ford 03 svt cobra wheels

[jtmcinder]

The key issue to rear-tire fitment on a 2G is the corner of the tire, which comes very close to the rear knuckle. When you go to a bigger-than-stock diameter, you must move the tire outwards to avoid contact here. So, while a 245/40/17 Kumho MX does not rub on a +40mm offset, a 245/45/17 of the same design would definitely hit the knuckle on the same wheel.

Given that the knuckle is at about a 45-degree angle at the point of contact, my first guess would be that you would need to drop the offset by about 10mm to get 245/45/17s to fit, but this will depend a lot on the brand of tire. Azenis, for example, have very wide treads for their stated width, while Kumho MXs are average. If you can learn the actual tread width of the tire that you are considering, then you might be able to figure this out.

The next issue, however, might change your mind. When you decrease the offset, the outside edge of the tire comes closer and closer to the fender lip (rolled or not). I'm doubt that a 245/45/17 on a +30mm offset will tuck in. Maybe it will if you don't have a rear camber kit, but I doubt it. And who runs a 2G will no rear camber kit?

- Jtoby

 

[TurboMike]

I've used many tire brands of 235/45-17 (on 17x8 40offset) and never had suspension rubbing (although its close as hell), so I was using that as a datapoint. I want to keep the tire as close to the suspension as possible to keep away from the fender. Fender rubbing can always be fixed with stiffer shocks/springs/cutting/bending, but suspension rubbing is time to sell brand new expensive tire and wheels on ebay.

This is what I've been using to help figure it out:
http://www.350zx.com/tire-wheel.html

With 245/45-17 (10mm wider, or 5mm inbound and outbound) and a 5mm change in offset (17x8 40mm to 17x9 35mm) I'd basically be moving the tire outbound (toward fender) and keeping it in the same inbound (toward suspension) distance. Add to that the sidewalls are getting 10mm wider and the tread/shoulder will be less, with a real move of 5mm from offset difference, I should be golden. I thought I was good to go until I realized a 17x9 wheel will move the sidewalls of the tire out, and also make the tread edge more square. So now I'm back to not knowing if they fit or not. Also I dont see any way of calculating how much more the tread edge will move inbound. I've found some website calculations (Yokohama.com) that say as a general rule every .5 inch of wheel width increase you get about .2 inch of sidewall increase, but thats the sidewall. Logic tells me the tread/shoulder should hardly be a factor, but logic and tire sizing dont always work out.

My next plan of attack was to try and look at my 235/45-17s on the car now and figure out if my real problem will be the sidewall or the tread edge (shoulder) hitting the suspension, and look around the web and see if anyone had 245/45-17 on 17x9 with 35mm offset and see if its been done. Thats how I found this post. Going with a 245/40-17 will give me a little more wiggle room, but I cant figure out if that will be enough, or if I even need it.

 

[wret]

Originally posted by TurboMike
I've used many tire brands of 235/45-17 (on 17x8 40offset) and never had suspension rubbing (although its close as hell

I calculate that 42mm is the practical maximum offset for 235/45/17's. Exactly how close is hell?

In my limited experience, you can pretty much disregard wheel width when determining tire clearance issues (within reasonable limits of course).

 

[jtmcinder]

TurboMike -

You missed an important part of my post.

245/45/17 is not only wider than 235/45/17; it's also larger in diameter. And, as you make the tire larger in diameter, you must move it outwards, even if you don't change the width, because the part of the rear knuckle that hits first is at a 45-degree angle to the corner of the tire. That's why I said that you've have to move outwards by 10mm, instead of just 5mm. You move out 5mm for the width of the tire and you move another 5mm for the diameter.

If you don't understand what I'm talking about, go out and look at your car. Look at the way the rear knuckles wraps around the top inside of the rear tire. That's the issue.

And, again, if you're thinking 245/45/17 because you want the big Azenis, then give it up right now. The tread on an Azenis is so wide that it won't tuck in if you have a camber kit. Yes, somebody put some 255s on a 2G, but the practical options are 245/45/16 (MX), 245/40/17 (MX), or 225/45/17 (Azenis). If it stays cool where you are and you don't go to open tracks, then the Azenis have the most grip and best response. If you have to face heat or wish to drag race (and therefore need to stay away from the Azenis' stiff sidewall), then 245/40/17 MXs are good.

