Tire Size Increase

[dicktill]

Originally Posted by booster

Interesting thought but I thought that scuffing of this sort was more related to bad ackerman caused in the front by the offset change to scrub radius. I know wheelbase can influence turning radius, but never heard it being a problem with scuffing, but it also very possible it might as ackerman also does have the rear axle angle included.

I just looked and the vans all use the same pitman, idler, knuckles, and drag link.

All I know for sure is that the right offset got rid of all noticeable scuffing, even going backwards, with our extended version. It must be something like the caster helping going forward and not when going backwards, maybe.

I don't disagree with anything you say here. His wrong offset will cause scrubbing, just not as much as on our 190's.

[booster]

Originally Posted by dicktill

I don't disagree with anything you say here. His wrong offset will cause scrubbing, just not as much as on our 190's.

Very possible. I wonder if the long vans and standard vans were designed together or separate. If GM were smart (which is certainly not for sure) they would pick a midpoint, I would think, but they may also intentionally generate some scuffing to induce the desirable understeer that is needed in the empty vans.

[Deano]

Just a little information I acquired years ago from an engineer at RT about the "AR" wheels.
He informed me that the optional aluminum wheels they used were not "AR" brand, that they used "AR" hub covers because the covers that came with the wheels were not as nice as the "AR" ones. I don't recall what brand he said.
My RT is a 2005 POP. I don't know if the information applies to any other years or models.

[booster]

Originally Posted by Deano

Just a little information I acquired years ago from an engineer at RT about the "AR" wheels.
He informed me that the optional aluminum wheels they used were not "AR" brand, that they used "AR" hub covers because the covers that came with the wheels were not as nice as the "AR" ones. I don't recall what brand he said.
My RT is a 2005 POP. I don't know if the information applies to any other years or models.

That is interesting. I think it was Campskunk who had said that his early Chevy, maybe 2003, had zero offset wheels and not the -6 offset the rest of us since had on the AR wheel. The wheels are marked on the inside of the rim with size and offset IIRC and it did match the actual AR wheel specs on the AR website. Perhaps they were knockoff clones of the actual AR wheel.

[peteco]

Originally Posted by Deano

Just a little information I acquired years ago from an engineer at RT about the "AR" wheels.
He informed me that the optional aluminum wheels they used were not "AR" brand, that they used "AR" hub covers because the covers that came with the wheels were not as nice as the "AR" ones. I don't recall what brand he said.
My RT is a 2005 POP. I don't know if the information applies to any other years or models.

Just a few thoughts on the AR wheels.
My 2006 RT 210P has AR wheels (and hub covers). I ordered another one to use as my spare in place of the steel spare. So far (145,000 miles) I have not had any handling or excessive wear problems. Last set still had 5-6/32 of tread left. I get 50-55,000 miles before changing them due to age (~5-6 years) and not wear. No bearing issues either. I do lube the front bearings and change differential grease every 30-40,000 miles. I agree these are not ideal due to the excessive offset, and that may get me some day (knock on wood). But I do like the weight savings from aluminum on my weight challenged 210. I wonder if there is an aluminum wheel that can take the 265 width tire.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[booster]

Originally Posted by peteco

Just a few thoughts on the AR wheels.
My 2006 RT 210P has AR wheels (and hub covers). I ordered another one to use as my spare in place of the steel spare. So far (145,000 miles) I have not had any handling or excessive wear problems. Last set still had 5-6/32 of tread left. I get 50-55,000 miles before changing them due to age (~5-6 years) and not wear. No bearing issues either. I do lube the front bearings and change differential grease every 30-40,000 miles. I agree these are not ideal due to the excessive offset, and that may get me some day (knock on wood). But I do like the weight savings from aluminum on my weight challenged 210. I wonder if there is an aluminum wheel that can take the 265 width tire.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Yes, there is if you go to 17". Vision has one that is quite nice and at +25mm offset so very close. There also was just mentioned an aluminum Silverado wheel in 17" that has the right offset. It appears that the used Silverado wheels are selling for more than the Vision wheels, but you might also find some in the UPick yard for $10 each I would imagine.


The downside of 17" is that you get about 150# per tire load capacity increase instead of the about 350# per tire with the 16".

