Mechanical trail vs. Pnuematic trail

[DangerousNerd]

All,

I'm curious about ratios of mechanical trail to pneumatic trail for performance and race applications. I understand that self alinging torque (SAT) falls off as the limit of adhesion in sideslip is reached. Because of this many books suggest that a good driver should sense the decrease in steering feedback and undestand this as a signal of the approaching limit.

However if one makes the mechanical trail to large this will likely drown out this delicate signal. unfortunately the books avoid making any reccomendations on this ratio. Should I be desiging this as 1:1 or what? Are there any rules of thumb for this design?

Thanks
Scott

 

[GregLocock]

The pneumatic trail moves around a lot more in practice than steady state measurments indicate. If the trail goes negative then the steering wheel will go 'over centre' - which, while it might be disconcerting to a road driver should be easy to cope with for a racing driver.

So my rule of thumb would be to use the same mechanical trail as other people using the same tyre!

Kevin probably has more experience with this, but I think this is just a matter of taste, it has no objective impact on the open loop performance of the car.

Just thinking about it if the steering does go over centre then it starts to load the suspension in the opposite direction. This might induce some wooliness at around that point, which would be a bad thing.

Cheers

Greg Locock