ARB Ratios

[mt1104]

Hello,

I'm building up my BMW to be a clubmans rally vehicle (so cheapo cheapo) and after reading the various posts and articles on here have discovered Hartge recommends a 20mm front ARB and a 16mm rear ARB - this gives a front to rear ratio of 1.25.

I currently have a 18mm front ARB, a 20mm front ARB and I am soon to have a 14.5mm rear ARB - now if I use the 18mm and the 14.5mm that will give me a ratio of 1.24 which is very near to the Hartge one and so I am assuming the oversteer / understeer ratio due to ARB influence will also be very close to that of a Hartge setup.

Or, should I put on the 20mm front one and go bigger is better and have a ratio of 1.38? Although from suspension setup research larger front ARBs will induce oversteer and larger rear ARBs will induce understeer. So putting a 20mm one will cause it to oversteer slightly more - although again, I believe mtech suspension had this setup and BMW mtech division aught to know what they're doing.

[zaust]

You will end up with too much force on the o/s to turning wheel and cause more understeer if you use the 20/ 14a

[caneswell]

Roll bar stiffness is proportional to the 4th power of the thickness. So a little change makes a lot of difference.

A thicker bar moves the grip away from that axle. Thicker front will tend to give understeer not oversteer.

[mt1104]

sorry, ingeniously typed typo at a crucial point there, promise, I meant to say understeer