hello from high altitude

[arkfit]

Hey guys new to the forum ive ben "ecomodding" for a bit though.
I have a 2007 honda fit automatic with a few things done and a few more to do figured id ask the experts for some advise. My goal for now is avg 40mpg hwy. With latest good number was 38.2 going north to chyenne
First off whats ben done:
Beatrush skid plate
Warm air intake
Scanguage
Light weight rims 15x5.5
175/85/r15 eco plus tires. (Was at 40 now at 35psi needed more traction for braking)

What still needs to be done:
Partial lower front grille block/ foglight protector
Finish underbody lining 1/8 aluminum
Header and exaust possible cat delete
Open to more suggestions

Any advise would be great

[RedDevil]

175/85/r15? Are you sure?
OEM should be 175/65/R15...

If you really are using 85's then your tires are 7 cm (almost 3 inch) taller than they should be, you'd get 10% more miles and speed than the car indicates.
Then you have already met your 40 mpg goal with room to spare!

Edit: Looking up the specs I see different tire sizes listed for the 2007 Fit model; some use 175/65/R14, some 175/65/R15 - which is an inch taller.
If yours is supposed to have the R14s your tires would be almost 4 inches tall...

Best to go by the manual...

[basjoos]

Driving in the thinner atmosphere at high altitude gives you a big advantage in attaining high mpg's over those driving through the thicker air at sea level. Lowered aero drag and a derated (if non-turbo) engine with reduced pumping losses.

[arkfit]

Sorry they are 65 tires dont know why i got that mixed up honestly the 175 with a hard compound was a bad idea works just fine for driving even in mud/snow but the low traction is a hazard with traffic

[RedDevil]

On my Insight (which shares its platform with the Fit) I have Continental 175/65/R15 on steels for winter tires and 185/55/R16 Bridgestone Turenzas on the OEM 16" alloys.

The Turanzas do have more grip that my winter tires if the temperature is well above freezing, also they seem to cope with high pressure better. But the Contis grip snow almost like tarmac - glad to have those when I need them.

Cold may be an issue.
I do not know what make and type of tires you have - but if they are anything like my Turanzas you will find that the grip level reduces fast with cold.
You may have no grip in the morning and tons in the afternoon on Colorado winter days.
A lower tire pressure would heat up the tire more by deforming it more, adding drag but also adding grip. If you have tires that grip well in the cold then they should do so at higher pressure too.

That said, pressure related grip levels are different for cornering and braking.
When you corner the tire deforms sideways; a higher pressure will keep it in line more. The higher the pressure was the better my car cornered, though comfort and probably braking definitely suffers above 40 PSI.

I keep my winter tires around 40 and my summer tires slightly above.

[snakester]

Originally Posted by basjoos

Driving in the thinner atmosphere at high altitude gives you a big advantage in attaining high mpg's over those driving through the thicker air at sea level.

It took me two years of hypermiling to realize this little gem of information. It's all about air density. Out here in the dry Colorado thin air I experience almost perfect driving conditions for high mpg's. The biggest factor being temperature.
The warmer it is, the thinner the air, and the better my mpg's.

[user removed]

Atmospheric density drops 25% from the freezing point to boiling point of water.

Atmospheric density drops 50% at 18,000feet altitude, compared to sea level.

regards
mech

[Fat Charlie]

Sorry I didn't see your post when you joined, welcome!

The Fit's an aero pig, and it's amazing what a grille block will do for it. But get some instrumentation so you can keep an eye on your coolant temps- high mpg is useless if you overheat. Real mpg feedback (instant, short route & long route) is also much more effective than OE displays.