| need4spd |
| It seems to me that stopping distances with the MDX are a tad longish. Maybe it's the ABS threshold, maybe the tires, but maybe the brake pad materials, size of discs or calipers. Has anyone upgraded their brakes in any way? Considering it? Are there even any packages available to do that? I know that aftermarket brake mfrs like Stop Tech make brake upgrade kits for BMW X5s, but does anyone make a kit for MDX's? Seems that could be a few thousand $$ well spent.... :eek: ,or maybe not :confused: |
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| hockeyplayer |
| Wow, that is the first time I have heard of someone unhappy with the braking distance. I have to say that was the first thing that impressed me about the MDX. With such a large "bus" the stopping is always predictable and distances are alot shorter than I would have thought. Interesting nonetheless.:( |
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| rvehock |
| I also am very happy with the braking of my MDX, I feel very safe in it:4: |
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| ardvarkus |
If you can cause the tires to lock up (and thereby active ABS) the brakes are 'big enough' ....
The ultimate determinant of stopping distance is the tire/surface contact friction.
HOWEVER, if you are using the brakes REPEATEDLY, speeding up and slowing down dramatically (motocross, severe off-road racing, etc) then the SIZE of the rotor and pad becomes important due to heat dissipation. This is the PRIMARY reason to upgrade brakes/increase rotor size (and thickness,ventilation) larger wheels, etc...
It is important to note that the ABS system is a fairly complex animal: the ABS computer is coded with firmware that 'knows' the dynamic characteristics of the brake system hydraulics. If you change the VOLUME of brake fluid (by going to larger calipaers) the system will not work as designed...period. Slapping a 'big caliper kit' on any vehicle with ABS is asking for problems, unless the kit has been designed with that ABS system in mind.
I'd venture the OPINION that spending $3k for larger brakes would (a) reduce your ABS performance and (b) marginally reduce first time. dry concrete stopping distance (maybe 5-10%)
Ard |
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| DaleB |
quote:
Originally posted by ardvarkus
If you can cause the tires to lock up (and thereby active ABS) the brakes are 'big enough' ....
The ultimate determinant of stopping distance is the tire/surface contact friction.
HOWEVER, if you are using the brakes REPEATEDLY, speeding up and slowing down dramatically (motocross, severe off-road racing, etc) then the SIZE of the rotor and pad becomes important due to heat dissipation. This is the PRIMARY reason to upgrade brakes/increase rotor size (and thickness,ventilation) larger wheels, etc...
It is important to note that the ABS system is a fairly complex animal: the ABS computer is coded with firmware that 'knows' the dynamic characteristics of the brake system hydraulics. If you change the VOLUME of brake fluid (by going to larger calipaers) the system will not work as designed...period. Slapping a 'big caliper kit' on any vehicle with ABS is asking for problems, unless the kit has been designed with that ABS system in mind.
I'd venture the OPINION that spending $3k for larger brakes would (a) reduce your ABS performance and (b) marginally reduce first time. dry concrete stopping distance (maybe 5-10%)
Ard
In addition, the material used in racing brake linings is most efficient at higher operating temperatures. So you will likely gain little in day to day driving for all that additional cost, and have brakes that require more effort and likely are noisier.
The best upgrade is simply better linings that fade less than stock, and perhaps have a higher friction coefficient. But that usually translates to some degree of faster lining and/or rotor wear.
Another upgrade is a totally flushed system, and converting to silicone fluid which has a much higher boiling point.
Again, these are not the best solutions in terms of cost and practicality.
