driving on 4 narrow spare tires (or similar) to reduce rolling resistance

[duffremle]

I'd call or e-mail Coker and ask them, maybe both. I'll bet there's an engineer or materials guy there who could give you a damn good idea of how sticky they are and how they'd perform for fuel efficiency.

[Ryland]

Originally Posted by mans

mwebb, does that still apply if my skinny tire has 50 psi?

How well do your current tires roll with 50psi? in theory they should roll easier then a narrower tire at the same pressure.
Any idea if there are any 175mm tires out there that would fit your car that are LRR? you might find that they are going to work better and give you better mileage.

[Ken Fry]

[QUOTE=mans;276425]

Originally Posted by Ryland

if there was a middle digit it would be like 125/150/R15 cuz the sidewalls are so tall while the width is so small!
see again here up close: Firestone F560 - 125R15

Remember... math is your friend.

125 tires have a 5" section width. 23 -15 is 8, so the section height is 4. Therefore the profile is .80.

http://www.wbdg.org/ccb/GREEN/REPORT...resistance.pdf
http://www.energy.ca.gov/2006publica...0-2006-001.PDF

Unfortunately the 560 is not listed in either of these, but the 560 is similar to the 680, and is probably about the same in Crr: .010. As you can see from the TRB report, most tires are pretty close to .010. The Bridgestone 381 is the only real standout.

Depending upon what you have done about aero on your car and how fast you drive, you might find that a a narrow tire has enough less aero drag to make up for average rolling resistance.

There is always tread shaving too. One characteristic of most Low rr tires is a thinner tread.

[CapriRacer]

Originally Posted by duffremle

I'd call or e-mail Coker and ask them, maybe both. I'll bet there's an engineer or materials guy there who could give you a damn good idea of how sticky they are and how they'd perform for fuel efficiency.

An educated guess: Coker's market is vintage cars. Those folks are not going to be interested in fuel economy.

Further, because the market is pretty unique, even the prices aren't very good. I wouldn't expect tires from Coker be anything other than generic tires - without any redeeming qualities.

[mans]

[QUOTE=Ken Fry;276478]

Originally Posted by mans

There is always tread shaving too. One characteristic of most Low rr tires is a thinner tread.

on tread shaving these are pretty good the tread is only 2.75" wide

[Ken Fry]

[QUOTE=mans;276589]

Originally Posted by Ken Fry

on tread shaving these are pretty good the tread is only 2.75" wide

You don't shave the tread to make it narrower. When you shave the tread, you make the tread thinner, so where it used to be 1/2" thick in the middle it becomes 3/8", etc.

The tread bends as it flattens onto the road, and then straightens when it leaves the road. This bending absorbs energy, and therefore the tire heats up. If the rubber is high hysteresis (not bouncy) a lot of energy is absorbed, (and relatively little is returned) and other things being equal, the tire rides better and is quieter, but less efficient.

In a low hysteresis tire, a larger part of the energy required to flex the tire is returned when it unflexes as it leaves the pavement. This makes the tire bouncier, but more efficient.

As you can imagine, a thicker tread is harder to flex, so absorbs more energy when it flexes, and (especially if high hysteresis) returns less when it unflexes.

Bonneville cars used to shave the tread on tires for these reasons -- both to use less energy (to make the car faster) and to generate less heat (tires convert wasted energy to heat) so the tires don't overheat (and also to reduce centrifugal force).

If you compare tread depth specs on the tire sites, you'll find that Low rr tires often have thinner treads for the above reasons.

[euromodder]

Originally Posted by mans

the results of metrompg's tests with the spare tire donuts baffle me, i cannot understand how the doughnuts performed so awfully on his RR tests.

They were never meant to have good RR.

They were intended to be light & cheap, with relatively good grip (so they won't last very long).


In 15", Continental have the older 135/70/15 Ecocontact EP - SI: T & LI: 70 - though they don't come cheap (85 euro apiece) and might not even be available in the US.

[mans]

Originally Posted by euromodder

They were never meant to have good RR.

They were intended to be light & cheap, with relatively good grip (so they won't last very long).


In 15", Continental have the older 135/70/15 Ecocontact EP - SI: T & LI: 70 - though they don't come cheap (85 euro apiece) and might not even be available in the US.

this is most interesting. is this continental a low RR tire? it sure sounds like it from it's name of "ecocontacct ep"

can you show me a link where I can purchase such a tire?

[oil pan 4]

I have found that taller tires give you lower cruise RPMs (there for more fuel economy) and the lower cruise RPMs effects fuel economy more than the tire being bigger or heavier.

[mcrews]

Originally Posted by oil pan 4

I have found that taller tires give you lower cruise RPMs (there for more fuel economy) and the lower cruise RPMs effects fuel economy more than the tire being bigger or heavier.

Since the skinny tires have a SMALLER OD, then that is a mute point.

He really is clueless.
Don't know the type of car.......if front wheel drive this borders on suicidal.
The will be no trade off as he suggests.
He is reducing his ability to react in an emergency to absolutely ZERO.