I am at 66 wms -wms. With 40 inch tires. I don’t remember my wheel back spacing
Tube/Hybrid Stretched 40 Frame and Suspension Design - Advice/Comments?
- Thread starter DirtSniffer
- Start date
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“Stock” body correct? Not stretched or anything? Obviously wheel base is, but not the body?
yes stock.
Thank you. I thought so.
- Thread starter
- #85
Alright here is some of the updated logic I am using for my suspension design after some more research.
Front:
Running upper at ~75% the length of the lowers as opposed to nearly equal lengths as this will reduce pinion change and help maintain caster and steering more throughout the range of articulation. Equal length links will have me steering more on the front of the tires when drooped out, not ideal. Having longer lowers is also supposed to give better AS/AD numbers.
A note, allowing the front pinion to rotate more will give you a hair more wheel travel, but I am more concerned about the other considerations than squeezing out every bit of flex in the front.
I also have the top link on the diff side which has two advantages. One is that the pinion angle will only change when the diff side drops. The other is that the front driveshaft torque is trying to lift the drivers side, and having the top link on the same side as the panhard axle mount helps counteract this. Top link on passenger side is not always done due to packaging issues and interference with driveshafts. With my setup, it should work out pretty well.
Rear:
I am more concerned about having the pinion angle change throughout travel on the rear as the rear driveshaft is more exposed than the front due to rear links being longer and the lower frame mounts being higher. Having longer uppers will rotate the pinion up more under droop and help keep it more out of harm's way. Another advantage, as stated earlier, is the pinion change gives a hair more wheel travel.
On the topic of pinion angle, how much pinion angle is too much for a street rig at ride height? Concerns for pinion bearing oiling at high angle? I am looking at about 13* to point the pinion right at the transfer case output, which puts the bottom of the pinion flange 1.5” or so above the bottom of the lower link. This is important to me as I don't want to be worrying about going up ledges and hitting/dragging the pinion/driveshaft being below the lower links. I don't think this is too much angle as oil will get slung at the pinion by the ring gear no matter what angle it's at. But I could be wrong.
On a similar note, if I am running a rear CV driveshaft, I should be fine running a flat drive train vs tilting down to the rear ~3*? That would help lower the CG, assuming I have oil pan clearance.
Convergence - After reading through the bible and numbers threads I have confirmed that the 40* minimum is in fact a combination of the upper and lower convergence angles. So not so concerned about that anymore, I should have more than enough. Having less angle will also help with keeping the axle pointing in the right direction when the suspension is articulated (flex steer?). My bracket locations have moved because when I measured out my split case, I included the dumb 3” extension housing on the later H42 trans housing, so my drivetrain shortened up a bit. I also decided to stretch the wheelbase to 110”, so my rear links have gotten longer and now have less convergence. Still enough, though.
Areas I have questions on:
Antisquat/Antidive- My understanding is you want these values to increase with suspension compression in the front and decrease in the rear, but try to keep the curve as flat as you can.
As for AS/AD values, still a bit lost on what I should be shooting for. From my research, the 70-100% recommended values for my use type are based on the old calculator version assuming 100% rear drive bias. It looks to me that with the newer versions that now allows us to split drive bias, you want them closer to the drive bias of 50% and for each to try not exceed the brake bias (typically 60%), which can cause wheel hop. Also want antilift below 50%.
So by my understanding, I am shooting for ~50-60% AD/AS. Looks like the 1” up/down adjustment I can get with the brackets I have should have a decent affect on AS/AD to play around with, too.
Link instant centers- Used to determining AS/AD, but generally best to have the ICs extend past the link ends. How much? Not really sure. Don't think its too important.
Roll center- I believe you ideally want the front higher than the rear. A lower roll center will cause more body roll, but provide more warning for when you are approaching your rollover angle. Higher roll center will reduce body roll and therefore reduce need for sway bars as well as lean when off camber, but less warning when near the tip over point. What is a good RC height? Not sure, i know its personal preference, doesn't seem to be a whole lot that can be done to change other than raising/lowering axle top links, which will affect AS/AD.
Roll slope- want negative pitch, and relatively flat. (how flat?)
Roll axis- recommended slight positive understeer for street driving, but oversteer close to 0 is fine or even preferred for more go-fast stuff. I am at -0.8* oversteer right now.
Here is where I am at right now. I am going to see if I can try and straighten out the front AD curve some, but may not be all that necessary as it curves more on the decompression side.
Driveshaft seems to have plenty of clearance with the new link locations.
Ride height:
Full bump. I shifted the tube portion of the frame forward to make room for the lower link to move all the way up.
Full droop.
Front:
Running upper at ~75% the length of the lowers as opposed to nearly equal lengths as this will reduce pinion change and help maintain caster and steering more throughout the range of articulation. Equal length links will have me steering more on the front of the tires when drooped out, not ideal. Having longer lowers is also supposed to give better AS/AD numbers.
A note, allowing the front pinion to rotate more will give you a hair more wheel travel, but I am more concerned about the other considerations than squeezing out every bit of flex in the front.
