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.