need rims for s13,

[Red coupe]

Im getting ready to start going over the suspention on my 92 coupe daily driver and I plan on getting coilovers, (most likely spl) so to fit I need spacers or new wheels. Originaly I was planning on getting the fn0cr-1 or whatever from spl, but the lowest width they have is 8', I plan on auto crossing so I want to get a maximum of a 7.5" width to stay in street touring. I was thinking 17" but most ive seen are so much money. I need a rim that is 7.5" wide max, clears coils,around $200 per rim, good tire options and a larger contact patch.

I dont realy care about sunken or flush, Id like it to look good but not realy important as I cant even see them while driving anyways, but fake rivets/bolts bother me. Do any rims come close to fitting my needs?

[hannibal]

Z32 wheels are 16x7.5" +45mm offest. They clear 30mm Z brakes (duh!) but I dont know how they fit with coilovers.You can get a set for around $250...

[cdlong]

the z32s won't fit with C/Os, they barely fit (the tire rubs sometimes, but the wheel itself fits) on s14s.

i don't know what your tech inspection is like but i doubt anyone would care or question you if you had an extra .5" of wheel, as long as you stayed with a 225 or under.

[Red coupe]

I dont know what tech inpection is like either cause I have been auto xing yet, Ive heard at lower levels of compitition and for beginners that they less likely to point out that kinda stuff. You make a good point about just staying under the 225 and not worrying about 1/2 an inch, might end up doing that, but it wou be nice knowing I was set up properly and couldnt be contested if it just so happens Im the best newbie autoxer ever

[Exar-Kun]

Volk/Rays Gram Light 57C they run 220-250 a wheel

17x7.5 30mm offset. its what I run. 225-45-17 or 215-45-17..

also, its just a wider contact patch, its not bigger.-Chet

[hannibal]

the z32s won't fit with C/Os, they barely fit (the tire rubs sometimes, but the wheel itself fits) on s14s.

Sorry to thread jack, but even the 7.5" NA wheels have fitment issues on S14?? I thought it was only the 8.5" TT wheels that couldnt fit up front.

[Red coupe]

also, its just a wider contact patch, its not bigger.-Chet

it does increase with tire diamiter though right?

[cdlong]

i helped a friend put some NA wheels on his s14. he had two different brands of tires, one rubbed, one didn't. it was the tire that rubbed, the wheel itself is fine. 215s would be fine, 225s are a crap shoot. or a 5mm spacer would be enough.

the area of the contact patch will stay the same for a certain car at a certain tire pressure. a larger tire (either wider or larger diameter) will deflect less at a given pressure.

[Red coupe]

SO Ive though about it more and it makes sense to me now, but it still seems that if I put somethen extream like a monster truck tire on that It would have to make more contact with the road, but i guess an undeformed circle would make the same contact with a line regargless of diamiter, and that how much a tire deforms is dependant on the load applyed and the pressure in the tire...so I guess not.Ive been looking around and its hard to find those volks rims, any one know of a good place to get them?

[BuudWeizErr]

it does increase with tire diamiter though right?

no, their theory is somewhere along the lines of no matter what tire you run, you will have the same overall area gripping the ground. I'm assuming its based on the cars weight. when the car leans is when it puts that extra tire width to use. otherwise, race cars would all use bicycle tires.

maybe chet will clear that up, but I'm pretty surethats the jist.

[Exar-Kun]

Well, most of this is covered in the TIRE FAQ....the "no one reads this" sticky...and also in my rant in a thread earlier...

but anyways. Ryan is correct, the contact patch area stays the same holding the weight and inflation prssure constant, regardless of tire width or OD.

now....for the "what does that mean"..well..everything and nothing..hehe. woohoo contradictions!

onto bizness:

If you increase the section width of a tire (assuming propper wheel width, etc) and keeping the OD the same (reducing sidewall height, usually) you'll go from a long contatch patch to a wide one (relatively).

for instance if you had a 205-55-16 tire, and went to a 245-40-17 tire (for example purposes) you'd widen the contact patch by a certain percentage, and reduce its length (relative to the car) by the same ammount...

this nets you the same contact patch area...if it helps, think of a balloon of differnet sizes..as long as the force you're pushing down on it with and the pressue in the baloon remains the same, the squished area may change shape, but it's total area of contact will remain the same.

now then, why go to a wider tire?

the biggest reason is wider tires typically com in stickier compounds. THe second reason is they have more total surface area and thus slighly better heat dissipation (if this is a concern).

but..in effect everyone tries for a "square" contact patch. A squarer (or even slight rectangle..skewed toward the wide side) give the tire a bit better lateral stability and turn in, if not necessarilly more "contact patch".

