Rear disc brake conversion
#41
10-29-2009, 01:31 PM
I was serious. Really perform a search on "self energizing drum brakes" on Google next time. This is in most basic auto mechanic starter classes at any vocational tech school.
So based on the Asian version stopping distances, is it worth several hundred dollars to swap to discs and stop 10 feet shorter? I wouldn't be surprised if you wouldn't get better braking by swapping the fronts out with bigger disks and calipers if you are really worried about stopping power.
So based on the Asian version stopping distances, is it worth several hundred dollars to swap to discs and stop 10 feet shorter? I wouldn't be surprised if you wouldn't get better braking by swapping the fronts out with bigger disks and calipers if you are really worried about stopping power.
#42
10-30-2009, 06:59 PM
Weighing in here as a mechanical engineer.
Oh, and my Honda Jazz has rear discs, and is the only car in it's class here that has them.
Some facts:
Firstly, in perfect dry conditions, drum brakes will give you more braking force than discs - the first time.
discs give you consistent results because they are linear (they don't self apply) and because if they do get wet, they shed the water quickly instead of trapping it inside.
Disc brakes work better under repeated hard usage because they are better at shedding heat.
Drum brakes are superior for a parking brake because they self energize and have a larger contact area.
If you have rear disc brakes, you have two choices for your parking/E-Brake:
1. Use a mechanically actuated caliper on the disc - adds weight and not very effective
2. Use a smaller drum inside the disc hub - less effective than a full size drum as an E-Brake and adds a lot of weight.
In the USA, I believe there are rules that govern the effectiveness of the secondary brake (which is why you call it an E-Brake and we call it a parking brake) This effectiveness is compromised when the size of the secondary brake is reduced to fit it inside the disc brake hub. Elsewhere in the world, the use of split hydraulic systems is deemed to cover the emergency eventuality.
In a light FWD car, most of the mass is at the front and most braking is done at the front. The rear brakes may in fact do nothing in extreme braking in an empty car.
In a light car, the weight saving from using drums rather than discs with an included E-Brake is attractive.
In an economy car, the cost saving of using a rear drum brake for service and parking brake is attractive.
Disc brakes give better pedal feel and work better with ABS.
Disc brakes are often fitted for "marketing" reasons to cars that don't really need them because there is a perception that they are "better".
I think the reason you get rear drums in the USA is for reasons of cost, fuel consumption, and meeting E-Brake effectiveness regulations.
The reason we get rear disc brakes everywhere else is for marketing.
You might fail your annual safety check (if you have them) with rear disc brakes if you can't achieve the mandated effectiveness of your E-Brake.
Oh, and my Honda Jazz has rear discs, and is the only car in it's class here that has them.
Some facts:
Firstly, in perfect dry conditions, drum brakes will give you more braking force than discs - the first time.
discs give you consistent results because they are linear (they don't self apply) and because if they do get wet, they shed the water quickly instead of trapping it inside.
Disc brakes work better under repeated hard usage because they are better at shedding heat.
Drum brakes are superior for a parking brake because they self energize and have a larger contact area.
If you have rear disc brakes, you have two choices for your parking/E-Brake:
1. Use a mechanically actuated caliper on the disc - adds weight and not very effective
2. Use a smaller drum inside the disc hub - less effective than a full size drum as an E-Brake and adds a lot of weight.
In the USA, I believe there are rules that govern the effectiveness of the secondary brake (which is why you call it an E-Brake and we call it a parking brake) This effectiveness is compromised when the size of the secondary brake is reduced to fit it inside the disc brake hub. Elsewhere in the world, the use of split hydraulic systems is deemed to cover the emergency eventuality.
In a light FWD car, most of the mass is at the front and most braking is done at the front. The rear brakes may in fact do nothing in extreme braking in an empty car.
In a light car, the weight saving from using drums rather than discs with an included E-Brake is attractive.
In an economy car, the cost saving of using a rear drum brake for service and parking brake is attractive.
Disc brakes give better pedal feel and work better with ABS.
Disc brakes are often fitted for "marketing" reasons to cars that don't really need them because there is a perception that they are "better".
I think the reason you get rear drums in the USA is for reasons of cost, fuel consumption, and meeting E-Brake effectiveness regulations.
The reason we get rear disc brakes everywhere else is for marketing.
You might fail your annual safety check (if you have them) with rear disc brakes if you can't achieve the mandated effectiveness of your E-Brake.
