FJ60 Gears and Tyres selection

[Umanad]

Hi,

I'll be changing my diff gears soon and I have been given a lot of thoughts around that idea so I guess I'm sharing my project here.

I found my truck, FJ60 2F engine, manual 4th gear transmission, running on 33in tires about a year ago. I have been driving this truck daily to pick up my daughter from school (around 8miles round trip) plus one offroad trip a month. I live in Costa Rica, Heredia and thats a lot of traffic. Also the offroading trips means mud, hill climbs, no rocks at all.

Truck was partially desmog, I 100% desmog, upgrade alternator, aircon pump, changed leaking steering pump (I haven't found the definitive solution for the power steering pump), change distributor cap, rotor, spark plugs, cables, engine mounts, brakes, dual diafram booster... so on... I have been catching up on maintenance. Car does not carry a lot of wait, no roof rack, no camping gear, only an ARB bull bar, winch and basic recovery gear.

On my offroad trips I found I was changing to 4L a lot sooner than the rest of the pack... I used to think the old truck is just old but talking about 35in tires with a friends we start talking about gear ratios.... so here is is what I found

- Gray line is the stock configuration meaning 28in tires and 3.7 diff. Every line is 1st (ratio 3.55), 2nd (ratio 2.292), 3rd (ratio 1.41) and 4th (ratio 1). And imagine you move to right as you increase RPMs in the engine while velocity increases.
- Red line is the what I have currently, stock setup but 33inches. Noticed that I have lost about 25% of my 1st gear... so now it is something less that the stock 1st gear but is not like I lost it totally and now my 1st gear is 2nd... Everything is off by a good amount... this is specially noticeable when driving on the mountain passes and I have to shift down from 4th to 3rd or even worse from 3rd to 2nd. On really steep climbs (pavement climbs is as bad as I have to engage 4L, no hubs to keep going).

For those of you looking to have a better fuel economy I can tell you the car is drivable, red light stops, it can climb hills.... go for it. I'm currently doing about 11mpg combined but as I mention the car does not see highway speeds almost never and I drive in bad traffic.

I dream about this truck running 35s and having 5th gear. I definitely need 35s for the off-roading I'm doing (or I pretend to do) so definitely not decreasing tire size. I'm definitely not going to fit 40in tires as I don't imaging myself cutting those fenders the amount needed for that. I might consider going SOA but Costa Rica has hills, curves and stability of the car is a concern (already compromised by using this car at all!). I shared all these so guys understand where this is going.

Gears upgrade is about $1200 dollars (labor, parts, seals... all stuff), manual 5th gear box is about $4000, rear ARB locker is $2700 (labor and air compressor included). 35" Tires are about $1300... I want everything but just don't have the money now! So gears are a good place to start and I have to be smart so I dont over shoot gearing while waiting those 35inches (could be a year or more) and 5th gear (for that could be 2 years!!!). Also, as I recently maintain brakes I know some seals are bad and work on the axels are needed.

Before continuing with gear ratios I forgot to mention. My current combo is great for my "highway" experience, basically I go with flow, folks from the pack don't have to wait for me at all. Calling Costa Rica roads "highways" is a bit of a stretch.... Totally remain in 3.70 diff ratio with 33in if where you live is flat

The following graph is the worse! but only way to analyze my options

- Gray line is the stock configuration meaning 28in tires and 3.7 diff. Every line is 1st (ratio 3.55), 2nd (ratio 2.292), 3rd (ratio 1.41) and 4th (ratio 1)
- Red line is what I have, basically stock plus 33in
- Dotted light blue line: 33in tires with 4.56 gears. I have to consider this because even though I want 35in I dont have the money and It can take me about 1 year to get them. Noticed that This blue line is basically taking the car back to stock ratios maybe a bit more punch, maybe a bit slower. I think event thought there is a mathematical difference I dont really think there is a practical difference you would notice... If that is what you are looking for, this is your 1st option. To me, It feels like a compromise as I'm loosing my current speeds at 4th gear but I know I can take it because I have another car (2017 Rav4 manual 6th gear tranny) for family trips where no offroad is needed. This op
- Orange line is 4.56 diff ratio with 35in tires. Notice this is right on stock. The line is above stuck (faster better mpg) but I don't thing the difference in the numbers is enough to actually feel it in the road or the gas pump.
- Green dashed line is the next available gear ratio 4.88 with 33in tires. Difficult to say how much punch you are going to have more on 1st gear with this. I can say I'm not going to load my truck with a bunch of camping gear so weight is no an issue for me. Thinking further into the future, 37in tires is not in my life plan so I dont need to gear for that possibility. Also noticed, compare to my current experience (Redline), I would lost my 4th gear as the 4th green dotted line is basically closer to the 3rd red line. This is too big of a compromise for me, I know at this point is not a diff gearing issue but a tranny issue but in my personal case, 5th gear tranny will come in like 2 years if any.
- Purple line is 4.88 diff ration with 35". As I'll be improving the car over time, years! this is not my option for what I just mentioned. If you have already a 5th gear tranny wait for the next graph because the ratios change!

