Tire size and MPG

[mpgx2]

.. after stripping the car of unnecessary things like radio,
aircon, trims, lady-mirror, spare-tyre and using lightweight
wheels..

why ruin all that by making it work for extra load?

Now that you've got less weight to hump about, take
advantage of it and downgrade your tires to suit your
new vehicle weight.



best part is, you actually get more power, and it
takes less fuel to do powerslides. And if people are
too scared to be passengers - well that's their problem.

never needed that deadweight anyway...

[CapriRacer]

Originally Posted by Old Tele man

...often, similar diameter "truck" tires with equal or greater load capacities have narrower widths due to their typical "dually" mountings.

...might be worth looking into what they offer!?!

"Truck" tires are NOT worth looking into if you consider rolling resistance important.

Not only are they designed with "truckiness" in mind - that is, heavier duty load carrying capacities, more tread rubber, and therefore more mass (and more rolling resistance), they also have tread compounds that are more oriented towards more rock cut resistance, more unit loading, etc - all of which hurt RR. In other words, it's all about treadwear and traction and RR really hasn't becomes a design factor in truck tires yet.

[WA1DH]

Switching from P175-65R14 to P185-70R14 tires has resulted in a 2.5% increase in MPG. This is based on the average of the last 5 tanks before the tire change, and the 5 tanks following the tire change. Odometer mileage was corrected based on odometer error for the different size tires.

I haven't entered the data on my MPG sheet here, but have it in a spreadsheet.

[mpgx2]

Yes, you have increased the size of the tyre profile
giving you a bigger wheel size. That gives you taller
gearing and has lowered fuel consumption.

[beer]

Choosing the right size off tyres for better milage, is always a comprimise.
You have to look at which roads you drive the most.
If you drive alot on highways, then you better of with narrow, but large tyres.
The frontal area is less, less rpm's, less rolling resistance, but much heavier.

If you drive a lot in a city, you're better of with small, but a bit wider tyres.
Less unsprung weight, less rotating mass, but more rpm's.
Even better is when you use a bit widther rim then normal, becouse your tyres walls get
stretched and get stiffer, so you can take corners at greater speed.

And always look at the rolling resistance and weight of the tyre, becouse these differ between manufacturers

Michelin is the only tyre producer that i know of that doesn't only look at rolling recistance.
They released a few new tyres 10" sizes and a relative narrow 195/55r21 tyre.
Becouse they to confirm that it always a compremise between the two.

[pgmomni]

Originally Posted by beer

Choosing the right size off tyres for better milage, is always a comprimise.
You have to look at which roads you drive the most.
If you drive alot on highways, then you better of with narrow, but large tyres.
The frontal area is less, less rpm's, less rolling resistance, but much heavier.

If you drive a lot in a city, you're better of with small, but a bit wider tyres.
Less unsprung weight, less rotating mass, but more rpm's.
Even better is when you use a bit widther rim then normal, becouse your tyres walls get
stretched and get stiffer, so you can take corners at greater speed.

And always look at the rolling resistance and weight of the tyre, becouse these differ between manufacturers

Michelin is the only tyre producer that i know of that doesn't only look at rolling recistance.
They released a few new tyres 10" sizes and a relative narrow 195/55r21 tyre.
Becouse they to confirm that it always a compremise between the two.

In my experience, which is 95% hwy driving at interstate speeds, 65-75 mph, larger diameter tires even if they are wider/heavier results in better mpg. The "taller" gearing results in lower RPM's which almost always improves hwy mpg.
Pete

[mcrews]

Peter,
I agree whole heartedly as I posted early on in this thread.

If you are building an 'eco-mobile' and are going all uot....by almeans go for the skinny tire.
But, and I am sure most will agree who have any type of hwy miles, you have to balance the vehicle you have with the 'eco-mods' available.
There is a certain amount of symetry and balance engineered into most cars. when you go too far outside the perameters of the car (the truck tire discussion is a perfect example) you are going to be disapointed in the vehicle ....regardless of the new mileage.

always remember on tires/wheels.....each extra unit of wieght(lbs, etc) is mulitpled times 4 as moving mass and how that plays on the existing suspinsion.