Why do sports bikes have far wider rear tires than at the front? Here
is an example of what I mean:
http://www.shakey.com/viewimage.asp?ID=148&Res=1

As the rear is so much wider, how, when the bike is going around a
sharp corner, does the front wheel not run out of tire long before the
rear? Would it not just be safer to give the front an equally wide
tire?

In the MotoGP series of bike racing, the more powerful bikes have
larger tires. Compare this 125cc bike with the one above:
http://images.motogp.com/multimedia2/503/503962_22905.jpg

Obviously the larger tire is somehow related to the power of the bike.
But why not just give the less powerful bike larger tires? Would this
give them more rear wheel grip and make them safer?

Thank you for reading!

Dear biffta-ga

Thank you for allowing me to answer your interesting question.
Actually the overly large SIZE of the rear tire on a racing motorcycle
is not the only issue relative to ?providing? power, traction and
stability. Here?s the deal: The wider and larger tire, by virtue of
it?s much greater surface area, is capable of absorbing and dispersing
much more intense heat that the friction of a powerful high-speed bike
produces than that of it?s more narrow or smaller counterparts. Rubber
tires, as you know, are made of vulcanized petroleum products.
Vulcanization is typically considered an irreversible process by which
the molecules of the rubber are chemically bound together with
polymers. However, since the vulcanization is a thermally produced
process it can, under the most intense heat, be undermined. When this
happens the petroleum in the surface rubber that is subjected to the
greatest amount of heat reverts to some extent back to its former
greasy, oily state and the result is literally a slick tire. This is
where the term ?racing slick? comes from on treadless tires that are
intended to reduce friction under heated conditions. On rail cars for
example a racing slick is heated so that it does not grab the road too
tightly on takeoff. Once the vehicle is underway the slicks cool by
virtue of their enormous surface area that aids in the rapid dispersal
of heat, regain tremendous surface tension and help propel the car
forward.

Likewise on a racing motorcycle the greater rear tire must disperse
heat under such power of the drive train in order to remain effective.
The front tire, which is not under such direct force of the drive
train, does not exceed a level of heat that rapidly jeopardizes the
chemical vulcanization of the rubber and does not necessitate rapid
cooling. Over time however the front tire, like the rear, will
eventually overheat or have reached it?s thermal limit and it too will
begin to break down. The larger rear tire increases the lifespan and
effectiveness of the rear tire roughly equivalent to the lifespan of
the front tire under the same conditions (measured in time, not use).
This not only allows for a safer and more effective ride, it also
allows for a remarkably fewer number of single-change pit-stops.

Why not just give the less powerful bike larger tires? It doesn?t need
it because it doesn?t generate the heat that a bigger bike generates
(remember, the big tire is relative to heat dispersal and not directly
to traction). Would this give them more rear wheel grip and make them
safer? Perhaps, but it would also make them much heavier, less
aerodynamic and more unstable. On a smaller, less powerful bike, since
the need for additional power to spin the bigger tire would undermine
any increase in speed that more traction would potentially provide,
the additional power needed to spin the greater/wider tire would most
likely detract from the power rather than increase it.

I hope you find that my answer exceeds your expectations. If you have
any questions about my research please post a clarification request
prior to rating the answer. Otherwise I welcome your rating and your
final comments and I look forward to working with you again in the
near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad-ga ? Google Answers Researcher



INFORMATION SOURCES

VULLCANIZATION
http://en.wikipedia.org/wiki/Vulcanization

CLASSIC MOTORCYCLES
http://www.classicmotorcycles.biz/mechanics/wheels/thread98.html

MOTORCYCLE TIRE RIEVIEWS
Stick to the road, Buddy
http://www.best-motorcycle-gear.com/motorcycle-tire-reviews.html

THE MOTORCYCLE
http://www.flamesonmytank.co.za/tyres.htm


SEARCH STRATEGY


SEARCH ENGINE USED:

Google ://www.google.com


SEARCH TERMS USED:

MOTORCYCLE

RACING

TIRES

TYRES

SLICK

VULCANIZATION

TRACTION

FRICTION

HEAT

Tutuzdad-ga   

 "On rail cars for example"

I have never heard of rail cars having rubber tyres.  is this a
mistake or can you give examples


Kemlo

I apologize if there was any misunderstanding. Perhaps this is
regional slang. What I intended to convey was "rail dragsters" or "hot
rods" as they are sometimes known in the sport of straight-line drag
racing.

Thank you for pointing that out.

tutuzdad-ga

Here is an example of what is known regionally as a rail car:

http://www.mrp.org/rad_carshow/Davin%20Costa%2014%20yrs%20old%20-%20555%20Jr.%20Dragster.jpg

I have just read about rail cars with rubber tyres

Parts of the Paris Metro the railcars have steel wheels with solid rubber tyres?

Klemo

"This is
where the term ?racing slick? comes from on treadless tires that are
intended to reduce friction under heated conditions. On rail cars for
example a racing slick is heated so that it does not grab the road too
tightly on takeoff. "

This is exactly 100% wrong.

Racing slicks are called slicks because they are smooth or slick.

A dragster's tires are headed to INCREASE friction between the tires
and the road. Heating softens the tires and causes them to grip
BETTER. You can Overheat a drag tire. At that point you are decreasing
traction. Which is bad.

The ONLY thing keeping top fuel dragsters from going faster is tire
traction. Those guys know how to get the most traction possible.
That's why they are doing the burnout.