Tire width impact on fuel economy / MPG

[MetroMPG]

Originally Posted by westygo

The BMW electric with the large diameter and narrow tires...

FYI: they released a "sport" version of the car for 2018 with wider tires, and the combined EPA range is down 6% vs. the regular version. (107 vs. 114 miles)

Differences of sport vs. regular i3:

• tires: front 175/55/R20 / rear 195/50 R20 vs. 155 & 175 19's on the regular
• rides 0.4 inch lower on a wider track
• 184 hp / 199 lb-ft vs. 170 hp / 184 lb-ft, via modified motor controls and tapered roller bearings

Source: REVIEW: The first delivered BMW i3 S in the United States

However, aside from the tire width / RR changes, we don't know what other changes they made that might affect rolling efficiency

[freebeard]

My target weight is 1 ton ± so the 155-70/19 would likely be adequate.

I've tired of visiting websites that don't tell the weight of OP's Honda Odyssey.

[Gasoline Fumes]

Originally Posted by freebeard

My target weight is 1 ton ± so the 155-70/19 would likely be adequate.

I've tired of visiting websites that don't tell the weight of OP's Honda Odyssey.

3,450 to 3,483 lbs according to cars.com via Google.

[oldtamiyaphile]

Originally Posted by Ecky

My understanding of this is that "faster" on bicycle tires isn't strictly rolling resistance. Having very hard tires increases rider fatigue, even if the bike rolls easier, so you find people can't put as much power to the road for as long. It's a human limitation which motors do not share.

Correct me if I'm wrong, but a smaller contact patch will result in less rolling resistance, and there are several ways to achieve this. Adding pressure reduces sidewall flex, and sidewall flex eats less forward motion. However, sidewall flex is also what gives a suspension effect, because it also eats vertical motion. The reason we use hollow tires filled with air is not for speed, but for comfort, and to prevent irregularities in the road from tearing our vehicles to bits.

All else being equal, it's better for rolling resistance if the contact patch is longer and less wide, so if you're shooting for lowest rolling resistance possible (often at the expense of ride quality) you'll want very narrow tires with a relatively large diameter - approaching the shape of a bicycle tire.

These are lab test results, considering only RR, not rider fatigue. The difference is even greater with a rider and suspension losses.

A smaller contact patch has a lower RR in theory. Even the smoothest concrete is too rough for that to work in the real world.

Tech FAQ: Again, bigger tires roll faster! | VeloNews.com

EM style coast down testing:

https://janheine.wordpress.com/2012/...ance-of-tires/

Shape of Contact patch:

FLO Cyling - The Contact Patch... Why Wider is Better

Remember also CapriRacer's various posts on the subject, I used to be skeptical too

The i3 could be an example of an evolutionary dead end. No OEM since has gone that way.

[RedDevil]

Racing bicycle tires cannot be compared to car tires. The shape of the contact patch, pressure on the tire, profile, construction, cross section are all completely different.

So Flo Cycling claims racing bicycle tires (with a extremely long and narrow contact patch) would have less rolling resistance if the patch was shorter and wider.
Sorry, I disagree wholeheartedly.
While it may seem logical at first glance it ignores what's really happening when the tire moves.

The contact patch is not static. As the tire rotates it shifts, obviously.
Now imagine the difference after shifting one inch. There'd be a new C-shaped section on one side while on the other side such a section is removed.
The total surface of the new section is the distance traveled times the width of the patch. That's the amount of rubber getting into contact with tarmac.

If the contact patch shortens and widens (assuming identical load and pressure) the C shape for the same distance will have shorter ends but a wider body. The surface still is distance traveled times width of the patch; as the patch is now wider, that area is also bigger; more new rubber getting in touch with tarmac, while the pressure is still the same.
That seems to indicate more friction for the wider tires, not less.
Now this was a simplified model; there are many other variables at play like the flexilbility of the tire, angle of attack on the contact patch, friction in the patch as the rounded tire progresses, etc.

Yet the truth is easy to find by looking at the tires used by professional road bicycle race teams. They typically use the narrowest tires possible at very high pressure.

As I wrote it is very hard to compare bicycle and car tires as they are fundamentally different. Yet, also on cars a wider tire does mean the contact patch area delta (change over a small distance) is equally larger, and so would be the rolling resistance.

Narrow tires with relatively high sidewalls and high pressure rule economy runs.

[California98Civic]

Originally Posted by MetroMPG

... However, aside from the tire width / RR changes, we don't know what other changes they made that might affect rolling efficiency

Absolutely. But it is a reasonably safe assumption that they would not be using narrower tires if they knew it would undermine any further changes they were making to improve rolling resistance and range. Especially in the era of wide and low profile tire popularity.

This is a great discussion thread in general, too.

When I bought the MINI seven hole 15" wheels recently, it was partly because it had 175/65 tires. That is the same width as the tires on my 13" VX wheels. The new wheels are just 12 pounds to the old ones 9.7 lbs.

In sum, same width, much taller gearing modest but significant weight penalty.

I learned all of that on EM (sure hope it is true, haha!).

[CapriRacer]

As has been pointed out, there are a lot of variables.

In fact, I looked at tire rolling resistance here: Barry's Tire Tech - Rolling Resistance and Fuel Economy

With a followup here: Followup an Rolling Resistance and Fuel Economy

Bottom line:

All other things being equal, a wider tire is better for rolling resistance - and it is likely that it will still be better overall - including aerodynamics, because tires are typically surrounded by the car body and only a small portion is exposed to oncoming air.

The biggest problem is that very rarely are all things equal. Proper selection of a tire can pay dividends in fuel economy.

[California98Civic]

Originally Posted by CapriRacer

... All other things being equal, a wider tire is better for rolling resistance ... The biggest problem is that very rarely are all things equal....

That's the problem alright. As the links you posted offer, there are four variables here (atleast). I'm certainly not about to put a 215 width tire on my car instead of a 175 and suffer an aero penalty unless I also take into account the publicly available "data" of weight, LRR reputation, and wheel face design (smooth or turbine?) for that 215 width tire/wheel combo.

[westygo]

Great discussion.
Freebeard, GVWR is 2150 kg according to door jamb sticker. Which seems incredibly high for. 2.3L 4 built on an accord chassis.
looks like I have to compare RR in tires in the size range I am looking for, as well as available rims. No real comparison to make, and once I bite the bullet and buy, I get what I get!

[aerohead]

Some other reports which confirmed a direct correlation between tire width and aero drag were found with the:
*Pontiac Trans Am
*Subaru XT
Also,many of the lowest drag concept cars ran narrow tires as a low-drag strategy,including:
*GM Aero 2000
*GM Aero 2002
*GM Aero 2003
*Renault Vesta-II
*Ford Probe-IV
*LOREMO
*Daihatsu UFE I,II,III
*VW 1-Liter 2002
*VW 1L c 2009
*VW XL1 2016