"Given an inflation pressure and a load, the contact patch will be a certain size. For example, at 10 pounds per square inch inflation with a 100 pound load, the contact patch will be 10 square inches.
A major component of rolling resistance, probably most of it, comes from deformation of the sidewall to produce the contact patch.
If the contact patch size doesn't change with the width of the tire, then its shape must. As you make it narrower, it gets longer; that means more deformation of the sidewall. If the contact patch is going to be 10 square inches and your tire is 2 inches wide, then the contact patch will be 5 inches long. If the tire is 4 inches wide, the contact patch (and required sidewall deformation) will be 2.5 inches long."

I think this is true in certain cases but not mine.

In my 1800 lb crx, running the 175/70/13s it had on it when I bought it, I could not exceed 35 psi on the rough roads around here or it would feel like the wheels were going to come off on bumps in the road. With 155/80/13s I can run my tires 20% higher pressure and get the same ride. So I am having the same sidewall deformation and the same ride on the new tires with a smaller contact patch and skinnier aero profile.

If your car rides nice and smooth already at high psi then this would not be an issue for you in your corolla

Actually looking now at Konig Helium 15" x 6.5" wheel at 11.6 LBS and not very expensive...with 195/55-15's....or FAST Synergy 14" x 6" with either of 185/65-14 or 195/60-14. I hate how many tires are not available in different sizes. I want a LRR tire in 195/55-15 or 195/60-14 and they're not easy to find...and especially hard to find is the 185/55-15. The 185/65-14 is easy to find.

I'm looking at some Enkei Racing RPF1 Bright Silver Paint rims from TireRack at 9.9lbs and $199 each I figure I may as well spend a little more money and get some seriously lighter rims and put some Pirelli P4 tires on them which someone in Chicago used on an xB and said they were WAY better than the stock Goodyear Eagle LS factory tires in the snow and have a much higher wear life. Also thinking about the 65 series instead of the 60 series for a little taller tire.

I TOTALLY AGREE I AM GETTING 42MPG AT 68MPH WITH SOME TOYOS THAT HAVE WIDER TREAD THAN MOST OTHER TIRES OF THE SIZE 195 65 15 ON MY SATURN. IM NOT TRYING TO HYPERMILE EITHER, TO IMPATIENT RIGHT NOW.

THE BETTER YOUR CAR HANDLES THE LESS YOU HAVE TO SLOW DOWN ON CORNERS, I ALSO HAVE A SET OF 1/4 INCH ALUMINUM SPACERS ON THE BACK WHEELS BECAUSE THE CAR WAS A LITTLE SHAKY BEFORE(20$), ALL BETTER NOW.ESPECIALLY IN THE 1999 VS 1991-95 BODY STYLE THEY CHANGED THE CAR AROUND BUT YOU CAN GET THE SPACERS AT ANY LOCAL SPEED SHOP.

I HAVE NEVER HAD MPG READING OF LOWER THAN 31 ON THIS CAR. EVER. :eek: AND THE WIDER TREAD= LESS ROLLING RESISTANCE.. I AGREE BECAUSE THE WEIGHT IS MORE PROPORTIONATELY DISTRIBUTED ON THE GROUND LESS WEIGHT PER UNIT. HENCE LESS RESISTANCE, PLUSS LESS SLOWING DOWN.:cool:

THE TOYOS ARE JAPANESE TIRES KNOWN TO LAST TO 70-80K MILES, PLUS ARE WIDER, AND HANDLES WAY BETTER THAN OTHER TIRES FOR THIS CAR IM SURE OF THE SAME SIZE BUT COST 130$ A PIECE NEW......360$ AFTER ALIGNMENT OR SOMETHING.. WORTH IT

no, the contact patch vs pressure is the same no matter the tire construction type (bias/radial) it's physics. if you go to a narrower tire, it will become a narrower longer contact patch BUT you also have to remember that the tire is round and the road is flat. thus the tire will have to flex more to conform to the flat surface, IE higher rolling resistance. you get a softer ride because of the extra flex. the wider tire, having a shorter wider contact patch will flex less to conform to the flat road (since width wise, the tire is essentially flat) so less heat, less RR, better cornering.

as for which size to go with, I'd go with the widest you can fit, as tall as you can fit. as mentioned above, unless the car's already geared crazy high, you'll get better FE (once you adjust your odometer numbers). If your mileage goes down, try going slightly faster: higher revving engine=more power to maintain speed. If the distance payoff outweighs the power/fuel pay-in either you'll get the same FE at higher speed or better FE. not guaranteed but a good chance of gains.

Too tall too wide.
 

My new car is an 02 Ford Focus auto, gas logs soon to come, it has the ZX3 rally rims and thy're huge. The door sticker calls for a 205/50 R16, the previous owner has 205/55 R16 on the front and smaller 205/60 R16 on the rear. I can't imagine the car with 50's all the way around. I have gone to the junk yard and and checked other Focus' door stickers for the stock sizes and they all come in at either a 185/60 R14 or a 195/60 R15. Now using my GPS I found my car is 3 mph faster and I have a problem on hills, I have to use the AC like a boost button. If Im on a hill and I dont take off the AC, I drop down a gear on hills, so I ride the AC button and turn it off on hills.

The tire I would like is the 195/60 R15, that way I get a 100 PRM boost to keep me from dieing on hills and I go with a skinnier tire. Currently I pull 2800 at 70, but Im doing 73. So what Im reading here is I should stick with as wide a tire as possible. So I have to see if they make a 195/50 R16. Honestly the 16's ride hard, I was hoping for a smaller rim that would give a bit of cush to the ride. I guess Ford doesnt care about speedo's either, the 185 will read 3 under and the 195 will read right on.

I do so much city driving and roaming parking structures the tires it has now are hard on parking handling, the 50's would be a pain. If I get a chance, I'll swap the fronts for the back and see what that will do, it wont change RPM, but it might play with some rolling resistance. As for rim weight, I was just going to go with a set of junk yard steelies, I have to weigh the aluminum rims and see how close they are.

Through a series of fate and luck I found a pair of cheap 205/50/16's, the diameter was of large concern, the tires that car came with were too tall and I'd bog out on the high way, meaning I'd have my foot in it and go no where, when you open up the throttle on a large hill, the extra air makes the computer throw in more fuel and create less gas mileage. I just got the new tires and so far my new numbers seem to be good since the engine is in its correct RPM on the high way.

I got Kumho's touring, a 60,000 mile tire and the ride is great, I need to build up some gas receipts to see the increase in mpg.

Your rears are larger in diameter than the fronts, not the other way around.

Yes, the rears come in at 26 inches tall and the front are now the factory 24 inch diameter tire. I got torque back on hills, the engine accelorates easier, less sticking your foot in the car to get it moving. Holy Cow set me straight on what the 3 numbers mean ie. 205/50/16, I used to think the first number was the overall metric height. Next month when I get paid, I'll throw another set of proper sized tires on the rear, that will lower the tail one inch, less of a stink bug profile.

This month's (May 2010?) Car and Driver magazine has actual test data regarding fuel mileage from a test car fitted with a range of tire widths. Here's the skinny:

Wider tires gave worse mileage and accelerated more slowly than skinny tires.

Wider tires cornered and stopped better.