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| Geometry [message #234542] |
Tue, 31 December 2013 05:59  |
dpottebaum
Messages: 100
Registered: January 2013
Location: Bondurant, Iowa
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I'm about ready to order a one ton conversion from Manny on January 2nd. In this last week I've had several people raise the geometry issue caused by the difference in knuckle height and possibly some other aspects. Getting the control arms that far out of parallel does seem concerning. I have not read all of the chatter on torque steer so maybe there are some facts in that thread?
What I need, please, are some facts from an engineer that can explain to me if this is truly an issue that cannot be compensated for safely (and how) and whether or not it will set off a chain reaction of other issues that need to be dealt with.
Thank you in advance.
Dave Pottebaum
Bondurant, Iowa
1978 Royale
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| Re: [GMCnet] Geometry [message #234551 is a reply to message #234542] |
Tue, 31 December 2013 07:49  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Dave,
I've been through most of a BS in ME and have BS & MSEE, so some might call
me an engineer. But that 6-7 years of schooling is worth nothing compared
to the 10,000 miles I put on the 1-Ton this summer. I don't see how having
the upper and lower control arms perfectly parallel could have improved the
steering. It was more nearly perfect than I could imagine for a vehicle of
the GMC's size, pulling a 3500# toad. No road wander or rut tracking. No
adverse tire wear. No problem of any kind.
Go ahead with the order; you won't be disappointed.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
On Tue, Dec 31, 2013 at 6:59 AM, Dave Pottebaum <pottebaum5@msn.com> wrote:
>
>
> I'm about ready to order a one ton conversion from Manny on January 2nd.
> In this last week I've had several people raise the geometry issue caused
> by the difference in knuckle height and possibly some other aspects.
> Getting the control arms that far out of parallel does seem concerning. I
> have not read all of the chatter on torque steer so maybe there are some
> facts in that thread?
>
> What I need, please, are some facts from an engineer that can explain to
> me if this is truly an issue that cannot be compensated for safely (and
> how) and whether or not it will set off a chain reaction of other issues
> that need to be dealt with.
>
> Thank you in advance.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Geometry [message #234556 is a reply to message #234542] |
Tue, 31 December 2013 08:33 |
dpottebaum
Messages: 100
Registered: January 2013
Location: Bondurant, Iowa
Karma: 0
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Senior Member |
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Thanks for the reply Ken. I appreciate hearing from a guy who has been there and done that (and your other credentials!). A couple of follow ons. I'm still using 16.5's and the original airbags (at least until 2015 when I plan to go to the Sully Bilt system). Any changes required to ride height due to switching to the one ton? Other tweaks from stock? This rig is pretty much bone stock. It still had the original ball joints at 103K miles. Probably would have been good for more, but I didn't want to chance it.
Dave Pottebaum
Bondurant, Iowa
1978 Royale
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| Re: Geometry [message #234564 is a reply to message #234556] |
Tue, 31 December 2013 09:55 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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| dpottebaum wrote on Tue, 31 December 2013 08:33 |
... Any changes required to ride height due to switching to the one ton? ...
|
Ride height is still controlled by the torsion bars. My Manny 1 ton is still in the crate awaiting install. We'll have to unload the torsion bars to remove the old control arms and reset them to the correct ride height. From what I understand this is a recursive process as things settle from driving.
As I understand it, the Manny 1 ton gives you the ability to have more negative caster. In addition, the wheels are spaced out so they are in line with the rears. Both these have a huge impact on improving tracking and reducing rut wander.
I'm looking forward to installing mine.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] Geometry [message #234583 is a reply to message #234564] |
Tue, 31 December 2013 12:25 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Guess I'd better quit goofing off and get back to work on the GMC. So I
can move it off so Kerry can come down here for us to install his 1-Ton --
ON MY RACK. :-)
Ken H.
On Tue, Dec 31, 2013 at 10:55 AM, Kerry Pinkerton wrote:
>
>
> dpottebaum wrote on Tue, 31 December 2013 08:33
> > ... Any changes required to ride height due to switching to the one ton?
> ...
>
>
> Ride height is still controlled by the torsion bars. My Manny 1 ton is
> still in the crate awaiting install. We'll have to unload the torsion bars
> to remove the old control arms and reset them to the correct ride height.
> From what I understand this is a recursive process as things settle from
> driving.
>
> As I understand it, the Manny 1 ton gives you the ability to have more
> negative caster. In addition, the wheels are spaced out so they are in line
> with the rears. Both these have a huge impact on improving tracking and
> reducing rut wander.
>
> I'm looking forward to installing mine.
