How do I know what tire size for VMR rim?

[BMWI6]

Hi, I am thinking about getting VRM 710 rims but I don't know what tires I need. I think the rims are 8.5 in the front and 9.5 in the back. how can I calculate what tire size I need? Thanks guys

[lucid]

1. Do you want to maintain the stock rolling diameter? If not, your speedometer readings and gearing will be affected slightly. Tirerack indicates 25.9" F, 26.0" R stock rolling diameters (never mind what they would be in reality; that's good enough as an estimate).

2. Do you want to maintain stock stagger? If not, handling/balance of the car will be affected. Stock stagger is 30mm.

3. You didn't mention the diameter of the wheels you will be getting. Sidewall specs will depend on that.

4. You didn't mention the offset of the wheels you will be getting. That will affect the amount of clearence the tires will have on the inside and outside.

Assuming you are considering 19" wheels, want to maintain stock stagger, and not moving away from the stock offsets significantly, 245/35/19 F and 275/30/19 R would give you a lot more rubber than stock while staying close to stock rolling diameters (~0.4" smaller in dia). I don't see the point of having more tire than that for the street.

235/35/19 F and 265/30/19 R would still give you more rubber than stock and provide a little under 3% additional mechanical advantage as that would be ~0.7" smaller in dia (your speedo would read higher by the same amount). Speedo normally reads high, so you'd get about the actual speed reading with that setup. I'd personally go with this one.

I believe the second setup is what the CSL came with--not that we are driving CSLs or anything.

Either for those setups will mount on the 8.5"/9.5" rims well.

BTW, I hear VMR wheels are somewhat heavy. I've seen mixed reports posted here, and most of them seem to point to heavier than stock weights for the rims.

[BMWI6]

Thank you very much for the info!!!! these are the wheels specifications.
18"x8.5" +40
18"x9.5" +22

How do you calculate your numbers though? Or you just know them by memory? Thanks, I am a complete noob when it comes to wheels.

Originally Posted by lucid

1. Do you want to maintain the stock rolling diameter? If not, your speedometer readings and gearing will be affected slightly. Tirerack indicates 25.9" F, 26.0" R stock rolling diameters (never mind what they would be in reality; that's good enough as an estimate).

2. Do you want to maintain stock stagger? If not, handling/balance of the car will be affected. Stock stagger is 30mm.

3. You didn't mention the diameter of the wheels you will be getting. Sidewall specs will depend on that.

4. You didn't mention the offset of the wheels you will be getting. That will affect the amount of clearence the tires will have on the inside and outside.

Assuming you are considering 19" wheels, want to maintain stock stagger, and not moving away from the stock offsets significantly, 245/35/19 F and 275/30/19 R would give you a lot more rubber than stock while staying close to stock rolling diameters (~0.4" smaller in dia). I don't see the point of having more tire than that for the street.

235/35/19 F and 265/30/19 R would still give you more rubber than stock and provide a little under 3% additional mechanical advantage as that would be ~0.7" smaller in dia (your speedo would read higher by the same amount). Speedo normally reads high, so you'd get about the actual speed reading with that setup. I'd personally go with this one.

I believe the second setup is what the CSL came with--not that we are driving CSLs or anything.

Either for those setups will mount on the 8.5"/9.5" rims well.

BTW, I hear VMR wheels are somewhat heavy. I've seen mixed reports posted here, and most of them seem to point to heavier than stock weights for the rims.

[lucid]

Originally Posted by BMWI6

Thank you very much for the info!!!! these are the wheels specifications.
18"x8.5" +40
18"x9.5" +22

How do you calculate your numbers though? Or you just know them by memory? Thanks, I am a complete noob when it comes to wheels.

In that case, you'll need to go for higher aspect ratio tires. The offsets seem fine, don't they have 18"x8.5" +35 for the front?

The overall diameter info is available at tirerack:

http://www.tirerack.com/tires/Spec.j...R8SPORTPS2XLV2

You can also try to get that info from the tire manufacturer. Different tires might differ slightly despite having similar width and aspect ratio specs, but I think the tirerack info is good enough.

[Rick Hunter]

http://www.carbibles.com/tyre_bible_pg4.html

[AWM3]

These are all negative offsets so the plus sign is not appropriate in any case. OEM sizes as you know are 225/45/18 and 255/40/18. You could continue using those same tire sizes. However, since you have increased your wheel width by one half inch front and rear, wider tires would be appropriate. Your choices come down to two options:
1 - 235/40/18 and 265/35/18
2 - 245/40/18 and 275/35/18

Option 2 will be closer to the original tire diameter. However, your rear offset of negative 22 is somewhat extreme, or as the ricer boys like to say, "aggressive", and there is a possibility of contact between the fender lip and the outside edge of the tire with the 275 size. If your car is lowered, a problem at the rear is more likely.

[BMWI6]

Thanks guys, I have been reading the links and I have familiarzed myself a bit more. I still don't get the offset though. Since these new rims are wider by .5inches, shouldn't I buy rims that have a .5inch lower offset than the OEM? thanks again.

[AWM3]

Originally Posted by BMWI6

Thanks guys, I have been reading the links and I have familiarzed myself a bit more. I still don't get the offset though. Since these new rims are wider by .5inches, shouldn't I buy rims that have a .5inch lower offset than the OEM? thanks again.

