MilesBFree

I measured the backspace on the wheel. Backspace is defined as the distance from the mounting face of the wheel (where it meets the face of the hub) and the back lip of the wheel. I am not that retarded, at least not today

MilesBFree

Backspace = Offset + ( width / 2 )

MilesBFree

http://www.tirerack.com/wheels/tech/...jsp?techid=101

MilesBFree

OK, I did a bit more research on the two versions of the 20" split spoke wheels that the dealer had proposed. He had stated that these were the same other than having a different offset.

Turns out that the difference is not just in the offset. but that the "other" wheels are 9.5" wide. (The ones we got were 8.5" wide.)

So there may not really be an alternative.

This is per the link:

http://www.service-shop.mercedes-ben...2502/OfferList

(Thanks for the link NYCGLK.)

The wheels they delivered to us are part number A2044012402, and the other ones that are 9.5" wide are part number A2044012502. The latter are the ones linked to above. The pricing is US$730 for the 8.5" ones, and $925 for the 9.5" ones.

The inch difference in width would explain them being almost $200 more. Just having a difference in offset would not explain the extra $200 a wheel, unless it was so rare that you would ned a different offset that they just did not make the more expensive ones in any sort of quantity. I just chalked it up to MB dealer pricing... Now the pricing makes more sense.

MilesBFree

But the question still remains - if the backspacing is different between the fronts and rears on the 20" wheels that came on our Appearance Package, then do we need the same difference in offset on the split-spoke wheels? Or is it close enough that we would not have problems?

NYCGLK

How wide are your tires in the back?

An inch difference in the backsapce means differene in offset of 162mm, which is impossible. However if your rear wheels are 9.5 inches wide then maybe, but then your tires in the back should look much different from front, or be wider 255 vs. 235.

It would make sense if 2WD comes staggered.

MilesBFree

A clarification: while I measured the backspace from hub face to the outer edge of the lip, the correct way to do this is to measure to the inside of wheel lip, where the tire bead mounts.

This will generally be around 1/2 inch less than measured to the outer lip.

This means that 8.5" wheels (measured bead to bead) are actually 9.5" wide measured from outer lip to outer lip.

I have seen certain unscrupulous wheel vendors sell 8" wheels as 9", due to measuring incorrectly. So when buying aftermarket wheels, always ask the vendor to measure bead-to-bead as well as overall width. If these are about the same, then they are measuring / selling them incorrectly.

MilesBFree

No. For the two different backspaces I roughly measured:

Offset = Backspace - ( Width / 2), so...

For standard rear wheels:

Offset = 155 - ( 216 / 2 ) = 155 - 108 = 47 mm (rough measurement error - stock is 45)

For the different offset fronts:

Offset = 127 - ( 216 / 2 ) = 127 - 104 = 23 mm

So the difference in offset is more like 45 - 23 = 22 mm, not 162 mm.

NYCGLK

wow i need to check my conversions haha

I don't even know why I took 1.62 (that's miles into km)

You are right 1 inch = 2.54 cm = 25.4 mm which is about 22mm difference in offset in your calc.

So do you have wider tires in the back?

Here is my math:

Front (stock)
127 - 108 = 19
19 + 23 (difference in measurement) = 42 (close to 45 stock)

Wider Rear

155 -120 (241/2) = 35
35 +23 (difference in measurement) = 57 (close to offset of 9.5 inch rims on the MB site)

My "difference in measurement" is due to the fact that you listed that measurement can be taken differenly.

MilesBFree

Good catch on the math error I had: 127 - 108. not -104.

The widths were the same.

It should be 35 - 23, not plus 23, so the difference would be 22 mm.

However, that doesn't matter, as the wheels I have on my car are the same front to rear - some idiot mis-measured (namely me I went out again and immediately saw I had measured to the wrong mounting surface.

Just to be safe, I pulled the wheel anyway and saw it had ET 45 stamped into it.

So the 2WD cars have the same offsets front and rear. At least according to the 20" wheels that come with the Appearance Package. That doesn't meant that the Appearance package is correct for 2WD cars. It also doesn't meant the dealer was wrong that the fronts on 2WD have different offsets than the 4Matic cars.

I think MB corporate is the only source of true information on this and it will be interesting to see what the dealer comes back with ...

MilesBFree

I am thinking the dealer threw a red herring out there by confusing the terms "width" and "offset". I think he was confused as to the two different part numbers on the split-spoke wheels, and only looked at the offset number, not the width too. I think he jumped to a conclusion.

I would bet that the widths and offsets are the same front and rear for either 2WD or 4Matic.

NYCGLK

Agreed. From the link I posted earlier there are just two sizes of 20's (for Canada and US):
8.5 x 20 +45
9.5 x 20 +57 - used for staggered setup in europe and not in US or Canada.

Offtopic, I think I'll create a separate thread for this, but people who changed wheels and such, do you think 255 will fit with stock offset. I'm pretty sure 255 can be mounted on 8.5 inch rim, and I would like do do that to have more grip and more rim protection.

MilesBFree

Yep, these are the numbers I have seen too.


According to the Tire Rack, the Pirelli Scorpion Zero tires at 255/45R20 will fit anywhere from 8 - 9.5" wheels. (I have these at 235/45R20 on mine.)

http://www.tirerack.com/tires/Spec.j...ro+Asimmetrico

Generally, an old rule of thumb to limit sidewall flex and improve performance, you would want to have the widest wheel for the tire (that is on a race car where you are either buying the widest tire available or are limited to a spec tire width). But in normal driving, the slightly wider tire would obviously offer a wider contact patch and as you pointed out, offer more protection for the wheel lip.

