Scion Xd Tire Size

[hachieroger]

Just got new tires for the Xd and discovered that the factory size of 195/60/16 is somewhat of an oddball size currently. I put 205/60/16 on it and the gas mileage is down quite a bit. Wondering if I can get the computer recalibrated for the taller tires?

Any ideas?

Roger

[HATEnFATE]

As much as I hate to say it. It's not something I know anyone doing. I'm sure someone out there could figure it out but as far as i know, Toyota ECU's are pretty hard to crack.

You really should only be off by maybe 1 mph around 70. The diff in your speedo should be neglegable.

[hswaters]

Are you calculating the mpg yourself or taking numbers from the car computer itself? The car computer will not calculate an accurate number if the tire size is changed. This does not mean you are getting more or less mpg. I for one intend to change to a more reasonably priced tire size when I need new tires. I can see that a size that only changes about one mph at 65 is available from several manufacturers.

[bobolinko]

Originally Posted by HATEnFATE

As much as I hate to say it. It's not something I know anyone doing. I'm sure someone out there could figure it out but as far as i know, Toyota ECU's are pretty hard to crack.

You really should only be off by maybe 1 mph around 70. The diff in your speedo should be neglegable.

The difference is:

When speedometer reads 60mph (96.6km/h) actual speed will be 57.4mph (92.4km/h): 4.3% slower.

[spokybob]

Originally Posted by bobolinko

The difference is:

When speedometer reads 60mph (96.6km/h) actual speed will be 57.4mph (92.4km/h): 4.3% slower.

I'm thinking you have it backwards. The new tires are slightly taller so each revolution makes the car go farther. And if you go farther, you must be going faster.

[bobolinko]

Originally Posted by spokybob

I'm thinking you have it backwards. The new tires are slightly taller so each revolution makes the car go farther. And if you go farther, you must be going faster.

Dude, the speedometer is in a direct relationship with tire revolutions.
Therefore a bigger tire rotates less times in the same distance as a small tire would. That would make the speedometer register less, since the bigger tires are turning less for the same given distance traveled. However, it's a free country and you can "think" however you want, right or wrong, it's your choice.

[spokybob]

Originally Posted by bobolinko

The difference is:

When speedometer reads 60mph (96.6km/h) actual speed will be 57.4mph (92.4km/h): 4.3% slower.

...
...

Originally Posted by bobolinko

That would make the speedometer register less

Which is it?

[HATEnFATE]

Ok.....compared to stock......

If you put on a taller tire(larger circumference) you're actually going faster then what you're speedometer says.

If you put a smaller tire(smaller circumference) then you're actually going slower then your speedometer says you're going.

[spokybob]

I agree

[bobolinko]

Originally Posted by spokybob

...
...
Which is it?

Dude,
You're absolutely correct. I used a wrong tire size in the calculations, it was for someone else in my office at the time, and got the two transposed. The correct calculation (as you suspected) is:

When speedometer reads 60mph (96.6km/h) actual speed will be 61.1mph (98.4km/h): 1.8% faster

Thanks for pointing that out... I had to go back to read what I posted when you said the above quote.