Driver awareness is proabably the biggest factor in having adequate brakes work for you in any situation. |
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| need4spd |
| Interesting replies. I don't see, however, how additional brake fluid volume would affect the ABS map. The ABS system functions by sensing the rotational speed differences of the wheels, which has nothing to do with fluid volume. Also, fluid is (relatively) incompressible, so pushing on one end of the system (the pedal) will push on the other end (the caliper piston) regardless of the volume in-between. What would be affected by a caliper change is the ratio of caliper piston area to master cyl. piston area, but again, I don't see how that would affect the ABS theshold since again, that depends on rotational speed and lock up threshold. Now, I agree that the X stops pretty well, but even among its peers, I think the others, like the X5 and ML, stop better, and the difference between the X and sports sedans is quite marked. I don't expect the X to stop as well as a sports sedan, of course. I guess I just have to make the mental adjustment when switching between cars (sort of like when you drive a rental car; man, one time I nearly lost it when I drove my econobox rental car "normally" on a freeway on-ramp!). |
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| DaleB |
quote:
Originally posted by need4spd
(sort of like when you drive a rental car; man, one time I nearly lost it when I drove my econobox rental car "normally" on a freeway on-ramp!).
Wow, does that bring back memories. How about driving a Chevy Chevette rental from San Diego to LA.
There was a vehicle that you feared any long upgrade because it would flatten out at about 50 mph. I remember pulling over to let an old VW beetle pass me.
Then fear again on the downgrade that you did not coast too fast, because you might have to use the brakes! (Maybe that should be "use UP" the brakes).
And that was on 101 not 5. They probably would not have allowed it on the Grapevine if they knew how it was so inadequate. |
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| mdxxxx |
quote:
Originally posted by DaleB
...Then fear again on the downgrade that you did not coast too fast, because you might have to use the brakes! (Maybe that should be "use UP" the brakes).
And that was on 101 not 5. They probably would not have allowed it on the Grapevine if they knew how it was so inadequate.
What a scary thought! I wonder of they will ever have 'car capability inspections' in regards to the formidable Grapevine!.. |
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| ardvarkus |
quote:
Originally posted by need4spd
Interesting replies. I don't see, however, how additional brake fluid volume would affect the ABS map. The ABS system functions by sensing the rotational speed differences of the wheels, which has nothing to do with fluid volume. Also, fluid is (relatively) incompressible, so pushing on one end of the system (the pedal) will push on the other end (the caliper piston) regardless of the volume in-between. What would be affected by a caliper change is the ratio of caliper piston area to master cyl. piston area, but again, I don't see how that would affect the ABS theshold since again, that depends on rotational speed and lock up threshold. Now, I agree that the X stops pretty well, but even among its peers, I think the others, like the X5 and ML, stop better, and the difference between the X and sports sedans is quite marked. I don't expect the X to stop as well as a sports sedan, of course. I guess I just have to make the mental adjustment when switching between cars (sort of like when you drive a rental car; man, one time I nearly lost it when I drove my econobox rental car "normally" on a freeway on-ramp!).
Yep, from a simplistic view you'd think so.
But you need to recognize the system is not static: in a dynamic process things get pretty complex. For example, as a wheel starts to lock, the ABS computer 'releases' the brake.
OK, fine-
It then waits a certain period of time, then applies the brakes again- all it knows is that when it was designed at the factory, if it simply waited 27 milliseconds (for example) between those two actions, the system would work properly- if you have more volume in the caliper (and perhaps a larger diameter piston) it takes longer for sufficient brake fluid to enter the caliper and apply brake force... All of a sudden, your big brake kit seems to just squash away when you you stop on it- not enough dynamic anticipation in the fluid management.
Keep in mind that the time constant between actions may in fact vary based on speed, how much slippage was detected, pressures, etc. In fact, the system may change the pressure applied to the caliper so it is DIFFERENT than 'so pushing on one end of the system (the pedal) will push on the other end (the caliper piston)'....
I've done a bit of research on this for another vehicle (which really does need bigger brakes) - you can find some pretty interesting info on this on-line...I could find the bookmarks I had otherwise I'd have posted them.
If you find a reputable vendor- (A company who has enough financial resources that they won't risk marketing an unsafe product)- you have a better chance of buying a kit that has been tailored to you vehicle.
