Gears for 37" tires

[jurfie]

First thing I did when looking at gears is I used this to compare the gear sets to my JK manual Rubi on 37s and 4.56 gears
Final drive was a concern but I really loved how my JK crawled. This calculator let me see down to the gear what I'd be looking at in both 4 low and high. This calculator also convinced me to avoid the manual in this truck. Comparing it to the JK the manual trans is very poorly geared to be running big tires.

Yes, I can see how powerful this calculator is now to compare different ratios for the exact conditions you want to research. For the majority of people who used the charts, I suspect they were looking for the gears to achieve stock performance and fuel efficiency when putting larger tires on. I also suspect most of the people on here are looking for that information; for those who want to improve crawling performance, the charts are irrelevant and the calculator is king. They also likely understand the nuances of the calculator better than those who rely on the charts.

The point is, the gear ratio you choose depends on what is important to the end user. What works great for a rock crawler won't work for a mall crawler. What works great for a daily driver whose commute is mostly on the highway won't work for a daily driver in the city. Mountainous roads vs. prairies. Near sea level vs. higher elevations. There are so many variables that relying on a chart could mean less than desirable results for the user's exact circumstances.

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[WXman]

On the 3.6: WHY Jeep used that engine and continues I have no idea, it is NOT a fit for a Jeep where rocks and off-road trails require way down low torque. Jeep picked it because it gets great mpg, I had no problem getting 19 mpg out of my Rubicon JK. The best ever engine for the Jeep was the old straight 6 in spite of its boatload of disadvantages, but if its trail performance you want it fits the bill.

Which is funny, because the 3.6L makes more torque than the 4.0L at EVERY single point along the RPM band. The 3.6L is also lighter, makes a gob more horsepower, and drinks less fuel. I wouldn't go back to a 4.slow if you gave me three of them for free.

As far as "do I need to regear for 37s?" the answer is no. My JL with 3.45 gears on 35" mud tires with the 850RE trans. would smoke the tires in 1st gear and would do 0-60 pulls in the 7 second range all day long. It would cruise in 8th gear on the highway and it would crawl off-road just fine. Now we've got 4.10 gears in these Gladiator JTs and we're worried about turning over 35s and 37s OK? Really?

Why waste $1,500 AND kill the factory warranty on two expensive axles when it's completely and totally unnecessary ?

 

[KennyKustom]

.....................AND kill the factory warranty on two expensive axles when it's completely and totally unnecessary ?

Dealer might have something to say, rolling in on 37's ( stock gears ) and asking for any warranty on the axles....

 

[Oscar Indy]

The point is, the gear ratio you choose depends on what is important to the end user. What works great for a rock crawler won't work for a mall crawler. What works great for a daily driver whose commute is mostly on the highway won't work for a daily driver in the city. Mountainous roads vs. prairies. Near sea level vs. higher elevations. There are so many variables that relying on a chart could mean less than desirable results for the user's exact circumstances.

For me the decision to finally go with 4.88 was the on highway experience. It turns out the 8speed is so deeply geared in first that its gonna be too deep for much use in 4 lo.
in the JK I had a 81-1 crawl ratio in first and it was good for super technical stuff. I found myself using 2nd in low a lot more which is 48-1 to crawl ratio. These ratios are actually closer to the 4.10 in the JT with the ratio changes from the JK.

The 4.88 in the JT gives me 92-1 crawl ratio in first and 61-1 and 41-1 in 2nd and 3rd respectfully. Which means ill get alot of use out of those 3rd most likely.

BUT the 23-1 in 4 high means 4 lo will rarely be used. That is basically 5th in 4 lo.

SO the on-road performance of not losing 8th was the deal-breaker. One thing to consider when going up in gears too is that the extra rotational mass of the big tires will put a little more strain on the drive train so going a little deeper when it doesn't make much difference numerically will be a benefit.

