lol. I was just changing my mind on which one to get. Will just laughs at my pm's now.

I really don't think the snow will be bad this time around.

I will be opening the shop for all those who still feel like racing.

Keep being fickle and I'll soon call you Bennett.

Wayne is me. UN4 is a friend of ours from the same local track.

It's really not that wild. He's one of our local racers. He gives us far more advice than we give him--that's for sure. We've been doing a lot of club racing with him, as he noted.

I'm sorry, but that just isn't correct. You're thinking of the forces wrong. A lot of people do.

When you go through a corner, the mass of the car pushes the outside arms against the hubs. This force is transmitted to the wheel/tire. The tire wants to stay in contact with the track thanks to the friction of the contact patch. This causes the tire/wheel want to lean over thanks to the hub hinge pin acting as a fulcrum. As the tire/wheel wants to lean over, it applies a pulling force along the upper camber link back to the chassis. The higher this link is on the chassis, the more mechanical advantage it has to pull the chassis over and produce more roll.

The problem is that people think that the tire is somehow resisting roll. It is not. If you disconnected the upper camber link, it would flop over in a corner. We've seen this happen in races plenty of times. What keeps the wheel from flopping over is the chassis resisting roll. The tire/wheel is asking for more please, to which we determine how much by tuning the mechanical advantage of that link, in which case, higher at the chassis or lower at the hub means more mechanical advantage and more roll.

I have a handy video that explains the concept and a demonstration with an actual car.

https://www.youtube.com/watch?v=tWdRQaz_Xq8
and
https://www.youtube.com/watch?v=44AlYI6lSX4

One is the demo, one is the explanation.

Wayne

Fair enough.

I have noticed, especially on my T4 over the summer, that I get better mid-corner stability with the inner ball studs lower in height (hard packed dirt/clay, light dusting, low to moderate traction). I had thought that this was coming from more weight over the outside tire due to more roll (although in your video, I see it is actually less roll), thus generating more grip, but it appears what actually is happening is that there is less camber change and so I am maintaining a larger contact patch throughout the corner.

So...

As far as the impact of roll center on traction is concerned, is there a good way to describe its impact without confounding the effect of camber gain (e.g., shorten the camber link as the inner ball stud is raised)? Otherwise, it appears to me that there are conditions whether either a low or high roll center can give you more mid-corner grip...

This is because your truck was previously rolling too much and going beyond the ideal contact patch available with your camber gain curve (i.e. camber rod length or other factors). You previously gained too much positive camber and broke free. Adding more roll to that situation only makes it happen sooner. Removing roll keeps the car more stable. On my T4.1 truck, I also found that playing with the rear limiters really helped as well as limiters put a hard limit on total roll, where as roll center affects everywhere. That way you can tune a little more at low speed with roll centers and high speed with shock travel, progression, or sway bars in 4wd cars.

So... here's where we get into trouble. "Mid corner" can mean a variety of different things. For the front of the car, "mid corner" lasts a long time—basically everything after initial turn in when the car starts changing direction until you are powering out and the rear has squatted. For the rear, "mid corner" is a crude way of describing a long transition that is different in every corner depending on the corner style. In pretty much every corner, your front end rolls over and you turn the front wheels—most of that time is mid corner. In the rear, depending on the corner, you may or may not be on or off power through the corner, on brake, or a whole host of other things.

Generally speaking, for the rear, if you are in a corner, and you let off, and the rear wants to slide out or rotate, a lower roll center that provides more roll will keep traction longer in that situation. If you let off, and the traction gets better, or you grab throttle, and the traction gets worse, the car was rolling over to far and you want less roll, either by way of a higher roll center, stiffer sway bar, stiffer springs, or less shock travel. That is not to say that there are not other applicable changes that could cause all of that such as poor weight placement, spring selection, bad ride height, etc.

For the front, if you are hard in a corner, and it pushes on corner entry, but then as you slow down it starts grabbing a lot more steering—more than you would expect from just slowing down, then the front roll center being raised may help. A low front roll center tends to be less responsive but have a lot more steering at low speed (because it rolls well at low speed), where as a high front roll center will make the car eager to change direction, but will stop steering as much at low speed. A really high front roll center will make the car far more likely to punish you on poor jump landings because the front "has no give" much like a stiff spring. A lower roll center in the front makes a car more plush in general, although it is not always faster by any means.

