Rotating Mass: You've Probably Been Misinformed - Page 6 - JeepForum.com

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post #76 of 81 Old 08-21-2013, 01:46 PM Thread Starter
mschi772
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Quote:
Originally Posted by mike_dippert
You could always glue weights to the inside of the tire. Keeping the wheel balanced would be tricky though.
I actually thought of that one last night. Yeah, the balancing issue probably makes that method more work than it's worth, but maybe it's doable.


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post #77 of 81 Old 08-21-2013, 09:10 PM
SLADE
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A stock tire (235, 245, 30x9.50) will weigh about 35lbs- 40lbs.

A 33x13.50R15 Toyo Open Country MT weighs 75lbs.

Just the tire alone is 30lb to 35lb heavier than stock. Add that to a steel wheel that's 10lbs heavier and your adding 45lbs per tire/wheel.

Using your 2:1 ratio, that's equivalent to adding 340lb (385lbs if you include the spare) to an under powered and under geared Jeep that has the aerodynamics of a brick.

That's nearly 400lbs of additional weight and you haven't even started adding a front bumper, Winch, rear bumper/tire carrier, body armor, skid plate or any gear.


A BFG KM2 33x12.50R15 weighs 59lbs.

Using the KM2 with an aluminum wheel will only weigh 19lbs - 24lbs more than the stock wheel/tire.

Using your 2:1 ratio, The BFG KM2/aluminum wheel set is equivalent to adding 152lbs (171lbs) instead of 340lb (385lbs ). (I Hate KM2's, but they are a lighter tire and the weights are listed)

That's a weight savings of 188lbs - 214lbs.... Take the weight into consideration when buying the rest of the bumpers, armor, and parts and you could easily see a difference of 500+ pounds. That seems worth considering to me especially when you can reduce that much weight with just the tires/wheels.


You can base your opinion on hypothetical worlds where real world numbers and real world variables aren't included if you wish, but there is much more to consider.

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post #78 of 81 Old 08-22-2013, 07:43 AM
mike_dippert
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Slade, those Toyo's are a good 15-20% heavier than your average 33x12.5 (maybe b/c it's a 13.5), and the KM2 is the lightest MT out there (Duratrac is NOT an MT, nobody mention it). Any good generalization removes the high and low extremes, instead you focus on them.
Make a list of the readily available MT's. Take out the lightest and heaviest 10%. Now compare what's left. You'll have a standard deviation of 5% or less, which is 3-4lbs.
Do you notice a difference in performance before & after you fill up? 15 gallons of gas weighs around 120lbs. That's 3-15lbs worth of tire, depending on the ratio you believe in. But that same 120lbs is only 3% of the total weight of a 4000+lbs Jeep.

Personally, I noticed a big difference going from 33x12.5 Baja Claws on steelies (60+28) to KM2's on Al wheels (49+20). It was a bigger difference than having a passenger with me. I'd estimate about 300lbs of cargo, which puts me in the ballpark of 4:1.
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post #79 of 81 Old 08-22-2013, 08:19 AM
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Quote:
Originally Posted by mike_dippert View Post
Do you notice a difference in performance before & after you fill up?
I definitely notice a difference offroad between a full tank and say a half a tank, in particular climbing. That is weight way back in the back and weight that can shift around. I usually try to start a day on the trails with how much gas I think I'll need for the day plus a little cushion. No need to haul the extra weight around.

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post #80 of 81 Old 08-22-2013, 09:38 AM
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I meant on the street. Acceleration to 30+. .. I definitely notice an extra 100lbs of sprung weight off road. After filling up on the street, not so much. I have the 42rle with too high gearing though so it wastes a lot of HP anyway. Maybe it's more obvious with a manual.
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post #81 of 81 Old 08-22-2013, 06:32 PM
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Quote:
Originally Posted by mike_dippert View Post
Slade, those Toyo's are a good 15-20% heavier than your average 33x12.5 (maybe b/c it's a 13.5), and the KM2 is the lightest MT out there (Duratrac is NOT an MT, nobody mention it). Any good generalization removes the high and low extremes, instead you focus on them.

Do you notice a difference in performance before & after you fill up? 15 gallons of gas weighs around 120lbs. That's 3-15lbs worth of tire, depending on the ratio you believe in. But that same 120lbs is only 3% of the total weight of a 4000+lbs Jeep.

Personally, I noticed a big difference going from 33x12.5 Baja Claws on steelies (60+28) to KM2's on Al wheels (49+20). It was a bigger difference than having a passenger with me. I'd estimate about 300lbs of cargo, which puts me in the ballpark of 4:1.

Yes, that comparison is on the high side of average. 33's are on the low side of the tire sizes. The extremes will get even larger as the tire sizes increase.

I only wanted it to show what an outcome could look like if a tire/wheel choice is made with total disregard for weight (like mschi772 recommends) and to point out that those extremes are out there. I also wanted to point out that not considering weight throughout a complete build can have a HUGE impact and saving a little here and a little there can make an extreme difference in handling, response, and overall performance of a Jeep.

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