#44
10-30-2009, 09:08 PM
the next time you slow down, pay attention to how delicate you have to modulate the brake pedal, then compare to a car with disc brakes. That alone is why I prefer discs over drums.
on a second note: does anybody else think the brake pedal is a bit too mushy?
on a second note: does anybody else think the brake pedal is a bit too mushy?
#45
10-30-2009, 09:18 PM
I feel a similar thing, but I don't think it's due to the drum brakes... I drove my sister's 97 CR-V, which has rear drum brakes, and didn't find the brakes any harder to modulate than my 97 Odyssey...
#46
10-30-2009, 10:07 PM
Weighing in here as a mechanical engineer.
Oh, and my Honda Jazz has rear discs, and is the only car in it's class here that has them.
Some facts:
Firstly, in perfect dry conditions, drum brakes will give you more braking force than discs - the first time.
discs give you consistent results because they are linear (they don't self apply) and because if they do get wet, they shed the water quickly instead of trapping it inside.
Disc brakes work better under repeated hard usage because they are better at shedding heat.
Drum brakes are superior for a parking brake because they self energize and have a larger contact area.
If you have rear disc brakes, you have two choices for your parking/E-Brake:
1. Use a mechanically actuated caliper on the disc - adds weight and not very effective
2. Use a smaller drum inside the disc hub - less effective than a full size drum as an E-Brake and adds a lot of weight.
In the USA, I believe there are rules that govern the effectiveness of the secondary brake (which is why you call it an E-Brake and we call it a parking brake) This effectiveness is compromised when the size of the secondary brake is reduced to fit it inside the disc brake hub. Elsewhere in the world, the use of split hydraulic systems is deemed to cover the emergency eventuality.
In a light FWD car, most of the mass is at the front and most braking is done at the front. The rear brakes may in fact do nothing in extreme braking in an empty car.
In a light car, the weight saving from using drums rather than discs with an included E-Brake is attractive.
In an economy car, the cost saving of using a rear drum brake for service and parking brake is attractive.
Disc brakes give better pedal feel and work better with ABS.
Disc brakes are often fitted for "marketing" reasons to cars that don't really need them because there is a perception that they are "better".
I think the reason you get rear drums in the USA is for reasons of cost, fuel consumption, and meeting E-Brake effectiveness regulations.
The reason we get rear disc brakes everywhere else is for marketing.
You might fail your annual safety check (if you have them) with rear disc brakes if you can't achieve the mandated effectiveness of your E-Brake.
Oh, and my Honda Jazz has rear discs, and is the only car in it's class here that has them.
Some facts:
Firstly, in perfect dry conditions, drum brakes will give you more braking force than discs - the first time.
discs give you consistent results because they are linear (they don't self apply) and because if they do get wet, they shed the water quickly instead of trapping it inside.
Disc brakes work better under repeated hard usage because they are better at shedding heat.
Drum brakes are superior for a parking brake because they self energize and have a larger contact area.
If you have rear disc brakes, you have two choices for your parking/E-Brake:
1. Use a mechanically actuated caliper on the disc - adds weight and not very effective
2. Use a smaller drum inside the disc hub - less effective than a full size drum as an E-Brake and adds a lot of weight.
In the USA, I believe there are rules that govern the effectiveness of the secondary brake (which is why you call it an E-Brake and we call it a parking brake) This effectiveness is compromised when the size of the secondary brake is reduced to fit it inside the disc brake hub. Elsewhere in the world, the use of split hydraulic systems is deemed to cover the emergency eventuality.
In a light FWD car, most of the mass is at the front and most braking is done at the front. The rear brakes may in fact do nothing in extreme braking in an empty car.
In a light car, the weight saving from using drums rather than discs with an included E-Brake is attractive.
In an economy car, the cost saving of using a rear drum brake for service and parking brake is attractive.
Disc brakes give better pedal feel and work better with ABS.
Disc brakes are often fitted for "marketing" reasons to cars that don't really need them because there is a perception that they are "better".
I think the reason you get rear drums in the USA is for reasons of cost, fuel consumption, and meeting E-Brake effectiveness regulations.
The reason we get rear disc brakes everywhere else is for marketing.
You might fail your annual safety check (if you have them) with rear disc brakes if you can't achieve the mandated effectiveness of your E-Brake.
As a fellow engineer who has designed and tested brake systems I disagree that drum brakes offer more braking force. The friction between disc and piston pad far exceeds that of shoes on drums. And disc brake systems actually weigh less than equivalent drums. That cast iron drum alone outweighs my entire disc and caliper. As a deciding argument note that nobody of consequence has drums up front. Guess why.
