Tire width impact on fuel economy / MPG

[CapriRacer]

Originally Posted by 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. ........

I don't think California ever finished the regulation. They got as far as requiring trucks to use SmartWay tires, but I don't think they got to the point where they mandated passenger car tire manufacturers to published rolling resistance information. I think they deferred to the Feds (NHTSA) and that regulation is taking a long time to work its way through the system. The last I heard, NHTSA was going to publish the regulation in August, 2018 with the end of comments due by Oct, 2018.

[aerohead]

Originally Posted by CapriRacer

I don't think California ever finished the regulation. They got as far as requiring trucks to use SmartWay tires, but I don't think they got to the point where they mandated passenger car tire manufacturers to published rolling resistance information. I think they deferred to the Feds (NHTSA) and that regulation is taking a long time to work its way through the system. The last I heard, NHTSA was going to publish the regulation in August, 2018 with the end of comments due by Oct, 2018.

I appreciate the heads up.'thought the consumer finally had an ally.Too bad for us.

[slowmover]

65-series covers relative safe handling & braking (in all conditions), plus not unreasonable FE.

Mercedes was equipping their sedans with such in the early 1970s. American cars, even with radials (a few years later) were still on 75-series tires. 78 on one of our cars.

Was hard to make the argument about noise, ride, etc, since suspension tuning was what was lacking.

I’ve not ever seen 60-series and wider do anything for FE. Like the the 60-mph aero wall, 65’s are the end of the pursuit of “wider” (as with “faster”; one needs to apply tools never used to chase higher speeds to understand compromise).

[slowmover]

Originally Posted by 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.

Kleber? I’ll bet you were trying to figure out how to fit Michelin XWX. Such a Beetle would indeed be Super with that, ah, (said with a straight face) “requirement”.

[freebeard]

OnlyOldiesGarage.com*::*Tires by Size*::*185/70VR15 185/70R15 185R15 MICHELIN XWX 'V' Sped Rating Black Tubeless

A very similar tread pattern. Perhaps there's some connection between Kleber and Michelin I'm not aware of.

215/70VR15 215/70R15 MICHELIN XWX 'V' Speed Rating Black Tubeless
Our price: $384.00

The Superbeetle has Federal Formoza FD-1 in 165-50/15. They were [at the time] available in -45, -50 and -60 aspect ratio in that size. Once the sidewall height is equal to a traffic bump strip height, it's good.

[slowmover]

Required tire on a Ferrari in 1970s

[JohnAh]

My personal real world report:
I've been hypermiling my old Saab for some years now, starting quite easy with reducing speed and changing over all gearing ration by changing tyre dimensions and experimenting with tyre pressure. The changes were quite marginal, but it appeared as larger circumference and higher pressure gave a small improvement of fuel efficiency. I had plans to go for the extremest possible with high and thin tyres on DIY-built rims.

All this suddenly got reduced to a "don bother" when I started hypermiling for real with engine shut-down and acceleration in one minute cycles. My mpg climbed like crazy! After I had learned to fine-tune this driving technique I got to a quite steady level of about 50% of the usual fuel consumption of this particular type of car. I then widened the rims heavily and replaced my 165R15 with 195/65R15, lowered the car quite a bit and went for a stylish rat-look.

I had already a heavy right foot so no change there. The dramatically improved road holding allowed me to take the corners a lot faster, but I still drove with safety as the number one priority. The interesting part is that the lower but wider tyres now was impossible to track in the fuel economy. When I earlier tried smaller tyres I noticed a slight loss of fuel economy.

I guess the answer is that tyre dimensions CAN change the fuel consumption, but the driving style do so much more that it's actually marginal. Then offcourse, there are tyres (threads in particular) that are really hard rolling. Some older winter threads are notorious, and there's probably no surprise that many offroad tyres are too. For modern "normal asphalt tyres" I think you can put almost anthing to the car and get a much larger benefit from changing driving style!

[gdcwatt]

Because I had them lying around, I once put a set of 205/xx-yy snow tires on steelies (15s or 16s, and either 65 or 70 series) from a 2001 Grand Caravan onto a 2005 Mazda 6 2.3L auto, in place of the Mazda's 215/50-17 tires. The snow tires were about 5 - 7 % larger in diameter (hey, it was a long time ago), but right from the start it was obvious that the Mazda's transmission did not like the change: in particular, up shifts while driving "normally" became unpleasantly abrupt. A month or two later I put the Mazda's summer rubber on the car, and everything returned to normal.

[RedDevil]

Jason Fenske (Electrical Engineering channel) had an interesting take on tire and wheel size versus economy:

https://www.youtube.com/watch?v=NYvKxsYFqO8

He focused on the effects on economy at 75 mph from a theoretical point of view, but also using EPA data. And he doesn't waste time; it is 11:47 packed with data and calculation.

[CapriRacer]

Originally Posted by RedDevil

Jason Fenske (Electrical Engineering channel) had an interesting take on tire and wheel size versus economy:

[Video omitted ]

He focused on the effects on economy at 75 mph from a theoretical point of view, but also using EPA data. And he doesn't waste time; it is 11:47 packed with data and calculation.

The problem with the video is that he exaggerates the affect of aero (He used 100mm more: Normal would be 10mm to 20mm increase), the rolling resistance effect (He uses coefficients of 3 times when the extreme range is about 60%, and like to like is a percent or 2.), then doesn't address the weight (moment of inertia). He then takes data submitted for the Mulroney label (the one on a new car's window that says the MPG's) which is the combination of all 3, and declares that to be the definitive difference.

What he leaves out is that the coast down values come in increments - which is one of the reasons why there is a difference in the models (15%, 8%, and 9%) for more or less the same 2" wheel diameter difference.

Do not get me wrong, I think his overall conclusion is correct, but he is doing a smoke and mirrors presentation and exaggerating the difference.

Here's my take on the tire portion of this:

Barry's Tire Tech