Determining the proper width size of the tire
 

How would you go about determining the perfect width of the tire in the front/rear relative to your application and power of the car.

I'd imagine for a car like this going any wider than 8inches in width would be too much unless you're hitting 330+hp.

I'm thinking a 7 inches in the front and maybe 8 inches in the back.
However, I have a feeling this car will come stock at 7 inches front and back.

Staggered is fine if the suspension is setup or it (ie setup for oversteer). If not having a traction bias in the rear is going to mean understeer. I'd wait until you were traction limited due to power then change rear tires and then change springrates/sway bars/alignment etc

That's not fully true. I used to know one Mx5 that was only 200whp-ish and using 9" on the rear and it was perfect size (don't oversteer or understeer). Like Dave state, it's all up on suspension setup.

I'm not gonna be staggered unless the car comes staggered.

+1
I'd rather keep it simple, hopefully Toyota agrees.

another +1. I like the look of staggered, but I think it's overkill unless I make some serious HP in this car, anything near stock I think should be kept the same, alot of engineering went into this car, and I trust that Tada-san and his cronies know more about correct engineering than I do :bonk:

Id agree that 7 all around in stock form should be ok, but it wont take much more power to reach the limits of that size. I would probably get rims to accomodate future plans.

With the 370z when you upgrade to the 19" wheels and tire grip increases from .92g to .98-.99g with the width only increasing by .5. I wouldn't go too aggressive with the width if I wanted to.

Subaru's PR already said 215/45/17 tires, so they will not be staggered. Since the tires aren't staggered then the wheels won't be either. OEM's tend to fit tires to the correct wheel size provided by the tire manufacturer.

For that size tire the appropriate wheel widths would be 7.0-8.0 for most performance tires. I honestly doubt they'd issue a 17x8 wheel so my guess would be 17x7 all around.

215/45-17? Ugh. Why an oddball size, I wonder? At least mfgs are starting to make some decent tires in this size now...though they can cost more than the larger, more common 225/45-17.

The other factor to consider when contemplating changing tires/wheels is the weight of the package. A car this light (2600ish lbs) and with this amount of power (190ish HP) will definitely feel different with just a 5lb per corner change.

Oddball size? That's common size. I use that size for my DD wheel.

Car is built around the tyres, not vice versa.

I would have preferred 225/45-17 as well but there are enough options for the 215/45-17 that I'll be able to find something.

At least there are RE11s, Star Specs, AD08s, RS3s and XSs in that size.. and some closeout R comps that are likely pointless to use at this point..

215/45/17 is extremely common. RSX, Civic Si, older Lexus IS to name some off the top of my head. I can't think of good tires that aren't made in that size, and plus nothing is stopping you from getting 225s afterwards (stock tires typically suck anyways).

I'd be happy with 17x8 at most. Anything more and I'd be shooting for form over function (concave TE37s, etc).

235... on a 10.5" wheel.

You laugh, but I guarantee some people will do it.

Hahaha, you're right, I do laugh. And cry a little too because I know you're right. :bonk:

& 3 months later, replacing wheel hub bearing

Gonna pull the **** move for the engineers and toss their shit out and slap on some RE-11s. Unless it comes with something like that from the factory (ha!).

i'm gonna run matched sets front and rear. that way i can still rotate tires.

Gonna try to tuck a nice 275 tire on my 9.5 CE28 on the rear.
Maybe a 245/255 up front for the 8.5

i bet the most amount of rubber the most amount of rubber that will fit under the fenders on the widest sized rims that they will fit on while clearing the suspension will be the best. i know that wider tires have disadvantages but from watching 120 hp miatas benefit from 225s on 9 inch rims i think you will run into fitment issues before you run into the point of drag taking more than width is giving

We should really have a Suspension tuning get together...

also a corner balancing day.


Anybody have scales and a good garage for a bbq weekend and suspension set up?

Now, a noob question: can the stock suspension be tuned? or do you have to buy coil-over first before trying the tuning the setup?

many stock suspension are capable of adjusting camber and caster angles. Tuning not always about height and dampening.

I have older corner weight scales i used on my rx7 and s14. I plan on having a get together for Seattle guys for people who want to corner weigh their cars.



to me when i pick the perfect tire setup, I have to consider the following,
1. Comfortablilty; are we looking at a noisy or quiet tire?
2. economic; does MPG concern you?
3. Grip (dry/wet); tred patterns that give better wet or dry performance, + channeling.
4. Tire life
5. Control

when i consider this on a 17x7.5in wheel, i can pick out sidewall height i desire, for example I want more control and a bit more steering sensitivity. I want it to look good too, so id go with a 45 or 40. I want more wet grip without sacrificing dry performance, So id go with an all season performance pattern with a Z rating and center channeling. id like to have more tire life but i dont mind sacrificing some milage or comfort, but not performance. so id go with a harder compound rubber. If i go with a harder compound rubber id like to increase my contact patch, so 225 sounds reasonable on a 7.5,

225/40/17 All Season performance on a 17x7.5 tire sounds like a winner to me.

if i wanted more dry performance id opt for a softer compound, and smaller contact patch and so a 215/45/17 sounds better

Do you offer a course in choosing correct tires for your application? I would like to sign up.

choosing a wheel size and a tire to match is backward in my opinion. especially when you start playing with diameter sized

hahah well its not really rocket science. Its pretty simple stuff when you learn and understand all the terminology. You can even learn a lot by tire brochures and reading on tire manufacturing processes.

