Brake ideas

THAWA · Post by **THAWA** » Wed Jul 14, 2004 8:43 am

Well, I need to replace the seals in the hub, and probably the whole hub, so I'm thinking while I'm in there why not just put in better brakes, right? So I'm trying to decide between Legacy Turbo, WRX or 4pots for the front. And pretty sure I'll be going with Legacy turbo in the rear, or 2 pots to complete the set

. anyway, what I need to know is, if I go with turbo or wrx brakes, do I need to rplace the hub/knuckle? What about the backing plates? Or can I prettymuch remove the calipers/rotors and put on the new ones?

BAC5.2 · Post by **BAC5.2** » Wed Jul 14, 2004 8:54 am

Remove calipers/rotors and swap it up. That's all you should need to do.

The 4-pots use the same rotors as the WRX brakes, but they won't clear your wheels.

The Legacy Turbo front brakes aren't to stellar. Get Legacy Turbo rear brakes. 2-pots wouldn't be worth it IMO.

Post by **Legacy777** » Wed Jul 14, 2004 2:04 pm

The 4-pots would definitely be nice. More expensive, but they will give better pedal feel, and not bias the front quite as much as the WRX front brakes will.

Honestly I'd say go with the H6 rear brakes, you'll get more benefit from reducing the frontward bias then having a vented rotor in the rear.

vrg3 · Post by **vrg3** » Wed Jul 14, 2004 2:58 pm

Yeah, you don't have to replace the hubs. If you put bigger brakes on, the backing plate will be a little smaller but it shouldn't be a big deal. You may have to trim the plate a little if it interferes with the caliper but otherwise you'll be fine.

What wheels do you have?

BAC5.2 · Post by **BAC5.2** » Wed Jul 14, 2004 3:26 pm

He's got those uber RS wheels if I remember correctly. The 4-pots won't slide under them.

Legacy777 - How will the 4-pots not allow more front bias than the WRX brakes will? Seems to me that the significantly stronger 4-pots will increase front bias.

THAWA · Post by **THAWA** » Wed Jul 14, 2004 4:37 pm

Cool beans, I'm glad to hear I dont need new knuckles.

Phil the 4pots will go under RS wheels. Part of the reason I bought the wheels (I eventually plan on upgrading to 4pots).

Post by **Legacy777** » Wed Jul 14, 2004 6:02 pm

BAC5.2 wrote:Legacy777 - How will the 4-pots not allow more front bias than the WRX brakes will? Seems to me that the significantly stronger 4-pots will increase front bias.

Caliper piston size. The caliper pistons on the 4-pots are slightly smaller then the caliper pistons on the WRX calipers. Therefore with the same given input pressure the 4-pots will output less clamping force.

Actually....I'm just working on the numbers....it's fairly substantial...assuming my numbers are correct. I'll post a link to the spreadsheet when I get done.

georryan · Post by **georryan** » Wed Jul 14, 2004 6:26 pm

They will have less clamping force, but would they have more stopping force?

-Ryan

BAC5.2 · Post by **BAC5.2** » Wed Jul 14, 2004 7:48 pm

georryan wrote:They will have less clamping force, but would they have more stopping force?

-Ryan

Exactly what I was thinking. Clamp with less force, but the larger pad gives more grip.

I find it hard to believe that $50 used WRX front brakes would work significantly better than $800 4-pots.

The added grip would effectively add front bias, I'd think.

Hardy - Really? I thought the RS wheels DIDN'T clear the 4-pots. Good to know I guess.

Post by **Legacy777** » Wed Jul 14, 2004 10:59 pm

I think you guys are misunderstanding what I'm saying.

There are so many aspects to how well a car stops, pads, temperature, tires, weight shift, rotor size, material flexing, etc, etc.

I simply said that in terms of piston size, brake bias will be shifted rearwards with the 4-pots compared to a setup that originally had the WRX front brakes on. Rearward shift in brake bias is NOT bad.

