The perfect tire width sweetspot for timeattack FC?
 

as my build is entering the suspension phase atm i figured ill start with the tires/wheels and go from there.
From the start i thougt about ronin widebody kit and 295/315 stagger but decided to go square setup. is there a sweetspot for tires or is more better? the car will have about 550-600hp from a tourqy 20b and some aero (splitter, huge wing, canards,diffuser and so on), about 1100kg and a full racing cage.
I can get a good deal on 10.5" rota wheels and 285/30-18 kuhmo semi slicks but i can go wider if needed i guess. the guy building my cage said he doubted i could go wider since i have to use alot of camber up front to avoid camberissues when i drop the rideheight and that will affect the contact patch of a wider tire in a bad way....any truth to that?

thanks

yeah you're going to need to run quite a bit of negative camber, probably -3 in the front, maybe more.

for race tires, they like a wide wheel, although you should measure the actual tire (sometimes the actual tread width is on the spec sheet). for example the 225/45/15 hoosier R6 is about 20mm wider than every other 225 tire we've put next to it.

we put the 225 hoosier on a 9" wheel, but the other tires can run an 8" wheel.

so for a 10.5" wheel, i'd run a 265 tire, give or take. 275 would be ok too

You have a LOT of leeway in the aero/downforce area in most time attack catagories.

There is a new trend toward downforce/aero in time attack that is reviving crap strut front suspension chassis like 240sx and FC RX-7.

Why?

All cars taking advantage of the downforce from aero have to run such high spring rates that the suspension is basically moot as long as its dialed in for the base ride height.

If you develop your aero to the limits of the class you should be cornering flat and using not too much negative camber (relative on strut front end). The front downforce is going to smash your contact patch flat even if you are running some decent negative camber.

Under Suzuki's winning Scorch Racing 240sx (strut front) used the widest of the competitive legal tires up front and rear (295/30-18).

True Dedication: Under Suzuki's S15 - Speedhunters

I wish they would do an aero take back in time attack so the cars resemble something that can drive on the street and to provide a reason for superior suspension/chassis development over brute power and downforce.

But this is your environment for now...

thanks for the usefull tips guys!
allthou i tend to disagree alittle with you BlueTII regarding 2 things, first of i dont buy the "go by an FD idea, i know that FD and similar cars (doublebwishbone) are sort of better starting plattform (sort of), but the building and developing of the cars are almost as appealing as driveing to most ppl doing TA, and aero is what makeing basicly all chassis viable, without it we would only see porsches and ferraris, restricting aero would be like ban turbos or rotarys or whatever, its all elements that makes u go faster. and the streetable aspect...this is racecars purely buildt to get the fastest time around a racetrack, thats it...and if that is mega aero and mcstrut with 315 tires then may that be it, there will be other race classes to do aswell (but they wont be as fast as TA if we talk production cars)I happen to build mine sort of dual purpous with a few hours of garage time to make it streetable (aero off and alignment) but most ppl do not.
Next thing is the mcstrut thingy...winner of the unlimited class in sweden 2 years in a row is a mcstrut porsche...in this class is a full carbon all out 800hp half a mil usd FD (super cool btw) and alot of very well developed cars. the porsche is bpu with rsr aero, suspention and a big rear wing. i can see your point thou as some cars look like shiiiet ;-)

All the Time Attack rules I have ever seen are for modified production based cars and not race cars.

The Time Attack rules all grew from the Japanese Time Attack format which is licensed street cars on street(able) tires.

If your rules allow race cars, you should buy an old formula car and add horsepower. The aero, suspension and light weight is already there.

I'm not saying you shouldn't build an FC into a Time Attack car.

In fact, I said the opposite- the current Time Attack rules favor the FC over the FD and RX-8.

