I went from a nice 27 to 29 mpg to 22mpg (20 with a head wind)when the temp dropped to the 20s.
Is this a true sign of the need for a tune up, or is this fact of life? I did just get 235s too but now my speedo is correct, go figure.
Jeff

Mine drops from about 29 to about 23 during the winter... 

I attribute it to the choke being on more, using gas idling to warm up, stiff lubricants, etc.

Don't forget about winter gas formulations, running the defroster...

Don't feel bad, my Ranger gets about 13mpg now while the Tracker is fixing itself...wait...

Well first off make sure the tires have the right amount of air in them. with the cold the tire pressure will drop and then your milage will suffer due to that. On my X-90 I get about the same.
(I also checked the tire pressure and adjusted.)

0-30Wt synthetic oil should help with cold starts,
but all the gear oil is stuff and doesn't get as warm
in the cold.

235 tires corrected my SideKick to read 100% correct
also, so your observation seems normal to me, do you
have an auto trans 3 speed

I noticed my speedo read 2-3 MPH off with stock tires,
telling you you went more miles than you did, and throwing
off your fuel milage readings    making them look better than
they really were/are

Wild

I have a 5 speed.  My speedo would read 3 to 4 mph faster than I was going.  Now it seems dead on.  I now run the airpressure at 23 psi on my new LT 235/75/15.  maybe thats it? is that too low for highway use?

When my tire pressure is that low, my gas mileage drops significantly.  I usually run at 32 psi or so on the highway.  Rides like a brick, but the increase in fuel economy is worth it in my opinion.  It also feels like it turns a better corner with the tires pumped up.

23 PSI is the recommended pressure on stock tires,
I think you are fine, and I don't like the brick feeling

...or the center of my tires wearing out before the rest of the tread...

i have 235's and I run at 26 psi they are not brick and I now have contact all accross the tread  but higher than that and it was hard the other thing is can you guys pls tell me in lts per 100kms so i know if it is the same as mine pls and thanks

i have 235's and I run at 26 psi they are not brick and I now have contact all accross the tread  but higher than that and it was hard the other thing is can you guys pls tell me in lts per 100kms so i know if it is the same as mine pls and thanks

Try downloading this. Its brilliant, I have it on all my machines

http://joshmadison.net/software/convert/

 
Don't worry about the reduced mileage in cold weather it is normal.  You can change things if you so wish.

1. Install an electric fuel pump.  That will allow you to run with no choke.

2. Remove the air cleaner to get at the carb.  Wrap florists wire around the little ear on the choke bell crank that is on the outside of the carb and wrap the other end around something stationary below the carb.  The idea is to hold he choke butterfly full-open u]at all times
         The Samurai is one over choked little machine.  Even in the summer time with just
a short stop for lunch the restart cycle will require it to choke..even when the engine is pretty hot.

3. Once that is done oil is important.  Use Mobile 1 straight 30 weight oil in your transmission an transfer case.  Yes I know it is intended for a motor but the capabilities of Mobile 1 exceeds most gear oils.  You will be quite surprised at how the vehicle moves along especially if it is below zero.

4. Mobile 1 oil is also a great alternative for your Sami engine.  It lubricates almost instantly when the engine is turned over.  Don't be afraid of 5 WT oil it is great stuff.

Don't worry about the reduced mileage in cold weather it is normal.  You can change things if you so wish.

1. Install an electric fuel pump.  That will allow you to run with no choke.

2. Remove the air cleaner to get at the carb.  Wrap florists wire around the little ear on the choke bell crank that is on the outside of the carb and wrap the other end around something stationary below the carb.  The idea is to hold he choke butterfly full-open u]at all times
         The Samurai is one over choked little machine.  Even in the summer time with just
a short stop for lunch the restart cycle will require it to choke..even when the engine is pretty hot.

3. Once that is done oil is important.  Use Mobile 1 straight 30 weight oil in your transmission an transfer case.  Yes I know it is intended for a motor but the capabilities of Mobile 1 exceeds most gear oils.  You will be quite surprised at how the vehicle moves along especially if it is below zero.

4. Mobile 1 oil is also a great alternative for your Sami engine.  It lubricates almost instantly when the engine is turned over.  Don't be afraid of 5 WT oil it is great stuff.

You do realize he drives a Sidekick/Tracker/Escudo, don't you?

That means fuel injection, no carb.

too much, even tho that's factory.  I compromised at 28 psi.  Rides rougher, no doubt, but not hemmoroid jarring.  My mileage also still takes a nose dive in cold weather, even with FI and an electric fuel pump.  Personally, I think its the drag on the front wheels, which I've been trying to figure out.  With the front end jacked up there is WAY more friction required to turn the wheel than any other car I have owned.  It's smooth and there is no noise, so I don't THINK it's bearings (and yes, they are unlocked), but until it warms up and I can get the pads off, I will not be able to find out.

Ok, its been warmer this tank, and not as much wind, and still the same 23 mpg.  I am going to 28psi to see.  I didn't notice much diffrence in the ride.  I have noticed that I have to have the revs up to start out in first gear now.  I can't imagine 31's or 33's with standard gearing in high range.
Jeff