Why not fix one ton scrub radius with wheel offset?

Joe Weir

Joe Weir

Member
Feb 13, 2013
743
9
18
Like the title says. If the One Ton kit puts the center of the tire @1.5" too far outboard, why not reduce the width of the spacer, or use a wheel
with 1.5" less offset?

Or, did I not see that discussion?

For example, if the wheels clear the calipers, This chevy wheel has 28mm of positive offset - just over an inch. Seems that would help.

https://www.bbwheelsonline.com/oe-creations-pr156-wheels-rims-16x6-5-8x6-5-8x165-1-polished-28mm-156p-668128/

https://www.bbwheelsonline.com/oe-creations-pr156-wheels-rims-16x6-5-8x6-5-8x165-1-polished-28mm-156p-668128/
--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
 
There is no space at the caliper against the wheel rim.

On Thu, Jan 21, 2021 at 3:56 PM Joe Weir via Gmclist <

> Like the title says. If the One Ton kit puts the center of the tire
> @1.5" too far outboard, why not reduce the width of the spacer, or use a
> wheel
> with 1.5" less offset?
>
> Or, did I not see that discussion?
>
> For example, if the wheels clear the calipers, This chevy wheel has 28mm
> of positive offset - just over an inch. Seems that would help.
>
>
> https://www.bbwheelsonline.com/oe-creations-pr156-wheels-rims-16x6-5-8x6-5-8x165-1-polished-28mm-156p-668128/
>
>
> https://www.bbwheelsonline.com/oe-creations-pr156-wheels-rims-16x6-5-8x6-5-8x165-1-polished-28mm-156p-668128/
> --
> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> Coachmen
> guys were really thinking about us second hand owners by including that
> beverage center...
> Columbia, SC.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
Jim,

Have you tried the wheels I posted?

My current -8mm wheels clear. As long as the wheel face is angled away from the disk it should clear.
--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
 
Joe,
I see.

On Thu, Jan 21, 2021 at 7:56 PM Joe Weir via Gmclist <

> Jim,
>
> Have you tried the wheels I posted?
>
> My current -8mm wheels clear. As long as the wheel face is angled away
> from the disk it should clear.
> --
> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> Coachmen
> guys were really thinking about us second hand owners by including that
> beverage center...
> Columbia, SC.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.gmcrvparts.com
1-800-752-7502
 
I looked and they don’t seem to list center hole size for hub centering, unless I missed it.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
My understanding is the same knuckle was used on the 3/4 and 1-ton 4x4 pickups in the late 80's and early 90's (the years the one-ton kits wear made
from).

The knuckle was designed for single-wheel pickups which from my Googling had OEM wheel offsets of 25-30mm with 28 being common.

For one-ton pickups, the dual wheels had offsets of 125mm. So to use a dual wheel on the front a spacer was required to compensate for the additional
offset of the dual wheel. (125mm - 28mm = 97mm = approx 4") So a 4" spacer puts the dual wheel at the same position as a single wheel which the
knuckle was designed for.

So a 125mm offset dual wheel with a 4" spacer should be at the same position as a wheel with a 28mm offset and no spacer.

So I guess you could run 28mm offset rims on the front with a one-ton setup if the wheel clears the calipers. But what would you then carry for a
spare tire? You would need to carry a dually for a spare rear and a 28mm for a spare front. OR carry a spacer so you could use a dually for the
front in case of a flat... but the nuts holding the aluminum spacer can be difficult to remove.

But I might be all wrong...

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Also moving tire inboard may be able to fix the steering axis or some of the error, but not sure that totally fixes scrub radius. Also this may not
fix camber vs changing ride height (suspension travel) issues .
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
If you want some REAL tire scrub to be concerned with, deal with the rear
bogies. Get out of your coach midway through a tight turn and have a look.
You will instantly know what I am referring to.
Jim Hupy
Salem, Oregon

On Fri, Jan 22, 2021, 6:55 AM John R. Lebetski via Gmclist <

> Also moving tire inboard may be able to fix the steering axis or some of
> the error, but not sure that totally fixes scrub radius. Also this may not
> fix camber vs changing ride height (suspension travel) issues .
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
The wheel I linked to is for a Suburban, so that makes sense. This is the only wheel I have found in an 8x6.5 bolt circle and 16" diameter.

Moving the wheel inboard 28mm moves the scrub radius closer to the correct point - not perfect. Seems like this would help correct the torque steer
issue. Does anyone have a link to the actual scrub radius difference? I know I saw a drawing somewhere. The spacers that came with my one ton are
3.25". Maybe this issue has been addressed with the current spacers. Was trying to have a non-spacer solution.