It starts to get tricky when picking out the perfect motorsports tire. Then you have to consider; type of motorsports(drifting,roadcourse,drag), type of driving style(conservative, aggressive), ambient temp, humidity, elevation, sports compounds (different levels of soft and hardness),

your not wrong, sometimes you do need to work backwards (AKA working outside-in). Especially when your building a wheel and tire package from scratch.

For example, on a street car, if your looking at tire with a hard slightly stretched sidewall to fit flush with those fenders, and a contact patch width that clears coils/suspension. You get the best height and width size, and the rest (quality of the tire) is up for personal preference. Then shop for the best width for your wheel then offset then wheel height, (but you have to be careful with the offset because people tend to miscalculate and shit doesn't fit right). I see this method used with lots of tuners, and the STANCE/FLUSH community.

vs

Working inside out, starting from the center of the wheel we consider; Backspacing->Offset->width->height->weight->sidewall height->tire width
(sometimes considering multiple or all at the same time)

My golden rule is +0.5~1Width on Front wheels, +1~1.5 Width on Rear wheels is ideal.

Going +2 needs to be justified... Extra Horse power etc.


Diameter wise, +1 is very common, +2 is again needs to be justified.


I think it will come with 17x7.5 +45 on 215/45 tyres.

Which means 18x8 +37 Front wheels, 18x9 +37 Rear wheels for me! hehe

When it comes to real motorsports, refer to my first post in this thread. Otherwise (grassroots, track days), it comes down to;

1- What you are allowed to run (full race compound/slicks, semis, r-compound, street only etc)
2- What are you running on (prepared surface, road course etc)
3- Where/when are you running (hot/dry/cold/wet/ high or low elevation)

Those factors will pretty much determine the compound and tread you select. Then

4- Car type (RWD, AWD, FWD)
5- Car setup and by extension, driving style.

Mostly in that order.

The last two will influence the size you want to run, the pressure you run them at and whether you stagger them or not.

It comes down to how serious you are at what you do, tyre selection can be quite the science depending on what rules you play by. Of course the criteria for the street is a whole different ball game and WoW's previous post pretty much summed it up, though different people have different priorities.

That is, of course, if you have the means to be able to justify swapping tires all the time. For me, I'll just stick with a decent summer tire since I won't be tracking it all that often.

many performance summer tires grip VERY well in the wet. i have a truck for snow/ice. my FT will have summer-only tires.

you absolutely do NOT need all-season tires for rain.

what about -1? Throwing on some 16s on smaller whell less rotational weight?

17 x 7,5 plus 5 x 114,3 would be great so I can use my oldskool BBS!

+1 on -1 although i think 17 is okay. it was sad to see what 18s on the elise when they first came over simply because theylook cool. i have a feeling that 16s might be too tough to shop for because of brake clearance i dont really know how the tire selection is for 16s. seems to be that 15s and 17s are where the coolest street sizes are

For 16s, the most perfect match in overall diameter is 245/45/16. Assuming they fit that'd be great... assuming you want to run R comps since that's all that's available in that size.

For a more reasonable 225/50/16, which is .3" total diameter larger than 215/45/17s you can get all of the normal suspects in the extreme summer category (RE11, XS, AD08, Star Specs and RS-3) plus a large selection of R comps.

I'd likely run 16s and either 225/50 or 245/45 if they fit for track use without a doubt. I doubt this car will have large enough brakes to prohibit the use of most 16" wheels.

For the street, in terms of pricing (TR)you can get (225/50/16 for 16" vs stock 215/45/17 for 17"):
Star Specs: 16"=$133, 17"=$144
AD08: 16"=$164, 17"=$172
RE11: 16"=$178, 17"=$199
RS-3: 16"=$102, 17"=$129
XS: 16"=$121, 17"=$128

So for the most part, there's not a great amount of difference there either way except for the RE11 and RS-3, $21/tire for the RE11 and $27 for the RS-3. I'd likely run the stock wheels on the street and 16s on the track/autocross (assuming R comps, I wouldn't want to go up in overall diameter to stick with street tires, the gearing change will more than offset anything else IMO - and there are no new/good R comps in the stock size) $40 or so extra for each set of tires is going to be cheaper than 2 sets of 16"s for a long time....

Now assuming you don't mind spending money.. if they'll fit 245/40/17s are only .1" overall diameter larger.. and all the tires are available in that size (extreme performance and r comps).. RE11s are only $244 each... AD08s my current favorite tire is $204 each.. ouch..

Now 235/40/17s will actually let you reduce the overall diameter by .5" (making for shorter overall gearing) and while tire selection isn't as good... you can get RE11s for $224, AD08s for $189 and Star Specs for $162. Better than 245/40/17s but worse than the OEM sizes price wise. Also the new gForce R1 is available in that 235/40/17 for $255 for those who want a R comp...

Load ratings change depending on the size selected and if lower than OEM could be a potentially dangerous setup, so check all that before making decisions on tire/size selections.

I just remembered if the rim is sold as 17 x 8 (which is what I want), the rim width is really 1 inch wider from bead to bead. That seems plenty wide for this car!
MY 2 Favs right now: SUMMER / WINTER
http://www.tsw.com/img/alloy-wheels-...er-std-250.jpg
http://www.tsw.com/img/alloy-wheels-...er-std-250.jpg

I always see people go on and on about fitting wide tires.....just to throw crappy all-seasons on the car. Compound is much more important than tire width. I'll take a 215 good summer tire before a 255 all season.

Hopefully some cheap used takeoff subaru wheels fit for use as winter wheels. Maybe make a coffee table for the wheels i'm not using. :lol:

- Andrew

Glad I'm not the only one!