Chassis Building 101. Ride Height

[Tincup]

I'm getting ready to start modifying my truck chassis and have a basic question. When you set up the bare chassis, you set it level, and at desired ride height, either on the shop floor or frame table. Do you actually set it at desired ride height or do you add a couple inches to account for when all the weight is put back on the chassis? I would think if I have a bare chassis, and I want a 6" ride height under the main rails, I should set it at say 8" so when everything is back together ( all the weight back on it ) it will be at my desired 6". I am running all coilovers so I will have some adjustment. Any help is appreciated...

[dirty rick]

Ride height is determined by the geometry designed into your suspension. You can replace the shocks with solid struts to maintain that height during construction. There is a sweet spot in every suspension design for ride height and that should not be deviated from by much (at all). If you are buying suspension components ask for design specs you then build the frame with the right drop to put the body where you want it at ride height.

[RobNoLimit]

It's all in the math. We like to set the chassis level (easier to measure from), and then calculate the position of the front and rear center lines at ride height. As Rick said, a Coil-Over manufacturer will be able to give you the 'Open', Closed', and 'Ride-Height' specs of their shock. Use the 'Ride-Height' dimensions to plan out the mount locations for your desired outcome. Remember to factor in the tire diameter here as well.

Tell you what, we are starting a build for an 89 C1500, I'll post up some picts and drawing to help out.

[RobNoLimit]

1. We're building a chassis for an 88-98 short bed. Our customer has a list of wants, 315 front tire, 345 rear tire, 5"R.H. (bottom of rail), air ride, full drop, tow a small trailer, 800 hp LSX, 6L80E, .... OK, well, at No Limit, if you're going to actually drive it, we will build in the suspension stops so that the frame WON'T hit the ground.First compromise, full drop will be 1" off the ground. Everything else on the list is fine. We start with wheelbase, R.H. of the main rail, and the tire sizes. 1/2 of the tires diameter is the center to the ground. We subtract .400" for tire squish at R.H.

[RobNoLimit]

2. Rear kick height. Start at the axle CL height, add 1.500" for half of the axle tube (assuming 3" axle), then add 4" for up travel (we add in another .500" for a bumpstop here, that I did not include in the simplified drawing), and then another 4" for the height of the rear frame rail (yours may vary, 4" to 5" is normal)

[Rod]

this thread is fun!!!

[RobNoLimit]

3. For the front rail height, you need some more info. The IFS you choose will have a 'sweet spot' or recommended ride height. ** Here's a tip - If the company your going to buy an IFS from can't give you this information, Your dealing with the wrong people. Hang up the phone.** On our No Limit Wide-Ride IFS (shameless plug), we spec from the 'top' of the rail down to the spindle CL. 5" for Std. spindle, 3" for drop spindle. On really low trucks, we prefer a drop spindle vs. raising the crossmember too high (this can upset motor height, driveline angles, and raise the CG) - as long as there is good ground clearance from the bottom of the crossmember to the ground.

With this info to start with, we can begin to layout a plan for the frame rails and suspension. I'll show you some more next week. Have a great weekend - Please leave a comment or two, or a question. If this is of no interest, I'll stop here.

[Peter Mc Mahon]

. If this is of no interest, I'll stop here.[/QUOTE]
Oh ya, this is of no interest at all. One of the guys at the top of the game explaining things from the beginning. Just cancel this thread now.
Continue on, please.......

[Rod]

If this is of no interest, I'll stop here.

WHAT!!! dang it Rob....always starting trouble....

[Tincup]

Thanks a ton Rob, I'll be doing some homework tonight. Please continue for both myself and all the other interested individuals. BTW, I am using your Fatbar on the rear.

[Guyt699]

I am very interested in seeing what you guys do with the 88-98 C1500 chassis Rob. Suspension is next on my list!

[72BBSwinger]

Another thing, at least this is how my brain works, is setting the upper control arm angle. Rob do you have it parallel to the ground at ride height or already starting into negative camber gain at ride height?

[andrewb70]

Please continue! This is very helpful not only from a practical perspective but for general knowledge. I may never build a frame from scratch, but I sure would love to know how it is done.

Andrew

[69_Sportsroof]

This is exactly the kind of advice I've been looking for. Please continue, it is very good info.

[Tincup]

Here is a pic of my IFS. The manufacturer could not provide me with the CL number because he did not have the spindles, I designed an machined my own so that I could run an OEM hub and brake setup. According to my measurements the number is 3" from the top of the frame mount to the spindle CL. My front tire is a 285-40-20 (29" dia.) so if I take half my tire dia 14.5" add in my 3" that should put the top of my frame rail at 17.5" from the ground. With a 5" rail height the bottom is at 12.5" but it all depends on the amount of kick up my frame has to determine rail to ground clearance. My chassis has a 5 5/8" kick up in the front, so that would put my ground clearance at 7.375" Does this make sense?

[Dr G]

If that is the ultimate position of your steering rack then I'd say you're going to have some bad bump steer. The tie rod should be coincident with a line pointing to the instant center of the two control arms. Yours seems to be pointing in a very different direction.

[Tincup]

If that is the ultimate position of your steering rack then I'd say you're going to have some bad bump steer. The tie rod should be coincident with a line pointing to the instant center of the two control arms. Yours seems to be pointing in a very different direction.

No big deal, I can flip the tie rod brackets...

[brawls43]

Great info Rob! Sub'ing to follow this one.

[XTRMEASURES]

Great info indeed

[RobNoLimit]

Good to see everyone chiming in.

OK, since Tin Cup started this, I am trying to follow along with what will fit his needs best. I did notice the steering issues, and possible another. So, to help out, I have some more chicken scratch for you.

The first is a very basic plotting of the Instant Center (henceforth to be known as IC) - (three extra points for that word). Also, this shows a basic concept of bumpsteer tuning. Once the A arms are set, you can plot out the IC. Next, a line through the inner Tie Rod End (TRE), and outer TRE (see how much easier that is for me to type?) should also intersect through the IC. As for the length of the TRE - inner pivot to outer pivot - it can be plotted by drawing a line through the Upper Ball Joint (UBL) and the Lower Ball Joint (LBJ), and drawing a line through the Upper Control Arm (UCA) and Lower Control Arm (LCA) pivot points. Measing from the intersection points of these lines as they pass the TRE line will give you the length of TR needed. Note** you CAN move the Tie Rod 'in' or 'out' on the TRE line as long as the TR length is correct.

So, take a look at this.
1. Looks like A) lower the rack as much as you can - you will need engine clearance. and B)Raise the outer TRE. Now, if your going to make a new steering arm, plot out the TR legth and see if you need to move the outer TRE in or out.
2. Also, if the upper and lower A-Arm lines are very close to parallel, you may want to make the spindle 'taller', to get the lines to cross for the IC a little sooner. Raising your spindle with a new lower ball joint mount may help.