I only stated I would prefer if the Time Attack rules allowed less Aero so the cars would be more balanced in terms of handling, chassis, aero and power and resemble the street-able "tuner" cars they are supposed to be.

well the rules state that you start with a car that has once been registred for the street (otherwise there would only be F1cars i guess), the unlimited class the car only has to be serie-produced...even if it is for racing, i have seen 1 car that looked like a F1 car sort of but he only did 1 race or 2 (car in pic) and it was no success. unlimited class can tubeframe, carbon everything, free HP and run on racing slicks, use nos, sequential gearbox and so on, the "series produced" rule is nice thou since it makes us relate to street cars and it makes timeattack viable for you and me (moneywhise)
I am gonna drive in pro street however and the rules are more like you described them, the car have to have been registered for the street at one point, max 600hp, street tires and only hood+trunk can be carbon (basicly)

Mr Tii underestimates the amount of fast cars in Sweden. we took a family trip there in 2011, and i've never seen so many muscle cars in my life.

Mr Tii underestimates the amount of fast cars in Sweden.

Oh hell no! If anything I have this notion that every Swede spends their long winter building cars for Gatebil...

The guy building rx7jocke's cage said he will only need skinny tires up front because of all the negative camber he will have to run from the strut front end on the FC.

I pointing out to rx7jocke why the cage builder is wrong and included an example of one of the fastest TA cars with similar front suspension that uses the widest front tire available.

I think someone got sensitive because I called the FC suspension crap.

Well, it is crap front and rear and you aren't going to have a fast FC until you understand how and why and learn the work arounds to make it fast despite the initial design.

Yes, very much like how Porsche has made a glorified VW Superbeetle fast.

lol, i missed that part...

um i went the other way, he's running a 10.5" wheel, and that is 266mm, so the tire needs to be somewhere in the 245-265 range.

just for clarificationality we used to run a 15x7 with a 225/45/15 because that was the spec size for that class, but since then we've changed classes, and so we were able to go to an 8" wheel, which was better, and now we're running a 9" wheel, which was better still. we took some points back, and are now on a 205 with a 9" rim, its slower than the 225 on the 9" rim, but not by much.

I agree with this. 10.5" width wheel I would run a wide 255mm or smaller 265mm tread width tire.

I am running a 285/30/18 on an 11.5" wide wheel. the little stretch works great for everything except ride comfort.

You can also run a 18x10.5" front and 17x10 255/40/17 rear. that would be good for everything except rotating.

just because holiday weekend, 205 on a 9" wheel, on a race car, at a track...

edit; this maybe shows it better, should still be 205 on a 9" wheel. the cup actually does clip into the wheel, which is kind of funny

I'm currently running square (rota) 18x12s w/ 315/30/18s on a ronin widebody, they fit fine with about -3* of camber...

the contact patch of the wider tire is always going to be at least as large as the smaller tire... except in the middle of the turn, when you actually need it (if you're static camber is right), then a wider tire wins... your cage builder's statement doesn't really make sense.


https://cimg6.ibsrv.net/gimg/www.rx7...b16f1a81e3.jpg

Yea none of that works very well on an FC. You need to cram as much tire as you can under it.

I can't even tell you how much better my car is with 275s on 9.5 inch wheels vs the old 255s on 9 inch wheel setup.

If you like sloppy by all means:)

notice how everyone is doing the whole slight stretch thing, like all of racing that gets paid to race.

if you can fit a 275 you can fit an 11" wheel.

Remember I'm doing this on a track with actual timing and data logging.. not on a mountain road by Braille. I could care less what it feels like if it is consistently faster... But on that note, it feels great.

Come talk to us about slop after you have removed all the rubber bushings from your car.

I don't get paid to race, it is a hobby. I'm going to get a hell of a lot more speed out of my $450 set of 17x9.5 wheels and $1500 of aero components than I would blowing $2k on a set of 17x11 wheels to stretch my tires to net another tenth or two.

race cars wheel fitment.

formula 1 limits the width of the wheels. hey look, they chose stretched tires onto the wheels cause its faster.

The Wheels And Tires Of Formula One

Mazdaspeed is figuring it out.

MAZDASPEED Motorsports Development

urge designs tuner

Grip Wheels | URGE designs

michelin engineers who design tires even says to stretch them on the porsche race cars.

