I'd be shooting for under 2 degrees of roll steer. 8 is pretty sketchy.
Decided to Be More Off-road Serious with the FJ40 (2 Viewers)
- Thread starter NikP
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
I'd be shooting for under 2 degrees of roll steer. 8 is pretty sketchy.
Cycling the suspension to max drop and max stuff on each side while watching the drag link ends to see if they are being pushed past their maximum angle.
Alot of times when building a link set up people find the suspension will travel more than the drag link will tolerate, hence full hydro steering. Same condition exists with drive line joints, often times the driveline will bind due to the increased travel of the link set up and will need different ends to accommodate the increased travel.
Alot of times when building a link set up people find the suspension will travel more than the drag link will tolerate, hence full hydro steering. Same condition exists with drive line joints, often times the driveline will bind due to the increased travel of the link set up and will need different ends to accommodate the increased travel.
Mike Shull
Let’s go…
Have you experimented in the calculator with moving your upper link upwards on your rear axle? Your anti-squat figures seem pretty low and I would wonder if more movement under suspension load (I.e: acceleration, braking, or load transfer like you might get in the corners) would amplify your roll steer issue. I’ve been advised to make my upper links horizontal. It might be hard to get your lower link to a horizontal position and that could push your instant center way out in front of your vehicle. One of the folks here could perhaps explain the risks of having the instant center too far in front of the vehicle?
I have not driven my truck yet with my current setup but some of the folks on your thread steered me towards doing a dual triangulated 4-link in the rear and my configuration has -4* of roll steer and I have between 88% and 93% of anti-squat (travel vs static).
Good luck with this. I’ll be staying tuned. Can you post a few pictures of the current configuration?
P.s. Moab will give you the bug every time
- Thread starter
- #24
I have played around with the calculator. I am assuming the number I'm trying to improve is the Roll Axis Angle. I'd love some input if that should be my focus. The biggest influencer for that number seems to be the lower link height from ground. If I simply do nothing more than lower the frame mount point by 4 inches my Roll Axis Angle goes from 8 degrees to 1 degree. I'd like someone to support this theory before I burn the existing mount off and lower it. Lowering it causes a drag point but I'm not sure I'm too worried about it.Have you experimented in the calculator with moving your upper link upwards on your rear axle? Your anti-squat figures seem pretty low and I would wonder if more movement under suspension load (I.e: acceleration, braking, or load transfer like you might get in the corners) would amplify your roll steer issue. I’ve been advised to make my upper links horizontal. It might be hard to get your lower link to a horizontal position and that could push your instant center way out in front of your vehicle. One of the folks here could perhaps explain the risks of having the instant center too far in front of the vehicle?
Playing with the upper link variables don't seem to change Roll Axis Angle. My friend said to keep upper link horizontal but I don't see how that plays into my issue here. The more I read, the lower seems to be the key to my rear steer sensation (at least my novice study suggests that and I wish someone could help me understand the correlations here).
I don't have room to bring the lower links into a more double triangulated orientation. I also played with making my lower links 10-12 inches longer but leaving at the same height from ground and it buys me a 2 degree improvement in Roll Axis Angle but makes my anti-squat number go from -7% to -58%.
I just did a 4 link in the rear of my 40 this winter. Have only put 50 miles on it so far. And I ran into similar problems that you are stating. And you are on the correct track. I had to raise the lower link on the axle and lower the lower link on the frame to correct the roll axis. From what I was told negative is ideal, but only a little negative. I ended up at -1 I believe.
And ofcourse, by raising the lower link at the axle, I had to raise the upper link on the axle.... to keep adequate spacing. There is not a ton of room under these things, so, it is a give and take, at least that is what I learned... Hope this helps.
And ofcourse, by raising the lower link at the axle, I had to raise the upper link on the axle.... to keep adequate spacing. There is not a ton of room under these things, so, it is a give and take, at least that is what I learned... Hope this helps.
Last edited:
Vertical frame seperation is key for roll axis angle with some added imput from the triangulation as well.
Its been a really long time since I've dived into all the variables. From what I recall roll axis is determined from a combination of intersecting lines when looking at the plan view intersection of the links, the convergence point of the upper and lower links forward of the rear axle in profile view, and a couple of other points in profile view. Triangulation of your links plays a big role in roll steer, not simply the separation of the links in a profile view. If you want to dig into it, you can deep dive any posts made by member "Triaged" on Pirate4x4. He was the developer of the excel spreadsheet you are using.
