SN95 RinerAutomotive's CAM-T Mustang Build Thread Profile - SN95 Mustangs

[Dave_W]

Saw this on another forum that I thought was interesting:

Believing the first part of that probably won't get you into trouble. But the second part is completely wrong, and suffers from the common fallacy that no body roll means no weight transfer (among other issues).

The amount of lateral weight/load transfer in a corner is a function of the lateral g-load, the CG height, and the track width. That's it. The roll center location does not affect the total amount of load/weight transfer. What the RC location does do is influence how much of the total load transfer goes through the suspension links directly (geometric transfer) versus how much goes through the springs, ARBs, and shocks (elastic transfer). If the RC and CG are at the same place, all the load transfer is geometric and none is elastic. There is no body roll because no load transfer happens through the springs, ARBs, and shocks - but there is load transfer, it's going through the suspenion links/arms. As the RC moves away from the CG, some of the load transfer changes from geometric to elastic, and body roll occurs.

Also note that geometric load transfer happens instantly, while elastic load transfer is slowed or "timed" by roll stiffness and shock valving - the initial energy of the load transfer is absorbed by the springs & ARBs until the suspension reaches steady-state, and shock valving changes how long it takes to get to steady-state (wavy-hands simplification happening here).

As the RC moves up from ground level, a portion of the lateral load transfer of the sprung mass starts to become a vertical force at the contact patch. This is sometimes referred to as "jacking force" and can reduce grip. Also, higher RC tends to introduce lateral tire scrub with lateral g-loading, which can create increased tire wear and dynamic toe change.

This does a good job explaining the force components -

Tech Explained: Roll Centre

racecar-engineering.telegraph.co.uk

I got a lot of "aha" moments when I first read this; read through all the pages (original site is gone) -

Dynamic Load Transfer

How weight (or load transfer) affects handling of a racing car, and terms used to describe load transfer

web.archive.org

 

[RinerAuto]

I was just reading about jacking forces in this article:
https://www.theautopian.com/our-sus...a-huge-effect-on-ride-handling-and-body-roll/

I'll read the links you posted as well. But definitely has me rethinking moving the control arms. I foresee more reading in my future

What I think I understand is the higher the angle of the roll center line (ie height of instant center) the higher the jacking force may be. So in my changed suspension screenshots above the instant centers were all higher than current, so jacking is likely worse. How much worse? I don't know at the moment. That's a lot of force calculations that I don't have all the numbers for.

 

[RinerAuto]

All this talk about suspension changes, I forgot to talk about my last event and one of the reasons I'm looking at the suspension.

This autocross was the first one at a reopened facility. This circle track closed more than 10 years ago. Some drifters recently purchased it and completely paved the infield. The circle track angle is steep, I think I heard 18 degrees (put not positive on that). There were a couple sections that transitioned between the flat and banking.

After my first run I was sitting at the top of the charts. The circle track has really good grip and its old asphalt. The newly paved infield had absolutely no grip. My second run was faster but dirty with 2 cones. On my third run after the first turn the car was feeling a little off, but I continued on. By the end I knew something was wrong with the right front suspension and limped across the finish line. Turns out I snapped the solid rod end that connects the LCA to the rear suspension tube. That tube mainly controls the front to back movement of the LCA so without it my caster was all over the place.

During previous events I had recorded video of the front suspension and noticed twisting of the LCA occurring due to the sway bar. This twisting puts a bending into that solid rod end. Which rod ends are not suited for bending forces. I knew it was something I needed to look into but that would be a redesign of the sway bar, so I put that off till the off season. I think this track and course layout exaggerated that issue and watching other cars on course that turn and transition was rough on everyone's front passenger side. But I'm the only one with a custom built suspension.

Some positives, only I was running this event so I didn't compromise Ashley's event. The car was able to drive off course and onto the trailer. I always trailer cause you never know what might happen, plus the truck is way comfier than the car. Lastly, my first run was surprisingly really good and kept me 9th in raw (46 cars), 8th in PAX, and 1st in class (3 cars).

 

[RinerAuto]

As for fixing the suspension, for now I am going to just replace the broken part to keep the season going. The rod ends were from Howe Racing, so I think a good reputable company. But I changed them to ones from QA1 as they are slightly beefier. I have ones from FK Rod Ends but it's body is too large to fit into my LCA without redesign.

As for the sway bar causing the twisting in the LCA. I use a stock style sway bar due to cost and time. I ran out of time to design in a new style like a spline rod and was trying to keep initial build cost down. The goal was always to upgrade, but it's going to wait until next off season. I want to install a spline rod style sway bar that attaches to the LCA centerline. This should eliminate the twisting that is occurring.

