Steering issues on my 40' CC 1992

[Lacota]

Originally Posted by Harvard

To put it in different words:

Almost every "too little caster" handling post starts out with wandering and an uncomfortable feeling at highway speeds.

Once the caster has been increased the wandering clears up and the feeling that the new found stability at highway speeds feels even more stable with increasing speed.

Here are the specs. on caster:
LEFT Initial +2.89 Final +2.89 Range +2.00 to +5.00
Right Initial +3.10 Final +3.10 " " +2.0 to +5.0
Side to side -0.21 Final -0.21 " " -0.50D to 0.00Degree
This is greek to me. I noticed when I started coach up the steering wheel move 2" to center. I am wondering if steer shock is not centered.
I will have king pin honed and check steer shock is centered while being aligned.
Thanks again for all the advice, Don.

[Lacota]

Originally Posted by Harvard

To put it in different words:

Almost every "too little caster" handling post starts out with wandering and an uncomfortable feeling at highway speeds.

Once the caster has been increased the wandering clears up and the feeling that the new found stability at highway speeds feels even more stable with increasing speed.

Here are the specs. on caster:
LEFT Initial +2.89 Final +2.89 Range +2.00 to +5.00
Right Initial +3.10 Final +3.10 " " +2.0 to +5.0
Side to side -0.21 Final -0.21 " " -0.50D to 0.00Degree
This is greek to me. I noticed when I started coach up the steering wheel move 2" to center. I am wondering if steer shock is not centered.
I will have king pin honed and check steer shock is centered while being aligned.
Thanks again for all the advice, Don.

[Harvard]

Originally Posted by Lacota

Here are the specs. on caster:
LEFT Initial +2.89 Final +2.89 Range +2.00 to +5.00
Right Initial +3.10 Final +3.10 " " +2.0 to +5.0
Side to side -0.21 Final -0.21 " " -0.50D to 0.00Degree
This is greek to me. I noticed when I started coach up the steering wheel move 2" to center. I am wondering if steer shock is not centered.
I will have king pin honed and check steer shock is centered while being aligned.
Thanks again for all the advice, Don.

This is a typical "tweak the toe and we are good to go" alignment.

The chassis mfg has recommended a caster range of +2.0 to +5.0 degrees.
In layman terms, this range can be interpreted as:
+2.0 Degrees for 100% city driving
+3.5 Degrees for 50% city and 50% highway driving.
+5.0 Degrees for 100% highway driving.

It does not take a rocket scientist to figure out that a Class A DP RV is going to be about 99.9% highway driven.

If you add 2.0 Degree Wedges you will have:
LH 2.89 + 2.0 = 4.89
RH 3.10 + 2.0 = 5.10

[Lacota]

Wow, it all makes sense to me now! I wonder if the 2 previous owners drove it 85K miles like it is now. One owner was a International pilot. I have never seen so many adjustments on a front suspension. Here are some more specs.
Camber: Left -0.22 Final 0.21 Range 0.00 to +0.50
Right -0.36 Final 0.35 Range -0.35 to -0.38 to +0.13
Side to side +0.14 Final +0.14 Range +0.25 to +0.25
Toe in: Left +0.11Final +0.02 Range .00 to +0.04
Right +0.12 Final +0.03 Range 0.00 to +0.04
Total: +0.23 Initial +0.05 Final Spec +0.04 to +0.08

You are right. The toe in was changed but nothing else was. Should I shoot for the higher figures on caster and camber based on 99% Highway driving? This all makes sense now and thanks again, Don

[Harvard]

Originally Posted by Lacota

...... Should I shoot for the higher figures on caster and camber based on 99% Highway driving? ......

Personally I would not hesitate to add 3.0 Degree caster wedges.
LH 2.89 + 3.0 = +5.89 Degrees
RH 3.10 + 3.0 = +6.10 Degrees

I do not think you have the option NOR the need to change camber.

[Harvard]

Originally Posted by Harvard

Personally I would not hesitate to add 3.0 Degree caster wedges.
LH 2.89 + 3.0 = +5.89 Degrees
RH 3.10 + 3.0 = +6.10 Degrees

I do not think you have the option NOR the need to change camber.

I am going to rescind the 3 degree wedges recommendation because we are dealing with larger wheels. One degree of caster change on a larger wheel creates a larger change in the caster trail then does one degree of change in a smaller wheel.

There are numerous accounts of reducing the tire pressure to that required for the load as causing a significant change in the caster trail. So, changing the caster angle by one degree is going to change the caster trail significantly more then a few psi of pressure. This is relationship would be more pronounced on the larger wheel. IMO.

[deandec]

"Air pressure is good. As I remember 95 in front and 105 in rear."

Tire air pressure can affect steering significantly. Your reported tire psi are not likely "good".

My Gillig Bus rig had the smaller 10Rx22.5 tires on the front axle.

The front tires required 110 psi (max sidewall pressure also) to carry the verified axle weight per the tire manufacturer's chart.

95 psi on the front axle could create steering issues if 15 psi underinflated.

10 psi higher in the rear tires than in the front tires likely shifts weight to the front axle exacerbating the steering issue?

[Lacota]

Hi Dean,
Long time no talk! Hope all is well. The air pressure might be reversed but I will check tomorrow. The tires are 11R and the inflation was to firestone specs for 32K lbs. They should be OK.
My main concern is the wandering steering. I have a better understanding on the front end now and am armed with information from all that contributed and will present to the alignment shop. Should be interesting. Thanks for the info, Don

[f360racer]

Originally Posted by Harvard

This is a typical "tweak the toe and we are good to go" alignment.

The chassis mfg has recommended a caster range of +2.0 to +5.0 degrees.
In layman terms, this range can be interpreted as:
+2.0 Degrees for 100% city driving
+3.5 Degrees for 50% city and 50% highway driving.
+5.0 Degrees for 100% highway driving.

It does not take a rocket scientist to figure out that a Class A DP RV is going to be about 99.9% highway driven.

If you add 2.0 Degree Wedges you will have:
LH 2.89 + 2.0 = 4.89
RH 3.10 + 2.0 = 5.10

Thank you Don for the explanation of the setup. Where do you find the recommended chassis mfg range? I have a 2007 Affinity. There were no manuals in my auction coach.

[Harvard]

Originally Posted by f360racer

Thank you Don for the explanation of the setup. Where do you find the recommended chassis mfg range? I have a 2007 Affinity. There were no manuals in my auction coach.

The range and specs given would be spit out by the alignment machine. Just be aware a range of +2 to +5 could also be documented as 3.5 +/-1.5 Degrees.

When you approach an alignment service provider just specify you want to have the caster set to at least the upper end of the given caster range or caster specification BECAUSE you are always on the highway. If that does not cut it then I suggest you find another alignment shop.

[Harvard]

Here is a link to phil-t who is driving an F53 (22.5 inch wheels, solid axel) with casters set in the 7 to 8 degree range:

Good Sam Club Open Roads Forum: Class A Motorhomes: Interpreting Caster Alignment Specs

[f360racer]

Originally Posted by Harvard

The range and specs given would be spit out by the alignment machine. Just be aware a range of +2 to +5 could also be documented as 3.5 +/-1.5 Degrees.

When you approach an alignment service provider just specify you want to have the caster set to at least the upper end of the given caster range or caster specification BECAUSE you are always on the highway. If that does not cut it then I suggest you find another alignment shop.

That is very helpful. Thanks