Alzen porsche and ford GT stretched tires. hell, I challenge you to find one race car that doesn't stretch.

www.cb-racing.com/PilotCup_Presentation.PPT

Michelin tire engineers even tell you if posed to run a wide tire on a skinny wheel....don't, run the smaller tire on the wheel and stretch.

I don't run rubber bushings.

Continental tire GS series runs 275/35/18 on 18x10s those are production based cars that actually relate to what we do with time attack and NASA, etc.

So based on the crap you just linked, Michelin says I'm running basically the IDEAL width for 275s. They recommend 265 on a 9.5 inch wheel and 285 on a 10 inch wheel.

I think I'll continue to be just fine. Honestly I would have bought 10s but these wheels were half the price.

How wide is the tread width on the 275's you run?

I'll look, they are Maxxis RC1. 10s would have been best, 11s would just be extra weight and expense.

I'm not arguing with you about the benefits of slight tire stretch, but you always seem to argue for stretch beyond the point of diminishing returns. I have not seen any full body production based race cars that run the type of tire stretch you are advocating - 275s on an 11 for example.

If I did 11 inch wheels, I'd be faster with 285s vs 275s.

The miata guys had THE SAME mindset until they tried it.

1” of extra wheel width is worth ~ 1 sec per min of track time

Over the last decade the Miata racing scene has followed this trend of plus sizing their front wheels. At first the fastest Miata’s where running 7” wide wheels. When 8” wheels broke onto the scene many thought they would be too heavy, soon however, the fastest Miata’s were all on using 8” wheels. When 9” wheels became available, doubt again set in about the weight penalty. Within a year, all of the top Miata teams where running on 9” wide wheels. Today, many are fitting 10” wide wheels on Miata’s and despite their lower engine torque, times are dropping further.

11 inch rims and 285 or 295 it is....damn now i gotto get ronin fenders instead of hotlineperformance +50mm ones ><
originally i wanted tamon design fenders but they are only +25mm.....
actually kuhmo states optimal rim width for thier semi slicks 285 tires as 10.5 btw

If you want to set it up right, look at the tire you are about to buy and look at the TREAD WIDTH. Your wheel width should be WIDER that this number. don't worry about anything else.

so for example. Yoko AD08R is a wide tire. 295/30/18 has a tread width of 11.5". I would run this on a 12" wheel. Same with the michelin pilot PS2 in 295/30/18.

The fastest autoX guys run slightly stretched tires and very wide wheels. 11.5 and 12" wide wheels. ad08R in 285/30/18 has a tread width of 11" run it on a 11.5" wide wheel. re-11 in 285/30/18 is only 10" wide tread width, run it on a 10.5" wide wheel.

Notice how everyone cheers the steering response of the re-11, the trick they did was run narrow tread widths because people don't look at the tread width to wheel width. their 255/35/18 is 9.4" tread width and people normally run them on 9.5" wide wheels. tire technology has also come a long way where the stretching isn't as big of a margin of improvement as before, but still an improvement.

the priority of wheels should be this.

1) wheel width (go as wide as practical)
2) strength/rigidity (stronger is better)
3) wheel weight.


notice how wheel weight is the last, yet everyone worries about it the most. lap times prove otherwise.

rc-1 for a 275/35/18

275/35ZR18 99W XL BSW 25.5 10.9 9.0-(9.5)-11.0 6 1709 50

run the widest, 11"

trust me you will be pleasently surprised.

You neglected to mention they are running wider tires as well... Imagine that. I run with many SuperMiata guys and they do not run rediculous stretch on their tires.

Saying that a 1 inch wider wheel is worth 1 second unilaterally regardless of track type and length is a rediculous statement.

Again, im sure it may run a little better on 10s or even wider, but I'm not going to gain a second for the extra spend on wheels.

I was more stretched before on 255s and the car feels better now with more tire, and ran the same times with 50+ degree higher track temps. Again, FCs don't respond to tire stretch like some other chassis do.

