Anti-Dive Gain

[Mr.Kennedy777]

Having a look at some of the control arm angles and movement of the chassis there seems to be quite a bit of change in anti dive from static to dynamic position. Now in order to keep everything more stable, I’ve ended up with some kind of funky control arm lengths and angles needed. Is this normal or am I going crazy here?

[TheJet-09]

I had to replace the strut crossmember on my chassis, and the new one (from the manufacturer) is 1/2" higher, presumably to keep the RF heim out of the ground. But after installing it, I too came up with some weird angles on the lowers like you mention. I called them and asked if I need to run a spacer in between, at least on the LF (not defeating the purposes of raising it in the first place on the RF), and they said no, run it up as high as you can as long as everything clears. I'm not saying that's right, but it may be if the ultimate goal is just where we are at race attitude.

So I ended up setting my front end at what I'm calling "set up height" as opposed to ride height. Using solid links instead of shocks/springs, I raised the LF up 1", the RF down 3 1/2" (which is the lowest I could go and still read caster), the RR down 1", and the LR as close to full droop as I could get it. The numbers are rather arbitrary, or a compromise, but for now it's what I used. I was really taken aback by how much caster was lost, as well as camber on the LF, between "ride height" and my "set up height."

In thinking on my own, and most certainly listening to what others have to say about the current attitude of cars (and that I feel they pretty much stay in that position while racing), I think we need to be more concerned with where things are at that racing attitude, and not at ride height or even getting to that attitude. But I'm often my own worst enemy, so we shall see.

[Mr.Kennedy777]

yeah I knew that the anti dive would change with pitch in the car, but I was shocked to find out how much. I was thinking to myself, this can’t be right. So I checked it all again and yeah.. the anti dive actually turned into pro dive in the RF once it was in position. I knew there was caster gain and bump steer changes when the chassis moved when there is anti dive, but to have that part change so much seems kind of crazy to me. So I don’t know.. was there a reason it was anti dive at first and then it turns into pro dive at race height, or was this just something that was overlooked when the chassis was built? That’s the next thing that I’m wondering before a guy starts gutting stuff.

[Kromulous]

I noticed on the 2018 MB cars, the entire rack plate and lower pick up points are angled up, higher from the ground, right to left standing in front looking aft. At the time i thought it was an attempt to gain clearance, but it would help with this various gains and losses as well, while not being dependent on 4.5 " of travel.

I think these sort of things are whats simulated on a pull down rig, and at the same time you can check for binds etc at full compression. Along with camber caster etc etc. Would be fun to be able to play with a pull down rig, but checking the way you describe with struts at full tilt is pretty ingenious.

I have done sort of the same with jacks, and bump stops. Take the spring off and let the RF sit on the bump, and jack up the LR, while on some scales. Just to check clearance and things while in a full tilt attitude, not sure if it helped or not thou LOL.

[Mr.Kennedy777]

I mean realistically the car doesn’t go from ride height to race height very often on the track, so perhaps just making sure it’s where it should be dynamically is best course of action? And not get caught up in how much it changes from static to dynamic?

[TheJet-09]

One obvious deficiency in what I did is the inability to duplicate tire deflection, and probably some other things I'm even unaware of. But if nothing else, it gave me an idea of where things are at that point.

[slipprey]

when you set car at set up height with the solid sticks instead of shocks, do you do anything with the 5th coil ? thanks!

[fastford]

One obvious deficiency in what I did is the inability to duplicate tire deflection, and probably some other things I'm even unaware of. But if nothing else, it gave me an idea of where things are at that point.

I came up with the idea a few years back, when we started working with bump stops , to use solid rods to hold the car as close to its dynamic state as possible , with out the body or engine and trans , then we took it to the track and pulled it around the turns with a 4 wheeler , we started at the bottom and one lane at a time moved up , that way I could watch the tires contact with the track , now , I know tire deflection can not be taken into affect , but you would be surprised what you can find doing this....

[TheJet-09]

@slipprey, I checked trans output angle, driveshaft angle, and pinion angle at both ride height and set-up height, each with no compression on the 5th coil, and then 2 1/2" of 5th coil travel. I was wanting to see how much pinion angle was lost under compression. My curiosity in that stemmed from a separate thread as I was wondering how others were measuring pinion angle.