I'm also just looking at the emperical brake torque increase/decrease in a percentage. The formula is:

Brake Torque Increase% = [(Caliper piston area new/old)*(effective radius new/old)*(brake pad friction coefficient new/old)]
** For Sliding calipers multiply areas by 2 **

Rotor size for the 4-pots & WRX brakes I believe is the same. So you get no added bias change from that term. If we assume pad friction coefficients are the same, we're left with the piston area.

What is "stopping force" It's not something you can quantify like I mentioned earlier. The 4-pots will perform better, will provide better brake modulation at higher pressures because they will not flex as much, plus you have a more even force exerted on the pad material then the WRX setup. Pedal feedback will also be greatly improved.

I'd gladly take the 4-pots over the WRX brakes. But like I said....they WILL decrease the overall brake torque in the front caused by piston size....

I suppose you could hook up a wheel to a reverse dynamometer or something, and apply the brakes, and measure how much torque the brakes can produce. However at that point, it'd be very difficult to discern what percentages came from what component. ie flex in the caliper, pad size, material compound, temperature gradiants in the rotor, etc, etc.

here's my calcs. Click on the brake torque tab.
http://www.main.experiencetherave.com:8 ... kemath.xls

BAC5.2 · Post by **BAC5.2** » Wed Jul 14, 2004 11:11 pm

Do the 4-pots have less area in total compared to the WRX 2-pots? I.e. the individual pistons might be smaller, but are all 4 pistons smaller than the 2 WRX pistons?

Post by **Legacy777** » Wed Jul 14, 2004 11:17 pm

that's a loaded question....

The direct answer to that is no, all four pistons on the 4-pots have a larger area then the two pistons on the WRX setup.

However. Did you see in the brake torque calculation that it says that if you have a sliding type caliper, ie what the WRX and turbo legacy have, you must multiply the piston area by 2. The reason for that is any object that has a force exerted on it will exert an equal and opposite force. (assuming the object remains stationary)

Since that is the case, you must treat the the sliding calipers like they have pistons on the opposite side exerting the same force upon the pad & rotor.

That answer your question?

BAC5.2 · Post by **BAC5.2** » Wed Jul 14, 2004 11:28 pm

I guess, thanks!

So the individual pistons are smaller than the individual WRX pistons, but effectively, the WRX pistons are twice as large (as they pull the other pads, like you said, acting as a piston on the other pad).

So the total effective piston area of the 4-pot (all 4 pistons individually) is less than the total effective piston area of the WRX setup (2 pistons x 2 "phantom" pistons)?

So the 4-pot upgrade is almost exclusively for brake feel? Is that the advantage of a 4-pot upgrade (in any situation)?

Effectively less powerful of a brake, but the increased pad surface area about makes up for that, and feel is the point of a 4-pot?

Would you say the 60-0 distances of a WRX with stock brakes and a WRX with 4-pots would be the same, or similar enough to chalk it up to conditions?

Brakes have always intrigued me (I'm obsessed with stopping for some reason. Right before I sold my downhill bike, I planned on upgrading to 6 piston brakes at each end

), so I want to learn anything and everything about them.

Post by **Legacy777** » Thu Jul 15, 2004 12:00 am

There is much to learn when dealing with brakes. I've learned a hell of a lot since messing with the brakes on my car. It was a little bit of trial and error, and pretty much caused me to get in an accident because the WRX brakes affected the car's braking dynamics so much with a massive 20% shift forward in brake bias.

Right now, the only thing stock in the brake system is the booster and hard lines, everything else has been altered to achieve the results I want.

Yes the individual pistons on the sti 4-pots are smaller then the individual pistons of the wrx calipers.

The WRX pistons aren't twice as large. Just think of the wrx caliper with two additional pistons on the opposite side. That's exactly what multiplying the areas by two gives you. An equal and opposite force. In reality you will get caliper flex and the surface area on the pads will be different on the outer pad, so the forces will not be "100%" the same. You will see more force at the top of the pad then the bottom of the pad.

