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31" on 4.56

Heck after reading this I may go with 31's and 488's. The only time I hwy drive is when I am pulling a 23' travel trailer and then I never get over 55mph.

Dave
 
georger said:
Thanks guys, you've pretty much validated my thinking. I may even move up in tire size as early as this fall, so it might not be a whole year. My main focus for this summer, however, is reliability.

Now, do I dare start another locker thread? I'm thinking Powertrax, but I have some reservations about winter driving. opinions?
Click to expand...
No, don't start another locker thread, read the ones already here...;)

I run 33s and 4.88s. On the highway I turn about 2500-2700ish rpms at 70-75. I see no need to go faster than that and the engine handles those rpms just fine.
 
i ran 4.88s with 31s for a short while
until the 33s got on
liked it .
freeway rpms werent too bad
dont expext to go faster than 80 tho
 
im assuming ur an auto trans blondejon? cuz i know if i had 4.88s and 31s on my manual i probly could get to 65 really fast but that would be about it.
 
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georger said:
Now, do I dare start another locker thread? I'm thinking Powertrax, but I have some reservations about winter driving. opinions?
Click to expand...

No. Put a no-slip in the rear, learn how to drive with it and you'll be fine. It'll help you significantly in the winter time and having both wheels spinning lets you drift around corners and do donuts in the snow much easier lol. You should have seen the look on people's faces when there was 5-6" of snow on the road and I'm getting sideways going through an intersection. :rof:


1990heepxj said:
can i say ur all nuts with ur over gearing way past stock performance. use http://www.therangerstation.com/tech_library/Gear_Tire_RatioChange.html. to the OP if u drive a manual ur going to be massively over geared at 4.56s and 31s if ur an auto u wont be quite as bad but still over geared.
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Seriously? You're scolding everyone for having aftermarket parts and not running stock gearing? On a wheeling website? Having higher numerical gears is way better for offroading performance.
 
Darky said:
I run 33s and 4.88s. On the highway I turn about 2500-2700ish rpms at 70-75. I see no need to go faster than that and the engine handles those rpms just fine.
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Ditto.
 
1990heepxj said:
can i say ur all nuts with ur over gearing way past stock performance. use http://www.therangerstation.com/tech_library/Gear_Tire_RatioChange.html. to the OP if u drive a manual ur going to be massively over geared at 4.56s and 31s if ur an auto u wont be quite as bad but still over geared.
Click to expand...

the auto trans does make a big difference because of the torque convertor. i agree that 4.56 with 31's with a manual will be deep, but not undrivable.
for my jeep 89 with a 5spd, i would rather be over geared then under geared.

stock gearing is about fuel economy not performance. when lifting my xj and adding larger heavier tires, my goal when regearing was to get it deeper then stock, not close to what stock was. so 31's, manaul trans, and 4.10 gearing is deeper then stock and perfect for my use. highway driving rpms are not over 3 grand and i have no need to downshift when passing someone or when there is an incline.
 
I ran 4.56 and 30s for a day and I thought it was awesome! the rpms werent terrible at all, and it wasnt like chirping your tires everytake off but you could.
 
1990heepxj said:
can i say ur all nuts with ur over gearing way past stock performance. use http://www.therangerstation.com/tech_library/Gear_Tire_RatioChange.html. to the OP if u drive a manual ur going to be massively over geared at 4.56s and 31s if ur an auto u wont be quite as bad but still over geared.
Click to expand...
You want to be deeper than stock. Run stock gearing and tires with about 500 extra pounds of gear in it and see what impact it has on your performance. An XJ with bigger tires has to overcome more than gearing with the larger rolling radius of the tires. Rotational inertia plays a big role in negatively impacting your "power". Bigger tires weigh more and that weight is at the end of a longer lever (radius), therefore one extra pound of tire/wheel weight has a larger impact than 1 extra pound of Jeep weight.
 
how i see it is over gearing past stock is def good but to an extent. gearing past stock to the point ur on 31s and 4.88s is way overboard. ur only putting 3 inch taller tires on theres no need for ur drive shaft to turn 1.25-1.75 turns more for that small of a tire its simply not necessary unless its a very dedicated crawler. i personally would run 37s with 4.88s on my ax-15 trans because if u use the calculators for gearing to match tires out there it tells you that from 3.07s and 28" tires to 37" tires i would want 4.10s to be almost exactly stock so 4.88s would have a ton of power on 37s. i guess my problem is i think of it more for my manual trans yet most people are on autos and need lower ratios then i would. and 89xj i know that the leverage and all that comes into play but thats why u regear cuz putting close gears to stock makes it so it turns that leverage just as easy as it would the little stock 28s but i still agree with over gearing just not as over geared as some people do. and sunburned im not scolding anyone if i said in person to u that i think ur nuts to run 4.88s on 31s in a totally normal just conversating voice u wouldnt take it as scolding u would simply give me ur side on it and talk about it so dont take it so serious its just an opinion sorry if i offended. personally i want another yota like my last one 5.29s and 37s and dual cases killin the 104 to 1 crawl ratio if only i had 4.7s in the rear case pullin a whoppin 219 to 1 crawl. also my little 2.3l 4 banger ranger i had was 3.54s stock on like 26s i believe, i put in 4.10s and it chirped 31s easily which is only a little over geared i always had 33s on it tho and wished i had 4.56s for that little motor. so anyway noone take this as me telling everyone what to do im just saying my opinion on the topic.
 
