Fuel Consumption and Tyres

[melinx]

One of the major factors causing increased fuel consumption in the cold weather is the increased rolling resistance of a cold tyre.

The hysteresis losses in the rubber when rolling help to heat the rubber and reduce the rolling resistance but continually coming into contact with a fresh bit of freezing road offsets this.

When running at speed, there is a standing wave produced in the tyre shape which absorbs power by having to continually deform the tyre into this shape.

This is shown in the link below on page 12 and the graphs of rolling losses on page 13.

http://media.wiley.com/product_data/excerpt/19/04713546/0471354619.pdf

[Johnny A]

So a simple burnout at the start of a drive will fix this

[Dave the Builder]

so we need to take our wheels off and warm them by the fire before driving in the cold ?  

[melinx]

No no; read and inwardly digest a burnout is no good if the tyre is continually contacting freezing road afterward and the same applies to warming them in front of the fire: Tut.

What is obviously needed is a flame thrower in front of each of the front wheels, intensity modulated by an electronic coupling to the speedo.

This warms the road in front of the tyres and allows the hysteresis of the rubber to heat the tyres normally.

The added benefit of this method is that when other drivers see this coming up behind them, they drive into the ditch or up the nearest lamp post, thus giving you unimpeded passage: Simples

[Johnny A]

flame thrower u say!
I am slightly concerned that the initial cost and fuel requirements MAY offset any savings from rolling resistances.

on the other hand, flame throwers are very cool

[melinx]

Do I have to think of everything

Government surplus flamethrowers and used cooking oil from the local chip shop or Napalm from your local American airbase will radically offset the costs

You know you want to Johnny all we ask is that you post the pictures of the mods. and of the system in operation

[kevinfourlegs]

I'd willingly pay good money to see that.

[Catho]

Flame thrower you say.........

....now where have I seen that idea before...............??

[melinx]

That rather reminds me of a cat that we had; partway down the garden was a wall which he used to hide behind in an attempt to catch birds.

The problem was that we threw the bread well beyond that at the end of the lawn and by the time he got there, they were gone.

This is absolutely true : - One day, I saw the cat sitting looking at the bread in deep concentration; he finally picked up a piece of bread, brought it into the house and took it upstairs, dropped it on the landing then hid behind the bedroom door.

The moral of the tale: Great idea but do think it through Mark ; you would only be warming up the road for the car behind you 

[Catho]

The moral of the tale: Great idea  but do think it through Mark ; you would only be warming up the road for the car behind you 

......Yes Mel.....but if you were the car behind then this would be working for you....

[melinx]

And taking all the paint off my bonnet

[Catho]

If you follow the '3 second rule' (like I know you do) I reckon your bonnet will be fine 

[melinx]

OK then you smooth talking devil I'll give you a call when the roads here get icy

Err ... I think I need to think that through !!

[chris]

Just blow the tyres up to 100psi and the rubber wont deform much at all, there will be lots less friction too.

Fitting space savers all round will also reduce friction, or even bicycle wheels.

[man of kent]

The most important factor is to keep the tyres at the correct pressure. As the rolling radius reduces then your fuel consumptionm will be worse even though any consumption figures will be the same. Also the rolling resistance increases. You will also get worse mpg if you change to a low profile tyre. If you do this then its best to fit a larger diameter wheel to compensate.

A word of warning about fitting larger non standard tyres. Although they may not rub anywhere at first sight its possible that on full bump the tyre will touch somewhere. Its even possible that on full bump, full lock you will touch a brake pipe!.

I have even see designs where vans and motorhomes have been fitted with brake pipes that get hit by axles at full bump when the rubber bump stop has gone. The assumption is that the rubber bump stop will stop the axle! When the bump stop has gone and the vehicle is at maxiumum GVW...................!

[melinx]

Chris's over-inflation suggestion seems valid but is contradicted by Wikipedia : -

"Extent of inflation - Lower pressure in tires results in more flexing of sidewalls and higher rolling resistance.[5] This energy conversion in the sidewalls increases resistance and can also lead to overheating and may have played a part in the infamous Ford Explorer rollover accidents.
Over inflating tires (such a bicycle tires) may not lower the overall rolling resistance as the tire may skip and hop over the road surface. Traction is sacrificed, and overall rolling friction may not be reduced as the wheel rotational speed changes and slippage increases.[citation needed]
Sidewall deflection is not a direct measurement of rolling friction. A high quality tire with a high quality (and supple) casing will allow for more flex per energy loss than a cheap tire with a stiff sidewall"

http://en.wikipedia.org/wiki/Rolling_resistance

The space saver/bike wheels suggestion is valid (subject to practical constraints)

The link below demonstrates the temperature/rolling resistance dependency (it refers to bikes but the science is transferable to car tyres) : -

http://www.recumbents.com/mars/pages/proj/tetz/other/Crr.html

From all the above, the solution that seems obvious to me is a car with a single very large narrow wheel.

The car would have to be gyro stabilised but the gyro could be used to store braking energy which is then made available to the wheel drive when needed, resulting in further considerable energy saving.

Remember folks, when you see the first 'Unicar' that you heard it here first

(Posting in haste because they're bringing my medication )

[kevinfourlegs]

Now you know why Citroen 2CVs had 125 x 15 tyres.

[PeterC]

If you rely on  a smooth but hard road surface then you can fit solid wheels. This will remove almost all the friction.

Problem is spinning, sliding and skidding is a lot more likely. You have lost the grip from the rubber.

Solution to part of that problem is to move the curbs close enough together that they provide guidance so keeping you in the correct direction. Still have a problem with acceleration and braking, just have to be gentle (which would save fuel also).

But why bother - just go by train as that is the result. But it would not be fun would it.

[Pedro]

Look at rally cars on snow and ice - they use very narrow tyres. Pure ice racers are fitted with very very narrow tyres.

Neither of these facts have anything to do with saving fuel though!