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Old 02-26-2012, 03:10 AM   #1
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Default Wheel offsets, particularly Roadtrek Chevy

A thread was started on the Yahoo board by a guy that wanted his spare wheel to match the aluminum (American Racing) wheels on his Chevy based Roadtrek. He bought another of the AR wheels, and then found it did not fit properly on the tire carrier because the offset was different. This has started a very interesting discussion, of which I have been very interested. It, at first, seemed to be no big deal, but when I looked into it further, I developed a different feeling about it.

It appears that Chevy light truck front suspensions are not like the old rear drive, twin a-arm stuff we are used to, which used zero offset wheels. The OEM Express wheels have 28mm of positive offset, which moves the wheel center in over the wheel bearings better, and also reduces the scrub radius a lot. The AR wheels that Roadtrek uses have a minus 6mm offset, so the wheel centerline is moved out 34mm, or nearly 1 3/8". I did some measuring and calcs, and it looks like it over doubles the load on wheel bearings, and reduces the spring, sway bar, and shock rates by over 10%. Perhaps, with the OEM wheels, the van wouldn't need the 5000# Tuff-truck springs, and could go with something softer. i would guess the Roadtreks with aluminum wheels sit lower in the front than the ones with OEM wheels.

We have the aluminum wheels, and have already had a wheel bearing failure at 12K miles, so it interests me a bunch. My current feeling is that we will change to the OEM wheels before we start traveling for real (Alaska and such).

I will be very interested to see how the wheel change will affect the handling and ride, since we have the 5000# springs, bags, Bilsteins, and the rear sway bar.

Anyone want to trade wheels, or buy our hardly used AR wheels and tires (13K)?
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Old 02-26-2012, 12:07 PM   #2
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Default Re: Wheel offsets, particularly Roadtrek Chevy

I picked a 2006 Chevy Express 3500 at Tire Rack to check wheel upgrade choices
http://www.tirerack.com/wheels/resul...6&autoModClar=
and the first option presented is the American Racing AR-23 wheel.

There is a warning if you click on "Important notes":
Quote:
Aggressive fitment! Depending on the tire size used, the tire could be between 1-1/2" to 2" further out than it is with the factory wheel/tire combination! Confirm the clearances especially if used on the Express (van model). There may be issues with the sliding door and clearance.
That does suggest the wheel center line is being shifted outward as you pointed out.

Quote:
Originally Posted by booster
.................. I did some measuring and calcs, and it looks like it over doubles the load on wheel bearings, and reduces the spring, sway bar, and shock rates by over 10%. ...................
I don't know how to do the math but that doesn't sound good at all.
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Old 02-26-2012, 09:26 PM   #3
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Default Re: Wheel offsets, particularly Roadtrek Chevy

The AR23 is the wheel the Roadtrek uses, in the 7" wide, minus 6mm offset version.
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Old 02-27-2012, 11:59 PM   #4
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Default Re: Wheel offsets, particularly Roadtrek Chevy

Booster; Well that is interesting & now another conundrum for me. We have the A/R wheels on our '02 C190 V. We've installed the truck springs & blocks for 2" lift. If the A/R rims are going to be a problem, I'll gladly give them up & install "ugly" (stock) steel wheels. They shouldn't be hard to find at one of our local 'Llanteras'. Might even be able to trade the A/Rs or save them for resale of the RoadTrek. Thanks for the info., very timely... Ric.
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Old 02-29-2012, 01:07 AM   #5
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Default Re: Wheel offsets, particularly Roadtrek Chevy

I have recently been looking into wheels, for a few reasons. Maybe I can solve a couple problems at the same time.

I want to change tires to a tire that can carry our load, without heating up so much. With the factory tires, our pressure gets up to 90psi; an increase of 10psi. Research suggests a tire with proper load carrying ability, should only warm up enough to cause a maximum of 4psi pressure increase. The factory 245/75R16 only has a 3000# rating @ 80 psi. Our rig weighs 5400# on the rear axle. That is 90% of the tire's max load capacity.

Note: The 16" X 7" AR-23 wheel (Roadtrek installed) is also only a 3042# load rated wheel.

Photos of the back of one of my wheels.



The 16" tires that can easily handle this load are slightly larger (265/75R16 or 285/75R16). These have 3400# & 3700# ratings @ 80psi.

These larger tires also need a 8"-9" wide wheel.

The next best tires fit on 18" wheels, also needing 8"-9" wide wheels.

