Tire width impact on fuel economy / MPG

[oldtamiyaphile]

Originally Posted by freebeard

Top Fuel dragsters use bias ply low pressure 'wrinkle wall' tires. At high RPM at the start line they grow visibly, at cruise would this not affect overall drive ratio? Belts would help.

Having your final drive increase at speed would not be a bad thing in general.

[Daschicken]

Originally Posted by oldtamiyaphile

As speed increases so does centrifugal force on a tyre. It would make sense to me for CRR to drop as speed rises- the tyre essentially becoming harder.

Cd isn't a constant either, we just tend to treat is as such.

Nope, CRR goes up as speed goes up. I looked up a study on bias ply vs radial tires trying to see what kind off CRR differences there were. They concluded that the difference between a bias ply and radial tire is about the difference between a normal tire and a LRR tire. My baby V4 is stuck with bias ply tires thanks to current tire manufacturers' lack of tire choices, and its weird tire sizes. The study also says the larger tires have less rolling resistance, but there was no mention AT ALL about the actual width of the tire, just the rim size.(I think)

[freebeard]

That was a big selling point when they were introduced to the American market. My first set were Goodyear fiberglass-belted bias.

https://en.wikipedia.org/wiki/Goodyear_Polyglas_tire

F-60/15s on 8" Buick rims with VW centers. Too much tire, I lost 5mph top speed, but it cornered like it was on railroad tracks.

What's your PCI (bolt circle diameter) and offset; and tire height/circumference. I'm thinking of the rim size going +1 or +2.

[CapriRacer]

Originally Posted by Daschicken

Nope, CRR goes up as speed goes up. I looked up a study on bias ply vs radial tires trying to see what kind off CRR differences there were. They concluded that the difference between a bias ply and radial tire is about the difference between a normal tire and a LRR tire. My baby V4 is stuck with bias ply tires thanks to current tire manufacturers' lack of tire choices, and its weird tire sizes. The study also says the larger tires have less rolling resistance, but there was no mention AT ALL about the actual width of the tire, just the rim size.(I think)

Attachment 23749

Can you post a link? My search didn't turn up that chart.

[Ecky]

I sent an email to a few tire companies with some of the questions brought up in this thread. I'll report back if I get any answers.

[Daschicken]

Originally Posted by CapriRacer

Can you post a link? My search didn't turn up that chart.

To find it, I just looked up on da googz "bias ply vs radial rolling resistance", it is the first link.

Variations in tire rolling resistance

https://nepis.epa.gov/Exe/ZyNET.exe/...kPage=x&ZyPURL

[Ecky]

Great article. I find it interesting that they tested them at 26 PSI. Looks like bias ply isn't necessarily much worse than radial, but the tires tested from Continental and Semperit were well below the rolling resistance of the other brands.

[CapriRacer]

Originally Posted by Ecky

Great article. I find it interesting that they tested them at 26 PSI. Looks like bias ply isn't necessarily much worse than radial, but the tires tested from Continental and Semperit were well below the rolling resistance of the other brands.

A couple of thoughts:

That paper was from 1978, and the tires were from vehicles produced as early as 1974! that's why the bias tire pressures were as low as 26 psi. That was the pressure that was sometimes used in those days.

Plus, all those tires were OE. Nowadays the RR values for OE tires is considerably lower than for replacement market tires - but back then??

If I had to fault the writers of the report, it would be that they didn't mention that it was very likely the radial tires had harder, more wear resistant tread compounds than the bias tires. That would also mean that the radial tires could have achieved better RR if they used the bias tire tread compounds.

And then there is the business of tire size. We now have evidence that tire size plays a role in RR - and larger tires are better than smaller tires. Their data seems to point that direction.

And brand? If I remember correctly, they said that this might be due to the particular tire size they tested. Besides we are some 40 years after that paper and a lot of research has taken place. I wouldn't draw any conclusions from the brand data because the data is so old. My experience is that there is very little difference between brands - that the difference between an OE tire and a replacement market tire is way, way more different.

[freebeard]

That era was peak automobiling for me. I drive much less now.

Continental was OE on Volkswagen. The fashion at the time was to upgrade to Kleber. It would be interesting to have data on them as well. The era ended when Kleber opened an American factory. They 'weren't as round', and the tread pattern changes. Who knows what else.

[aerohead]

It is California state law,that rolling resistance data for all tires sold in the state be provided to the consumer.
You should be able to contact a seller and request the data for your tire options.
Old school logic from the days of GM's TPC was that with an increased diameter/radius/circumference,each individual tread block would visit the road surface less often for each revolution.
Heat generated at the hinges of each block,as well as sidewall deformation would be reduced,as there would be fewer deformations per revolution with the 'larger' tire.
Hysteresis of the rubber itself is an issue,as it determines the amount of entropy(energy lost to friction heating) during cyclic deformation.In a perfect rubber,there'd be no heat generated,but you might not have any traction or tread wear life either.Lots of trade offs.