ford 03 svt cobra wheels

[jtmcinder]

Originally posted by TurboMike
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.

Right. I went all through this myself, after measuring how much room there'd be between the knuckle (after the spacers were installed) and a rolled fender lip, and came to the conclusion that a 245/40/17 or a 245/45/16 on a +37 to +40 mm offset was the best option. This was assuming a Kumho MX, which is only about average in terms of how much tread you get for a given sidewall width. Keep in kind that some tires (e.g., Azenis or KDs) have more tread than an MX for a given rating, so you have to do a lot of homework.

- Jtoby

 

[candela]

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.

I think it is just you. I am a wiseman because I try to help in lots of areas. My post was not directed towards you AT ALL in teh beginning--though it is now . It was directed towards the original FWD (VERY LIGHTY MODDED) car asking about stuffing these wheels/tires on his car. Look at my very first post... I have not edited anything thus far except for spelling (which I am notorius for sucking at).

I still agree with my 99% point to. You know that there are like 25k members on this board and if 250 (1%) are like you, me and a few very fast straight line guys (running street tires for w/e reason) I woudl be surprised...wouldn't you? Theres no need to argue this point.. I just thought it sort of relevant according to my original post. Now I KNOW for a fact that more than 1% want better handling and looks... but you know damn well that that percentage will never take advantage of jumping to such large tires. Who ever said to keep a stock settup? Thats pretty silly Mike, I am here the same reason you and others are--to learn, give/receive input about PERFORMANCE-- and will continue to be as well.

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 do not try to convince anyone of anything. I am just giving input dude, that is all. This post was made by someone else and thats where my input was originally directed to. Noone is wasting time and money... everyone has taste. Just take a look through the gallery and see for yourself. If everyone thought like me then 90% of those cars woudl look different...but who wants that? I am glad people are different and do different things. I love modding cars--its all I have ever done and will continue to do as well, I will never aruge that a stock car cannot be improved upon either, so lets disregaurd the though that " I am arguing that 99% of everyone here keep their cars stock". Mike, my point is that I dont think you went over the top... I just like to keep this stuff under control man you know? No need for anyone to argue or get fresh with anyone else. If you want help then Ill try to give it, simple as that...

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.

I can only recommend measuring dude. If you have 235's on there and all you want are some lighter wheels (same size/offset/hub bore) and to go to 245's with the same sidewall...just measure. I do not know what type of suspension you have on there so I cant really help and I also do NOT have a DSM anymore. However thats all I ever did when trying to clear new coilovers or tire/wheel combo.

My question before was do you think you will notice a difference in handling with 10mm of tire. You may or you may not...more than likely you will if you know how to set them up and practice solo events like I do. I will just drop my point though about the whole contact patch thing as it seems its only myself that is getting it now

PS- a 235/45/17 RR is about 321mm -- a 245/40/17 RR is ~214mm
so in fact it is smaller and may fit your car just fine, just keep in mind what tire you go with may have diff. tread designs resulting in different overall diameters.

 

[candela]

Jtoby-

I do not want to keep going because I think that we agree in more aspects than you happen to... it is just not coming across that way.

Beleive me a realize that a lot of what you say is true, however there are things we disagree on, so this will be my last post.

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.

I guess we just do not agree on the whole area thing.

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

I disagree as I am sure you know IMO the area remains the same and the shape is what really changes things (after the actual compound is established ofcourse). Simply becuase a wider contact patch IS better for cornering becuase my theory does not play a part in this--as the forces and corner weighting change. Thus contact patch AREA CAN change and constantly is changing. What I said is basically of a car standing still. I explained this before, but Ill just say that the wider shape of the contact patch area WILL make a dramatic difference and feel in handling/feedback.

Mike- good luck on yout settup man

EDIT: heres a cool site with some cool info for anyone to read up on http://www.chris-longhurst.com/carbibles/index.html?menu.html&tyre_bible.html

 

[jtmcinder]

Originally posted by candela
EDIT: heres a cool site with some cool info for anyone to read up on http://www.chris-longhurst.com/carbibles/index.html?menu.html&tyre_bible.html

I'm glad you posted this link. Now I understand why you keep saying such nonsense.

Read something else. I beg you. Before you post any more about contact patches, read almost anything else on the subject. This guy's idea that the car sits on the tire pressure only, such that the sidewalls play no role, is total nonsense.