No, To be proper, you would not include the "phantom" pistons in your effective piston area ......So then No, the total effective piston area of the 4-pots is greater then the total effective piston area of the WRX. However for simplicity sake, IF you include the "phantom" pistons in the calculation the total WRX piston area would be larger then the 4-pot total piston area.

I would not say the 4-pot is almost "exclusively" for feel. I would say the majority of it is feel. Any opposing piston type caliper will provide less caliper flex and more even braking force on the pads then a traditional sliding caliper.

You can however argue. Since you are getting a more even force distribution on the pad, the pad is working more efficiently and therefore braking performance will be increased. In terms of the pedal feel. If you have less caliper flex, and better brake modulation, you will be able to control the braking system better at the limit that lockup occurs. So in a round about way, you improved the total braking performance of the vehicle, simply by improving the feel, and the ability of the driver to control it.

Have you ever seen the pads for a 4-pot setup? They're almost the same if not a little smaller in terms of suface area, compared to the sliding caliper pads. One of the reasons for this is pressure is more evenly distributed throughout the pad, therefore, less surface area, and less force is required to exert the same output brake torque. Remember I said the 4-pots delivered less braking force at a "given input" pressure. So at the same pressure the 4-pots will produce less force.

I'd say a wrx with 4-pots would probably stop better.

If you want to get into high end calipers, they have varying sized pistons along the caliper to help normalize the braking force along the horizontal plane of the pad.

Brakes are definitely cool stuff.....and yeah.....I'd say my legacy will out brake a WRX any day

One other comment about brakes. No matter how good your brakes are.....if your tires suck......your brakes won't mean shit.

I found this out.....nitto 555's vs. the goodyear gs-d3's. OMG.....it's amazing the difference. Also when I had the WRX wheels & tires on....which were a larger overal diameter, I still could lock the brakes up more easily then compared to the gs-d3's.

So yah....tires make a hell of a difference too.

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 12:50 am

The two additional pistons thing is what I was talking about.

Just for reference, we aren't talking about the STi Brembo 4-pots, but the Subaru Factory 4-pots that come on all non-USDM WRX's.

I think I get what your saying. It seems that car brakes aren't much different fundamentally than Mountain Bike brakes. Other than the fact that we have dual piston (one per side) calipers and cars usually have dual pistons with 2 pistons on one side.

With the 6 pot brakes I was speaking of, all 3 are different sizes, and they engage 2x2, meaning the first 2 pistons engage, followed by the second 2, and finally the 3rd set. They allow significant modulation, and after riding on them, it's blatantly apparent why they are so cool. Lever throw is more than with my 2-pot brakes, but they have a more vauge feel overall. Your brake input doesn't fluctuate so drastically with each mm of lever movement. with my 2-pots, I could be at full lock (front or rear, which is scary) within, say, 4 degrees of movement. Full lock on the 6-pots comes in 6 degrees or so. The extra few degrees allows a margin of modulation that is nearly impossible to balance with the 2-pots. It appears that the car brakes are similar, where actual pedal travel on higher pot brakes allows a more stable modulation of braking force. If you sneeze, you aren't going to mess up your threshold like you would with super big, fewer pistons.

I don't know if that made sense or not...

Thanks for the info Josh!

Post by **Legacy777** » Thu Jul 15, 2004 1:35 am

Correct, we're not talking about the brembro sti calipers, rather the subaru factory 4-pots.

Yeah I think I get what you're saying. I'm a little curious how they are able to stage the pistons like that. I think valving would get too complicated, and probably wouldn't hold up too long under the high temps. However I may be wrong. A simpler solution, and probably one I think they do is to vary the piston size which varies the force being applied.

welcome

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 2:32 am

Whoops, my bad. 2 of the pistons are the same size, the third is larger.

