Big brake kit for 08 F250/350 - Page 3 - Diesel Forum - TheDieselStop.com
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post #31 of 42 (permalink) Old 03-19-2012, 12:54 PM
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Originally Posted by FMTRVT View Post
Here's the calc's. So the Wildwood calipers need to be using a higher COF friction materiel, a larger swept radius, or a combination of both.
WOW, you took me back to college..

I am not sure what the figures are for the WILWOODS, i do know that my wifes brother who is burning up my fuel so that I can ship it said that the truck brakes felt spongy. I am going to do the pads, lines and rotors first to see if that helps. If not then I am forced to move to this setup. I am guessing the 22" rims and 40" tires are making it hard to stop the truck.
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post #32 of 42 (permalink) Old 03-19-2012, 02:53 PM
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Changed the graph adding titles.

Going from the stock size to 40" tires puts a way, way larger amount of leverage against the brakes.

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post #33 of 42 (permalink) Old 03-19-2012, 03:12 PM
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Changing tire size puts the brake leverage at a greater disadvantage.

Jack
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post #34 of 42 (permalink) Old 03-19-2012, 04:18 PM
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Jack,

Bottom line is what exactly?

Stock F350 system is really that good ?

I, as most plan on lifting the truck. Really want to do it properly ( stopping included ) and I do tow.

What would you suggest.

I am going 6" lift and 37" Toyo Mt all on 22" wheels.

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post #35 of 42 (permalink) Old 03-19-2012, 05:09 PM
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Jack's correct: the larger tire has a huge effect on the required brake torque.

The data's a bit off on comparing them however. (no offense meant just giving it correctly)

Wilwood front have 1.88/1.62/1.62 bores. Netting about 6.9sq". Combine that with the 16" rotor, factor equal pad Mu and you have about 7% less rotor torque still. Say what? Correct, but to achieve the same final value you'd need only add 5lbs of leg effort to recover that.

The flip side is that you also shift the bias back about 2% making the rear brakes work a bit harder for the same given leg effort. Not a bad thing at all.

Now...combine front and rear big kits and you actually pick up about a 1% total torque gain. Sure, that's not huge. But it doesn't need to be. The issue for most truck owners is not about more torque or shorter distances- most are "tire limited" as was already discussed- it's about repeated stopping and durability. Stopping as well on that twisty hill road five miles in as you were two miles in.

Here more rotor mass, a better rotor design, lower operating temps and tactical feedback trump most factory systems all day long. That's the true benefit. You want to stop quicker; run a shorter tire and a very sticky compound.
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post #36 of 42 (permalink) Old 03-19-2012, 09:11 PM
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Sorry Todd, I thought I had read in another forum you were using the mid sized pistons, hence what I used in the clamp calc.

Glad you stated bring up the rest of the data, I was trying to stay out of that area.

Not sure you want to push that rear bias too much though. There was a lot of debate about right where it is stock. Pickups with light rear axles don't like rear braking in wet turns. Unless you've got the stability option, which pickups should have had long ago. Still trying to figure out how -7% = 2%.

To the rest of you guys, going to larger then stock tires are a big deal with braking. Even the change within the stock 18" to 20" tires was enough to have some people feel very, very uncomfortable.

Mongus,

The stock setup was designed for the weight mass, it's the leverage that gets problematic. The same amount of thermal energy is being dissipated (rotor heat load). To keep the stock rotors and calipers and maintain the same pedal effort (other then a big rotor kit) you need to up the friction level. As CaryT stated earlier in this thread, you best stock choice of pads would be to go with the Hawk LTS front and rear. They are a high met compound of ancient times, but the friction coefficient is higher and like all decent high metallics, they get way more aggressive under high temperature conditions.

You brought up towing, so I'll do my standard soapbox that truck brakes are designed around the capacity of the truck, not an unknown weight of a trailer. If you don't want to go overcapacity on the truck brakes everyone needs to make sure the trailer brakes are designed and working correctly to do their share. It's always amazing to me how many trailers out there are do doing their share.