- Jtoby

 

[jtmcinder]

Originally posted by candela
PS- a 235/45/17 RR is about 321mm -- a 245/40/17 RR is ~214mm
so in fact it is smaller and may fit your car just fine, just keep in mind what tire you go with may have diff. tread designs resulting in different overall diameters.

One more set of specific comments.... Here are the problems with the above.

#1) a 245/40/17 has a radius of 314 mm, not 214 mm.

#2) nobody talks about radius, anyway; it's always diameter.

#3) tread design has absolutely no effect on diameter; it often changes how much tread you get for a given sidewall width, but it has nothing to do with diameter.

#4) saying that something may fit when it's been posted several times (some in this very thread) that a 245/40/17 does fit on a +40 mm offset is kind of unhelpful.

- Jtoby

 

[jtmcinder]

Originally posted by candela
I think it is just you. I am a wiseman because I try to help in lots of areas.

My guess is that you were made a wiseman for your knowledge of something other than suspension or handling. (No problem with that ... nobody knows all areas.) To be a wiseman, however, in a given forum means that you both know the area and can explain it to people in a way that they can understand. So far, you have made several claims (although you've been good to call them "theories" in some cases), then backed away from them when I've asked if you really mean it, then brought them back several posts later, sometimes adding other, vaguely related topics. Your only explanation for your most outrageous claim is to post a URL to a page that simplifies matters to the point of being so wrong it isn't funny. Other claims you have not explained at all.

At the same time, you keep calling people "young lad" or "dude" and keep telling us to "chill out" when we argue. I'm glad that you seem to be conflict-avoidant (although I, personally, consider passive-aggression to be an attribute of people who really want conflict), but please understand the following if you're going to continue to post: when I see something that I know is wrong - especially when it is packaged in technical terms to make it seem to be sensible or wise - I will rip it. Do a search and you'll see. I have two kinds of posts: ripping and helping. No middle ground. And if you try to hide behind vague responses or URLs to BS sites, I will rip harder. It won't be personal (unless you make it so), but I will make it as clear as I can that what you are spouting is crap. And repeating crap that has been spouted by others makes you worse. If you don't both understand and agree with what you are repeating, and can explain it when asked, then shut up.

- Jtoby

ps. if this was last post on this board ... cheers!

 

[crankbender]

Sigh here goes guys

Where to begin.....

I stumbled across this thread by chance and I wanted to clear up a few things.

Before I begin I am going to correct a few things I saw.

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.

I can not ignore that a line has zero width then use the line to calculate area....I can only get lengths with lines. I can never reach infinite pressure and nothing (pun intended) weighs nothing. When using scientific reasoning to prove a point it is important to use scientific reasoning....otherwise you can draw a picture of anything and say it is true.

Contact patch area is never a linear function of tread width....I don't care how extreme you take it.

I have not seen a statement as to the destructive forces large offsets have. They really torque your bearings and can cause failure.



#1
With a given axel with constant load any tires with similar characteristics (design, pressure, and materials) will have the same contact patch area within a few percentage points. This is backed up by F1, CART, BF goodrigh, Goodyear, etc. I can do a lengthy derivation as to why this happens if you would like me to but it probably won't be pretty and will confuse alot of people. If somebody has serious research to prove these "experts" wrong then lets see it. I don't like when people say something and do not give a reason.

#2
Tires do not work simply on friction like most people think. In fact because the tire is a viscoelastic system the area of the tire touching the ground is not rigidly attached to the car. This brings up slip angles and their effect on driving. I could attempt and others have succeeded at explaining slip angles over hundreds of pages and simply it doesn't fit here. Suffice it to say that you can't use simple friction models to look at tires.

#3
are wider tires better in a corner? During cornering what is actually applying the radial force on the car is the slip angle of the tire not the friction of the tire to the ground. Yes slip angle is a function of friction (as well as many many other things). wider tires generally allow for less of the contact patch to be sliding at a given slip angle and therefore allow for more grip (part of the contact patch is always slipping if ou are getting any force out of the tires). However because of the self aligning torque and its increase as tires get wider you can get past the grip gain and cause your car to understeer by having too wide a tire.

#4
looks.....we all like different things we like so lets not get on each others case about what an individual likes or dislikes. I will always try and keep my opinions on looks well seperated from any good data.

#5
If you really want to grip in the snow almost all the tire manufactures say teh most important thing to look at is sipes. I have not seen any info to back up that skinnier tires are better in snow and ice.

