Phx to LA, full load, 75-80mph, manual trans, no cruise control, A/C full blast, 38 mpg. LA to Phx, same conditions, 34 mpg.

 

I drive alot over 100 miles everyday I keep my tires at 40 psi I check about once a week. If I left my tires at 35 psi I lose about 5 mpgs I avg 5 tanks together on each fo my numbers I lost te paper were I dd it or I'd post the #s I'm gonna try 50 psi and I post results

 

Hi,

I am an Insight (2001 manual) hypermiler and just got a 2007 Fit
Sport to replace an Element as my 'big' car.

The Fit has Hercules MR IV tires (new set) on it from the previous owner. I have not idea if they are good mpg or not - probably not?

Anyway, in the Insight we always put our OEM tires up to 50 psi for the best mpg out of them. After 50 it doesn't make much difference. For the OEM insight tires, going up to 50 made a big difference.

On the other hand, with a set of wide grippy tires on the same Insight, once I was about 40 psi going any higher made no difference at all.

Soooo....

If you are able to run on a reliably reproducible road section, I recommend starting with about 35 psi, and then putting it up to 40, 45, 50 and see if you start to see an tapering of benefits.

The 2001 Insight only weighs about 1700 lbs, and the fit is about 800 more, so it may respond differently to super high psi.

I'll be trying my Fit with the Hercules MR IV at mid 40s, but I am leery of going to0 high because they are only rated to 35 max (the Insight OEMs were 44 psi rated max).

I am sure there must the threads on with tires are best for mpg - my experience indicates that different tires respond differently to the pressure increase so you need to test to find out and can't guess.

 

The insight is not 1700 pounds

2010 Honda Insight specs, auto safety at Edmunds

More like curb weight 2723 pounds

Honda Fit 2010
Curb weight 2604 pounds

 

You are looking at the Gen 2 Insight (the big bulky blobby one).

 

FYI (for the Gen 1 Insight)

SPECIFICATIONS
2001 Honda Insight

Base Price $ 20,180 with air conditioning
Engine Type single overhead cam 12-valve 3-
cylinder with VTEC-E Lean Burn and
Integrated Motor Assist electric motor
Engine Size 1 liter / 61 cu. in. plus IMA permanent
magnet electric motor
Horsepower 67 @ 5700 rpm, 73 @ 5700 with IMA
Torque (lb-ft) 66 @ 4800 rpm, 91 @ 2000 with IMA
Transmission 5-speed manual
Wheelbase / Length 94.5 in. / 155.1 in.
Curb Weight 1887 lbs. with air conditioning
Pounds Per Horsepower 25.8
Fuel Capacity 10.6 gal.
Fuel Requirement unleaded regular, 87 octane
Tires P165/65 SR14 Bridgestone Potenza RE92
Brakes, front/rear vented disc / drum, antilock standard
(auxiliary braking provided by the
IMA electric motor in generator mode)
Suspension, front/rear independent MacPherson strut /
twist beam axle
Drivetrain front engine, front-wheel drive

EPA Fuel Economy
miles per gallon city / highway
61 / 70
0 to 60 mph 11 sec (est)

 

Stock tires are pretty good rollers, not a bad starting point if MPGs are your sole concern. 51psi max per the sidewall but a fair number of people here have done up to 60. They kinda suck in wet weather and are pretty much useless in serious winter conditions, even more so at higher psi's. I ran mine at 45 as a compromise between MPG and control.

After that I think I'd start looking at the new crop of LRR (low rolling resistance) tires coming out from various makers.

