Wheel offsets, particularly Roadtrek Chevy

[Photog]

Thanks for the update.

It is good to know the higher tire pressure did not increase the ride harshness too much.

Let us know how it performs, on your longer trip.

[booster]

We just got back from our illness shortened trip. Miles traveled was the same, but time shortened a bunch do to DW getting a nasty intestinal issue.

With the now factory offset, oversize wheels and tires, we are extremely happy with the results. We had horrible wind conditions on this run with 30-40 mph head/20* cross winds going and the same as tailwinds on the way back. This was the first run we have had at fully loaded (short trip) weight. The van handled very well, with several improvements over the factory aluminum (-6 offset) wheels with Brigdgestones, and no downside that we have seen to this point.

The upsides we have seen,

The Michelin MS2's are much smoother riding, even with the reduced offset that should make them harsher.

There is a major reduction in understeer and scuffing, most noticeable at low speeds and on gravel, but also very evident at highway speeds. No more noise from the the fronts scuffing, responsive handling on gravel and at low speed. I can now hold the steering wheel in one place on a sweeping highway curve without having to "saw" it. Exiting a curve the straightening is right on with now overshoot that requires a correction.

Corrections on the steering wheel to stay in line are under 1" now, which is about 2/3 of what it was. Much easier to stay in the center of your lane.

The MS2's are very quiet.

Even though the tires are up two sizes at 265-75-16 they still seem to like the 65/80 psi most of us run on our stock setups.

The stock offset seems to match the Bilsein shock setup better. The ride is smoother and more controlled without porpoising or excess motion. The front wheels no longer pound hard into low speed potholes on gravel roads, as they would in the past. Didn't expect this to happen, but really like it,

The wheel hubs, both front and rear, run substantially cooler. It was near 90* when we came home today, and you could lay your hand on the hubs/wheels comfortably. In the past they would get too hot to stay on them. I assume this is because of the reduced strain on the wheel bearings.

Rear tires went up about 6 psi, fronts about 4 psi after two hours at 55 mph and 90* weather.

The van feels much more car-like with stock offset, compared to the original aluminum wheels.

[Photog]

That is great feedback, on the wheels.

I am looking forward to updating my tire/wheel setup on my R/T 190 V.

[peteco]

Have you been able to check the gas mileage with the new tires?

[booster]

Originally Posted by peteco

Have you been able to check the gas mileage with the new tires?

Good question, as it was one of our unknowns, also, when we did this. We went with the MS2 tires partly because of their low rolling resistance claims.

Our test wasn't the best for checking mileage, as the winds were very strong. With a 25-40mph head to 20* crosswind we got 14.1mpg on the trip out at 57mph in 75* weather. On the return trip with a 25-40mph tail to 10* cross we got 20.0mpg at 57mph in 90* weather. We have always lost a bit more to wind than we gain, so I would guess the equivalent no wind mpg would be in the mid 17's, which is similar, perhaps .25mpg higher, than we had with the AR wheels and Bridgestones. We need a lot more testing over longer distances to be sure, but we appear to not have changed much in mpg.

[peteco]

Originally Posted by peteco

Have you been able to check the gas mileage with the new tires?

Now that it has been a few years, what is your take on the gas mileage difference?

[booster]

Originally Posted by peteco

Now that it has been a few years, what is your take on the gas mileage difference?

The best guess would be that it is close to a wash. If it has gone down, it would only be a couple of tenths. The handling has gotten so good that we are driving considerably faster than we used to, usually averaging 67 mph on a 72 mph cruise speed on the freeway, wind or not, so that certainly influences things a lot. We get low 14's most of the time at those speeds with neutral winds. We also now have 3 solar panels on the roof now. We used to cruise at about 10 mph less on the freeway and would get close to 16 mpg most of the time

Mighty difficult to tell for sure, but definitely not a big deal for us, as we really like the clearance and the way it drives

[peteco]

Originally Posted by booster

The best guess would be that it is close to a wash. If it has gone down, it would only be a couple of tenths. The handling has gotten so good that we are driving considerably faster than we used to, usually averaging 67 mph on a 72 mph cruise speed on the freeway, wind or not, so that certainly influences things a lot. We get low 14's most of the time at those speeds with neutral winds. We also now have 3 solar panels on the roof now. We used to cruise at about 10 mph less on the freeway and would get close to 16 mpg most of the time

Mighty difficult to tell for sure, but definitely not a big deal for us, as we really like the clearance and the way it drives

Thanks. I may keep an eye out for a set of stock Chevy rims. So far I have not had a problem with the AR rims and Bridgestone V-Steel tires, but can see the benefit of a larger tire and stock rim offset.

[booster]

Keep in mind that if you want to go with bigger tire, you would have to get the proper offset pickup truck wheels as the van ones are too narrow for the bigger tires.

Has anyone ever found out what offset and width the current Roadtrek aluminum wheels are. They look like Asian made by their style, but I have never seen a manufacturer or spec mentioned.

[User1213]

I've been looking at other wheel options as I'm interested in getting wheels closer to the factory offset of 28 mm.

I've found a lot of 18 in wheels, usually 8-9 in wide that have either 20 or 25 mm of offset. These would be closer to factory offset but I wonder how much actual inside clearance there would be (backspacing).

Did you measure the backspacing on the 16x7 in factory rims Booster?

I also noticed that Hummer wheels will fit our Chevrolet based rigs (as far as rim offset goes).

