I see that some of you have put different size tires & wheel combinations on your Scions.
I was curious to know if it has effected your gas mileage.

If so, what tire size do you have and what is the new MPG?


MY STORY:
In an effort to make my xB ride a little smoother I switched to the slightly larger tire size of 195/60/15.
I got a great deal on BF Goodrich Touring TA's and now the box handles and rides MUCH better than the OEM 185/60/15 tires.
Before the switch did a lot of research on the web and even contacted the Toyota service department. The Toyota/Scion mechanic said "the slightly larger tires were within spec and would not void the warrantee".


I also found these specs on the internet:

OEM tires 185/60R15----------------NEW TIRES 195/60R15
Width: 7.28" (185 mm)---------------7.67" (195 mm)
Diameter: 23.74" (602.99 mm)-------24.21" (614.93 mm)
Height: 4.37" (110.99 mm)-----------4.60" (116.84 mm)

Revs per Mile: 876.1-----------------859.1
Actual Speed: 60 mph (100 km/h)----New Speed: 58.8 mph (98.0 km/h)

Speedometer Difference: 1.978% too slow
Diameter Difference: - Diameter Difference: 1.95%


So, the only things I have noticed is that the speedometer reads about 2 Mph slower and that the gas mileage calculations are about 2 Mpg lower.

What do you think?

 

A larger tire does not necessarily translate into better gas milage. there are a number of factors that make up what you get as an end result. Assuming all other things are equal harder tires such as 90k mile tires may give better milage that stickey performance tires that get only 2k5-30k. Incrementally it is small but adds up over the long haul. Wider tires put up a higher rolling resistance than narrow tires. Tires that are bigger around like you have described affect the odometer unless it has been corrected for the error. The manufacturer deternimes the official tire size based on the collective design of the car taking into account size, weight, power output, torque, available clearance, etc. to determine the proper size. If you have lowered, tweaked or modified the components from standard differing sizes or widths may provide a benefit.... or not.

 

You have lots of good points. I was not thinking that the larger tires would provide better gas mileage, just hoping it would be close to the same. Should I switch back to the OEM size?

 

Are you correcting your mileage for the change in odometer readout? It might not make a big difference, but that change in tire diameter will make your odo run a few miles off. Say for every 100 miles you travel, your odo only sees 98 miles of them... (I might be thinking about it backwards though)

 

When doing your fuel mileage calculations, use the actual distance travelled, rather than the odometer reading. You yourself identified the inaccuracy of the odometer.

 

As long as you are considering the odometer variance, now is a good time to point out this if you are leasing a vehicle...
It might not matter in this case, but over the life of a lease, it could add up to paying a penalty.

 

He's putting on more miles than the odometer thinks. Why would that be bad with a lease?

 

I'm glad I found this post because I had the same questions pretty much. First of all, does anyone have any specific wheel/tire sizes that will keep the same MPG and not change the way the odometer works? If not and I do end up increasing the wheel size and putting a lower profile tire on there, can I get the odometer recalibrated?

 

Actually, if the new overall diameter of your tires and wheels is LESS than the overall diameter of the OEM tires and wheels, the odometer will read HIGH. The odometer is based on stock wheels and tires, and every revolution moves it a little. With smaller tires/wheels, it still gets moved the same every time the wheel makes a revolution, but the circumferences of the new tires are less, equalling LESS distance travelled.

Based on your calculation of "1.95%" difference between the new and old tires, that means that for ever 10,000 miles your odometer reads, you'll have only travelled 9805 miles - a difference of 195 miles, or 1.95%. At 100,000 miles, you'l have only travelled 98,050 miles, and so on.

My car (1995 TBird) also has bigger wheels than the OEM ones, but with new lower-profile tires than stock, my overall wheel and tire diameter is less. My odometer reads ~124,000 miles now, but my car doesn't have that many miles on it (more like 120,000). Good thing I'm going to keep my car. If I ever sold it, imagine trying to tell the buyer "I SWEAR it really doesn't have that many miles on it!!!

You can play around with different tire and wheel sizes and get close to the OEM size. You might even find a combination that matches the original sizes. Recalibrating the speedo/odo isn't easy, or at least it wasn't in 1995. It required changing gears and such in the instrument cluster I was told.

 

I think he means this:
http://www.miata.net/garage/tirecalc.html

 

My story so far.

First week of having car, stock tires & wheels still installed. Got about 32mpg for my first tank of gas.

Around day 6 of me having the xB, I got my 17" wheels with 215/40R17 tires installed. From then my gas milage track reads like this:

2nd tank = 33mpg
3rd tank = 39mpg
4th tank = 35mpg
5th tank = 39mpg

So looking at that, I would say my set up has had no negative effect on the xB. I also have a SRI & Axle Back exhaust, these being things that are claimed to reduce xB gas milage

 

If you can find a GPS to use, check your milage with that, Go ten miles with gps on and compair it with your odometer, I think you will find that your actual mileage is better with your new tires.

 

That tire/wheel combo should only make your speedo off by like 0.1%, right? Unless those wheels are super light your mileage should have actually gone down, at least according to dumb logic.

It all comes back to how you drive though. Drive like a bat out of hell and you get low mileage, keep it under 85 and no gunning it from a standing start, and you get high 30s...

 

Sort of. I used this one...
http://www.1010tires.com/TireSizeCalculator.asp

 

Good info and GREAT gas mileage! The fact that your tires are VERY close to the stock size give you only a speedometer difference of: 0.125% too slow which is 59.9 mph when traveling 60 mph.

I am beginning to think that my new tires are a bit too tall and causing too much drag, but the ride is so smooth now.
So... I might switch mine back to the OEM size but I'm not sure.
Any more feedback?

 

Just bought a scion so this is my first post. My xb is still stock, but I went from 16 to 22 inch wheel on my Yukon. Tire size is a 6.71% diffrence and a 100% better look. The wheels of course are heavier and wider then stock, but the motor cruises at a lower rpm so the gas mileage remained almost exactly the same. I think in some cases where diameter goes up and you install a lite wheel, your mileage will actually get better. As far as recalibrating the speedo I didn't, I just checked my speeds with a GPS so I know exactly how my speedo reads, you get use to it. Hope this helps.

 

Thank's for the feedback and welcome aboard.
Congratulations on your new Scion!
:D

BTW: Does anyone know how to do the calculation to figure out my real gas mileage by adjusting
for my new larger (195/60/15) tire size?

 

The way I figured the mileage for my new tires was by GPS. I filled my tank to the rim then drove a long trip and filled up the next tank to the rim again, note how many gallons. Then take the total GPS miles and divide it by how many gallons it took to refill your tank. Miles/Gallons=mileage per gallon.

 

BIGGER TIRE UPDATE

I used the 30 day ride guarantee to thoroughly test out the new, slightly larger, 195/60/15 tires and compared my xB -vs- my sisters xB (with OEM tires) in regards to Mpg, handling, acceleration, etc.

Surprisingly, even though the new tires were only 1/2" wider and 1/2" taller than stock, they changed the gear ratio just enough to make the box a little bit too sluggish and unresponsive. I also noticed that the gas mileage (after calculation adjustments) was about 3 Mpg lower.

So… I switched back to the OEM size of 185/60/15, but kept the brand "BF Goodrich Traction T/A" tires.
Now the box handles great and still rides much better than the stock Goodyear tires.

 

I have never been impressed with the ride of Goodyears....Swapped out a set on a Bonneville with some Goodrich Touring and it was a whole new car....