Need advice on tire size for track duty??

[7thgear]

Originally Posted by Matt Andrews

But a strut is different. As the car roles, camber is basically static. Lots of fast strut cars are bone jarringly stiff in order to keep the proper amt of camber on the road.

ive been tracking macstrut cars for 7 years, both of which roll quite a bit, and i've been doing fine.

first of all, camber is not static.. far from it, it is very dynamic on a macpherson strust

and it's different from every car, there are bad mac strut implementations and there are good.

M3 vs Yaris, for instance... are you saying a stock M3 needs to be low and on coilovers to be fast?

here is a graphical representation for reference (not modeled on any particular car)



there are, of course, other factors at work

but i just shake my head at the notion that you NEED this or that part to make the car handle and that without these things it's shit and should just go die in a ditch somewhere

There are many applications where MacStruts work quite well, they simply require a different tuning approach and a first and foremost understanding of their strengths and limitations.

[Matt Andrews]

good points. Have you or anyone measured camber gain on compression on these cars yet?

and for the record, I don't think stiff is better. my time attack miata, that actually ended up being an aero car, was sprung softer than most spec miatas and ran no rear bar...

[7thgear]

Originally Posted by Matt Andrews

good points. Have you or anyone measured camber gain on compression on these cars yet?

i don't have the car yet (arrived today, actually!)

i don't know of anyone that has done formal analysis of the dynamic movements of the components, i myself have no access to such software but i'm sure a few people do... just a matter of their willingness to share the models.

[Matt Andrews]

shouldn't need the models. just an alignment rack and a jack, right? remove the spring and sway bar end link and jack up that corner. see what happens to toe and camber.

but that is a pain. I will likely do it when I put my dampers on. (JRZ or AST)

[jamal]

I would be surprised if the front suspension sees much more than 1/2° of camber gain under bump. Here's a curve someone made for a wrx a long time ago:



If anything the brz will be a little better but probably not far off. 2" of bump would come from around 4° of roll. It also shows why lowering the car very much is a bad idea.

[ultra]

Hm. Before we get overly serious let's not forget that the ideal set up will depend a lot on the use case for the car - street only, street and occasional track, track and street or track only.

Finding the sweet spot(s) along the modification continuum between OEM and all out track setups while maintaining the playful nature of the car will be the interesting part. If all that mattered were speed this would be the last car I'd have ever considered!

I don't mean to be negative but I don't think that building an 'ultimate track' setup will be very challenging at all.

It's pretty much the same old formula for every car out there:

High end coil overs + adjustable top hats & bolts + poly bushings + sways & adjustable links + strip it out as much as you dare + cram as much purple crack into the wheel wells as you can & you're done. The crazier/richer guys will go with FI setups, carbon bits and perhaps aero.

Much like they said in Battlestar Galactica, all this has happened before and it will all happen again.

So, if it's tires we're talking about then I'd suggest AD08s or RE11s for versatility, resilience and performance.

Track only tires - Hoosier R6s, Hankooks, BFG R1s, whatever. They'll all stick something fierce if dedicated track tires are your thing. NT-01s if those are too hard core.

[Silp3]

http://www.miata.net/garage/tirecalc.html

[949 Racing]

Originally Posted by ultra

Sure, someday somebody will come out with a great set of coilovers that slash lap times and plant the car nicely (will probably involve offset bushings, camber bolts and top hats too by the looks of things).

Lots more R&D to be done before I'd consider spending any $$$ on coilovers in the name of better lap times though personally. Need to see what AST, RCE and Ohlins will come out with, never mind the serious stuff like Motons etc.

If we had somebody like Emilio from 949 racing selling custom valved and sprung Tein Monoflexes, or Robispec tuned KW V3s, that'd also change things.

Just not big on off the shelf, unproven coilers for the sake of it unless I see data.

Soon

[D1cker]

Originally Posted by s2kdrew

Federal is not great track tires, if you take it to track then you are asking for trouble.

Don't listen to this guy, the 595 RS-R is a fine track tire, and probably the best value in tires today. Just don't expect them to wear well or be quiet

[robispec]

Originally Posted by ultra

Given the info that's slowly trickling out from people on this forum who have actually tracked their cars, why on earth are people still so quick to assume that coil overs will automatically improve anything at all, let alone everything?

This isn't some Accord or TC. It's been extremely well up out of the box by all accounts I've read.

It will be tough to improve on and very easy to ruin if someone just throws parts at it.

Of course this is the Wheels, tires, brakes& suspension sub forum so some hellaflush is to be expected but this particular thread is about performance IIRC.

BTT - for competitive AutoX I'd favour maximizing the contact patch but for track duty I'd go for something that fits well even if it's thinner. I'd be more interested in getting a compound that's heat cycle friendly and not prone to overheating or getting greasy.

I can vouch for RE11s or AD08s on track but have no clue how the Kumhos perform.

I know only that CG is EVERYTHING (or at least affects everything!). but you cant give up too much travel to get it..part of our solution was to got to the 245/35/17 R1R to loose 3/4" ride height (even stock it looks DOPEY) so using coilovers to loos anothe 1" is a great way to drop your CG 1.75"

[gmookher]

Originally Posted by 7thgear

have you ever bothered to race a stock car on good tires and brakes for a solid season?

Yes.

Neither the oe coil or damper or sway is up to the task on track with sticky tires

Don't assume everyone can't drive at the oe limit. The oe limit isn't that high here....

[Not4off]

Originally Posted by Vracer111

Why no 215/45-17 consideration? Lighter and more responsive with just about as much grip.... Just came off a track day at MSR Houston running 215/45-17 Kumho Ecsta XS's (because lighter than RS-3's) and man what a chassis the FR-S has! Lightweight wheel/tire combo (less than 37 lbs) with sticky tread and responsive sidewall = AWESOME. More like what DOT-Rs on an Integra felt like to me...(other than the FWD characteristics)

Vracer111...

I'm inclined to want to stay with the stock wheel and tire size as you have. What are you running in terms of negative camber and how did you get there ie
camber bolts? plates? lower control arms? If you resorted to any of these...who did the install in Houston? Thanks.

...Richard

[Vracer111]

Not4off, I haven't touched the suspension at all since I've gotten it. I do plan to get the whiteline Com-C mount and camber bolts eventually and install them myself sometime in the future, but it's not a priority at this point and time because it's good enough as is with no excessive front tire wear. #1 priority for me is piecing together an oil cooler and oil pressure/temp gauge setup.