breaking

[A]

hello guys im doing knuckle and wishbone force analysis for our car and i have 1 doubt...while breaking there will be
1. friction force between the tyre and ground
2.and there will be friction between caliper and break disc, this force will give reaction on caliper mounting
which is on knuckle
do we have to consider both of these forces while doing analysis??

[Z]

A,

I think your car will do a lot of "breaking"...

Z

[A]

can u please explain.... as this is our first time i might be asking bad question im sorry for that

[Edward M. Kasprzak]

You have made an error that is far too common. You're not the first, just the most recent. I see it regularly in design reports http://fsae.com/groupee_common/emoticons/icon_frown.gif. Check out the definition of "breaking", as opposed to what you meant.

[Racer-X]

The way you are wording this is rather confusing. You will want to consider the forces acting on the part you are analyzing.

The friction of the tire on the ground is only as great as the force trying to break that traction, ie push a book and if it doesn't move the friction force is equal to the force you are applying. When it comes to tires they can only take so much force before they will skid. That limits the amount of stopping power you have, therefor limiting the forces on the upright to whatever the tire can handle. So the friction of the tire is not included in the math to figure out the mounting on the bakes, but will limit the forces that the caliper will see. You want to look at the force from the caliper on the rotor. You would use tire friction on the design of the upright as a whole though.

By the way if you do this wrong your car will be breaking a lot.

Don't ask me how to get these numbers I am the engine guy.

[A]

sorry i forgot to mention,we are considering all forces at the tyre contact patch and transferring them to the knuckle

[Edward M. Kasprzak]

The "FBD Police" seem to be on holiday today...by now someone usually suggests/snipes that you need to draw a free body diagram and see how it goes.

Where you draw your system boundaries determines what is considered an external force and what is considered an internal force. And where you draw your system boundaries is determined by what you want to learn from the FBD analysis.

[wagemd]

I don't really intend to sidetrack or troll this conversation, but I cant help but be amused that its bouncing between A and Z... Maybe the coffee hasn't kicked in yet...

[Owen Thomas]

Originally posted by Edward M. Kasprzak:
The "FBD Police" seem to be on holiday today...

A,

Draw a Free Body Diagram. http://fsae.com/groupee_common/emoticons/icon_wink.gif

You will very quickly find out why your question appears to be silly. One of the forces you asked about is a reaction to the other. If it does not become obvious why, I would suggest having a sit down with your first year mechanics professor to review some (all) concepts.

Oh, and just so you get the running joke, "brakes" stop a car. Your uprights will break when your brakes are applied if you cannot do this analysis correctly.