#6
contact patch shape plays a much larger role in defining the slip angles and consequent forces than contact patch area. As was already stated with similar tires the only ways to change the area significantly is to lower the pressure in the tires.

A good book to read on all this is by paul haney. The title if i remember is just TIRE. You can get it from his website for like 50 bucks or like 60+ at a book store (amazon)

Peter.

If you believe any of this is wrong do say so but back it up with reasonings...

 

[Revolution]

That a smaller rim 15/8 with 235 drag radials will benefit me more down the 1320 than say a 16/8 with 235 drag radials .

Ok less wheel for the car to pull, pluss less weight but my question really was if you have two identical cars running identical setups the difference would be made up by the tires and rims. So is the smaller 15/8 better then the larger 16/8?


Lastly they are just for drag racing ass for the street i use 225 kuhmo 711 tires on tenzo r rims wich weigh in at 20.25 lbs. But I dont really know how much the stock rims weigh though. Do you

Any how some one pls help since their are so many knowledgable ppl in this thread .

 

[candela]

#1) a 245/40/17 has a radius of 314 mm, not 214 mm.

It should have been clear that it was a typo...since 3 comes right after 2 and 100mm is quite the difference I figured you may have given me that much credit...

#2) nobody talks about radius, anyway; it's always diameter

There was a tire calculator in front of me and I used it. I do not have that settup, do you? We are talking about radius... is it so bad?

#3) tread design has absolutely no effect on diameter; it often changes how much tread you get for a given sidewall width, but it has nothing to do with diameter

That is PRECISELY what i was thinking of when I typed that

#4) saying that something may fit when it's been posted several times (some in this very thread) that a 245/40/17 does fit on a +40 mm offset is kind of unhelpful

That was his question was it not? To my knowlege I did not see anyone else post an answer when he asked it....

At the same time, you keep calling people "young lad" or "dude" and keep telling us to "chill out" when we argue.

Is there truly a "proper" way to speak. Im not going to lie... these are words I use in my everyday vocabulary. I type what runs through my mind, period. You can argue all you want dude , I'm not upset and I doubt you are either...are we arguing?

I am ALWAYS willing to learn. I am not hiding behing a "wiseman" title in anyway or anythign else for that matter. The thread came to be this way and has drifted far from its normal/intended course (as do most threads on boards w/so many members). The site I gave--IMO ofcourse-- is NOT bull in anyway. Granted he does not talk about slip angles or even mention that a car is moving in any of his reasoning. In fact I think he mentions all being equal; in which case when a car inches away from a stand still then "all things being equal" no longer holds ANY ground as everything starts to change/vary from that point on. It is very difficult to relate to any type of condition like this when someone does not post what the car will be used for, or where that particular wheel/tire package will see most of its duty. BIG difference between giving advice to someone that drives to and from school/work/friends...etc occasionally tooling around on the street and/or dragging on the weekends to someone who is an avid auto-x'er.

Its pretty difficult for me to get my messages across. That could be do to many other things that don't pertain to this. I am in no way hiding behind anythign JTM, theres no reason to. What woudl one (myself in this case) have to be scared of, or have to lose on a internet board? Thats silly man.. I think thats a great site with good info. I did a quick search to try to see what I could dig up that went along the same lines with what I was saying so it could be better understood, as I am obviously not to great and portraying mind sets and thoughts into words as the wonderful crankbender is.

Example:

wider tires generally allow for less of the contact patch to be sliding at a given slip angle and therefore allow for more grip

This is what I mean by stating that the wider tire will grip more in cornering due to the area shape of the contact patch as it gives less rollover when compared to a narrower counterpart--more stability.
Does this mean I am tryign to hide behind crankbenders statements?

Overall, Im not in any way trying to sway you to do anything. I was TRYING to explain good enough to the original poster that such tires are mot likely NOT needed for him, to which I still concur.

 

[TurboMike]

Hoo boy. You guys can techno babble yourselves to death. I still want a 245 tire. I know its not over that theorical limit where the car will understeer from being too wide. If anyone else who might have tried any of the tire sizes I mentioned and is still bothering to read this thread with the battle of the "my brain is larger than yours while I theorize to death" please let me know what you found to fit.

Rev- since you're getting a set of wheels and tires just for drag, you want the smallest wheels and tires that will fit to save the most weight. That also means getting light wheels, its not just the size. There are some expensive 17s that are lighter than cheapo 14s. Get the stickiest drag tire you can get in a size that you wont spin too much at the line. There are tons of drag DSMers I'm sure someone could point you the way of the best tire to get and what size to match your car's hp.