New Version of my 4-link Analyzer & Request for Help
Easy for me to say on the other end of the keyboard, but I would not be dropping my frame end mounts 4" on my lowers to solve this problem. There is a better way to do it, it's just going to take a lot of time iterating on different geometries on the excel spreadsheet to get to a happy point.
Last edited:
Mike Shull
Let’s go…
Here is another resource on anti-squat. 4-Link Suspension Guide | Anti -Squat, Anti-Dirve, and Roll Center Explained - https://www.crawlpedia.com/4_link_suspension.htm
You are right, this won’t fix your problem. Set your anti-squat dependent on your driving style. I wouldn’t want low anti-squat figures for rock crawling as it could cause wheel hop and reduced traction at low speeds, but it might be good for high speed desert running. I was making the connection above that you might want to look at this while you are in there as the geometry might impact a number of factors.
The more your vehicle is susceptible to squatting, the more likely that it will amplify a high roll steer situation. It’s a balloon. You squish one side and the other side balloons. Dial them in together as close as you can with the tight space that you have.
You are right, this won’t fix your problem. Set your anti-squat dependent on your driving style. I wouldn’t want low anti-squat figures for rock crawling as it could cause wheel hop and reduced traction at low speeds, but it might be good for high speed desert running. I was making the connection above that you might want to look at this while you are in there as the geometry might impact a number of factors.
The more your vehicle is susceptible to squatting, the more likely that it will amplify a high roll steer situation. It’s a balloon. You squish one side and the other side balloons. Dial them in together as close as you can with the tight space that you have.
- Thread starter
- #29
It's been some time but I thought an update is warranted. I played with the calculator to determine two possible actions to take. I could move the upper link mounts inward which created more of a double triangulated solution. I also experimented with lengthening the lower link arms with the calculator. This option couldn't get me all the way there with regard to roll axis numbers. I also found that practicality dictated that it wasn't possible with the location of the transferase and rear driveshaft.
Action two in the calculator was to drop the front link mount to make the links more parallel to the ground. The calculator suggested dropping the front 4 inches and raising the axle-side mount 1 inch would result in a 0-roll axis number.
I didn't want link mounts dropped 4 inches below the frame so I took a combination of these two options. I moved the frame end of the lower links inward as far as I could without having issues with the transfer/driveshaft. I was able to move each mount about 4 inches inward. I also dropped the mounts 1 inch. According to the calculator I went from a roll axis value of 8 to 1.
This resulted in a highway drivable vehicle that can take corners with causing my to clean my pants.
Action two in the calculator was to drop the front link mount to make the links more parallel to the ground. The calculator suggested dropping the front 4 inches and raising the axle-side mount 1 inch would result in a 0-roll axis number.
I didn't want link mounts dropped 4 inches below the frame so I took a combination of these two options. I moved the frame end of the lower links inward as far as I could without having issues with the transfer/driveshaft. I was able to move each mount about 4 inches inward. I also dropped the mounts 1 inch. According to the calculator I went from a roll axis value of 8 to 1.
This resulted in a highway drivable vehicle that can take corners with causing my to clean my pants.
Thats rad! Pics? Do you still want an anti-roll bar, or is it sufficient with just the geometry changes?
Mike Shull
Let’s go…
Pictures would be awesome, and your rough estimates of your final geometry calculations.
dam i wish i would saw this thread earlier.
-couple things that may help or may not. but coil spring rates are very simple to calc. Wide open desigh=n made a you tube that explaines it super easy. no scale needed or anything. i will link it.
How to Calculate Spring Rate for Coilover Shocks Video - https://www.wideopendesign.com/blog/calculating-spring-rates-video
- seems like everything is a compromise. when i did mine i cut this and cut that. it was head scratching all the way. there is a new version of that calc on IRATE4x4.com. it has everything in it. including drive shaft travel distance. you do both wheels at one time. this is mine in 6.7, there is a newer one out there yet. you maybe able to put it in here and see what will happen. not trying to high jack or anything.