The aluminum wheel options typically have a zero offset or -6mm offset. I did find one that has a +18mm offset (only 3/8" out from factory). It is not my first choice in "style"; but it should work well. http://www.discounttire.com/dtcs/findWh ... &rc=WASINT


Buy one of these for the spare also, and modify the carrier to fit.

We are also starting to lose a front hub bearing (18,000 miles). In researching the replacement options, there is a wheel bearing assembly for under 10,000 pounds GVWR and one for over 10,000 pounds GVWR. I measured the parts on the R/T and they seem to be the larger (over 10,000#) size. I will be replacing both front bearings with the 10k#+ bearings, soon. Which brand (Timken or ???)?
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Old 02-29-2012, 01:37 AM   #6
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Default Re: Wheel offsets, particularly Roadtrek Chevy

Quote:
Originally Posted by booster
A thread was started on the Yahoo board by a guy that wanted his spare wheel to match the aluminum (American Racing) wheels on his Chevy based Roadtrek. He bought another of the AR wheels, and then found it did not fit properly on the tire carrier because the offset was different. This has started a very interesting discussion, of which I have been very interested. It, at first, seemed to be no big deal, but when I looked into it further, I developed a different feeling about it..................
Now this is very interesting. We have a spare tire/wheel, mounted at the rear of the RV. If we get a flat, and need to use the spare, we can not mount the flat tire/wheel in the location of the spare?

I wonder how it would work, if remove the cover from the spare and mount the AR-23 wheel/tire? Would it fit any better with a 2.0" wheel spacer attached to the carrier, or would that make the problem worse? Hmmmm, time for some testing.

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Old 02-29-2012, 05:16 PM   #7
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Default Re: Wheel offsets, particularly Roadtrek Chevy

Quote:
Originally Posted by Photog
Quote:
Originally Posted by booster
A thread was started on the Yahoo board by a guy that wanted his spare wheel to match the aluminum (American Racing) wheels on his Chevy based Roadtrek. He bought another of the AR wheels, and then found it did not fit properly on the tire carrier because the offset was different. This has started a very interesting discussion, of which I have been very interested. It, at first, seemed to be no big deal, but when I looked into it further, I developed a different feeling about it..................
Now this is very interesting. We have a spare tire/wheel, mounted at the rear of the RV. If we get a flat, and need to use the spare, we can not mount the flat tire/wheel in the location of the spare?

I wonder how it would work, if remove the cover from the spare and mount the AR-23 wheel/tire? Would it fit any better with a 2.0" wheel spacer attached to the carrier, or would that make the problem worse? Hmmmm, time for some testing.

He said that when he tried to put the AR wheel on the holder, it stood proud by about 1" (gap between the tire and the carrier upright), so he couldn't put the cover back on. He was going to get 1" out of the mount to move it back in closer. I would worry more about putting two different offsets on the front, in case of a flat, as it could pull horribly.

I haven't had time to really look into alternate wheels, as I am hoping someone wants to trade for factory steelies, but the little I have done would indicate that wheels for a Chevy Silverado might work well. They come in 8 bolt by 6.5 for the 2500 and 3500, which are probably the same wheels, and it appears they are 31mm offset, which is not much off, and a 1/8" spacer would put you right on, if you chose to. I have seen alloys listed in various diameters and widths, so you would have some choices.
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Old 03-02-2012, 07:37 PM   #8
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Default Re: Wheel offsets, particularly Roadtrek Chevy

I measured our spare tire/wheel this morning. It is a 28mm offset.

I understand what the fellow on Yahoo was saying. He could mount the tire back on the carrier, but he could not mount the metal ring, because wheel offset placed the tire 1" forward, and away from the upright (vertical post the tire is mount on). This would mean there is also a 1" gap, between the fiberglass cover and the tire.
Note: The wheel spacer would compound the problem; not eliminate it.

In that case, he could have probably just mounted the metal ring on the tire, and not over the lip of the fiberglass cover. This would work, if we had a flat tire, to get us to a repair shop. But it would not be a good solution, if you were wanting to run 5 tires/wheels that were all the same (adding a 5th AR-23 wheel). In that case, he would probably want to remove the fiberglass cover completely, and leave the tire exposed. Then rotate it into the mix, when rotating the tires.