 

[Revolution]

well they are light and wide wich is what i want and you are right but it seems that these "drag" guys are just lying dormante.

Im going to ask marco from magnus what he thinks. But the funny thing is even though he is my bud and knows what he is talking about , he doesent like to talk about cars with his friends , go figure.

Any ways If their are any drag guys give me some info as to which rim size is better. I unfortunatelly cannot go and buy some expensive rims cause i already have a set and need to focus my money on different things.

Thanx for the tips turbo mike.


E=MCsq but it doesent give you the root number for pie now does it

 

[jtmcinder]

Originally posted by crankbender
With a given axel with constant load any tires with similar characteristics (design, pressure, and materials) will have the same contact patch area within a few percentage points. This is backed up by F1, CART, BF goodrigh, Goodyear, etc. I can do a lengthy derivation as to why this happens if you would like me to but it probably won't be pretty and will confuse alot of people.

Yes, please. I'd like to read your explanation. Thanks in advance.

- Jtoby

 

[crankbender]

Your pms are not turned on. This thread has gotten stagnant but if you would like I can pm you with the information on why tire pressure dictates contact patch area.

Here is the short version

In order for the individual axel to not accelerate vertically the forces between gravity (the axel pushing down) and the normal force from the ground (ground pushing on tire) must be equal. This says that no matter how we change the tire the only difference in the total force provided by the contact patch is basically equal (tire weight is assumed a constant because it is very small in relation to the vehicle)

Now If you look at a unit area of the tread in the contact patch it can be seen that the pressure from the air inside the tire is pushing down and the ground is pushing up. Because the tire is deformed at this point and the sidewall is already buckled there is little force being applied by anything other than the air and the ground (some from the sidewall at the edge but it effects -5% of the total contact patch area and even less on wider tires). as the unit area of the tire is again not accelerating vertically the force must balance. This says that the area of the tire is basically dependent on tire pressure .

this can go out the window at very high speeds and high torque but in general this is the way it works.

Your car is actually held up by the top of the tire not touching the ground .

 

[jtmcinder]

Ok, so you're telling me the same story as Candela, which is the same story as on that website cited above.

Well, you are all making the same mistake. Here it is in very simple terms: tires are not balloons!

Yeah, sure, if tires were balloons, which expand in all directions equally when inflated, then the contact patch would only depend on corner weight and tire pressure, but your premise is wrong, so your story is wrong. Your premise is only close to being accurate when you are talking about racing tires for motorcylces, which is where some of you might be getting your ideas.

Car tires, however, have sidewalls that start stiff and get stiffer as tire pressure goes up. Car tires also have a tread that is roughly flat. These are not trival things.

This is not the 19th century, people.

- Jtoby

 

[jtmcinder]

One last point. I, of course, don't deny that - for a given tire on a given wheel on a given car - tire pressure has an effect on contact-patch size and shape.

What I am rejecting is the idea that tire width has no effect on contact-patch size (all else being equal) and/or that contact-patch size is independent of tire width, which was claimed above.

- Jtoby

 

[TalonRacer18]

(The Govenator Voice) I demand Pictures NOW

 

[crankbender]

Car tires, however, have sidewalls that start stiff and get stiffer as tire pressure goes up. Car tires also have a tread that is roughly flat. These are not trival things.

#1 uninflated sidewalls can't hold the weight of the rim most of the time.
#2 the sidewall does not get stiffer when air is added...in fact it is put in tension and not compression at all.
#3 As you inflate the tire the sidewall is actually pulling on the rim not pushing on it...otherwise the tire would fly off.
#4 The area of the sidewall above the CTP is being forced into buckling and therefore can not support compression. It actually pulls up a bit on the side of the tread.

Where are you getting the idea the the sidewall is supporting significant weight?

tires are not balloons!

Please explain why you say this.

What I am rejecting is the idea that tire width has no effect on contact-patch size (all else being equal) and/or that contact-patch size is independent of tire width, which was claimed above.

What are you basing this on.

 

[jtmcinder]

I never said that the sidewalls support the entire weight of the vehicle.

Please read the entire thread. The argument is about whether the width of the tire has an effect on the size of the contact patch. At least one person said that this is not true, going so far as to say that tire width had no effect on the size of the contact patch at all, and cited a rather silly idea from some web-site written by a computer programmer as support. I pointed out that the formula being used to make this argument requires that tires be balloons with, inter alia, no sidewall stiffness and no predefined shape. Because these are both known to be not true, the argument falls apart.

