| [GMCnet] My new Manny 1 ton [message #240963] |
Sun, 23 February 2014 09:40 |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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From my web site, jerrywork.com, or from the web sites of several of our clubs like GMCWS.ORG you can download a presentation I gave at GMCWS Casa de Fruita a couple of years ago that outlines why we now need alignment specs that are different from the GMC maintenance manual. Basically, radial ply tires behave very differently from bias ply tires and require different alignment specs. When GM began offering radial ply tires on our motorhomes around the middle of the production run, they continued to offer bias ply tires as well. While they did change the alignment specs when changing to radial ply tires on the Olds and Cad passenger cars, they did not do so for the motorhome. Because of the behavior of radial ply tires under speed, a radial ply tired car will benefit from greater caster than the same car shod with bias ply tires. But, there are definite limits. The greater the caster, the greater the load on the front end components for a given weight. For our coaches
running radial ply tires, 3 to 5 degrees of caster seems to be the sweet spot IF the ride height front and rear is correct. More than 5 and we are on the edge of over loading the front end components and over running the angle at which some of the front end components were designed to run. Less than 3 and we are on the edge of wandering. Camber for our coaches is also a balance where too much tilt in at the top is as bad on handling and tire wear as too much tilt out at the top. Zero (straight up and down) seems to be the best balance given that most of us now run radial ply tires. Toe in or out is largely a function of the condition of all the front end components. Again, zero seems to be a good balance for most coaches.
Since we all own and drive only one or two of these things it is natural to think that what works for our coach(s) is correct for all other coaches. As a result, there are many different opinions one will read on this forum. If you really want to deviate from the 3-5 degrees of caster, zero camber and zero toe, be sure to do the iterative process described in the presentation required to get your ride height at the factory spec front and rear first. Then set the 3-5, 0, 0 and drive your coach for a while. From there, do your own thing if you wish, but keep a close eye on tire wear front and rear.
Hope this helps.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Message: 1
Date: Sun, 23 Feb 2014 14:49:42 +1100
From: "Robert Mueller" <robmueller@iinet.net.au>
Subject: Re: [GMCnet] My new Manny 1 ton
To: <gmclist@temp.gmcnet.org>
Message-ID: <AB9B81FE435846FF92698B4F4C860A5E@DellDesktop>
Content-Type: text/plain; charset="iso-8859-1"
Ken,
I have Dave Lenzi's offset upper control arms in Double Trouble and when I installed them he noted NOT to set the caster above 5?
because the outer CV joints were at or getting close to the max they could handle at 5? caster when you turn hard left or right.
It might be a good idea to check and see what you've got.
He also noted that 0? caster was what was desired because radial tires like to run flat against the road surface.
Regards,
Rob M.
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
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Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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