Short answer - no.

The Z4M has been on the street since 2006. There are plenty of postings on various forums that will tell you what will work and what won't work. The wheels will work and there are a few choices in tires sizes that will work. Do your homework and make your choice.

[O-cha]

You want 18x8.5 x35mm and 18x9.5x33mm

255/35/18 in front, 275/35/18 in the back



/thread

[vicj]

BTW, I hear VMR wheels are somewhat heavy. I've seen mixed reports posted here, and most of them seem to point to heavier than stock weights for the rims.[/QUOTE]


I wouldn't worry so much about the weight. Our factory rims are not exactly lightweight themselves. The factory wheels, style 242, are:

Front: 11.2kg, or 24.69 lbs.
Rear: 11.7Kg, or 25.79 lbs.

The VMR 710 style wheels are:

18" front: 24 lbs.
18" rear: 24.5 lbs

19" front: 25 lbs.
19" rear: 25.5 lbs.

As you can see, the VMR wheels are actually LIGHTER than stock in the 18 inch size, and even the 19 inch wheels are very close to what our factory 18's are.

I wouldn't let weight be an issue here.

The only thing to worry about with the VMR 19 inch wheels is lowering. With 275/30-19's, I have experienced some rubbing if the car is lowered more than about 4/10's of an inch in the rear. The offset is a little aggressive. This size wheel and tire combination sticks out about 18mm further than stock, creating issues when lowered. Stock ride heights are not an issue at all. However, simply switching to a 265/35, or even a 255/35 rear, eliminates the rubbing issue. If you want to keep the stagger, just be sure to also downsize the front tire appropriately.

[lucid]

Where did you get the VMR numbers? Did you weigh them? I saw a post somewhere on this forum, which put them heavier than what stock. I think the poster was stating that he weighed both the VMR and stock wheels. He might have weighed the 19" VMRs though.

[vicj]

For this case, I took the posted weights from VMR themselves, but have also weighed my own. The weights on my examples were actually slightly LESS than VMR's weight specifications.

[lucid]

I found some numbers here for the 18" VMR (since they don't have the OEM wheels on the same scale, calibration differences will result in some variation):

18x8.5: 23.8 lb
18X9.5: 25.6 lb

http://www.m3post.com/forums/showthr...ht#post4743432

Offset differences will affect the numbers slightly as well. Regardless, you are probably correct that there won't be a significant difference for 18".

[vicj]

That's right. Plus, unless your tracking the car and trying to squeeze out every last gram of performance, these small differences we're talking about won't even be felt.

The surprising thing whenever I post this info, is how heavy the factory wheels are. Just because BMW calls them "lightweight", don't make it so....

EDIT: I also don't weigh mine on a home scale, which will post different weights just by where you place something ON the scale. I weighed mine on a commercial meat packing scale. Pretty accurate.

[lucid]

One can "feel" a difference at about 5lb/wheel IMO, so based on perception, this is all kind of a wash to begin with. But, as a principle, I wouldn't want to buy aftermarket wheels that are 2-3 lb/wheel heavier than stock. Some folks spend hundreds of $ to get another 7-8hp out of the engine, which is also not noticable, and then slap heavy wheels on their cars for instance. Factory wheels are not necessarily light, but I would guess that they are somewhat stronger than the VMRs; no way of knowing for sure though since we are unlikely to find any controlled study on that.

[vicj]

I'm not disputing the quality. Of course the factory wheels have a higher quality finish, and probably ARE stronger. If however, one wants to change wheels for the look, or if you think the factory wheels look a little feminine, as I happen too, then I was only stating that weight wasn't as big an issue in this case as people proclaim.

For example, Take MY rear tires/wheels. I went from a factory wheel with Conti's. The combined weight of the two was:
Wheel 25.79 lbs + Tire (Conti Sport 3, 255/40-18) 27 lbs = 52.7 lbs. each.

In going UP a size with VMR, and changing tires to Khumo tires, It looked like this:
Wheel 25.5 lbs + Tire (New Evo 255/35-19) 26 lbs. = 51.5 lbs. each.

A larger size, and still slightly LESS weight. It's not just about the wheel weight, but the wheel and tire weights combined. For those that buy lightweight wheels such as BBS, Volk, etc, they often talk about their tire and wheel weight, but forget to add things in like Centering Rings, Spacers to get the right offsets, etc. I looked at BBS, but to get the offsets right, you often have to add 2 lbs spacer and centering ring, negating some of the weight savings. For me, that just wasn't worth spending 3-4X the money, cause I'm cheap, and I know that I'll just mess up the wheels after a while anyway.

[lucid]

Yes, the same brand and width tire usually weighs less as you go up in rim dia while preserving rolling dia, but that pretty much turns out to be a wash in the 18"-20" range (as the savings are more or less offset by the increase in rim weight for the same brand rim), so, it is actually pretty much about the rim weight at a given size. Your VMR rim weight data simply support that. Also, there is another variable that is often overlooked, which is rotational intertia, which you won't find data on. I don't like centering rings or spacers, and would do whatever I can to avoid them. The bottom line is that a somewhat pragmatic objective metric for a rim is strength/weight ratio. Of course, looks are subjective.