Question for Porterbuilt....dropmember ?s

[-Greg72]

PB,

Just a couple of quick questions for you after reading the article on your dropmember in ClassicTrucks...

The article mentioned (and I think you've said it on this board a few times) that a 27" tire will lay frame up front. I'm assuming that is truly the limit of the suspension travel, since I think the article mentioned that a 29" tire would still be 1" off the ground at max drop...

Questions (assuming the 27" front tire scenario):

1. What is the angle (in degrees) of the front A-arms at full drop? I'm imagining they are upswept from the frame to the spindle, but I'm just wondering by how much.

2. What is the angle (in degrees) of the front A-arms at full ride height? I'd imagine that thay are sweeping down in that case??

3. What is the frame height, when the A-Arms are completely parallel to the ground? I can probably calculate this based on the answers to #1 and #2 above, but if you already know it you can save me the trouble...!!!


The reason I'm asking all this, is because I'm trying to understand what ride height is going to give the best ride quality....A softer psi in the airbags generally gives a smoother ride, but depending on how low the a-arms are attached to the crossmember, it might take a lot of air to get the truck to an acceptable "street driving" height and the ride quality might suffer.... does this make sense?

You may remember that I asked a while ago about using the Dropmember in my '72 Burb with a BBC. Now that you've solved the motor mount issues, all I need to understand is how to best overcome the steering rack issues (My truck is going to be very close to the maximum recommended weight of the current offerings).....would using a C4 version of the Dropmember all me to use a C4 steering rack? Would that have a better weight rating for my "portly" Suburban application???

Thanks for any info or clues you can send my way...

[SCOTI]

Hopefully Nathan will chime in & answer your questions but I wanted to say that less air pressure doesn't always equal a 'better' ride.

Sometimes if there's not enough air it feels uncontrolled/bouncy as it travels from compression to extension. I had this issue w/my 68. My guess is he does know what's 'optimum' for his Dropmember set-up & that's prob good info to have as you decipher all the info from your questions.

[PBFAB.COM]

Originally Posted by -Greg72

PB,

Just a couple of quick questions for you after reading the article on your dropmember in ClassicTrucks...

The article mentioned (and I think you've said it on this board a few times) that a 27" tire will lay frame up front. I'm assuming that is truly the limit of the suspension travel, since I think the article mentioned that a 29" tire would still be 1" off the ground at max drop...

Questions (assuming the 27" front tire scenario):

1. What is the angle (in degrees) of the front A-arms at full drop? I'm imagining they are upswept from the frame to the spindle, but I'm just wondering by how much.

2. What is the angle (in degrees) of the front A-arms at full ride height? I'd imagine that thay are sweeping down in that case??

3. What is the frame height, when the A-Arms are completely parallel to the ground? I can probably calculate this based on the answers to #1 and #2 above, but if you already know it you can save me the trouble...!!!


The reason I'm asking all this, is because I'm trying to understand what ride height is going to give the best ride quality....A softer psi in the airbags generally gives a smoother ride, but depending on how low the a-arms are attached to the crossmember, it might take a lot of air to get the truck to an acceptable "street driving" height and the ride quality might suffer.... does this make sense?

You may remember that I asked a while ago about using the Dropmember in my '72 Burb with a BBC. Now that you've solved the motor mount issues, all I need to understand is how to best overcome the steering rack issues (My truck is going to be very close to the maximum recommended weight of the current offerings).....would using a C4 version of the Dropmember all me to use a C4 steering rack? Would that have a better weight rating for my "portly" Suburban application???

Thanks for any info or clues you can send my way...

Hopefully this equation will help in figuring which tire diameter, spindle, and bag combination will work best:

29" tall tire + Stock spindle + Slam Specialties RE7 bag + Strong Arms = 3" off the ground at dump, 8" ride height (lower arms parallel to ground), and 11" at full lift. (all measurements are taken from bottom of frame-rail to ground. If you substitute a Firestone bag you can subtract .5" from the measurements.

29" tall tire + 2.5" drop spindle + Firestone bag + Strong Arms = Frame on ground at full dump. (I have to recommend the use of a bumpstop to limit travel at full dump, with this combination, to eliminate the possibility of the frame dragging the ground due to a bag/air component malfunction or failure at driving speeds. We all know that it is 'unsafe' for the frame to be able to lay on the ground.)

You can substitute different combos into the equation to figure where the truck will sit. Remember if the diameter of the tire increases by 1", the heights will only be effected by .5"... 2" diamter increase will effect the height by 1" and so on.

Now to answer your other questions...

I am not positive on the angles of the control arms at full dump or full extension. The lower arm is designed to be parallel to the ground at ride height. Ride height being 5-6 inches with a 2.5" spindle and 29" tall tire. Obviously, there may be some preference to run the truck at a slightly lower or taller ride-height... that's OK. I have driven the 66 at 3" off the ground and at 6" off the ground and it doesn't seem to FEEL too different. The geometry is such that there is less than .1 degrees of bumpsteer through the cycled bump and less than .2 degrees through the cycled droop. The camber gain is -2 degrees at full dump.

I hope the information is a little help to you in your decision making process. I don't think you would notice too much of a difference in ride quality with a couple inches variance and the amount of p.s.i. increase or decrease that would be necessary to achieve that difference.

If you would like to know exact angle of control arms at different heights I can get the information to you, but I think the above info. will be enough.

[lvscott]

[QUOTE=porterbuilt;2066477]29" tall tire + Stock spindle + Slam Specialties RE7 bag + Strong Arms = 3" off the ground at dump, 8" ride height (lower arms parallel to ground)QUOTE]

When you say that the lower arms are parallel to the ground do you mean the plate that the bag mounts to (on StrongArms) or do you mean the actual arm?

[PBFAB.COM]

I mean the imaginary line that exists through the ball joint pivot center, and the control arm bushing pivot point. The lower arm itself (the tubing) will not be quite parallel to the ground.

[PBFAB.COM]

Here's a pic of the lower control arms a couple inches above ride height.

[-Greg72]

PB,

This is great info.....thank you for the help!

Where is that "buy you a beer" emoticon??


-G

[lvscott]

Thanks for the help. I am finishing up my frame and this info made me question where I have my ride height set.
Thanks.