The wider tire at the same aspect ratio will be slightly taller, however. The following equation shows this:

OD = 2 x H + WD
= 2 x (W x AR) + WD

where: OD = Overall Diameter
H = Height of the sidewall
W = Width of the tread
AR = Aspect Ratio
WD = Wheel Diameter
So if all other variables are the same then the tire will be taller.

W will go from 235 to 255.

AR stays .45.

WD stays 508 mm (20").

So for stock, the OD is:

2 x (235 x .40) + (20 x 25.4) = 696 mm.

For 255 width, the OD is 712.

The impact of this is that the speedo will be off a bit.

( 712 - 696 ) / 696 = 0.023 = 2.3%

So when you are going 75 MPH, The speedo will be reading 2.3% low, or about 1.7 MPH low.

Not exactly a huge difference, but if you set the cruise a 7 MPH over the limit thinking that will be safe, you could be doing more like 9 MPH over.

This becomes more of a factor when doing a more significant tire size change.

NYCGLK

thanks for all calcs, but that isn't my concern

I would actually go from 235/45 to 255/40, which would affect OD by 1% (712 vs. 720). I think you made a mistake in calc of stock tire as it has 45 sidewall not 40.

I'm more concerned with extra 10mm on the inside of the wheel without changing the offset, I wanna make sure it doesn't rub on the inside esp. when cornering or having 5 people in the car. I had aftermaket rims on my old car and going in turn with 4 people in the car would generate rub, even tho the rest of the time it was fine.

The OEM 9.5 inch rims that comes with 255 tires are shifted 12mm to outside (+45 vs. +57 offset). However, tirerack does offer wider rims with same +45 offset, maybe they would come with 12mm spacers or there is simply enough space. I guess I'll wait to see if anybody with aftermaket rims have any rubbing issues.

MilesBFree

Good catch - I copied an old formula with the 40 aspect ration. You are correct that stock is 45.

I would trust MB with the proper offset for the 9.5" wheel and the tire they install with that (255), if you choose to go to a wider wheel.

I would also trust Tire Rack, since if they were wrong they would likely exchange the wheels for ones with the correct offset.

I would bet that in the size and offset range discussed here that there is enough clearance to work with either a 57 or a 45 offset. That is only a half inch difference. And going from a 8.5" wheel to a 9.5" wheel results in a half inch difference on the inboard and outboard sides. I bet the factory allowed way more clearance / tolerance than that.

EnigmaAW

wow????? you guys sure get technical!! i just crawled under my glk. the US glk350 with 4matic and 20"x8.5 rims has et45 on back of the front and rear rims. so do you think i'm going to have any issues running a 22"x9, et40 rim, with 265/35/22tires??

NYCGLK

I would be curious, you better search for Madlord's posts since he has your tire size and see what offsets he has.

your smaller offset (40 vs. 45 means) the wheel would be mounted 5mm inwards. It's also .5 inch or 13mm wider which means the inside lip would be 11.5mm closer to frame or whatever is there (5 offset + half of the rim's additional width or 6.5mm)

However the tire might be the problem, while your rim is only half an inch closer to the frame or whatever it's next to, the tire is 30mm wider, which means half of that (15) plus 5 offset and the tire is almost and inch (20mm) closer to the the frame.

Again this might be all good with no rubbing, since somebody already tried 265 with not issues, given he has the same offset of +40, but I'd be curious if there is rubbing when car is loaded taking a turn.

MB moves moves their wheels in the opposite direction (outward as they increase offset from 45 to 57) with 255 tires, not sure if there is real purpose behind this.

EnigmaAW

i searched old posts and madlord has a 22x9.5 and he thinks they are 42 offset. he also has the 265/35/22. i'm starting to think the 265's are going to be to wide. if i go down to a 255, would i keep the 35's or go to 40 profile.

NYCGLK

If his offsets are 42 and he hasn't reported any rubbing I'm sure it's ok for 95% of situations. GLK was designed for some offroading, so it should allow for long wheel travel (much longer than in any cornering), which means that a lil wider tires should still be fine.

Also going with 255/35 is fine, but 265/40 makes overall diameter fo the wheel too big compre to stock, which might affect electronics (ABS, ESP etc.)

overall diameter = width (255) times sidewall which is given as percentage of the width (35%) times 2 (since you have tire on both opposite sides of the circle) plus the diameter of the wheel (22 inches times 24.5mm) = 717.5mm stock is 712. 5mm difference is very small in this case. With 40 sidewall the overall diameter is 743 which you will be able to notice by having two wheels next to each other.

Shake

I can't wait to see GLKs with proper aftermarket rims installed.

EnigmaAW

i called the service dept. at the dealer i bought from. i told them what i'm doing, with putting 22's on. they said as long as all the rims have the same offset and the tires are the same width, i will not have any issues with the 4matic system. it's like a limited slip. the rears start spinning faster, the fronts assist to help along. they did say that 265's might be to wide, but discount tire says their computer says they will fit. we'll see.
discount tire called and my tires are in, i probably go in tomorrow to have them installed....i'll keep my fingers crossed????

Baby G

Post pics upon installation...

mybabybenz11

can someone please tell me where to get 22 inch oem wheels for a glk350 somewhere other than the dealership? please and thank you

NYCGLK

nowhere, they don't exist, only aftermarket 22's

EnigmaAW

22" glk OEM's don't exist?...other models have 22" replicas that can be bought on ebay and other sites.