Its easier to put ebrakes on drums I agree but the difference is slight.
And there is no comparison when servicing is involved; the drum fails quickly. And yes, there are SAE standards for how much the e-brake will hold in terms on the incline.
Its not a perception; discs brakes are superior in performance, cost, and weight. As I said no one uses drums in front. And you can bet your last hamburger if they were cheaper they would.
Only the leftover suppliers who can provide drum brakes because their fabrication lines have long since been paid for and thus their cost can be less are the reason anyone uses drum brakes.
When you look at the active surface area between the drum and the brake shoe you quickly see that they are not as much in contact as you might assume. Therein the so-called self-energizinfg just isn't there. Its not quite the case that because the shoe travels into the drum rotation that self-energizing occurs. The secret is the force pushing the shoe into the drum and its much less than the force that a piston can apply perpendicularly to a pad against the disc compared to the force applied axially to the drum. And multiple pistons offer far more.
As in most things you can make a drum so wide and large diameter compared to a tiny pad on a small diameter disc that it will be the better performer but in reality that doesn't exist. Well, except at leMans decades ago. But it didn't take more than a year to change.
PS: be careful of the stuff on google. they're the same people who say synthetic oils aren't any better than hydrocarbon oils. Those of us with dynos know better.
Last edited by mahout; 10-30-2009 at 10:11 PM.
#47
10-30-2009, 10:45 PM
Do you have an AT fit? Is what you're describing due to the AT shifting down into first right before you stop? (https://www.fitfreak.net/forums/2nd-...n-slowing.html)
I feel a similar thing, but I don't think it's due to the drum brakes... I drove my sister's 97 CR-V, which has rear drum brakes, and didn't find the brakes any harder to modulate than my 97 Odyssey...
I feel a similar thing, but I don't think it's due to the drum brakes... I drove my sister's 97 CR-V, which has rear drum brakes, and didn't find the brakes any harder to modulate than my 97 Odyssey...
#48
11-01-2009, 01:04 AM
PS after converting to disc rears we compared prior stopping distances with the new ones. On average, stopping distance from 60 mph were reduced 8.82 ft and 3 sigma statistics clearly showed the discs were superior.
And changing pads is a half hour work compared to 2 hours for drums. Which is probably why Honda puts disc rears on Fits sold elsewhere.
And changing pads is a half hour work compared to 2 hours for drums. Which is probably why Honda puts disc rears on Fits sold elsewhere.
I HATE our rear drums with a passion. I don't care how many engineers with advanced degrees chime in on this thread about the effectiveness of drums, because they were put on our car for one reason only, cost savings. Drums are inferior in just about every driving condition to disc brakes. As others have said drums are also a good bit heavier, and esthetically they look cheap. Plus it's because of drums the braking pedal has that slightly "mushy" feel for lack of a better word, I hate it. Our cars are routinely trashed in reviews due to long stopping distances, and I know a lot of that is because of the tires, but rear drum brakes certainly don't help the cause. I would love to have my Fit stop 8.82 feet shorter distance.
The 10.2 rear disc brakes from the Civic would have been perfect on our car's. How much extra cost would that have added to the Fit's MSRP? Not much I imagine, and I would have gladly paid for it as I'm sure every other owner would have. The Sport model should have rear disc brakes, save the drums for the base model Fit. The minute I learn about a successful rear disc conversion kit for the 2009 Fit I'm all over it.
Last edited by dgs; 11-01-2009 at 01:06 AM.
#49
11-01-2009, 01:56 AM
That is quite a statistic. 8.82 feet is the difference between a crash and no crash.
I HATE our rear drums with a passion. I don't care how many engineers with advanced degrees chime in on this thread about the effectiveness of drums, because they were put on our car for one reason only, cost savings. Drums are inferior in just about every driving condition to disc brakes. As others have said drums are also a good bit heavier, and esthetically they look cheap. Plus it's because of drums the braking pedal has that slightly "mushy" feel for lack of a better word, I hate it. Our cars are routinely trashed in reviews due to long stopping distances, and I know a lot of that is because of the tires, but rear drum brakes certainly don't help the cause. I would love to have my Fit stop 8.82 feet shorter distance.
The 10.2 rear disc brakes from the Civic would have been perfect on our car's. How much extra cost would that have added to the Fit's MSRP? Not much I imagine, and I would have gladly paid for it as I'm sure every other owner would have. The Sport model should have rear disc brakes, save the drums for the base model Fit. The minute I learn about a successful rear disc conversion kit for the 2009 Fit I'm all over it.