[phantomjock]

Dirty Harry; "Do I feel lucky? Well, do ya, punk?”
Punk; "Hey. I gots to know."

So I pulled the wheels and tires to clean and prep for next week when I get new ones in.

My RT Owner's Manual has details stapled to the inside cover giving the RIMS as 16x7, for both front and rear. The "range" of rim widths for a 265/75R16 is 7"-9" so I'm confident the fit will be "just fine."

I measured the backspace, and it is 4 inches.



Using the Summit Racing chart, I have Zer0 offset (0mm) on these.



Which means unless the Chevy factory rims have something other than Zero Offset, I am going to order up those 265/75R16 E-rated tires next week.

Also on the list a set of new TPMS sensors for the tires - install while mounting; a TPMS "tuner," and perhaps the key-less remote+TPMS receiver. It mounts under the top dash, and being as we have both TPMS errors and the key fob works intermittently - I suspect the receiver is a co-conspirator as it is the hub for both.

Charts in text.

Cheers - Jim

[booster]

Originally Posted by phantomjock

So I pulled the wheels and tires to clean and prep for next week when I get new ones in.

My RT Owner's Manual has details stapled to the inside cover giving the RIMS as 16x7, for both front and rear. The "range" of rim widths for a 265/75R16 is 7"-9" so I'm confident the fit will be "just fine."

I measured the backspace, and it is 4 inches.



Using the Summit Racing chart, I have Zer0 offset (0mm) on these.



Which means unless the Chevy factory rims have something other than Zero Offset, I am going to order up those 265/75R16 E-rated tires next week.

Also on the list a set of new TPMS sensors for the tires - install while mounting; a TPMS "tuner," and perhaps the key-less remote+TPMS receiver. It mounts under the top dash, and being as we have both TPMS errors and the key fob works intermittently - I suspect the receiver is a co-conspirator as it is the hub for both.

Charts in text.

Cheers - Jim

The AR wheels are normally listed as -6mm for the 7" version with the 3042 load capacity and depending on how the wheel is measured the thick flanges on aluminum wheels can make a 6mm difference pretty easy to do. Especially if you do the normal lay the rim on the floor and measure to the mounting flange as the backspace usually is called 1/2 the wheel width which normally be to inside of the flange. Our AR wheels had the load capacity and offset cast in on the backside of the wheel, so you probably have that also.


Here is a link to American Racing site for the AR23 specs.


https://www.americanracing.com/american-racing-ar23


But 6mm is the minor part as the Chevy stockers are +28mm and would have much more backspace. That is why I get concerned about the offset as 34mm is a lot. The previous generation Chevies had zero offset, I think.

[phantomjock]

Originally Posted by booster

The AR wheels are normally listed as -6mm for the 7" version with the 3042 load capacity and depending on how the wheel is measured the thick flanges on aluminum wheels can make a 6mm difference pretty easy to do. Especially if you do the normal lay the rim on the floor and measure to the mounting flange as the backspace usually is called 1/2 the wheel width which normally be to inside of the flange. Our AR wheels had the load capacity and offset cast in on the backside of the wheel, so you probably have that also.

Ehh, OK +/- 6mm, For this vehicle I don't see that as a "huge" delta. Now if we want to talk racing, that is a different setup criteria.

Originally Posted by booster

Here is a link to American Racing site for the AR23 specs.


https://www.americanracing.com/american-racing-ar23

Hmmm. First, Thanks. Second, makes me think about the effort to clean these up vs purchase new.

Originally Posted by booster

But 6mm is the minor part as the Chevy stockers are +28mm and would have much more backspace. That is why I get concerned about the offset as 34mm is a lot. The previous generation Chevies had zero offset, I think.

I'm guessing, the 28mm you are referencing is the offset from the wheel hub (face) to the kingpin axis? I've never referred to that as "offset" per se. But I can understand why it might be used that way. When I get the front wheels off, I'll have a chance to see where the kingpin axis and wheel set up to get a better idea of the real scrub radius. Then make a "prediction of where it ill be with the up-sized tires.

For this upgrade, though, I'll want to measure now, because the increase in tire diameter will change the scrub radius. It will certainly move, I've grabbed a CAD from my corvette build to illustrate:



This picture illustrates the scrub radius is decreased, which may not be the case in the Chevy RT. If the wheel were initially more inboard - much larger offset, the Scrub radius would move into the negative territory (contact patch inside of kingpin axis). I just intend to show that it does change, and could be good, or not so. All TBD.