 

[Dave_W]

I agree that the rod end failed on that "stabilizer bar" from a bending load on it. With it being a solid rod end, instead of a swivel, and being solidly mounted in double shear between the ears on the main control arm, when the sway bar load rotates the main control arm the stabilizer bar rod end is seeing a lot of bending load, which it's not designed for.

Is that the first time you've seen the tire hit the fender above the flare? Putting the left side of the car into that banking transition while in a right-hand turn put a lot of load on the outside wheel, causing it to hit the fender. Hitting the fender means it overpowered the spring and sway bar to get to the fender. The sway bar transferred some of that force to the right side, and probably twisted the control arm more than it ever had been previously. So that rod end saw the highest bending force it ever had. But it may have already been weakened from the control arm twisting that you saw with the GoPro. Check the rod end on driver's side for signs of fatigue.

Take a look at this article, you may want to do something like this on the rod ends every few events. https://grassrootsmotorsports.com/articles/testing-cracks-home-diy-dye-penetrants/

I wonder if adding some taller/stiffer bump stops might help as well, both to make sure to keep the tire from getting driven into the fender, and to reduce the amount of force the sway bar is transmitting in roll (by reducing the suspension travel). The downside is if you start hitting the bumpstops too much in normal driving, you'll get instant understeer if they're stiff. Sometimes you can use longer, softer bumpstops to have a more radual effect instead of a harsh limit, acting like a progressive spring.

 

[stevbd]

Believing the first part of that probably won't get you into trouble. But the second part is completely wrong, and suffers from the common fallacy that no body roll means no weight transfer (among other issues).

The amount of lateral weight/load transfer in a corner is a function of the lateral g-load, the CG height, and the track width. That's it. The roll center location does not affect the total amount of load/weight transfer.

@Dave_W With apologies for maybe being hyper-technical, I just want to be clear: Although the TOTAL vehicle weight transfer is only a function of the three factors you describe, the roll center location (among other things) does affect the total amount of weight transfer on that end of the car relative to the other end. Although you can't change the total load transfer with things like roll center, sway bars, and spring rates, you can definitely tune the distribution of that load transfer between front vs rear and thus find more total grip. I don't think you're saying any different but I just want to be sure I have this right, thanks!

 

[Dave_W]

you can definitely tune the distribution of that load transfer between front vs rear and thus find more total grip. I don't think you're saying any different but I just want to be sure I have this right, thanks!

Yes, you're correct, I was simplifying to one axle. Tuning handling balance is all about the roll stiffness of each end of the car compared to how much the body wants to roll at that that end of the car (RC to CG), and matching (or mismatching) the difference of that between each end.

 

[RinerAuto]

I agree that the rod end failed on that "stabilizer bar" from a bending load on it. With it being a solid rod end, instead of a swivel, and being solidly mounted in double shear between the ears on the main control arm, when the sway bar load rotates the main control arm the stabilizer bar rod end is seeing a lot of bending load, which it's not designed for.

Is that the first time you've seen the tire hit the fender above the flare? Putting the left side of the car into that banking transition while in a right-hand turn put a lot of load on the outside wheel, causing it to hit the fender. Hitting the fender means it overpowered the spring and sway bar to get to the fender. The sway bar transferred some of that force to the right side, and probably twisted the control arm more than it ever had been previously. So that rod end saw the highest bending force it ever had. But it may have already been weakened from the control arm twisting that you saw with the GoPro. Check the rod end on driver's side for signs of fatigue.

Take a look at this article, you may want to do something like this on the rod ends every few events. https://grassrootsmotorsports.com/articles/testing-cracks-home-diy-dye-penetrants/

I wonder if adding some taller/stiffer bump stops might help as well, both to make sure to keep the tire from getting driven into the fender, and to reduce the amount of force the sway bar is transmitting in roll (by reducing the suspension travel). The downside is if you start hitting the bumpstops too much in normal driving, you'll get instant understeer if they're stiff. Sometimes you can use longer, softer bumpstops to have a more radual effect instead of a harsh limit, acting like a progressive spring.

I changed that same solid rod end on the driver's side as a precaution. The tire(s) have hit the fender flares, but never the actual fender. At least that I have noticed.

I plan to change the sway bar attachment this off season to attach on the LCA centerline. I don't know how Griggs or Cortex handle the sway bar force as I thought they used a similar design.

