Tire width impact on fuel economy / MPG

[freebeard]

CapriRacer — You seem to know your tires. In the crowd I ran in (the undersize-the-end with-the-speeometer-cable one) the tribal wisdom is that the best tires were Klebers. When they opened an American factory and the tread pattern changed and the American-manufactured version 145s weren't 'as round'. Is roundness an actual thing? Don't they shave tires to concentricity?

It's easy enough to see that the surface and the weather all come to bear. I watched a Youtube video of a contest between a Tesla Model S and a Hummer starting and stopping on, and backing up an incline of solid ice. It wasn't a contest between the vehicles as much a between studded and unstudded but sipped tires.

[CapriRacer]

Originally Posted by freebeard

....... Is roundness an actual thing? . Don't they shave tires to concentricity? .......

The actual term is *Uniformity*, which is more than just roundness. It's also variation in stiffness.

So, Yes! It is a thing. Vehicle manufacturers specify the type and amount of each type of uniformity they allow - and usually the specs are pretty tight. The tire manufacturers have machines in their factories that measure uniformity. There are 2 types of machines: Tire Uniformity Graders (TUG's) and Tire Uniformity Optimizers (TUO's) The TUO's have a grinding mechanism that will reduce the amount of uniformity in addition to their measuring capability. BTW, these types of machines are in the million dollar range - per machine, and a tire factory will have dozens of them.

So, Yes! They do *shave* tires, but it's a bit more sophisticated that just shaving for roundness.

If you look up Hunter GSP9700, you'll find a shop level machine that closely resembles the more expensive TUG's, but is much smaller and less expensive, but doesn't have the capability of correcting uniformity - except by reorienting the tire on the wheel.

[Ecky]

Do you know if there are any "bicycle" tires which have flat treads, which would be appropriate for use on trikes and quads? How would their performance be when compared with standard round tires?

[CapriRacer]

Originally Posted by Ecky

Do you know if there are any "bicycle" tires which have flat treads, which would be appropriate for use on trikes and quads? How would their performance be when compared with standard round tires?

I worked for a major tire manufacturer in the passenger car tire and light tire area. I don't know other types of tires very well.

- BUT -

I would think that bicycle tires are by definition at least moderately curved in the tread area or they wouldn't function correctly. (Yes, I am aware of "Darkside" in the motorcycle arena.)

So either a trike or a quad would use bicycle tires or some other type of tire (which would in turn, not be appropriate for a bike)

[Ecky]

Right - trikes and quads use bicycle rims, but the angle of the road relative to the tire does not change, which suggests to me that bicycle tires are probably not most appropriate for these uses.

EDIT: I found one example of what I was asking about, on Amazon:

https://www.amazon.com/Schwinn-Cruis...ser+bike+tires

[oldtamiyaphile]

Originally Posted by CapriRacer

...because I had had other conversations where some folks assumed the RRC was a constant at a given pressure. I would really like to clear this up, but so far I haven't been able to.

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.

[aerohead]

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.

The only thing I've run across had to do with the first Audi Quattro.
They mentioned that a 'driven' tire had less rolling resistance than a 'coasting' tire (my terminology),and that over 100-mph,the Quattro actually had less rolling resistance than it's 2WD stablemate.But only above 100-mph.

[freebeard]

http://cdn.dragzine.com/wp-content/b...ch.Burnout.jpg

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.

[aerohead]

Originally Posted by freebeard

http://cdn.dragzine.com/wp-content/b...ch.Burnout.jpg

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.

They've got to engineer for the 'growth' of the tire diameter.

[California98Civic]

Originally Posted by aerohead

The only thing I've run across had to do with the first Audi Quattro.
They mentioned that a 'driven' tire had less rolling resistance than a 'coasting' tire (my terminology),and that over 100-mph,the Quattro actually had less rolling resistance than it's 2WD stablemate.But only above 100-mph.

How on earth did they measure this? On a dyno or something similar, I guess?