Monoshocks again.

[D J Yates]

I've been doing some research on monoshocks. Ignoring any design issues, the i've figured that the desicion for and against a monoshock is the importance of one wheel bump vs cost and weight saving.

Wether a dual or mono shock design, an anti-roll device (ideally damped) of some description is required. Considering that one wheel bump is equivilent to a combination of roll and pitch, and that an anti-roll device links the wheels together reducing their indepencence, a car's ability to handle bumps depends on the roll stiffness of the anti-roll device (as well as the obvious spring/damper). Since a monoshock has zero roll stiffness, to achieve the equivelent roll stiffness of a dual setup, the anti-roll device has to be stiffer and as a result the wheels are less independent than for the dual setup. If the ARB of a dual design contributed only 20% of the roll stiffness, then a monoshock design with equivelent roll stiffness would need an ARB 5 times stiffer and so would suck in one wheel bump. However, if the ARB contributes 80%, then it is probably worth going for a monoshock and stiffening up the ARB slightly for the purpose of cutting costs and weight saving.

There's my logic. Now what i need is to quantify is the distribution of the roll stiffness due to spring/dampers and the ARB of a typical FSAE car. Anyone care to help me out with some numbers? I don't need actual spring rates, just the rough distribution.

As i mentioned, this is ignoring the design issues. I'm confident in my abilty to get round those issues and design a reiable system. And don't worry, i have considered roll damping. But for the reasons stated above, if a monoshock is a viable option for your car then the ARB should be damped anyway.

[D J Yates]

I've been doing some research on monoshocks. Ignoring any design issues, the i've figured that the desicion for and against a monoshock is the importance of one wheel bump vs cost and weight saving.

Wether a dual or mono shock design, an anti-roll device (ideally damped) of some description is required. Considering that one wheel bump is equivilent to a combination of roll and pitch, and that an anti-roll device links the wheels together reducing their indepencence, a car's ability to handle bumps depends on the roll stiffness of the anti-roll device (as well as the obvious spring/damper). Since a monoshock has zero roll stiffness, to achieve the equivelent roll stiffness of a dual setup, the anti-roll device has to be stiffer and as a result the wheels are less independent than for the dual setup. If the ARB of a dual design contributed only 20% of the roll stiffness, then a monoshock design with equivelent roll stiffness would need an ARB 5 times stiffer and so would suck in one wheel bump. However, if the ARB contributes 80%, then it is probably worth going for a monoshock and stiffening up the ARB slightly for the purpose of cutting costs and weight saving.

There's my logic. Now what i need is to quantify is the distribution of the roll stiffness due to spring/dampers and the ARB of a typical FSAE car. Anyone care to help me out with some numbers? I don't need actual spring rates, just the rough distribution.

As i mentioned, this is ignoring the design issues. I'm confident in my abilty to get round those issues and design a reiable system. And don't worry, i have considered roll damping. But for the reasons stated above, if a monoshock is a viable option for your car then the ARB should be damped anyway.

[syoung]

I've got no numbers accessible, but I can tell you an anecdote! WFS currently runs as a final year project with less-than-ideal continuity between years. One of our first tasks was to benchmark test last year's car (we're entering 1(200) this year). It didn't have an anti-roll bar of any kind fitted - body roll, even running our stiffest springs (400 lbs/in on a near-1:1 bellcrank), was pretty massive, with at least 3-4 inch front suspension compression travel.

We're hoping our ARB linkage will make a massive difference when we implement it in 3 or 4 weeks' time. Is this a naive hope? Are we running far too soft a spring rate? Anybody care to share some numbers on this as well as on David's question?