New tires - size up! - Fuel Economy, Hypermiling, EcoModding News and Forum

mcrews · 08-03-2011, 06:50 PM

I went into to RADIAL TIRES of SACRAMENTO this morning after researching sizes this past weekend.

Background:
THe 02 Q45 Sport came from the factory w/245/45/18 (26.5 inch diameter)on 18x7.5 alloy rims.
At 60k miles I went to a 255/45/18 (27.0" diameter)

The base of the Strut tower on the front is the limiting factor to how tall a tire can be without using 30mm spacers( BAD

)

We tried a 245/50/18 and there is an 1/8 inch gap!!!

THe diameter is 27.7 inches.
The tire weighs 31lb and the current size weighs 30 lbs.

They ordered them today and will install tomorrow.

320touring · 08-03-2011, 07:41 PM

You could cut off the spring platform and fit threaded sleeves so you can fit 2.5" diameter springs

mcrews · 08-04-2011, 04:47 PM

Got the tires on today.
new 245/50/18 27.7" dia. at 55mph 1625rpms
old 255/45/18 27.0 dia at 55 mph 1725rpms

will do mpg runs in a day or so.

mcrews · 09-06-2011, 12:30 AM

as you can see there is no more room!!!

talk

about cutting it close!!!

gone-ot · 09-06-2011, 01:09 AM

...do you think there's "contact" when driving at high speeds and centrifugal forces are attempting to "enlarge" the wheel diameter?

Vekke · 09-06-2011, 11:08 AM

If you install coilover suspension you dont need so big spacers to get more room. Or change you ET on your wheels.

mcrews · 09-15-2011, 03:46 PM

Quote:

Originally Posted by Old Tele man

...do you think there's "contact" when driving at high speeds and centrifugal forces are attempting to "enlarge" the wheel diameter?

Well, it's been a month. Had a round trip from Sacramento to LA.....450 miles each way.
No problem with any rubbing.

I had some obdII codes that I had to resolve. And am still addressing some ecu issues pior to my TTT (trip to texas) on Oct 12.

But I just ran a brief highway run.

At 63mph 1775rpms got 30.9mpg (didnot have the grill block or the front underbelly panel in place)

epa is 22mpg highway.

gone-ot · 09-15-2011, 07:20 PM

...cars need an "electronic" wheel diameter compensation "box" to allow for use of different diameter wheels & tires!

mcrews · 09-16-2011, 01:38 AM

somebody was posting that in europe it's illegal to go up or down in size........
I run a garmin gps on the dash right above the scangauge, so it gives the correct speed.
That way I don't tie up one of the 4 displays on the scangauge.