I HATE our rear drums with a passion. I don't care how many engineers with advanced degrees chime in on this thread about the effectiveness of drums, because they were put on our car for one reason only, cost savings. Drums are inferior in just about every driving condition to disc brakes. As others have said drums are also a good bit heavier, and esthetically they look cheap. Plus it's because of drums the braking pedal has that slightly "mushy" feel for lack of a better word, I hate it. Our cars are routinely trashed in reviews due to long stopping distances, and I know a lot of that is because of the tires, but rear drum brakes certainly don't help the cause. I would love to have my Fit stop 8.82 feet shorter distance.
The 10.2 rear disc brakes from the Civic would have been perfect on our car's. How much extra cost would that have added to the Fit's MSRP? Not much I imagine, and I would have gladly paid for it as I'm sure every other owner would have. The Sport model should have rear disc brakes, save the drums for the base model Fit. The minute I learn about a successful rear disc conversion kit for the 2009 Fit I'm all over it.
The Civic doesn't do very well for braking despite having rear discs; Edmunds measured about 130 ft for a 2006 Civic EX with rear discs, which is on par with what they got for the Fit, which was 134 ft, though granted the Civic is about 200 lbs heavier (reference: 2006 Economy Sedan Comparison Test: Honda Civic vs. Mazda 3).
I know discs are better, I just don't think the drums are holding back the braking performance on a stock Fit in normal driving. I'm pretty sure I can lock the rear wheels with the handbrake, which would seem to suggest that the drum brake is plenty strong (unless my arm has more power than the brake system, but I don't think I'm that strong
).EDIT: Actually, I wonder, if I really wanted to improve the braking performance of my Fit, what order should I do things in? I'm guessing it's Tires -> Front pads (and rotors?) -> rear disc conversion?
Last edited by clicq; 11-01-2009 at 01:12 AM.
#51
11-01-2009, 05:47 AM
That is quite a statistic. 8.82 feet is the difference between a crash and no crash.
I HATE our rear drums with a passion. I don't care how many engineers with advanced degrees chime in on this thread about the effectiveness of drums, because they were put on our car for one reason only, cost savings. Drums are inferior in just about every driving condition to disc brakes. As others have said drums are also a good bit heavier, and esthetically they look cheap. Plus it's because of drums the braking pedal has that slightly "mushy" feel for lack of a better word, I hate it. Our cars are routinely trashed in reviews due to long stopping distances, and I know a lot of that is because of the tires, but rear drum brakes certainly don't help the cause. I would love to have my Fit stop 8.82 feet shorter distance.
I HATE our rear drums with a passion. I don't care how many engineers with advanced degrees chime in on this thread about the effectiveness of drums, because they were put on our car for one reason only, cost savings. Drums are inferior in just about every driving condition to disc brakes. As others have said drums are also a good bit heavier, and esthetically they look cheap. Plus it's because of drums the braking pedal has that slightly "mushy" feel for lack of a better word, I hate it. Our cars are routinely trashed in reviews due to long stopping distances, and I know a lot of that is because of the tires, but rear drum brakes certainly don't help the cause. I would love to have my Fit stop 8.82 feet shorter distance.
The 'mushy' feel comes from the drum shoes wearing in the same direction of the wearing of the drums and the self-adjusting mechanism not working past the second day of use - that way, once the brakes are applied, the slave cylinders in the drums have travel further...you get mush and not feel.
#52
11-01-2009, 07:35 AM
Just a thought but...
Maybe with the move of production to the US, the Fit will get rear Discs. Probably wouldn't happen until the next generation (or maybe the MMC) but hey... you never know.
tires are definitely the best upgrade you can do to improve stopping distance. The stock brakes have enough power to lock up the current tires so your contact points with the road will be the best 1st upgrade.
Something's not right with the above statement. If you are saying that a car that is 200lbs heavier and stops shorter than the fit isn't doing very well, the fit must be AWFUL. Also, Im sure some of the civic's stopping distance has to do with it's wider tires and probably less to do with the rear discs. (there's 11% more contact patch stopping only 8% more weight)
Almost any brake would be fine in normal driving. Brakes are most necessary at the extremes, like when jamming on the brakes to avoid a collision. Rear Discs would improve the extremes.
From a cost standpoint, I would say that the order would be Tires (and lighter wheels - to cut rotational mass) --> big brake kit. - I wouldn't spend money on replacing the rotors and pads and would save up for a better brake system altogether. Pads alone is one thing but once you get into the price range of replacing all of the pads and rotors, you might as well consider an entire upgrade. (I'm not saying that it's just a few bucks more for the kit but you're getting "closer")
~SB
Maybe with the move of production to the US, the Fit will get rear Discs. Probably wouldn't happen until the next generation (or maybe the MMC) but hey... you never know.
