Roll Centers

[race12345]

Can someone explain the correct way to measure your roll angle and dive for roll center programs....also is there a generic height and to the left of centerline on steel block late models for roll ceters on 3/8 mile medium bank tracks....also how far right do you want the roll center to move under dive. Theres not much info on internet about these questions. All info on roll centers would be helpfull. Thanks

[Ralphy]

As far as how to measure roll center google "Roll Center Understood" and see if this helps.

[MasterSbilt_Racer]

Can someone explain the correct way to measure your roll angle and dive for roll center programs....also is there a generic height and to the left of centerline on steel block late models for roll ceters on 3/8 mile medium bank tracks....also how far right do you want the roll center to move under dive. Theres not much info on internet about these questions. All info on roll centers would be helpfull. Thanks

You need data acquisition to get roll/dive data.

[FlatTire]

I've asked for all this stuff in the past and got little to no help. I finally took my own ideas to the track and figured out what worked and what didn't for myself. After all this trial and error, it dawned on me that this is how one should do this and its how guys like Smokey Yunick and some of the other great's in the late model world accomplished what they did. Knowledge is power and it also wins races. Its best to keep those cards close to your chest.

[drtrkr244]

Bob Bolles did post a table of roll center placement years ago in Circle Track. It was based on track conditions. I saw it a while back on their website.

[7uptruckracer]

Yeah but thats static and most on here don't pay much attention to BOB. We kind of laugh about some of his theories. What MOST guys pay attention to now is spindle heights, camber curves and camber thrust caster change ackerman, and car attitude. In MOST cases if you get your curves right your in the ballpark. There is more work going on in the spindle area to get the cars to steer more positively and "weight jacking" Most keep it close to their vest, ALSO there are so many variables its hard to give someone numbers. For example your moment arm places leverage on your roll centers and that can be determined by your engine height so I could give say 2" high and 8" left static roll centers numbers and you might be out to lunch because your COG is different or engine is different weight etc. Also when you run a 19" arm on an 8 1/4 upper your migration is going to be way different from what Bobs sheets say lol . ON top of the LF rolling up and losing angle and going all over the place its really really hard to get dynamic roll center without data aquisition

[drtrkr244]

Im pretty sure he is referring to dynamic not static, because all of his software is based on the dynamic. I have used his software before but never tested his different placements for roll centers based on track conditions.

[hpmaster]

Yeah but thats static and most on here don't pay much attention to BOB. We kind of laugh about some of his theories. What MOST guys pay attention to now is spindle heights, camber curves and camber thrust caster change ackerman, and car attitude. In MOST cases if you get your curves right your in the ballpark. There is more work going on in the spindle area to get the cars to steer more positively and "weight jacking" Most keep it close to their vest, ALSO there are so many variables its hard to give someone numbers. For example your moment arm places leverage on your roll centers and that can be determined by your engine height so I could give say 2" high and 8" left static roll centers numbers and you might be out to lunch because your COG is different or engine is different weight etc. Also when you run a 19" arm on an 8 1/4 upper your migration is going to be way different from what Bobs sheets say lol . ON top of the LF rolling up and losing angle and going all over the place its really really hard to get dynamic roll center without data aquisition


I've asked for all this stuff in the past and got little to no help. I finally took my own ideas to the track and figured out what worked and what didn't for myself. After all this trial and error, it dawned on me that this is how one should do this and its how guys like Smokey Yunick and some of the other great's in the late model world accomplished what they did. Knowledge is power and it also wins races. Its best to keep those cards close to your chest.

Good points, thanks.

[MasterSbilt_Racer]

Im pretty sure he is referring to dynamic not static, because all of his software is based on the dynamic. I have used his software before but never tested his different placements for roll centers based on track conditions.

Moving roll centers for track conditions?

Lets say your car is perfect when turning 14 second laps at track X. It is balanced perfectly. Not loose or tight anywhere. You are driving the car, not throwing it. Tire temps also tell you the car has great balance.

Now the track slickens off during the course of the night and 15.5 seconds is a fast lap. Why would the front and rear of the car quit working together? Are the front and rear tires not both riding on the slicker suface? What really changed?

[drtrkr244]

I cant answer that MBRacer. You'll have to ask Bob for those. What I believe he proposes is too maintain similar roll angles, front and rear, whether the track is heavy or slick.

[zeroracing]

Bob is a firm believer in a 1:1 front to rear roll ratio. He has pantented some stuff relating to that if I remember correctly, method or something. If your a bob fan then you want to reach a 1:1 roll amount.

If that is good or bad is up too you to decide...

[hpmaster]

If you want to learn about chassis and front end design read everything by William F. Milliken. Bob Bolles wouldn't be qualified throw out Miliken's trash if he was still alive. http://www.millikenresearch.com/books.html

[grt74]

so I'm reading this and yes your not going to get a direct answer on this because there are just to many factors,what works for 1 roll center may not work for another because of weight placement (engine,ect),i myself like 2 different roll centers and there based on weight placement but i do or will change things from time to time if the car wants it,i also look at tire loads according to dynamic wheel load,and ill say this i never stop learning and i hope i don't,the biggest part of this to me is if you do find something that works great,you need to be able to measure it out so that you can duplicate it again and again