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Re: [GMCnet] Why not fix one ton scrub radius with wheel offset? [message #361945 is a reply to message #361908] Fri, 22 January 2021 22:12 Go to previous messageGo to previous message
Zandr Milewski is currently offline  Zandr Milewski   United States
Messages: 12
Registered: September 2020
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Junior Member
Lots of things can contribute to torque steer, sure. but the GMCMH
starts from a pretty good position, since it has a fixed intermediate
shaft that equalized the halfshaft length. Minimizing scrub radius is
the next big lever, as you describe. Spindle length would be next, and
that's rather harder to deal with.

On 1/22/21 20:00, James Hupy via Gmclist wrote:
> 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 gmclist@list.gmcnet.org> wrote:
>
>> 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
>>
>> On 1/22/21 17:18, James Hupy via Gmclist wrote:
>>> 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@list.gmcnet.org>
>>> wrote:
>>>
>>>> Yes, My bad. The point was that while not completely fixing the issue,
>>>> it certainly moves it closer to correct.
>>>>
>>>> Zandr Milewski wrote on Fri, 22 January 2021 16:15
>>>> > On 1/22/21 06:55, John R. Lebetski via Gmclist wrote:
>>>> >> 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
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>>>> --
>>>> 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.
>>>>
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