This following graph is very focus on my current and future driving experience

- Gray line is stock conditions with 4th manual tranny meaning 28in tires and 3.7 diff. Every line is 1st (ratio 3.55), 2nd (ratio 2.292), 3rd (ratio 1.41) and 4th (ratio 1).
- Red line is my current condition adding 33in tires to stock combo.
- Dotted blue line will be 4.56 gear ration with 33in tires BUT 5th gear tranny meaning 1st (ratio 4.843), 2nd (ratio 2.619), 3rd (ratio 1.516), 4th (ratio 1) and 5th (ratio 0.845). Notice how with this combo I endup having a punchy 1st, 2nd, 3rd but also having my current top Speed/RPMs on 5th gear. I have to say this again, if you live in flat lands and want fuel economy and highway experience first buy tires and later buy 5th gear tranny. I don't have the lines for 5th gear tranny with stock diff ration 3.70 and 33in tires because too many lines! but if you read until here you can anticipate having lower RPMs at the same or higher velocities on highway, plus, 5th gear tranny has better ratios
- Green dashed line is the golden future state for me 4.56 gear ratio, 35in tires and 5th gear tranny. Stronger 1st, 2nd and 3rd. Notice how my 2nd will be almost what I currently have for 1st (Lower Red line)!!! and my 5th gear will be as fast (sounds like a joke!! but if you follow till here you know what I mean) as my current top speed.

I found no need to add the 4.88 diff ratio lines here because I already found what I wanted. 4.88 with 5th gear tranny will be overkill for me with even stronger 1st, 2nd and 3rd. Notice that I'm also not comparing against stock 5th gear tranny lines but stock combo was okay for engineers back in the 80s and I am more interested in how my current driving experience will be improved. I have been driving this car for a year already and I thinks this is the best option I can take. If you are considering rock crawling (adding heave rock sliders, under armor) and overlanding (roof rack, camping tent, fridge, gas stove, so on) for a very very heavy truck totally yes... rock the 4.88, 35s and 5th gear!

Again, I'm just sharing this as I have put a lot of thought into it. I'm definitely not a mechanical engineer so if anybody spotted something I'll appreciate all the feedback. And also, depending on what are you plans for your truck the gear ratios might change.

Asking around about this I've found people recommend things without considering the different variables of the actual owner and driver of the car. A guy recommend me 5.29 diff gear! After looking into all this lines I'm pretty sure that would only work on a buggy with 42in ++ tires, nothing wrong if that is what you drive it is just not my scenario.

 

[DrRock]

Hola! My truck currently runs 33’s (Yokohama G003’s which measure out at just under 33.5 for 255/85 16). I’m running an h55 now and find this the perfect combination for on road rpm’s and with the lower 1st gear on the h55, it’s a great setup for off road as well. Bear in mind I have a fresh motor with larger valves and pistons which help this topic as well. What’s driving your decision to go to 35’s? Is it mud performance? I’ve driven off-road in Mexico and felt that the tall, skinny approach worked fine but your conditions might be different.

I can’t see your graphs so can’t offer feedback there. Maybe try re uploading them?

 

[Umanad]

Hi, thanks for replying... H55 is the way to go! I know at some point next year I'll have it. Are you running stock diff gears? (3.70 ratio?)

I'm basically looking for clearance, axel/diff to ground clearance as that is what first get stuck on the mud trails we do. As more and more cars go over the muddy climb, holes on the tires path get deeper while the ground on the middle remains high so you get stuck. Currently the people I drive with are running 35s, 37s and even 40s. A lot of the time what I do is just to drive first but also the 60 is not the most capable rig neither (I'm also planning on getting lockers) I get points for style lol!. 35s will let me drive second or third so we can put a more capable car leading.

I got the car back from the shop already. Thing was more expensive than I though but it is back on the garage. New 4.56 gears are in. Happy with change so far! Definitely 1st and 2nd feels stronger and I feel myself going into third and fourth sooner. On my way back from picking my daughter from school I have to climb a bit of a hill and It feels better, I can change from 2nd to 3rd while before it was slow and 2nd all the way up.

