effect of wheel offset on mpg
 

I am planning to swap the steel wheels on my Honda fit with a 55 mm offset with lightweight alloy wheels with a 45 mm offset. If i understand offset correctly, my wheel will stick out by about 10 mm from the fender. Will the gain in mpg by lighter wheels (low rolling resistance) be more then the additional drag caused by the wheels sticking out or I am just being paranoid and 10 mm will be barely anything at all.

I dont think it will be a problem, 10mm is only a touch more than a 1/3rd of a inch. Aero shouldn't be affected esp if the rims and tires are still in the fenders.:thumbup:

What about when you go over an unexpected bump, won't your tires wack the crap out the top of your fender? Don't think you'll avoid all bumps because all it takes ia one good wack to leave a pretty dent.

THe 10mm is not from the fender.
THe 10mm is added to the current outside edge of the tire. I dont think it will rub, but you should measure. Again, from the outside edge of the tire.

Whoa! Just gave me an idea: get offset wheels the OTHER direction for the rears & then can do a more "complete" fender skirt!!!

there you have it!

..so you can tuck in all the wheels inside all the skirts...

http://s.images.boldride.com/saab/19...197314-304.jpg

http://images.thetruthaboutcars.com/...97a-119008.jpg

crews is right.

http://recstuff.com/images/trailerfa...-backspace.gif
Offset (wheel) - Wikipedia, the free encyclopedia

It should not make a discernible difference in fuel economy.

The Bonneville speed guys carefully place the wheel offset for minimum drag. That said, I don't know if you can do it by eyeball, and furthermore at highway speeds I doubt it makes a detectable difference. But if you are going whole hog, it should be investigated via tuft tests or ?

Or go to one of those speed runs at airports and do coast-down testing from 100mph. You'd need to have the same tires on each set of wheels, though, for consistency.

Best way to test this is to pick up some hubcentric spacers and see what happens.

But how to test the opposite direction offset?????

Pick up a set of wheels with a high offset, then gradually move it out with spacers. If you change the wheel design, that will affect the airflow and it won't be an apples-to-apples comparison.

Thanks for the replies just ended up getting one of the most lightweight and aerodynamic wheels that Honda made:
http://i53.photobucket.com/albums/g5...ps2352c199.jpg
Best of all they are made for a Honda fit with the same offset!!

I am at the moment doing CFD simulation to the offset matter. I am using a Drivaer 3d model with just drivers side and front wheel. Wheel is fully closed in the simulation so there is no cooling holes at the moment. So far it seems that if you move wheel inwards it helps with the drag. In first simulations wheel is not rotating.

- mm is inward movement
+mm is outward movement

+40mm 0,4961
+30mm 0,4870
+20mm 0,4908
+10mm 0,4896
STD 0,490
-10mm 0,4926
-20mm 0,4900
-30mm 0,4829
-40mm 0,4835

Next I will put convex hubcab there which will come outwards +20mm at the center. And for next runs I will also take down the actual forces as the frontal area changes little bit so the drag coefficient calculations are not exact. Frontal area grows from A=1,0218m2 to A convex capsels=1,0226m2

My guess for sweet spot is between -20 to -30mm range. Specially when wheels are rotating
After that I will try to put it then rotating. Pics will follow later

any thoughts on the hyundai ioniq blues hubcaps?