- Jtoby

 

[TurboMike]

Hm thats right, the tire is now 4/10th of an inch taller. I can solve that by running a 245/40-17 and have the speedo be off by 2mph. That way I can use 35mm offset wheels and not get too close to the fender with 30mm. The wheels I want are 35mm.

So like I assumed (I havent had to chance to get to the car and try and use a mirror and see how close the sidewalls the suspension is) the shoulder of the tire is the real problem with the suspension, and I dont have to worry about the sidewall moving out with the 9inch rims? So if I ran a 245/40-17 on 17x8 or 17x9 it should make no difference?

These will also be my street and occasional roadracing tires so I wouldnt get the highway greasy Azenis. I've looked at the MXs and they're great for the price, but based on Tirerack's testing I was looking at S02s (if I can find them) or S03s, Pirelli Zero Nero, or the new Goodyear somethings. I forget all the stupid letters on the Goodyears. They all tested a lot stickier than the MXs. Those are all in the $180 to $200 range compared to the MXs in the $150-$160 range.

So you think I'm safe with 245/40-17 on 17x9 with 35mm offset? I'm still worried I'll have problems and am hesitant to order.

 

[wret]

Max offset for 245/40/17 should be around 45mm. With 35mm offset, you should have enough clearance for snow chains.

 

[TurboMike]

That sounds off to me. I know 235 tires are almost on the suspension with 40 offset, you're 5mm closer with a 10mm wider tire. The stock wheels are 46mm. How do you increase tire size by 30mm but only move 1mm away from the suspension than stock?

 

[jtmcinder]

Guys -

You can get close to the right offset using general statements based on various formulae, but when you're pushing the limits, it all comes down to the tire. A 245 Kumho is no where near as wide (at the tread, which is what matters on a 2G) as a 245 Azenis, for example. So, you have to start talking to people who have run the combo or you have to go and measure the tread on a car (with the right width wheel, of course).

I run 245/40/17 Kumho MXs on a 17x8 +40mm wheel. It is close but never touches the knuckle and it just tucks inside a rolled fender lip, even when I have about 3/8" of spacers to take out camber. This is about the maximum (in terms of width and performance) that you're going to get in a summer and rain tire.

A 235/45/17 also works on a 17x8 +40mm wheel (at least a Kumho 712 was no problem), because the extra diameter is compensated by the smaller width. The problem with that set-up was the grip of 712s.

- Jtoby

 

[TurboMike]

Unfortunatly tire manufacturers dont release tread width info, so I have to go with what I can. So it seems like I'd be ok with an MX tire in 245/40-17 17x9 35o, too bad thats not the kind of tire I want to try.

I guess it will come down to buying what I want, and if the shoulder of the tire hits the suspension I ebay them and go for MXs.

 

[jtmcinder]

A 17x9 +35mm will not cause a 245/40/17 MX to hit the knuckle. The issue is going to be the other side. 245 on 9"-wide wheel with only a +35mm offset is going to bring the sidewall against the fender lip. Even if you roll the lip, you won't be able to use a full set of spacers to take out camber. So you'll either have to keep the car up (which isn't always a bad thing), run high rear rates, or risk rubbing.

- Jtoby

 

[candela]

Im not really going for looks Im just going for the rubber...looks are a by-product

eclipse4G63: young lad we have a lot to learn I really do not want this thread to turn into somethign stupid and have a bunch of people arguing with me, so hear me out before you shit your guys' pants and start trembling on the keyboard ready to type what biggot I am....

If you are going for rubber than go for rubber. There is NO need to go so wide unless you REALLY plan to hit the twisties in auto-x or something and a 9" wheel is still to much for AWD. THere are LOTs of cases I can think where it would be beneficial but for 99% of everyone on this board anything wider than 225 is silly. Your contact patch area will remain the same regardless of how wide you go. SO if you think by going to a 245mm tire over a 215mm tire you will be gaining more of a contact patch you are mistaken... it only gets wider, it does not cover more area. In some cases that can be beneficial, but with a nice sized sidewall on the 215 (like 45) all you will really notice for the outcome is more $$ out of your pocket.