I didn't write that, Urge engineers did.


They mean 1 second per 1 minute of lap time.

so 3 minute lap = 3 seconds faster.

LOOKatme-

The FC does not respond well to a low profile, stiff sidewall, flat tread surface tire

because it has crap suspension.

----------------------------

On the FC chassis the tire's contact patch has to be able to deform to stay flat on the ground DESPITE what the suspension and chassis is doing to it.

If you want to go really fast in an FC its going to be big sidewall bias ply slicks on 16x12s.

Yeah, they feel gross to drive- but its fastest.
-----------------------------

Having a tire with a stable contact patch predictably located relative to the wheel as you are arguing for only works when the suspension is doing its job.

What part of the job aint the suspention on the fc doing right? i have not yet driven it since my last version of the suspention (pillowballs evrywhere and groundcontrol/konis and wide ass tires) but last year i had poly bushings and tein type HA and 235 yokohama semis and i thought the car drove well....a little pushy in the corners but nothing major....

The FC suspension is what it is. It's a Mac strut front and a semi trailing arm rear so nothing about it geard toward race inspired handling.

To really oversimplify it, all you need to do to make it work is plant the front tire contact patch on the ground as best as possible and let the trailing arms articulate in the back.

It ain't the best but it's far from the worst and it still works pretty well relatively speaking.

Well is sounds like you are on the right track. What is your setup and alignment?

Mine is all solid bushings, 275s all around, Custom coilovers etc. I have about 7000 track miles on the car developing it from a nearly stock NA FC with basic mods to a 400WHP track focused setup. So you can listen to people like Eage8, BlueTII, and myself and others who actually have experience with the FC on a track, or Lookatme that just reposts irrelevant conjecture and jargon.

While you are learning about suspension, aero and 20B trailing split here is some inspiration to keep you going on your pursuit of Time Attack FC3s.

Super Motobei and SuperNow FC3s are the ones to watch.

Current fastest Time Attack FC3s?

Super Motorbei FC3s-
FC???????FC3S?Blog?????Minkara - The Car & Automobile SNS (Blog - Parts - Maintenance - Mileage)

Relevant to this thread, note Super Motobei FC3s tire and Tsukuba lap time progression.

February 2014 current of the original Samurai ☆ FC specs

https://cimg8.ibsrv.net/gimg/www.rx7...643afb8c97.jpg


F spoiler Tamon design
F fender Tamon design-based one-off + 60㍉ (Auto sonic processing)
R Quarter 〃 + 60㍉ (ditto)
F lip Tamon design base
Canard auto sonic one-off [m: 66]
Undercover Tamon design
Side Tamon design
Bonnet Tamon design
Rear Diffuser over manufacturer unknown (not served by only brackets?)
GT wing super ☆ Now (Garni w bought in 1800㍉ + hardware store)
Door hatch FRP + acrylic (SK SERVICE processing)
Engine 13-B base Bridge port Top Fuel Racing (TFR)
Turbine Trust 07-25G (2009. December change)
Westgate third TypeJ gate silencer (auto Sonic one-off)
Computer V professional (TFR setting 500ps)
Intercooler TFR one-off
Oil cooler auto Sonic both sides distribution (one-off) (2010. March)
Radiator TFR one-off
Clutch Exedy twin metal
Transmission FD3S genuine (super ☆ Now conversion kit) + circuit shifter
Engine mount super ☆ Now (rigid)
Differential mount super ☆ Now (rigid)
Underbody Super ☆ Now "羯徒 毘" ← this Onunume! !
Spring Rates F11.6k R8.0k (2012. December)
Upper sheet super ☆ Now
Stabilizer bracket Super ☆ Now
R undercarriage (pyro) Super ☆ Now (lateral, scan Con main, Kyankonsabu, Tokon)
LSD Cusco RS (1.5wey)
Muffler GP Sports (propeller canceled)
Catalytic converter KTS Tyco
Dash Four site-based FRP (SK SERVICE one-off)
Meter Defi white (octopus, oil temperature, oil pressure, water temperature, boost)
Full backet of sheet D sheet ... Brit
Seat belt Takata 5-point

