How's my numbers?

[Treefrog]

This is an amazing resource. Thank you Treefrog

I am looking for some help with a a rear 4-link on a silverado build. Building the IFS so only concerned about the rear now. Intent is for a general purpose trail wheeler type build- boogey through the desert but also compliant on any technical trails I can smash this pig through. It's backhalfed so not too many constraints for the links.

Any input is much appreciated. TIA

Your mass and CG seem to be quite a bit off from what would be expected for the tire and vehicle size.

Am I correct in assuming that you are planning on running trailing arms? If so you will want whichever links that the shocks are mounted to to be more parallel.

 

[mclean.fab]

Your mass and CG seem to be quite a bit off from what would be expected for the tire and vehicle size.

Am I correct in assuming that you are planning on running trailing arms? If so you will want whichever links that the shocks are mounted to to be more parallel.

Thank you for your help!

Understandable on the weight. This is a stripped down single cab so about a light as you can get one of these. I scaled it at 4151 while it was still a rolling chassis, then stripped a bunch more weigh off before starting to add tube, shocks, 40s, etc... I can scale it again before final welding and rerun the numbers.

Looks like I missed the CG. It's about 36" off the top bolt of the bellhousing. It's definitely low for a silverado, potentially too low @ ~17" belly height

Correct on trailing arms. I can definitely get them more, or completely parallel. My hope was to tuck the frame side mounts flush with the belly, but I can outbord them on the frame rails too. Or inboard them on the axle side? I can play those scenarios in the calculator a bit more. Is there a factor should I be looking to improve with increased parallelism?

Fixed CG and got the lowers a bit more parallel:

 

[Treefrog]

Thank you for your help!

Understandable on the weight. This is a stripped down single cab so about a light as you can get one of these. I scaled it at 4151 while it was still a rolling chassis, then stripped a bunch more weigh off before starting to add tube, shocks, 40s, etc... I can scale it again before final welding and rerun the numbers.

Looks like I missed the CG. It's about 36" off the top bolt of the bellhousing. It's definitely low for a silverado, potentially too low @ ~17" belly height

Correct on trailing arms. I can definitely get them more, or completely parallel. My hope was to tuck the frame side mounts flush with the belly, but I can outbord them on the frame rails too. Or inboard them on the axle side? I can play those scenarios in the calculator a bit more. Is there a factor should I be looking to improve with increased parallelism?

Fixed CG and got the lowers a bit more parallel:

I would guess that it will end up closer to and most likely over 5000.

It may be better to have some slight angle to the trailing arms such that the links do not cross past vertical at full flex. Generally, the more outboard the trailing arms the better. It provides roll stability and roll damping.

As for the numbers, for a rig that is expecting to go fast in the desert, you should try to get the antisqaut down. With the current drive biases you have, you should be aiming for low 10s. Easiest way to do this will be to raise the uppers at the frame. The other numbers look okay.

 

[mclean.fab]

I would guess that it will end up closer to and most likely over 5000.

It may be better to have some slight angle to the trailing arms such that the links do not cross past vertical at full flex. Generally, the more outboard the trailing arms the better. It provides roll stability and roll damping.

As for the numbers, for a rig that is expecting to go fast in the desert, you should try to get the antisqaut down. With the current drive biases you have, you should be aiming for low 10s. Easiest way to do this will be to raise the uppers at the frame. The other numbers look okay.

Thanks for your feedback & recommendations. Pardon my ingorance, but I thought go fast suspension was typically recommended to be 100%+ antisquat? (which also seems to yield absurd link angles) Am I missing something?

 

[Treefrog]

Thanks for your feedback & recommendations. Pardon my ingorance, but I thought go fast suspension was typically recommended to be 100%+ antisquat? (which also seems to yield absurd link angles) Am I missing something?

Just about the exact opposite, go fast tends to be the lowest of all offroad. Though I don't know the current state of the art geometry, historically they put the IC 2-3 times the wheelbase in front of the vehicle.

 

[06h3]

Where is strictly rock crawling at now? Treefrog

 

[Treefrog]

Where is strictly rock crawling at now? Treefrog

I could not tell you for certain. I believe the trend is 30% - 50% or maybe less with 100% rear bias. I wish some of the moon buggy builders would share. The water in the tires can make anti calcs weird.

 

[ash]

Anything unique needed to input a 'wishbone' style rear upper link with a single pivot at the axle? Do I just set the horizontal separation to zero?

 

[Treefrog]

Anything unique needed to input a 'wishbone' style rear upper link with a single pivot at the axle? Do I just set the horizontal separation to zero?

Nothing unique. Yes, set y to 0

 

[06h3]

2 questions, under 100% for anti lift sucks the front end down on throttle in the front?