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post #37 of 42 (permalink) Old 03-20-2012, 03:03 AM
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Originally Posted by FMTRVT View Post
As CaryT stated earlier in this thread, you best stock choice of pads would be to go with the Hawk LTS front and rear. They are a high met compound of ancient times, but the friction coefficient is higher and like all decent high metallics, they get way more aggressive under high temperature conditions.
What is the difference between the Hawk LTS and the Hawk SuperDuty Brake Pads?
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post #38 of 42 (permalink) Old 03-20-2012, 09:43 AM
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It depends on how you use your truck.

Every friction material has a temperature/friction bell curve. On the OE design side engineering want a relatively stable friction level from cool brakes all the way up to at least 1200°F. That’s why you generally see a low-met or Ceramic (Potassium Titanate fiber) friction material off the production line today rather then the organic or semi-metallic pads of the past. Historically the organics were on vehicles under 5000lbs GVW and semi-met on everything above.

True organics tend to not to have a true bell curve, being relatively flat until around 700-800°F then start to lie down (hot fade). Semi-mets do have a bell curve, with low dynamic friction at the cool temperatures (<150°F) and a sweet spot in the >150°F to 1000-1200°F range if they are compounded well. After that they can have some hot fade as well. You can have a poor compound that fades just like an organic at the lower temps.

When we get into the higher metallic or “performance” materials the bell curve can be even steeper or the sweet spot of the friction is at a higher temperature range. And the sweet spot is where the friction material switches from abrasive friction to cohesive friction where a consistent but thin friction material transfer is applied on the rotors. This provides the high friction level.

The Hawk LTS starts off with a cold friction level lower then the OE pads, crosses over at a higher friction where the edge code testing is for the “cold” rating, then continues higher until I’m going to guess the 1300-1500°F range before you start to see some fade. The Superduty pad compound moves the curve farther out by temperature, so you need to get more heat into the rotors and friction before you develop the higher friction level sweet spot. And the downside of that is at cooler temps you working on the lower level of abrasive friction, with the potential for more dust and noise. It’s all about how you operate you truck. If you carry a fair amount of weight all the time, operate with a higher count of stops per mile (keeping temps up), or count on you truck to offset poor trailer brakes, the Superduty can be an acceptable choice. UPS and FedEx are good candidates for a Superduty type friction material. Commuting to work or substituting your truck where an Accord would work just as well, not so much. You’re better off with the LTS if you’re running big tires and not working the truck hard.

I could go on about how the OE pads are actually better for people then the LTS with 17-18" tires, but this thread is about the Wildwood bling and talking about Hawk pads is already going over the edge.

Jack
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post #39 of 42 (permalink) Old 04-06-2012, 02:27 PM
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Hawk pads will help
Which hawk pads would be best for an f-350? Dont do an awful lot of heavy towing, a truck here and there during the summer, but thats about it to be honest.

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post #40 of 42 (permalink) Old 04-06-2012, 02:30 PM
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Wow.... nevermind, should have read the rest of the posts before i commented, ignore my last post please

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post #41 of 42 (permalink) Old 04-16-2012, 08:05 PM
 
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Todd!! Long time no chat! Great to see you on these boards, Sir.

I'm a little late to this thread, but I'd like to add a couple of points. There are about 5 things that make up and define a brake. Swept Area per Ton, Torque Arm, Rotor Mass, Coefficient of Friction and Hydro-mechanical Functions. The later was covered in depth with your calculations...nicely done, Jack. But some might not know the correlation of the first items in my list.

Swept Area per Ton - This is the surface area of the rotor that actually touches the pad, times both sides, times all 4 rotors. This surface area is then divided into the weight of the vehicle. If you take an F-250 4x2 Regular Cab Long Bed and do a 60-0 stop, it might take 180' (estimating. ABS, road conditions and adhesion are assumed). If you put a pallet of concrete blocks in the bed, it'll take 260' or more to do the same thing. Conversely, you take the same brakes and put them on you Ranger and it will suck the eyeballs out of your head and stop in about 100'.

