Post by ES_97Sport on Mar 24, 2016 21:04:00 GMT -5
... Yea I was browsing the other day and the rotors are quite a bit larger on the vr4 compared to the sport. So unless there is a rotor from something else that could be used it would do any good.
I found some of this on the 3sx.com brake FAQ. I thought this was somewhat interesting.
Mitsubishi
91-93 TT/VR4 AWD Front - 11.625" - 13.5 lb
94-99 TT/VR4 AWD Front - 12.3125 - 17.55 lb
Gen 1
15" Sport Front AWD/4WD - 10.86" - n/a lb - vented
15" Sport Rear AWD/4WD - 12.406" - n/a lb - solid
Gen 2
15" Sport Front AWD/4WD - 10.86" - n/a lb - vented
15" Sport Rear AWD/4WD - 12.406" - n/a lb - solid
16" Sport Front AWD/4WD - 12.365" - n/a lb - vented
16" Sport Rear AWD/4WD - 12.406" - n/a lb - solid
Gen 1
15" Dual piston front - 1.68" dia
15" Single piston rear - 1.68" dia
Gen 2
15/16" Dual piston front - 1.68" dia
15/16" Single piston rear - 1.68" dia
GM
60s-80s Standard Duty D52 Front - 11.88" - 19.5 lb
I don't think rotor diameter in the rear is an issue.
The Gen 2 'big brakes' front rotor is significantly larger than the Gen 1 and the smaller Gen 2 rotor.
The calipers don't appear to change between Gen 1 and Gen 2. That would explain why I can't tell the difference between my Gen 1 and Gen 2 brakes as far as brute braking goes.
The goal with this however would be to more or less improve brake fade from the "overburdened" issues I spoke of where frequent stops even in non emergency situations would be greatly improved. The temps here in Atlanta can breach 100 which adversely affects the situation.
In this case going from the 10" to the 12" rotors would probably help. I couldn't find weights for the Mitsu rotors but I'd guess that the 12" is close to 20-20.5 lbs where the 10" rotor is probably about 12 lbs. I can't see a down side here.
My rear Exploder rotors are 11.22". These are 1.186" larger in diameter which is just crazy. I have NEVER had heat issues with the rear Exploder rotors even in a 6K lb vehicle. The rears are not where the majority of the heat is generated. I don't see any reason - even if you could - to mess with the rear.
All the experts seem to say on paper that their is no difference in braking performance when going from 2 pot to 4 pot calipers but, everyone that has done it ends up with better braking performance all around. It does make sense where you have 4 pistons pushing against the rotor rather than two is like the two heads are better than one saying.
They are correct. Total piston area and fixed vs floating are all that count. If the total piston area is the same between a single piston caliper and a dual or quad piston caliper, how many pistons is irrelevant.
Now what they THINK is happening who knows. This is just math and the math is what the math is.
If the area stays the same, the only time increasing the number of pistons makes a difference is if there is a problem with the original caliper design or materials. Multiple piston calipers in theory are supposed to distribute the force more evenly across the pad so this has a lot more to do with more even pad wear.
If x caliper flexes and y caliper doesn't, then changing calipers can make a difference because you loose clamping force if the 'clamp' is flexing under load. But, then its back to a not too good design or poor materials.
The problem is is there's absolutely no way to quantify this. Changes are made to two or three things at a time, and changes are not made from apples to apples. Calipers get changed from single to dual or dual to quad and the piston area changes. Because they don't know how brake hydraulics work, they think, "Oh, my God! Dual piston calipers are the hotness!", completely ignorant of the fact that the total piston area just changed and THAT is actually what caused the effect.
Unless there is some specific reason to go from a single piston caliper to a dual (or more) piston caliper, its always best to stick with a single piston caliper.
Yea, I agree. Well, you know, if one piston clamps hard when you stomp the brake, then two pistons clamp down twice as hard, right?
Also the diameter of the pistons (not sure the size on either/relative to bmc bore Im sure ) plays a large part in this
No, not a "large part", the pistons play the ENTIRE part. All calipers do is hold the brake pad in place and try to stay cool. I won't get into fixed vs floating calipers since ours are all floating. So excluding that, the piston area is the only thing that matters.
The BMC only does one thing. It moves fluid when you stomp the pedal. The BMC must have the capacity in volume sufficient to move the pistons their entire stroke in one press of the pedal. In other words if the volume of the calipers is 1 cup of fluid, then the BMC has to be able to move at least 1 cup of fluid.
Your leg, the pedal (pedal ratio) and booster (booster ratio) supply the force to the BMC that creates the pressure within the hydraulic system. The BMC itself just reacts to the force and move fluid through the system.
What is important is that the larger the diameter of the BMC, the more fluid it moves but the lower the pressure created in the hydraulic system. The smaller the diameter, the more pressure that's created but the less volume of fluid it moves.
So, yes, the BMC has to be matched to the calipers. Pressure does no good if the BMC can't move enough fluid in one stoke to move the caliper pistons. Likewise it doesn't matter how much fluid the BMC can move if you can't actually apply enough pressure to the pads through the pistons.
Changing the BMC will only have an effect if it isn't adequate in some way for the calipers installed. If its properly sized to the calipers, its just properly sized to the calipers - you're done.
but yea, without the larger rotor to help dissipate heat it wouldn't do any good.
Correct.
They also say that whenever you are increasing the size of the wheel and or tire you should upgrade to a bigger brake setup. One of the biggies they tell people when going from a stock 15/16/17" wheel to 22/24" and such.
