Wheel offsets, particularly Roadtrek Chevy

[peteco]

Originally Posted by Hondo

Installed new 275-70R-17 tires onto the 17 X 7.5 28mm offset Chevrolet alloy wheels today. Before I did I reinstalled the 2 inch steel wheel spacers on the rear axle, so the rear track is just barely wider than the front now.

I guess I haven't been paying attention, but is the standard Express rear track width about 4 inches less than front? Why would the vehicle be designed that way? I am trying to understand why you needed the 2" spacer.

[booster]

Hondo's drop knuckles move the fronts out a long ways. Stock there is very little track difference front to rear.

[peteco]

Originally Posted by booster

Hondo's drop knuckles move the fronts out a long ways. Stock there is very little track difference front to rear.

That explains why the front tires look like they are sticking way out in his pictures. I had been puzzled by that especially since he had gotten rid of the AR23 wheels and their more outward offset.

[User1213]

Originally Posted by peteco

That explains why the front tires look like they are sticking way out in his pictures. I had been puzzled by that especially since he had gotten rid of the AR23 wheels and their more outward offset.

The latest set of wheels have the stock 28mm of offset vs 0mm with the AT Ledge wheels..this is abut 1 inch less track per side.

If you look at my thread you'll see that now the front tires are just about flush with the fender lips. Adding the rear spacers moves the rear track outward and now is wider than the front.

[cruising7388]

Originally Posted by booster

I wanted to with the 265-75-16 in the rear, and 245-75-16 in the front, but when I started looking into it, I found that the ABS wouldn't like that much diameter difference and would probably disable itself, so we went with the 265's on both ends.

I was under the impression that the ABS system addresses each wheel discretely rather than addressing all wheels collectively. If that is true, why would the ABS system care if different wheels have different diameters?

[booster]

Originally Posted by cruising7388

I was under the impression that the ABS system addresses each wheel discretely rather than addressing all wheels collectively. If that is true, why would the ABS system care if different wheels have different diameters?

The rear drive vans look at it as a 3 zone system with independent front sensors and one for the rear unless it has stability control, AFAIK. The system compares wheel speeds to determine in any are slipping.



The sensors read rpm, so a different diameter at the same speed rotates at a different speed and different speed on different wheels indicates loss of traction, as it would with a wheel skidding. This will trigger the ABS to pulse the brakes, and eventually disconnect itself and go to standard brakes.


The consensus that I got from the good mechanics that I talked to was that they thought the 1" diameter bigger, 3-4% wheel speed difference would be an issue. There doesn't appear to be a method available to program it out of the ABS computer.

[Sensei]

Hi Hondo, I made some research but I wasn't able to find the wheel weight for the factory 17'' alloy wheel that you chose. Do you have this info?

[tlillard23]

Originally Posted by booster

The rear drive vans look at it as a 3 zone system with independent front sensors and one for the rear unless it has stability control, AFAIK. The system compares wheel speeds to determine in any are slipping.



The sensors read rpm, so a different diameter at the same speed rotates at a different speed and different speed on different wheels indicates loss of traction, as it would with a wheel skidding. This will trigger the ABS to pulse the brakes, and eventually disconnect itself and go to standard brakes.


The consensus that I got from the good mechanics that I talked to was that they thought the 1" diameter bigger, 3-4% wheel speed difference would be an issue. There doesn't appear to be a method available to program it out of the ABS computer.

Correct. I've experienced it in other GM vehicles, and have seen it on the Tech2 scanner. the ABS and traction control will see the 3-4% difference as wheel slip. negatively affecting braking and reducing power because the controller sees the difference as a biiig fat burnout! eventually faulting the ABS/TCS , which disables the system. The newer vehicles have electronically controlled brake bias and will set ~all front brake, minimal rear - cuz its "safe". Try slowing down an overweight pig with just front brakes, lots of weight shift causing all sorts of nasty.

this goes for 3 or 4 channel/zone brakes. Need to keep factory tire RATIO to keep the systems happy.

[Steve & Berta]

Great info everyone! I need to read it all again after watching the video with a better understanding of offset and backspacing. I wonder if the same rims Booster used will work on my 00D190V? It sounds like the handling improvement may be well worth it.

[booster]

Originally Posted by Steve & Berta

Great info everyone! I need to read it all again after watching the video with a better understanding of offset and backspacing. I wonder if the same rims Booster used will work on my 00D190V? It sounds like the handling improvement may be well worth it.

You Dodge would use different wheels as the offset is likely at zero instead of the +28 that the Chevies are starting in 2003. The previous generation Chevies were at zero like most rear drive vehicles back then.


You probably also have a different bolt pattern and maybe stud size and thread.


It is best to get the specs for offset, width, diameter, load capacity, bolt pattern, lug size and thread for the OEM wheels for your year Dodge so you know what to look for. Unless you are looking to go with bigger tires, you are probably fine with stock wheels. The Dodge handling issues are related to a multitude of other problems.

[SailorD]

Hey Booster, I know this is an old thread but I'm curious to know if you think the 16x7 oem truck wheels you found would fit a stock 2003 gmc/chevy van with 265/75/16s. I see that you guys might have different track widths on your camper vans so just thought I'd ask. And I'm also wondering if they're still working well for you. Thanks for sharing your work and experience on this!

[booster]

Originally Posted by SailorD

Hey Booster, I know this is an old thread but I'm curious to know if you think the 16x7 oem truck wheels you found would fit a stock 2003 gmc/chevy van with 265/75/16s. I see that you guys might have different track widths on your camper vans so just thought I'd ask. And I'm also wondering if they're still working well for you. Thanks for sharing your work and experience on this!

Assuming that the 2003 is the chassis year and not a conversion year they should fit fine. If you have the 6.0 engine it will be a 2003.


The only exception would if for some reason the van is sitting lower, perhaps even if it was a 1500, as all the bigger tires I know of were on the heavier vans. If you get very low you might hit something but there are some full conversion 3500 van using them without lifting I think. We are about 1.75" higher than a stock Roadtrek 190 and at essentially the factory spec for an empty 3500 van.



Ours have worked well for years. We are about 10 years in and on our second set of tires. We have found no downside at all, except for having to modify stuff to carry a full size spare to match.


Be absolutely certain you get the correct 16X7 wheels with 6 scalloped cutouts on them and +28mm offset. They can be hard to find. I just recently got one for our spare and the junkyard in North Dakota still has 3 left, I think.