luseboy Posted January 25, 2012 Share Posted January 25, 2012 Hey, So I want to do a rear disk conversion on my car before I finish the resto-mod, but I can't decide what I want to do. I have planned already on getting the silvermine stage 4 front brakes (vented toyo 4x4 4 piston set), and was thinking of doing their stage 4 rear conversion. The trouble is, the wheels I'm set on (rota aleica's) only come in 15's, and I'm not so sure they'll play nice with the rear brakes, as peopls have complained of fitment issues with 15's, and the center of these wheels really steps down. I will be using ZG flares, so I can run a big spacer in the rear, but I'm also going to be running about -2 degrees of rear camber, by means of adjustable LCA's. I have read that the s13 rear brakes don't have enough bite to be used with the toyo front's, but how bad is it? Would I notice on my primarily street-driven Z? I will post a picture of the back of the wheels when I'm on my computer (at school right now). I guess I'm just trying to figure out if the rear brakes are as wimpy as I have heard... Quote Link to comment Share on other sites More sharing options...
cockerstar Posted January 25, 2012 Share Posted January 25, 2012 "... I'm also going to be running about -2 degrees of rear camber, by means of adjustable LCA's..." Why not by camber plates? Quote Link to comment Share on other sites More sharing options...
Zmanco Posted January 26, 2012 Share Posted January 26, 2012 I have read that the s13 rear brakes don't have enough bite to be used with the toyo front's, but how bad is it? Would I notice on my primarily street-driven Z? With that brake setup, unless you go with a pad material for the rear with a higher coefficient of friction, the brakes remain front-biased (fronts lock first) even if you open the rear proportioning valve fully. On the track it means you can't optimize the front/rear braking balance. It's not as much of an issue on the street where you'll want more front bias for safety. Of course, the stock drums would also be fully adequate for the street, but they obviously don't look as good. Quote Link to comment Share on other sites More sharing options...
luseboy Posted January 26, 2012 Author Share Posted January 26, 2012 I guess I could run camber plates, but I like the idea of running LCA's instead. I don't want to have to trim away any sheetmetal, or weld in camber plates. Plus the fronts would allow me to increase caster, when accompanied by adjustable t/c rods. It was my understanding that the LCA's could handle -2* pretty easily (I'd be using the techno toy tuning arms, and this is according to them). They also would allow me toe adjustability and wheel position adjustability in the rear end. I guess I mainly just wonder how bad the s13's really are. Is it such a bad bias that the rears never really would do much, or is it just slightly not enough? I know I'd want slightly more front bias anyways, but I'm wondering if this is even possible with the s13's, or if it is way too weak to have any noticeable usage. As I understand it, most people have been using 280zx rear disks, but the s13's are supposedly more powerful. How come I don't hear complaints about the s130 brakes? I know I could stick with the stock brakes, but idk I really like disk brakes. I was told that I need 13.6" at the tallest point of the caliper (right where the hub mounting surface is). The wheels are 15's as I said, and step down to 11.4 inches in the middle. Here's a pic of a 15x8 et0 from the back. . I'd be using a 15x8 et -5, and however much spacer I'd need to get the right fitment with the Zg flares. Judging by other people's set ups, I'll probably end up with about 25mm of spacers (equivalent to a -30 offset). I know there's no way to know for sure, but I just want to know if other people think it will fit? I can't decide if it will. I am willing to shave some material off the brake caliper if need be (assuming that's safe?). I guess I won't really get any concrete answers out of this, but I'd really like a second opinion. Edan from silver mine said most of his customers were able to fit 15's with a 1/4 inch spacer in the rear. What do you guys think? I guess I'm just going to have to install the ZG flares, get the wheels, and measure everything before I can figure out what I have room for. Neither rota or silver mine take returns... Sorry for the novel Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted January 26, 2012 Share Posted January 26, 2012 (edited) 280zx and 240sx brakes are nearly identical. A typical 280zx setup usually uses 280zx calipers and 280zx or maxima rotors. This gives you 258mm rotor diameter and a 43 mm caliper piston. The modern motorsports 240sx setup uses 240sx calipers (34mm) and 300zx rotors (289mm). Brake pads are identical. Which one is better? I'm sure there is a formula out there that can tell which is better theoretically but I coulnt say which setup has the advantage. 280zx brakes also suffer from a front bias if you use the toyota 4 piston calipers in the front. I've run HPS pads all last year and have recently ordered HP+ pads to get more rear bias. I'll be installing those next week, very curious to see the results. Edited January 26, 2012 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