Ard |
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| DaleB |
quote:
Originally posted by mdxxxx
What a scary thought! I wonder of they will ever have 'car capability inspections' in regards to the formidable Grapevine!..
I think it's selective evolution. Survival of the fittest. The one's that don't make it they just pick up on the side of the road somewhere, probably near the bottom, or they have fallen off at some point never to be seen again! :eek: |
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| DavidM |
I just want to upgrade my brakes so that they don't click when changing directions!!!!:3:
I had the shop put in the shims as recommended on this site. It worked for a few days, but now it's right back to the same old crap.
What can be done.....
Surely if the cause of the problem can be identified, then a solution can be crafted......right???:8: :1zhelp:
I am so sick of clients asking me
"What's that clicking sound.....?"
I just know what they're thinking.......
"Gee, a $42,000+ vehicle (almost brand new)....what a piece of (*&^*@!^%(^+^%!?#_!!!!!!"
ACURA ARE YOU LISTENING!!!!!??????? FIX THIS!!!!:14: :28: |
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| cmdpm |
i started a thread on this subject, related to the recent car and driver article that compared the MDX to the vw touareg, lexus gx470,(MDX), bmw x5, volvo xc90, land rover and gmc envoy. they finished in that order in the review, incidentally.
the stopping distance of the MDX was 200 ft from 70 mph. this was 30 ft longer than the 1100 lb. heavier vw.
when driving the MDX the braking performance may seem fine but in an emergency situation i feel that compared to the much heavier vw (and many cars on the road with shorter stopping distances) 30 more ft can be HUGE!-the difference between avoiding an accident or....
it seems that the most reasonable/cost-effective way to improve the stopping distance is to switch to higher friction brake pads. i wouldn't care too much if this meant quicker wear or rotor work at some point. i am only concerned about avoiding accidents.
from articles i have read the front brakes generate 80% of the braking effect, so to upgrade would involve "only" changing the front rotor/caliper/pad/cable set-up (to brembos?).
i speculate that acura designed the brakes for most buyers who are not driving enthusiasts and may not be able to handle or live with high performance brakes.
does anyone know of a source for high performance brake pads?
chris |
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| DaleB |
quote:
Originally posted by cmdpm
does anyone know of a source for high performance brake pads?
chris
You might check tirerack.com I know they carry some. I am sure many auto shops carry stuff that is better than stock, like the higher end Raybestos.
I am not sure they have fits for the MDX yet, but should soon you would think. |
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| ardvarkus |
quote:
Originally posted by cmdpm
so to upgrade would involve "only" changing the front rotor/caliper/pad/cable set-up (to brembos?).
i speculate that acura designed the brakes for most buyers who are not driving enthusiasts and may not be able to handle or live with high performance brakes.
does anyone know of a source for high performance brake pads?
chris
So which is it? A cosmetic upgrade to the pads (so we can add it to our 'equipment list' under the posts) or an actual upgrade to the calipers/rotors/etc? $100 or $3500??
I speculate that 'high performance brakes' are easy to drive and "handle"- they just cost a lot to keep repaired- rotors and pads wear quickly.
Keep in mind that if you change pads to a high friction compund, and don't address the removal of the heat, you may have premature rotor warpage.
BTW, let's look at stopping distances specmanship: in stopping from 70MPH over 200 feet, how fast will you be going at that last 30 feet- the Touareg will be stopped, and the MDX will be going maybe 10mph... So I suppose in the event that the sole determinant is stopping distance, and there is no way to avoid an obstacle dead ahead, you may be right- better brakes may avoid a minor accident.
I'd be interested to see if changing pads improves braking distance dramatically- and even if it did, I'm not sure it is worth it!
Ard |
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| ardvarkus |
BTW, has anyone had to replace brake pads yet?
I've got 45k on mine, and just measured the pad thickness yesterday. Around 7.0 mm on the fronts and 5.8mm on the rears...
In retrospect, perhaps there IS room for softer pad material....If my pads needed replacement, I'd be OK with 45k miles. Although I remain (somewhat) concerned how increased pad friction affects dynamic ABS performance.
