240sx tire clearance question...

[Re_Joshua]

Ok, I am ordering my wheels come mid next week. There are for a 4 lug 89 240sx. 17x7 on the front and 17x9 on the rear. I know I am going to be going with 215/45/17 for the front but I was wondering what is the best size to put on the rear and still have clearance. The car sees a dirt road everytime I drive it...so I need as much as tire as possible w/o killing the looks of the car. I looking around a noticed people having 255/40/17 on a 17x9 but didn't see any pictures....thanks for any help.

[InsanityInc]

if you use a 255/40/17 you may as well just unplug your speedometer for how accurate it'll be. Also, you will have massive understeer with 215 on the front and 255 on the back. There's no reason for tires that wide unless you're putting down 350+whp.

[chmercer]

you might consider switching to a 225 tire in front and maybe a 245 in rear. or 235 f 255 r. i personally dont like having more than 20mm worth of rear stagger. but if it works for you then go for it.

also insanity, please dont go spreading misinformation. going from a 205/60/15 tire to a 255/40/17 tire will alter the spedometer reading by a measly 1.4%.when the spedo reads 60 mph, you will actually be travelling 60.8 mph.

[Exar-Kun]

I just wish people would search and read the FAQ's before making comments, or threads for that matter.

Suffice to say, I'd run the same size all around, the car understeers naturally anyway, why make it worse by running a higher load index and wider tire on the back?

bleh.-Chet

[chmercer]

^^^

good advice.

[InsanityInc]

you might consider switching to a 225 tire in front and maybe a 245 in rear. or 235 f 255 r. i personally dont like having more than 20mm worth of rear stagger. but if it works for you then go for it.

also insanity, please dont go spreading misinformation. going from a 205/60/15 tire to a 255/40/17 tire will alter the spedometer reading by a measly 1.4%.when the spedo reads 60 mph, you will actually be travelling 60.8 mph.

205/60/15 isn't the proper size for the car. It's 195/60/15 or 205/55/15. Also, your percentage difference completely forgets to take into account the difference in diameter. 15" wheel = 381mm in diameter. 17" wheel = 431.8mm in diameter. 205/55/15 sidewall = 112.75mm (x2 for diameter) so 225.5mm, meaning a total diameter of 606mm for the 15" with a proper tire. 255/40/17 sidewall = 102mm (x2) = 204. 204+431= 635mm, so you're actually looking at a 6% difference. Not to mention your ride height in the rear would be higher, and your car would understeer like crazy, and you don't need a tire anywhere near that big in the rear unless you're making massive power.

[Re_Joshua]

Well that is why you lower the vehicle back down...

Also I did read up on the FAQs and stuff, didn't find the answers I needed.

Just trying to figure out how those tires would match up together on the car...seems not all that well. Also I can't run really run the same tires on the front and rear....7" wide on the front and 9" wide on the rear...I need a good amount of tire...basically the sidewall of a 215/45/17 works great for the roads I drive this thing on everyday. Bad dirt roads don't mix with no sidewalls.

[AZhitman]

Insanity -

No offense bro, but who taught you how to calculate tire sizes?

The OD of a 205/60/15 tire is 24.7".

The OD of a 255/40/17 tire is 25.0".

This is a difference of roughly 1.5%, hardly relevant or even noticeable.

I don't disagree that this is an awful lot of tire, but I have that size on my S13 and it's perfect.

[AZhitman]

Joshua - I'd advise not ordering those wheels at all - No reason for a 2" difference front to rear. At all.

[Re_Joshua]

Well that is what I've seemed to find out from some articles I've read. At this point I am back to step one...finding wheels. I don't want to spend a butt load on wheels. I've looked and looked for a wheel that has different "Lip" sizes from the front and rear but not finding anything that is nicely priced. The wheels I was going to order don't offer a 17x8 ... guess I'll see what I can find...

[Re_Joshua]

I've got another question...how well do 17x7 or a 17x7.5 hold up during acceleration...I know the stock wheels don't get any grip at all in first or second under hard acceleration. But aren't the stock wheels 6" wide...something like that I think.