Try to err on slightly too low of a roll center in front and too high of one in the rear if you're hunting. That way, at worst, your car will be a plush push wagon that rotates in corners but doesn't wash out when you grab the throttle hard -- it can be "wheeled" or driven hard, but it may not be the fastest setup, but it will feel very comfortable. Then start tweaking from there to find your comfort zone... perhaps lowering the rear RC for more in field grip at the expense of high speed corner exit stability, and perhaps raising the front RC for more responsiveness at the expense of low speed steering (good if you plan on straight hitting corners harder and you want it to steer instead of pushing while it waits for you to slow down).

Wayne

Well my question has more to do with when it is appropriate to adjust roll center and when is it appropriate to adjust camber gain. I would view roll center adjustment as having more to do with how much traction/friction there is (more traction = less need for weight on the outside tire "mid-corner" to generate grip = higher roll center), which is a combination of the track surface and the type of tire you're using, while camber gain has more to do with optimizing the tradeoff between forward and side bite for a given track layout. The problem here is that, when you change your roll center, you change how much the chassis rolls and therefore how far along the camber gain curve you end up traveling (camber gain itself also changes slightly, but let's ignore that). So basically, if I set my car up for a lower roll center, I may need more camber gain (shorter upper link) to keep the wheels from going too far positive at full "roll," while if I have a higher roll center, I may need less camber gain to keep the same contact patch at full roll. In other words, changing only the roll center without changing the camber gain can result in a misleading interpretation of where you're getting your "grip" from (i.e., weight transfer or contact patch).

Applying this to my T4, the reason my T4 got loose on me, I think now, had less to do with roll center and more to do with not enough camber gain for that particular roll center setting. I probably could have increased the camber gain and achieved the same cornering stability, albeit at some cost to forward bite (which could be addressed with more anti-squat).

I like to think of roll center as living inside springs, ride height, camber gain, and to some degree pistons / oil (+/- a washer for fine tuning a dramatic change in damping).

Camber gain is something that most people should never be changing unless they're really wanting to change how their cars work. The "team" settings are almost always right, and anything more than a notch different than those is almost always totally wrong, especially in the rear. In the front, caster blocks play a much larger part in camber than the camber rod length so you can get away with more in the front in terms of changing the lengths of links. Having said that, I have played with all of them, but its usually the last thing I do after determining that all other changes just aren't doing it and I want to go fishing, because it just totally changes how the car works.

Stage Settings
I like to think of camber gain (i.e. link length primarily, but sometimes height changes it too, but to much less of a degree), especially in the rear, as one of the "stage" settings that you don't change often or that much. Other settings in this area are wheel base, and shock down travel. These settings all together define the "stage" that the suspension performs on. Much like performers on stage, the suspension cannot go past these "hard stops". At these hard stops, such as fully chassis rolled, the amount of camber gain on the outside wheel and how far the car can roll is fixed. On this stage, things such as dampers, springs, weight placement, ride height, and roll centers determine how quick you move around the stage and get to the edges. Your job tuning the suspension should be to get your performers to dance correctly on that stage. If, and only if, the type of performance you need to do changes, should you be changing the stage.

If you need to change the stage, then think about camber gain.

That's how I like to think of it.

Wayne

Can't wait to test all that new knowledge at the track on Saturday?

Great discussion from both of you. Thanks wayne for clarifying these issues. I remember reading some of your explanations in the other threads (AE BB shocks and spring setups). Great info.

Good discussion and great videos, so much easier to understand when you can see it happen. Thanks to everyone for the info.

planning on racing Saturday....

2wd buggy
4wd buggy
2wd sc.

Guys, we are having a club race sat night. The shop will be open at noon, there will be open practice all afternoon and we will start racing at 5pm. We will do 3 quals and a main. We will be getting pizza for dinner for all the racers. Between the holidays and old man winters latest visit it feels like its been a while so I hope to see you all there!

If the roads are clear enough, I plan to make it. Here is what I plan on running:

Vintage 2wd buggy
Vintage 4wd buggy
Mod ST and/or 4x4 SC