For one those wheels will stick out if they are anything less then like +38'ish mm offset since they are 9" wide. I had cobra wheels on a 240sx that could handle those offsets. I bought them for cost reasons as well, but they were 17x8 +35 F/R. Even though they werent hubcentric I still used them....

If you truly want to increase your performance from tires than get stickier ones period. Most likely the reason for going wider w/smaller sidewall is that more manufacturers make sitckied compounds in those sizes. Smaller sidewalls have advantages, and everything plays a give and take relationship... but if you are really into performance than maybe just consider some cheap/light Rota's in a 17x8 or 16x7 or 8 or so. Get a 225/45/17 cause the overall diameter with tire is only a few mm's off from the stock sizing and yoru speedo/gearing will for the most part remain accurate.

No offense to all those that want to stick such bigger tires on there car cause they have so much more "grip"... most of the time when they want 235's or 245's they realize the price of tires at those sizes are a crap load and spend less on the quality of rubber. Give me some 195/55/14's or something with some good rubber and I will wax the floors with some joker who thinks there "275's" that they rolled their fenders for are going to concuer all....

muhahahahhaha ANyhow, good luck with your choice man. if anything buy them and resell them cause they definetly go for more than $600 a set.

Austin

 

[jtmcinder]

Originally posted by candela
Your contact patch area will remain the same regardless of how wide you go. SO if you think by going to a 245mm tire over a 215mm tire you will be gaining more of a contact patch you are mistaken... it only gets wider, it does not cover more area.

GMFB!

Yes, a 215 tire, because it will have a higher aspect-ratio, will have a slightly longer contact patch than a 245 (assuming the same wheel diameter, the right tire pressures, and the right wheel widths). But if you think that the gains in contact-patch length will make up for the difference in width....

- Jtoby

 

[candela]

Dont be one of those guys that turns threads into something they aren't, nowhere in my post does it show I even hinted that. So just stop before its gets silly k...

I agree, my point being the kid does not need to be putting on expensive tires (as I said more than 225's) instead just some good rubber as he has awd. period.... dont change it at all thanks

 

[jtmcinder]

Originally posted by candela
Dont be one of those guys that turns threads into something they aren't, nowhere in my post does it show I even hinted that. So just stop before its gets silly k...

Oh, I'm sorry. You see, when you wrote that a 245 will have the same contact-patch area as a 215, I thought that you were claiming that a 245 would have the same contact-patch area as a 215. Again, I'm sorry for misreading that. Please don't call me a young lad, too. English is clearly not my strong suit.

- Jtoby

ps. moths move toward flames; I am likewise attracted to the technical terms of handling - especially when they seem to be being used to merely give the appearance of wisdom and/or brow-beat someone who is actually here to learn - and this can bring us back to the issue of flames

pps. a 245/40/17 Kumho MX costs about $125, which is about half the price of a 215/50/17 RS-A (which is the OE tire)

 

[candela]

Take a pill man, as I said im not here to argue with anyone.

However if you want to try and prove me wrong then go ahead
Show me, pics/writing w/e you possibly can how the entire area of a contact patch grows when upping the size-- ofcourse assuming that all pressures and everything else remain equal...

245/40/17 Kumho MX costs about $125, which is about half the price of a 215/50/17 RS-A

Well when you compare the same thing then my point will come into effect. I am sure I could find a nice set of used v700's for less than your mx's and get the same point you tried to make but its not the same thing. PLainly put a 215 mx will be cheaper than a 245

BTW-jtm my point is not to make prove you wron, its simply to point out you will gain and save more buy going with a settup that require less modding and $$ in the short term and long run. I am not a dumb ass.. and clearly understand that a 205/55 will have mroe rollover than something a little wider with a smaller sidewall. i understand the gains you get from that as well. All things the same (as said above) like wheels, pressures, corner weights...etc the patch is the same. WHen you go to a sidewall with less flex then you gain a lot in a lot of situations and when things change (like cornering and corner weighting) then contact patches area's change as well. We both know this...but when you get to a point (like I said in my earlier post again ) where the side wall is small enough on both widths (tires compared) then this is sort of the breaking point to where maybe you shoudl stop and say "I do not really need anythign wider than this as it wont do much for me--espeically since I am AWD--aside from make me spend more money on tires).

