Tire Size and Gear Changes for my FJ
I have been working on a project to upgrade my Toyota FJ Cruiser with larger tires and better gearing. Initially I was not planning doing this upgrade; however, this last summer there were a few situations that where the additional 1.5 ” of clearance would have helped.
To help me decide on the tire size and gearing to go with I created the following charts:
Gearing and tire size options:
| Current | Opt 1 | Change w/ 33.81 | Opt2 |
Change w/ 34.36 |
|
| Tire |
31.61 |
33.81 |
+2.2” |
34.36 |
+2.75 |
| Axle Ratio |
3.91 |
4.58 |
.67 |
4.58 |
.67 |
| Final Ratio @ hub |
41.9 |
48.87 |
6.97 |
48.87 |
6.97 |
| RPM @ 2 MPH (L) |
891 |
976 |
85 |
960 |
69 |
| RPM @ 60 (5th) |
2494 |
2731 |
237 |
2687 |
193 |
| RPM @ 75 (6th) |
2494 |
2731 |
237 |
2687 |
193 |
| Speedo @ 3000RPM in 5th |
72.18 |
66.20 |
-5.98 |
67.28 |
-4.9 |
Gear Ratios
Transmission:
| Gear | Ratio |
| 1st | 4.17:1 |
| 2nd | 2.19:1 |
| 3rd | 1.49:1 |
| 4th | 1.19:1 |
| 5th | 1.00:1 |
| 6th | 0.80:1 |
Transfer Case:
| Gear | Ratio |
| Hi | 1:1 |
| Low | 2.57:1 |
This site was lots of help in calculating all the information: http://www.ramblerman.com/blazer/gearcalc.htm
Parts Required:
Gears: 4.56 Ring Gears and carrier
Tires: 315/70/17 All terrain tires
Body Lift 1”: Provided by Toytec
Speedo Adjuster: There are a few companies that now offer this product.
Rims: 17 x 9 with 4.5” back spacing
Beadlock: This is an option and I would consider the internal beadlock from Staun
For the tires I am considering the following options:
Option 1 Goodyear Wrangler MT/R
|
Tire Size |
Service Description |
Sidewall |
Rim |
Section |
Diameter |
Max Load |
|
LT305/70R17 |
119Q | OWL |
8.0 – 9.5 |
12.2 |
34.1 |
3,000 @ 50 |
Option 2 BFG All-Terrain T/A KO
|
Tire Size |
Service Description |
Sidewall |
Rim |
Section |
Diameter |
Max Load |
|
LT315/70R17/D |
121S |
BSW |
8.5 – 10 |
11.8 |
34.5 |
3195@50 |
Steps:
First I will need to get the body mount cut to provide clearance for the front tires.
Second will be to lift the body of the FJ 1” to provide more tire clearance at full up travel. The bump stop will also need to be lengthened to prevent the tires from rubbing the top of the fenders.
While all this is going on I will be working on getting tires and wheels so one the re-gear is done all I need to do is swap the mounted tires out.
As I proceed with this upgrade I will be writing about each step.
This is very interesting im going up to a 33.4 tire and planning on re gearing aswell i also have a 6 speed after your finished i would love to hear about the difference the gears made
Can your axle shafts and other drivetrain parts handle larger tires, or do they need to be upgraded as well?
Also, remember that once you do this your braking will be noticeably poorer, though still functional with this small a change.