The next part is Torque Arm - This is the distance from the center of the pad to the center of the axle. The longer the torque arm, the more negative torque the brake can develop. So, you take a 13" rotor with a fat pad that reaches all the way from the OD of the rotor to the inside radius of the hat...and a 15" rotor that has these little skinny pads. Same swept area, but the bigger rotor will make a lot more negative torque than the smaller rotor. The same principle occurs in reverse with regard to tire height. The bigger the tire, the less torque the brakes can apply to the road surface because of reduced leverage. Rule of Thumb - Every inch of tire you go up, you loose almost 10% of the braking power. This principle is lost on our urban youth that feels the need to put 24" solid aluminum wheels on their 99 Ford Crown Vic Police cars. Sometimes I just have to shake my head.

The next part is Rotor Mass - The brakes turn kinetic energy into heat energy. The only job the rotor has is to get hot and dissipate that heat. The bigger the rotor, the heavier the rotor, the more mass, the better it can absorb that heat and dissipate it back to the atmosphere. There are aberrations to this with respect to sprung and unsprung weight, but for most stock style vehicles, the principle still applies.

Pad material and coefficient of friction has been outlined above. But the best way to understand the bell curve for high temp pads is this. Say you've been driving down the interstate for 20 min at speed, and you need to slow down for an exit. You reach over and put your foot on the pedal and start a slow deceleration. If you've got an organic type of compound for light duty, the truck will slow down in a linear fashion given the same force on the pedal. If you've got the higher temp pads on, the truck will start to slow, then about 4-seconds in, it will be like you throw the anchor out. As the temps come up, coefficient of friction comes up and the truck will slow more dramatically without moving your foot on the pedal. Personally, I like the ceramic pad compounds that have come out lately. Ceramic compounds are what comes OE on most of the newer vehicles. It gives you a linear CF through the transitional brake temps. If you get them too hot, they will fade, but they stay good for quite a while.

Which brings me to my last point. Todd and I have had many conversations about this over the years, and I respect him greatly, but my point has to do with cross-drilling. Todd's Kits aside, CROSS DRILLING ROTORS IS THE BEST WAY TO SCREW UP A BRAKE SYSTEM. Given the points I outline above, when you cross drill a rotor, you're reducing the swept area of the rotor. If it's not touching the pad, it's not part of the swept area. So if you punch 100 holes in the rotor surface, you've just reduced the swept area by the diameter (Pi*R^2) of the holes and the hole count. This adds up quick. You also reduce the mass of the rotor. The cuttings that end up on the floor used to be part of the rotor and the mass. You have just reduced the mass of the rotor by the cuttings, so now the rotor has to get that much hotter to do EXACTLY the same job. Yeah, it cools quicker, but now you're heat cycles become more dramatic leading to thermal stress and cracks. The holes also concentrate the heat load and give the rotor a place to crack.

Todd's kits are all designed and engineered with this in mind. So too are the Porsche GT3's that have 15" rotors that look like Swiss cheese. If you engineer it that way, it works great. But when the kids order cross-drilled rotors for the Honda Civic and think it's gonna stop quicker, you just have to laugh.

Doug Lewis

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post #42 of 42 (permalink) Old 04-17-2012, 08:49 AM
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Hi Doug, hope you're doing well.

I pretty much gave upon the drilled vs non-drilled rotor thing some time ago. With so many ideas, opinions, references etc I've come to learn its best to just let the custom select what he/she wants. Unless it's a dedicated track application...in which case the buyer should know better anyhow.

And in the case above I'd say the overall mass increase is large enough to support the option without too much of a gamble. When used within reason I don't have a problem with the drilling, like you; I just think folks should make a smart decision.
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