I hadn't planned on an in depth suspension analysis. I was thinking just bar napkin analysis:
1. Will they fit? Signs point to Yes. ( I asked the Magic 8-Ball!)
2. Will it handle about the same? I think so. The contact patch will still be relatively in the same location. Better load characteristics, and all-terrain option, with better (small) ground clearance raise.
3. Will steering be more or less the same? I'll have to make notes before purchase (scrub radius is the question I want to answer. On the other hand with power steering, maybe no biggie.)

All I know for now. Clean more tomorrow, then pull a front wheel and get some ideas.

Cheers - Jim

[Deano]

In addition to my previous post, I recall why I called RT and spoke with the engineer.
I too wanted a matching AR wheel for my spare tire. (Before being enlightened by Booster about the drawback of the wrong offset/backspace). I had looked through the AR web site and could not find the matching wheel. So, I called RT to find out which model AR wheels I had. After Booster posted I sold the ??? wheels and bought the 16x7, 6 hole Chevy wheels and 265/75x16 tires. Yes, I could tell the improvement.

[phantomjock]

Deano -

Thanks for that update. MPG, better, ride, handling, wear, road noise? The 16x7 as I posted previously are in the acceptable range for the 265/75x16, hence my choice. Now your positive feedback, I'll pull a front tomorrow and check the scrub radius.
Latter I'll pull the CC.


I need to ask - which tire did you go with?

Cheers - Jim

[Deano]

Unfortunately a now no longer made Michelin.
I just looked on Tire Rack. There are lots of load range E in 265/75x16 to choose from.
I didn't look at the ratings.
Good Luck!

[booster]

Originally Posted by Deano

In addition to my previous post, I recall why I called RT and spoke with the engineer.
I too wanted a matching AR wheel for my spare tire. (Before being enlightened by Booster about the drawback of the wrong offset/backspace). I had looked through the AR web site and could not find the matching wheel. So, I called RT to find out which model AR wheels I had. After Booster posted I sold the ??? wheels and bought the 16x7, 6 hole Chevy wheels and 265/75x16 tires. Yes, I could tell the improvement.

Are you referring to the 8 hole steel wheels from Chevy that have the +28 offset?

[booster]

Originally Posted by phantomjock

Ehh, OK +/- 6mm, For this vehicle I don't see that as a "huge" delta. Now if we want to talk racing, that is a different setup criteria.




Hmmm. First, Thanks. Second, makes me think about the effort to clean these up vs purchase new.




I'm guessing, the 28mm you are referencing is the offset from the wheel hub (face) to the kingpin axis? I've never referred to that as "offset" per se. But I can understand why it might be used that way. When I get the front wheels off, I'll have a chance to see where the kingpin axis and wheel set up to get a better idea of the real scrub radius. Then make a "prediction of where it ill be with the up-sized tires.

For this upgrade, though, I'll want to measure now, because the increase in tire diameter will change the scrub radius. It will certainly move, I've grabbed a CAD from my corvette build to illustrate:



This picture illustrates the scrub radius is decreased, which may not be the case in the Chevy RT. If the wheel were initially more inboard - much larger offset, the Scrub radius would move into the negative territory (contact patch inside of kingpin axis). I just intend to show that it does change, and could be good, or not so. All TBD.

I hadn't planned on an in depth suspension analysis. I was thinking just bar napkin analysis:
1. Will they fit? Signs point to Yes. ( I asked the Magic 8-Ball!)
2. Will it handle about the same? I think so. The contact patch will still be relatively in the same location. Better load characteristics, and all-terrain option, with better (small) ground clearance raise.
3. Will steering be more or less the same? I'll have to make notes before purchase (scrub radius is the question I want to answer. On the other hand with power steering, maybe no biggie.)

All I know for now. Clean more tomorrow, then pull a front wheel and get some ideas.

Cheers - Jim

Offset as stated by the manufacturers is totally independent of the kingpin inclination angle of the vehicle and is only related to the wheels themselves. It is the dimension from the centerline of the wheel to the mounting hub surface. A zero or -6 wheel on a Chevy with the sealed hub bearings will give a very high positive scrub radius and the issues that can go with that. The 34mm more outboard wheel centerline of the AR wheels makes the scrub radius change much more than the .5 change in ride height will and in the opposite direction, IIRC.


