Going to 4.88 or 5.13 for 37s?

[COJeeper]

Agreed with others comments. I am in a 2.0L auto at altitude and have no issues running 37's on stock gearing. I don't see 8th gear too often and that is fine with me. I am using a Pulsar XT inline tuner so that helps and I have no plans on regearing either.

Good to hear because my 37" Wildpeak AT3Ws are coming this week and I'm just North of you with the same motor!

I plan on going 4.88s I think, at least, that's the plan. Time will tell if I make that move or not. I figure by the end of 2023, if I don't like it and want some more crawling torque or a slower crawl, I'll buy some gears on a Black Friday sale. If I'm good with how it all feels and runs, I'll leave it alone.

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[kapk22]

I am not saying that you will not need to re-gear a 2.0T, but people with 2.0T engines re-gear far less often than those with a 3.6L due to the torque of that engine versus a 3.6L. Typically, you can also gear a 2.0T one full ratio less than a 3.6L and maintain the same level of performance.

In the end, these conversations are all about the lack of torque in certain RPM ranges that change when larger tires are added and gears are not changed.

I couldn’t help myself. I did not realize there would be so much feedback on this. I am concerned about the stress the 37s have on the transmission (since I installed them). The restored power and better fuel economy (minimal) on long trips will be nice. However, the later two are just bonuses for my situation. I had a quote for $1850 to gear when I was in Oregon. I will have to find a reputable shop in the San Antonio area when funds allow.

Based on what people are saying, it sounds like it would be a good investment, at least preventative wise.

Thanks for all the info guys

 

[Creeker]

Earlier, someone commented the chart provided regarding gear ratios/RPM/Tire speed was for a JK.

On a post from 2018, the gear ratios were listed, as shown in the link below:

https://www.jlwranglerforums.com/forum/threads/gear-ratio-chart-for-jl-wrangler.1781/

From that data, and using some gear, rpm, speed (in this case 70 MPH), tire size ratio calculations. Excel was used to create a draft chart, as shown below for JLs with automatics and manual gearboxes, as shown below:

The above is a draft and is work in progress.

Hopefully, others are out there that can confirm the calculations and data.
Please send me a PM, if you can help verify the data and the calculations. I can email you a copy of the spreadsheet.

The goal is have a spreadsheet that people can enter their speed, tranny gear ratios, and gear selection and determine what combination of tires and gears would work best for them based off the RPM calculated.

Please be patient as we work through this draft.
Thx.

 

[CarbonSteel]

@Creeker - what MPH are those RPMs for? (I may have missed it).

 

[Creeker]

@Creeker - what MPH are those RPMs for? (I may have missed it).

My bad, edited the post for 70 MPH...

 

[c20040215]

I thought @AnnDee4444 has one already? Pretty comprehensive, too.

 

[c20040215]

Earlier, someone commented the chart provided regarding gear ratios/RPM/Tire speed was for a JK.

On a post from 2018, the gear ratios were listed, as shown in the link below:

https://www.jlwranglerforums.com/forum/threads/gear-ratio-chart-for-jl-wrangler.1781/

From that data, and using some gear, rpm, speed (in this case 70 MPH), tire size ratio calculations. Excel was used to create a draft chart, as shown below for JLs with automatics and manual gearboxes, as shown below:

The above is a draft and is work in progress.

Hopefully, others are out there that can confirm the calculations and data.
Please send me a PM, if you can help verify the data and the calculations. I can email you a copy of the spreadsheet.

The goal is have a spreadsheet that people can enter their speed, tranny gear ratios, and gear selection and determine what combination of tires and gears would work best for them based off the RPM calculated.

Please be patient as we work through this draft.
Thx.

There is a discrepancy. The table you shared listed 4.88 manual tran with 37s is turning 1915 rpm @ 70mph.. My real world reading is about 2350rpm @ 70mph

 

[jhackathorne]

Earlier, someone commented the chart provided regarding gear ratios/RPM/Tire speed was for a JK.

On a post from 2018, the gear ratios were listed, as shown in the link below:

https://www.jlwranglerforums.com/forum/threads/gear-ratio-chart-for-jl-wrangler.1781/

From that data, and using some gear, rpm, speed (in this case 70 MPH), tire size ratio calculations. Excel was used to create a draft chart, as shown below for JLs with automatics and manual gearboxes, as shown below:

The above is a draft and is work in progress.

Hopefully, others are out there that can confirm the calculations and data.
Please send me a PM, if you can help verify the data and the calculations. I can email you a copy of the spreadsheet.

The goal is have a spreadsheet that people can enter their speed, tranny gear ratios, and gear selection and determine what combination of tires and gears would work best for them based off the RPM calculated.

