13" Wheel upgrade mpg drop...

[94metroxfi]

Well my mileage has been great... Until I changed to 13" Rims and 155/80 13's.

Now it seems like I am fighting to keep it around 30 mpg. I know this "upgrade" throws everything off, but no way should a 5% different cause a 40% drop in fuel efficiency. Anyways, Not sure why this would have dropped. Car is running the same as it has since rebuild.

Only thing I noticed was it looks like the previous owner once played wth the tbi and chose screw. Allan wrench and socket to adjust....

Maybe my mileage is just reading this far off with these new wheel's and tires but if not something is seriously wrong....

Now that I am writing this I remembered one evening back in early mid May I remember the car seeming like it was running on 2 cylinders when I started it. (Almost like when it had a burnt valve) I pulled the plug wires and reattached them and i seemed to idle better. Maybe the problem is within the ignition system

Sorry, Just venting here...

Any suggestions?

Thanks

[91Caprice9c1]

Bigger tires will give you better high-way economy.

Depending on how you drive, however, it can ruin your city fuel consumption. The car has to work harder with a larger diameter tire to accelerate at the same rate compared to a smaller diameter tire. And if you do a lot of decel/accel, this is not an upgrade at all.

It isn't good for braking either because of the longer lever created by the added diameter... and the added unsprung weight isn't good for handling.

Hence the differences in gear ratio, braking and suspension systems between 89-94 and 95-01.

-MechanicMatt

[DOCTORBILL]

With a larger tire, are you taking into account the change in your odometer readings?

The larger tire will give fewer revolutions for the same distance driven showing
less miles than you actually drove.

If you've taken this into account, disregard my comments.

There is a web site that gives the change in speedometer and odometer readings
with different size tires.

http://www.miata.net/garage/tirecalc.html

DoctorBill

[lancekilgore]

when I went to 13 in rims and tires I went from 50 to 40 and a loss of power. so I went back to the 12's and every thing is back. one of my problems is the altitude 7000 +, now at sea level or around there you should not have the problem as I do.

[DOCTORBILL]

If you had said at the start of this thread that you are at 7,000 ft altimetertude,
I think everyone would have said that your engine needs all the help it can get!

It is being starved of Oxygen by maybe 25%....

I remember driving a V8 up in the Inyo National Forest in Kalifornya years ago
and my vehicle had the power of a VW with two squirrels in a cage power!

Strap an Oxygen Tank to your Metro and then 13" tires would be OK...

DoctorBill

[94metroxfi]

Well I have a new issue. I noticed the old owner played with the throttle body and at one time must have adjusted the throttle and not the idle screw.

A few weeks ago I sprung a leak in the fuel line by the drivers side rear tire. I replaced the lines by cutting back some of the metal lines and running a longer piece of rubber gasoline rated line.

Anyways, I am not getting what seems like the dead spot issue in the throttle. I got all new vacuum lines because I thought maybe I was leaking someplace. This did not take car of the issue.

I would like to change the o2 sensor just because I do not have a clue the last time this was changed but when I has the exhaust work done, the welded a blot on the exhaust near the o2 sensor and now I cannot remove the nut to remove the o2 sensor.

The only way I can describe the "dead spot" is liek when an older carb was either flooding or starved for fuel.

Just looking for all the great peoples ideas before I spend more money on this car.

The mpg has terribly dropped as on late and is getting worse. City before I was getting 40+ and Highway was around 50 and now I am lucky to get 25/30.

So please give me any ideas. Maybe time for a new throttle body? Fuel filter?

I just don't think the fuel filter would hurt the gas mileage that bad as well.

Thank you in advance.

Mike

[RossT]

When someone says they have a "dead spot" in the thottle, they need to check the TPS adjustment. You may need a new TPS or more than likely just adjust the old one.

Try and adjust your old one, if it doesn't work, post the numbers on yours. I more than likely I have one that I can send to you.

Also, when going to 13's if you drive 100 miles on the odometer, you have actually gone 105 miles, so you need to add that 5% into your miles driven to calculate you MPG

I to am going to 13's I will post my fuel consumption latter this summer

[flashlight]

When I got my metro last year it came with 13" tires and there is a bit of noticeable difference. Like when you're cruising on the highway when it says that you're going 55 you're actually going closer to 60. I only found that out when I used my GPS to check my speed. Also when I've checked my fuel mileage I average between 40-45 miles per tank of gas, and that's both city and highway mileage together. If you want I can post some of my fill ups and the mileage that I've been getting.

[RossT]

Flash thats good info about the gps!

Did you every resolve your high idle? I am curious as to what year your vin# indicates too. Go back to your latest post and update us. Thanks