G500 - Tire Sizes/Lift Height and Computer Reprogramming

Bikeman71

Observer
I just bought a one owner 2004 G500 with 39,000 miles on the clock. It is in fantastic condition....I am thrilled.

I plan on using it off road...a lot. I live in Pollock Pines...about 25 miles from the Rubicon trailhead and countless other trails. I'm not sure I'll be taking it on the Rubicon in the near future, but I'll be doing many overlanding style trails on the eastern side of the Sierras and to Death Valley several times each winter/spring.

I just ordered the 30mm lift spacers from Viking Off Road. From everything I've read, this should get me enough space to run 275/70R18 = 33.2x10.8R18...thinking of Good Year MTR or Toyo M/T.

I've heard different reports on whether the computer needs to be reprogrammed because of different tire sizes and ride height. Some say there is no way to change the computer and others say Mercedes can reprogram it for specific tire sizes. Is there a definitive answer on this?

I want to do this right the first time. I almost ordered 275/70/18 tires today, but figured I would go with the "measure twice, cut once" theory. I would hate to have the tires installed at Les Schwab and then the car shuts down and goes into some kind of limp mode on my way home....or maybe the lift isn't enough for the tire size.

Any advice or suggestions based on the above information would be terrific. I think this could be a good way to get this information into one thread...I'm sure I'm not the only one cross referencing from 3 different forums from three different builds on each forum to try and figure this out.

Thanks!
Brent
 

shaggag

New member
Congrats on the truck. I have an 08 and ran the 30mm spacers with the oem springs and 285/65/18 (Diameter 32.6" Width 11.22") for a bit.

Although I didn't experience issues with the ESP at that time, the front right tire would rub the fender-liner on full lock for left turns. The rubbing is more severe when loaded with passengers and/or under compression (I now have a hole in my liner : / ) i see you're planning to run 275/70R18 = 33.2x10.8R18 - that may have different results.

I am currently running the ORC springs with oem shocks (which i love btw) and there is no longer any rubbing. The ESP can come on briefly on 50+ mph turns (usually downhill). Depending on how often you hustle your truck through freeway on/off ramps this may or may not be an issue.

I wish I had any info about dealer or independent shops reprogramming for the tire sizes but the dealer and shop I have been to were not familiar with that option.
 

Bikeman71

Observer
Thanks for the information! Hopefully we can get enough folks chiming in on this subject in one space to gather some conclusions about all kinds of set-ups.

I have continued my research and would like to provide some information regarding the computer issue. I spoke with Dan at El Dorado Hills Mercedes Benz and his team have worked on several G rigs with bigger tires/lifts and off-road in mind. He stated the G500 allows for the computer to be changed to, "one tire size bigger or one tire size smaller than the original size." 275 70 18 is probably two tire sizes up, so I will still be off by 3-4 mph on the speedometer, but very close. He also stated everything will work fine with the bigger tire size with the exception of a rare ESP engagement. He stated the cost to reprogram the computer is $165. It seems expensive, but I will probably do it just to ease my mind.

Hopefully this helps someone with computer questions like I've had.

BTW, I just ordered Good Year MTR Kevlar in 275 70 18....the 30 mm spacers have also been ordered. If you have any reason to believe I'm making a big mistake, please don't hesitate to tell me I'm an idiot. :sombrero:
 

All-Terrain

No Road Required
Congrats! Let's see some photos!

You really need to go to the more prominent G forums - www.pointedthree.com and www.clubgwagen.com - that's where the good info is at. No discussion of imaginary gas mileage there...... There are some good threads on tire size adaptation at PointedThree.

To answer your question, any shop that has a Mercedes STAR machine/computer can plug into your G and tell its systems what your new tire size is. There are photos of the exact process, one mouse-click at a time, at PointedThree.

Good luck!

EDIT - You won't go into Limp Home mode with just an increase in tire size. The consequence will be that your stability/traction control (ESP) will think that each of your wheels are traveling faster than they actually are (as in, 65mph when you're actually doing 60mph), being watched by the wheel speed sensors, so the ESP will kick in sooner/act more conservatively. As a practical example, the ESP will get scared when you go down an off-ramp and will force the brakes to act to slow you down to a silly speed like 25mph when you could safely be doing 35mph if your ESP had been programmed to your new tire size. Hope I explained that properly...?
 
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Haf-E

Expedition Leader
Wouldn't bigger tires make the computer think it was going slower than actual? Bigger tires > fewer rotations per mile > lower speed displayed on the speedo...

Based on my experience with MB Sprinters (but not 4x4) it will be fine as long as all four tires are the same size. The speedo will be off a bit - but they come that way so, and at least on my sprinter, the speedo is more accurate than original with the bigger tires but now reads a bit low instead of high.
 

All-Terrain

No Road Required
Wouldn't bigger tires make the computer think it was going slower than actual? Bigger tires > fewer rotations per mile > lower speed displayed on the speedo...

Based on my experience with MB Sprinters (but not 4x4) it will be fine as long as all four tires are the same size. The speedo will be off a bit - but they come that way so, and at least on my sprinter, the speedo is more accurate than original with the bigger tires but now reads a bit low instead of high.


Sorry, you're right, I didn't think that through. It's probably the increased height raising the center of gravity - the accelerometer is probably sensing that change, the increased pitch and roll, and adjusting due to that change.
 

