s-one

i just got a call from a tire rack guy stating that the tires i ordered won't fit on 7.5 inch rims?

Turbonut

iTrader: (1)

He's right. If you check, for proper fitment a 8"-9.5" rim is required.

A 235/45-18 will fit on a 7.5" rim, but the tire will be 1/2" taller (26.3"). Haven't done a research to see if anyone is using this size. As an example, I'm running 245/45-17 (25.7")

tyger

What are the side effects of "improper" fitment?

Reason being, i am running on 18x7.5 with 235\40\18. Got them at discountire.com.

None there mentioned anything about fitment.

I did look at the specs for the tire later and did realize that they were for only 8"+ rims. I don't notice anything unusual driving on them though. Should i be worried?

Turbonut

iTrader: (1)

I don't believe you'll experience any problems, as the 8"-9.5" size is the recommended width, and should be used when possible, especially with the lower profile tires with stiffer side walls.

Here's an example of one 235/40 series exception:

Additionally, some vehicle manufacturers and tire companies have permitted rim widths that are not within the tire's original approved rim width range. For example: BMW has combined 235/40R17 sized tires on 17x7.5" rims (which are 0.5" less than the narrowest 8.0" wide rim listed for the size).

Enjoy the TL!

ARX-01b

iTrader: (1)

Dude, you are going the wrong way on wheel width.

tyger

I realize that i should have gone 8"+ width size but the rims i wanted didn't come any wider (Enkei PKR). I had a budget to stick to.

Michael03TLS

Can you show me which model, year, technical data and evidence where it can prove the part where you said BMW has " combined 235/40R17 sized tires on 17x7.5" ???

Even on the current models, a wider than normally required rim width is usually the case for BMWs because they know how to make awesome cars. Look at the technical data/specifications:

BMW 335i

BMW 328i

I am just curious and not trying to be a prick or anything. I don't think BMW would ever put a setup like that because oversized tires on undersized rims is a NO, NO. First off it makes the car handle more like crap in terms of cornering, acceleration, overall driving, and doesn't fully utilize the maximium potential of the tire with so much extra overhanging rubber of the oversized tire. Much like a person with size 10 trying to wear size 11 or size 12..think about what kind of "handling" this person has when he walks/runs/stands in them.

What I do notice about BMW, especially on higher end models, is that they put oversized rims with undersized tires so that you have more rim width to fully maximize the undersized tire; by having more metal planting the tires to street/road contact you're, you are actually creating more of a contact patch for optimal handling, cornering and utilizing the tire fully. You would actually see that the tire's upper shoulder crown kinda curve inward while it's mounted on the rim on these BMW cars.

Acura/Honda, in general, has always cheaped out and put smaller, "just barely enough", with little tolerance, rim width to mount on wide tires. The Acura TL-S, years 2002-2003, is an abysmal and notorious example of incompetent engineering. Mounting skinny tires on a 6.5" rim on such a large car and especially for a "luxury-sport" model...blah.

As far as people on this forum "giving" advice saying it's okay to mount oversized tires on undersized rims, I would have to disagree on it. Sure it's "possible" and "probably" not going to cause damage, but for liability issues (e.g., tire manufacturer, insurance company), optimal suspension and handling characteristics, possible fuel economy, more money for tires and even your own safety, I do not recommend it despite its "cool" look or bragging rights for putting wider tires on improper rim width.

Hope this helps. My two cents.

Turbonut

iTrader: (1)

Here it is directly from the TireRack site:
http://www.tirerack.com/tires/tiretech/tirespecskey.jsp

Turbonut

iTrader: (1)

Did some quick research and found that the E46 M3's were equipped, from the factory, with 17" x 7.5" wheels and 235/40-17 tires.
Looks like BMW did a NO, NO.

Michael03TLS

Where exactly are you referencing to and can you show me the link to this "from factory" specification, other than just tire rack? You sure this wasn't a prototype car fitted with those tires and rims for TireRack R&D purposes? I don't recall E46 M3's being fitted with 17" rims? It was either 18" or 19" rims, at least for Canadian versions of this M3.

That TireRack article was interesting but self-admittedly they write "While these applications have received the approval of the vehicle and tire manufacturers, staying within the approved rim width range helps assure that the tire's internal stresses are within its design parameters. "

In additionally, if you have notice the affects of putting on wider rims for undersized tire trends in the TireRack chart they put up, having a wider rim with undersize tires helps to maximize tire section width - rather than the opposite way around with oversized tires on undersized rims.In other words, it gives you a de facto, wider contact tire patch to road for optimal handling, much like the "current" supported documentation, from BMW's current website on new models, that I linked for the 335i and 328i models. For example, typically a 225/45/17 tire is measure on industry standard measuring rim of 7.5", yet the 2007 335i model has 225/45/17 on 8" rims, a 0.5" wider than typical industry standard measuring rim width of 7.5" Why is this so? Is it because BMW learned from their mistakes in the past "NO,NO" and through better engineering design, they among the many car manufacturers learned to truly maximize tires for the most optimal handling for cars - hence making them well-known for their cars - OR did they just do this for the fancy of things? I think the former is undisputely the correct answer.

