Gear Help!!!!!

[SKINUM]

SKINUM previously said:

So, does the size of the tire alone warrant regearing? A 33 inch tire comes in different weights. So, for instance if you go with a 33x10.50 in comparison to a 33x12.50 the 10.50 is going to be less weight. Does the overall height change the revolutions of the tire which would cause a gearing issue or does the weight cause this issue? I guess it could be combined.

To me it seems that if your overall weight increases by 3-4lbs per tire over stock then regearing isn't really needed.

For instance a 255/85/16 tire: weight 53lbs Rim width 7in rpm's 625 33.3
265/75/16 tire: weight 51lbs Rim width 7.5 rpm's 652 31.9

Net difference 1.4 and 8lb increase

Seems to me your decreasing your rpm's by the increase in tire height then a increase in weight. So, the rpm's run lower with only a increase in weight of 8lbs. To me this combination would seem to give the advantage of clearance and no real reduction in torque or gas mileage.

However, if you go with a 35 then your total weight of each tire is 64lbs. So, your total weight increase is 52lbs. and rpm's drop to 598. 31.9 stock and 34.8 =2.9 difference. In this case it seems that rpm's decrease more because of the additional weight rather then height.

With my reasoning it seems that with the 33 inch option there would be no real disadvantage. Actually, with the added height, less rpm's and a increase of only 8lbs to me it would seem more advantageous.

So what am I missing?

Anyone?

[Mtbcoach]

I think that your premise is sound and why I run the 255/85/16's instead of anything larger. The weight and change the overall diameter doesn't cause a great deal of loading of the drive train as compared to a 34" or 35" tire.

I have a couple friends who run SS LTB's in 34" and they both said that if they were to do it again, they would have stayed with the 33" tires. They can feel the difference in how the overall diameter impacts the gearing, thus the loading of the drive train.

However, with all that said, I'm presently waiting for the 4.56 Nitro gears from JTS. The MAIN reason I'm doing with these gears is to eliminate the "questionable" early build rear ring and pinion gears (at least, that is what I told my lovely spouse), secondary is the added help the lower gear ratio will give me when attempting challenging obstacles. Since mine isn't a daily driver, I can "afford" to make this change.

So, IMHO, the cumulative effect of increased weight of larger tires (which I think is greater than your reference numbers, at least in my case with SS tires) and the mechanical change in effective gear ratio with a larger diameter tire. My experience says that 33's are about as large as I would want to go before considering re-gearing the drive train...

[breauxtus]

Great thread. I'd love to have Sean K weigh in on this thread!

[SKINUM]

Mtbcoach previously said:

I think that your premise is sound and why I run the 255/85/16's instead of anything larger. The weight and change the overall diameter doesn't cause a great deal of loading of the drive train as compared to a 34" or 35" tire.

I have a couple friends who run SS LTB's in 34" and they both said that if they were to do it again, they would have stayed with the 33" tires. They can feel the difference in how the overall diameter impacts the gearing, thus the loading of the drive train.

However, with all that said, I'm presently waiting for the 4.56 Nitro gears from JTS. The MAIN reason I'm doing with these gears is to eliminate the "questionable" early build rear ring and pinion gears (at least, that is what I told my lovely spouse), secondary is the added help the lower gear ratio will give me when attempting challenging obstacles. Since mine isn't a daily driver, I can "afford" to make this change.

So, IMHO, the cumulative effect of increased weight of larger tires (which I think is greater than your reference numbers, at least in my case with SS tires) and the mechanical change in effective gear ratio with a larger diameter tire. My experience says that 33's are about as large as I would want to go before considering re-gearing the drive train...

I was referencing bfg KM's. Thanks for the response.

[DEWFPO]

SKINUM previously said:

So, does the size of the tire alone warrant regearing? A 33 inch tire comes in different weights. So, for instance if you go with a 33x10.50 in comparison to a 33x12.50 the 10.50 is going to be less weight. Does the overall height change the revolutions of the tire which would cause a gearing issue or does the weight cause this issue? I guess it could be combined.

