Topic: Gear ratio with 37" tires and 3RZ?

[swilson]

Did a bunch of searching on this figuring it would be a sticky someplace, but no luck.  I've previously run 4.88s with 35x12.5 (with a 3VZE)  and more recently 5.29s with 38.5x14.5 (with a Vortec 4.8L)... my next build is getting a 3RZ and 37x12.5... but I've not decided which ratio to go with.  I'd appreciate any experience here... especially if you're also running the 3RZ.

My old 4Runner would cruise around at 75-80mph no problem on the 35s and 4.88s.  I'm hoping to do the same with the 3RZ and 37s.

[redneckcustoms13]

5.29 if you want to actually do interstate speed. If you are going to wheel it like a bat out of hell stick with 4.88 for the strength of the actual gears.

[H8PVMNT]

The 3RZ does pretty well.  I like to use 5.29s but I ran 4.37s and 35s for a while with a 3RZ and it still did pretty good.  I would think 4.88s could still get it done.

[SqWADoosh]

I can tell you as I have that exact setup. If you are sticking with 15" wheels then run 4.88. If you are going to 17" wheels then 5.29 is perfect.

[swilson [OP]]

What makes you say that?  Wheel diameter has nothing to do with tire diameter. 

What are you currently running?  37s & 4.88 or 37s & 5.29?

[SqWADoosh]

What makes you say that?  Wheel diameter has nothing to do with tire diameter. 

What are you currently running?  37s & 4.88 or 37s & 5.29?

Because I've tried both. I tried on my buddies 37x12.5x17 before getting my 37x12.5x15 purely to check for clearance in my fenders. His setup was a perfect match for my 5.29s. My 15s have been dogs with a 37" tire. However I get a lot more sidewall wrapping around rocks so it is a give and take.

[mudmaster]

15" wheel has more rubber = more weight.

[SqWADoosh]

Larger diameter wheels roll faster as well.

[Snowtoy]

Toyota matched diff gears to trans and tire size, assuming you are going with 3rd gen or older drivetrain, that would be 4.10's for 5-spd w/28's, or 4/3?'s w/28's.  37's are 24.3% bigger than 28's, 5.29's are 22.5% taller, while 4.88's are only 16% taller, 6.5% isn't a lot, but then 37's will weigh more and have a greater rolling resistance, so that needs to be considered as well. 

If you are buying new gears, go with the 5.29's, if you already have the 4.88's run them and see if the performance is tolerable, then decide if regearing is needed/wanted.

[blackdiamond]

Because I've tried both. I tried on my buddies 37x12.5x17 before getting my 37x12.5x15 purely to check for clearance in my fenders. His setup was a perfect match for my 5.29s. My 15s have been dogs with a 37" tire. However I get a lot more sidewall wrapping around rocks so it is a give and take.

Are referring to the MTRs on  17 inch wheels that you borrowed for the clearance testing?  I'm fairly certain that you're talking about your Pit Bull Rockers on your 15 inch wheels, right?  If so, here are some relative weights:

Goodyear MT/R
35x12.50x15, C, 34.8", 67 lbs (+3 to 17)
35x12.50x17, C,  34.8", 64 lbs
37x12.50x17, D,  36.8", 73 lbs

BFG KM2
35x12.50x15, C,  34.8", 62 lbs
35x12.50x17, D, 34.8", 69 lbs
37x12.50x17, D, 36.8", 73 lbs (+4 to 35)

Pitbull Rocker
37x12.50x15, 37.00", 88 lbs (+15 to 37x12.50x17 MT/R & KM2)
37x12.50x17, 37.25", 90 lbs

It looks like your 37x12.50x15 PBR tires weigh about 15 lbs each more than both the MT/R or KM2 in a 37x12.50x15.  It also looks like the difference between an otherwise identical tire on 15s vs. 17s to be about 3lbs.

I think between the 15 extra pounds per tire, softer rubber compound, the new PBRs being bigger than the worn MTRs, and slightly more give in the sidewall from the 15 inch wheels, I am not surprised that they feel like "dogs" compared to the other tires unless they were of similar weight.  I would expect the weight of the tires to be by far the biggest factor.  I felt it going from my BFGs to the Coopers.

I don't think the OP would notice a significant difference between a 35x12.50x15 MT/R (67 lbs) and a 35x12.50x17 MT/R (64 lbs) knowing that the 17 inch wheel will weigh a little bit more than a similar 15 would.

[blackdiamond]

15" wheel has more rubber = more weight.

15 inch wheel has less metal = less weight.  It looks like the difference in tires is about 3 lbs or less, but I can't find any wheels for quick comparison.

