Roll center

[tomislavp4]

Ok, so, for a good handling car the front R.C. should be located 1-3 inches above ground and the rear 6-10 inches....
Unfortunately, I have a small problem: the rear rc is fixed at ground level
So from where I see it, I have 2 options:

1. move the front rc below ground, and follow "the rear should be higher than the front" rule, or
2. locate the rc 1-3 inches above ground and follow "front rc 1-3in above ground" rule.

I´ve heard a bit about spooky handling characteristics with cars that have their rc below ground and even worse for the ones with the rear one lower than the front one! So I wonder what would you guys recommend here

[Jersey Tom]

Ok, so, for a good handling car the front R.C. should be located 1-3 inches above ground and the rear 6-10 inches....

Not true. Or at least not necessarily. On SOME cars, that RC split might be good.. on others, you might want something completely different.

And bear in mind, the RCs will move considerably under braking and accel.

RC is one of the last things I would worry about in suspension design. It is generally misunderstood and misused.

[donskar]

Can someone recommend a good book or (preferably) magazine article discussing roll center?

I know enough to slog through reasonably heavy tech discussion.

Thanks!

[West]

You can read Race Car Vehicle Dynamics. I had to re-read the tire section a few times over but it shouldn't be too hard to understand.

[Jersey Tom]

http://www.neohio-scca.org/comp_clinic/ ... cs2007.pdf

This is pretty eye opening.

RCVD, as mentioned, is also good. But, to summarize, the way I think of it...

• The lateral load transfer distribution (front vs rear, how much each gets) is a big influence on chassis balance.
• For the most part, total load transfer is a function of CGH and track width.
• Of the total load transfer, a portion of it (proportional to distance from CG to roll axis) is a rolling moment, and is taken up by the springs and bars.
• The remaining portion (proportional to distance from roll axis to the ground) is non-rolling overturning moment, and is taken up and split by the roll axis inclination.
• The relative amount of front spring and bar, to rear spring and bar, decides how the rolling moment is split as load transfer to the front and rear suspensions
• The roll axis inclination decides how the non-rolling moment is split as load transfer to the front and rear suspensions
• You can also think of the slope of the line from the contact patch to the instant center (or RC) as showing the proportion of jacking load on the sprung mass, to cornering force of the tire.
• Roll axis inclination is not static, it will change when the car pitches.

That said, since roll axis is generally pretty low to the ground relative to the CG, I'd say spring and bar effects (as well as tire load transfer sensitivity and friction combined slip effects) are going to by far dominate the handling of the car.

You can still use RC's and front vs rear ride height as a slight chassis balance tuning tool, and you can probably use it to do trick stuff for handling, but in the grand scheme of thing there's a lot I'd focus on first.

Tires tires tires tires tires.

[Carlos]

Donskar. This is Sebastien Allibert's Cranbrook University MSc Thesis. "Implementation of the Force Roll Centre OptimumK" , 108 pages.

http://dspace.lib.cranfield.ac.uk:8080/ ... t-2007.pdf


Edit - Apologies to both Sebastien Allibert and Cranfield.

[twoshots]

You mean Cranfield ofc.

Thanks for reminding me why I still believe an MSc and PhD thesis should never have an acknowledgements section. I can only imagine who 'The Three Devils' were and I've seen a few interesting sights in the Cranfield bar over the years