4:56 VS 4:88...been there..done that

[bulldog-yota]

Its all in the math if your torque converter is locked up

4.88(rear end) 34.5(tire dia) 60(mph) .76(final tran drive in OD) = 2167 RPM
4.56 " " " " = 2025 RPM

Like Dan said 7% gear change 7% RPM change

Maybe with the 4.56s it didn't lock up and with the 4.88 it does lock up now. Would explain the difference and also the improvement in MPG

Agreed on the math though.

 

[MTNRAT]

I get:
315/75R16 tires, 4.88 gears = 2000 rpm at 50 mph.
all the same......................= 3000 rpm at 80 mph.

You get:
at 50 MPH with 4:88's, my Speedo indicated 2,910 RPM.

Somthin ain't quite right. It is known that a properly calibrated speedo, 315s and 4.88 gets 80 mph at right around 3000rpm in a FZJ80. If you are getting 2910 rpm at 50 mph then you would have a sceaming mimi at interstate speed.
Cheers,
Sean

 

[Tapage]

Maybe not aplicable in your cases .. but I share my info.

HJ-60 4.56 + Marks Underdrive t-case gear set + 37" MTR

My speedo 100 km/h GPS Garmil III Plus 100 km/h exactly ! ( 2200 rpm )

 

[Nay]

Please refer to the chart below:

The problem with paper math is the assumption that all tires have the same air pressure and same rolling characteristics at that same air pressure at all speeds, i.e. the radius of the tire from center of hub to center of contact patch is always the same. That is a terrible assumption.

Comparing the Toyo MT, BFG AT ko, and Nitto Terra Grappler in 315/75/16 sizes, the Toyo has a manufacturer spec of 595 revolutions per mile, BFG has 601, and Nitto has 602. But BFG is careful to state that this is at 45 mph. Why does this matter?

People will typically run a bit more air in an AT than an MT because you don't have as much sidewall strength and MT's run harsh at even slightly higher pressures. What does that mean in your MT's at 75 mph at 30 PSI compared to AT's at 35 PSI? Does the MT run a bit flatter? How can a gear chart tell you this? Does RPM go up on a Toyo MT that has 14/32 of tread left vs. the brand new tire at 21/32?

He took pictures, although quoted them at 1K RPM too high. How can this be wrong and a paper chart that assumes no variation in tire characteristics somehow be right?

 

[BillyGoatMTB]

***Bump***

Afternoon Mud

Reading through this thread, does anyone have any final numbers for 4:56 vs 4:88 at speed in the real world?

If you had to do it all over gain which way would you go?

My 1997 FZJ80 is running stock gears, no lockers and 315/75r16 BFG ATKO2. I do lots of snow trips, lots of highway to trails in the sierras with the family.

Are the 4:88 nuts on the highway at 75ish?

I am working with Georg at valley hybrids @orangefj45

Typically i try and do everything myself but everyone i know and trust says have a pro do the gearing, I know of no one better or well versed in my 80 than Valley Hybrids 4x4. I'm looking at Eaton Elockers with the regear to work with the factory switch, i do however have onboard air.......

I have also considered 4:56 and 4:88 but doing the reduction gears in the transfer case for low as well.

Thanks Mud!!!

 

[LandCruiserPhil]

real world....... stock gears on 35's speedo corrected

 

[BillyGoatMTB]

Hahaha, love it!

Maybe i should stay with my stock gears and stay in 2nd too.....

 

[woodsman 44]

Im going 4.56's when Im ready to do a gear change with Yokohamas 315-75-16 on stock rims...

Oh, and the original poster is Way off on his calculations....

 

[BillyGoatMTB]

Im going 4.56's when Im ready to do a gear change with Yokohamas 315-75-16 on stock rims...

Oh, and the original poster is Way off on his calculations....

yes I'm tempted to go 4:56 as well and when I rebuild my transfer case put in reduction gears if needed, I'm kind of thinking Best of both worlds.

If I'm in 4 low I want all the gear I can get. But on highway 4:56 might be the way to go.

And yes the original posters calculations did not make any sense to me either that's why I was asking. Wondering what real world RPMs are at 75 mph with 4:56 and 4:88.

 

[spazzyfry123]

Want "true" factory gearing with 315's? 4.56.
Want a little more oomph with your additional rotational mass? 4.88

 

[COYS]

yes I'm tempted to go 4:56 as well and when I rebuild my transfer case put in reduction gears if needed, I'm kind of thinking Best of both worlds.

If I'm in 4 low I want all the gear I can get. But on highway 4:56 might be the way to go.

And yes the original posters calculations did not make any sense to me either that's why I was asking. Wondering what real world RPMs are at 75 mph with 4:56 and 4:88.

My take:

If you have no plans to go 37s and sticking with 35s long term, do .56s.

35/.88s, while more than tolerable, ultimately pair much better with 37s esp for hwy driving. The math shows it and so does NVH in my FZJ80. I’d rather go back to a bone stock setup than do 35/.88s again. 200-300RPMs is quite the NVH delta in our industrial class engines.

It’s one of those things where if you don’t know, ya don’t know.

Gl!

 

[BillyGoatMTB]

My take:

If you have no plans to go 37s and sticking with 35s long term, do .56s.

35/.88s, while more than tolerable, ultimately pair much better with 37s esp for hwy driving. The math shows it and so does NVH in my FZJ80. I’d rather go back to a bone stock setup than do 35/.88s again. 200-300RPMs is quite the NVH delta in our industrial class engines.

