tyre v/s steering?

[Ax]

hlo all,
anybody for explaining how exactly are my tires affecting the steerin and to what extent? and wat exactly am i looking for while goin thru tyre data with respect to steering?
i have already got an idea by running thru the other posts but would jus like to confirm my findings. A brief explanation would suffice.

regards
ankit.

[Ax]

hlo all,
anybody for explaining how exactly are my tires affecting the steerin and to what extent? and wat exactly am i looking for while goin thru tyre data with respect to steering?
i have already got an idea by running thru the other posts but would jus like to confirm my findings. A brief explanation would suffice.

regards
ankit.

[J.R.]

Most basic, divide your aligning torque by lateral force, and this will give you the force in your tie rods, then use that and your rack ratio, you can figure out the steering effort.

More advanced, you can figure out through a quasi static simulation what your front slip angles would like to be given your load transfers etc etc and then determine the steering angle you would like to have to create this slip angle, and then do this through your range of motion, and come up with an Ackermann profile.

More More Advanced, realize that max lateral force may not actually be the best set up at smaller course radaii that we see, then design steering with more Ackermann to avoid scrubbing tyres along corners and creating loss in steering

More more more advanced... it never ends... Get out while you still can! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[MalcolmG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by J.R.:
Most basic, divide your aligning torque by lateral force, and this will give you the force in your tie rods, then use that and your rack ratio, you can figure out the steering effort.
</div></BLOCKQUOTE>

Maybe I'm completely missing something, but it doesn't seem like there's any way that's right. Dividing aligning torque by a force will give you a distance - eg pneumatic trail. You combine the moment arms of pneumatic trail and mechanical trail (caster trail) to find steering torque, then divide that by the steering arm length to find force in the tie rod. Or am I overlooking something basic?

[Mike Macie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by MalcolmG:
Maybe I'm completely missing something, but it doesn't seem like there's any way that's right. Dividing aligning torque by a force will give you a distance - eg pneumatic trail. You combine the moment arms of pneumatic trail and mechanical trail (caster trail) to find steering torque, then divide that by the steering arm length to find force in the tie rod. Or am I overlooking something basic? </div></BLOCKQUOTE>

Nope, you got it. You can also look into the affect of the longitudinal forces and scrub radius on the steering system when the longitudinal forces between the left and right wheels are different.

[J.R.]

Sometimes what I'm thinking and what I say get disconnected, thanks for finishing my thought!

[turb_u_lent]

I dont know if this is an outdated post or what but if somebody can answer my question then do plz.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> Maybe I'm completely missing something, but it doesn't seem like there's any way that's right. Dividing aligning torque by a force will give you a distance - eg pneumatic trail. You combine the moment arms of pneumatic trail and mechanical trail (caster trail) to find steering torque, then divide that by the steering arm length to find force in the tie rod. Or am I overlooking something basic?

</div></BLOCKQUOTE>

rack and pinions do not have steering arm so should the steer torques be divided by tie rod length to give force in the tie rod itself...

[exFSAE]

Uprights on a car that use a rack and pinion most certainly do have a 'steering arm' and associated length.

[BillCobb]

Skip the concern about tierod force unless you have a plastic rack housing and glass gear parts. The moment in the steering column felt by the driver is the principle concern. That includes the lack of a moment or perhaps a negative moment at max cornering. Pick the caster, tire construction, tire pressure and overall steering ratio based upon what your driver has the ability to 'handle' for the level of maneuvering severity the course requires. This is an engineering problem, not a fabrication problem...

[blister]

Has anyone ever calculated the energy needed to scrub the tire trough a corner (eg small ackermann and big slip angle on outer tire). Very rough calculations give me around 2-4hp...

[Edward M. Kasprzak]

Hint: You meant "power" and "induced drag" instead of "energy" and "scrub".

[abc]

how does steer arm length directly effect the steering torque calculation? i have basically done steering calculations from erik zaptal's paper.

[Jay Lawrence]

Really? It's a moment about the king pin, where the moment forces originate from the contact patch. Larger/longer toe-base/steering-arm = lower torque. Conversely, larger castor = higher torque. In a nutshell...