Toyota Truck Calipers, Ventilated Brake Rotors, MM rear Disc Brakes

[tamo3]

Thank you for the great data. I wonder how can you adjust brake balance like this?

I don't know whether there is a digital adjustable proportioning valve to measure the balance.

[Leon]

I think this is the type of curiosity and thinking that we welcome at HybridZ.

 

Looks good to me, at a glance. I would call those "torques" and not "moments", but that's nitpicking. Luckily, designing brakes isn't as complex as engines or suspensions.

 

To dial in the balance mathematically, you need to now the friction force between the tires and road, vehicle weight, wheelbase, CG height and CG longitudinal placement. With that said, our car is already designed so jumping in and finding optimal balance empirically makes more sense, especially given the lack of info on CG locations and tire data. Brake force needed can then be back-calculated to see how much pedal force is needed, knowing tire, rotor, and piston sizes, and pedal lever ratio.

 

The Brake Handbook by Fred Puhn is cheap and a good read, if you're interested.

Edited June 26, 2013 by Leon

[Sideways]

Well this brings up a rather tricky question.  Whats a good "ball park" front/rear bias to be aiming for on a z car?  I know this is a pretty loaded question,  but just something in the neighborhood would be interesting to know.  I can gather that 70/30 is less than ideal considering everyone complains that set up doesnt have nearly enough rear bias.  So hows 60/40? 50/50? Etc.  Any "ball park" figures to aim at?

[duragg]

I wasn't good at math so I put aggressive race pads rear and mild race pads front and my Wilwood BPV is dialed about 50% out.

Pull e-brake and rears lock up easy.

S12w front / ZX rear

[Nigel]

I haven’t found a way to calculate brake torque for drum brakes. Apparently they have a non-linear curve in relation to hydraulic pressure. So calculating the stock bias of an S30 isn't easy. Regardless, there is no one magic ratio though because there is so much variability between our cars. However, a 280ZX has a 63.5/36.5 split. Assuming an S30 has roughly a similar CG, that’s a starting point. Just from anecdotal evidence, around 70% front bias appears to be borderline. I’d avoid anything beyond 70% front bias.

 

There are on-line brake force calculators, or you can create a spreadsheet, so you don’t have to calculate everything out by hand. You just have to make sure you understand the parameters you’re entering.

 

Seatlejester, I’m curious where you got your brake rotor diameters for your SX and 280ZX rear brake calculations? The data I have shows the Z31 rear rotors used with the SX swap are 290mm, and I wasn’t aware of a ZX swap that uses anything other than ZX rear rotors, which are 258mm for ’82 rotors. Earlier ZX rotors 269mm.

 

Nigel

[seattlejester]

The drum brakes were indeed giving me a headache, I would have enjoyed having a brake bias ratio available of the stock setup to compare but given I think the calculation of drum brake bias is fa beyond me.

 

I've been doing some reading and that seems to be the money point 60-70/40-30 for a FR layout, you want your braking force to never outweigh the weight transfer or you experience lockup. If the car is balanced 50/50, one would think that 50/50 bias would be a good idea, but as you brake the weight is lifted off the rear making the rear brake bias too high and prematurely locking the rear (granted the rear shouldn't lock since they are being driven by the engine, rear lock=stall). So at 50/50 it seems that the increased rear bias is wasted, and from anecdotal evidence as Nigel points out, it seems going much above 70/30 seems to have the opposite effect. This is of course without the use of the proportioning valve, I would imagine having a 60/40 and dialing the rears out until the car brakes evenly in a straight line would be preferred, but once again all from reading technical articles that may have been over my head.

 

For the rear brake rotor I used the rotor that is on my car, an early 300zx rotor turned down 285mm so shaved 5mm or so. The kit was sold by a gentleman on craigslist I believe he turned them down so that his kit allowed the use of 14's, or so that he would be the only supplier of the rotor (ingenious), but I doubt many users are using the same kit. I did not have the rotor size that most people use at hand so I just did the math with what I had. 

 

But with the numbers you provide I can redo the math and make a more accurate generalized approximation. 

So with the 240sx kit most people are using the stock early 300zx rotor at 290mm,

with the 280zx kit, most people are running stock later 280zx rotor at 258mm?

[Leon]

Regardless, there is no one magic ratio though because there is so much variability between our cars.

 

Not only that, but optimal brake ratio changes depending on grip. You want more rear bias in rain and less in the dry, due to weight transfer effects.

 

I've attached a chart I have from a braking spreadsheet I did back in my vehicle dynamics class (don't look at the discontinuities at the tips ). The model is a generic "street sedan" weighing 3220lb, with a 55/45 weight distribution and 3ft high CG. It shows three conditions: wet, low grip, and high grip. In the wet, optimal brake force distribution is 60/40. If your brake force dist wanders to the left of the vertex, your rears lock up first (too much rear brake force). The opposite is true when going to the right of the vertex. This applies to all 3 braking conditions.