 

[ShadowsPapa]

Yes, it's about 4 screens filled side to side, in one long page. And you have to enter several steps worth of info.
When one is interested only in engine RPM with a given tire and gear ratio compared to another tire or gear ratio, it's a lot of form to fill out. With a chart I can look at a spot where my engine RPM at a given speed intersects with my tire size and don't even have to know my exact transmission gear ratio. I know the differential, I know the tire, I see the RPM, I can look down and say ok, what if I was running xx tire instead.....with no computer/tablet or phone. So charts still have their place even if you personally think they suck and are for wimps and fools. So don't use them if you don't like them - but calling others and the charts stupid - well...... it's a tool and may work fine for a lot of folks.

Internet - I'm not talking speed although that's an issue at times - I'm talking total loss or drop of internet where if you make a change to a page or click and it calculates and refreshes the page, it has to reconnect and reload. I wish it was only slow - you see the connection icon drop - even on this forum now and then I had to start over - but this forum does an occasional "save draft".
There is no dialup, no DSL, no cable here. Phone lines are too long and old and don't support such things and no cable company will run out here - not enough profit in it for them. Most people can't even get their cell phones to work here - they have to drive a ways away - so how could they use such a tool here? Can't - NO connection if they can't get a signal with their iPhone they just bought.

But major kudos to whoever built that page because I have done the work that it takes- I know the scripting and calculations that have to happen in the background. Web development for the state....... online calculators, as well as business web development - and my son an upper-level manager for Gannet's web marketing and development.

 

[Oscar Indy]

Yes, it's about 4 screens filled side to side, in one long page. And you have to enter several steps worth of info.
When one is interested only in engine RPM with a given tire and gear ratio compared to another tire or gear ratio, it's a lot of form to fill out. With a chart I can look at a spot where my engine RPM at a given speed intersects with my tire size and don't even have to know my exact transmission gear ratio. I know the differential, I know the tire, I see the RPM, I can look down and say ok, what if I was running xx tire instead.....with no computer/tablet or phone. So charts still have their place even if you personally think they suck and are for wimps and fools. So don't use them if you don't like them - but calling others and the charts stupid - well...... it's a tool and may work fine for a lot of folks.

Internet - I'm not talking speed although that's an issue at times - I'm talking total loss or drop of internet where if you make a change to a page or click and it calculates and refreshes the page, it has to reconnect and reload. I wish it was only slow - you see the connection icon drop - even on this forum now and then I had to start over - but this forum does an occasional "save draft".
There is no dialup, no DSL, no cable here. Phone lines are too long and old and don't support such things and no cable company will run out here - not enough profit in it for them. Most people can't even get their cell phones to work here - they have to drive a ways away - so how could they use such a tool here? Can't - NO connection if they can't get a signal with their iPhone they just bought.

But major kudos to whoever built that page because I have done the work that it takes- I know the scripting and calculations that have to happen in the background. Web development for the state....... online calculators, as well as business web development - and my son an upper-level manager for Gannet's web marketing and development.

This reminded me why I have you on my ignore list. You just like to argue and you're kind of a douche about it when you do. So back on the ignore list you go. Waste of my time talking to you.

 

[ShadowsPapa]

Which is funny, because the 3.6L makes more torque than the 4.0L at EVERY single point along the RPM band. The 3.6L is also lighter, makes a gob more horsepower, and drinks less fuel. I wouldn't go back to a 4.slow if you gave me three of them for free.

As far as "do I need to regear for 37s?" the answer is no. My JL with 3.45 gears on 35" mud tires with the 850RE trans. would smoke the tires in 1st gear and would do 0-60 pulls in the 7 second range all day long. It would cruise in 8th gear on the highway and it would crawl off-road just fine. Now we've got 4.10 gears in these Gladiator JTs and we're worried about turning over 35s and 37s OK? Really?

Why waste $1,500 AND kill the factory warranty on two expensive axles when it's completely and totally unnecessary ?