 

[monotalonawd]

I have a 1g and last summer I was running Cobra R wheels with 235/40/17 with Eibach Sportlines and blown stock shocks and never had rubbing problems with the shocks or fender or anything. But I have to admit those Eibach are stiff as hell Yes the tires stick out a little but when lowered, it makes a Talon look very mean I got a lot of compliments from people on the streets.

Last month I bought some 255/40/17. I now have KYB AGX's. The tires are mounted on the rims but I did not have the chance to put them on the car because of the weather so I don't know if it fits. If it doesn't, that's not too bad because those wheels fit better on my 93 Probe GT(more space for larger tires)

Like it has been told previously, it is not because you have larger tires that it is going to grip more. I could spin the tires in 1st with my 14b and awd! I bought them because they were cheap for 17's (about $145 us new) and because of the look it would give (wider track). And also the model year I got looks like just any simple 5 spokes wheel on the market except for a larger outer lip. So it is not like you tried to look like a Mustang

 

[Revolution]

Wow I guess we are all lucky to have some guys who know wtfk they are talking about because halfway through this thread I was honestly lost.

But back on topic I will be trying some thing new this year as far as drag racing is concerned . I have found within my grasp a set of four light 15/8 rims and a set of 16/8. I currently think they are both from ford or one is from pontiac Well that doesent matter.

What I wanted to know wich would be better for my awd in drag racing ?
At first I thought that the 15/8 would be the if all and all. Then I realized whatever I gained down low as far as traction and a quick trap speed /rpm I would ultimately lose in the top end when the car is in full motion.

So I started looking really closely at all of the pro driver interviews you see in magazines. And their split some have 16 and others the 15 (mostly honda with the smaller rim).So what do I do?? I will be running with the bfgoodrich drag radials as it is pro street but I dont even think 15" would slip over the calipers.

I am stuck in the crossroads I'll be happy with 225 to 235 tires. I could run 225/45/ 16 on the stock rims as that is what the previous owner had done, but how much do they weigh??


The time to begin racing is almost upon me and my car is under surgery so im strugalling with things like this.

 

[jtmcinder]

Candela -

I, honestly, can't figure out what you are trying to say. I don't know if you really believe that 215s have the same contact-patch area as a 245 (all else being equal, blah, blah, blah) or if you simply believe that the typical 215 setup has the same patch or if you just got caught posting BS and are now trying to back out. And, at this point, I don't really care. I think my counter-point to your argument against widening tires has been made.

To the extent that this forum is about handling (as opposed to being specific to suspension mods), then, everyone, please keep the following in mind. The single most important aspect of your car for handling is the tires. "Tires is what wins races" and all of that sort of thing (which is one of the few accurate things in that movie). You plan a race car with the tires in mind. You design the suspension to work with the tires, not the other way around.

Put another way, if you are starting with a bone-stock 2G, the first $1000 goes to the wheels and tires. Not lowering springs. Not even shocks. And with the exceptions of rallying and ice-racing, what you want are the widest tires on the lightest wheels that you can afford. The only long-term issues that you have to think about are your brakes. You want the smallest wheels that fit over the brakes.

Yeah, OK, maybe a lot of people aren't going to reap all of the benefits of 245s on 8"- or 8.5"-wide wheels, for a variety of reasons. But it will always be better than 215s. And the main reason for this is the larger contact patch. And larger contact patches are always better because the function that relates weight to grip is sub-linear.

- Jtoby

 

[candela]

Well I am glad this has not turned into an argument of any kind. Tis why I will gladly reply and try to get my point across. Sometimes it can be fun an/or a learning type thing for at leist some one who reads this.

I, honestly, can't figure out what you are trying to say. I don't know if you really believe that 215s have the same contact-patch area as a 245

I will explain... something to remeber, a wider tire means a wider contact patch, not a larger one.

The contact patch is a function of tire pressure and vehicle weight. There is a formula i once saw somewhere but there is no way that I remember it. If weight stays the same and tire pressure stays the same then the AREA of the contact patch will stay the same. There are caveats for tire void ratio or vehicles with other than 4 wheels. If you put wider tires on your car/wheels then contact patch will just get wider; and along with wider comes shorter... Think of the tire as being something like a inner tube or balloon. Regardles of what shape the balloon is, if the pressure and weight over it remain the same then you can change it all you want and the area of balloon to surface contact will remain the same.