I think if you want your car to stop in a shorter distance, better tires will get you a lot more than 8 feet. For example, switching from a Michelin all-season tire to a summer tire made a 10ft difference in stopping distance in the dry, and 20 ft over the next best tire in the wet (reference: Tire Test: All-Season vs. Snow vs. Summer).
The Civic doesn't do very well for braking despite having rear discs; Edmunds measured about 130 ft for a 2006 Civic EX with rear discs, which is on par with what they got for the Fit, which was 134 ft, though granted the Civic is about 200 lbs heavier (reference: 2006 Economy Sedan Comparison Test: Honda Civic vs. Mazda 3).
I know discs are better, I just don't think the drums are holding back the braking performance on a stock Fit in normal driving. I'm pretty sure I can lock the rear wheels with the handbrake, which would seem to suggest that the drum brake is plenty strong (unless my arm has more power than the brake system, but I don't think I'm that strong).
).~SB
Last edited by specboy; 11-01-2009 at 07:38 AM.
#53
11-01-2009, 11:07 AM
Something's not right with the above statement. If you are saying that a car that is 200lbs heavier and stops shorter than the fit isn't doing very well, the fit must be AWFUL. Also, Im sure some of the civic's stopping distance has to do with it's wider tires and probably less to do with the rear discs. (there's 11% more contact patch stopping only 8% more weight)
From a cost standpoint, I would say that the order would be Tires (and lighter wheels - to cut rotational mass) --> big brake kit. - I wouldn't spend money on replacing the rotors and pads and would save up for a better brake system altogether. Pads alone is one thing but once you get into the price range of replacing all of the pads and rotors, you might as well consider an entire upgrade. (I'm not saying that it's just a few bucks more for the kit but you're getting "closer")
.
#54
11-01-2009, 12:30 PM
)~SB
#55
11-01-2009, 12:57 PM
Disc Brakes dissipate heat better and also shed water/snow/foreign objects much better than drums. This helps prevent brake fade, especially under repeated braking. When you add better tires, this will put more work on the brake system itself (as cheap tires that would lock up with the stock brakes and slide don't grip as well as sticker ones) The resulting work is put on the brake system. (many other reasons but I gotta go outside and play in the sandbox with my son )
~SB
)~SB
I understand and agree with the advantages of discs over drums -- front discs are ubiquitous now for a reason -- I'm just not sure how much it buys you at the rear.
I thought rear discs were probably the last upgrade to do for better braking, after better tires/lighter wheels and front brakes... but if you're saying rear discs are going to save me, moreso than the others, in a possible collision situation, then I'll move that up in my list of upgrades (assuming a conversion kit ever comes out
).
Last edited by clicq; 11-01-2009 at 12:59 PM.
#57
11-01-2009, 03:50 PM
Isn't it too cold to play outside in VT yet?!
I understand and agree with the advantages of discs over drums -- front discs are ubiquitous now for a reason -- I'm just not sure how much it buys you at the rear.
I thought rear discs were probably the last upgrade to do for better braking, after better tires/lighter wheels and front brakes... but if you're saying rear discs are going to save me, moreso than the others, in a possible collision situation, then I'll move that up in my list of upgrades (assuming a conversion kit ever comes out).
I understand and agree with the advantages of discs over drums -- front discs are ubiquitous now for a reason -- I'm just not sure how much it buys you at the rear.
I thought rear discs were probably the last upgrade to do for better braking, after better tires/lighter wheels and front brakes... but if you're saying rear discs are going to save me, moreso than the others, in a possible collision situation, then I'll move that up in my list of upgrades (assuming a conversion kit ever comes out
).44deg F here at 9am and I saw people in short sleeves, shorts, etc... We've had a few overnights here below freezing but today it was in the 50's and yesterday in the 60's. Have also seen some snow on the Mountains and i'm sure Killington and a number of the others are gearing up for the ski Season.
As for the Discs, I would definitely say those are the last to upgrade but would consider doing a full upgrade to a Big Brake system before going to OEM rear Disc. Getting oem parts is usually expensive and for the performnce gain you would get out of adding OEM rear Disc, you would probably be 3/4 of the way towards a complete brake upgrade (upgrade all 4 calipers, discs, etc...) which would definitely be a huge improvement over stock.
~SB
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