Effect of wheel offsets - Fuel Economy, Hypermiling, EcoModding News and Forum

LeanBurn · 02-23-2012, 09:46 PM

Still a noob at this stuff, although I am #1 for fuel economy on the other forum I frequent all because of stuff I found on here!

So, recently I upgraded from 20lbs stock steelies to 14lbs 2010 Prius wheels on my 09 Corolla. The Prius wheels sucked the wheels into the wheel well 10mm. Will this hurt fuel economy or help it? I can if needed get wheel spacers to push the wheels out further, but I am hesitant to spend money and yield nothing.

I have chloroplast upper and 3/4 lower lower grill block, lowered the front 0.5" rear 1.5", my mirrors are folded in and I have alright results so far in my 133K kms of ownership:

Lifetime : 6.121L/100km(38.714mpgUS)
Maximum: 5.082L/100km(46.287mpgUS)

Anyways, any feedback would be appreciated...and if there is already a thread on this I apologize as I did a search but didn't see it.

jsatter · 02-23-2012, 10:08 PM

I can't say what the affect on your mileage would be, be I would think the wheels be in the wells an extra 10mm would make skirting a bit easier.

LeanBurn · 02-23-2012, 11:10 PM

I don't think I am pursuing wheel skirts at this juncture.

I just need to know which is worse, a deepened pocket where the turbulent airflow catches more on the inside of the wheel well or all the turbulence of the rotating wheel that poke out further being more flush with the outside lines of the car.

drmiller100 · 02-24-2012, 12:37 AM

probably doesn't matter.

lighter wheels for sure are better.

IsaacMTSU · 02-24-2012, 10:33 AM

Having the wheels slightly inside the wheel well would be better than having them sticking out and I would think slightly inside would also be a little better than having them more flush like the Corolla wheels. I've read that 25% of a car's total drag is caused by the wheels alone... although, if you add up all the crap stats I've read you'd have a number way over 100%

I can't find a good photo example of the turbulence caused by the face of a spinning wheel, but here is a bike wheel...

On a car, the pocket of turbulence on the face (where the yellow specs are) would be much thicker and stick out further away from the face.

WARNING: Terrible MS Paint Drawings Below

Flush Fit

Inside Fit

Those are not exact science, just the best I can do on my laptop without COSMOS FloWorks. If it were my car, I'd say leave them tucked in there, especially since you lowered the car already and that helps git rid of the wheel well drag more than anything.

LeanBurn · 02-24-2012, 10:55 AM

SWEET !!

That was exactly the information I was looking for. Those are great drawings too as they really give a good idea what is happening. Good job IsaacMTSU

I will be leaving them alone.

ProDarwin · 02-24-2012, 11:25 AM

Just an FYI : Prius wheels are likely narrower as well, so if there is a 10mm change in offset, they are actually sitting in 16mm more, not 10. This is assuming the Prius wheel is 5.5" (quick google yielded this) vs. 6" on a Corolla

LeanBurn · 02-24-2012, 11:38 AM

Interesting. I was able to transfer the tire over without noticing any change in overall width. I'll have to check that.

aerohead · 02-24-2012, 06:46 PM

Quote:

Originally Posted by IsaacMTSU

Having the wheels slightly inside the wheel well would be better than having them sticking out and I would think slightly inside would also be a little better than having them more flush like the Corolla wheels. I've read that 25% of a car's total drag is caused by the wheels alone... although, if you add up all the crap stats I've read you'd have a number way over 100%

I can't find a good photo example of the turbulence caused by the face of a spinning wheel, but here is a bike wheel...

On a car, the pocket of turbulence on the face (where the yellow specs are) would be much thicker and stick out further away from the face.

WARNING: Terrible MS Paint Drawings Below

Flush Fit

Inside Fit

Those are not exact science, just the best I can do on my laptop without COSMOS FloWorks. If it were my car, I'd say leave them tucked in there, especially since you lowered the car already and that helps git rid of the wheel well drag more than anything.

I believe that rotating tire drag is Cd 0.005.It would depend on the wheel/cover/combination.

LeanBurn · 02-24-2012, 07:25 PM

I was more after whether the air moving down the side of the car would get caught on the wheel well right under the side mirrors or would having the tire more outwards would minimize/eliminate it, not so much how much turbulence the wheel itself created. If it was as the drawing above suggests the "fan-like" turbulence created by the wheel would push the air to more align with the rest of the body side that would be great. If the fan-like turbulence is negligible then there is more of a chance the air gets snagged on the wheel well, creating drag. If the wheel was pushed out to more in line with the body air would have less of a chance to get caught there.