Race cars run wide tires for a few reasons- first being they run rediculously low pressures (hows 24psi HOT sound?) which takes their contact patch into the more 'square' realm...secondly they typically ahve far more downforce to deal with, so the flattening out of the contact patch is important at speed to add to lateral sability. Also, race cars are willing to sacrafice some of one to get another..IE they may run a wider tire than is "optimal" for a necessary result like better turn in, etc.

One thing to note, a wider lower profile tire can generate a greater cornering force for a given slip angle, within reason. The means it does this by is when weight transfers, it widens the contact patch (making it squarer) and also the tire has less distortion of its contact patch because the sidewall itself is stiffer...

I think that does it. I'm going to be uploading some nice pics of slip angles and things soon...

-Chet

[Red coupe]

SO Ive though about it more and it makes sense to me now...but i guess an undeformed circle would make the same contact with a line regargless of diamiter, and that how much a tire deforms is dependant on the load applyed and the pressure in the tire

I think it has to do with the fact that no matter what diamiter the tire is it still only come in contact with the road plain at its very edge(with no load, assuming the undeformed tire is a perfect circle) so changes in diamiter dont affect the point wwere the road and tire meet. As load is aplyed it squishesh the tire(almost like cutting off the bottom of that perfect circle so that it meets the road plain with a flat edge) how much the tire is deformed, and thus how much area there is in the flat edge of the tire touching the road is dependate on how much tire pressure there is resisting deformation and how much load there is as the rim.As tire width expands the area of contact between the tire and road is widened and the load is distributed over a wider surface, and the tire does not deform as much as it did on the narrower rim so not as much of the circumferance of the tire come in contact with the ground and the contact patch becomes shortened.. right?

edit: looks like you posted while I was typing this...guess that answers my question...
Modified by Red coupe at 8:56 PM 1/5/2005

[Red coupe]

wait... just ran numbers through the offset calculator and im looosing 9mm of strut clearance with a 30mm offset. If these wheels clear coilovers, then so would my stock wheels wouldnt they? but I though Ive read many times that stock wheels need a spacer to run coilovers? soo.....

[Exar-Kun]

they'll clear most coilovers. I evne think they clear the HE's....

but coilover clearance hasn't been an issue. I know 3 people that run this setup (similar offset wheels, etc) one runs a slightly wider 8" wheel and it still cleared....

-Chet

[sdtouge]

look around on the net, i am sure you could find some cool 16x7.5 5zigen fno1rc or whatever. tires will be cheaper, whels will be chaeper. only thing that will be worse than 17 is the wheel gap but dump it with your coilovers and no more gap.

he cant get the z32 wheels, he has s13 4 lug.

for coilovers i really recomend the tanabe pro-ss type 2. you can dump them alot. they are easily adjusted, and veru stiff. they also fit with the stock wheels:)

[crzycav86]

I'll take this thread as an opportunity to learn more about contact patches, and perhaps get some reasons as to why the following ideas about contact patches are wrong..

Exar-kun: Perhaps this visual aid will help you understand what I'm trying to I'm trying to understand: http://members.aol.com/skybolt86/cp.jpg

The top right picture shows the length of the contact patch of a tire on an unmoving car.The top left picture shows the length of the contact patch of the outside wheel of a car that's cornering.

The bottom pictures are the ones that I'm trying to figure out...Without the other factors involved, won't the maximum theoretical length of the contact patch be that of the bottom left figure?(remember, no factors)If that's true, won't the a higher sidewalled tire shown in the bottom right figure have an even longer maximum theoretical contact patch?

Think about it, is a 225/35/20 tire going to have the same contact patch area as my 225/55/16 tires?(on the same car, at ~ same pressure)

Please, no one take this as fact by any means, I just want to understand why this doesn't hold true.

[Exar-Kun]

"Think about it, is a 225/35/20 tire going to have the same contact patch area as my 225/55/16 tires?(on the same car, at ~ same pressure)"

yes...a higher sidewalled tire will have a longer contact patch while wider tires have wider ones..but the area itself will remain the same.

that picture you have doesn't hold up real world though dude..."no factors" isn't something you can freely assume. higher sidewalls mean a lot of things, deflection etc..and in those pics you have the tires running akin to deflated also...which will increase the overall contact patch at the expense of handling unless the tires are capable of running lower pressues without hitting the rim (which your illustration shows).

and you'd enver see a tire hit the apoint unless it was about to blow out. load or inflation wise.

like I said before, its easiest to think of different shapped baloons. the only thing affecting total area of contact will be load and inflation pressure....

-Chet

[crzycav86]

Well, I meant for that point to be theoretical. Think of it as the limit that the length of the contact patch approaches, with infinite amount of weight put on it.(without blowing)

So now that we clarified that I'm not completely incorrect, it brings me to my next question.. Isn't the maximum area of the contact patch(when cornering) limited by the width of the tire, as well as the maximum theoretical length of the C.P? I'm still just speculating...