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 35's to 37's

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shakedown
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PostSubject: 35's to 37's   Mon 25 Jun 2012, 12:33 pm

I pulled the trigger and ordered 37's (37x12.50R17. I run 4:10's with an auto. The weight of the set-up on there now is 123lbs and what I am going to weighs 114lbs. I plan on regearing to 5:38's but it will probably be 6 months or so before I get that done. Am I taking a huge risk by running this for 6 months before I can regear? I figure since the weight is less I won't see an difference than running the 35's as I do now. Thanks, Jon.
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Tvernon
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PostSubject: Re: 35's to 37's   Mon 25 Jun 2012, 12:53 pm

What tire did you go with that weighs less than your 35??? And no. There are several people on here who have run heavy 37's with 4.10's and had no problems. You should be just fine.
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shakedown
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PostSubject: Re: 35's to 37's   Mon 25 Jun 2012, 1:08 pm

Running 35x13.50R20 Mickey Thompson Claws (76lbs) and I ordered Goodyear MT/R's 37x12.50R17 (74lbs).
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lanrod
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PostSubject: Re: 35's to 37's   Mon 25 Jun 2012, 6:05 pm

I'm not a physics major, but having the weight spinning farther from the center definitely makes a difference. Any math majors going to help us out?
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Maverick1701
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PostSubject: Re: 35's to 37's   Mon 25 Jun 2012, 6:56 pm

lanrod wrote:
I'm not a physics major, but having the weight spinning farther from the center definitely makes a difference. Any math majors going to help us out?


no but I did stay at a holiday inn express last night
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PostSubject: Re: 35's to 37's   Mon 25 Jun 2012, 10:54 pm

I ran 37's on my JK for two years with 4.10s without issue. I did not put a lot of miles on it, but I did wheel it hard.
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Tvernon
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PostSubject: Re: 35's to 37's   Tue 26 Jun 2012, 12:21 pm

What lanrod is referring too is centrifugal force. It makes a huge difference in most cases. To put it in an easy picture, imagine a nut on a long bolt has rusted on and you can't get it off with your basic socket wrench. So, like all men, we grab the breaker bar to take advantage of the leverage it creates. Larger tires operate the same way on your ring and pinion gears and axle shafts as a breaker bar does and a nut and bolt.

That said, if the tires are actually lighter, you will probably not ever notice it. In fact, with your 4.10's comes a substantially larger pinion gear than 5.13's or even 5.38's. This means your pinion will be positioned to handle a heavier load than perhaps some of the more lower gears can. Sort of counter intuitive.

So like I said above, you'll be just fine.
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shakedown
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PostSubject: Re: 35's to 37's   Tue 26 Jun 2012, 2:52 pm

Thanks for the insight fellas. 37's will be delivered today. Now just to find some 17" wheels.......oh wait......I found em, just can't afford em right now. DAMN!!
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Deacon
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PostSubject: Re: 35's to 37's   Wed 04 Jul 2012, 3:16 am

shakedown wrote:
Am I taking a huge risk by running this for 6 months before I can regear? I figure since the weight is less I won't see an difference than running the 35's as I do now.
It's not about weight or centrifugal (or centripetal) force. It's about mechanical advantage. Think about those factories or refineries with steam valves wheels. Some are large, and some are small. The small ones are smaller because they can be: it doesn't take that much effort to turn a small valve under low pressure, so a proportionately small wheel is fine, just like turning off the spigot when you're done watering the lawn. But on a much bigger valve, there's no way it'd be appropriate to expect a normal adult man to close it easily with a small wheel. So they fit it with a much larger wheel, because just like a cheater pipe allows you to put a whole lot more torque on whatever you're trying to break loose, increasing the diameter of the wheel (or using a longer cheater pipe) means the same amount of force applied (over a greater distance) will exert a lot more torque on the valve or whatever is trying to be moved.

When you move to a larger wheel, the same forces are at play. That's why it takes either a more powerful engine or deeper gearing to get a tire with a larger diameter moving the same as stock. In this case the valve (axle, really) is trying to turn the wheel while the wheel resists somewhat. Imagine a single-speed bike where you double the size of the bike tires--even if they weigh the same, it'll feel like trying to get started on a 10 speed in a taller gear instead of 1st. Remember that gears multiply torque. If you have 4.10's, then for just over every 4 revolutions of the pinion (driven by the engine) the ring gear turns once. If you move up to 37's, those same 4.1 revolutions of the pinion gear have to now push you further down the road, because while it's still turning the axle shafts the same amount, the larger circumference tire means it has to cover more ground for every single revolution of the whole mechanism. Deeper gearing (e.g. 5.38's) means that engine turns the pinion just shy of 5 and a half times to move the ring gear around once...more revolutions of the engine are used to move the larger tire. The same torque applied over a longer distance gets the tire turning much more easily, and it puts the engine back in the power band like it was designed to run when it left the factory. Does all that make sense?

It's also why people with stock brake setups often underestimate how long it's going to take them to stop, because resisting the torque that rolling stock size tires (and the weight of the vehicle they're carrying) put on the brakes is one thing while trying to use the same brakes to stop a much larger diameter wheel is much more difficult. I almost rear ended a lady in a BMW shortly after I got my 35's on, because she was a clueless idiot and a terrible driver--but also because I was surprised how hard I had to stand on the brake pedal and still felt like not enough was happening.

