Hello new here 2008 Suzuki SX4 Sport Sedan MT

[Lazarus]

Originally Posted by yepvegas

Ok I took some notes on the way into work these are my RPM's on the highway no cars in front of me in 5th gear
70mph 3000RPM
75mph 3200RPM
80mph 3500RPM
85mph 3700RPM

If you could stand to run 60 MPH you could see a pretty good increase in FE.

[euromodder]

Originally Posted by yepvegas

So my plan was to change the tires ... from 205/50/17 to 225/55/17.

It might be different in the US, but 205/50/17 is unusually narrow for 17" here, so wider tyres are cheaper !

I think it will help the final gearing a little, do I have that right?

It will make all gears longer.
Tyre size calculator.

I wll be droping the ride 2.5 inches maybe 3.
Will blocking the lower opening on bumper make that much of a difference? How much can I gain from underpanning, the entire car?

They'll all help, but it's difficult to say by how much as every car is different.

The biggest gains are usually to be made thru driving style and lower speed, unless you want to go all out on aerodynamic mods and start adding very visible things like a boattail, wheelskirts and a redesigned front fender.

Speed and high fuel economy takes something like basjoos' aerocivic.

Any mods I do has to look good so I'm at a loss on how to block the lower bumper opening it is pretty big.

Block it on the inside and paint the block black - car manufacturers are doing the same.

I will not block the upper portion I will not risk overheating the car.

See if the radiator extends down to the lower opening - it probably will - if so it can grab cold air down there.

Obviously, it's advisable to monitor intake and coolant temp. before and after this kind of mod.

[yepvegas]

I ran those speeds to answer the question someone had for me. I ran the tire caculation and this is what I came up with.

Stock Tire - 205/50R17 >Search Tires Tire 1 - 225/55R17 >Search Tires
Section Width: 8.07 in 205 mm
Section Width: 8.85 in 225 mm

Rim Diameter: 17 in 431.8 mm
Rim Diameter: 17 in 431.8 mm

Rim Width Range: 5.5 - 7.5 in
Rim Width Range: 6 - 8 in

Overall Diameter: 25.07 in 636.77 mm
Overall Diameter: 26.74 in 679.19 mm

Sidewall Height: 4.03 in 102.36 mm
Sidewall Height: 4.87 in 123.69 mm

Radius: 12.53 in 318.26 mm
Radius: 13.37 in 339.59 mm

Circumference: 78.75 in 2000.2 mm
Circumference: 84.00 in 2133.6 mm

Revs per Mile: 829.6
Revs per Mile: 777.8

Actual Speed: 60 mph 100 km/h
Speedometer1: 56.2 mph 93.7 km/h

Speedometer Difference: - Speedometer Difference: 6.659% too slow
Diameter Difference: - Diameter Difference: 6.25%
If I could drive 60 the entire way to work that would be great but 18 miles of my trip is in a 75 zone, so unless I can trail a semi that is going that slow I have to go at least 65.

The rest of the drive is in a 65 zone so it is easier to keep the speeds down, it is also a good deal of stop and go traffice getting into downtown Denver, so the speeds are usually pretty slow. We have a hour glass freeway 5 lanes to 3 lanes to 5 lanes again so the traffic backs up and then flows ok to bottleneck again. We could all save alot of fuel consumption if the roads were better designed.

I have no problem with driving slower and saving gas. But on the weekends going up to the mountains, I will drive for the enjoyment of it and not for fuel economy. I can alway coast most of the way home coming back to recoupe the fun I had on the mountain roads. I am not trying to save the world, I just want to save some money so I have more funds for toys in the car. My next project is a car PC, that will make it nice for monitoring the car. I will be installing a second monitor to replace the insrument cluster to monitor all of the stats of the car.

Right now i am looking into how I want to do the grill block upper and lower. I think I will block the lower opening completely and block the middle of the upper one leaving a 1 inch opening around the outside so the engine can still bring in fresh air to keep it cool and whatch the temps closely after that. I think all that is left to do is my method of exicution.

Good news my dash is reading an an average of 40.2mpg I think it could be better but the last coulple of days the traffic has been really bad. I still need to adjust the air pressure in the tires maybe I will get to that this weekend, not sure how much of a differnce to expect from the tires. Is there a limit or recomendation as to what is safe?

Thanks again for all the suggestions and support.