Some stock suspension calculations and measurements

[TeocaliMG]

I think it's pretty excellent, when I get some time, I will take measurements and draft an SLA/IFS model in cad to track the ratios precisely based off the lengths and hardpoints of all the critical components. That would be great for precision, but there are subtle things that need real data that just can't be drawn, like the control arm bushing compliance.

This chart is exactly why I wish more aftermarket companies would focus on making high clearance fenders to allow larger tires or larger travel (or both) in jounce. We have a lot of CV margin left in jounce. OEM IFS always does. The advantage of the Bronco over the usual OEM IFS is it can already fit large tires and the fenders, both front and rear are bolt on. Adding about an inch of downtravel isn't the end of the world, as your chart shows, but we have multiple inches of jounce on the table.

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[Snacktime]

@TeocaliMG don't forget the body lift being an important tool in the toolkit.

I know I am on the opposite end try to get as much "safe" ground clearance as possible. As much as I want full travel that extra 1-2" of clearance has proven to be more useful for me.

@87-Z28 you should do a plot with a 1" differential drop. The benefits to daily driving and wheeling are huge!

 

[builtMIbronco]

I think it's pretty excellent, when I get some time, I will take measurements and draft an SLA/IFS model in cad to track the ratios precisely based off the lengths and hardpoints of all the critical components. That would be great for precision, but there are subtle things that need real data that just can't be drawn, like the control arm bushing compliance.

This chart is exactly why I wish more aftermarket companies would focus on making high clearance fenders to allow larger tires or larger travel (or both) in jounce. We have a lot of CV margin left in jounce. OEM IFS always does. The advantage of the Bronco over the usual OEM IFS is it can already fit large tires and the fenders, both front and rear are bolt on. Adding about an inch of downtravel isn't the end of the world, as your chart shows, but we have multiple inches of jounce on the table.

I completely agree with you about jounce and how much uptravel we leave on the table with the setups available now. I have measured and I think with some cutting and relocating like what Bigmeatsbronco did to clear 40s I could pickup at least 3.5" more of wheel travel on 37s in the front. I think it will take at a minimum a redesign or some modification to the upper coil mount to make that happen. I've emailed quite a few major coilover manufacturers and the general consensus is that there isn't a ton of room to shorten compressed length more than it already is on the actual coilover itself, especially when you have to clear the cv axle on the lower side and most are already using a pin-over-hat design on top.

I'm going to use king for example because they've been the most forthcoming with data. An 8" King 2.5 compressed to extended is 16-24" from eye to eye. The top hat design they use puts the top eye roughly 1/2" higher than the mounting point on the hat which allows them to stuff a longer coilover in theoretically. But then they use a 2" extension on the lower point of the coilover to clear the cv axle, plus the bar pin mount on the lca further extends those lengths down which eats up a ton of what could be available shock travel.

I think the differences in the numbers we see now are mainly just differences in how companies measure for clearance and using what's available to them. I do think we could see an extra inch come out of a better design/bronco specific long travel coilover, but anything more I think would take at a minimum a new/better top hat solution.

 

[Snacktime]

Well let's add some more information! I have a 1" differential drop so this is skewed a bit from stock.

I have about 1/4 of clearance between the CV balls and the snap ring at max droop 5100s and .625 thick leveling kit.

Wear pattern

Snap ring with 8 notches where the balls pinched it. Didnt even snap in and was probably loose inside banging around.

 

[87-Z28]

1” diff drop should corrects 3/4” of shock spacer. Should be just slightly outside of SAS geometry.

you do lots of hard miles. You are sitting pretty low near droop at ride height? Preloaded high? Your alignment just barely in spec? Forward LCA cam bolt max out laterally to get camber and rear pulled out a little less to get caster? CV joints stretched maybe with >10 degrees CV and hard miles. not very good durability.

SAS cv angle for easy on raad driving miles is <5 degrees with good LCA positioning. Should be durable

any thoughts? Does wear pattern look like stretched cv?

 

[Snacktime]

@87-Z28 I am .625" of spacer lift with a negative 1" of diff drop. So max CV angle for me is less than factory.

My ride height is 3.5" over factory non SAS or 2.5" over SAS. This is the current setup. Maxed lower cam adjusters to make alignment (all the way out).

I ran these CV axles for 4k miles at 4" of front lift (5100s) with a 1" spacer on top. Pretty much over extended both axles causing the passenger axle to fail. This is the driver side.