However I am not saying wider tires are crap, as that would be silly. But going too wide and you are just wasting money IN MY OPINION (on certain cars that changes ofcourse). A wider tire does have some benifits over its narrower counterparts. With a wider contact patch comes a bit better lateral stability (to a point, lateral stress doesnt vary to much between narrow and wide tires), but sacrafices some ride comfort, and less noise cancellation (in theory). Wider tires will have more lateral stability because the contact patch will stay wider when under stress/cornering (obviously) distributing the focrce a bit better across the patch, in theory, whereas a thinner (longer contact pach) will distributre it more length wise, causing it to possible feel "less stable".
Now obviously the benefits can be seen, though narrow tires really only make a difference in snowy/icy or REALLY wet/slippery conditions will a tire with a narrower patch/tall sidewall be more beneficial than something wider. Wider+tall = good in that case as well...


Grip is dictated by friction first, all other variables second. Those other variables are very important however. Wider tires DO grip better in most cases. The load index is higher on a wider tire and less of a "rollover" feel is noticed. The wider contact patch is--as said earlier-- more stable in turns and IS a good benefit to have. However in most cases a stickier tire will prove MUCH more valuable. A nice combo of wide/short sidewall/sticky is optimal...going to wide is overkill.

My initial point however is not to prove this, it is just that on DSM's (relatively light when compared to cars that naturally come with 245mm+ tires, as in heavier like supra's and stangs) you will be better off with NOT trying so hard to fit those 9" wheels with 245's in there for time/money issues. Everything is a balance in life... in most cases wider is better but I do not agree with what was said earlier about "wider always being better"...

But it will always be better than 215s

In this case you were referring to 245's..in which I disagree. Since we are on a DSM board I will be car specific. I do not see ANY benefit to going to a 245 tire over a niec 215 or 225 (even 235). Why? Well even though in SOME cases it may be beneficial, those cases will MOST likely NEVER be seen by any of these people on this board. Which in my mind means one thing- more money spent in the long run (where it coudl be better spent upon other things)....

Any questions feel free to ask JTM- I hope this has helped a little; if not...well i tried right.

 

[TurboMike]

Oooook. Point taken. So for everyone who wants to save time and money, doesnt care about looks, and doesnt care about handling, stick with the factory tire size.

Contact size being equal, a thin (and long) patch will be great in the snow and very stable while going straight while a wider (and shorter) patch will have better handling. Then we get into the fact that the tire track (distance from outer edge of each tire) is now wider (better handling). And keeping the diameter/roll of the tire the same yet changing the aspect ratio, the contact size does get larger. AND it looks killer on a car.

I think we're all talking about a set of tire/wheels to make our cars handle and look better in this post, without moving to race rubber which usually cant be run on the street. So if you dont care about looks or handling and just straight line launching (if you have AWD), there you go! For everyone else, keep the input coming.

 

[candela]

I want to go from 235/45-17 17x8 40offset to 245/45-17 17x9 35offset and am having a whore of a time figuring out if the 9" wide wheels will make the tires too big to fit on the rear of a 2G (rub suspension).

This is my point exactly Mike... what do you look to gain from this? What will you gain over your current settup? Will it be noticeable?

I don't want to argue, but if you don't "like" my input then theres no reason to bag it man. I have first hand experience with this subject--especially on AWD DSM's-- and have been through lots of different wheel/tire/auto-x combo's, so don't take what I said and try to make a tool of me man, you know don't stress peopel stay on stock settups.
I explained in my post the benefits of all.

 

[TurboMike]

Well, I see a post someone asking about certain wheels to get more rubber on his car and also have it look better than stock wheels and tires. Then some replys asking about different (larger) tire sizes and fitment for better handling. Your input into this is that stock sizes should be good enough for 99% of us and we're wasting our time and money. Hows that look to you? Maybe its just me.

What I was trying to say (granted rather sarcastically) is that maybe more than 1% of us want better handling and or looks and your long post isnt going to convince us we're wasting our time and money. I didnt mean to bag your reply, but after "bagging" everyone in this thread into the 99% of people who dont know shit I dont think I was too over the top.