Bikeman71

Observer
Here she is. The only thing I've done so far is remove the running boards and start to plan how the National Luna Fridge and Powerpack will be installed.



 
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otiswesty

Regular guy
The 275/70/18 does not require a spring or a wheel spacer to fit. Just bolt it on and go. There is a slight touch at full compression at the top of the rear fender liner but that is it. I used the 30 mm spacer as well, but added them later for a bit of body lift.
Here is a description of the necessary steps to change the computer for the 33" tire size.
http://www.clubgwagen.com/forum/viewtopic.php?f=18&t=1541&p=8162&hilit=275/70/18#p8162
I had it done at the dealer and there was one hour of tech time charged.
Very nice truck you got there.
 
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Bikeman71

Observer
The 275/70/18 does not require a spring spacer to fit. Just bolt it on and go. There is a slight touch at full compression at the top of the rear fender liner but that is it. I used the 30 mm spacer as well, but added them later for a bit of body lift.
Here is a description of the necessary steps to change the computer for the 33" tire size.
http://www.clubgwagen.com/forum/viewtopic.php?f=18&t=1541&p=8162&hilit=275/70/18#p8162
I had it done at the dealer and there was one hour of tech time charged.
Very nice truck you got there.

This is getting good! I love the idea of using the ratios of tire size and gearing to come up with the proper setting. Thank you!
 

RBA

Adventurer
If you're National Luna fridge starts chirping when connected to the Power Pack, know that it's the connection. Unplug and replug it.
 

mk216v

Der Chef der Fahrzeuge
Looking shiny Brent!

Thanks for that better link Eric, much easier for others to follow vs the P3 link.

If you're National Luna fridge starts chirping when connected to the Power Pack, know that it's the connection. Unplug and replug it.
Good to know, thx!
 

Bikeman71

Observer
Since I started this thread, I thought I would report back on my findings regarding tire size, lift, computer reprogramming etc.

I started the process by adding 275 70 18 Goodyear MT/Rs. For normal daily driving, I can confirm they do not rub with stock suspension set-up. I didn't get the car off-road to test in this configuration.

A week or so later, I added the 30 mm spacer and changed the computer settings as described in post #9. The overall look of the truck is better with a slight lift, but I'm not sure if it will help with clearance or not. The day after getting the G back, we took a family day-trip to Tahoe. For those that know highway 50 from Pollock Pines to Tahoe, you know that the curves are the perfect testing ground for the ESP. During this trip, I was extremely disappointed in how often the ESP was triggered...it took very little to get aggressive correction happening.

I came home and did some more research on ways to correct the problem. I started with an overreaction, and looked for ways to completely disable the ESP. Luckily, I backed off and started with the easier suggestions first.

The first correction I tried made all the difference in the world...tire pressure. The shop that did the suspension work put in the recommended stock tire pressure. I took the tire pressure to 42 front and 44 rear and took it out for a test drive...the ESP issues got much better but the ride was terrible. I continued to play around with pressures until I found the right balance. I ended up with 38PSI front and 41PSI rear as the ideal pressure. It is ideal for both ride quality and ESP.

We took another trip to Tahoe this past weekend. While the ESP still comes on during some high speed turns, it is much less frequent and the correction is much less aggressive. Before it was something I could not live with...now, I hardly notice it.
 

merctaf

Member
Since I started this thread, I thought I would report back on my findings regarding tire size, lift, computer reprogramming etc.

I started the process by adding 275 70 18 Goodyear MT/Rs. For normal daily driving, I can confirm they do not rub with stock suspension set-up. I didn't get the car off-road to test in this configuration.

A week or so later, I added the 30 mm spacer and changed the computer settings as described in post #9. The overall look of the truck is better with a slight lift, but I'm not sure if it will help with clearance or not. The day after getting the G back, we took a family day-trip to Tahoe. For those that know highway 50 from Pollock Pines to Tahoe, you know that the curves are the perfect testing ground for the ESP. During this trip, I was extremely disappointed in how often the ESP was triggered...it took very little to get aggressive correction happening.

I came home and did some more research on ways to correct the problem. I started with an overreaction, and looked for ways to completely disable the ESP. Luckily, I backed off and started with the easier suggestions first.

The first correction I tried made all the difference in the world...tire pressure. The shop that did the suspension work put in the recommended stock tire pressure. I took the tire pressure to 42 front and 44 rear and took it out for a test drive...the ESP issues got much better but the ride was terrible. I continued to play around with pressures until I found the right balance. I ended up with 38PSI front and 41PSI rear as the ideal pressure. It is ideal for both ride quality and ESP.

We took another trip to Tahoe this past weekend. While the ESP still comes on during some high speed turns, it is much less frequent and the correction is much less aggressive. Before it was something I could not live with...now, I hardly notice it.

Thank you for the update. I just ordered the 30mm spacers. Could you post some pictures of your gwagen?
 

Bikeman71

Observer
I failed to give my hypothesis on why tire pressure matters so much...

When using bigger tires, there is more give in the sidewalls (at an equal PSI) which equates to body lean and a more sensitive ESP reading.
When tires are overinflated, there is less grip which equates to slippage....I'm betting that plays into the ESP as well.

Does this sound right?
 
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