Estimating pneumatic trail

[murpia]

Is there a simple way to estimate the peak pneumatic trail of a tyre? I need to calculate some likely peak steering forces without any tyre data.

I can estimate the contact patch length, would e.g. taking the trail to be 75% of the way along the patch length be OK?

Thanks, Ian

 

[GregLocock]

It tends to move forward as the tire approaches peak grip, so 75% will give a high estimate, assuming you use peak Fy.

Have you got any tire data for a similar tire? Mz/Fy is the trail.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cibachrome]

Peak as in lane change (sine with dwell) or peak as in max curb pushaway for pump sizing, tie rod strain and gear mounting durability loads?

Max P-Trail is load, pressure, rim width and tire structure dependent. If its an existing tire, the tire manufacturer can get you scrub torque values or P-trail from routine slip/load/camber tests.

 

[murpia]

No tyre data (yet). I should add that this is a track car with some downforce.

I can estimate the expected Fy from expected car performance. Using the current amount of steering trail suggests the steering wheel force will be too high for driver comfort. We can reduce steering trail by up to 20mm (easy), or we could go for power assistance (not so easy), but without knowing the pneumatic trail I'm unsure that the 20mm reduction would have enough of an effect.

Regards, Ian

 

[GregLocock]

Reducing the mechanical trail will increase the sensivity of the steering as you saturate the tire - which is a good thing for a circuit car.

It'll make the car feel less linear which is bad for a road-car.

There are other effects, those are the biggies (IMNVHO)


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.