 

[87-Z28]

What do you think the allowable axial tolerances is in these cvs? Surely 0.25” for 1/2” on the axle?

 

[Snacktime]

@87-Z28 the wear is all the way to the snap ring. This axle was ran over extended for 4k miles and was a ticking time bomb. Hard to prove much other than yah it's pretty easy to over extended factory axles.

 

[87-Z28]

Seems like hard miles for angles >20 degrees will tear up these cvs pretty quickly. Makes a diff drop seem wise to stay under 20 degrees.

 

[Snacktime]

What do you think the allowable axial tolerances is in these cvs? Surely 0.25” for 1/2” on the axle?

Lower control arm cam adjusters maxed is less than 1/4" of gap between the balls and the snap ring stock. This is subjective and not directly measured. I was able to measure a 1/4" on my bronco and stock has to be less.

 

[87-Z28]

Are you going to stick with oem half shafts now that you have a diff drop?

Are the spicer extreme one
the same on inside geometry , so same angular limits? But have more splines for strength?

 

[mpeugeot]

There is really nothing here that is not already known by many of you with abundant experience. It is nonetheless interesting to plot all of this data on a single chart with increasingly accurate numbers and calculations. This helps others to understand and think about the data.

I have taken the data compiled by @Merc4x4 and added to the chart showing wheel motion wrt shock travel and CV angles. Ride heights are not included since that depends on springs chosen and vehicle weights. SAS, fox, and king data are accurate and all use the same reference points for measurements. Thanks to acutune. The ICON data is just notional until measurements can be verified. Thanks to all the info and input from others.

@Snacktime, @V1Rotate, @GreyZ, @TeocaliMG, @Tex and any others with interest. I would like to further refine this to increase accuracy so please take a critical look and provide feedback. I believe the geometry calculations for the CV and tie rod angles are accurate. errors are likely introduced from the length measurements, CV halfshaft and tie rod lengths from “knuckle to knuckle”. Those were measured on my truck. Within 1/4” at best, so possibly 10-15% errors. Those errors can get compounded so if someone has exact lengths, or parts on the bench to measure, this can be updated and improved.

I do believe the chart is fairly reasonable, especially since the +/- 18 degree CV angle limits from the OEM shop manual plot nicely with SAS shock travel. That is surely how ford would have designed it.

the SAS bump stop is also a guess and only notional. No idea how much that will compress so just assumed 2” from full compression as the limit case.

@TeocaliMG it is easy to see how much space there is at full compression between SAS OEM and the fox/king aftermarket shocks. It seems they were designed to keep the big wheels from the fenders during high speed severe shock compression, at the sacrifice of CV angles and tie rod angles (which affect steering rack).

just a note wrt bilstein 5100 and 6100/6112 shocks. They are same length as SAS with very similar shock travel. So they will plot similar to SAS shocks. Ride height will of course vary depending on springs/preload used and vehicle weight.

So quick question, what are the downsides to a 1" diff drop in the front? If I remember correctly, the M190 sits up pretty high (yes, I still have the M190 in there). Would one be at risk of binding at full compression?

Asking for a friend... LOL.

 

[userdude]

Hmm. One day we'll look back and wonder how portals solved all these problems and improved things to boot. Then we'll look at it and go, "well, I couldn't afford aerospace engineering in my rig", at least until Ford et al. worked out a way to include it factory (and Quinn gets his own movie). Then you'll say, the good ol' days. Back when geometry was important: With portals, we just take it for granted. Because of course we do will.

 

[87-Z28]

I will add the diff dop to the chart so it can be visualized. But essentially a 1” drop extends wheel 1” from frame. So if shock length is increased 0.66” (1.5 motion ratio) then original geometry is retained. If shock length is not increased then yes over extension in compression is possible Everything moves towards compression side. Pretty sure that is correct. I will run the numbers and update.

 

[Snacktime]

Are you going to stick with oem half shafts now that you have a diff drop?

Are the spicer extreme one
the same on inside geometry , so same angular limits? But have more splines for strength?

I plan on moving up to a M210 with factory CV axles. I dont think upgraded cv axles are worth if you blow out the center diff. I am not going to go spicer as you can go fully custom fabricated 9" for less.

So quick question, what are the downsides to a 1" diff drop in the front? If I remember correctly, the M190 sits up pretty high (yes, I still have the M190 in there). Would one be at risk of binding at full compression?

Asking for a friend... LOL.

The differential sits at the same spot on both the m190 and m210. First negative is you putting more force/leverage on the mounts. Second is the differential hangs lower.

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