This guy does a great demonstration
Roll Center Question = Answered

+ YouTube Video

See http://www.rccaraction.com/blog/2014...center-tuning/

Post #89, the bulleted one by Razathorn, in this link is the best roll center tuning description in hundreds of pages of rctech roll center debates.

http://www.rctech.net/forum/electric-off-road/686770-official-camber-link-roll-center-debate-thread-6.html

I've read this thread from start to finish over a six week period but I'm still not clear on the correct definition of pack.

Some people seem to be describing pack as the point where a shock effectively reaches a hydraulically locked state.

Others seem to describe pack as a gain in dampening rate as piston velocity through the oil increases, which may or may not ever reach a hydro lock state.

I think the latter is the more correct description but I'm just not sure from what I've read. Am I close or am I still off on my understanding?

I believe I understand now how to adjust the amount of pack I get but I'm trying to visualize what happens when I land a jump with more or less pack in my shocks. I'm not completely sure if it's a sudden stop of suspension travel at a certain point or not. I think the answer is that it can be a sudden stop but that's probably not what you want to tune for.

Anywhere close? Am I even making sense?

The RC Car Action link corroborates the video and quote 1 and 3 below... "Using a higher roll center prevents the car from leaning as much, which is helpful on high-bite tracks to minimize traction rolling and will also give the car a snappier feel—good for smooth, high-bite tracks."


1) 2) There is confussion, but lower on the tower = higher roll center and vice versa.

3) 4) Great info!

I have a feeling there is a LOT more to this than just raise or lower the link as quote 3 warns. I swear I had a lower front roll center (higher on tower) that was dealing with the traction rolling better than when I went to a higher front roll center (lower on the tower). Steering became more immediate with the higher front roll center and my car traction rolled more immediately. I will do more testing with this specific info in mind. Thanks for the great info everyone.

That was a great video. I have no idea how to put a Youtube video on here, but his part 2 "Roll center demo 2" makes it even more clear.

Doh! I was zoomed in on the wrong link (lower inner pin height can be changed on my car).

If you want to see what is happening to your roll centre plot it on some paper. One advantage is that you are using a 1/10 scale car, so you could hold the front and rear of the car up against some paper and mark off all the pivot points, move the suspension in increments and mark it again. Do this for all your normal link positions and you will get a plot of what is happening to the roll centre.
Someone at the weekend said you have lowered your roll centre because I had gone to a shorter link on the front, but I could have lowered the outer link height and raised the inner link height and had the same roll centre as the longer link at the same ride height. I would have had a roll centre that would have moved more due to changes in ride height and one that changed camber on the wheel more through the suspension movement.
The weight will transfer to the front through the roll pitch which is the difference in heights of the front and rear roll centres, so normally most rwd weight rearward cars have the front roll centre lower at the front than the rear to transfer the weight forward.
Also the higher the centre of mass the more weight transfer to the front and rear and side to side. If your rollcentre is higher than the centre of mass you get negative transfer of weight about the roll centre as you corner ie the part of the weight transfer equation that is weight transferred due to the roll centres reduces load on the outside wheel. At this point there is still an increase in weight on the wheel due to weight being transferred globally from its central roll centre (where the centre of mass hits the pitch angle between the front and rear roll centres).

Its all a bit of a fluid system so realistically you are back to just trying things out. The only way you could make sense of it would be to work out the G pulled by the model in a corner and record loads of setup data and calculate the load transferred in a corner. Then at some point you might have enough data to find some magic numbers that work on different track surfaces that require different tyre slip angles (that's also a big bit of data missing in the RC world compared to fullsize).
Also you wont find too many fullsize race cars with 50/50 weight distribution as that tended to give inconsistent handling, most seem to have going up towards 60pc weight at the driven end.

Also a lower roll centre has the potential to create more vertical downward grip on the tyre during cornering if the correct springs are used. If you use the same springs and you lower the roll centre the body will roll more as more load is being pressed on the springs of the same poundage. In the full size world you would go up to stiffer springs to control the chassis and tyre angles. The stiffer the spring the more load the wheel is seeing. If the tyre can handle that load you will gain grip, if you overload the tyre you will strub the tyre and the tyre will slide.
What you are dealing with in RC sometimes is grip roll on high grip tracks, therefore you probably have tyres that can grip far more that in the fullsize world and therefore you are tuning outside of the parameters of most fullsize competitive vehicles.

Think of chassis roll they way we use anti-squat.
Basically, the rolling motion, side to side, or front to back, is energy being absorbed, rather then sending it to the tires.

More anti-squat uses the chassis energy to push on the tires, rather then squatting.
More chassis roll, absorbs the energy the tires would see as chassis roll instead.

Keep in mind though that sometimes traction rolling can't be tuned out. So if tuning to the max doesn't help, you may need to attack the track differently, try different compounds, sauce, etc. to reduce or eliminate the issue.

Hope this helps.

If anyone doubts the roll center tuning discussion as it looks, think about old versus newer cars.
Older cars were raced on bumpier, lower traction, even sandy tracks. Pin spike tires, etc.
They came with short arms, short camber links and had high roll centers. Lots of camber change to produce traction and aid in bump handling.

New cars...longer arms, longer links that are also flatter. They are trying to take camber gain away and lower the roll centers as much as possible to reduce traction on high bite, smoother tracks. Making modern cars easier to drive fast on today's tracks.

I'm not looking to argue the point, but it's seems black and white to me. Even at the highest roll centers our new cars probably can't get to where an RC10 was as far as HRC.

I think you have high and low roll centers backwards there. I believe the older cars had lower roll centers, resulting in more roll and higher traction on old bumpy tracks.

This is completely backwards.

Nope. He's right.

What am I missing? A lower roll center results in more chassis roll during cornering, right? Are you saying the video posted on this page is wrong?

Did I at least get close with my description of pack toward the top of the page?