Roll center and roll axis do not change the actual tipping point of a rig it just has more body roll? Ill caveat that with, in theory, if the body has a ton of body roll, it can roll over sooner due to weight transfer.

For example, if you SLOWLY raise one side of the vehicle up to the tipping point with a high roll center and then do it again with a low roll center they will tip at the same point but if you do it quickly, the one with a lower roll center could happen sooner due to the quick weight transfer flinging the body from side to side, if that makes sense?

 

[Treefrog]

2 questions, under 100% for anti lift sucks the front end down on throttle in the front?

Not quite. Front anti lift is a prediction of how much the front resists lifting. 0% is no resistance. 100% means that it does not lift or suck. Over 100%, it sucks down.

Roll center and roll axis do not change the actual tipping point of a rig it just has more body roll? Ill caveat that with, in theory, if the body has a ton of body roll, it can roll over sooner due to weight transfer.

For example, if you SLOWLY raise one side of the vehicle up to the tipping point with a high roll center and then do it again with a low roll center they will tip at the same point but if you do it quickly, the one with a lower roll center could happen sooner due to the quick weight transfer flinging the body from side to side, if that makes sense?

I'll use two scenarios as to answers.
Two rigs, same CGs and width. One has a high RC, the other a low RC.

Scenario 1: Load bearing shocks/springs replaced with a solid link. Both rigs will tip at the same time. That time is when the CG is no longer over the tires.

Scenario 2: We have springs and the rig can lean. As we raise one side, the CG will lean down hill. The vehicle with the higher resistance to body roll will lean over less. The higher roll center rig is expected to have a higher resistance, and is expected to require a slightly steeper slope to roll.

Scenario 1 is the fast raise. The shock forces resist body roll. Scenario 2 is the slow raise, we are moving slow enough that the shocks do not dampen the body leaning.

 

[YeeP]

Not quite. Front anti lift is a prediction of how much the front resists lifting. 0% is no resistance. 100% means that it does not lift or suck. Over 100%, it sucks down.

THIS! This is something to remember for all "anti" measurements. Thank you for wording it this way.

 

[Treefrog]

THIS! This is something to remember for all "anti" measurements. Thank you for wording it this way.

The prediction part of that is probably the most important part. And I'm not exactly sure that antis are a good prediction anymore following some discussion in the linked suspension bible thread.

 

[busteddodge]

I posted in the general forum before I saw this thread. Thanks for any feedback you guys can give.

I'll be doing some East Coast trail riding and slow crawling. No rock bouncing or racing. I've read quite a bit, but never built a suspension like this before. When I read, it's hard to tell what the advice I'm reading about is for, be it full throttle hill climbs, or desert racing, etc.

What I'm building is a 120" wheel base tube chassis four seater that will eventually be on 42's. Chrysler 440, np435, np241. 14BFF, kingpin 60 with 4:56's. Goat Built Ibex style chassis.

Targeting a 22" belly height, but I'm open to advice on that. I'm trying to keep an eye on COG, of course.

I'm particularly interested in hearing what you guys think about the link geometry and anti-squat numbers. Thanks in advance.

 

[Treefrog]

I posted in the general forum before I saw this thread. Thanks for any feedback you guys can give.

I'll be doing some East Coast trail riding and slow crawling. No rock bouncing or racing. I've read quite a bit, but never built a suspension like this before. When I read, it's hard to tell what the advice I'm reading about is for, be it full throttle hill climbs, or desert racing, etc.

What I'm building is a 120" wheel base tube chassis four seater that will eventually be on 42's. Chrysler 440, np435, np241. 14BFF, kingpin 60 with 4:56's. Goat Built Ibex style chassis.

Targeting a 22" belly height, but I'm open to advice on that. I'm trying to keep an eye on COG, of course.

I'm particularly interested in hearing what you guys think about the link geometry and anti-squat numbers. Thanks in advance.

Your rear antis are higher than recommended for a crawler, especially as the suspension extends. It may be worth double checking all of the weights and the CG. Watch out for clearance with the links as you turn the wheels.

 

[06h3]

I agree. CG seems low

 

[busteddodge]

Thanks a ton for the feedback guys.

I took some advice and made some changes.

COG is up 6 inches.
Front lower links are pulled in to clear the tires when turning. I'm not sure how much they need to be moved, actually. This is a guess.
Changed the uptravel to 8" up and 10" down. I'll probably limit it to 8" down with a strap if the pinion angle doesn't work out.
Moved the upper and lower links to get a little lower anti-squat number in the rear. The lower link is slightly angled up to my desired belly height of 22". Upper goes down towards the chassis a bit. I'll make the link mounts adjustable up or down by 4" either way.