Perhaps some of you city traffic folks have different pad lifes?
Ard |
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| need4spd |
| Here is a site for Mintex high performance pads. Mintex Brake Pads Click on the "Applications" button and you'll find they have pads for both front and rear MDX brakes. This is a UK site, but Mintex pads are available from a number of U.S. suppliers on the web and locally at your high performance imports parts places. |
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| tigmd99 |
I was just reading on the MDX when i read that the '03 MDX has twin-piston front calipers, which is apparently new this year. So, i assume the '01-'02 had SINGLE piston calipers. I will also assume the rear calipers are also SINGLE-piston for all years.
Not to be a prick, but that braking system on MDX is certainly substandard. MDX is about 4500 lbs. Just for comparison, my lowly 2002 4Runner (weighs about 4100 lbs) has FOUR-piston 13" front v-disc calipers on each side. My 4runner weighs less, yet has MORE piston on the front calipers. (My rear brakes are 11.6" drums.) The GX470 has four-piston front calipers and two-piston rear calipers (same for 2003 4Runner Ltd.). I am sure the VW is just as well equipped.
Changing pads will not improve braking distance that much. Nor changing to wider tires (which weighs MORE than OEM-sized tires; thus, somewhat offsetting the greater contact area). The equipment is not up to standard set by the class. With an SUV weighing that much, you need more than just twin-piston front calipers on 11.8" discs...certainly, you need more than single-piston calipers in '01 and '02 models.
Thanks. |
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| donsev |
At the risk of repeating myself I have included the slightly edited text of my reply as well as a link to a previous discussion on the MDX's braking performance.
Here is a good article from Car and Driver on automotive brakes; Shedding Light on Fading Brakes.
It is a comparative review of aftermarket brake kits for the Suby WRX with baselines against the stock pads and Hawk replacement pads. The article focuses on brake fade but the principles are wholly applicable to the discussion on the MDX braking performance and answers most of the above questions.
Some sample quotes:
quote:
Assuming a brake system is ...strong enough to lock a wheel... the stopping distance is largely a function of tire traction, not brakes. Think of it this way: All brake systems, stock and aftermarket, are able to activate the ABS, so how could a stronger brake shorten a stop? Eric Dahl, a brake engineer from Brembo.
quote:
Brake pads have a huge effect on both pedal feel and fade. Pads are designed to operate in predetermined heat ranges. For example, a pad made for the demands of racing — and the subsequent intense heat that is generated — might not perform well when "cold." Conversely, a pad meant for street use — one that has to work well when it's cold as well as when it's moderately hot, without squealing — could lose effectiveness once it's punished on a track. There's no such thing as a pad that works perfectly at every temperature. Since street pads have to work when they're at minus-30 degrees, they tend to give up performance at higher temperatures
Now, when looking at the braking performance of the MDX as conducted by automotive reviews, you have to look at three issues; 1)How good is the dry braking performance of the tire that it is is shod with, 2)What is the size of the contact patch (i.e. tire width), and 3)How does it compare to other vehicles.
Unfortunately, there is no definitive answer to the first question. I have not found a comprehensive review (ala Consumer Reports) that has assessed the dry braking performance of the Michelin Cross Terrain. And also unfortunately, the best anecdotal evidence that we have shows (at first glance) the Cross Terrain dry braking capabilities to be subpar. In the Car and Driver article "The Bradsher Bunch", the two worst performing tires in the 70-0mph test were Michelin Cross Terrains, even though they were on the two lightest vehicles (Acura MDX, and GMC Envoy). But, to be fair to the Cross Terrains, almost every other vehicle in that test was wearing "higher performance" rubber. Also, they were wearing wider (sometimes MUCH wider) tires, which leads to the next issue - contact patch.