As I mentioned, no actual highways in Costa Rica, so I haven't had a problem with my new slower fourth, but it does feel slower, Ill be driving to the mountains on Saturday and putting a lot of miles in it... so we'll see.

Gas mileage still to be calculate, I topped off the gas tank after picking the truck from the shop and I'll report back after a few tanks.

I also feel the entire drive train better as I changed a bunch of bearings, seals, new grease, new oil so on... so the car feels great.

I haven't go offroad yet but I'm eager to see how the Low range feels.

Not sure how to edit the first entry... I can see them in my computer and phone but not in my ipad safari/chrome...

 

[Umanad]

I realize my first entry is already horrible as I'm not able to attach the graphs on the right spots

1st Graph: Stock FJ60 with 33s

Second graph: evaluating all options

Third Graph: future state with h55

 

[JaxFJ]

Hey! Not sure if the below helps at all or just repeats what you already know.

Current Setup:

• Vehicle: FJ60 with a 2F engine, 4-speed manual transmission.
• Tire Size: 33 inches.
• Differential Gears: 3.7.
• Driving Conditions:
  • Daily driving: Short trips in traffic-heavy Heredia, Costa Rica (8 miles round trip).
  • Off-road: Mud, hill climbs, no rock crawling.

Challenges with Current Setup:​

1. Lost Low-End Torque:
   • Moving from stock 28-inch tires to 33-inch tires shifted the effective gear ratio higher (approx. 25% reduction in torque).
   • You’re engaging 4L sooner than your trail group due to the lack of crawl ratio.
2. Steep Climbing Issues:
   • On-road steep climbs require dropping to 3rd or even 2nd gear, and occasionally 4L for tough grades.
3. Highway Driveability:
   • With the 33s, your 3.7 gears still perform adequately for moderate highway speeds, but it’s not ideal for climbs or high-speed travel.

---

Proposed Gearing Options:​

1. Stick to 3.7 with 33-inch Tires (Your Current Setup):​

• Pros:
  • Works for daily driving and minimal highway use.
  • No additional costs.
• Cons:
  • Off-road and steep hill climbing will continue to suffer.
  • 35-inch tires in the future would make this setup impractical.

---

2. 4.56 Gears with 33-inch Tires (Dotted Blue Line):​

• Pros:
  • Brings the truck closer to stock performance with 33-inch tires.
  • Improves low-speed power for climbing and off-road use without over-gearing.
  • Makes a smoother transition for a future move to 35-inch tires.
• Cons:
  • Slightly higher RPMs at highway speeds, but this is not a significant concern since you rarely use highways.

Feedback:
This is a balanced option and an excellent first step, especially since you're planning on 35-inch tires in the future.

---

3. 4.88 Gears with 33-inch Tires (Dashed Green Line):​

• Pros:
  • Significant improvement in crawl ratio and off-road performance.
  • Future-proofed for 35-inch tires.
• Cons:
  • High RPMs on the highway; 4th gear would effectively feel like 3rd gear, reducing usability on-road.

Feedback:
This setup may feel too "short" for your current 33-inch tires unless you’re fully prioritizing off-road capability. It’s better suited for a 5-speed transmission or heavier builds with 35-inch tires.

---

4. 4.56 Gears with 35-inch Tires + 5-Speed Transmission (Dotted Blue Line with 5th Gear):​

• Pros:
  • Matches stock performance with improved crawl ratio for 35s.
  • The 5th gear keeps highway RPMs reasonable, improving efficiency and driveability.
• Cons:
  • Significant cost: gears ($1,200), tires ($1,300), and transmission upgrade (~$4,000).

Feedback:
This is the "golden setup" for your build if you’re committed to long-term upgrades. It balances off-road capability, daily drivability, and efficiency.

---

My Recommendation:​

1. Start with 4.56 Gears:
   • This setup strikes a good balance between your current 33-inch tires and the future move to 35s.
   • It will immediately improve your off-road experience and eliminate the need to engage 4L prematurely.
2. Plan for the 5-Speed Transmission Later:
   • Adding a 5-speed transmission will future-proof your setup for highway driving and allow you to fully utilize 35-inch tires without over-revving.

---

Other Considerations:​

1. Brake Upgrades:
   • Ensure your braking system is capable of handling 35-inch tires, especially on steep Costa Rican terrain.
2. ARB Locker:
   • While expensive, the rear locker is a worthwhile investment for off-road performance, especially if you’re climbing muddy hills with larger tires.
3. Weight and Stability:
   • A suspension upgrade or keeping a low center of gravity will help with stability, particularly if you move to 35s or consider a spring-over-axle (SOA) conversion.

