here’s getting technical: when you add surface area, force per unit decreases. so say your tire is “grabbing” (key word here) amongst the road surface ///////. say a thin rubber tire is grabbing half of the pyramid. (tire is bulging into the revene of the road grains by half of the pyramids’ height or depth.)
now, when you add surface area, the tire does not “grab” as deep into the pyramid. (this is why some of you say wider is same as thin) HOWEVER, when you add 2x as much surface area, the grab doesn’t always decrease proportionally. (maybe the grab would ONLY decrease by .4) the grab decreases less and less the more and more surface area added. and the grab increases less and less when surface area is taken away making really really thin tires useless and really wide tires much more beneficial. it’s an asymtotic situation.
this grab is what matters. if more pyramids are being grabbed by the rubber, without having to sacrifice a corresponding decrease in each single grab, you will have more friction. thus wider = more available force resistance.
So is letting some air out of your 4X4 tires to allow them to flatten slightly and have more s.a. on the mud/gravel related to this… and does that give any significant advantage?
Originally posted by mmmiiikkkeee
So is letting some air out of your 4X4 tires to allow them to flatten slightly and have more s.a. on the mud/gravel related to this… and does that give any significant advantage?
quote:
Originally posted by scotth
This is to keep floating on the surface of very soft terrain.
Well since were on the topic of tires and contact, if you lower the air pressure below the recommended pressure and if its a radial tire, you lose performance. Because the center of the tire, will buck upward and the only contact you have is the outer edges, not good. However special race tires (sprint car tires) will give you a more contact area if pressure is lowered.
The Land Rover guys I know lower their tire pressure to ensure that most of the tire stays in contact with something, even if it is not level ground. Whether this actually works or not I don’t know, but that is their justification.
andy_fl: could rubber be considered adhesive, by any stretch of imagination? could you define adhesive, as it is used in that quote? i am trying to figure out (for myself) if rubber on road is a different can of worms than classical physics. please consider my last post very carefully, it makes sense to me…
i am so sick right now, i can’t read the deformation link. when i am feeling better…
Fuel, your post sounds likely to me. Which means nothing, because I don’t know one dang thing about it.
I will say this. A college physics professor of mine said that the primary reason tires become bald is NOT “friction” in the sense that word is being used in this thread; but rather molecular contact transference.
In other words, when a section of the tire touches the road and then pulls away, a few molecules remain behind, stuck to the road surface. Multiply by a billion.
Some roadway molecules are also transferred in the reverse direction, but the rate of transfer is obvious very different. (Fred Flintstone’s rock tires are, of course, the exception.)
Yes, rubber can be adhesive and for race cars it usually is. They use very soft rubber. If rubber was not adhesive, it would’nt leave these marks on white pavements when u drove on them. Also, at hot places, you’ll see the skid sign posted on roads. Read more in the quote and read the links in the link too.
Guys, andy_fl has shown you the physics side to it. Surface area is not a factor in friction which is why it isnt mentioned in the Howstuffworks page.
Wider tires are used (and are effective) because it gives the car more area to contact the road should parts of the tire lose their grip or contact. This is not a factor of friction but in keeping the tire in contact with the road. So the grab doesnt necesarily increase in proportion of the area, it just makes it more likely. If we follow the logic of wider area produces more grab then a wider tire would produce so much friction, it would actually be detrimental to the efficiency of the car.
The type of tire used is a factor in friction because tires do tend to be sticky (adhesive) when running hot. Thats why dragsters spin their tires before the actual drag to produce that sticky slick just before they take off. When it cools down, its not as sticky anymore so the next car does the tire spin again.
Threads are used to offset any wind or fluid dynamic that might prevent the tire from effectively contacting the road. A wide no thread tire is better on dry flat conditions but become hazardous in any kind of rain or a loose gravelly road.
I DID understand your post, and was trying to say that it made good sense to me–but then adding, in a modest and (thinks-he’s-) humorous way, that my approbation is pretty meaningless, in that I’m a lay person. That latter does not really negate the former. No criticism of your excellent contribution was intended.
I apologize for my intended positive sounding negative. These are the perils of thinking you’re just too cute for words!