Circuit time until now

TC2000 only

1 minutes and 15 seconds 2 (01R F225 / 40/18 R245 / 40/18) 2008. April
1 minutes and 10 seconds 8 (55S / F225 40 17 R255 40 17) 2009. April
1 minute 09 seconds 6 (55S / F225 40 17 R255 40 17) 2009. October
1 minute 05 seconds 0 (050M / F235 40 17 R255 40 17) 2009. November
1 minute 04 seconds 9 (undefined undefined) 2009. December
1 minute 03 seconds 4 (undefined undefined) 2010. January
1 minute 02 seconds 9 (11S / RS F245 / 40/17 R255 / 40/17) 2010. February
1 minute 01 seconds 086 (050M / F255 40 17 R255 40 17) 2011. January
1 minute 00 seconds 731 (050GS / F255 40 17 R255 40 17) 2011. February
59 seconds 321 (050GS / F255 40 17 R265 35 18) 2012. January
58 seconds 322 (050GS / F295 30 18 R295 30 18) 2013. February
57 seconds 866 (050GS / F295 30 18 R295 30 18) 2013. December
56 seconds 495 (050GS / F295 30 18 R295 30 18) 2014. February

My setup as of today is:
Supernow pillowballs everywere
Fully seam welded
Full racing cage(to come next month)
Groundcontroll/konis 11k/8k (on its way)
Supernow tie rods
Re amemiya diff
Evo 9 front brakes/large FD rear brakes with yellowstuff all around and dual MBC
Fc2000front bumper/w home made splitter (150mm allowed only)
600hp 20b
Bmw 6speed gearbox
Speedway style swaybar up front
Manual rack
Very very lightened

Thats where i am now....alignment will be done after wheels are bought but i have last years figures somewhere

Thanks for the porn ;-) i can definatly see the pattern in tirewidth/lap time!

My setup as of today is:
Supernow pillowballs everywere
Fully seam welded
Full racing cage(to come next month)
Groundcontroll/konis 11k/8k (on its way)
Supernow tie rods
Re amemiya diff
Evo 9 front brakes/large FD rear brakes with yellowstuff all around and dual MBC
Fc2000front bumper/w home made splitter (150mm allowed only)
600hp 20b
Bmw 6speed gearbox
Speedway style swaybar up front
Manual rack
Very very lightened

Thats where i am now....alignment will be done after wheels are bought but i have last years figures somewhere

I would also suggest-

A rear wing (which you probably just didn't mention):nod:

Roll center correction at the lower front suspension arms if they aren't already done from the SuperNow parts.

Some form of positive location on the rear "subframe" to unibody (such as Powered By Max sub frame risers) and use the individual SuperNow or Powered By Max camber links to adjust camber if you don't have this already.

You might find you need to upgrade the the front spindle/bearing to something with wider spacing because of brake pad knock back issues when you go to the 295mm or wider front tires.
____________________

Sounds like your aero is actually pretty limited for a Time Attack series with just a 6" front splitter.

Are you allowed additional front canards and or splitter fences?

How much rear wing area allowed?

forgot to mention the rear wing....its limited only be the width of the car and height of the car and mounts must not protrude past rear bumper, so a 2d-bigass apc wing is probably what ill get

ill look into the roll center corrections but im not sure what u mean with subframe risers? mine is alu mounted (diff and subframe) and i got ronin links in the garage for camber, pbm toe adjusters and so on, i do have supernow hubs up front so i hope thats enough, otherwhise there is a guy in sweden that had porsche gt2 hubs and spindles on his fc and i might cooy it :-)

as for canards i can have 4 of them 50mm wide, cant find restrictions as of splitter fence or rear wing area....i do think front end downforce will be the biggest issue

the porsche/fc hybrid front end, claims 0 bumpsteer and very low rideheight, also gives you porsche brakes and struts...to expansive for me (since i built mine on fc parts already) but an epic setup!