Great to hear how others are looking at things! Not everyone can afford a pull-down rig, or time on one, but as fastford said, there is definitely something to be learned through other methods.

[Matt49]

The other thing that I find interesting is how much the j-bar angle changes with 5th coil travel.

[slipprey]

thank you for this imfo, the set up sticks will be a great learning tool tor me to learn more about my car I retired from dirt latemodel racing in 2002, and I was sitting on my front porch one night last year and said to my youngest child that just graduated from college, " I don't think im done racing yet " lol so I took the money I had and went and bought a 2010 mastesbuilt 2in round tube smackdown with a open trailer. car is beautiful and was a back up car for a team that was selling out. they never ran it, its like brand new! it had 30 laps on it.it has 700hp steelblock alum heads, s7 spindles with the wide right front. ran it 4 times last year and these cars are a lot different then 20 years ago & my old driving habbits don't work either lol. so im going to just start from scratch with learning what this car wants and try and figure out how it wants to be driven. driving a dirt latemodel is the funnest most exciting thing I have ever done, and now that im back doing it again its a win & a blessing for me! now I just have to figure out how to get er to the front! thanks!

[CCHIEF]

The other thing that I find interesting is how much the j-bar angle changes with 5th coil travel.

......ANd how much the whole rear axle shifts L to R with that 5th coil travel

[TheJet-09]

And from what I recall checking the pinion angle change at 2 1/2" compression, was that at "ride height" it took a fair amount of effort to raise the lift bar (I was just doing it by hand while laying next to the car), yet at my so called "set-up height" it took very little effort at all. I suspect it may have been due to the RR being stood more straight up, and the increased J-Bar angle, that when raising the lift bar (compressing the 5th coil), it was shifting the chassis back to the left (over the rearend), in turn taking weight off the RR. It was around 2:00 am when I was working on that stuff, but that's what I recall, and my guess as to why.

And hey @slipprey, we're pretty similar in backgrounds. I started racing in '88 and was burnt out around '02. Stayed away for 11 years and got back into it in '13, also buying an old MasterSbilt. A lot changed in that time too, mainly shocks in my opinion. And my driving habits are a detriment as well. Thanks for sharing!

[collateralDamage]

the resistance you feel is more a function of the load on the LR spring than anything else, at ride-height or race attitude. I would say that 2 1/2" of actual 5th coil travel is out of range of anything I have been able to accomplish. Is anyone actually getting 2 1/2" with successful rear loading?

[MasterSbilt_Racer]

the resistance you feel is more a function of the load on the LR spring than anything else, at ride-height or race attitude. I would say that 2 1/2" of actual 5th coil travel is out of range of anything I have been able to accomplish. Is anyone actually getting 2 1/2" with successful rear loading?

Are you saying that is too little? I have certainly been a part of plenty of wins with travel near that number.

[collateralDamage]

i would consider 2 1/2" a lot of travel, but that also depends on a lot of other factors.

[Basecircle]

I’ve never really thought of the effects of 5th coil on rr loading and rearend lateral location before. I’ve always just kind of thought of it as set for the type of track (stop and go, or momentum) as far as how much instant traction you need to get off the corner. Maybe something to think about as I’ve struggled in some track conditions getting the rear to roll. I’ve blamed it on possibly too much jbar angle, or too short of a jbar. Maybe it’s lift arm travel allowing too much jbar angle dynamically if that makes sense? Might have to tinker in the garage a little to get a better understanding of everything that’s going on. It’s too good when it’s good to make any drastic changes.

[TheJet-09]

For what it's worth, I had 3" of 5th coil travel this past weekend: #325 spring at 37", 1/4 mile, semi-banked, relatively slick throughout the night, and we were on a hard rear tire (LM40).

[collateralDamage]

<blockquote>For what it's worth, I had 3" of 5th coil travel this past weekend: #325 spring at 37", 1/4 mile, semi-banked, relatively slick throughout the night, and we were on a hard rear tire (LM40).</blockquote>

Are you using a travel indicator to come up with this number or are you actually recording a potentiometer? Rolling the car around under caution will skew travel indicators A LOT.

[TheJet-09]

Just the travel indicator on the shock shaft.