[blackdiamond]

Toyota matched diff gears to trans and tire size, assuming you are going with 3rd gen or older drivetrain, that would be 4.10's for 5-spd w/28's, or 4/3?'s w/28's.  37's are 24.3% bigger than 28's, 5.29's are 22.5% taller, while 4.88's are only 16% taller, 6.5% isn't a lot, but then 37's will weigh more and have a greater rolling resistance, so that needs to be considered as well. 

If you are buying new gears, go with the 5.29's, if you already have the 4.88's run them and see if the performance is tolerable, then decide if regearing is needed/wanted.

4.88s match up pretty much perfectly with a 35 inch tire.  The math give you 34 inches, but between many of them being less than 35 plus the rolling diameter is even less from the weight of the vehicle.  I think my speedo on my 4Runner is more accurate with 4.88s and my 35 inch Cooper SST Pros than my Sequoia is with one size taller tires.

[swilson [OP]]

Hmmm.. thanks for all the input.  I hadn't considered the extra weight.  I'll stick with the 5.29s.  I'll be going with a 17" wheel for more choice in tires... and bigger brakes.

Now I just have to decide on a tire!  On my FJ40 I was using 38x14.5 Super Swamper TSL SX.  While great off-road... I'm ready to trade in a little toughness for some tread life and better freeway manners.

[blackdiamond]

Hmmm.. thanks for all the input.  I hadn't considered the extra weight.  I'll stick with the 5.29s.  I'll be going with a 17" wheel for more choice in tires... and bigger brakes.

Now I just have to decide on a tire!  On my FJ40 I was using 38x14.5 Super Swamper TSL SX.  While great off-road... I'm ready to trade in a little toughness for some tread life and better freeway manners.

My previous set of tires were BFG KMs and I would have gone with he Toyo Open Country MT except they were only available in a 13.50 width and were not a C load rating. With my 22RE I won't run a tire that much heavier than is necessary.  This round I did the Cooper STT PRO that was a bit heavier and I could feel it initially but I don't really notice the difference anymore. My daily street driving is minimal these days as well so performance matter less on the pavement.

[H8PVMNT]

I run 5.29s with 33s with a 3rz. for me it's a trade off. I have single case gearset so my crawl ability is increased in 4low. The real benefit for me is a very usable 4hi for sand and mud. The only drawback is higher rpm's on the freeway which means less mpg's (if I want to go real fast)and the need to shift sooner especially from 1st gear(2wd).  If I had dual cases I think 4.88's would be perfect for my 3rz w/33's.

 In regards to the original question, I wouldn't even consider anything but 5.29's for 35's and especially 37's for the 3rz unless it's a trailer queen. If you were going with the 3.4 swap, the 4.88/5.29 decision would be more difficult.

A 3RZ, 33s w/5.29s you must be pulling on everybody up the passes.  You wheel with a bunch of guys with bigger equipment, do you find you can wheel most everything with 33s or do you feel there's a need for more tire?

I have this theory the we really don't need much more than 33s and I want to hear your take on that with the trails you run.

[Snowtoy]

4.88s match up pretty much perfectly with a 35 inch tire.  The math give you 34 inches, but between many of them being less than 35 plus the rolling diameter is even less from the weight of the vehicle.  I think my speedo on my 4Runner is more accurate with 4.88s and my 35 inch Cooper SST Pros than my Sequoia is with one size taller tires.

Correct on the 4.88's being right for 34's by the math, but you have to work with what is available, I would rather run a little over geared than under.

With 35's and 4.88's I found my '90(3.0) performed similar to when I ran 33's on 4.56's, i.e. Sierra passes were in 3rd or 4th, where with the 33's and 4.88's it is in 5th gear.   I run 5.29's w/35's on my '91(22re), and wouldn't want to run anything shorter, it isn't all that fun to drive now with it only slightly over geared.

I think it all comes down to what one will tolerate performance wise, when I just drove my '91 tofrom the trail/occasional trip to town, I didn't mind the lack of power w/the 22re, but with my '90 in the middle of a slight restoration I have been driving the '91 a lot more, and find the 22re less desirable each time I drive it.

Oem speedo's accuracy is a hit and miss, w/the six vehiclces I own, the only speedo that is accurate with the gps is my '90 and 3 of the six all have stock rims and tires.

[BigMike]

Good discussion here, not much to add.

One thing to note that many seem to forget is that a 35" tire rarely measures thirty-five inches, and even if it did, after a season or two it will be closer to 34". When I sold my old 35x12.50x15 MTR (original-style) that had about 35-40% tread left, they measured 33.5" mounted on my truck.