I also have the top link on the diff side which has two advantages. One is that the pinion angle will only change when the diff side drops. The other is that the front driveshaft torque is trying to lift the drivers side, and having the top link on the same side as the panhard axle mount helps counteract this. Top link on passenger side is not always done due to packaging issues and interference with driveshafts. With my setup, it should work out pretty well.
Rear:
I am more concerned about having the pinion angle change throughout travel on the rear as the rear driveshaft is more exposed than the front due to rear links being longer and the lower frame mounts being higher. Having longer uppers will rotate the pinion up more under droop and help keep it more out of harm's way. Another advantage, as stated earlier, is the pinion change gives a hair more wheel travel.
On the topic of pinion angle, how much pinion angle is too much for a street rig at ride height? Concerns for pinion bearing oiling at high angle? I am looking at about 13* to point the pinion right at the transfer case output, which puts the bottom of the pinion flange 1.5” or so above the bottom of the lower link. This is important to me as I don't want to be worrying about going up ledges and hitting/dragging the pinion/driveshaft being below the lower links. I don't think this is too much angle as oil will get slung at the pinion by the ring gear no matter what angle it's at. But I could be wrong.
On a similar note, if I am running a rear CV driveshaft, I should be fine running a flat drive train vs tilting down to the rear ~3*? That would help lower the CG, assuming I have oil pan clearance.
Convergence - After reading through the bible and numbers threads I have confirmed that the 40* minimum is in fact a combination of the upper and lower convergence angles. So not so concerned about that anymore, I should have more than enough. Having less angle will also help with keeping the axle pointing in the right direction when the suspension is articulated (flex steer?). My bracket locations have moved because when I measured out my split case, I included the dumb 3” extension housing on the later H42 trans housing, so my drivetrain shortened up a bit. I also decided to stretch the wheelbase to 110”, so my rear links have gotten longer and now have less convergence. Still enough, though.
Areas I have questions on:
Antisquat/Antidive- My understanding is you want these values to increase with suspension compression in the front and decrease in the rear, but try to keep the curve as flat as you can.
As for AS/AD values, still a bit lost on what I should be shooting for. From my research, the 70-100% recommended values for my use type are based on the old calculator version assuming 100% rear drive bias. It looks to me that with the newer versions that now allows us to split drive bias, you want them closer to the drive bias of 50% and for each to try not exceed the brake bias (typically 60%), which can cause wheel hop. Also want antilift below 50%.
So by my understanding, I am shooting for ~50-60% AD/AS. Looks like the 1” up/down adjustment I can get with the brackets I have should have a decent affect on AS/AD to play around with, too.
Link instant centers- Used to determining AS/AD, but generally best to have the ICs extend past the link ends. How much? Not really sure. Don't think its too important.
Roll center- I believe you ideally want the front higher than the rear. A lower roll center will cause more body roll, but provide more warning for when you are approaching your rollover angle. Higher roll center will reduce body roll and therefore reduce need for sway bars as well as lean when off camber, but less warning when near the tip over point. What is a good RC height? Not sure, i know its personal preference, doesn't seem to be a whole lot that can be done to change other than raising/lowering axle top links, which will affect AS/AD.
Roll slope- want negative pitch, and relatively flat. (how flat?)
Roll axis- recommended slight positive understeer for street driving, but oversteer close to 0 is fine or even preferred for more go-fast stuff. I am at -0.8* oversteer right now.
Here is where I am at right now. I am going to see if I can try and straighten out the front AD curve some, but may not be all that necessary as it curves more on the decompression side.
Driveshaft seems to have plenty of clearance with the new link locations.
Ride height:
Full bump. I shifted the tube portion of the frame forward to make room for the lower link to move all the way up.
Full droop.
Last edited:
- Thread starter
- #86
Cross posted on the Irate numbers thread.
- Thread starter
- #87
Treefrog over on Irate responded and this was his recommendation an AS/AD values for me. Will be playing around with the calculator more.
"For your application, I would say probably 60-80% AS at 100% rear drive bias, so 30% to 40% with a 50% drive bias. Generally the front should be a bit lower. So about 25% to 35% with a brake bias of 60% front."
"For your application, I would say probably 60-80% AS at 100% rear drive bias, so 30% to 40% with a 50% drive bias. Generally the front should be a bit lower. So about 25% to 35% with a brake bias of 60% front."
Ditcherman
SILVER Star
I think we have real similiar goals with our trucks, and somewhat similiar trucks, I’m a bit longer, heavier, and maybe taller, but driving goals sound the same.
It will be interesting to me if, as you start packaging things in the real, if you have to make compromises; if you do, I would say keeping understeer slightly negative is the top priority. Roll centers have been about last in my list, and I have struggled with even knowing what to shoot for for AS/AD. It seems to me even Treefrog has undergone some evolution of where those numbers should be, trending lower all the time.
The latest version looks a lot different than 6.1 and I’m curious if it reports the As Ad numbers differently. I should load it and see.
You did start out by copying DN’s layout IIRC, and he commented in here he was happy how his drove, with some pretty low AS\AD numbers. That was good news to me, as I have been told I needed to get my numbers higher.