I have sitting here with me 2 vehicles with the 4.0 and two vehicles with the 3.6
(not counting the restoration I'm doing for another person and the one car I need to find a new body for and one I am parting out that has a 4.0)
Anyway, I can directly compare the 3.6 to a 4.0 - and one of my 4.0 powered vehicles has a not-so-stock 4.0. Head shaved .024", Comp xtreme 4x4 cam, roller rockers, better Bosch injectors and more. My built 4.0 is a lot more powerful than my stock 4,0 but the JT 3.6 will leave them both in the dust. I have towed with both of the 4.0 powered vehicles - meh, don't count on anything over 4,000 pounds no matter WHAT the tow rating is.
OK, so the gear ratio in one is 2.87 I believe, can't recall the differential ratio on the WJ. Even in low neither is as gutsy as the JT 3.6
I can burn rubber in 1st and second with the built 4.0 and I'd love to try the prototype head I have on my shelf- it's one of three made and supposedly builds better torque and HP for a 4.0 but it would still be a 4.0 - they are not high-revving engines.
My WJ with 4.0 does about 18. My JT does about 20+
My Eagle with 4.0 - blows the JT away in mileage - mid 20s and have according to my spreadsheet touched 27 with at least one tank of gas.
As much as I love the 4.0 - I'm quite happy with the 3.6 so far.
Now to see if I have to re-gear to pull my trailer........ that's the next thing to tackle.

 

[ShadowsPapa]

This reminded me why I have you on my ignore list. You just like to argue and you're kind of a douche about it when you do. So back on the ignore list you go. Waste of my time talking to you.

And you hate other points of view, even when laid out with logic, and hate anyone who doesn't love your way of doing things.
I don't call other people's tools or ideas stupid anyway or imply others are stupid for using them.
If someone doesn't bow to your superior ways........
Don't know how laying out facts is so bad or pointing out other ways of doing something. You assume everyone is like you - or should BE like you.
Thank you for ignoring me - I actually do appreciate it. I can talk with civil and reasonable people who are open to learning or doing things differently.

 

[jurfie]

Ok y'all; first run at it. This is for those who want to try to maintain stock performance and fuel economy when going to a larger tire size.

I used the stock RPMs to determine 1800-2200 is the range to maximize MPGs since that is where the RPMs fall on the various models and I assume FCA felt 2000 RPM is the sweet spot for fuel economy. The green boxes fall between that range.

As per the discussion, this is just a rough starting point to see if you think regearing will help you to maintain STOCK performance on the highway at 70 MPH and regain/maintain all 8 gears on the automatic. IT DOES NOT APPLY TO THE MANUAL.

You'll notice that going to 37s with the 4.10s is not that far outside the range, hence why many feel it is unnecessary to regear - YMMV.

Edit: Note I included the stock Rubicon tire size with 3.73s for those who put take-offs on their Sport/Overland.

 

[Factoid]

Excellent chart!

My conclusion is that I can keep the 4.10's with 37" tires as long as I do 80. Good outcome!

 

[Oscar Indy]

Excellent chart!

My conclusion is that I can keep the 4.10's with 37" tires as long as I do 80. Good outcome!

I linked a video earlier in the thread about trying to do 80 on 37s. The 4.10s don't have enough torque to hold 8th and 80mph. it'll do it perfectly flat and downhill. any headwind or SLIGHT incline and it'll gear down to the 7th or 6th depending on severity. I tried locking it into 8th and seeing what it would do. 71 is all it'll hold at my altitude.

 

[Factoid]

Good intel, thanks.

 

[KennyKustom]

Excellent chart!

My conclusion is that I can keep the 4.10's with 37" tires as long as I do 80. Good outcome!

Good chart indeed...
This also shows how horrible 37's and 4.10 gears would be.. Even more so, with a lower speed limit ( 100 kph (62mph here )
It is not holding 8th at 1746 rpm.....

 

[Oscar Indy]

Good chart indeed...
This also shows how horrible 37's and 4.10 gears would be.. Even more so, with a lower speed limit ( 100 kph (62mph here )
It is not holding 8th at 1746 rpm.....

See thats the problem with charts.
4.10 and 37s will turn 1877 in 7th at 60mph which is in the powerband that trans will try to keep the RPMs in anyway. The 8 speed is an awesome trans and the programming will keep it in the ideal band for the speed and rpm given if it can support it. at 60 4.10 were not a problem on 37s.

 

[ShadowsPapa]

Excellent chart!

My conclusion is that I can keep the 4.10's with 37" tires as long as I do 80. Good outcome!

LOL Love pure unadulterated logic!

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