Anyway, enough internet bullshit lets get back to talking about cars. I apologize if I insulted your reply.

You asked what I expect from my post to this thread, here it is again:
I run 235/45-17 on 17x8 40o right now. The rims I use are too heavy, so I'm shopping for new rims. So I can go with any rim/tire combo I want. They're going to be street and autox tires, so race rubber is out. 18s are too heavy and I have Baer 13" rotors so 16's wont fit. 245 tires would be 10mm wider at the sidewall, and since the aspect ratio is the same the tire width will be wider, the patch will be larger, the tire track will be wider. So handling will improve. If I go to a 9" wide wheel the sidewall will be straighter, the shoulder of the tire will be more square (increasing tread width). So handling will improve.

This would be great, if it fits. Since the sidewall is 10mm wider (5mm in each direction) I'm decreasing the offset of the rims 5mm. Toby pointed out that the diameter of the tire is slightly larger, that puts the shoulder of the tire closer to the suspension, so 245/40-17 would be better. Then he pointed out that the sidewall of the tire is 10mm closer to the fender so even if the shoulder/tread of the tire doesnt rub the fender the sidewall probably will.

So now I'm back to not knowing hows its going to fit if I order very expensive wheels and tires. If you had any input, I'd love it.

Rev- drag racing is all about grip/weight/and aerodynamics. If you can afford a seperate set of race tires, get the grippiest ones you can get as small as you can get. The smaller the wheels the less they will weigh, and the less the tires will weigh. Less work for the motor (less weight to turn) is a higher trap speed. Less air that has to get around the tires over 100mph is a higher trap speed. If you're going to run the same tires street and drag racing, then you have to balance the grip of the tires with the size you use. I'm not a drag racer so I cant comment on what street tires are good for a drag launch

 

[jtmcinder]

Originally posted by candela
The contact patch is a function of tire pressure and vehicle weight. There is a formula i once saw somewhere but there is no way that I remember it. If weight stays the same and tire pressure stays the same then the AREA of the contact patch will stay the same.

That's what I thought you were saying, although you've added a bit.

Yes, for a given tire on a given wheel, the size of the contact patch is a function of tire pressure and weight, but the idea that this function holds for any and all widths is simple nonsense.

Try this as an extreme example to make a point. Assume that you have pumped the tire up to infinite pressure and/or the car weighs exactly nothing. In this case, each contact patch is a line (from left to right). Ignoring for a moment that a line has zero width, you can see that, in this case, the size of the tire patch is exactly equal to the width of the tread. Hence, at least in the extreme, contact-patch size can be a linear function of tread width.

My guess is that you are taking the relationship between tire pressure, corner weight, and contact patch that exists for any given tire and thinking that it applies to all tires, which just isn't true.

- Jtoby

 

[jtmcinder]

Originally posted by candela
In this case you were referring to 245's..in which I disagree. Since we are on a DSM board I will be car specific. I do not see ANY benefit to going to a 245 tire over a niec 215 or 225 (even 235). Why? Well even though in SOME cases it may be beneficial, those cases will MOST likely NEVER be seen by any of these people on this board. Which in my mind means one thing- more money spent in the long run (where it coudl be better spent upon other things)....

It does not matter how many of us experience the advantage. That you do not see any benefit of 245s over 215s tells me one or two things: you either haven't tried both or you don't have much feel for handling. A 245 is worth at least three-quarters of a second over a 215 on a typical autoX course. Again, this is based on actual experience and I'm pretty good at getting a majority that a car has to offer.

- Jtoby

 

[jtmcinder]

Originally posted by TurboMike
Contact size being equal, a thin (and long) patch will be great in the snow and very stable while going straight while a wider (and shorter) patch will have better handling.

Disagreement #1. The reason why thinner tires are better in the snow is mostly because the contact patch is smaller, so the weight of the car is concentrated on a smaller area. Remember: while it is true that larger contact patches are better in the dry (because the weight-to-grip function is sub-linear), when the tire is on a loose surface (i.e., snow or dirt or gravel), it's better to have a smaller contact patch.

Disagreement #2. The shape of the contact patch is relatively unimportant. What matters is the area. Don't think of wider contact patches as being better for cornering and long ones being better for acceleration and braking ... all other things being equal, the shape is irrelevant.

- Jtoby