>
> --
> Kerry Pinkerton
>
> North Alabama, near Huntsville,
>
> 77 Eleganza II, "The Lady", 403CI, also a 76 Eleganza being re-bodied as
> an Art Deco car hauler
> _______________________________________________
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Geometry [message #234607 is a reply to message #234577] |
Tue, 31 December 2013 16:49 |
dpottebaum
Messages: 100
Registered: January 2013
Location: Bondurant, Iowa
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[quote title=dwayne jacobson[1] wrote on Tue, 31 December 2013 11:31]Dave
I have about 20,000 miles on the coach with a manny 1 ton front end and can
take my hands off the wheel, go back and use the washroom and return to the
drivers seat and the coach is still heading down the road straight as you
would want.
Sounds like great material for a movie...HA!
Thanks for all of the feedback. I guess no one regrets making the move. Does this mean it was perfect out of the box, or was there a fair amount of recalibration (other than the ride height settling and of course an initial wheel alignment)?
Dave Pottebaum
Bondurant, Iowa
1978 Royale
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| Re: [GMCnet] Geometry [message #234613 is a reply to message #234601] |
Tue, 31 December 2013 17:41 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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I am! I'm not about to sit here with the temperatures headed for freezing!
Tampa on 10 Jan for GMCSS followed by GMCDL rallies. After that...? May
even wind up in Key West, despite sometimes seeing things that turn my
stomach. :-)
Ken H.
On Tue, Dec 31, 2013 at 4:19 PM, Kerry Pinkerton <Pinkertonk@mchsi.com>wrote:
>
> ...
> I'm not going anywhere till next spring so there is absolutely no rush.
> ...
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Geometry [message #234631 is a reply to message #234542] |
Tue, 31 December 2013 19:18 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| dpottebaum wrote on Tue, 31 December 2013 03:59 |
I'm about ready to order a one ton conversion...
...the geometry issue caused by the difference in knuckle height and possibly some other aspects. Getting the control arms that far out of parallel does seem concerning. ...
|
IF the system was being designed from scratch, it would be designed with parallel arms of unequal length. (Like most OEM systems.) As normally designed, the unequal arms are to increase camber when the suspension is not at ride height, as when cornering or other maneuverers that flex the front suspension. What is NOT desired is changing from positive to negative camber under hard cornering. But this is mostly of interest to applications that actually are expected to corner hard... not motorhomes.
It is a compromise, a little loss of handling at extremes we'll never use for ease of installation and lower cost. The one ton set up COULD be better, but not without increasing the cost and it would NOT be a bolt on kit.
Bottom line:
When all is done, my keeper coach will have a one ton kit.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
[Updated on: Tue, 31 December 2013 19:21] Report message to a moderator |
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| Re: Geometry [message #234640 is a reply to message #234631] |
Tue, 31 December 2013 20:53 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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| mike miller wrote on Tue, 31 December 2013 18:18 |
| dpottebaum wrote on Tue, 31 December 2013 03:59 |
I'm about ready to order a one ton conversion...
...the geometry issue caused by the difference in knuckle height and possibly some other aspects. Getting the control arms that far out of parallel does seem concerning. ...
|
IF the system was being designed from scratch, it would be designed with parallel arms of unequal length. (Like most OEM systems.) As normally designed, the unequal arms are to increase camber when the suspension is not at ride height, as when cornering or other maneuverers that flex the front suspension. What is NOT desired is changing from positive to negative camber under hard cornering. But this is mostly of interest to applications that actually are expected to corner hard... not motorhomes.
It is a compromise, a little loss of handling at extremes we'll never use for ease of installation and lower cost. The one ton set up COULD be better, but not without increasing the cost and it would NOT be a bolt on kit.
Bottom line:
When all is done, my keeper coach will have a one ton kit.
|
SLA (short/long arm suspensions are great in that they allow engineers to vary many parameters. Not only can the lengths be different, they do not have to be parallel, nor do they need to be on parallel axes. Steer characteristics are also dependent on the position of the steer arm on the knuckle and the length and angle of the tie rod ends. Modern computers can run thousands of combinations in seconds. Camber compensation is desirable and it is normal for an outside wheel to go to negative camber and the inside wheel to go to positive camber so that as the vehicle leans or rolls, the tires actually stay perpendicular to the road surface. Normal suspensions compensate for about 85% of the roll angle. Given all that, pure geometry is only important within the normal ride height and roll angle range. At the extremes, the loads are so low that no one (including the tires) will know the difference. It's not unusual to have artificial geometries at the extremes in order to "fix" other issues. EG it is common to stop wheel turning angle on one side with a knuckle stop while continuing to turn the other wheel by over travelling the gear or rack. Also, most vehicles do not have true Ackerman due to packaging and turn circle constraints. Some vehicles have parallel steer that leave nice black marks on your driveway. The bottom line is that the 1 ton appears to have acceptable geometry in the range where it matters. Text book stuff is nice if you don't have to design a real car.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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