Critique my brake build

danford.lau said:
Would love to try your brakes over the rubicon weekend .

No problem, you’re more than welcome to try them. I piecemealed the kit and saved some money and used the best Wagner ceramic pads from AutoZone with a lifetime warranty. I’m super happy and stops better from 60 to zero than my neighbors 300zx after I installed a big brake kit in his car.




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Thought I'd report back. Just got my Jeep back yesterday. Brakes are Mopar big brake kit front (calipers/pads/brackets/rotors + master cylinder and booster), Dynatrac rear (pads/brackets/rotors).

This is an "Oh My God!" improvement. Easy to activate the antilocks now (and I've also gone from 33's to 35's), and the braking in general feels effortless. A huge amount of coin but also a huge amount of improvement. I'm really pleased.
 
FenderBender said:
I really wish we knew the pad compound used in all the available kits. We'd be able to do a much better on-paper comparison them all. Figuring out the braking mechanics (at least as far as clamping area and rotor diameter) isn't difficult.

Based on piston size, piston count, and rotor diameter we can compare them as if they had the same pad compound and hydraulic pressure.

The normal force, F, applied by the caliper will the piston area multiplied by the hydraulic pressure: F = A*P

The torque, call it tau, applied to the rotor is proportional to (not equal to because we don't know coefficient of friction of the pad) the caliper normal force multiplied by the distance from the center of rotation to the center of the piston (call it r): tau = F*r

Keep in mind that the distance from the center of the rotor to the center of the brake piston is not the diameter of the rotor. It's the radius of the rotor minus (roughly) the radius of the piston cylinder. The stock pistons are 66 mm in diameter (1.3 inch radius). The radius of the stock rotor is 5.95 inches; Dynatrac is 6.75 inches. The relative torque would be (6.75"-1.3")/(11.9"-1.3") = 1.17 or a 17% increase in stopping torque from the larger rotor. The rest of the gains come from the pad material.

I made a spreadsheet some time ago when I was deciding on my brakes. The spreadsheet did the above calculations and compared to the stock arrangement for many aftermarket kits. I found that the Dynatrac didn't fare well at all in the comparisons, even bearing in mind that Dynatrac also upgraded the rear brakes (KEEP IN MIND THAT THIS DOESN'T INCLUDE PAD MATERIAL). This is probably similar to what the OP and his friend did. The Teraflex kit had the best numbers of anything below $1500, while the Dynatrac kit had the worst numbers of anything over $1000.

To put numbers on it, I found that the Teraflex kit had a total mechanical advantage (torque and normal force combined) that was 70% greater than stock (assuming same pad material and fluid pressure). Consider that in a 60/40 front/rear braking scheme, that comes to about 40% increase for the total system just by upgrading the front brakes.
The Mopar kit (and the Crown/RT kit) ended up with about 55% increase in the front stopping torque, or 33% for the total system.
The Dynatrac kit ended up in the ballpark of 20% improvement for the total system.
The SSBC Tri-Power Caliper-only kit had about 20% improvement for the total system just by changing the front calipers (the exact opposite philosophy from Dynatrac but the same mechanical increase and can fit in smaller wheels).

The pad material and the pedal stroke required to get the same fluid pressure are the elephants in the room, obviously. A pad made with unobtainium is how Dynatrac gets such a good product using relatively modest geometry changes. More piston area means squishier pedal if you keep the same booster/master cylinder, which is a strike against the Teraflex and similar kits.

Mostly because of their reputation and cost, I couldn't bring myself to buy Terror-flex kit. However I also couldn't convince myself that Dynatrac was the best bang for the buck if so much of the performance comes from proprietary pads.

Obviously this is all on paper and I only write this up to show a quantitative approach to some of the options. Seemingly everyone who has the Dynatrac kit has been happy with it, so it's clearly great. I only offer this a way to compare what we do know about the specifications of each system.
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As an engineer, i applaud your theoretical approach and love the quantitative calculations. This is a very good start at a "back of the envelope" approximation, but when considering manufacturing tolerances and real world conditions, it's good practice to rely on experience as well.

I have been wondering about this topic when comparing brakes on the dynatrac PR60/60 axles vs. the Currie D60 crate axles. The brake rotors are the same diameter on both setups and both use dual piston calipers, but Currie strongly recommends a master cylinder upgrade whereas Dynatrac does not. Some on this forum have said the master cylinder upgrade is not needed for the PR60/60 axles, even when running 37s, but i dont understand how that make sense. On both axles the dual piston calipers would presumably require more hydraulic fluid than the OEM setup, so wouldnt the brake pedal have a longer stroke if the master cylinder was not upgraded? Wouldnt the longer stroke also mean slower response time for stopping, even if the dynatrac pads had a better friction coefficient?