luseboy Posted January 27, 2012 Author Share Posted January 27, 2012 Well sounds to me like the s13 brakes are more powerful... If the rotor is bigger... seems like that's more important than the piston size. I could be wrong on that though. The s13 brake set up would end up being only marginally less expensive than the silver mine kit, and finding the calipers could be tough. But I guess if I had to, I could do that. I'm more set on wheels than brakes, and chances are I'll get bored of them after a while anyways, especially if they don't fit the silver mine brakes. I will just order the wheels when the time comes, measure up, and decide then. Unless anyone else is going through the same thing as me? Anyways we'll just have to wait and see what happens. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted January 27, 2012 Share Posted January 27, 2012 (edited) I was thinking about this and it seems we should be able to calculate this out rather easily with some simple assumptions Pressure = Force / Area So, Force (as in braking force onto the brake pad made by the caliper) = Pressure (pressure inside the hydraulic system) * Area (area of the caliper piston) Area = pi * r^2 The brake pad applies a torque to the rotor to stop the wheels. Torque = moment arm * Force For simplicity we will assume all of the braking force will be applied at the outer edge of the rotor. This will result in the best-case braking capability and will work to accent any differences between our two setups. Next comes force. The brake pad takes the force of the caliper and applies a frictional force on the rotor. To be able to calculate the frictional force on the rotor we would need a lot more information. However since both calipers use the same brake pad we can assume that the ratio of caliper force to frictional force is the same on each setup. Since this is the case we can throw that part out. Note, this is ONLY for comparing brake pads of EXACTLY the same area, dimensions, and compound. So what are we left with? Caliper Force = System pressure * Caliper piston area Caliper piston area = pi * (caliper piston diameter / 2)^2 Stopping Torque = outer rotor diameter * Caliper force If you take the time to put all the equations together you get something like this: Stopping torque = outer rotor diameter * system pressure * pi *(caliper piston diameter / 2)^2 You can see from this equation that the biggest factor is the caliper piston diameter because its value is taken to the power of two. So in our case the 240sx brakes would be inferior because the caliper piston is much smaller. The brake rotor would have to be much larger to get the same braking capability. I put together a spreadsheet but it seems this forum does not allow you to upload Excel files... Edited January 27, 2012 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
luseboy Posted January 27, 2012 Author Share Posted January 27, 2012 I was thinking about this and it seems we should be able to calculate this out rather easily with some simple assumptions Pressure = Force / Area So, Force (as in braking force onto the brake pad made by the caliper) = Pressure (pressure inside the hydraulic system) * Area (area of the caliper piston) Area = pi * r^2 The brake pad applies a torque to the rotor to stop the wheels. Torque = moment arm * Force For simplicity we will assume all of the braking force will be applied at the outer edge of the rotor. This will result in the best-case braking capability and will work to accent any differences between our two setups. Next comes force. The brake pad takes the force of the caliper and applies a frictional force on the rotor. To be able to calculate the frictional force on the rotor we would need a lot more information. However since both calipers use the same brake pad we can assume that the ratio of caliper force to frictional force is the same on each setup. Since this is the case we can throw that part out. Note, this is ONLY for comparing brake pads of EXACTLY the same area, dimensions, and compound. So what are we left with? Caliper Force = System pressure * Caliper piston area Caliper piston area = pi * (caliper piston diameter / 2)^2 Stopping Torque = outer rotor diameter * Caliper force If you take the time to put all the equations together you get something like this: Stopping torque = outer rotor diameter * system pressure * pi *(caliper piston diameter / 2)^2 You can see from this equation that the biggest factor is the caliper piston diameter because its value is taken to the power of two. So in our case the 240sx brakes would be inferior because the caliper piston is much smaller. The brake rotor would have to be much larger to get the same braking capability. I put together a spreadsheet but it seems this forum does not allow you to upload Excel files... This is interesting to think about... I'd always been under the impression that rotor size had a bigger effect on the braking power. I mean the sort of leverage difference seems pretty substantial. Most of my brake experience comes from hydraulic disk brakes on mountain bikes. I work at a bike shop and used to be really into riding. With bikes, you can choose your rotor size usually. I used to think that bigger rotors= more power. But now that I think about it, the rotor size made a bigger difference on the feel than the actual power. Larger rotors wouldn't lock up as easily, and didn't get as hot. The more powerful brakes tended to have larger pistons (or 4 pistons) and a larger master cylinder. So I guess I already knew this but hadn't really pieced it together in my head. I guess the next question is what other factors between the two affect brake power. I had read that the s13 set up is more powerful than the s130 set up... but I can't remember who wrote that. Has anyone used both systems? If so, was one better than the other? Obviously the 280zx brakes will have more clearance (due to the smaller rotor), but power is really the most important issue here. I really hope I can fit those mustang brakes under the wheels, that would be awesome haha. I haven't really heard of anyone not being able to fit 15's over their silver mines. Has this happened to anyone on here? Are there any other rear brake options that'd work well? Quote Link to comment Share on other sites More sharing options...