Well yea you are certainly on your way. Is your front sway bar custom or the AWR one? I am looking to go to a speedway bar this year.

Also notice that the FC BlueTII posted does not have a ton of tire stretch...

i just want to add, that Mazda's stock fit is a 205 on a 7" wheel, 225 on an 8" wheel, and this hasn't varied since the FC came out. we are running a 205 on a 9" wheel, but hoosiers run wide, so its really more like a 225 tire

we've tuned a few suspensions at the track with pyrometers and such, and we've found that even the double wishbone cars want about -3 camber in the front, the FC isn't that different. i will grant you that we're tuning cars that are running 205 or 225 tires, i would expect a 295 to be different.

i did measure the FC camber curve, and found that there isn't one, its basically a flat line through most of the travel.

its been a LONG time since we ran an FC at the track, and we've learned a LOT since then, it would be really fun to set one up, they are great race cars, its like a big happy dog. like a labrador with some st bernard in it, or something.

On the FC we have in our group he stretches a 225/45/17 on a 17x9 wheel on the front. he pulls 1.1G on extreme sport street tires with a peak of 1.2G observed. only gets better with wider wheels. I should mention that this person ran the 4th fastest time at autoX last year in a field of 148 people, he beat some very good drivers.

The Miata that races in our group of people runs a 205 on a 9" wheel and runs 225 on 9" depending on the tread width. We both started stretching some years ago.

The group has many many many miles on track.

one vid for fun. He pulls 1.3G peak or so on extreme street tires with this set up. runs very fast laps as well with a miata at high altitude (not much power).

The perfect tire width sweetspot for timeattack FC?
 

Any miata examples you have are completely invalid. You can't get normal 23" tires in wider than 225s, so of course they're going to throw wheel width at it to make them as wide as possible.

There are a thousand examples of race classes being limited by wheel width and everyone running silly wide tires on narrow wheels because it's faster than narrow tires.

Bottom line, both tire and wheel width are important, get over it. You should fit the widest wheel you can with the widest tire you can in that order. If you're tire is too big for the wheel you did it wrong. If you can fit more tire, you did it wrong. Please stop distracting every thread you're in from more important discussion points.

the thread is about the perfect tire width.


its completely on topic. and many other cars can be used to help us determine what could be the fastest. my vote, fit the widest tire, exactly, then figure out the widest wheel width for the tire.

The perfect tire width for an FC is as much as you can reasonably fit on a given wheel. I'd stay on the wider wheel size of a given tire MFG recommendation.

Something to take note of is that the further you stretch the tire the snappier the car can become. I've noticed the car tended to snap loose whit less notice than when I went with a larger tire. This is also a function of running a smaller tire.

Since you are still on this jihad of misinformation, he would be even faster with MORE TIRE on that rim.

I ran 235/40/17s on a 9 inch rim, then ran 255/40/17s on the same rim. I was faster on the 255s. Both sizes were NT05s.

rx7jocke

but im not sure what u mean with subframe risers? mine is alu mounted (diff and subframe

Yes- same thing. You have what I was thinking of to keep the rear subframe from moving.:icon_tup:

rx7jocke the porsche/fc hybrid front end, claims 0 bumpsteer and very low rideheight, also gives you porsche brakes and struts...to expansive for me (since i built mine on fc parts already) but an epic setup!

Customized Porsche parts do sound expensive!

Your aero limitations sound a lot like my autocross class (street modified).

I'm running a ciro designs racing wing on my car. it uses custom length (to get exactly close to the width of the doors) APR GT-1000 elements. my current uprights fit all your rules except they go 6" above the roof, he can easily made some 6" shorter for you.
Wing | CiroDesign Racing


https://cimg6.ibsrv.net/gimg/www.rx7...d187aeffd1.jpg

eage8 thanks for that wing tips! i will definatly look into it!

This simple concept even a rotard could understand. If I hear anyone argue to the contrary I will find you; and I will kill you.