How much MPG do the HCH wheels account for? Should I upgrade to aftermarket wheels would I be sacrificing mucho mpg?

 

Just make sure that your new wheels are light weight the lighter the better and then get the data on the tires you want have low rolling resistance. then go for it. you can google tires for low rolling resistance.

 

Looking aftermarket may not yield good results: As much as light weight may sound like an important variable, more critical is the actual spoke design, wheels surface(s) and related overall rotational wheel turbulance. Notice how flat & flush the OE wheel is. IMO the OE wheel can not be bested w/ most aftermerket designs. Form follows function in this context .

 

I think tires are the killer on FE. I used spocked wheels for a time and noticed no change in FE. I went back to the pie plates because of ease of cleaning and I like the look. H

 

I agree with Harold, the wheels aren't going to make much difference (aerodynamically) at the speeds you (probably) drive at. But I also agree with others that tires are THE most important part you can easily change to get better mileage, and the weight of the rotating mass comes next (wheel + tire weight)

 

Unsprung rotational mass: one reduced LB of URM equals the effect of a reduction of 4 pounds of carried mass. If you choose wheels that are 5 lbs lighter that the OE wheels you will enjoy the benefits of an effective 80lb weight reduction of riding mass. But in real car terms it takes a greater reduction to produce a benifical difference that you can either feel in steering, turn-in, braking or acceleration. It my years with the of hobby tuning & sport driving Mini Coopers I tended to run 11lb forged racing wheels that were 16 lbs lighter than most OE wheels. My hunch is you don't want super light wheels on the HCH as it might produce a less than ideal ride.

 

does it make for a rougher ride, having lighter unsprung weight?

 

In the Mini's if you run super light wheels the steering is very responsive & "razor" like but bumps & irregular road surfaces can produce jarring & wheel bending results. Fuel economy may be improved a bit but tire resistance is a more critical variable. In a car like the HCH I would guess the typical 22-25lb OE wheels is just about ideal for the suspension & battery regenerating system. IMO 15"s would be about perfect on the HCH especially given the very over-boosted electric steering rack: One would not want hypereactive or jumpy steering reactions.