The larger tires on the AR wheels will handle about the same as you have now, but with a bit more traction and a bit less positive scrub, but the +28mm steel wheels or other wheels with the same offset will give and handling improvement due to lower scrub radius which is where Chevy intended it to be.

[Deano]

No, Chevy 16x7 steel wheels with 6 holes.

[booster]

Originally Posted by Deano

No, Chevy 16x7 steel wheels with 6 holes.

Oh now I get it, you are talking about the scalloped cut outs, not the number of lug stud holes.


I was referring to the lug stud holes because that is how the wheel manufacturers list them in the catalogs. The AR23 link I posted shows basically the same dimensions, wheel in 6 lug and 8 lug and they have very different load capacities. I wanted to make certain that everyone needed to look closely so they don't get the wrong wheels. A lot of wheels do have 6 lug stud holes, also, as do a lot of the 2500 and under vans.

[phantomjock]

Originally Posted by booster

Offset as stated by the manufacturers is totally independent of the kingpin inclination angle of the vehicle and is only related to the wheels themselves. It is the dimension from the centerline of the wheel to the mounting hub surface. A zero or -6 wheel on a Chevy with the sealed hub bearings will give a very high positive scrub radius and the issues that can go with that. The 34mm more outboard wheel centerline of the AR wheels makes the scrub radius change much more than the .5 change in ride height will and in the opposite direction, IIRC.

I concur 100% I was trying to guess where the 28mm was coming from - and wildly guessed - perhaps the delta between KP axis and the face of the mount (hub/wheel interface.) I've spent too much time on suspension work (practical and theoretical). Ten years ago I thought I should "challenge" a PhD program to get my creds - but who needs that? The Millikens, Staniforth, and Smith have just about all you need to know, I'd only confuse things...

Originally Posted by booster

The larger tires on the AR wheels will handle about the same as you have now, but with a bit more traction and a bit less positive scrub, but the +28mm steel wheels or other wheels with the same offset will give and handling improvement due to lower scrub radius which is where Chevy intended it to be.

This is now clear where you get the 28mm dimension - other wheels. I got it! And I believe your comments regarding the "slightly larger tires" on my wheels (AR23s) will be just about OK - as I mentioned previously, I expect it will "slightly" decrease the positive scrub radius. I'll know more as I pull the front wheels.

With that clarified, I'll forego any rush to measure the IFS and press on with a more mundane task - cleaning/polishing rims.

Cheers - Jim

[Deano]

I guess I should have been more specific, but as I knew you changed to the same wheels I thought you were on the same page as me.
So, yes, Chevy steel 16x7 with 6 pockets and 8 lug holes.

https://www.finishlinewheels.com/pro...-steel-oem-rim

Just for illustration. Other sites have them for less money.

[Serrakuzz]

Personally, I haven't gone with the larger tire size, but I have heard from others who have made the switch with positive results. The added safety margin for off-road use is definitely a plus, but I think it's also important to consider any potential negative impacts such as decreased fuel efficiency and speedometer discrepancies. It's great that you're already aware of these possibilities.

[booster]

Originally Posted by Serrakuzz

Personally, I haven't gone with the larger tire size, but I have heard from others who have made the switch with positive results. The added safety margin for off-road use is definitely a plus, but I think it's also important to consider any potential negative impacts such as decreased fuel efficiency and speedometer discrepancies. It's great that you're already aware of these possibilities.

I was early into the larger size tires on the Chevies and as far as economy goes, we haven't seen any measurable difference in mpg in the about a decade of use of the larger tires.


Speedo difference, yep, but not as bad as you would expect, I think. Our stock Chevy would read about 1.5mph high from the factory and with big tires read about 1.5mph low so same amount other direction. I have corrected the speedo with a programming tuner now so it is right on.


Biggest downside I have seen is that they are heavy so harder to put on and off the van for those of us that do their own rotations and other repairs. We currently have 265-75-16 Michelin Agilis tires and the 16X7 GM pickup truck steel wheels that have the correct +28mm offset. We use Wheelskin hubcaps for appearance.