[hek1620]

sport max makes those fresh *** five spoke staggered wheels in a non-staggered 17x9(all four). pretty cheap like $420. i don't care what anyone says, i'm getting the 18x8.5/9.5 for my s13. it's never too much tire when some ******* cuts u off hardcore and you know you wouldn't have made it with thinner tires. does anyone know the sizes i should use for those wheels? dont want to go too low on the profile.

[Re_Joshua]

The sport max wheels were the ones I was looking at, pretty much the same as the FastWheels version also, except half the price. But I wanted a staggered setup....still need to know how a 17x7 or 17x7.5 would hold up...I don't have to worry about traction while launching the car, hense I won't be drag racing this car...

[AZhitman]

Not sure what you mean by "hold up"....

Traction is more dependent on the tire than the wheel. 7 or 7.5" is more than enough for 90% of the 240's out there...

A good sticky-compound tire, in a high speed rating, good load rating, properly-sized for the wheel and the car, is MUCH more important.

[Re_Joshua]

As in "hold up" I mean getting good traction. Im sitting around 215-230hp at this moment and the stock size wheels do not grip at all, any kind of aggresive acceleration and the tires start spinning.

[AZhitman]

That's a tire compound/design issue, more so than a width issue.

Wider is SOMEWHAT better, but keep in mind the contact patch SIZE does not change, only the shape.

[Re_Joshua]

Thank you very much...hopefully I will hunt down a wheel design that I like...the car needs a new set of wheels/tires very bad...oh not to mention weeks of body work, lol.

[sil80drifter]

I'm still a little confused, but after reading multiple FAQs, could you quickly explain to me why it's mostly the shape that changes and not the actual patch area? I'm thnking it has something to do with the weight distribution on the tire, but I can't quite place my finger on it. It just seems to me that the 265mm patch would be just as tall as the one for the 205mm patch, but wider. So I don't get it. Also the pic shows different size wheels, but what if you had a 9" wide 15" diameter wheel and you put a 205 tire on it adn a 265 tire on it. Would that make a difference as compared to your picture?

sil80

[chmercer]

static contact patch will always the same size. 205/55 16 or 355/25 19 its going to be the same size. smaller tire will have a patch shaped like a rectangle. bigger tire will have a patch shaped like a very thin horizontal line. the way to increase the area of the contact patch is to add more downforce, not to get a bigger tire. this is not to say that bigger tires are useless, the shape of the patch changes differently when cornering when the tire is wider, etc. somone smarter should explain this more in depth.

[AZhitman]

Contrary to common opinion, while there is *some* increase to be gained by a wider tire, it is not even CLOSE to a 1:1 ratio. In other words, doubling the width does NOT double the contact patch. Matter of fact, it's actually pretty minimal (if kept within the restraints of a practical "+2 or +3" fitment). "Ricer math" is a *****.

*Assuming equal weight (load) and equal air pressure, sidewall stiffness, small differences in tire weight, all that crap... A wider tire will deflect from front to rear LESS than a narrow tire.

If you were to park your car on a piece of glass and look at it from beneath with 195/65/15's and 275/40/17's, and measure the surface area (assuming * above) of each contact patch (disregarding tread voids), they'd be remarkably similar in area.

A narrower tire's contact patch will be long (front to back) and narrow (side to side). A wider tire's contact patch will be shorter (front to back) and wider (side to side). Keep in mind, the weight is distributed the same over both tires.

It's pretty hard for most people to comprehend, so take it to the extreme: Put your car on a set of 44" monster truck tires (with no "tread lugs"). Your car will not have sufficient weight to distort the patch, therefore the patch will look like a pencil perpendicular to the direction of travel. Put the same car on some 155/80/13's, and it will distort the contact patch into a narrow shape parallel to the direction of travel.

There IS a "sweet spot" in tire sizing, at which point the negatives (increased rolling resistance due to deformation of a wider tread, increased weight and increased ground-to-tire interface friction) are superceded by the positives (better contact patch "shape" - rectangular rather than oval, more predictable breakaway at the limit and better sidewall stiffness.

Contact patch SHAPE is far more important than SIZE, and the 295mm wide tire will result in a contact patch that is more conducive to lateral adhesion (and a far more linear loss of adhesion).

To an extreme, a 335/20 would theoretically be an even bigger improvement on the track (or maybe a full rubber cylinder stretching the width of the car like a steamroller), which we know not to be true.

