Wheel offsets, particularly Roadtrek Chevy

[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.

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)?

[markopolo]

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":

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.

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.

[booster]

The AR23 is the wheel the Roadtrek uses, in the 7" wide, minus 6mm offset version.

[AZ ADVenturist]

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.

[Photog]

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 ???)?

[Photog]

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.

[booster]

Originally Posted by Photog

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.

[Photog]

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.

[peteco]

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.

Pete
2006 RT210P

[booster]

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.

[Photog]

Booster,
It sounds like you are getting the tires/wheels sorted out.

Have you ever tried to mount the spare on one of the front axle positions? I peeked under our van yesterday, looking at the clearance for the AR-23 wheel. It does not look like there is room for the wheel to move in another 35mm (factory spare). It must be an optical illusion, but I know it will be close. With the 29mm offset of the factory wheel, it should have a 5.00" backspace. I am thinking the maximum backspace is going to be between 5.00 & 5.25". A wider wheel with the same offset, has a deeper backspace.

I hope your new wheels fit, without any issues. Please let us know what the backspace is, and how they fit on the front. I would have test-fit the spare myself, but I have to many customer deadlines this month.

[booster]

Originally Posted by Photog

Booster,
It sounds like you are getting the tires/wheels sorted out.

Have you ever tried to mount the spare on one of the front axle positions? I peeked under our van yesterday, looking at the clearance for the AR-23 wheel. It does not look like there is room for the wheel to move in another 35mm (factory spare). It must be an optical illusion, but I know it will be close. With the 29mm offset of the factory wheel, it should have a 5.00" backspace. I am thinking the maximum backspace is going to be between 5.00 & 5.25". A wider wheel with the same offset, has a deeper backspace.

I hope your new wheels fit, without any issues. Please let us know what the backspace is, and how they fit on the front. I would have test-fit the spare myself, but I have to many customer deadlines this month.

I have the spare on the left front right now. I used it to do the measuring for the larger tire possibility, as it has the offset I will be using (within 3mm). In and out clearance doesn't appear to be much of an issue. Diameter is where you run into trouble. Adding 1" of diameter put me within 1/2-3/4 inch of hitting various things like the running board, body mount, grey tank. The unknown is how much the wheels move around, for and aft, on bumps. The other issue is that the wheel can move over 1" for and aft, depending on the wheel alignment.

There is a way to go wider, that I looked at, but you don't gain any load capacity to speak of. You can use a 265/70/16 tire, but tire choices are very limited.

The wheels I have coming are probably at about 4.875 backspace with the 31mm offset. Steel wheels will usually have a slightly smaller backspace at the same width and offset as an alloy wheel. (width is measured inside the mounting flange, backspace outside, and the flange is thicker on alloy wheels.

[Photog]

Booster,
Any status on your new wheels & tires?

[booster]

Everything finally showed up and got put together for the conversion to the "correct" offset wheels on the C190P. As an FYI for anyone interested, here are the wheels we considered when trying to figure out which way to go.

OEM Express steel wheels. 16X6.5 wheels with 28mm offset. Silver paint. Chrome or painted center caps. Also can get a chrome "wheelskin" to go with the centercap. That is what Roadtrek and Pleasure-way do on the steel wheels.



Silverado alloy wheels from a 2500HD/3500. 16X6.5 wheel with 28mm offset. Polished aluminum with clearcoat.



Silverado alloy wheels from a 2500HD/3500. 17X7.5 wheel. Painted and cleared aluminum. 28mm offset.



Silverado steel wheels from a 2500HD/3500. 16X7 painted steel wheel. 28 or 31 offset depending on who you believe.



The goal was to get the right offset, but also to increase the load capacity of the rear tires, if possible. That limited what we could do for wheels by a whole bunch, because of the lack of space in the wheelwells. Stock 245-75-16 tires are 30.5" diameter, and you can squeeze in maybe 32" diameter. With the 6.5 wide 16" wheels, you are out of luck because you can't go up to a 265-75-16 on that width (there is not 255 wide available). The 17X7.5 would be nice, but a 245-75-17 is a big as you can go in a 75 aspect ratio without getting to big a diameter, and you only gain about 150# of capacity over the stock tires. You can go to a 265-70-17, but it loses capacity just about to the stock tire level. The only wheel left is the 16X7 steel wheel. A 265-75-16 tire will fit on it and give nearly 350# more capacity per tire. The tires are 31.7" diameter, so they fit. Alloy would have been nice, but Oh Well. The good about them is that they are 6 spoke, instead of 5 like the originals, and have some scallops also, so they are not quite as plain. They also are hub centric, which is always a good thing, and they are cheap. They were the only 7" wide 16" I could find that had the correct offset.

We ordered NOS chrome center caps for them, and decided to paint them up to make them brighter. I read up on wheel paints, and many folks liked 06 Rover sparkle silver wheel paint, so I got a pint in Detron 2000 basecoat and added two coats of clear. They looked OK.



Since we didn't want to go too far backwards from the AR23's in appearance, I decided to try to perk them up a bit by doing an aluminum flake "candy" over the existing clear. It was several dust coats of the .004 aluminum flake in clearcoat, and them 3 full wet coats of plain clear to level it out. It brought them to to life pretty well.





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. Decided to try Michelin LTX/MS2 tires, based on TireRack reviews, particularly concerning ride quality and handling.

Here is what the setup looks like on the van.



And a bunch of pics from different angles to show how far in the sit compared to the side of the van.











This is from a bit back so is shows the way it now sits. We think it actually looks more in proportion with the bigger wheels set in further. We also gain almost an inch of clearance in the front, about 50/50 from bigger tires and raising because of the less offset.