-couple things that may help or may not. but coil spring rates are very simple to calc. Wide open desigh=n made a you tube that explaines it super easy. no scale needed or anything. i will link it.
How to Calculate Spring Rate for Coilover Shocks Video - https://www.wideopendesign.com/blog/calculating-spring-rates-video
- seems like everything is a compromise. when i did mine i cut this and cut that. it was head scratching all the way. there is a new version of that calc on IRATE4x4.com. it has everything in it. including drive shaft travel distance. you do both wheels at one time. this is mine in 6.7, there is a newer one out there yet. you maybe able to put it in here and see what will happen. not trying to high jack or anything.
- Thread starter
- #33
Sorry for not posing sooner. Life gets in the way sometimes.
Here's my link calculator result afterwards for reference.
Here's my link calculator result afterwards for reference.
- Thread starter
- #34
Also a few pictures. I ended up installing an anti sway bar in the rear from a FJ55. I did this before I started repositioning the lower mounts. It help with body roll but didn't do anything for the tendency for the rear to steer in corners. It's a strange sensation to steer into a left-hand corner and then have to counter-steer about midway through the turn. The counter steer was not just a minor adjustment, it was enough to cause you to change underwear.
In this pictures you can see the link mount relocated to the bottom of the upper link mount. The Barnes 4x4 upper link mount stuck down below the frame so it allowed me to drop about 1 inch and bring the links inward. I could have probably gone further inward but I didn't want to re-do my axle mount. The original lower link mount was welded under the frame rail.
Her you can see the tubing which replaced the tubular frame cross-member. I to mount the sway bar I dropped it down with blocking my exhaust to clear. It's all packed in there nice and tight with no contact a full-droop.
In this pictures you can see the link mount relocated to the bottom of the upper link mount. The Barnes 4x4 upper link mount stuck down below the frame so it allowed me to drop about 1 inch and bring the links inward. I could have probably gone further inward but I didn't want to re-do my axle mount. The original lower link mount was welded under the frame rail.
Her you can see the tubing which replaced the tubular frame cross-member. I to mount the sway bar I dropped it down with blocking my exhaust to clear. It's all packed in there nice and tight with no contact a full-droop.
- Thread starter
- #35
I'm not sure I mentioned along the way, I decided to go with TRE4x4 air lockers. I saved $1500 or more vs. the ARB lockers. I know there's a lot of debate about the "cheap Chinese ARB" locker but I go into this after studying it. I know my driving style will not even come close to finding the upper limits of the locker. I'll winch before I tear up my gear and push the edge. All-in-all the TRE locker install was painless for the front. All went well and the instructions are a plagiarized from the ARB locker (even with the same pictures).
The rear lock was a pain. First the instructions call for the use of "enclosed" c-clips. There weren't any included. Secondly the spider block configuration in the kit was not the proper spider block for this Toyota Axle. TRE China said I should be able to use stock c-clips but they were wrong. I could not get the spider block into position with stock clips.
After 6-weeks of emails back and forth, they finally sent me three things that allowed me to install the locker. First, you do need a c-clip pack of various thickness c-clips. Secondly, the driver side spider gear was recessed differently than the left and they sent me a set of new spider gears from which I swapped out the driver's side to recess the c-clip far enough. Third, they send me a proper spider block which now fits between the axle shafts. (this picture shows the original spider block which doesn't work).
All good now.
The rear lock was a pain. First the instructions call for the use of "enclosed" c-clips. There weren't any included. Secondly the spider block configuration in the kit was not the proper spider block for this Toyota Axle. TRE China said I should be able to use stock c-clips but they were wrong. I could not get the spider block into position with stock clips.
After 6-weeks of emails back and forth, they finally sent me three things that allowed me to install the locker. First, you do need a c-clip pack of various thickness c-clips. Secondly, the driver side spider gear was recessed differently than the left and they sent me a set of new spider gears from which I swapped out the driver's side to recess the c-clip far enough. Third, they send me a proper spider block which now fits between the axle shafts. (this picture shows the original spider block which doesn't work).
All good now.
Last edited:
- Thread starter
- #36
Installed the Orion 4:1 transfer case, new flywheel and Centerforce clutch. What a game changer for crawling the rocks in Farmington NM.
Make sure you loctite the inner mounting bolts. Don’t ask why I know this…
Similar threads