 

[Dave_W]

I think I remember a video of you cycling the suspension with the spring removed, but check that the inner rod end on the stab bar doesn't bind when the suspension is fully compressed.

I think getting the sway bar force aligned to the control arm pivot axis is the best solution.

 

[RinerAuto]

Mid season results were posted for the main local club that I run with. We have completed 5 of 8 events and there will be 2 drops. I have a comfortable lead in class.


Ashley is in a very tight race for first place in Ladies class. She needs to get a few more first places to lock that in.


For Overall PAX Championship it is very close. I thought I had first place, but those pesky DS/ES cars. I need to finish of the end of the year strong.


Normally I start to fall off at the end of the year due to tires getting worn out. But this year I have a new set of RE-71RS tires waiting to be installed when I need them . I want that Overall PAX trophy. Each year's winner gets a plaque with their name and class on the side of it.

 

[RinerAuto]

As shown in previous post my current roll center was pretty low around 1.5" above ground. Raising just the lower control another 1" (2" over stock) raises the roll center a lot to almost 5". If I then raise the upper control arm one hole (1/2") then the roll center drops to around 3". Also the FVSA length changes a lot between the different settings, which give an indication of camber gain and jacking effects.

I posted the above screenshots on my Instagram and got some good feedback. Interestingly the chassis builder Christopher Robin, who I respect, suggested the highest roll center for an autocross car to limit the body roll. But he also said I need to check with rear suspension roll stiffness or adjust spring rates. I currently don't have the rear suspension modelled so I'll need to review that later. Additionally, at the time he commented I had already went with the 3" roll center configuration. But changing just the UCA is fairly easy. The LCA move was quite time consuming.

By the end I have -3.75* of camber, +6.5* of caster, and 0 toe.

I'm really interested to see how the new setup feels. Less body roll, more negative camber, but increased jacking (how much??). Camber gain is the same as it was.

Video:

 

[Dave_W]

Good luck with the revised geometry. You didn't mention in the video, but did you check bumpsteer after moving the arms?

In the suspension program you have, is it possible to roll the body and see what you end up with for outside tire camber and roll center height? Maybe try it with small changes in ride height at the same time to simulate brake dive as well. Since you're really looking for increased grip in corners, checking the geometry at static ride height isn't as important as under a lateral load. See how much the roll center moves as well. I don't remember where I saw it, but I think I read that reducing roll center migration is a higher priority than lowering the RC, as an RC that moves around a lot gives the feeling of unpredictable handling.

 

[RinerAuto]

Good luck with the revised geometry. You didn't mention in the video, but did you check bumpsteer after moving the arms?

In the suspension program you have, is it possible to roll the body and see what you end up with for outside tire camber and roll center height? Maybe try it with small changes in ride height at the same time to simulate brake dive as well. Since you're really looking for increased grip in corners, checking the geometry at static ride height isn't as important as under a lateral load. See how much the roll center moves as well. I don't remember where I saw it, but I think I read that reducing roll center migration is a higher priority than lowering the RC, as an RC that moves around a lot gives the feeling of unpredictable handling.

Thanks, yea I adjusted the bumpsteer lower but still need to bust out the gauge and measure it. After a short drive to cars and coffee I could feel some bumpsteer.

Yea the Suspension Analyzer can do dive, roll, and steering. I have looked at all of them. The RC does not move much laterally during roll. I wish I had actual data to know how much the body rolls and steering angle to plug in to the software. But it is cool to put in roll and steer to see cambers while turning. Caster helps so much. I can get some screenshots later.

 

[RinerAuto]

Here are two graphs one is camber vs roll and the other is camber vs steering. I added a Supra curve that were in the program as comparison. I looked at roll center height during these as well, but it didn't move very much so wasn't very interesting.

My suspension seems to be similar to the Supra just a little more aggressive on the camber gain.

MiddleLCA = LCA in middle hole (1" higher than stock) and UCA in lowest hole. Previous setup
TopLCA = LCA in top hole (2" higher than stock) and UCA in lowest hole.
RaiseUCA = LCA in top hole (2" higher than stock) and UCA in middle hole (raised 1/2"). New setup

 

[RinerAuto]

I bought a new thing (well new to me).....

It's a 2017 24 ft Vintage Trailers LTD enclosed trailer. Low miles/usage. It has built in cabinets, wired for 30A with generator box (no generator), and the driver side access door. I bought it from a local car club member.

One of my goals is to travel to further, bigger events. This trailer will allow me to do that with confidence and security that the car will be safe no matter where we stop. I also plan to sleep in this trailer at events that allow onsite camping.