As long as we were messing around, and I had used the spare as a test for the aluminum flake, we picked up a center for it also. It always irritated me to be able to see the ugly double thread lug nuts and such from the side of the van.





I was concerned the lower mechanical advantage of the new wheels would make the front to harsh, but our test drive today didn't show that. It was actually smoother than before by a noticeable amount. It could be the different tires, which most say are very good riding, or that we ran them 5 psi lower because of their size (75/60). The van handled at least as well, probably better, than it did before, in the fairly strong winds we had today. It will be interesting to see how it does when we get fully loaded and take off for a real trip.

When we backed into the driveway and down to the second garage, we noticed that there was one big thing missing--all the skid marks in the driveway from backing in. With the old wheels, by the time I wiggled my way to the garage and into it, the driveway would look like we had held a burnout contest. Today there were none. I think that also explains why the steering felt much smoother at low speed turns, as the tires aren't fighting each other now. I had read that offset could cause such issues, but was surprised it went away completely.

We also added a TST TPMS system at the same time, which seems to be well built and is working well. Hopefully, with the TPMS and the 750# capacity cushion in the rear tires, we can avoid the very damaging rear blowout that has ripped up quite a few Roadtreks.

We are very happy with the way it turned out, and have not seen any downside to this point. Bearings and things should also last longer. DW likes the way it looks and rides, but did have me order a set of chromed plastic lug nut covers to replace the black ones, so she can see how that will look.

On edit--no going back now--just sold the original wheels and tires!

[Photog]

It looks great. Thanks for posting up the details. Now we know it will all fit together.

It will be comforting to know your tires have enough load capacity to avoid a blow-out due to overload.

How much room do you have left, between the tires and the front fenders, when turning from lock-to-lock?

Did you happen to look at the clearance between the front wheels and the knuckle? It must be getting fairly close between the wheel and the upper section of the knuckle.

Cheers.

[booster]

Originally Posted by Photog

It looks great. Thanks for posting up the details. Now we know it will all fit together.

It will be comforting to know your tires have enough load capacity to avoid a blow-out due to overload.

How much room do you have left, between the tires and the front fenders, when turning from lock-to-lock?

Did you happen to look at the clearance between the front wheels and the knuckle? It must be getting fairly close between the wheel and the upper section of the knuckle.

Cheers.

We are the closest at the rear of the wheel well on the right side and the front lower lip of the bumper cover on the left. Both are when turned and within about 1/2 to 3/4 inch static, not moving. I didn't look closely about going any wider, because it would be an exercise in futility for me. I can't go bigger diameter, so I can't go wider without reducing the aspect ratio. That reduces the load capacity almost as much as the size increase. The 750#/axle of extra capacity is fine for us, we wouldn't want to go bigger anyway.

[Flashman]

One thing I'd personally be wary of here is altering the handling characteristics. It would seem important to me to preserve an understeer tendency, which sounds like what might have been happening with the scrubbing. Oversteer tendencies would be bad in a tall tippy vehicle with a lot of weight in the back. Ergo, after personal testing, I might want a custom alignment after I'd changed wheels, just to make sure it was had understeer/neutral tendencies.... last thing I'd want is my wife rolling us if a deer ran in the road...

However, most shops with alignment racks can use them with the precision and accuracy of a 10lb hammer. Then even if they can manage to set factory specs 9 times out of 10, they'll wanna put you in the middle of them, not even let you go to one side or the other, citing liability concerns... to get a custom alignment is difficult... may be more difficult still with this size of vehicle, because I'd otherwise suggest race/performance specialists, I dunno if most of them would even have the bay clearance to get a B in.

Personally, I'd do what I always do, roll around on the driveway with measuring tapes and framing squares, tweak, test, tweak, test....

[booster]

We got out today for a 200 mile drive to check the speedo, odometer, and Scangauge to the GPS and mile markers. Everything moved about as expected, and our Scangauge guess calibration was right on, so no correction needed. The bigger tires don't seem to have changed anything in regards to how the engine and transmission perform (now at 2029rpm at 60mph). The steering is definitely lighter with the lower offset, and you don't hear the front tires working as hard on tight, low/moderate, speed turns. The steering response is also "softer", but that is more likely to be because of the tire brand change and low pressure we ran today (60/72). We were very light, with no water, less than half a tank of gas, and most of our stuff out of the van, which is the worst handling for us, and it was still fine. We don't seem to have lost anything to the swap, at least that we have seen yet. The wheels were very cool when we got home, much cooler than usual, but it was a pretty low temp day, so we don't know if they will run cooler with the reduced bearing loading. Next time out, we will go to the normal 65/80 pressure and fill the tanks to see how that works.

DW didn't like the black plastic lug nut covers, so I found some chrome ones, which she ordered.

[Photog]

It seems to be an improvement for bearings, steering, tire load capacity, and a little bit of driving comfort.

[booster]

We got out today after sanitizing the fresh water system and bedding in the new brakes. This test was done with the MS2's at 65/80psi, which is the same as we ran in the smaller Bridgestones. Drove it with everything empty and very light, and then with the fresh and black tanks full. It handled fine both ways, but better with the tanks full, as it always has. The 65/80 handles a bit better than the 60/73 we tested before, and didn't get a lot harsher so that is where we are going to stay. The MS2's are a lot less harsh than the Bridgestones were.

The overall handling is a bit different with change in offset, I think, not because of the tire change. Low speed turns, and even faster ones, don't feel like we are pushing the front tires sideways like it did before. It also understeers much less, and you don't hear the front tires working so hard in turns. As I mentioned before, no more skid marks in the driveway from backing in, so there is definitely a huge reduction in scuffing of the front tires.

We have a couple hundred mile camping trip scheduled in a few weeks, so we will see how we like on a longer run.