Rain vs MPG

[Sonic]

I made a 180 mile round trip the other day. Flat roads both ways. 65 mph both ways. On the way there, full tank of gas, no rain I got 41.8 mpg indicated. On the way back, half tank of gas, so the car was lighter and in theory should have gotten better mpg, but it was raining I only saw 38.2 mpg. I thought about it and the rain and the rolling resistance it created had to be the answer. No real wind either leg of the trip either.

 

[silversurfer]

What octane?

 

[MGDavis]

Pretty sure its the rolling resistance. Picking up and evacuating that water creates drag, making your engine do more work than if it were maintaining the same speed in the dry.

 

[wingman]

Agreed on the rolling resistance but also I think the rain beating on your car may have also been a factor.

 

[Sonic]

Yeah, I meant the rolling resistance plus the brute force of the rain beating on the car.

 

[Sonic]

92 octane

 

[SteveSonic]

We have a "wintery mix" this morning in Richmond Va but the roads are only wet. I noticed when I attempted a few Pulse and Glide maneuvers that it was like I had the Ebrake on a notch. Even going down light grades .. I slowed down a lot. I have the stock Hankooks on my LTZ. They earn no points for low rolling reistance.

 

[AndrewGS]

I tried pretty hard to get 40MPG a few weeks ago on a trip, but the rain that I experienced over about half the trip and the traffic in Austin meant I only got 38MPG.

 

[oldertech]

Anyone experimented with over inflation of their tires? Yep, controversial, but I did it on my Honda with success in boosting mpg.

 

[SteveSonic]

Anyone experimented with over inflation of their tires? Yep, controversial, but I did it on my Honda with success in boosting mpg.

I bumped mine up to about 38 psi this past weekend from 34 during the first 1,200 miles of ownership. The ride gets more "sporty" as pressure is added. The air temps in Richmond are changing wildly, of course, but I'd guess averaging around 45*F.

No way to gauge the benefits of increased tire pressure while the early Spring temps change so much day-to-day.

 

[Danny5]

With 2/3 of the car sitting on the front tires, a little over inflation should be mandatory as it would only improve the cars handling and assist in emergency maneuvers.

Gonna guess 40-42psi. I think I'll start doing this.

 

[dvn]

Just checked my tires and they were all under inflated from the dealer. My 17's call for 35 so I'm gonna try 36 r and 38 f.

 

[gsxr1000]

With 2/3 of the car sitting on the front tires, a little over inflation should be mandatory as it would only improve the cars handling and assist in emergency maneuvers.

Gonna guess 40-42psi. I think I'll start doing this.

This don't sound right... over inflated tire has less road patch contact. i think the bumpy feeling of sporting is actually decreasing turns

 

[oldertech]

It's one of those controversial things like oil types and break-in procedures. I was a sceptic but ended up 10 over on my honda with no ill effects ('cept a harder ride) and higher mileage. I had heard our local police department overinflates on their cruisers based on some research that someone had done.

 

[RichieRocket]

This don't sound right... over inflated tire has less road patch contact. i think the bumpy feeling of sporting is actually decreasing turns

gsxr1000, I used to think the same way, then I read an article about autocross. I was shocked how much tp they were running! They are trying to balance contact area (lower pressure) with preventing the side wall from rolling over in hard cornering (high pressure).

From the Solo2 autocross class basics: Solo II Novice Handbook

Tire pressures should be higher than used for the street, usually 45psi-Front/35psi-Rear for a front-wheel-drive car, or 40psi all around for a rear-wheel-drive car.