How I look at this is for the future:
If you do NOT have any plans for going over 35" tires, then I'd recommend 4.88:1 for the above size discrepancy reason.
If you're unsure or do have plans to run 37" or taller, than I'd recommend 5.29:1. To run 4.88s now only to regear to 5.29s in two years is a big expense down the road.

I built a nice Engine RPM and Truck Speed Calculator on our R&P page: https://www.marlincrawler.com/differential/ring-pinion Plug in some numbers, write down the resultants, and then go drive your truck how it sits now and compare. See if the RPMs vs speed is what you're looking for. If the calculator calls for 3,500 RPM for 65 MPH on the freeway then run your truck in 4th gear at 65 MPH to see if those high of RPMs is something you'd want to live with.... etc.

Tips:
Use your cell phone or actual GPS device to make sure you'll getting accurate speed reading.
Measure your tire height right now and use that number (or close to it) in the calculator. If you're sit'n on 33s now I wouldn't be surprised if they only measure 32".

Regards,
BigMike

[BigMike]

A 3RZ, 33s w/5.29s you must be pulling on everybody up the passes.

I run 5.29s and when I had my worn 35s (that measured 33.5"), I could pull the "Four Lanes" 6% ave grade up CA HWY168 east of Prather, CA in 5th gear @ 65 MPH the whole way with all my wheel'n/camp'n gear with *barely* power to spare. Never needed to downshift to 4th. One time a guy in a Cummings diesel swapped 2nd gen 4Runner asked me if I had a "big block or something" and I said "yes, a big block 4cyl".

Then I moved up to 37s (that probably measured 36.5" new) and holy smokes what a difference. Now I can only pull the grade in 4th and there are two sections that if I don't get my speed up just enough then I'll have to drop into 3rd gear to maintain > 55 MPH.

For reference most 22R(-E) powered rigs with 37" tires run 3rd gear the entire length of the climb. They just hold it at 4k RPM. I know of people who will shift their Marlin Crawler Crawl Box into Low and run 5th gear @ 4K RPM which is about 45-50 MPH.

People don't seem to realize the increased torque requirement when moving from a 35" tire to a 37". Because I like to jam in the hills I would not want to run 4.88s + 37" + 3RZ-FE.

Another thing that comes to mind is the 3RZ-FE's open loop. I have a narrow band AFR gauge in my truck (monitoring the upstream factory O2) and for my 5.29:1 + 37" combination the ECU switches from closed to open loop at approximately 76 MPH. This when there is no or minimal headwind. What this means for me is that at approximately 74-75 MPH I am making 19-20 MPG and then at approximately 76-77 MPH I am making 10-11 MPG (verified via OBD-II scanner). I've never ran 4.88s, but I'd imagine this load-point that triggers open loop would occur at a lower speed, perhaps at only 70 MPH in 5th. Now you're efficient highway cruising speed has a lower speed rating, and your poor catalytic converter would be cooking for hours and hours for all your high speed long distance road trips. Add an exo cage or similar high drag modification, headwind, wide heavy tires, and the ECU loop switch point MPH will drop even more.

Regards,
BigMike

[emsvitil]

I like the idea of 33 x 10.50 tires..........  Narrow enough to just still fit in the fenders.    And diameter-wise you shouldn't have to trim the fenders either   (Plus I can keep my stock 15x7 aluminum SR5 rims).     

You'll then need to make sure you have some protection underneath.............


Most tires do seem to be .5" less than stated diameter.    With about .5" tread depth you'll be an 1" smaller at half tread wear and 1.5" shorter when worn out.      And that doesn't take into consideration rolling diameter.....  (According to tire rack, a BFG 31 10.50 has a diameter of 30.50 and 682 revs per mile; 682 revs per mile is a rolling diameter of 29.57".     So rolling diameter is 29.57/30.5 = 97% )

So your average 37" tire at midlife becomes a 34.92" tire.........


And full throttle in 5th gear isn't a good idea for transmission life........

[BigMike]

And full throttle in 5th gear isn't a good idea for transmission life........

I should have wrote that for the grade in question and those with 22R(-E) engines, they have plenty of power in 3rd gear but not enough power to pull 4th. So as has been Marlin's advice, if you're going to run mid-throttle for a while in this scenario, then don't exceed 4,000 RPM. He'll say such things as, "Give the engine a break and just hold back at 4K" ... "Is getting to the top 5 mins sooner really worth the wear and tear on the engine?"

In my opinion this has just been a hunch by Marlin all along but it does make sense as the 22R's peak torque comes in at only 2,800 RPM, so if you can't pull a taller gear at a lower RPM where it's supposed to shine, then downshift and hold back for a while.