This does not fix the issue of the non-parallel control arms, but, as Bob would say, I'm comfortable with that.

The centerbore of the Chevy 2500 wheels linked above is 5.15. Aluminum hub spacers are available.
--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
 
> Also moving tire inboard may be able to fix the steering axis or some of the error, but not sure that totally fixes scrub radius.

Scrub radius is literally defined as the distance between the center of
the contact patch and the point where the steering axis touches the ground.
 
On 1/22/21 08:22, Joe Weir via Gmclist wrote
> This does not fix the issue of the non-parallel control arms, but, as Bob would say, I'm comfortable with that.
Control arms are rarely parallel. Is there a camber gain issue we're
worried about here? (Sorry, I'm missing context, but considering a one-ton)
 
One of the members had some driving professionals give an opinion on the one ton, and they did not like how it handled at the limits due to the
geometry.

I'll let others chime in on the details.

--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
 
Yes, My bad. The point was that while not completely fixing the issue, it certainly moves it closer to correct.

> > Also moving tire inboard may be able to fix the steering axis or some of the error, but not sure that totally fixes scrub radius.
>
> Scrub radius is literally defined as the distance between the center of
> the contact patch and the point where the steering axis touches the ground.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

--
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen
guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
 
The GMC Motorhome is NOT a performance vehicle. It wallows in tight curves,
barely stays straight on good roads. It is at least 40 years old, and
designed around parts plucked from production lines of various automobiles
of the era. Nothing state of the art about the suspension and drive train.
It does a fair job of point to point transportation of a heavy vehicle
that has a great deal of its weight centered above the tops of the tires.
A race car, it definitely is NOT! If you do not expect sports car
handling, and maintain the drive train/suspension parts well, it is safe
enough to drive in traffic if you don't follow too closely and drive "eyes
way down the road ahead", you won't get in too much trouble.
There are upgrades that improve braking quite a bit, and that is one
huge reason for the 1-ton conversion. That and much stronger lower control
arms and front wheel bearings as well as upper and lower ball joints.
Handling? Very subjective at best. It still is a top heavy front wheel
drive vehicle. Not much will ever change those facts.
Do I love them? Yep! But, don't put lipstick on them. Underneath, they
are still a very good looking pig.(grin)
Jim Hupy
Salem, Oregon

On Fri, Jan 22, 2021, 4:55 PM Joe Weir via Gmclist
wrote:

> Yes, My bad. The point was that while not completely fixing the issue,
> it certainly moves it closer to correct.
>

> > > Also moving tire inboard may be able to fix the steering axis or some
> of the error, but not sure that totally fixes scrub radius.
> >
> > Scrub radius is literally defined as the distance between the center of
> > the contact patch and the point where the steering axis touches the
> ground.
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> --
> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> Coachmen
> guys were really thinking about us second hand owners by including that
> beverage center...
> Columbia, SC.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Not you, I'm trying to figure out what John Lebetski meant, since the
difference between the Dave Point and the center of the patch (in track)
is that actual definition of scrub radius.

> Yes, My bad. The point was that while not completely fixing the issue, it certainly moves it closer to correct.
>

>>> Also moving tire inboard may be able to fix the steering axis or some of the error, but not sure that totally fixes scrub radius.
>> Scrub radius is literally defined as the distance between the center of
>> the contact patch and the point where the steering axis touches the ground.
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
I’ve hit canyon rd south into Ellensburg in The War Pig pulling a two axle
14’ trailer full of dirt bikes and was a steady 10 over by the yellow
corner speed signs. It was epic. As long as I picked good lines an didn’t
think about what would happen if I blew a front tire. ;)

Sully
Bellevue wa

On Fri, Jan 22, 2021 at 5:19 PM James Hupy via Gmclist <

> The GMC Motorhome is NOT a performance vehicle. It wallows in tight curves,
> barely stays straight on good roads. It is at least 40 years old, and
> designed around parts plucked from production lines of various automobiles
> of the era. Nothing state of the art about the suspension and drive train.
> It does a fair job of point to point transportation of a heavy vehicle
> that has a great deal of its weight centered above the tops of the tires.
> A race car, it definitely is NOT! If you do not expect sports car
> handling, and maintain the drive train/suspension parts well, it is safe
> enough to drive in traffic if you don't follow too closely and drive "eyes
> way down the road ahead", you won't get in too much trouble.
> There are upgrades that improve braking quite a bit, and that is one
> huge reason for the 1-ton conversion. That and much stronger lower control
> arms and front wheel bearings as well as upper and lower ball joints.
> Handling? Very subjective at best. It still is a top heavy front wheel
> drive vehicle. Not much will ever change those facts.
> Do I love them? Yep! But, don't put lipstick on them. Underneath, they
> are still a very good looking pig.(grin)
> Jim Hupy
> Salem, Oregon
>
> On Fri, Jan 22, 2021, 4:55 PM Joe Weir via Gmclist <
> gmclist>

