[jdbower]

I found this excellent diagram on the Internet:

http://robrobinette.com/wheel_offset.htm

I also found this calculator:
http://www.miata.net/garage/tirecalc.html

From this I have a few questions:
1. Why is the offset such an important measurement? I would think that the caliper height is what we'd really be concerned about. I'm assuming that rim width divided by two minus offset must be greater than or equal to a certain constant for the ML (this is labeled as caliper height). Seems like a lot of extra math...
2. Why is it that most of the places I've visited don't change the tire size when the rim width changes? I would imagine that going from a 9.0'' rim to a 9.5'' rim would result in going from 285mm tires to 295mm or 305mm tires (an extra 12.5 mm or so).
3. Why doesn't anyone list the weight or load bearing capacity of the wheel? Putting on wheels made out of lead will do nasty things to your mileage and performance, but spun sugar probably won't support more than two tons of German steel. This is less of a technical question and more of a gripe against the wheel dealers out there from someone who's not looking for bling but actually hoping for better performance and/or mileage!

One last comment for the TireRack guys:
I can forgive the fact that you show a 2001 ML instead of a 2002 and I can overlook the fact that the ML55 looks just like the ML500, but since the calipers for the ML500 and the ML55 are the same (except for the color) I'd imagine that the wheel selection should also be the same...[]

 

[[email protected]]

our listing on the ML500 and ML55 are the same...

our listing on the ML500 and ML55 are the same

 

[jdbower]

You may want to check the following...

For a 2002 ML55 I have options for:
AMG 5-spoke 163
AMG 5-spoke 163 2pc
BBS RXII

For a 2002 ML500 I have options for:
AMG 5-spoke 163
AMG 5-spoke 163 2pc
BBS RXII
moda R3

This last one is a 17" wheel which is probably why it doesn't show up under the ML55 options (since the 55 has stock 18" rims).

 

[jdbower]

On a more important note...

Is my interpretation of how a wheel offset works correct? Is there any correlation between rim width and tire width? If not, why not?

I guess more specifically, would 19x9.5 (offset of 35) rims work with 295/45ZR19 SP9000s? There would be about a 3% speed difference according to the calculator but I think it assumes the same rim width...

 

[[email protected]]

03 ML500
1 AMG 5-spoke 163
2 AMG 5-spoke 163 Chrome
3 AMG 5-spoke 163 2p...

03 ML500
1 AMG 5-spoke 163
2 AMG 5-spoke 163 Chrome
3 AMG 5-spoke 163 2pc
4 BBS RXII
5 Carlsson 1/6
6 Carlsson 1/6 Chrome
7 Carlsson 1/6 Evo
8 Mille Miglia A-SUV
9 Mille Miglia Evo5
10 Moda R3
11 O.Z. Opera PL
12 O.Z. Opera 1pc

03 ML55
1 AMG 5-spoke 163
2 AMG 5-spoke 163 Chrome
3 AMG 5-spoke 163 2pc
4 BBS RXII
5 Carlsson 1/6
6 Carlsson 1/6 Chrome
7 Carlsson 1/6 Evo
8 Mille Miglia A-SUV
9 Mille Miglia Evo5
10 O.Z. Opera PL
11 O.Z. Opera 1pc

the only difference is that 17" Moda

 

[jdbower]

Wow! That's a much more impressive list!

Maybe I'm missing something, but how do you get to it? I went to the home page and selected a year and make. After that I selected a model and got only three entries. Here's the URL:
http://www.tirerack.com/upgrade_gar...ke=Mercedes-Benz&autoModel=ML55&autoYear=2003

 

[[email protected]]

I have that looked into ... I think it is only showing what's currently in-stock...

I have that looked into ... I think it is only showing what's currently in-stock

 

[jdbower]

That would explain things...

I don't suppose you want to give me access to the backend database [:0]...

I guess my biggest outstanding question is the rim vs. tire width. Is there a formula I can use for changing tire sizes when going between various rim widths?

 

[[email protected]]

here's a list of all of the tire sizes that can fit your ML55 with the diameters

285...

here's a list of all of the tire sizes that can fit your ML55 with the diameters

285/50-18T 29.2
285/55-18 30.3
285/45-19 29.1
265/50-20 30.4
295/40-20 29.2
295/45-20 30.4

 

[jdbower]

So the width of the rim doesn't matter?

Sorry, if there's a tutorial site that you know of I'd appreciate it.

I'm assuming that the last number is the diameter from the top of the tire to the road (assuming, of course, decent air pressure!).

What effect, if any, is there upgrading from a 9" rim to a 9.5" rim? (We'll take an example with all other constants the same - if I moved from my 9.0x18 rims to 9.5x18 rims, would my tire size still be 285/55R18? - I guess changing a rim dimension without changing a tire dimension is counter-intuitive so I'm having a hard time grasping it...)

 

[[email protected]]

you can find all of the info here .... there's alot of reading .... just find the catagory...

you can find all of the info here .... there's alot of reading .... just find the catagory you need more info on


http://www.tirerack.com/a.jsp?a=CQ4&url=/about/techcenter.html

 

[jdbower]

So from what I can gather...

From the TireRack tutorials and pages like this:
http://www.dirtroad.com/tires.htm

It appears that the rim width enables you to go to wider tires, but there is no real ratio between increasing the rim size by half an inch and adding 12.7mm of tire width.

This would lead me to believe that wider rims will probably allow the same tires to have a better contact patch since the sides of the tires would not be as "pinched" as with the narrower rims. This may provide better traction and stopping power and may even improve cornering a bit (have to think about that one), but at the expense of an obviously heavier rim.

Thanks for all of your help, hopefully I've got things straight now!