 

[Umanad]

Hey! Not sure if the below helps at all or just repeats what you already know.

Current Setup:

• Vehicle: FJ60 with a 2F engine, 4-speed manual transmission.
• Tire Size: 33 inches.
• Differential Gears: 3.7.
• Driving Conditions:
  • Daily driving: Short trips in traffic-heavy Heredia, Costa Rica (8 miles round trip).
  • Off-road: Mud, hill climbs, no rock crawling.

Challenges with Current Setup:​

1. Lost Low-End Torque:
   • Moving from stock 28-inch tires to 33-inch tires shifted the effective gear ratio higher (approx. 25% reduction in torque).
   • You’re engaging 4L sooner than your trail group due to the lack of crawl ratio.
2. Steep Climbing Issues:
   • On-road steep climbs require dropping to 3rd or even 2nd gear, and occasionally 4L for tough grades.
3. Highway Driveability:
   • With the 33s, your 3.7 gears still perform adequately for moderate highway speeds, but it’s not ideal for climbs or high-speed travel.

---

Proposed Gearing Options:​

1. Stick to 3.7 with 33-inch Tires (Your Current Setup):​

• Pros:
  • Works for daily driving and minimal highway use.
  • No additional costs.
• Cons:
  • Off-road and steep hill climbing will continue to suffer.
  • 35-inch tires in the future would make this setup impractical.

---

2. 4.56 Gears with 33-inch Tires (Dotted Blue Line):​

• Pros:
  • Brings the truck closer to stock performance with 33-inch tires.
  • Improves low-speed power for climbing and off-road use without over-gearing.
  • Makes a smoother transition for a future move to 35-inch tires.
• Cons:
  • Slightly higher RPMs at highway speeds, but this is not a significant concern since you rarely use highways.

Feedback:
This is a balanced option and an excellent first step, especially since you're planning on 35-inch tires in the future.

---

3. 4.88 Gears with 33-inch Tires (Dashed Green Line):​

• Pros:
  • Significant improvement in crawl ratio and off-road performance.
  • Future-proofed for 35-inch tires.
• Cons:
  • High RPMs on the highway; 4th gear would effectively feel like 3rd gear, reducing usability on-road.

Feedback:
This setup may feel too "short" for your current 33-inch tires unless you’re fully prioritizing off-road capability. It’s better suited for a 5-speed transmission or heavier builds with 35-inch tires.

---

4. 4.56 Gears with 35-inch Tires + 5-Speed Transmission (Dotted Blue Line with 5th Gear):​

• Pros:
  • Matches stock performance with improved crawl ratio for 35s.
  • The 5th gear keeps highway RPMs reasonable, improving efficiency and driveability.
• Cons:
  • Significant cost: gears ($1,200), tires ($1,300), and transmission upgrade (~$4,000).

Feedback:
This is the "golden setup" for your build if you’re committed to long-term upgrades. It balances off-road capability, daily drivability, and efficiency.

---

My Recommendation:​

1. Start with 4.56 Gears:
   • This setup strikes a good balance between your current 33-inch tires and the future move to 35s.
   • It will immediately improve your off-road experience and eliminate the need to engage 4L prematurely.
2. Plan for the 5-Speed Transmission Later:
   • Adding a 5-speed transmission will future-proof your setup for highway driving and allow you to fully utilize 35-inch tires without over-revving.

---

Other Considerations:​

1. Brake Upgrades:
   • Ensure your braking system is capable of handling 35-inch tires, especially on steep Costa Rican terrain.
2. ARB Locker:
   • While expensive, the rear locker is a worthwhile investment for off-road performance, especially if you’re climbing muddy hills with larger tires.
3. Weight and Stability:
   • A suspension upgrade or keeping a low center of gravity will help with stability, particularly if you move to 35s or consider a spring-over-axle (SOA) conversion.

Thanks for the feedback! Good summary, this will help future folks 100%.

I drove the car more than 100 miles today and from 3000ft altitude to about 7000ft. Pavement all the time. Car felt great with 33s and 4,56 manual 4th gear box. 1st and 2nd is awesome from death stop and climbing I found everything I need on 3rd and 4th. Going down hill I didn't look for 5th gear as it was very curvy. I probably though about 5th gear for 3miles of straight road and that was it.

Rainy season is out so probably I'm not thinking in 35s for the next 6 months. I'll try to get my H55f next year with even better ratios on 1st, 2nd and 3rd. Then suspension and finally 35s.

I hope to go off-road soon to test the car and report back. But as of now, I'm happy with the change, car feels awesome and one step closer to it's final form.