[jmasin]

holy cow it's still going!

[robncar]

Originally Posted by jmasin

holy cow it's still going!

Yep, looks like it is...

[Vandano]

Originally Posted by Junky burp

Okay. (Someone check this)

Scenario one is a 4000 lb. Jeep with 28" diameter tires pulling a 2500# trailer GVW=6500lb.
Torque=14(tire radius) x 6,500lb. this is 91,000in.lb.F

As stated before, the force must be cancelled out by the rotor in order to stop.

Let's say the rotor radius is 5". (10" dia. rotor)
The ratio of the two levers (14" and 5") is 14:5 or 2.8:1.
The tire has an advantage of 2.8 times over the rotor.
so...91,000 x 2.8 = 254,800in.lb.F

(If we divide that figure by 12, we get ft.lb.F....so...254,800 divided by 12=21,233ft.lb.F)
That'll tighten your lugnuts....

Scenario two is the same 4000 lb. Jeep with 35" diameter tires all by itself ( I'm going to add 250 lb. for tire mass from an earlier statement)

Torque=17.5 (tire radius) x 4250lb. this is 74,375in.lb.F

It's the same rotor and brakes so the drag coefficient values are not important.
Nor does the "real world" rotor radius. Only that they are the same in both cases.

so...we go to the lever ratios (17.5" and 5") or 3.5:1
This tire has an advantage of 3.5 times over the rotor.
so...74,375 x 3.5 = 260,225in.lb.F

254,800 vs. 260,225

So, is that to say stopping a Jeep with 35" tires is comparable to a Jeep with 28" tires with an added load of 2500 pounds?

Assuming you take into account none of the other variables associated with that scenario... yes.

You forget to account for added weight to the front wheels of the vehicle, decreased weight to the rear with the 35's. The fact that the weight distribution changes when you have a trailer as the loaded tongue weight keeps weight on the rear.

Your calculations are also assuming brakes stop a car instantly not progressively over time. It does not take into account heat build up and brake fade if the test is done more then once.

Math can prove a lot of things but it can also prove nothing.

[jmasin]

This thread is like a jeep with 35's and stock brakes, it just won't stop!

ba-dum bum!

Couldn't resist!

PS. that's a joke, I'm not making statement on the topic

[LuckRider]

Originally Posted by Vandano

Assuming you take into account none of the other variables associated with that scenario... yes.

You forget to account for added weight to the front wheels of the vehicle, decreased weight to the rear with the 35's. The fact that the weight distribution changes when you have a trailer as the loaded tongue weight keeps weight on the rear.

Your calculations are also assuming brakes stop a car instantly not progressively over time. It does not take into account heat build up and brake fade if the test is done more then once.

Math can prove a lot of things but it can also prove nothing.

When I first saw the math, I read for a second, and then remembered the braking bias. What you said is exactly what I thought of, with more weight at the rear the brakes would change the bias. A properly loaded trailer puts typically 60-75% of the weight in front of the trailers wheels to keep the trailer from gaining an advantage on the rear end. That means that my 2300lb trailer would have about 1700lbs in front of its axle (yes I load my trailer properly, and the trailers axles were placed in this proper balanced position) leading to a tongue weight of about 400lbs (yes, I know a little above the Jeeps capacity, I know I was over the recommended weight, but it had to be done). 400 lbs is 10% of the vehicle weight. That means the braking bias should now shift about 10% towards the rear?!?!? At least that is what I believe it is mrblaine, a confirmation on this would be helpful. And even if my math isn't fully right, my original post mentioning the trailer was to show a slightly exaggerated situation.

[Junky burp]

Originally Posted by robncar

Guess I didn't realize that one tire (two levers) performs all the braking? I thought there were four tires (eight levers)?

Ob.. Ob.. Ob.. I was thinking 4 levers supplying the force, 4 supplying resistance.

[Junky burp]

Originally Posted by Vandano

Math can prove a lot of things but it can also prove nothing.

So.. is that why my arms will get ripped off?

[RakHard-187]

ive been runnung 35's on my 05 LJ. I PERSONALY have not had any issues whatsover with brakeing. they lock up and stop when needed. I was communting every weekend between atlanta and nashville and was fine. Worked great off road too.....good luck

[mrblaine]

Originally Posted by RakHard-187

ive been runnung 35's on my 05 LJ. I PERSONALY have not had any issues whatsover with brakeing. they lock up and stop when needed. I was communting every weekend between atlanta and nashville and was fine. Worked great off road too.....good luck

To give you and everyone else the other side of the coin, I worked on an 05 LJ, built an awesome set of prototype 13" rotor brakes for it and still couldn't get them to lock up.

I went through the whole rig and replaced every single component of the braking system including going over the kit I built and the brakes were still only pretty good and not awesome.

Before the work I did, the rig was pretty scary to drive.

[cyberiv]

Well my brakes passed the 35" tire test last night! a truck dropped a load of cones in the lane and the car in front of me slammed on the brakes (i would have just driven over the cones!). Slam on the brakes, they lock up, i stop a good 18 inches away from the car in front of me. I was actually quite impressed that i had that much room to spare. Let me caveat this by saying they aren't completely stock brakes, i have ebc yellow stuff pads in front with stainless brake lines. And they just paid for themselves by saving me the cost of a new trunk on a lexus. all in all, im very happy with my braking performance!

[Unlimited04]

Originally Posted by RakHard-187

ive been runnung 35's on my 05 LJ. I PERSONALY have not had any issues whatsover with brakeing. they lock up and stop when needed. I was communting every weekend between atlanta and nashville and was fine. Worked great off road too.....good luck

I'm running 31s on stock brakes with EBC/Centric's and I think its tolerable...not great. I noticed the difference between 30s and 31s, I don't wanna find out how scary 35s is going to be.

[justanotherjpr]

Originally Posted by jmasin

This thread is like a jeep with 35's and stock brakes, it just won't stop!

ba-dum bum!

Couldn't resist!

PS. that's a joke, I'm not making statement on the topic

HAHA AMAZING!!