All that said, I have no idea whether running 37's on 4.10's will be "acceptable" to you and your sensibilities or how quickly you'll realize you hate it. I know it will NOT be ideal. I have a friend with a 2-door JK (not a Rubi) on 35's with an auto, and while it does eventually manage to roll down the road under its own power, it would drive me nuts to have to drive it around town like that. I feel like I want to hop out and give it a push to get going from a stop. Again, imagine trying to start out a 10 speed bike from a dead stop in 7th gear. Not fun. Your engine doesn't think so, either Smile I'm surprised you seem fine with 35's on 4.10's, but jumping up to 37's is that much more. In my case running 33's on stock gearing was...tolerable. Moving to 35's was a massive difference, pushing tolerable over a cliff onto the jagged rocks below. I realize I'm talking about a TJ, but the same principle applies. If you feel like your Jeep is way overpowered today, then you'll be fine with 37's. If you feel like it's already trying its hardest just to get you moving, 37's will make it much worse.
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Tvernon
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PostSubject: Re: 35's to 37's   Wed 26 Sep 2012, 11:58 pm

Deacon wrote:
shakedown wrote:
Am I taking a huge risk by running this for 6 months before I can regear? I figure since the weight is less I won't see an difference than running the 35's as I do now.
It's not about weight or centrifugal (or centripetal) force. It's about mechanical advantage. Think about those factories or refineries with steam valves wheels. Some are large, and some are small. The small ones are smaller because they can be: it doesn't take that much effort to turn a small valve under low pressure, so a proportionately small wheel is fine, just like turning off the spigot when you're done watering the lawn. But on a much bigger valve, there's no way it'd be appropriate to expect a normal adult man to close it easily with a small wheel. So they fit it with a much larger wheel, because just like a cheater pipe allows you to put a whole lot more torque on whatever you're trying to break loose, increasing the diameter of the wheel (or using a longer cheater pipe) means the same amount of force applied (over a greater distance) will exert a lot more torque on the valve or whatever is trying to be moved.

When you move to a larger wheel, the same forces are at play. That's why it takes either a more powerful engine or deeper gearing to get a tire with a larger diameter moving the same as stock. In this case the valve (axle, really) is trying to turn the wheel while the wheel resists somewhat. Imagine a single-speed bike where you double the size of the bike tires--even if they weigh the same, it'll feel like trying to get started on a 10 speed in a taller gear instead of 1st. Remember that gears multiply torque. If you have 4.10's, then for just over every 4 revolutions of the pinion (driven by the engine) the ring gear turns once. If you move up to 37's, those same 4.1 revolutions of the pinion gear have to now push you further down the road, because while it's still turning the axle shafts the same amount, the larger circumference tire means it has to cover more ground for every single revolution of the whole mechanism. Deeper gearing (e.g. 5.38's) means that engine turns the pinion just shy of 5 and a half times to move the ring gear around once...more revolutions of the engine are used to move the larger tire. The same torque applied over a longer distance gets the tire turning much more easily, and it puts the engine back in the power band like it was designed to run when it left the factory. Does all that make sense?

It's also why people with stock brake setups often underestimate how long it's going to take them to stop, because resisting the torque that rolling stock size tires (and the weight of the vehicle they're carrying) put on the brakes is one thing while trying to use the same brakes to stop a much larger diameter wheel is much more difficult. I almost rear ended a lady in a BMW shortly after I got my 35's on, because she was a clueless idiot and a terrible driver--but also because I was surprised how hard I had to stand on the brake pedal and still felt like not enough was happening.

All that said, I have no idea whether running 37's on 4.10's will be "acceptable" to you and your sensibilities or how quickly you'll realize you hate it. I know it will NOT be ideal. I have a friend with a 2-door JK (not a Rubi) on 35's with an auto, and while it does eventually manage to roll down the road under its own power, it would drive me nuts to have to drive it around town like that. I feel like I want to hop out and give it a push to get going from a stop. Again, imagine trying to start out a 10 speed bike from a dead stop in 7th gear. Not fun. Your engine doesn't think so, either Smile I'm surprised you seem fine with 35's on 4.10's, but jumping up to 37's is that much more. In my case running 33's on stock gearing was...tolerable. Moving to 35's was a massive difference, pushing tolerable over a cliff onto the jagged rocks below. I realize I'm talking about a TJ, but the same principle applies. If you feel like your Jeep is way overpowered today, then you'll be fine with 37's. If you feel like it's already trying its hardest just to get you moving, 37's will make it much worse.




Best example ever. I will copy and paste this onto every thread with a gear ratio question for sure. And good call on the spell check, I was to damned lazy to do that myself.
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Deacon
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 1:42 am

Thanks Smile It took me a while to figure all this stuff out, and nobody seems to be able to explain it in a way that makes sense (to me). If it'll help make sense to others, by all means, use away!
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Tvernon
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 11:30 am

cheers2
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lanrod
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 11:48 am

I really want to move to 37s from 33s. I am willing to regear, but I need to find a fair deal on appropriate wheels, and good performing tires.
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 12:17 pm

lanrod wrote:
I am going to regear.

Fixed that for you lol.
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lanrod
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 12:46 pm

Tvernon wrote:
lanrod wrote:
I am going to regear.

Fixed that for you lol.


Ha! Thanks for the nudge.
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PostSubject: Re: 35's to 37's   Thu 27 Sep 2012, 5:26 pm

No problems. cheers2
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PostSubject: Re: 35's to 37's   Mon 01 Oct 2012, 7:56 pm

Maverick1701 wrote:
lanrod wrote:
I'm not a physics major, but having the weight spinning farther from the center definitely makes a difference. Any math majors going to help us out?


no but I did stay at a holiday inn express last night
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