 

ok not to burst peoples bubbles two words camber and caster if you notice when you turn your wheels they kind of have an angle on them even the back wheels so you need that recommended tire pressure to get max traction and tires will wear unevenly especially if you do alot of turning on back country roads and your car will slide cause with max pressure there is no cushion or sway which max traction is needed. hard tires wipeout easier ask any race car driver or mech(built two race cars) somthing will give especilly when it is slippery out

 

watch nascar look at camber,caster and tire pressures i learned from that and i was on a pit crew for dirt cars thats how i learned and also use to watch alot of manufacturers videos and reasons why things are the way they are

 

That sounds great for race car drivers, but this isn't nascar, the Fit is not a race car and no one should be driving that way on a road. During the 25,000 miles I owned my Fit the tires wore perfectly even at ~50 PSI, and I am not one to slow down for corners.
This also goes for my other current and previous vehicles as well.
Ford Escape 25,000 miles at ~42 PSI (44 max)
STi 24,000 miles at 48 PSI (OE and Kumho ASX)
Transit connect at 50 PSI (Ford actually recommends 49 rear, max sidewall is 51)

The only side effects here are better mileage, less tire wear, a firmer ride and fewer heat cycles.

 

I can attest to Rich's comment. I ran my Kumho ASX's for 30,000 miles at 51 PSI (excluding autocross events), and they wore as evenly as I could imagine.

That said, I've been running my second set of ASX's at about 42 PSI for a few thousand miles. I'm still evaluating the wet traction difference.

By the way, I ran 44 front, 48 rear for autocross events. Amazing balance in handling.

 

Caster does indeed add camber to outside front wheels and lessens inside front wheels but the reason why additional tire pressures are useful is to stiffen the sidewalls in radial tires. As long as you don't overdo it with 50+ psi your cornering and mpg will improve because the tire patch stays more consistent.
Caster doesn't exist on rear tires so the tires develop positive camber outside and virtually no negative camber on the inside tires.
If you've ever watched rotating tires turning on a glass plate overhead you can easily see the effect of an optimum tire pressure on the resisting force on the tire measured by load cells on the inboard end of the axle.
The optimum on street tires is always higher than manufacturers recommended pressures simply because they rightly assume that the great majority of drivers value a soft ride over performance.
Ask any racer or autocrosser for verification.
I don't know about you but my street cornering gets pretty strenuous at times, bordering on my driving on the track.

 

Why not? If you corner a bit on the strong side the side wear on the tread will equal the center wear on the center at elevated tire pressures. My tires on almost all my cars werar evenly across the tread with 45 psig tire pressures front, 40 psi rear because I stress the outer and inner tread sections with hard cornering. Any car can be a race car as showroom stock SCCA or IMSA has proven for decades. With a little setup the Fit handles peretty wll; its no Porsche but it can run with any 'usual' street car. besides, its fun. As you indicated.
cheers.

 

I like to run 40psi. The ride is ok and tire wear is pretty even. Traction is good on the corners no tire squealing. I'm going to switch to nitrogen and see what happens. I'm running on Falken 912's They are good in the rain and dry. You don't want to run too much pressure on long trips because you can have a blow out same way when under inflated due too tire overheating.

 

Very much so, I was just suggesting that no one's driving should be approaching race conditions outside of a track.

This is not true at all. The higher the tire pressure, the less heat is generated due to lack of flexing.

 

When you drive pressure and heat rise regardless of being over inflated or under inflated. Under inflated tires might do it more rapidly but over inflated tires will exceed the maximum pressure and still might cause a blowout. I worked in a tire shop before.

 

Pressure goes up 3-4 PSI from a cold start, maybe 6 if you thrash it. But pressure (and temperature) do not continuously keep building up. There is no chance at max sidewall that the pressure will go up high enough to cause a failure.

 

ok then risk it.

 

all i can say is hey run em over but there set that way by honda for honda and for all good reasons hope you guys in the northern belt never hit a pot hole cause you can do some serious damage to a tire or suspension as time goes by. just tryin to save money on your suspension systems and tires cause i hate having to replace stuff prematurely especially with the cost of suspensions and tires nowadays.

 

and almost all new cars have camber and caster adjustments on independent suspension sytems the top of the strut usually has some room to move and adjust