>
> > Yes, My bad. The point was that while not completely fixing the issue,
> > it certainly moves it closer to correct.
> >

> > > > Also moving tire inboard may be able to fix the steering axis or
> some
> > of the error, but not sure that totally fixes scrub radius.
> > >
> > > Scrub radius is literally defined as the distance between the center of
> > > the contact patch and the point where the steering axis touches the
> > ground.
> > >
> > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> >
> > --
> > 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> > brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> > Coachmen
> > guys were really thinking about us second hand owners by including that
> > beverage center...
> > Columbia, SC.
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Jim-

At first approximation, no argument. These are six-ton beasts, and you
have to scale your expectations accordingly.

On the other hand, if we can understand the suspension geometry at play,
we can make the best of our lot. Certainly, the concerns about scrub
radius have a basis in minimizing torque steer. The "non-parallel
control arms" question is more interesting, as that relates to camber
gain, and depending on other factors, bump steer.

Zero camber gain is not always the answer. The only doc I've seen with a
discussion of suspension geometry didn't really understand how it
worked, as it concluded incorrectly that every one-ton coach should be
sitting on the bump stops.

-Zandr

> The GMC Motorhome is NOT a performance vehicle. It wallows in tight curves,
> barely stays straight on good roads. It is at least 40 years old, and
> designed around parts plucked from production lines of various automobiles
> of the era. Nothing state of the art about the suspension and drive train.
> It does a fair job of point to point transportation of a heavy vehicle
> that has a great deal of its weight centered above the tops of the tires.
> A race car, it definitely is NOT! If you do not expect sports car
> handling, and maintain the drive train/suspension parts well, it is safe
> enough to drive in traffic if you don't follow too closely and drive "eyes
> way down the road ahead", you won't get in too much trouble.
> There are upgrades that improve braking quite a bit, and that is one
> huge reason for the 1-ton conversion. That and much stronger lower control
> arms and front wheel bearings as well as upper and lower ball joints.
> Handling? Very subjective at best. It still is a top heavy front wheel
> drive vehicle. Not much will ever change those facts.
> Do I love them? Yep! But, don't put lipstick on them. Underneath, they
> are still a very good looking pig.(grin)
> Jim Hupy
> Salem, Oregon
>
> On Fri, Jan 22, 2021, 4:55 PM Joe Weir via Gmclist

>
>> Yes, My bad. The point was that while not completely fixing the issue,
>> it certainly moves it closer to correct.
>>

>>>> Also moving tire inboard may be able to fix the steering axis or some
>> of the error, but not sure that totally fixes scrub radius.
>>> Scrub radius is literally defined as the distance between the center of
>>> the contact patch and the point where the steering axis touches the
>> ground.
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>> --
>> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
>> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
>> Coachmen
>> guys were really thinking about us second hand owners by including that
>> beverage center...
>> Columbia, SC.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
If you put 2" wheel spacers on a stock GMC front end, it will also torque
steer. I have done that very thing on my coach, and installed another set
on a different coach, with the same results. Torque steer that will yank
the steering wheel out of your grip.
So, I do not equate torque steer with the 1-ton, but with front wheel
drive vehicles. I have a P.T. Dream Cruiser that has 220 horsepower in it's
turbocharged 2.4 L. engine. It weighs just over 2000 pounds, and is a real
rocket ship. If you turn the front wheels slightly and turn the traction
control off, it becomes a real handful if you jump on the throttle. I have
torn out the engine mounts twice doing stupid stuff like burnouts with it.
So, front wheel drives with surplus torque are more guilty than the 1-ton
in my opinion. But, opinions vary.
Jim Hupy
Salem, Oregon

On Fri, Jan 22, 2021, 7:37 PM Zandr Milewski via Gmclist <

> Jim-
>
> At first approximation, no argument. These are six-ton beasts, and you
> have to scale your expectations accordingly.
>
> On the other hand, if we can understand the suspension geometry at play,
> we can make the best of our lot. Certainly, the concerns about scrub
> radius have a basis in minimizing torque steer. The "non-parallel
> control arms" question is more interesting, as that relates to camber
> gain, and depending on other factors, bump steer.
>
> Zero camber gain is not always the answer. The only doc I've seen with a
> discussion of suspension geometry didn't really understand how it
> worked, as it concluded incorrectly that every one-ton coach should be
> sitting on the bump stops.
>
> -Zandr
>