It’s one of those things where if you don’t know, ya don’t know.

Gl!

Awesome, that's why I'm asking, enough time has passed that people know.

Thanks for the input, it helps in making an informed decision.

 

[COYS]

Awesome, that's why I'm asking, enough time has passed that people know.

Thanks for the input, it helps in making an informed decision.

Love the Delta full guard bumper you picked out. It’s the only way to fly. Wish we had a Valley Hybrid in LA.

 

[BillyGoatMTB]

Love the Delta full guard bumper you picked out. It’s the only way to fly. Wish we had a Valley Hybrid in LA.

Thanks, I'm super stoked I went the @Delta VS route. The stuff's just unbelievably next level. When I was installing the rear bumper I was playing with the locking mechanism and was just completely blown away with the design.

Anyway I'm hooked on Delta stuff I'm 100% willing to wait for frame sliders and a roof rack not even knowing if and when they're going to make them or what they're going to look like because I know they're going to be epic!

I don't know......... Stockton's what 5 hours from LA? I haven't had Valley hybrids do any work yet but a bunch of people I know and trust including this community has nothing but great things to say.

Like I said I do most everything myself but I'm not touching my regear.

How about you are you geared you got any feedback?

 

[FirstToy]

4:88s if you use 4lo and want good control offroad
It goes fine on the freeways w/ 315s

 

[Bludozer]

4.56 is a waste of time IMO. If you want that ratio, just do the t-case gears instead, they are pretty equivalent. Everyone has a different tolerance level, IMO the difference in NVH with 4.88s/35s over stock is barely even noticeable and not even worth considering.

 

[BillyGoatMTB]

4.56 is a waste of time IMO. If you want that ratio, just do the t-case gears instead, they are pretty equivalent. Everyone has a different tolerance level, IMO the difference in NVH with 4.88s/35s over stock is barely even noticeable and not even worth considering.

This is awesome thanks, really help with perspective and decision making.

I'm not to sensitive to NVH and plan to dino mat as I work through the interior, between dino matting the doors a new rear driveshaft and @landtank lower control arms I'm in heaven and the NVH is night and day.

For those running a 315 tire what's your rpm at 75mph with 4:88?

 

[alia176]

I have 4.56 and 315s but that was done for elevation of IL, less than 1,000'. For out West, I'd do 4.88s and 315s which is what seems to be the norm. I tend to gear my rigs based on the elevation where I live, not where I play. With that said, the Tcase gear reduction at the hi and lo end of things might just take care of everything while maintaining a strong R&P by keeping it 4.10s. Factory R&P are uber strong with great teeth coverage.

Now, I have the Witt's end turbo so 315s and 4.56s is just dandy. The ECU is always been happy but now with the extra power, she just scoots right along w/o overrevving the engine on the hwy. The transmission shifts crisply and the cruise control doesn't stay in the downshifted gear as long as it used to. I didn't do the valve body mod on the transmission as recommended when you go to forced induction but it's not out of the realm of possibility either.

Speaking of NVH, I take this very seriously and have gone to great lengths at minimizing this. I spend a LOT of time behind the wheel and arriving at the trailhead fatigued just from the hwy driving is no bueno. I'm glad this topic is being discussed. I have swapped out the seats from a 2006 LR3, applied sound deadening material by following the 25% coverage rule on all but the ceiling panels and drive on AT or hybrid AT tires. A wind fairing is in front of the RTT goes a long way at wind reduction. As of late, I'm having wind noise around both front window frames which I need to address as it annoys the s*** out of me

 

[LINUS]

4:88s if you use 4lo and want good control offroad
It goes fine on the freeways w/ 315s

Bingo.

4.56 is a waste of time IMO. If you want that ratio, just do the t-case gears instead, they are pretty equivalent. Everyone has a different tolerance level, IMO the difference in NVH with 4.88s/35s over stock is barely even noticeable and not even worth considering.

More bingo.

I had a 4.56’d 315’s LX450 that was converted to 4.88’s same 315’s prior to me buying - it was kinda wonky on technical trails in lo where you wanted the creep.

Paul the PO came home from Moab & sent it right to Just Differentials for 4.88’s - he wasn’t into the 4.56’s, at all.

I love 4.88 / 315‘s - good creep & control, absolutely fine on the highway.

If (huge if) I ever did 37’s to the 80, I’d probably add the lower lo range TC gears so I’d keep/slight improve my lo range creep/control/TQ.

 

[on the rocks]

I ran 315's for 20 years with 4:11 and it did fine on the highway, it was just sluggish off-road and needed a lower gear but works unless you do a ton of off-roading. If your going both T-case low gears and differential gears I would go the T-case first(low range only) and see what you think. I didn't try my 315's with the new 4:88 gearing but the 37's are spot on with the speedometer and a little sluggish around town(probably just because they are so damn heavy) but feels good on the highway. If you do a lot of highway driving I think the RPM may be a bit high on the 315's, no proof, just my .02. This way you get the low gearing you need on the trail and high gears for the highway. And maybe not now but when you think you may need 37's you don't have to re-gear the diff's. It's not cheap and why do it twice? I said I would never go 37's and here I am.... I don't do extreme off-roading either, the 315's just start looking "small".
I know its not a 37's topic but just helping you look into the future lol.