As the Hope rep explained to me, the largest piston engages first, with the other two trailing in. Or that's how he made it seem. It might be varying piston sizes that effect the force from each piston. The Caliper is one peice, and the pistons are Titanium (great for high-temp applications).

Post by **Legacy777** » Thu Jul 15, 2004 2:40 am

that's sweeet!!!

I would like to convert my mtn bike over to disc brakes.......but I don't ride it enough down here in houston to justify it.

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 2:44 am

The only excuse to not have discs is money, and weight. They FAR outperform V's if you can suffer the weight penalty.

It's like saying "I can stick with 4 wheel drums, I don't drive that much."

When you DO ride, wouldn't you want it to be the best experience it could be? I know that's why I loved to bike...

Post by **Legacy777** » Thu Jul 15, 2004 2:50 am

how much weight do they add....and how much does an average conversion cost.

You probably need new hubs too huh?

Like I said....if I rode any where near as much as I did when I lived in seattle, I'd have 'em. I haven't been riding riding in over a year....it's pityful.

I'm hoping with the truck purchase, I'll be able to go places now.

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 3:13 am

A GOOD set (like the Avid Juicy 7's, the Hope Mini's, or even the Hayes Mag-carbon's) will only add maybe 150 grams overall to the brake system. That comes out to something like 3/16th of a pound. The benefit is that it's all at the axle. Most of the weight comes from the lever body (no big deal), and the rotor (slightly more unsprung weight, but it's centralized on the wheel).

Going from V's to Disc is pretty expensive.

If you want a nice, light, reliable, and beefy setup, then get these wheels:

http://www.pricepoint.com/detail/12010- ... --Rims.htm

and these brakes...

http://www.pricepoint.com/detail/12963- ... -Brake.htm

Total cost, out the door, would be about $560 or so. TOTALLY worth it.

You could cut a wee bit of cost (30 bucks) by getting the straight gauge version of the wheelset above. I'd say stick with the Double Butted though, they are stronger and lighter than straight gauge.

If you want to go UBER budget, then get this.

Wheels: http://www.pricepoint.com/detail/12001- ... e-Rims.htm

Brakes (Avid Mechanical):
http://www.pricepoint.com/detail/12605- ... -160mm.htm

That'll set you back right around $250. You would be MUCH happier with the hydro setup though. There is simply no replacement for a good set of hydro brakes.

It's cheaper to buy a wheelset like above rather than have someone build a wheel.

In spokes, nipples, and labor alone, I charge around $60 bucks for a 32 hole, and $70 for a 36 hole wheel. Add to that a rim and hub, and you're working on a good bit of money. I've built $500 wheelsets before, and even spec'd (but the guy never ended up buying) an $800 REAR wheel.

Post by **Legacy777** » Thu Jul 15, 2004 3:21 am

Yeah.....I remember the days when I sank all the money into the bike....now I have the car, house, women, and other crap.....

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 3:27 am

Lol, I know that feeling. I spent like $1300 on my downhill bike. Finally sold it for a profit.

If I didn't work at a shop, I wouldn't have gotten the bike. Paying full retail, I would have spent almost $7k on that thing.

Post by **Legacy777** » Thu Jul 15, 2004 3:29 am

yeah I can imagine.......I spent 1000 bucks on my gt avalanche back in 96......back then that was a lot of dough. Plus I swapped the mag 21 shocks over as well.

So I had a good 1400 into it.

I still love the bike.....only weighs 24 lbs.....

BAC5.2 · Post by **BAC5.2** » Thu Jul 15, 2004 3:32 am

That's as much as my single speed!

I miss the days of my fully geared, 23lb, Stumpjumper

. The next $800 bones I get freed up, I'm getting an 05 Stumpjumper FSR Expert. Sub 26lb full suspension, can't be beat

.

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Brake ideas

Brake ideas