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Noble Woodsman said:
As an engineer, i applaud your theoretical approach and love the quantitative calculations. This is a very good start at a "back of the envelope" approximation, but when considering manufacturing tolerances and real world conditions, it's good practice to rely on experience as well.

I have been wondering about this topic when comparing brakes on the dynatrac PR60/60 axles vs. the Currie D60 crate axles. The brake rotors are the same diameter on both setups and both use dual piston calipers, but Currie strongly recommends a master cylinder upgrade whereas Dynatrac does not. Some on this forum have said the master cylinder upgrade is not needed for the PR60/60 axles, even when running 37s, but i dont understand how that make sense. On both axles the dual piston calipers would presumably require more hydraulic fluid than the OEM setup, so wouldnt the brake pedal have a longer stroke if the master cylinder was not upgraded? Wouldnt the longer stroke also mean slower response time for stopping, even if the dynatrac pads had a better friction coefficient?


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When you say Currie recommends this and Dynatrac recommends that, what are you basing that on? Marketing literature? Have you called them and discussed it?



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Noble Woodsman said:
As an engineer, i applaud your theoretical approach and love the quantitative calculations. This is a very good start at a "back of the envelope" approximation, but when considering manufacturing tolerances and real world conditions, it's good practice to rely on experience as well.

I have been wondering about this topic when comparing brakes on the dynatrac PR60/60 axles vs. the Currie D60 crate axles. The brake rotors are the same diameter on both setups and both use dual piston calipers, but Currie strongly recommends a master cylinder upgrade whereas Dynatrac does not. Some on this forum have said the master cylinder upgrade is not needed for the PR60/60 axles, even when running 37s, but i dont understand how that make sense. On both axles the dual piston calipers would presumably require more hydraulic fluid than the OEM setup, so wouldnt the brake pedal have a longer stroke if the master cylinder was not upgraded? Wouldnt the longer stroke also mean slower response time for stopping, even if the dynatrac pads had a better friction coefficient?


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My master cylinder isn’t upgraded and I can stop my 40’s on a dime with Dynatrac 60/80. The brakes are noisy as hell but they can stop.


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fiend said:
When you say Currie recommends this and Dynatrac recommends that, what are you basing that on? Marketing literature? Have you called them and discussed it?



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Basing this on their website (currie screenshot for Extreme 60 front axle is below). Havent had a chance to call them yet; planning to this week.

IMG_4721.JPG


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Since I’m not an engineer, but only a backyard/my own garage wrench turner, I’d like to mention that the Dynatrac kit uses the OEM calipers. No need to change booster or master cylinder to see major improvements.

My butt dyno says the ProGrips are well worth the money in the short time I’ve had them. I actually enjoy braking now and I’m just on 315/70R17’s.
 
Progrips really are a good set of brakes. Saved my ass many times and even just last week, I was an inch from hitting someone. Dude went from 30 to 0 in about 5 feet. Brakes saved my ass and his. I'm not an engineer though.
 
I think we are talking about different things. Yes, the Progrip kit uses the stock calipers, but the PR60/60 hard core axle set includes new dual piston calipers (screenshot below). Their website does not mention needing to upgrade the master cylinder tho, and i have not heard of anyone needing to. I will call dynatrac this week and see what they say.

IMG_4722.JPG


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Talked to Steve at Dynatrac today. Dynatrac does not recommend a master cylinder upgrade for their Hardcore PR60/60 axle set, as they have engineered it work with the OEM master cylinder, however, if customers prefer to upgrade the master cylinder, they recommend Mopar P/N 5160050AB. Steve did say that upgrading the master cylinder would be a good idea for running 40s, but not necessary for up to 37s. For the Hardcore Plus XD60/XD60 package, however, Dynatrac does recommend a master cylinder upgrade.

The Hardcore PR60/60 Package uses 1997 F350 dual piston calipers for the front axle (piston dia. = 55.9 mm), and 2010 Ram 1500 single piston calipers for the rear axle (piston dia. = 53.3 mm). This represents a 35% greater total piston area vs. a stock 2015 JK.

The Hardcore Plus XD60/XD60 Package uses 2014 Ram 1500 dual piston calipers for the front axle (piston dia. 53.3 mm), and 2010 Ram 1500 single piston calipers for the rear axle. This represents a 27% greater total piston area vs. a stock 2015 JK.

Assuming equal piston stroke lengths, this suggests the brake pedal travel should be slightly longer vs. stock for both setups (by about 27- 35%) with the OEM master cylinder, but it also suggests that Dynatrac's recommendations for when to upgrade the master cylinder are more based on stopping torque instead of brake pedal travel.
 
Final update: Just completed a 3600 mile road trip to Moab. Brakes are fantastic. I was able to easily stop on downhill fins (Hells Revenge, Fins and Things) that I could not stop on in 2015 (before the upgrade). Likely multiple paths to better braking--I am happy with the path I chose.
 
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