 

For a "set-it and forget-it" setup, you need a bias that never locks the rears first. This means setting your bias to the highest grip condition. The con is that your braking distances will be further increased when using this bias on a lower grip surface. For example, you set bias to 86/14 for the high-grip condition. Then it rains. You now have 70% of optimal maximum deceleration on that surface with your set-and-forget bias.

 

Again, these are numbers using a made-up car and approximate mu values for grip conditions. It's simply an example that illustrates what's going on.

 

Braking Chart.pdf

[Leon]

Another thing to note from that chart, is that the higher your grip conditions the more sensitive brake bias becomes with regard to maximum deceleration.

[seattlejester]

So I just put all the values in a spread sheet. Hopefully it pops up.

 

Prepost Edit:

Looks like it doesn't like the format

 

Using the numbers in this thread and the equations as well with the correct rotor diameters...

 

Toyota 4x4 and Nissan 240sx         65/35

Toyota 4x4 and Nissan 280zx         63/37

Toyota 4x4 and Nissan Maxima      66/34

 

Toyota 4runner and Nissan 240sx  70/30

Toyota 4runner and Nissan 280zx  68/32

Toyota 4runner and Nissan Maxima      70/30

 

Datsun S30 and Nissan 240sx       63/37

Datsun S30 and Nissan 280zx       61/39

Datsun S30 and Nissan Maxima    64/36

 

For reference:

Manufacturer, Model (Piston 1, Piston 2), Corresponding Rotor

Fronts:

Toyota, 4runner (43mm, 43mm) 271mm vented

Toyota, 4x4 (43mm, 34mm) 271mm solid

Datsun, S30 (54mm) 271mm solid

Rears:

Nissan, 240sx (38mm) 290mm solid

Nissan, 280zx (43mm) 258mm solid

Nissan, Maxima (38mm) 285mm solid

 

Note the ratios are once again a term known as pad bite, it is the ratio front to rear of the braking torque the caliper exerts via the pad onto the rotor when you step on the brake with no proportioning valve. Actual brake bias exerted on the road will change with tire width, tire compound, wheel diameter, pad material, etc etc.

Edited December 13, 2016 by seattlejester

[zgeezer]

I really am embarrassed.

 

So with that corrected, we are then comparing moments? As in Moment = Force x Radial Distance from rotational axis, where Force equals the area multiplied by line pressure, and the radial distance is the corrected radius of rotor - radius of piston.

 

So to calculate ratio Moments...

 

Front Bias = (Moment of Front / (Moment of Front + Moment of Rear)) x 100.

Rear Bias = (Moment of Rear/ (Moment of Front + Moment of Rear)) x 100.

 

Moment Toyota 4x4 front caliper = 2360mm^2 x Line pressure x (135.5mm-21.5mm) = 269040mm^3 x line pressure (in kg/mm^2)

Moment Toyota 4-runner = 2904mm^2 x Line pressure x (135.5mm-21.5mm) = 331056mm^3 x line pressure

 

Moment Nissan 280zx = 1452mm^2 x Line pressure x (142.5mm - 21.5mm) = 175692mm^3 x line pressure

Moment Nissan 240sx = 1134mm^2 x Line pressure x (142.5mm - 19mm) = 140049mm^3 x line pressure

 

The ratio removes line pressure from the equation assuming same line pressure goes to front and back (for our very simple calculation)

 

So we end up with biases of:

Toyota vented 4-runner and Nissan 240sx rear caliper setup

70%:30%

Toyota vented 4-runner and Nissan 280zx rear caliper setup

65%:35%

Toyota solid 4x4 and Nissan 240sx rear caliper setup

66%:34%

Toyota solid 4x4 and Nissan 280zx rear caliper setup

60.5%/39.5%

 

This would be my calculations using the slightly strange fact my rear rotors are larger than my fronts and using the stock z rotor for the front (not sure if the 4-runner guys run a different diameter, or if there is another size that most people run for the rear).

 

To calculate the actual braking force applied we would have to then start accounting for the leg pressure, master cylinder bore, mu of the tire, the radial distance from the rotational axis to the contact patch of the tire, and on and on, and factor in the weight shift of the car as one is braking and cornering, so this very brutal calculation is a very simple way of looking at comparable pad bites?

 

Well regardless, thank you very much Nigel for helping me fumble through all this math, I definitely need to pull out my physics books and brush up on them again.

This is really good stuff!  Would run the math using stock s30 rotors and caliper with the  240sx caliper and the MM rear rotors?  Thanks for the great read.

 

g

[30 ounce]

Can you plug in the Toyota 4runner fronts and the 06 Ford GT 500 rears that Silvermine Motors sell?  I have this setup and it seems to work well at the track.

[seattlejester]

I would suggest that you run the formula your self to check, but what I got...

 

Silvermine stage 4, 11.4 inch rear rotor (300mm) 1.6 piston (41mm)

 

Toyota 4 runner and Ford GT500 rear 66/34

 

Oh and Leon, thanks for the graph, and I'm actually going to go and check out that book, looks like an informative read!