- Thread starter
- #89
Still making adjustments but took me a while to get my roll axis to understeer. Biggest things I had to do were narrow the rear lower frame mounts to 8" of horizontal separation and raise the panhard frame mount. I was also able to get the front roll center higher. I think I am ditching the front lower frame links I have in favor of another tube cross member and mounting to that for a flatter belly. Those brackets I have are more meant for a rear trailing arm, but could still work out for the front here.
I have noticed though that even small changes in my rear upper frame mounts makes a big difference in AS, so the adjustable bracket will be key when building for real.
Here's where I'm at right now.
For comparison's sake since you mentioned it, here are DJ's numbers in the new version. Graphs are laid out a bit different and values are slightly different I believe from the old one.
- Thread starter
- #90
By keeping understeer slightly negative, do you mean a slightly positive roll axis (understeer) or a slightly negative roll axis (slightly oversteer)?
Ditcherman
SILVER Star
Sorry that wasn’t clear.
Treefrog has said that better highway manners will be achieved with understeer, and others I have read have backed that up.
A serious go-fast dude might prefer oversteer. My understanding is that oversteer can be somewhere between uncomfortable and dangerous at highway speeds.
Getting things to fit with understeer was my main priority, then trying to balance the two ends and their as/ad’s.
- Thread starter
- #92
Understood. I think I'm getting to a close enough point in the suspension design that I can get the frame design nailed down now.
Ditcherman
SILVER Star
Not sure what you’re building, but 100”-110” I bet is a higher percentage of weight up front, the other thing I noticed is that in all but the rarest cases a 37” tire is more like 35.5-36, and there will deflection depending on pressure. If you want to see rock climbing parameters, your radius might need to come down.
Not sure that any of this really matters but when things get close they could.
Your rear links look short to me, have you played with lengthening them to see if that can help anything?
- Thread starter
- #94
As far as people telling you to get your numbers higher, that may be coming from people used to calculating AS/AD using 100% rear drive bias. We are calculating with 50/50 drive bias, which cuts the calculated AS/AD numbers in half. When I first looked up what values to shoot for, that is definitely what I was seeing as they were saying 70-100%.
- Thread starter
- #95
For the purpose of link position on the axle vs frame location on my model, I assumed no deformation. I know my actual Z values will sit a few inches lower with tire deformation like you say, but everything will come down together and geometry will stay the same.
You might be looking at DJ"s lowers, mine are over 10" longer than his. I think they are right about where I will want them in relation to the rear output. Might be able to lengthen the uppers a bit more.
Sitting at 110" now, I will have a spare tire off the back and going to try and squeeze a tank between the links. So hopefully not too front heavy but I might have to play around with the weight distribution.
Last edited:
- Thread starter
- #96
Updated numbers after making adjustments taking Treefrog's advice. Changing up a few link brackets, think I will add a second tube cross member for the front lower frame links. Makes for a nice flat belly, and lets me inboard them more for steering clearance. Front portion of the bottom skid plate will somehow tie into the body mount brackets at the front. Will be adjusting some parts of the frame now.
- Thread starter
- #97
Not exactly frame or suspension related, but I've got this cool latch that I'd like to use on the swingout and have been playing with how I want to do it. I will be finishing up the rear bumper and swingout before I start on the rest of the frame. Things are warming up around here, so should be dragging stuff out soon.
Method one is simpler, but I'd like to put something on this side of the swingout, possibly a metal storage box for recovery gear and it may be inconvenient to reach under for the latch.
Method 2 moves the latch to a convenient spot to grab and also allows me to mount it at an angle to suck the swingout up tight on the poly backing. Leaning towards this, but still playing around. I don't think it looks too ugly sticking out like that. But, maybe it does...
Another option I am considering is offsetting the swingout to push it out from the body more so I can fit a 4XInnovations lever latch. This is very tempting.
Method one is simpler, but I'd like to put something on this side of the swingout, possibly a metal storage box for recovery gear and it may be inconvenient to reach under for the latch.
Method 2 moves the latch to a convenient spot to grab and also allows me to mount it at an angle to suck the swingout up tight on the poly backing. Leaning towards this, but still playing around. I don't think it looks too ugly sticking out like that. But, maybe it does...
Another option I am considering is offsetting the swingout to push it out from the body more so I can fit a 4XInnovations lever latch. This is very tempting.
Ditcherman
SILVER Star
Love the looks of that German latch, but is the hook cast? Just wondering if it would need to be welded as cast, with preheating, etc.
The 4x hook looks interesting too.
The 4x hook looks interesting too.
- Thread starter
- #99
It's intended to be welded and I believe it is forged but haven't looked that closely at it. I haven't welded cast before so would need to take that into consideration. However, I was thinking about it more and I think that lever latch would be a great fit and not too difficult to make work. The pedestals/brackets to make a typical latch work just aren't that visually appealing. Waiting to hear back from them, they have 2 different striker height variants and I wanted some more info.
Ditcherman
SILVER Star
Many many moons ago I built a swing away for my Tundra. This latch setup has worked great. The swing away comes off when it goes back to work truck status, and the latch stays with the swing away, not the bumper.
Just made think that if you turned your latch around it might be cleaner.
Just made think that if you turned your latch around it might be cleaner.
