tire width vs. drag (Cd)

[MetroMPG]

A problem that could be solved with gap filling.

[Otto]

Originally Posted by CapriRacer

I don't know about that. My calculations say the opposite.

Barry's Tire Tech

Last bit on the page.

OK, so from your perspective, what's the best 15" tire to put on my BMW 325is?

[CapriRacer]

Originally Posted by Otto

OK, so from your perspective, what's the best 15" tire to put on my BMW 325is?

First, my expertise is in the engineering side of tires - how they do what they do and the like. I don't - and can't - keep up in what is currently available and how they compare to each other.

But you said "best". Best for what property? Wear, RR, cost? You have to answer that question first before searching for what you want.

[Varn]

Have always figured that the accident risk is several times higher under adverse weather in that vein I set up my car for worst case. Dry handling is a no brainer, slip angles are only a fraction of bad weather.

I always try and pick tires that have a tread no wider than the wheel rim width. Going bigger means that I will have a tire tread that is bowed a lot more and is subject to uneven wear particularly at higher pressures.

Wide tires make for slippery handling in the wet and snow. Wide has to clear a lot more material in front of tire so that it can come in contact with the road.

[Otto]

Originally Posted by CapriRacer

First, my expertise is in the engineering side of tires - how they do what they do and the like. I don't - and can't - keep up in what is currently available and how they compare to each other.

But you said "best". Best for what property? Wear, RR, cost? You have to answer that question first before searching for what you want.

RR and fuel efficiency @ ~75mph

[aerohead]

There is an SAE Paper from the 1970s which includes the relationship between aero drag and mpg obtained with the Federal Test Procedures for HWY and City cycles.
I'll dig that out when I can.
Revisiting an article for GM's 1984 Chevrolet Citation IV concept car,GM mentioned to CAR and DRIVER that narrower tires(P195/70R-13) were part of their strategy for their low drag.
Ford,for their Probe IV concept,choose P155/75R-16 Goodyear LDC-1 concept tires.

[Vekke]

Narrow tires:
BMW I3 155/70R19 at front and 175/60R19 at rear on sporty versions
Renault Scenic IV 195/55R20
MB EQXX 185/55R20 (concept)

[Joggernot]

Originally Posted by Varn

I always try and pick tires that have a tread no wider than the wheel rim width. Going bigger means that I will have a tire tread that is bowed a lot more and is subject to uneven wear particularly at higher pressures.

Let's see if I understand this. I have wheels that are 18 by 7. Does this mean you would only use tires that are ~178 mm wide? e.g. 178/70 R18? Recommended by the manufacturer (Honda) for these wheels is 235/60 R18. Per Discount Tire, the narrowest I can fit is 225/65 R18. DT doesn't allow searching for all tires that fit 18" wheels.

[Blacktree]

Originally Posted by Joggernot

Per Discount Tire, the narrowest I can fit is 225/65 R18.

That's probably the narrowest tire they have available. On a 7" wide wheel, you should be able to go down to 195mm tire width. But if nobody makes a tire in that size, you're SOL.

[Varn]

For best winter traction narrower has always worked best for me.

Styles have changed, my vw is recommended to have 175/70x13. I have in the past run 155/80 snow tires on it. Seems like the only 155 tires I can get any more are no name chinese.

This last time, I put on 175/70 dunlop wintermaxx as 175's were all I could get. I don't have the traction of worn 155 firestone winterforce which are nla.

Both tires are about the same height.

So like you, I had to compromise as the tire companies have this perception that consumers want wide tires. Which being wider increase the frontal area of your car and don't work as well under the most adverse weather. Our local roads don't get much maintenance or plowing. Winter is gravel covered by ice and snow. No pure winter tires you don't go.

I get my tires from a mechanic who searches all the consumer and professional tire online sites. He buys discount and passes the savings along. He is usually cheaper than the online places and his prices include mounting stems and balance. He knows I am particular.

Keep looking. obviously your search isn't working. Maybe you can google the tire size that you are looking for or ask your tire installer.

With your location as being texas, do you need winter tires?

Originally Posted by Joggernot

Let's see if I understand this. I have wheels that are 18 by 7. Does this mean you would only use tires that are ~178 mm wide? e.g. 178/70 R18? Recommended by the manufacturer (Honda) for these wheels is 235/60 R18. Per Discount Tire, the narrowest I can fit is 225/65 R18. DT doesn't allow searching for all tires that fit 18" wheels.