If you want to go off on tangents about what supports the vehicle weight, that's fine, but it has little to do with the debate. As it turns out, I agree that the sidewalls play only a small role in keeping the car off the ground, but so what? That has rather little to do with the fact that tire width helps to determine the size of the contact patch.

- Jtoby

 

[ACM]

What I really want to say is
"And what was the point again ?"

This thread reads like the intermingling of two very interesting but disparate discussions. I freely admit to having trouble sperating the two.

Observation - for a given vertical load, tyre width affects the contact patch by streting the oval laterally. A narrow tyre produces a longitudinally aligned oval, a wide tye will produce a laterally aligned oval. This has a significant effect on stability, as all motorcyclists (should) know.

Higher pressures caue the tread area to 'bow', lifting the edges up and reducing the effective width, which is why it's an easy tuning step to balancing DSMs.

I have no idea if the above is even germaine to any of the discussions in this thread, so apologies if I'm intertwining yet another (though hopefully interesting) topic into this thread

Charles

 

[14.5 drift]

WoW!!! That was a good one

it started out slow, then got ugly, then got really interesting with 2 reasonable debated well explained theories, and then nuthin. You guys give up or what?


I agree with every thing on this page but must support jtoby on the balooning theory. The sidewalls and corner edges are made to distribute load they dont directly respond equally to opposing forces as the rest of the tire was the impression I was getting from crankbender.

Just out of curiousity, a ???? for crankbender, you seemed to have a definative stance on correcting miisstrued concepts and idea's but you never gave your opinion if the wider tire would benefit a dsm. You made clear that there was a line where wider would not always be better, but did not clarify if an eclipse/talon had crossed it. Is the dsm weighted enough to effectivly increase the patch width of equally compressed but wider tires?


The only reason I am bringing back the dead, I have found a rim I am willing to buy enkie bortex rpm2, they are light, strong, incredible looking, and cheap. Thing is, it's the same price for 8 inch as a 9 inch, would it be worth the extra money in tires to put the 9 inch on my car? As for use intended, I really enjoy togue type events or tight technical canyon type roads, but at the same time and of equal importance or better I would like to improve my 100-0 braking times.

I rear ended some one last year and now I am taking alot more attention to the whole braking aspect these days.

Thanks for being here, jtoby, crankbender and candela. You guys rock!!!

 

[wret]

That was an interesting discussion. Here are some statistics for consideration:
McLaren F1
235/45ZR-17
315/45ZR-17

Saleen S7
275/30ZR-19
355/25ZR-20

Ferrari Enzo
245/35ZR-19
345/35ZR-19

Koenigsegg CC
245/40ZR-18
315/40ZR-18

Ruff Porsche 911 Turbo
225/40/18
295/30 ZR18

Average diameter 18.3
Average front width: 245
Average rear width: 325

Looking at tire sizes of these supercars, the obvious trend is larger tires at the drive wheels. It would seem that superwide tires are not necessary for front end grip.

 

[ACM]

You're missing another important dimension - weight distribution.

If you calculate the contact pressure on the tyres you'll find another reason why mid- and rear-engined cars have larger rear tyres.

Charles

 

[wret]

You're missing another important dimension - weight distribution.

If you calculate the contact pressure on the tyres you'll find another reason why mid- and rear-engined cars have larger rear tyres.

Charles

Good point. My sampling was biased toward non-front engines. Here's a couple front engine samples to add to the pool:

Corvette Z06 04
265/40/17
295/35/18

Viper 04
275/35/18
345/30/19

They seem to follow the wider drive wheel trend. I believe all the vehicles listed are close to a 50/50 weight distribution.

 

[SlowSpyder]

Heres site where various offsets were tried including the mustang wheels
http://www.martincheck.com/wheel_tire_fitment_FAQ.html
I apoligize if this is a repost

 

[Rx3]

Unfortunatly tire manufacturers dont release tread width info, so I have to go with what I can.

Just for the record, Tire Rack and other tire distributors all list tread width info (and a whole lot more) under the spec info for each tire. Just FYI, for those that can't seem to find it.


You can also go to the tire manufacturer webstie directly and obtain that info. I have never heard or seen any manufacturer or distributor worth their salt not list tire specs. That's ludicrous.