FJ-62 Tires and Spedo (3 Viewers)

[musgravecycles]

I've got a '89 FJ-62 that needs new tires. It is a daily driver and is pretty much stock.

I was thinking about putting 31's on instead of the stock 235's. Currently I get 10-12city and 15.5-16.5 highway. One of my motivations for bigger tires is to hopefully improve the mileage, even if just a bit. Is the experience here that 31's improve the mileage?

If I go with 31's, I will need to correct the spedo, does anyone happen to know off the top of their head what tooth gear I need to make the correction.

 

[Doc]

I think, bigger tires decrease your gas milage... It did for me. But I went from 31's to 33's.

 

[musgravecycles]

I think, bigger tires decrease your gas milage... It did for me. But I went from 31's to 33's.

Are your 33's a lot wider than your 31's were? In my case the 31's have about the same width as the 235's. I thought that slowing the RPM down some at 65-70 would help bring me closer to the engine's 'sweet spot' am I wrong?

 

[Doc]

Not wrong, and on long trips it might save you a bit of gas, but for around town driving (mine is mostly 6-8 mile trips) the extra effort to start those big meats spinning takes more energy (gas).

My 31's were 10.5 wide, my 33's are 11.5. So I don't think it's all because of the width. I did go from a passenger radial to an agressive off-road tire with large lugs though. So wind resistance is also up quite a bit.

 

[Moby]

If I go with 31's, I will need to correct the spedo, does anyone happen to know off the top of their head what tooth gear I need to make the correction.

I don't know if you can just change the gear (although I'd be interested to hear if others have had success with this). I had a small t-case mounted correction box (custom callibration) built when I went to 31s. Try looking for a speedometer shop in your area and ask them if they make correction boxes for speedo cables.

 

[musgravecycles]

Moby,

I used to have a K-5 Blazer and when I put bigger tires on it I just bought the spedo gear with the correct number of teeth and put it in myself, took all of 7 minutes (including time to get it on and off the hoist), so I had just assumed that I could do the same thing on Natalie.

btw what was your experience in regards to gas mileage with the switch to 31's...

 

[Moby]

Moby,
btw what was your experience in regards to gas mileage with the switch to 31's...

No mileage difference that I could tell. I could tell that I was down on rpms at highway speed (torque converter locked up) and as a result a bit down on power. I run 4.56 gears now so I'm back to stock ratios. Haven't had them in that long but haven't noticed any mileage difference with them so far.

 

[Mike S]

In an FJ62 - which has 4.11 gearing - a moderate set of 31" tires (31 X 9.50 or 31 X 10.50) should have a small positive effect on mileage over the long haul. At some point the additional weight and rolling resistance of larger tires will negate the 'rubber overdraive' effect of taller tires.

The key to better gas mileage is your right foot.

M

 

[musgravecycles]

The key to better gas mileage is your right foot.

M

I've already bought a set of 31x10.5's. I learned a long time ago that a conservative foot goes a long way. I have once or twice gotten 19mpg on a tank, but usually get upper 16's highway. Thanks for the info on tires, now i just gotta figure a spedo correction...

 

[yooper]

The speedo correction varies a bit. Use a GPS to figure your actual speed and go from there.

 

[DBS311]

From my experience, when I went from stock to 31's my gas mileage went down. Thought a spring over and 35's would help, but it didn't.

 

[Spook50]

The speedo correction varies a bit. Use a GPS to figure your actual speed and go from there.

Word. It's way down on the list, with all my other projects going on while I'm home, but I plan to install a laptop mount and buy a GPS for my Dell laptop that displays a moving map and true ground speed. Looking at that for my true speed will work until I can figure out a way to rig up the sender for an Autometer electronic speedo to my tcase.