With the tire sitting 1inch forward of the upright, the tire would also be 1 inch closer to the rear door. If the tire mount could be modified, to pull the wheel back 1 inch, he might be able to mount all the covers back on, in the normal fashion.
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Old 03-05-2012, 09:36 AM   #9
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Default Re: Wheel offsets, particularly Roadtrek Chevy

Hey, I'm the guy that posted on the Yahoo Roadtrek site. Here is the link:

http://autos.groups.yahoo.com/group/roa ... sage/69449

Regarding the extra load on the bearings. I plan to put some grease in the hub next time I lube the front end. Sounds like this is helpful even if there is not the extra load concern with the AR23 rims. See this discussion, and especially the links to other discussions on truck boards about lubing the hubs:

http://autos.groups.yahoo.com/group/roa ... sage/69571

It would be nice if Roadtrek provided some engineering analysis to alleviate any concern over use of the AR23 rim. Doubt they would though, if they even studied it at all.

Also, I modified the spare tire carrier for the AR23 rim.

1. Measure the distance of the edge of the tire (on the AR23 rim) to the vertical square support bar. Mine was about 1-1/8". I should have measured the distance on the steel rim but I was not aware of the offset difference before I had the tire mounted on the AR23 rim. I assume the tire on the steel rim rests very close to, or on the vertical square bar.

2. Cut the lower horizontal 1/4" thick support 1-1/16" from the square support.

3. Cut the upper horizontal 1/4" thick support just inboard of the weld bead to the square support. Scribe a line on top of the square support 1-1/16" from the cut.

4. Place the cutoff tire carrier piece on top of the other piece with the lower horizontal support butted against the square support and the top horizontal support edge on the scribe line from 3.

5. Weld all 4 joint locations.

I assume you need to knock the paint off all the weld locations (I'm not a welder). My neighbor has a welder at his shop so I just gave him the pieces and alignment instructions and he welded it. The tire edge is right at the square support bar. Fiberglass cover goes on and all is well. If I ever need to mount a steel rim I will make a spacer. I plan to put pictures on the Roadtrek site soon.

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Old 03-06-2012, 05:00 PM   #10
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Default Re: Wheel offsets, particularly Roadtrek Chevy

After a ridiculous amount of very frustrating spec and vendor chasing, I finally ordered some wheels and associated parts today. Wheel vendors are right in there with used car salesman, I think. Never call back, very vague on what you would get, nothing in writing, etc.

What I finally decided on was to get some late 2000's Silverado factory steel wheels, which they have one part number of that is a 16X7. Almost all the other wheels for Express or Silverado are 6.5 wide. As near as I have been able to find out (nobody would actually measure one for me) the wheels should have 31mm offset, but I won't know for sure until they get here. The 3mm extra offset shouldn't be an issue, and even if it is, a 3mm spacer would fix it. The wheels come in chrome, if you can find good ones, but I ordered reconditioned painted ones as they are much much cheaper. I also ordered chrome center caps (painted would be cheaper, but wanted the bright ones) that are OEM new. Used lug nuts also. I may still need to get the plastic lug nut caps that hold on the center, as it was unclear if they will come with the cover.

It would have been easy to get the 16" wheels in the 6.5 wide and 28mm offset, but I wanted to get to the 7" rim to allow a bigger tire size, If I chose to.

As of now, the plan is to use two tire sizes on the 7" rims. The fronts will be the stock size 245-75-16, and the rears will be 265-75-16. I measured pretty carefully to see if the bigger tires would fit the front, and they "probably" would, but would be very close. All the upsize tire charts list a 30.5" diameter as max for the Express (that is what the 245-75-16 is). The back looks to have much more room.

I think this will work out pretty well, as the front tire load is well within the tire capacity, so the bigger tire isn't needed, and it will help keep the steering effort down. The rear can run just about at the tire capacity of the smaller tires, but the 265's will give something like 750# of extra axle capacity and tire headroom.
I don't think I have ever heard of anyone having a blowout on the front, but quite a few have on the rear, so the extra safety factor will be useful.

The spare will remain as stock, in the 245 size. The only issue would be a rear flat would put two different diameters on the drive axle, which can overheat the differential. It would necessitate driving slowly until the tire could be repaired or replaced.

The good news is that I have under $390 in the wheels to this point. If I need the caps it will be another $35 approx. Of course, I could see me spending $100+ on some very nice PPG urethane paint to make them look better!

I think we will go with Michelin LTX/MS2 tires to see how they do. Folks report smoother ride from them (which we may need because of the front end stiffening up from the lower offset), and they are also, allegedly low rolling, resistance.

I am looking forward to seeing if the handling is affected, as well as the ride, but very happy to have the extra rear capacity.
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