Tire size and MPG

[WA1DH]

I have a Ford Escort with P175-65R14 tires on it. 3 of them are worn out, so I'm probably going to be buying a set of 4 for it. I also found out my stock tire size is P185-65R14. Running the 175s has made the speedometer/odometer off by about 2%.

So, my question is, if I go back to the stock 185s, will I notice any difference in MPG? I realize there is more tire on the ground (~.35" wider tread) which means increased rolling resistance. But, will it be enough to notice? I get about 35 MPG highway right now and would like to keep it that way.

Thanks.

[ShadeTreeMech]

does your 35 mpg figure factor in the difference in tire size? Generally a longer legged tranny/bigger tires means worse acceleration, better top end, either way, more info needed.

[WA1DH]

Originally Posted by ShadeTreeMech

does your 35 mpg figure factor in the difference in tire size? Generally a longer legged tranny/bigger tires means worse acceleration, better top end, either way, more info needed.

Average of last 10 fills = 36.67 MPG
Corrected for odometer error (2.2%) = 35.86 MPG

[CapriRacer]

Differences between tires are going to have much more of an affect than tire size will - so choose carefully. Just be aware that there is a technology triangle between rolling resistance, treadwear, and traction (especially wet traction).

[Frank Lee]

And your mpg will probably drop with the new tires, as the old worn-out ones will have the lowest rr.

[Thymeclock]

Originally Posted by CapriRacer

Differences between tires are going to have much more of an affect than tire size will - so choose carefully. Just be aware that there is a technology triangle between rolling resistance, treadwear, and traction (especially wet traction).

Good advice.

I don't think it will affect your fuel economy much, if at all. Why not stick with the size originally specified for the vehicle? At least that way your speedometer and odometer will read correctly.

Personally, what I look for in a tire is the best wet traction available and good tread wear. On dry pavement even bald tires will work. On wet pavement it's a whole 'nother ball game, as it may save you from being involved in a crash. To me having the optimal advantage in bad weather is worth more than the few cents saved in fuel.

"Always buy the best. You'll never be disappointed."

[cfg83]

WA1DH -

I agree with Thymeclock's advice. Don't forget to find out how much the new tire weighs in comparison to the current tire you are using.

I am one-size-up from stock. I considered two-sizes-up from stock, but whereas one-size-up added maybe 1 or 2 lbs per tire, two-sizes-up added maybe 4 lbs. Bigger tire sizes make all your gears taller by x%, but heavier tires increase the load on the engine during acceleration (right guyz?!?!?!).

CarloSW2

[mcrews]

Originally Posted by cfg83

WA1DH -

I agree with Thymeclock's advice. Don't forget to find out how much the new tire weighs in comparison to the current tire you are using.

I am one-size-up from stock. I considered two-sizes-up from stock, but whereas one-size-up added maybe 1 or 2 lbs per tire, two-sizes-up added maybe 4 lbs. Bigger tire sizes make all your gears taller by x%, but heavier tires increase the load on the engine during acceleration (right guyz?!?!?!).

CarloSW2

I run one up also (way to go CarloSW2!!)
255/45/18 instead of 245/45/18 on stock rims.
It's worth 3.4% to me on the Q45.

And cfg83 is correct, there is a dimishing return due to the added weight. When a tire is rolling the static weight 1-2lbs is now X 4. 4-8lbs per wheel. THis can dramaticly increase the wear and tear on the other componets ...brake parts.....bushings etc......
In my case, since I drive on the freeway for 65% of my 40k a yr, the up size is VERY much a win for me due to the lower rpm at 55mph.
If I was just doing intown.....I'd probably still do it.

and as far as the speedo being correct....
I JUST LOVE!!!!!! multipling my mileage times 1.034 to get my TRUE MPG!!!!

[pgmomni]

Its real easy to lose 1-2mpg when buying new "sticky" tires.

I totally agree with the post regarding wet traction. In my 30+ yrs of driving most of my accidents, especially in my younger days, happened in the rain or snow. Dry traction isn't really a issue unless your racing.

Take a look at the Yokohama Avid Touring tires. Inexpensive, good wet traction and decently good rolling resistance. Good LRR if you over inflate into the 40's up to limit of 51 lbs. I am currently riding on 45lbs front, 40lbs back. The tires only bulge slightly and with the 45/40 setup they bulge the same front and back. They are 6.3% oversized. Stock was 195/70-14, using 205/70-15's. Lowered my RPM's almost 200 rpm at 75 mph.
Wheel/tire setup is slightly heavier but it dont feel it with the 5 speed manual tranny.
As for added wear and tear and drive train, its a 2000 Camry and virtually indestructible.
I figure the added wear on tranny and axles is easily offset by the reduction in rpms/engine life. I do like 95% interstate driving and hyper mile all my local driving anyway.

Gained a whole inch of ground clearance on the Camry. I can drive right over most normal sized curbs now if i need too!

Added hieght makes my need for underbelly pan and front air dam even more important to get done. "I need more time C'ptain,"

Mounted them tires myself with a crowbar and Stanley Wonder Bar.
Need to get someone to edit the video clips doing it.

Pete

[bgd73]

a 99 escort has plenty of engine...
you may be able to go even bigger, if clutch, body, suspension can handle it.

also the 185 going on the same rim will be taller, more than wider.. the width of rim did not change, the tire did.. on the same skinny rim.