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

[mans]

the od of the tire can be seen at the address I mentioned earlier, I could not post proper links till I had 5 posts.

it's 23" OD for the 125 and 23.57" for the 135's. stock od's are 23.75".


as to handling and safety concerns I imagine it would be a trade-off where wide tires would equal good handling and low economy while narrow ones would give low performance and higher economy.

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.

4 vehicles would have been in for the mod if this was proven to work, the lightest of them 2500 lbs but the heavier ones would require slightly higher loading capacity. however I don't think these 125mm tires are really what is needed for this type of job.\
http://store.cokertire.com/catalogse...sult/?q=125R15

[mans]

yay!!
I can post links!!

here we go, for everyone to see.
Search results for: '125R15'
Search results for: '135R15'

the 125's have a 695 pound load rating per tire, but the 135's are much better. however metro mpg's tests show this is a total shot in the dark.

[Frank Lee]

Where is that r.r. value for the classic 2CV and VW sizes- 125/15 and 135/15?

[mans]

Originally Posted by Frank Lee

Where is that r.r. value for the classic 2CV and VW sizes- 125/15 and 135/15?

yeah, kinda what I'm looking for!

yes the coker tires that are on my links were intended for vehicles similar to the 2cv or others from several decades ago.
these tires are highly unusual cuz they will go on a 15" rim and your outer diameter will match or even exceed your stock tire's od even tho they are only 2/3 of it's width cuz the sidewalls are so tall!

I now see where people were getting confused when I wrote the tire is a 125/15

these numbers are from way back when tires didn't have 3 numbers like we do today.
125/15 means 125(width)/R15 there is no number for the section height, just width and rim diameter

[FastTrack]

anyone know anything about the rolling resistance of snow tires?

[mans]

[QUOTE=Ryland;276367]You don't say what kind of car you have or even your full tire size



the full size of the tires I was LOOKING TO ACQUIRE is 125/15 there is NO middle number for these old tires. see link http://store.cokertire.com/125r15-fi...wall-tire.html

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

[Ryland]

Originally Posted by mans

these numbers are from way back when tires didn't have 3 numbers like we do today.
125/15 means 125(width)/R15 there is no number for the section height, just width and rim diameter

When a tire doesn't have the middle number it's assumed to be 85 or the height is 85% of the width, more or less a round cross section of a balloon tire.
Reproduction tires for classic cars tend to be hit and miss as far as quality because they are designed for classic cars that have a top speed of 55mph and spend most of their life going to car shows.
Rubber compound has as much to do with low rolling resistance as anything else does, narrower tires are lighter weight and have less air drag, that is about it, low rolling resistance has more to do with tire deflection then how narrow the tire is, for low rolling resistance you want a tire that creates a foot print that is not as long, the flat spot caused by deflection is not as great so it is not climbing as large of a hill as it rolls.
That is why if you put me on a bicycle with narrow tires I have to pedal harder then if I'm on a bicycle with wider tires, of course the trend is that wide tires are soft and sticky, narrow tires are stiffer rubber, but how do you tell what is what? you look for the Low Rolling Resistance tires as they are often made with silica rubber, a stiff but grippy rubber so you get good traction with less resistance.

[mwebb]

the tall skinny tires do not have lower rolling resistance than tall fat tires
because
the patch (area of tire that contacts the road )size remains the same so the skinny tire must deflect the sidewall more as the tire rolls , which causes more heat and
higher resistance to rolling

a ten speed bike tire will have the same "patch" size as your car's tires when loaded to the same value ,the bike tire would fail very quickly , the comparison is not valid

your basic theory is incorrect , listen to what the others have said
making this switch would cost me around $425.

worth it?

anyone know what kind of mpg gain the decreased rolling resistance would equal?

right now I have no idea if it's 1% or its 20% or so I'm having trouble deciding if I should go for it.

can anyone shed any light on this?


(I do know that 10 speed bike tires are really low rolling resistance, so the smaller your footprint is the better your mpg's should be but I have trouble calculating what the gain would be for this car tire project, I welcome all feedback)

[QUOTE=mans;276425]

Originally Posted by Ryland

You don't say what kind of car you have or even your full tire size



the full size of the tires I was LOOKING TO ACQUIRE is 125/15 there is NO middle number for these old tires. see link Firestone F560 - 125R15

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

[mans]

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

[Frank Lee]

I think perhaps there could be a r.r. improvement with skinny tires IF the vehicle is never heavily loaded and it would also help if the vehicle went through a weight loss regimen.

One of the questions is do these 125 and 135 tires have low r.r. and Mr. Fry insinuated that he's seen the values? The low amount of plies suggest they might. The thin sidewalls suggest they might. Some have nice tread patterns that suggest they might. Unknown is if they are made with nice low hysteresis compounds.