I am over the moon with this purchase! Maybe SCCA Nationals next year?!?!

Video Tour:

Car looks at home in there

 

[PatientZero]

If it helps get you out west you always have a spot to park at my house.

 

[RinerAuto]

If it helps get you out west you always have a spot to park at my house.

Really appreciate that.

 

[RinerAuto]

This past week was a rollercoaster of emotions. Saturday I had to put down my dog of 16 years. She lived a long full life.


Sunday we had an autocross with the local club we are trying to do our best in. I was really nervous about the front suspension changes that I made. In theory should be better, but never know until get out on course. I ran in the second heat and Ashley ran in the third, out of four heats. The street cars that have been out PAXing me ran in the first heat. So I at least knew what I needed to do to beat them.

After my first run I was flirting with FTD, being only 0.398s off of a E46 on Hoosiers. I put chalk marks on the tires, which are RE-71RS with 160+ runs, to see any roll over. Boy were the fronts still rolling over. Even with -3.75* camber 35 psi. By my third run I was ahead of the street cars in PAX and had FTD. However, in my bump class there is a quick CAM-S Corvette that just installed a new AJ Hartman wing and the CAM-C GT350R with new front canards and AJ Hartman spoiler. For my fourth run I increased front pressure to 37 psi to help reduce front roll over and the car went even faster, but still had roll over. I may need to do more work to get more camber or go for the suggested high roll center setup which also has the highest camber gain.

I took a rider on every run (4 total), which typically I try to get one by myself. I don't know if it helped balance or I just didn't care, but the car was a rocket ship. By the end of the event, I held onto FTD by 0.164s and FTP by 0.325s. I'll note the Corvette had a scratch time that would have been faster raw than me, but not PAX. I think this is my first FTD and FTP event. Additionally, this was exactly the event I needed to move from 2nd to 1st in the overall PAX championship for 2023. With 2 events left I'm close to being able to lock in the win. I have locked in the win for my class.

For Ashley's heat rain started to sprinkle but didn't downpour so there was still good time to be found. She's in a close battle for first in Ladies for the 2023 season (3 points separate top three). She needed a win at this event. The course was a little confusing, but when putting the car in the right place there was a lot of speed and time. Her first run had 3 cones and her second had 2 cones. She also was taking riders, but she likes how the car feels with riders. I told her that she is the fastest lady, just needs to clean it up. On her third run she ran clean and was close to her raw time from second run, but the other ladies also found the time. After PAX she was in first but there one run left. On her last run she dropped another 0.4s and was able to hang onto first in Ladies by 0.221s. So that last run was crucial, the lady in second place dropped 2.4s between third and fourth run! She hasn't locked in the Ladies Championship yet, but this win is almost making it certain she will be the Ladies Champion.



This was such a good event for our respective championships and a huge relief on that the suspension change was in the right direction. I have a 2-day event next weekend that I may try the highest roll center setting. Then I travel to KY for Ford Fest where I want to be competitive for the Grand Champion event.

If you've read this far, I'm starting to edit video for this event and it will be available Friday.

 

[PatientZero]

After my first run I was flirting with FTD, being only 0.398s off of a E46 on Hoosiers. I put chalk marks on the tires, which are RE-71RS with 160+ runs, to see any roll over. Boy were the fronts still rolling over. Even with -3.75* camber 35 psi. By my third run I was ahead of the street cars in PAX and had FTD. However, in my bump class there is a quick CAM-S Corvette that just installed a new AJ Hartman wing and the CAM-C GT350R with new front canards and AJ Hartman spoiler. For my fourth run I increased front pressure to 37 psi to help reduce front roll over and the car went even faster, but still had roll over. I may need to do more work to get more camber or go for the suggested high roll center setup which also has the highest camber gain.

That's wild! I'm not even running that much camber on my struts and not rolling over past the triangles on the sidewall at 27psi. Do you maybe need more spring rate or sway bar?

 

[RinerAuto]

That's wild! I'm not even running that much camber on my struts and not rolling over past the triangles on the sidewall at 27psi. Do you maybe need more spring rate or sway bar?

I run a Steeda sway bar (I think one of the stiffest on the market) and 400lb springs. I can't remember what my wheel rate works out to but it would be less than strut setup. So I could need stiffer springs, but wanted to run a slightly soft setup for bumpy tracks.

I'm thinking it could be the 295s on 10.5 wheels. Just too much sidewall flex. I have 285s that will be installed next week before Ford Fest.