The #1 reason is because you don't have a choice. Larger diameter rims are needed to fit the larger diameter rotors and calipers. My 15" rims JUST BARELY fit my 11.88" rotors and D52 calipers. Going to the D60 12.5 rotors, even though the 3.15" piston D52 caliper is the same physical size, wouldn't fit with the 15" rims.
The #2 reason is cooling. How important #2 is is largely dependent on the vehicle application and the type of rim.
A solid center, un-vented rim like on the big Sport obviously isn't going to have very good air flow. A larger rim may allow more air circulation around the rotor and caliper. However if the rim is vented properly then what size - so long as everything fits - will make virtually no difference.
If every little tiny bit of cooling counts - like on a real twisty, high speed road track - then I guess having a large area between the rim and caliper and rotor might be worth something. On a street or off road vehicle? No, putting a 20" rim on a 12" rotor isn't going to make any appreciable difference. No, scratch that, its not going to make ANY difference.
Rims only absorb a vary small percentage of the heat generated by the brakes. If that were not the case, then the rubber of the tire beads would melt. Brakes rotors can hit 1000-1500 degrees. If the rim got to 1000 degrees, very ugly and life threatening things would happen.
In real life ducting for the brake rotors along with rims that vent the air the correct direction are a LOT more important than the diameter of the rim.
Albeit that changing the wheel size sometimes increases the rotating mass of the wheel/tire package more so than increasing the tire size, it still increases sometimes dramatically. Some of these aftermarket wheels are as light as a feather sometimes much more so than the tire going on it. I guess the point being that real world testing scenarios are usually a better way of determining the outcome of something rather than just relying on what is written on a sheet of paper. I'm sure you know this all to well.
Rotating mass of the wheel isn't relevant in a street vehicle. The total weight of rim, tire and air inside doesn't vary significantly because you can't change the overall size that much. 10-20 lbs more or less doesn't make a big difference.
Now, if you're were talking about going from say a 80-100 lb combination to a 44" 350 lb Bogger and rim, that would be a different story. In braking, though, the difference is how far the mass is from the center. The majority of the weight of a tire is in the tread. So if you go from a 35" tire to a 44" tire, you are moving the weight out 11".
Look at a rotor and caliper as a lever. The lever length is measured from the center of the caliper to the center of the pad AREA (not the center of the pad). If you have a 500 lb weight on the end of a lever and you increase the length of the lever, its easier to lift the 500 lbs.
If you increase the length of the 'lever' by increasing the rotor diameter thereby moving the caliper further away from the center, less force is needed OR the same amount of force can be used with more weight. Now, the further you move the mass of the tire out from the center, the more 'leverage' is needed to slow that mass. This is the point of going with larger diameter rotors when big, heavy tires are used
But, again, you need a really big, really heavy tire spinning at high RPM for this to really be a consideration. I don't know anyone that runs 40" Boggers doing 70 MPH down the highway.
What IS a consideration has nothing to do with braking. Well, it kinda does. Wheels are un-sprung weight. The mass of lighter wheel/tire combinations is easier to control and thereby making it easier to maintain traction with the road surface.
EXCEPT for off road where having very heavy tire/rim combinations actually is a GOOD thing and really DOESN'T have anything to do with braking. It goes back to my post on soft vs stiff suspensions and sprung and un-sprung weight. The more unsprung weight you have the harder it is for the sprung weight to tip you over. That's why the buggy guys 1/3 fill their tires with water. It adds a lot of un-sprung weight making it much harder to tip the vehicle over.
Back to the OEM Sport stuff ...
Caliper - Total Piston Area (sq in) Left+Right
Mitsubishi
Piston 1.68" - 4.43
Piston 1.68" x 2 - 8.86
Ford Exploder
Piston 1.88" - 5.55
GM D52
Piston 2" x 2 - 12.56
Piston 2.92" - 13.39
Piston 3.15" - 15.58
Just for grins I tried a dual 1.68" piston Mitsu caliper on a 12.5" rotor (15/16" BMC) and compared it to a GM 3.15" single piston caliper (1.25" BMC) on the same diameter rotor. Hydraulic pressure required went from 1467 PSI to 2579 PSI. To get the equivalent braking with the Mitsubishi calipers requires a 1000 PSI increase. The numbers here are not important nor represent actual Mitsu brake behavior, but the DIFFERENCES are relevant.
Take a good look at the numbers above. There is more than a square inch of difference in area between the Mitsu dual calipers and my REAR Exploder calipers. The OEM GM 2.92" calipers used on almost every GM car and light/medium truck for 20 years is THREE TIMES the area on a rotor that is 1/2" smaller in diameter.
This is simplified because 'piston area' does not equal 'pad area'. In theory you could have 12 sq in of piston area and 2 sq in of pad area but that doesn't really ever happen. This is close enough for purposes here.
So, we have these ginormous rotors and little tiny calipers. Yes, having the big rotors is good for heat and good for leverage, but like I already said above, JUST rotors doesn't really do a hell of a lot. In my opinion, we are only just slightly better off with the larger Gen 2 'big brakes' than the original size Gen 1 brakes.
Since the calipers never changed between Gen 1 and Gen 2 apparently, changing to the larger rotors doesn't seem to have a point except for what may be gained in the area of heat management.
If I were going to re-engineer the OEM brakes ...
I wouldn't touch the rear brakes. I think I'd go with the larger Mitsu front rotors and whatever caliper would give me the equivalent of the Wilwood 2"x2, .45 friction coefficient pads and I'd play around with the 1 1/16", 1 1/8" and 1 1/4" BMC to get the pedal to feel how I wanted it, starting with the 1 1/16" BMC.
Edward