To me it seems that if your overall weight increases by 3-4lbs per tire over stock then regearing isn't really needed.

For instance a 255/85/16 tire: weight 53lbs Rim width 7in rpm's 625 33.3
265/75/16 tire: weight 51lbs Rim width 7.5 rpm's 652 31.9

Net difference 1.4 and 8lb increase

Seems to me your decreasing your rpm's by the increase in tire height then a increase in weight. So, the rpm's run lower with only a increase in weight of 8lbs. To me this combination would seem to give the advantage of clearance and no real reduction in torque or gas mileage.

However, if you go with a 35 then your total weight of each tire is 64lbs. So, your total weight increase is 52lbs. and rpm's drop to 598. 31.9 stock and 34.8 =2.9 difference. In this case it seems that rpm's decrease more because of the additional weight rather then height.

With my reasoning it seems that with the 33 inch option there would be no real disadvantage. Actually, with the added height, less rpm's and a increase of only 8lbs to me it would seem more advantageous.

So what am I missing?

Good question. IMO, re-gearing really depends on what your needs are and what your tolerance for degraded performance are.

There are indeed several things going on here.

Size : Changing the diameter of the tire changes your effective axle ratios. So a tire that is 10% larger diameter will effectively lower your rear axle ratio by a similar amount, affecting performance to that degree.

Weight : If you go to a heavier tire/wheel combo, the engine has to spin the 4 heavier tires to get you going (with a now effectively lower gear ratio), the brakes have to slow the heavier tires (at a slightly slower rpm now) and the suspension has to manage a higher unsprung weight.

Friction : Many folks go with a more aggressive, wider tire. That also adds friction that the drivetrain had to overcome, not just during acceleration, but during cruising as well, this can sometimes really cut down on mpg.

So all of these factors work against the drive train and suspension.

Some folks go to a taller tire but go narrower to try to keep the weight and contact patch similar. This still lowers your RPMs at a given MPH but reduces the acceleration, braking, and suspension effects of the larger tires, as well if the contact patches are similar in size and pattern, the effects of any added friction is minimized as well.

Another option is to go with a lighter wheel to make up some of the weight loss from the heavier tires.

The stockers are ~31.6 inches tall, going to a 33 inch tire is a change of only 4.4%. You probably wouldn't feel much difference unless you went with a wider tire and added more weight.

Going to 35's, you'd feel the difference, and it would be up to you whether the degradation in performance (acceleration, mpg, braking, ride) would warrant the cost of the re-gear. But, re-gearing wouldn't help the braking or ride changes caused by the larger, heavier tires.

Every person has a different tolerance for this sort of stuff. Some folks will put 35 inch, MT's on and say they don't feel any difference. You might.

I hope all my jibberish makes some sense.

DEWFPO

[ringpinion.biz]

Many people are ok with running 33's with stock gears. As you say, its not that much of a difference. The thing is, once a bunch of weight is added (sliders, bumpers, winch, etc) on top of the slightly oversized and heavier tires, it can effect the performance to the point that many consider doing something about it. Now, you could go 4.10 from the 3.73, but it is ridiculously expensive as it requires oem gears, and a new carrier, etc. The gain is very minimal to go to 4.10 and I dont think justifies the cost.

We now have developed and have in stock 4.56 Thick gear that will fit on the stock 3.73 carrier. This allows useage of the highest quality materials available in an aftermarket gearset and at a great price. 4.88 and 33's may be on the low side for some people. But others prefer it.

DEWFPO previously said:

With all due respect to your experience ringpinion.biz. The stock tires are 31.6" in diameter. I can't see how going to a 33" tire would make going from the stock 3.73's to 4.88's a normal event.....? The tires increase in size by only 4.4%, the gear ratio would increase by 30.8%. If you're just trying to correct for larger tires, that just doest't make any sense to me, at all.

DEWFPO