Justinp551 Posted January 30, 2012 Share Posted January 30, 2012 Useful info. If I am following this correctly would the preferred route be to use larger piston 280zx calipers and the larger diameter 300zx rotors. I assume the caliper bracket is the same so is the calipers set for different diameter rotors? Would the 280zx/300zx combo work or would custom brackets need to be made? Quote Link to comment Share on other sites More sharing options...
luseboy Posted January 30, 2012 Author Share Posted January 30, 2012 Useful info. If I am following this correctly would the preferred route be to use larger piston 280zx calipers and the larger diameter 300zx rotors. I assume the caliper bracket is the same so is the calipers set for different diameter rotors? Would the 280zx/300zx combo work or would custom brackets need to be made? Well I'm sure that combo would be nice, but I don't think it can really be done, maybe if you make a custom bracket, but I think still the caliper is designed for a certain diameter rotor. I'm pretty sure you need different brackets for them, as I haven't seen it advertised anywhere that you can use either caliper on the same bracket. I might be wrong though. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted January 31, 2012 Share Posted January 31, 2012 I was thinking about this and it seems we should be able to calculate this out rather easily with some simple assumptions Pressure = Force / Area So, Force (as in braking force onto the brake pad made by the caliper) = Pressure (pressure inside the hydraulic system) * Area (area of the caliper piston) Area = pi * r^2 The brake pad applies a torque to the rotor to stop the wheels. Torque = moment arm * Force For simplicity we will assume all of the braking force will be applied at the outer edge of the rotor. This will result in the best-case braking capability and will work to accent any differences between our two setups. Next comes force. The brake pad takes the force of the caliper and applies a frictional force on the rotor. To be able to calculate the frictional force on the rotor we would need a lot more information. However since both calipers use the same brake pad we can assume that the ratio of caliper force to frictional force is the same on each setup. Since this is the case we can throw that part out. Note, this is ONLY for comparing brake pads of EXACTLY the same area, dimensions, and compound. So what are we left with? Caliper Force = System pressure * Caliper piston area Caliper piston area = pi * (caliper piston diameter / 2)^2 Stopping Torque = outer rotor diameter * Caliper force If you take the time to put all the equations together you get something like this: Stopping torque = outer rotor diameter * system pressure * pi *(caliper piston diameter / 2)^2 You can see from this equation that the biggest factor is the caliper piston diameter because its value is taken to the power of two. So in our case the 240sx brakes would be inferior because the caliper piston is much smaller. The brake rotor would have to be much larger to get the same braking capability. I put together a spreadsheet but it seems this forum does not allow you to upload Excel files... Your formula is not quite correct. The stopping torque is calculated using the rotor radius, not diameter. It really should be the mean radius, about half way between the outer and inner radii of the rotor where the pad makes contact with the rotor. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted January 31, 2012 Share Posted January 31, 2012 (edited) That's embarrassing, you are correct, I forgot to divide by 2 for my moment arm. Luckily this does not do much to the formula other than change the final value (which is relatively meaningless on its own) by a constant. The caliper piston diameter is still the biggest player in this equation. Thank you for catching my mistake. Since I did not have the inner radius of the rotor I opted to make a simplification and just use the outer radius of the rotor. Since the brake pads are the same the difference between the outer and inner radii should be the same so I felt this was a reasonable simplification to make. Regarding using 280zx calipers and 300zx rotors. If the bolt pattern and location is the same you may be able to bolt the 280zx caliper onto the Modern motorsports 240sx brake caliper bracket, and potentially have it work with the 300zx rotor. You would have to take the two calipers and compare them side by side to make sure. Edited January 31, 2012 by h4nsm0l3m4n Quote Link to comment Share on other sites More sharing options...
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