Most people are terribly guilty of equating GRIP with SPEED, which is NOT definitively the case.

Read that again, and let it sink in. You can have PHENOMENAL grip in a corner and still go slower. Again, take it to the extreme: 335mm wide tires, made of hyper-sticky compound, will be SLOWER through a corner (and the straights) than a 245mm tire designed for track performance. There comes a point when the tire width is actually a DETRIMENT.

The gains are not linear, they are not limitless and they actually resemble a bell-shaped curve (which you're familiar with from statistics).

Wider tires generate a more gentle breakaway. They eat up horsepower and momentum doing it, but the margin of safety is greater. A narrower, harder tire will be nimble, but you'll get little warning when it's about to get away from you.

Again, you CAN'T argue with the picture I posted - it's obvious that the sizes are the same. That's not hard to accept. The patch size hasn't changed noticeably.

Even when you DO achieve a bigger patch, by extreme increases in section width, PRESSURE, in pounds per square inch, that the tire applies to the track surface decreases.

----->Imagine if you had to wear 6" stiletto heels vs a pair of Nike Air Trainers. How much of your weight would be concentrated on that heel? Would you agree that the heel is pretty firmly planted into the surface? Would you agree that it's harder to move that heel laterally? Would you agree that if / when it DOES move, it will do so violently and with less warning? Not so with the Nike. It will be predictable and manageable - which is where your skill as a driver is enhanced. Would you prefer that Nike to be twice or three times it's width? Nope. There's a sweet spot for performance.

Keep in mind if wider ALWAYS AND UNEQUIVOCALLY meant better, NASCAR / F1 / Indy would be running monster widths. They're not. They've found the "sweet spot".on the bell curve, the "sweet spot" for tire width is at the peak (with coefficient of friction, lap times, whatever on the y axis).

Too wide, and speed suffers. Too narrow, speed suffers. Different reasons, same outcome.

[Nismo_Freak]

Contact patch SHAPE is far more important than SIZE

Shape is just as important as size.

More or less due to heating principles of the tire and the limits of tread adhesion.

They are a relationship; yet another trade-off.

Most people are terribly guilty of equating GRIP with SPEED, which is NOT definitively the case.

Read that again, and let it sink in. You can have PHENOMENAL grip in a corner and still go slower. Again, take it to the extreme: 335mm wide tires, made of hyper-sticky compound, will be SLOWER through a corner (and the straights) than a 245mm tire designed for track performance. There comes a point when the tire width is actually a DETRIMENT.

The gains are not linear, they are not limitless and they actually resemble a bell-shaped curve (which you're familiar with from statistics).

Wider tires generate a more gentle breakaway. They eat up horsepower and momentum doing it, but the margin of safety is greater. A narrower, harder tire will be nimble, but you'll get little warning when it's about to get away from you.

Spelled out, Greg is talking about overall time on a lap.

Time gained in the corner, braking zone, and acceleration points with the greater grip tires can very easily be eaten away by the parasitic loss associated with friction and rotational force required.

There are soooo many angles to the tire when deciding on a optimal tire sizing. Not 1 tire size is ideal for two 240's, the best you can do is to test one out and go from there. Try to not adapt too much of your setup to accomodate inability in another part else you will be chasing too many problems at once.

[Veriest1]

Quote »: Put your car on a set of 44" monster truck tires (with no "tread lugs"). Your car will not have sufficient weight to distort the patch, therefore the patch will look like a pencil perpendicular to the direction of travel. Put the same car on some 155/80/13's, and it will distort the contact patch into a narrow shape parallel to the direction of travel.[/quote]Will offset have the same effect? As in will having the hub bolted on the the center of the wheel on an 8 inch wide rim (with four inches on each side) be better for traction than having a monstrous lip with 6 inches on oneside compared to the other sides 2 inches?

It seems to me the centered hub would have a better traction "circle" when compared to the cool looking lipped wheel since the wieght of the car will be pushing down on the center of the rim rather than the inside edge.

Hopefully that made sense.

[Veriest1]

Its been a few days. Bumb for the Q.

[BaliLover]

I run a 17x9" +20 rear wheel, lowered pretty low on Megan coilovers, and a 235/40/17 clears everything with no rubbing on stock body S13. I didn't even roll the inner lip.