Incidently, If everyone thinks that BMW is the one of the undisputed car king manufacturers for setting standards, since I did a bit of "researching" too, take a look at this page:
BMW E46 M3 Engine Failure Archive
Way to go BMW! Paying ~>60K US for a new BMW, to have these problems; No thanks. I was tempted to buy one of these things used too - thank God. Almost seems on par with Acura's transmission F@#K ups. The point is: no car manufacturer is perfect, although there are some car manufacturers that definitely build reliable cars, more powerful ones, or more luxurious ones,etc.

Turbonut

iTrader: (1)

You're a tough one to satisfy.
First, my mistake as my counsin has a E46 M3, and I should have stated the E36 M3 has the 17 x 7.5 wheels with the 235/40-17 tires

Hopefully the BMW registry will help:
http://www.bmwmregistry.com/model_faq.php?id=14#4

What size wheels and tires was the 3.0-liter E36 M3 equipped with?
For the E36 M3 3.0, BMW M specified 235/40ZR17 tires on all four corners. However, each body style was given a unique set of wheels. The coupe (both Euro-spec and U.S.-spec) wears 7.5x17-inch M Double Spoke cast alloy wheels. A lighter forged M Double Spoke version was optional on European-spec models from the start of production, and became optional on U.S.-spec M3s starting in December, 1994. These are always fitted in a staggered configuration, with 7.5x17-inch wheels in front and 8.5x17-inch wheels in back. A polished version of this wheel was standard on the E36 M3 convertible. The sedan has its own wheel design, the M Contour II, also in the staggered (7.5x17-in./8.5x17-in.) configuration. This wheel is also fitted to the U.S.-spec M3 coupe with Luxury Package, though only in the narrower 7.5x17-inch version.

Michael03TLS

Isn't being tough, picky, and srutinizing good ?

Humm, let see if I can get everything straight and shed some light on all of this... So you must know that your cousin's E46 M3 has a staggered formation for rear and front wheels. And if so, does the same principle of putting oversized tires on undersized rims still apply for this version of the BMW M3. Meaning, are the REAR or FRONT set of rims undersized for minimum required rim width for the mounted tire in the rear or front? And does E46 M3 still satisfy your previous premise for supporting the idea of improperly fitting tires on undersized rims; For example, "which are 0.5" less than the narrowest 8.0" wide rim listed for the size" for the E36

I don't think so. If your cousin has the E46, standard package, it should have "8x18-inches in the front and 9x18-inches in the rear" rims ,now fitted with
"225/45ZR18 and 255/40ZR18 tires" (respectively). Now if we begin to srutinize:
We can certainly see that the front tires only require minimum 7" rim width now and for the rears it requires minimum "8.5". Now we see a 1" and .5" differential parameter for fitting tires with the "minimum" rim width required, rather than a " 0.5" less than the narrowest 8.0" wide rim in the E36 M3 case. Even the optional 19" rims for the E46 M3 does in fact meet or exceed the minimum "required" rim width.

Weeding through all this data with two generations of M3s, I can possibly see that the "less refined" E36 M3 might have had the same, inadequate rim width (using industry standards) and same tire size mounted all around consistently. So what happened and why the staggered rim formation now in the "refined" E46 M3 production models that do meet required, minium rim width?

It certainly looks like BMW cleaned up their act, probably through better engineering and research , plus lest possible liability issues may arise, to finally put on rim widths that meet or exceed the minimum industry standard. Or they realized, as I have, that wider than required rims vs. industry standards make more of a tire contact patch to road for optimal tire ulitization and handling behaviour. Furthermore, they could have just been cheap car manufacturers to make less wide rims to yield more profit and less cost for those old E36 M3, but still be able to claim bragging rights of being able to put more wider tires than their competitors.

Regardless, I have finalize to say put on tires with at least minimum rim width for your own safety, optimal handling/cornering, braking, overall driveability or "feel" of the car (not to feel sluggish/sloppy in response), and possible liability issues that may arise from tire manufacturers (e.g. manufacturers denying tire claims/warranties or not wanting to mount on an oversized tire) or insurance companies. But then again, it's your car, your style and liking, your life . That's the good thing about our good old N. American culture.

Turbonut

iTrader: (1)

Don't know how the questions pertaining to the new M3 are relevant, as you had asked for documentation as to what year/model BMW came factory equipped with 7.5" rims and 40 series tires, which I supplied, indicating that BMW did in fact use this combination. Don't believe we have ever heard of any safety issues that came from this combination.
:surrender

TheBigWhite 21

what about 245/40/18? will it fit on a 8.5" wheel?

Turbonut

iTrader: (1)

Yup. They can be installed on 8"-9.5" rims.