Edited June 28, 2013 by seattlejester

[NCchris]

Great info guys! Could another consideration for front calipers to pair with the 240SX rears be the Willwood Superlight Billet? These are available with (4) 1-3/4" or (4) 1-3/8" pistons and can be adapted to the Z strut fairly easily. The 1-3/8" version is about 35mm which is smaller than the Toyota caliper. 

 

My thoughts are the 1-3/8 Superlight with a 12.2" dia. vented rotor that is .810 or so thick. The downside to this combo is you have to machine a hat and caliper bracket and it is not a junkyard setup. Could this work on a street Z?

chris

Edited July 13, 2013 by NCchris

[RebekahsZ]

Trying to design a marginal front brake system around marginal rear brakes seems kind of crazy to me. But it must be a fun mental exercise. Put a dollar figure on the time you have spent contemplating this and you could have bought a full Silvermine or AZC kit, front and back. I'm waiting to hear back from AZC about a wheel I mailed them to test fit for clearance. If it fits, I'm writing the check.

[NCchris]

Trying to design a marginal front brake system around marginal rear brakes seems kind of crazy to me. But it must be a fun mental exercise.

Yeah, it's called mental masturbation! I am guilty of thinking and over thinking most every detail. Guess my design expertise is better suited to production tooling instead of reinventing the wheel.

chris

[RebekahsZ]

Me too. Not meaning to bust your chops-I'm guilty of same thing. Do as I say, not as I do!

[Z Doc]

Very nice analysis.  Sorry that I am late to the party here, but do you know what the bias of the stock 240Z discs/drums are?

[EvilC]

Nice read, I remember having this discussion a few yrs back with someone I know. One thing to keep in mind too is why the vented rotors work "better" in real world driving if used at the track, they have better capabilities to dissipate the heat.

 

 

I had a small laugh to myself with the earlier mention of big brake kits being sold for newer cars because it is true. Factory bias is normally not changed and how often do you see aftermarket prop values thrown into newer factor cars that have plug N play kits.

 

 

To make sense out of non-sense let us take Arizona Z car brake options into play. Keep tire compound and pad compound the same here is how it plays out.

 

 

The 12.2 inch rotor/4 piston setup technically would have nearly the same clamping force of the 13 inch rotor/ 6 piston setup based on the piston sizes from the part numbers that were supplied years ago and sorry for a half a$$ effort to find the exact numbers. So if clamping force is nearly the same, the only advantage is the rotor size. In theory and depending on the bias desired, the 4 piston calipers should be used on a 13 inch rotor. Only the mounting bracket needs to be changed.

 

 

Stopping distance vs pedal effot vs pedal travel – can be confusing when trying to dial in brake setups.

 

[ktm]

There's a huge difference between the non-vented 4x4 calipers and the vented V6 4-Runner calipers. The non-vented caliper piston surface area is not that much bigger than stock 240Z calipers. It's only about a 3% increase. The V6 4-Runner calipers have an almost 27% increase in piston surface area! That results in a huge difference in brake torque. So, saying your "Toyota" front brake and 240SX rear brake combo is balanced is meaningless without specifying exactly which Toyota front calipers you have.

 

Keep in mind that stock 240SX front brakes are actually LESS "powerful" than stock Z front brakes. So, don't expect 240SX rear brakes to be suited to anything more than stock Z front brakes.

 

An engineered solution is doable. It's just a matter of gathering the appropriate data and doing the math, which is all available on-line. It's not voodoo magic, or guess work. By crunching the numbers, I can tell you that a V6 4-Runner/240SX brake combo has approximately a 74/26 front/rear bias, assuming equal pad coefficient of friction and full line pressure to the rear brakes. Non-vented 4x4 caliper/240SX brake combo has approximately 70/30 front/rear bias.

 

 

Nigel

 

Where is the pad coefficient in your calculations?  If you want to be picky, you also need to consider pad compound.  By adjusting pad compound you can change the bias.

 

For the record, I have the vented Toyota calipers and rear 240sx (later model I believe).  I am using Porterfield R4S pads in the front and KVR pads in the rear.  I have not tested the bias lately, but when I first did the install I had the rear locking up first until I dialed them back.

[Xnke]

Interestingly enough, it appears that the S12W (vented caliper with 43/34mm pistons) and the 240SX (38mm piston) using the 300ZX front and rear rotors (vented front rotor and solid 290mm rear rotor) has VERY SIMILAR brake bias to the Silvermine Motors kit...actually slightly more!

 

This all neglects pad area, which is a big contributor to overall braking...For a given piston diameter, the larger friction surface of the pad makes for not only more drag on the rotor, but also more heat absorption area. You can't convince me, nor will the mechanics show, that a 38mm piston with a 38mm circular pad area can apply just as much friction to the rotor as a 38mm piston with a pad with double the surface area, but the same top and bottom heights, such as an elongated kidney shape. Pad size does make a difference in braking capability of a given caliper, even if the piston sizes are the same.