titanjc

I love my stock 18" polished Bullitt wheels. Ford could not have equipped the car with a better wheel from the factory (well, unless they were deep dish, but can't be too picky I suppose). The only thing that I don't like about them are the tires. 235/50-18's = 235's out back just look so.... wimpy. 275's on the other hand... now we're talking. I know this should be possible, the wheels are 8.5" in width, and I've seen plenty of 18x8.5's with 275's on them.

Does anyone have pictures of such a setup? Anyone currently running like this and have any input? I'm assuming there will be a bit of bulge to the sidewall, since it's a bit wide, but as long as it's safe and looks good, it sounds like a winning combination to me.

RhinoGT

I have 275/40s up frt. and 285/ 35 nitto DRs out back. The 275s bulge ever so slightly.

titanjc

Is this on the polished Bullitts? Do you have any pictures of your setup?

bob

An 8.5 inch rim is too small for a 275/40R18 - A 255/50R18 would be the proper size tire

--->edit<----

err, 255/45R18 is what I mean - forgot the 17 inchers are 235/55R17 and the 18 inchers are 235/50R18

Phorty

255/45/18's fit perfect. I was thinking of trying some 275/40's and putting them in back. Many people run 285's on 9" rims. I had 275's on my 7.5" wide 93 cobra rims. That bulged a lot. I really don't think it would be that bad.

bob

Guys, if you would take a second and go to the tire manufacturer's website, they generally contain the critical tire data. I know both Michelin and especially BFgoodrich posts the same data available to thier dealers as well as Nitto. I say this because tires are the most critical safety component on your vehicle and while they tend to be very forgiving, when they fail due to abuse of any sort, it can range from an inconvience to a major disaster, not only for yourselves but possibly other people around you, for the most part, the information imparted to you will help the tire perform under its designed intent.

msully

I am going with the 275's on the stock rims. I have seen two cars locally with them and they look fine. Supposedly the Nittos are a little narrower than the BFG's I was looking at so I am going with the Nittos.

eci

275 is too wide for an 8.5" rim. It doesn't matter if they "look" fine. It is not SAFE which is what matters.

Phorty

How is it not safe?

1993 Cobras from the factory had 245's on a 7.5" (190 mm) wide wheel. The tread is 55 mm wider than the wheel.

1994-1995 Cobras from the factory had 255's on a 8" (203 mm) wide wheel. The tread is 52 mm wider than the wheel.

A 8.5" wheel is 216 mm wide. A 275 wide tire is 59 mm wider than the wheel. You could probably run 275's on all four corners if you wanted.

LEO_06GT

This looks interesting.

titanjc

It seems there's no definitive answer really. The more I look around, it seems that the tire manufacturers don't recommend running a 275 on an 8.5" wheel, but I know of MANY people on the 350Z forums (my old hangout) running that exact setup with the Toyo T1-S tires, 18x8.5" wheels, 275/40-18 tires Front, 18x9.5" wheels, 295/35-18 (I believe) Rear. A sponsor on the site sells that wheel and tire package as a street setup, and there are many members running that setup on their daily drivers.

bob

These tires are designed to run on the narrower rims, the 275's are designed to run on a minimum of a 9" rim (actually 265 to 275 and 285mm tires need at least a 9.5 inch rim). At best the 275's offer only a cosmetic enhancement on an 8.5" rim, at worst the improper rim/tire fitment can lead to a failure which might prove only to be an inconvience at best or life threatn ing at worst, not only for the driver but the other motorists who might be near the vehicle at the time of tire failure.

Now the real sticky part. The person who mounts this unapproved tire/rim combo is responsible for any and all consequences which occur as a result of essentially telling the engineers responsible for setting these guidelines to shove it up thier collective butts.

To be honest, except for the accelerated wear and cracking that will result because of this boned combo, probably not much will happen, however be warned that you are setting yourself up for a bad situation if other factors come into play (overloading combined with low air pressure are the most probable) and the decreased safety margin that is a result of installing a tire 20mm wider than is reccomended for an 8.5" rim.

bob

Yes there is, if the the tire manufacturer implicity states that said tire only fits on a certain range of rim widths then that is the definitive answer since it has been backed by extensive testing and it is their products and they are the experts. Anybody who ignores or goes outside these guidelines (irregardless of thier own experience and testing) are in error.

Now if I am coming off sounding like a frigg'n *****, I make no apologies, but tires are the number one piece of safety equipment on a car, without them you cannot control your vehicle and its just plain silly to disregard the information provided so that a safe and informed descion can be made.

Phorty

Are you saying there is difference in design between a 255 tire and a 275 tire of the same model? The only difference I was aware of is the width.

If the width of an OEM wheel is 77.5% of the OEM tire's width (93 Cobra- 190mm/245mm), why can't that same ratio apply to a 8.5" wide wheel? A 8.5" wide wheel (216mm) is 78.5% of a 275mm tire.

titanjc

This is an interesting point, as is the previous data you posted about the Cobra wheel / tire sizes.

bob

Construction is generally the same, however when you place a tire on a rim that isn't designed for that rim width you place additonal stresses on the tire, unfortunately I can only take what the data says at face value since I haven't really asked a tire engineer that very question as to what forces are acting on the tire and why specifically they reccomend a limited rim width range. That said, you have to also take into account the height of the sidewall (if the sidewall were considerably taller you could fit a 275mm wide tire on a 8.5" rim).

Consider also that the tire is also more than just a slab of tread that hits the ground, you also have the bead to contend with and the way it interfaces with the flange on the rim and possibly that could be the crux of the problem as this is the area that often develops problems when the same scenario is applied to big heavy trucks.

Also there is the sidewall to consider and the bulge that some people notice when installing to wide a tire on a specified rim (the reason I say you will probably see cracks along the side wall earlier than if the tire were mounted on the approved rim width range).

That said, I think I will take the initiative and call the tech department of the tire company we deal with and see if I can get a pointed answer as to why you have to install tire on an approved rim width range (in your case to wide a tire on the rim).

QCmustang

I have been running 285-40-18 good year f1's on 8.5 inch stock premium wheels in the back for 4 years road racing 1/8 mile 1/4 mile on week-ends very hard driving and never ever had any problems in fact it handles incredibly much better with lowered suspension than stock . I just wanted people to know it's possible and very safe despite what some people say !!! My opinion

tbear853

Yeah ..... reading through the thread .... the reason that for the recommendations (that's what they are, not "law") is simply engineers and manufacturers making sure no one can come back and sue them in our "too many lawyers / overly litigious" society ... and they throw in a margin. They will only stand behind the product when used within recommendations.

I'll agree that low profile (like a "40 series") tires of a given width are less tolerant to narrower or wider rims than the same width tire with a taller aspect ratio (like a "70 series"). It's not simply will a 275 work well and safely under all intended conditions on a 8.5" wheel, one has to consider tire sidewall height. Shorter sidewalls simply mean a shorter distance to transition from shoulder to bead ... and a narrower rim increases the chances of a tire bead pulling over/off the rim lip in the event of a flat in which case .... the already flat tire's diminished steering becomes even more diminished.

Back in the old days, we ran tires that were much wider than the narrower rimes, 8" was a wide wheel on a street car, many used 7" DD wheels on back. My '65 GTO had 14x7 deep dish Cragar SS wheels on back, I trimmed the lips of the fenders to fit L60-14 tires, never rubbed, worked great .... a L60-14 is the same as a 295/60-14 in today's terms, and they worked perfect. 295 mm is 11.6 inches section width.