How's this look? Any thoughts on the roll center?

 

[Treefrog]

Thanks a ton for the feedback guys.

I took some advice and made some changes.

COG is up 6 inches.
Front lower links are pulled in to clear the tires when turning. I'm not sure how much they need to be moved, actually. This is a guess.
Changed the uptravel to 8" up and 10" down. I'll probably limit it to 8" down with a strap if the pinion angle doesn't work out.
Moved the upper and lower links to get a little lower anti-squat number in the rear. The lower link is slightly angled up to my desired belly height of 22". Upper goes down towards the chassis a bit. I'll make the link mounts adjustable up or down by 4" either way.

How's this look? Any thoughts on the roll center?

I would recommend raising the rear upper frame slightly to get the anti's down in travel, or move the axle end up slightly.

You may need to move the front lowers towards the centerline to clear the tire, but it is hard to tell.

The roll centers are probably about as low as you will be able to get them with what your building. Nothing to worrying for a crawler.

 

[endless CJ]

Hi Guys,

I am rebuilding my CJ7 for the fourth or fifth time in 30 years, this time with a new TDK frame and Aluminum body. Last rebuild introduced a 5.3LS, which tends to wrap leaf springs up like pretzels. I'm looking to keep it fairly streetable, with a trip out to Moab thrown in every couple years... Unfortunately, i am East Coast near DC, so most of the time this thing sees pavement. The numbers below are where everything is currently tacked in place at and measured, Before i started burning everything in, i wanted to check in on this thread for a sanity check...

thanks!

 

[Treefrog]

Hi Guys,

I am rebuilding my CJ7 for the fourth or fifth time in 30 years, this time with a new TDK frame and Aluminum body. Last rebuild introduced a 5.3LS, which tends to wrap leaf springs up like pretzels. I'm looking to keep it fairly streetable, with a trip out to Moab thrown in every couple years... Unfortunately, i am East Coast near DC, so most of the time this thing sees pavement. The numbers below are where everything is currently tacked in place at and measured, Before i started burning everything in, i wanted to check in on this thread for a sanity check...

thanks!

Looks reasonable for the use case. One recommendation would be to aim for below 60% anti-squat, or 100% with the drive bias set to 100% rear tires. Another recommendation would be to try to get understeer in the rear as well.

 

[endless CJ]

Looks reasonable for the use case. One recommendation would be to aim for below 60% anti-squat, or 100% with the drive bias set to 100% rear tires. Another recommendation would be to try to get understeer in the rear as well.

thanks, I agree on the understeer goal, but have not found which part of the geometry to alter to affect that number. I have read numerous posts and articles saying what roll under/oversteer is, but not what geometry will change it, unlike AS which is more documented and was easy enough to change, i have it at 65% now, i had forgotten this version of the calculator has drive bias...

 

[cagcig]

Where do I find the download link? I keep going around in circles from link to link. But I can’t find the one to put in the numbers.

 

[RustyC]

Where do I find the download link? I keep going around in circles from link to link. But I can’t find the one to put in the numbers.

 

[Home_brewd]

Where do I find the download link? I keep going around in circles from link to link. But I can’t find the one to put in the numbers.

I did the same thing. I kept missing the Download icon on the top right of the 4 link calculator thread.

 

[Treefrog]

thanks, I agree on the understeer goal, but have not found which part of the geometry to alter to affect that number. I have read numerous posts and articles saying what roll under/oversteer is, but not what geometry will change it, unlike AS which is more documented and was easy enough to change, i have it at 65% now, i had forgotten this version of the calculator has drive bias...

If you have settled on the side view geometry, you will need to change the Y values. Turning the axle convergence lines back on will show the points that control the role axis.

 

[cagcig]

Is there a secret to downloading this? I can’t seem to get this to download on either of my two computers. We have tried excel and sheets.

 

[Treefrog]

Is there a secret to downloading this? I can’t seem to get this to download on either of my two computers. We have tried excel and sheets.

Resources Tab
Calculators on the left
4 Link Calculator
Download in the upper right

If downloads doesn't work

History tab
download the newest version

 

[cagcig]

Ok, got something to load. Never mind the mm I put it in as inches. How’s my numbers?

 

[EVolveRacing]

Good afternoon working on the new chassis for the race truck. Haven't played with this since back in the pirate days early versions. Just curious how my numbers look and am I doing something wrong why I'm not getting data. Thank you Keith with Evolve Racing

 

[Treefrog]

Ok, got something to load. Never mind the mm I put it in as inches. How’s my numbers?

The numbers don't look to bad. But the rear frame lower is extremely high. I don't entirely believe the anti values for the rear. The links are also pretty narrow.