> > The GMC Motorhome is NOT a performance vehicle. It wallows in tight
> curves,
> > barely stays straight on good roads. It is at least 40 years old, and
> > designed around parts plucked from production lines of various
> automobiles
> > of the era. Nothing state of the art about the suspension and drive
> train.
> > It does a fair job of point to point transportation of a heavy
> vehicle
> > that has a great deal of its weight centered above the tops of the tires.
> > A race car, it definitely is NOT! If you do not expect sports car
> > handling, and maintain the drive train/suspension parts well, it is safe
> > enough to drive in traffic if you don't follow too closely and drive
> "eyes
> > way down the road ahead", you won't get in too much trouble.
> > There are upgrades that improve braking quite a bit, and that is
> one
> > huge reason for the 1-ton conversion. That and much stronger lower
> control
> > arms and front wheel bearings as well as upper and lower ball joints.
> > Handling? Very subjective at best. It still is a top heavy front wheel
> > drive vehicle. Not much will ever change those facts.
> > Do I love them? Yep! But, don't put lipstick on them. Underneath,
> they
> > are still a very good looking pig.(grin)
> > Jim Hupy
> > Salem, Oregon
> >
> > On Fri, Jan 22, 2021, 4:55 PM Joe Weir via Gmclist <
> gmclist>

> >
> >> Yes, My bad. The point was that while not completely fixing the issue,
> >> it certainly moves it closer to correct.
> >>

> >>>> Also moving tire inboard may be able to fix the steering axis or
> some
> >> of the error, but not sure that totally fixes scrub radius.
> >>> Scrub radius is literally defined as the distance between the center of
> >>> the contact patch and the point where the steering axis touches the
> >> ground.
> >>>
> >>> _______________________________________________
> >>> GMCnet mailing list
> >>> Unsubscribe or Change List Options:
> >>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>
> >> --
> >> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
> >> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
> >> Coachmen
> >> guys were really thinking about us second hand owners by including that
> >> beverage center...
> >> Columbia, SC.
> >>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Are we going to beat the Vixen at its own game? With a bit of thought,
we could. :)

> I’ve hit canyon rd south into Ellensburg in The War Pig pulling a two axle
> 14’ trailer full of dirt bikes and was a steady 10 over by the yellow
> corner speed signs. It was epic. As long as I picked good lines an didn’t
> think about what would happen if I blew a front tire. ;)
>
> Sully
> Bellevue wa
>
> On Fri, Jan 22, 2021 at 5:19 PM James Hupy via Gmclist <

>
>> The GMC Motorhome is NOT a performance vehicle. It wallows in tight curves,
>> barely stays straight on good roads. It is at least 40 years old, and
>> designed around parts plucked from production lines of various automobiles
>> of the era. Nothing state of the art about the suspension and drive train.
>> It does a fair job of point to point transportation of a heavy vehicle
>> that has a great deal of its weight centered above the tops of the tires.
>> A race car, it definitely is NOT! If you do not expect sports car
>> handling, and maintain the drive train/suspension parts well, it is safe
>> enough to drive in traffic if you don't follow too closely and drive "eyes
>> way down the road ahead", you won't get in too much trouble.
>> There are upgrades that improve braking quite a bit, and that is one
>> huge reason for the 1-ton conversion. That and much stronger lower control
>> arms and front wheel bearings as well as upper and lower ball joints.
>> Handling? Very subjective at best. It still is a top heavy front wheel
>> drive vehicle. Not much will ever change those facts.
>> Do I love them? Yep! But, don't put lipstick on them. Underneath, they
>> are still a very good looking pig.(grin)
>> Jim Hupy
>> Salem, Oregon
>>
>> On Fri, Jan 22, 2021, 4:55 PM Joe Weir via Gmclist <
>> gmclist>

>>
>>> Yes, My bad. The point was that while not completely fixing the issue,
>>> it certainly moves it closer to correct.
>>>

>>>>> Also moving tire inboard may be able to fix the steering axis or
>> some
>>> of the error, but not sure that totally fixes scrub radius.
>>>> Scrub radius is literally defined as the distance between the center of
>>>> the contact patch and the point where the steering axis touches the
>>> ground.
>>>>
>>>> _______________________________________________
>>>> GMCnet mailing list
>>>> Unsubscribe or Change List Options:
>>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>>> --
>>> 76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator,
>>> brakes, Sully airbags, fuel lines, seats, adult beverage center... those
>>> Coachmen
>>> guys were really thinking about us second hand owners by including that
>>> beverage center...
>>> Columbia, SC.
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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