scathcart

Ok, I have heard all the arguments based on why 3 mm seals are unnecessary and why they are a good idea but create more frcition, and I get all that, but I need enlightenment.
How does a 3mm apex seal create more friction and wear to the block than a 2 mm seal does? F (friction) = F (normal) x u (coefficient of friection). The normal force would be created by the apex spring on the seal and rotor housing, and unless this was upgraded to a higher srping rate would have no effect. The coefficient of friction, would not increase as long as the 3 mm seals were made out of the same material as the 2 mm ones.
If you darag a book widthwise or lentgthwise on a table, the contact area of the book changes, but the force to pull it, and thus the oppsing force of friction remains the same.
What am I forgetting here, or am I on the right track? would 3 mm seals ACTUALLY create more friction?
Sean Cathcart

xiaomingming50

your idea SEEMS right, but think about this

how does a car with wider tires have more grip than a car with thinner tires?

the gravitational force of the mass of the car times 9.8 is still the same, only wider tires, yet more frictional force results, which helps the car grip, same with the seal and the spring
same spring force, but larger area means more grip no matter what

scathcart

No, this is a huge misconception. With tires, you get more grip usually from getting a softer stickier tires. Wider tires them selves do not create any more friction. Alright, so now you're all calling me an idiot for saying that your car will hook and corner just as well with tiny tires, and why would racing cars ever run slicks? True, with just that phrase, I am an idiot. Here's the deal:
No road is the same. When you get down to it, it is rougher in some spots and smoother in the others. With bigger tires, you have a much more likely chance of hitting those rougher spots. The rougher spots have a higher coefficient of friction between the tire and the road, and thus the friction increases. So yes, you'd feel a huge difference upgrading from a 2 inch tires to a thirty inch tire. Try driving on a uniform surface (near impossible to find one) You'll get the same traction no matter what you got bolted on. Big time racers run huge slicks mostly for the force(gravity) they put down. That's also why they fill 'em with water.
So no, you would get no more friction going from a 255 to a 275 tire, except maybe that the 275 woud weigh more.
Inside of a rotor housing is uniform, almost 0 changes in surface coefficient. Comparison cannot be made.
Sean Cathcart
Just did a case study on this.

xiaomingming50

hhmm you're right, after reading that i realized that on thinner tires there is more normal force due to the smaller surface area as well as the friction coefficient.. heh whoda thunk

scathcart

No, that would be incorrect.
On tires, the normal force is equal to the force of gravity on the car if it is on a level ground. If it is on a hill, the normal force is equal to the vector component of the force of gravity. The normal force is always perpendicular to the surface it is acting upon.
Provided the mass (and thus the force of gravity and the normal force) does not change when upgrading to wider tires, and the rubber compound is made of the same stuff, (same coefficient of friction), the force of friction will not change.
So, on thinner tires, there is not any more normal force. Surface area has no effect on friction.

on cars for level ground F(friction)= U (coefficient of friction) x mass x gravitational consant of accleraton. Surface ares never plays a part, only the mass of the vehicle and the too materials in contact.