[User1213]

This is my front runner-

FUEL DEEP LIP BEAST - D564


18X9 8x165.1 D56418908257 - MBD-Matte BLK MACH - 125.20 Bore - 20mm Offset - 3500 lb rating - 36 lbs weight

[booster]

Originally Posted by Hondo

I've been looking at other wheel options as I'm interested in getting wheels closer to the factory offset of 28 mm.

I've found a lot of 18 in wheels, usually 8-9 in wide that have either 20 or 25 mm of offset. These would be closer to factory offset but I wonder how much actual inside clearance there would be (backspacing).

Did you measure the backspacing on the 16x7 in factory rims Booster?

I also noticed that Hummer wheels will fit our Chevrolet based rigs (as far as rim offset goes).

Backspacing is easy to figure if you know the offset and width

Backspace = width/2 + offset

for a 7" wide wheel with 28mm (1.1") offset 7/2 + 1.1 = 4.6"

Normally if the offset is the same on the wheels as stock, you can look at the stock wheels in place and see if they will clear the suspension if they are more backspace, which may be even more important with the drip spindles there.

The closer you get to the 28mm offset the further inboard the tires are going to be also, which could be an issue, especially if they are wider and larger diameter. 265-75-16 on a 7" wide, 28mm offset wheel come very close to a lot of things, with the swaybar probably the first thing after the front and rear wheelwell edges.

[booster]

With all the other changes you have made, and their effects on the handling and loads, getting the last 8mm to get to factory offset would probably not be noticeable in handling or durability, especially if you leave the rear spacers in place. The change from factory aluminum to the correct offset wheels is a change of 34mm as is quite noticeable to some of us, and not really noticed at all by others, for reference.

[User1213]

Do you think that there would be much felt/handling difference between the current 16 X 8 0 offset and wheel with 20 mm of offset?

2 in rear wheel pacers not installed now but probably will.

Published mfg numbers-

Current ATX Ledge-

16 X 8 - 0 offset - 4.5 in backspace

The Beast wheels could be had in 2 options-

17 X 9 - 20mm offset - 5 in backspace

18 x 9 - 20mm offset - 5.75 in backspace

i'll have to look close at my clearances now and take into account having a wheel with a larger inside diameter.

[booster]

I don't understand how those offset vs backspace numbers are done. Wheel diameter doesn't even matter, but they have different backspace with just that change. An 8" wide wheel is 4" backspace from everything I have seen.

Here is a pic of what the numbers mean.

[User1213]

Those numbers are off of the mfg's website.

I agree though- you'd think that the backspace would be different doing the math-

ATX Ledge-

8 wide, 0 offset puts it at 4.0 inches- add 1/2 bead width and you get the published 4.5 inches

Beast wheels-

9 inch wide 17 " wheel -div 2 = 4.5 inches, add 20 mm/.79 inch = 5.29 inches backspace.

Not sure why the 18 inch wheels would be any different with the same offset.

[booster]

I know there is often a lot of discussion over where to measure the wheels. From a technically correct aspect it should be at the bead location of the rim, but in reality a lot of folks use the outside of the edge of the wheel, lay it on the floor and use a tape measure routine. Since aluminum and steel wheels, and various brands, have wider flanges outside of the bead area, you can get different actual tire positions for wheels of the same measurements if you go to the outside of the lip.

That ignored, if you measure both measurements off the same places, either at the bead or at the outside, a 9 inch wide wheel with zero offset has 4.5" of backspace. I can't imagine how they got the numbers they got, as you can't add the flange width to one of the dimensions and not the other, as it is just not correct.

For the same reasons, if you measure to the outside of the rim width, and not the bead location, nearly every steel wheel will be effectively wider at the bead than the aluminum ones that almost always have a wide flange for strength, for the same outside measurement.

[cruising7388]

Originally Posted by booster

I don't understand how those offset vs backspace numbers are done. Wheel diameter doesn't even matter, but they have different backspace with just that change. An 8" wide wheel is 4" backspace from everything I have seen.

Here is a pic of what the numbers mean.

Is there general agreement that positive offset displaces the wheel and tire inward toward the differential and negative offset displaces in the opposite direction?

[User1213]

Originally Posted by cruising7388

Is there general agreement that positive offset displaces the wheel and tire inward toward the differential and negative offset displaces in the opposite direction?

Yep, that's it, and here's a good explanation-

https://www.youtube.com/watch?v=8EvMdbWB6MA

[User1213]

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.

Here are 3 views -

As I bought it, stock ride height, American Racing AR-23 factory wheels with 245-75-16 tires-



After lifted 4 inches, 16x8 0mm offset American Racing ATX Ledge wheels with 265-75R-16 tires BF Goodrich T/A KO2 tires-



As it sits now- Chevrolet 17X7.5 28mm offset wheels with 275-70R-16 BF Goodrich T/A KO2 tires-



The front on the ATX Ledge wheels -



And with the Chevy wheels- the 28mm of offset brought the tire edge in about an inch-



Tuned all the way in, no interference-



turned out, about an inch to spare-



I think it looks best with these factory wheels

With the new wheels & tires it felt like a different vehicle! Slow speed turning was much better (less scrubbing) and at city speeds it drove great. I took it briefly onto the interstate but the winds were really blowing so I couldn't get a really good feel of the change but it did seem more planted.

I'm not sure if these tires would fit on a stock van or Roadtrek because the lift spindles in the front do push the wheels out some and I'm using spacers on the rear. As Booster has said he's had success using the stock offset wheels with 265-75R-16 tires.

If I was to recommend an aftermarket solution I would try to get a wheel with as close to the stock 28mm offset as possible. I found a lot of wheels with 20mm of offset and a few with 25, but I really had to search for them.

Thanks for all of your research & help Booster!