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You're misunderstanding what rotational inertia is. Regearing to be comparable to stock will be regearing to move the stock rotating mass. Our rotating mass is much heavier than stock as well as taller, thereby acting like a much larger increase in overall vehicle weight. Why do sports cars, race cars and drag cars go with the lightest wheels possible before removing weight from the rest of the car? Because removing rotating mass, thereby decreasing rotational inertia, has a much larger impact on performance than shaving the same weight from the vehicle itself.
 
Too deep for road use, your MPG will drop big time. I ran 31s & 4.56s for a bit & my MPG's dropped from 18 average to 13 average, going to 32s brought my mpg back up to 16avg.

4.11s is perfect for 31's
 
Darky said:
You're misunderstanding what rotational inertia is. Regearing to be comparable to stock will be regearing to move the stock rotating mass. Our rotating mass is much heavier than stock as well as taller, thereby acting like a much larger increase in overall vehicle weight. Why do sports cars, race cars and drag cars go with the lightest wheels possible before removing weight from the rest of the car? Because removing rotating mass, thereby decreasing rotational inertia, has a much larger impact on performance than shaving the same weight from the vehicle itself.
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I think the rotational inertia thing is exaggerated a lot. Yeah it matters but it's not a reason to go 2x as deep as you need to. I'm not sure there's a physical reason why rotating mass would be worse than regular mass. The top of the wheel is moving 2x as fast, but the bottom of the wheel isn't moving at all relative to the ground. So it should average out to being identical to if the tire is just sitting in your cargo bay.

I think what makes people think the bigger tires are much worse is they are adding lift at the same time, which means a lot more air resistance.
 
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Post #12 confirms what I said about the mass of bigger tires not mattering much

http://www.solsticeforum.com/forum/f11/rotational-inertia-energy-42639/

Normally, you're looking for the moment of the mass. That would be mass of the body multiplied by the radius. But in this case, both masses have equal distribution so we can use the ratio of masses as a guide. The ratio is .75, so the lighter wheel will be 25% easier to spin.

[For nonbelievers we'll go through the physics...

We have 75% of the weight at a radius of 8.5 inches. and 25% of the mass "in the center". Well, we'll still need a radius for this mass, so let's use the bolt radius or about 2.5 inches. Hopefully that will be OK with everyone. So the equation for the moment of the wheels would be:
moment (in pound-inches) = .25mass(2.5inches) + .75mass(8.5inches)

Moment for the heavier rim = 168 pound-inches
Moment for the lighter rim = 126 pound-inches

There, the ratio of the moments is the same as the ratio of the weights.]

We all remember F=ma. Force equals mass multiplied by acceleration. In angular terms;
Force equals moment multiplied by angular acceleration. This is a direct relationship. The amount of force needed varies directly with the magnitude of the moment.

So... the 18 pound rim will accelerate the same as the 24 pound rim using 25% less force.

But aww shucks it doesn't matter a hoot, because we're spinning more than just the rim. The rotational mass on our cars consists of far more than just the rim. It's the hub, the break disc... heck, on the rear wheels we even have the axle, differential and drive shaft!!

And let's not forget the tires themselves!!!
willy_nilly.gif
Assuming the tire weighs about 20 pounds and the center of mass is at 12 inches, the moment would be 240 pound-inches, far more than either rim.

When all of these moments are averaged in, the 25% advantage quickly gets "lost in the sauce" of the entire rotational system and any difference in rim weight is truly inconsequential, really.

In fact, the weight reduction would matter much more for linear acceleration purposes. Considering a 3000 pound vehicle, a reduction of 24 pounds gives you almost a 1% increase in acceleration. The differences in angular acceleration for the lighter rims is far, far smaller than that.

As others have said, the main benefit is in unsprung weight. A lighter wheel, will allow the suspension system to react faster to changes in the road, resulting in better handling. When considering unsprung weight, we're again talking about linear acceleration. We no longer worry about moments, so the tire will not dominate the equation as it does with angular acceleration. Also, only about half the mass of the axle will be involved and none of the drive shaft or other rotational masses of the system.

So... reduce the weight of the rims for handling purposes and not for any other reason. Well... maybe cosmetics.
wink2.gif


If drag racing is your bag, you'd want to reduce every pound for linear acceleration purposes primarily.
Click to expand...
 
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It's physics (which i won't pretend to have a firm grasp of). Hold a 5 lb weight in your hand with your elbow bent 90*. Now extend it out so your arm is straight. The weight is the same, but the leverage exerted by the longer lever causes more strain to support the same weight. Now imagine doing that but increasing the weight when you increase the length of the lever (your arm). It's gonna feel like a LOT more weight. Tests have been done involving sports cars where they run the same overall height tire but change the wheels out. Either plus sizing or just experimenting with lither and heavier wheels. The heavier the wheel and tire combo was, the slower the car got, by a higher degree than would have been predicted by just adding the weight to the car.

EDIT: I actually had the benefit of going from 30" tires to 33" tires without changing the lift. Obviously, with the stock gears, it was a dog. But when I regeared to 4.88s, it did indeed improve by quite a bit, but still considerably slower than when I was on 30's with stock gears and steel wheels, which was somewhat slower than when it was stock all around.
 
gay, you were on a solstice forum
 
Darky said:
Except that post is isolating the weight difference in the wheel itself. We are referring to the wheel and tire combo. They argue that the extra weight of the tire cancels out any small differences in wheel weight.
Click to expand...

Are you saying bigger tires alone has a bigger effect because you're adding the mass to the outside? Well I agree but it still seems like it wouldn't be that bad. Anyone understand the physics enough to do some calculations?
 
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