I was just trying to make a point, not put bicycle wheels on the FEH. by narrower tires, I would expect 185 0r 195 mm. that would require larger dia. rims or an aspect ratio that is not available. And, it would no longer look like an SUV, which may be why it does not alredy have narrow tires!

 

I probably didn't take the time to make my point well. A tires rolling resistance is related to the energy absorbed in deflection of the tire material. A wider tire increases drag losses but, at the same pressure, has less rolling resistance than a narrow tire because less deformation is caused. Narrower bicycle tires have less resistance because they are run at higher pressure than a wider tire. If you overinflate the wide tire, much of the advantage goes away, although you still have more drag and weight. I've seen a number of bicycle articles on this and know from experience that riding an underflated narrow tire causes a major increase in resistance.

Interestingly enough (given all the discussion here on cold weather mpg woes) bicycle data also indicates that temperature is as much a factor in rolling resistance as pressure. Tires suck up much more energy in flexure in cold weather than in warm weather.

Diameter is also very important. This why bicycles haven't reduced diameter and why folding bikes are such a compromise. Maybe a little body work and some 30" rims would result in a really high mpg FEH.

 

Ya mean you don't want to cut out the wheel wells & install some Model T wheels?!?

I wonder if you did that would it still be considered OEM?

 

It is more than rolling resistance, narrower wheels should have lower mass.

 

Checked mine this morning...front wheels maintained psi after 1 week, but both rear tires were below 32psi.
Is this normal to have the rear tires lose more pressure?

 

Can somebody here give me real numbers on their claim that higher PSI gave them better MPGs from recommended PSI.

I have not noticed any difference in MPG (actually a small gain but nothing worth talking about) from recommended PSI to MAX (max on sidewall of tire). The only reason I put more PSIs than recommended is the performance gains in handling and braking. At the cost of a slightly rougher ride.

 

Did you check while your car was cold (like in the morning)? If not, do so in those conditions. Your front tires will always be warmer than your rears because most of the weight is on the front, plus your car is a FWD (or mostly FWD). So that could explain it.

If not, you could have more moisture in the rear tires somehow. Which would explain the difference from the front.

 

I drove about 1.5 miles to the gas station, where I checked and inflated the tires. It was 35 degrees F this morning.

 

Performance gains in handling I can understand... I'll be darned if I can figure out why it would help with braking though.

 

For me, I have a feel when everything is rolling right and can tell if I have a low tire (44psi). It's almost like dragging an anchor you can't hear. I think I started out at around 40psi from the factory. It may have been cold at the KC plant when they shipped my FEH to me in warm Jupiter in January '05.

When I seen I could get 40mpg tanks within my first few fills, I was hooked on the challenge to maintain and improve my mileage. I cranked the tires up to 44psi and it stayed there for a year. I thought exceeding the max sidewall would take any liability away from the tire company and put it on myself back then. I was at the time exceeding 45mpg tanks and satisfied with that results.

During one of the test I was working with Wayne Gerdes on in my FEH, I crank the tires up to 52psi. I didn't lower them back down after the test and thought I'd try and see how much a difference it would make on a tank. You can see by my Miles To Empty on this sig page the results. After hitting a 53mpg tank, I'm convinced that 50psi is an acceptable risk I'm willing to take. Wear has slowed down on my tires and I feel my FWD FEH handles best here in So. FL. We get heavy rain at times and my tires hold the road in cornering and hard stops better I think then they did with 40psi.

BTW, I've had a tire that leaks air from the day I got my FEH. I can tell when one tire is below 44psi just by the drop in mileage and the drag when coasting in neutral. Neutral coasting is most likely the reason I can tell the tires need air right away. When I go EV on the downside of a big bridge, I can tell how my speed increases as I often have to go from "N" to "L" for regen to stay under 40mph.

All the top Hypermilers all agree that tire pressure will effect rolling resistance. Most the top hypermilers I've talked with think I should put more than 50psi in my tires, but that's my limit.

GaryG