Please be patient as we work through this draft.
Thx.

I always assumed the goal was to be close to stock RPM from these charts. Is that the case? I know I used a similar chart for my JK when regearing, but can't recall what I based my decision on.

 

[CarbonSteel]

My bad, edited the post for 70 MPH...

So with BFG K02 37's (which measure about 35.7" new) and ZF8/5.13's I am turning exactly 2500RPM at 75MPH, so it would seem that your chart is erring on the slower RPM side.

 

[grimmjeeper]

The biggest problem with accuracy in those charts and calculators (including mine: www.grimmjeeper.com/gears.html) is getting the true rolling diameter of the tires.

A 35" tire is never truly 35" in diameter. Most of them have an advertised diameter of 34.8 or 34.6. Some 315/70R17 tires are 34.4

But even then your rolling diameter is smaller than that. The 315/70R17 Duratracs I ran on my JKcwere actually 33.5" true rolling diameter.

Best bet is to look up the revolutions per mile in the tire specs. To get rolling diameter from there it's 63360 ÷ 3.14 ÷ revs per mile.

Once you use an accurate tire diameter, all of the calculators and charts work better.

 

[AnnDee4444]

I thought @AnnDee4444 has one already? Pretty comprehensive, too.

It's a sticky in the Transmission, Axles, Gears section

The biggest problem with accuracy in those charts and calculators (including mine: www.grimmjeeper.com/gears.html) is getting the true rolling diameter of the tires.

A 35" tire is never truly 35" in diameter. Most of them have an advertised diameter of 34.8 or 34.6. Some 315/70R17 tires are 34.4

But even then your rolling diameter is smaller than that. The 315/70R17 Duratracs I ran on my JKcwere actually 33.5" true rolling diameter.

Best bet is to look up the revolutions per mile in the tire specs. To get rolling diameter from there it's 63360 ÷ 3.14 ÷ revs per mile.

Once you use an accurate tire diameter, all of the calculators and charts work better.

I found that the BFG K02's have an average rolling diameter about 97.1% of the calculated height. My calculator uses this percentage to adjust the tire height entered, and is shown as "Tire Effective Diameter". You also have the option of entering revolutions/mile to be more accurate (the "Tire Diameter" field is a drop-down menu).

 

[JT1]

Why try to reinvent the wheel? The chart on grimmjeeper already has all this info and you can do a side by side comparison (if you are trying to decide between gearsets).

Going from 3.73s with my 6spd to 5.13s, both on 37's, 6th gear after and 4th gear before are almost identical.
The RPM drop from 4th to 5th when I was on 3.73s was enough where I couldn't maintain speed in a headwind on the highway. After the regear, I wish 6th was a little taller overdrive, but downshifting to maintain highway speed is a thing of the past.

 

[AnnDee4444]

Why try to reinvent the wheel? The chart on grimmjeeper already has all this info and you can do a side by side comparison (if you are trying to decide between gearsets).

Some people want something JL specific.

Also Grimmjeeper's is gearing only. Mine can calculate anything I want it to... like road force.

 

[JT1]

Some people want something JL specific.

Also Grimmjeeper's is gearing only. Mine can calculate anything I want it to... like road force.

Not bashing your work at all. There is a ton of info there. However, choosing between 4.88s and 5.13s when you already have the lift and tires is a use case. If you are trying to determine a future build, what you have created is amazing.

Too many new jeepers get analysis paralysis and think if they only went to 4.56s their jeep will jump off the closest bridge to a fiery death because it's wrong..

 

[Pinky Tuscadero]

So much information and so many answers which clearly conflict with each other and so many charts created by salesman trying to sell unneeded items (which, I myself do )
Some are right and some are total BS
If you have a standard Rubi you have the 4.10 already so just try that out with the 37's first and see how it feels. If you're concern is 8th gear then simply check to see how its doing now - no forum needed for that although one of these posts has a vid showing how to have the gear displayed all the time, sadly I've lost that one
If you are looking for mpg than you've chosen the wrong vehicle and certainly the wrong tires. If you think a bigger tires increase wear on your transmission then get the extended warranty although reading these posts I've never heard of that particular issue once.
Go from 31.5" and 3.45 on a Sport or 33"and 4.10 on a Rubi and put 37's on either one and you're mpg will most certainly drop. Both are 100% drivable though with plenty of power.
Jump the gears to 4.88 or more and you'll fare better off road, and be faster off the line but overall you're mpg will still suck - sorry
And yet, If you can swing it I'd recommend it fully because you bought your Jeep for fun

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