below a racing slick.
Honestly I'd probably call them SH on the Miatas in the game with 205mm tires. On older models one could throw SM's on, since they run 185/195's.

So the rear shocks are essentially 3.5-3.7x stiffer on the ext , yes?

If you have any more information I can use, don't hold back. I'm going to play around with some Miatas tomorrow night and see what I find. I have some theories.
The one thing I could really use is detail on the toe/camber amounts possible in the real world. That would really help make this thing have some proper over-steer.

 

[Motor City Hami]

I have driven most of the Miata years in the game. I also did the early Flying Miata races here on GTP.

Mx5 '07 handles best, by far. Most balanced.
Premium '89 for some reason is faster than the premium p91.
UCD Miata NA versions '89-'98 seem to understeer. Preferred by most wheel users.
UCD Miata NB versions 2000 and higher seem to oversteer. Preferred by most DS3 users.

I will see if I can find some of the stock specs.

 

[CSLACR]

I have driven most of the Miata years in the game. I also did the early Flying Miata races here on GTP.

Mx5 '07 handles best, by far. Most balanced.
Premium '89 for some reason is faster than the premium p91.
UCD Miata NA versions '89-'98 seem to understeer. Preferred by most wheel users.
UCD Miata NB versions 2000 and higher seem to oversteer. Preferred by most DS3 users.

I will see if I can find some of the stock specs.

That would be awesome, hopefully they aren't to impossible to find.

I'll have to try some of these, I've never heard of wheel users preferring more understeer than DS3 users, I'll have to see which ones I have and can find though.

 

[Motor City Hami]

That would be awesome, hopefully they aren't to impossible to find.

I'll have to try some of these, I've never heard of wheel users preferring more understeer than DS3 users, I'll have to see which ones I have and can find though.

No. You have to look at it from the other way. When using the DS3, you just cannot tune the understeer out of the NA models. With the wheel, the NA model seems near perfect. So the DS3 users have to choose the NB models that is more on the razors edge, but can be a bit faster than the NAs on the DS3.

 

[CSLACR]

No. You have to look at it from the other way. When using the DS3, you just cannot tune the understeer out of the NA models. With the wheel, the NA model seems near perfect. So the DS3 users have to choose the NB models that is more on the razors edge, but can be a bit faster than the NAs on the DS3.

That's what I mean. I've not commonly found cars where DS3 users would need to take a looser version but the wheel users loved it. There are oddities , I'm not saying you're wrong.
I haven't driven any except the '89 in forever, so I don't have a clue what they drive like except the '07, in which I agree is easily the most stable and best handling/fastest cornering. Lovely car that one.

 

[BrianJ129]

I have an 07 as well. Great car, it's fun with just a bit more horsepower. With some tuning I manage to keep that out of the wall some, but it is on sports softs so that's a bit easier.

If I am absolutely perfect with my line I managed a 1:54 dead at laguna with the comforts online. That was perfect in the back section just to keep it out of the wall. There is a little more time in it, but I have to back it down to keep it on the track

I have not tried going to a really high lock on the rear diff, but when it snaps I can't say I definately thing its a one wheel spin issue.
Boy that thing is tricky. Makes me question my desire to build. Real SM racecar in real life