Regarding 5th gear, they are doing this with the Crawl Box in low range. A reduced load by 2.28-times what the transmission is used to plus only going about 45? MPH isn't the end of the world for the transmission.

As a 3RZ owner with 37% more peak torque 43% higher in the RPM range, I abuse my 5th gear in different ways

Regards,
BigMike

[Snowtoy]

Good discussion here, not much to add.

One thing to note that many seem to forget is that a 35" tire rarely measures thirty-five inches, and even if it did, after a season or two it will be closer to 34".

I built a nice Engine RPM and Truck Speed Calculator on our R&P page: https://www.marlincrawler.com/differential/ring-pinion Plug in some numbers, write down the resultants, and then go drive your truck how it sits now and compare. See if the RPMs vs speed is what you're looking for. If the calculator calls for 3,500 RPM for 65 MPH on the freeway then run your truck in 4th gear at 65 MPH to see if those high of RPMs is something you'd want to live with.... etc.

Regards,
BigMike

Correct, most 35's aren't 35" tall when mounted, however, neither are most other tire/wheel combos, most are 1-2 inches shorter than the sidewall size or the metric-to-inch conversion.
6 of my vehicles, all tires at 35psi
225/50R16 24.9", mounted 23.75"
265/75R16 31.6",mounted 29.5"
205/65R15 25.5", mounted 24.5"
205/75R14 26.1", mounted 25.125"
33x12.50 R15 mounted are 32"
35x12.50 R15 mounted are 34"

The calculator shows that there is very little difference when you use stated tire size or actual size providing you use the height discrepancy of the original tires w/the stock gear ratio.
Calculator results,
My '90 w/R150/5th gear/70mph
4.56 w/31's(stated size) 2907rpm's, mounted size 30" 3004rpm's
4.88 w/33's(stated size) 2923rpm's, mounted size 32" 3014rpm's(Confirmed w/Stock tach and gps).
If I ran my 35's BFG MT's
5.29 35's stated size 2987rpm's, mounted size 34" 3075rpm's or 2837rpm's w/4.88's

My '91 '91/W56c 5th gear 70mph
4.56 w/31's(stated size) 2942rpm's, mounted size 30" 3040rpm's
4.88 w/33's(stated size) 2958rpm's, mounted size 32" 3050rpm's.
5.29 w/35's(stated size) 3023rpm's, mounted size 34" 3112rpm's, or 2871rpm's w/4.88's. Stock tach at 70mph(gps) 3250rpms
Could not start with the stock 225/75R15's and w/4.10 gears, the calculator starts at 29", and the 225/75R15's ar.3" unmounted, which would likely be about 27" when mounted.

However, if you use the stated size of the original stock tire w/stock gear ratio and the mounted size of the tire you are now running/plan to, you get false results.
My '90 w/R150
4.56 31's stated size...........2907rpm's
4.88 33's(32" mounted size) 3014rpm's
5.29 35's (34" mounted size) 3075rpm's or 2837rpm's w/4.88's

My '91 w/W56c
4.56 31's stated size....2942rpm's
4.88 33's(32" mounted) 3050rpm's.
5.29 35's(34" mounted) 3112rpm's, or 2871rpm's w/4.88's.
The results make it look like 5.29's would increase the rpm's by 170 at 70/5th gear, when they would actually only be increased by 60-70rpm's, on the other hand it looks like the the 4.88's would only lower the rpm's by about 70, when they actually lower the rpm's by about 170.

[BigMike]

The results make it look like 5.29's would increase the rpm's by 170 at 70/5th gear, when they would actually only be increased by 60-70rpm's, on the other hand it looks like the the 4.88's would only lower the rpm's by about 70, when they actually lower the rpm's by about 170.

Very nice info Snowtoy, was fun to read all the differences. I thought about having the tire size select be a text field instead so the user could input his or her mounted size(s), but my prehistoric Determine your Actual Vehicle Speed calculator already does this. In the end I felt it reads better having the sizes listed. I added the metric sizes to provide for some variances between whole inch-numbers.

Regards,
BigMike

[blackdiamond]

For a real test you guys need to run the two main passes on I-70 in Colorado. They would pull my 85 down into 2nd gear for miles at a time. The grade in combo with the altitude was murder.

Much more fun in my 2000 SS Camaro where it would keep pulling strong until 5th gear and about 130 mph.

[88_Pathy]

I'll just answer the question. I have an 85 x-cab 3rz with 37's and 4.88s. It runs great. I wouldn't want 5.29s on the highway. Only time I wanted a little more juice was when I swapped to beadlocks... A ton more rotating mass and it dogged her down a little. It's purely up to you. Light build 4.88s are great.