All other things being equal, braking traction will increase proportionally to the size of the contact patch adhering to the road surface. Also, all other things being equal, the contact patch will increase proportionately to the tire width. Thus, with a properly calibrated braking system, wider tires will stop the vehicle shorter than narrower tires. Almost every other SUV of comparable size to the MDX wears wider tires. In the "Bradsher Bunch" review, the Aviator and Envoy wore 245s, the Touareg, Discovery, and BMW X5 wore 255s, the GX470 even wore 265s. The only other vehicle equipped with the MDX's narrow 235s was the Volvo XC90 (which to compensate, was wearing Pirelli Scorpion Zeros). This undoubtedly contributed to the MDX's 200 feet 70-0mph stopping distance which was 16 feet longer than THIS test average of 184. But how does that distance compare to other cars.
Since many people are replacing family sedans with SUVs, how does the MDX's dry braking performance compare to those more traditional cars. In the Car and Driver family sedan comparison Concealed Carry the 70-0MPH braking distance average was 203 feet. This is with bread-and-butter family sedans weighing over 1000lbs LESS than the MDX. The MDX's stopping distance is better than the Chevy Impala LS, the Dodge Intrpid SE, the Ford Taures SEL, the Honda Accord LX V-6, and the Hyundai XG350. And within 9 feet of the class leader Toyota Camry SE V-6.
In a comparison of SPORT SEDANS (Waiting for a Bimmer Beater ) the MDX's stopping distance is within 9 feet (96%) of the distance required of all but two cars; the Acura 3.2TL Type-S require 192 feet, the Audi A4 required 194 feet, the Infinity G35 required 191 feet, and the Volkswagen Passat 4Motion required 191 feet. Only the BMW 330i and MB C320 stopped in less than 190 feet.
So if you wish to improve the dry braking performance of your MDX (to beyond sport sedan levels, and at the expense of foul weather performance) simply replace the tires with wider, "grippier" tires - that's what the other SUV manufacturers have done.;)
But just as important as braking distance for a safe driving experience (perhaps more important) is braking feel - and many automotive reviews comment very positively on the good linear feel of the MDX's brakes (C&D "Bradshers Bunch";
quote:
Steering was precise, the brakes unfailingly predictable
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| ndahbar |
I got the solution for you: Ditch the MDX. Buy a Porsche. Best brakes period. :p
On a more serious note, uhm, I personally think the 2003 MDX has SUPERB brake feel, I dunno about brake distances, never measured, and it's tough to determine, especially w/o trying a FULL EMERGENCY brake application, which I have yet to do. =p
I don't think it's a function of the ABS, I mean it's not the state-of-the-art version, as it's 4-channel only (as opposed to higher in more expensive machines) but I am sure the tires have something to do with it.
Brake feel and vehicle stability are the vital factors you should look at, not minimum brake distance. |
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| ardvarkus |
quote:
Originally posted by ndahbar
especially w/o trying a FULL EMERGENCY brake application, which I have yet to do. =p
.
Had the opportunity to try one this afternoon....
On the way home from skiing, tired, futzing with my GPS, look up and the truck in front is stopped on US 50... just stomped and waited.
Stopped 5 feet from his bumper.
Had I installed twin cylinders up front, plus better pad material, I'd have had AT LEAST 10 feet. :)
Ard |
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| need4spd |
quote:
the two worst performing tires in the 70-0mph test were Michelin Cross Terrains, even though they were on the two lightest vehicles (Acura MDX, and GMC Envoy). But, to be fair to the Cross Terrains, almost every other vehicle in that test was wearing "higher performance" rubber.
Has anyone put tires other than Cross Terrains on their MDX? If so, which ones and do they perform better than the Michelins? I would think that if you drove your X 90-100% of the time on highways, that you'd be better off with more streetable tires. But which ones? |
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| tigmd99 |
Nad,
4-channel is the most you can have! You have 4-wheels. All cars nowadays have 4-sensors. High end cars have 4-channels to INDIVIDUALLY control each wheel...you have 4-wheels and you have 4-channels (along with 4-sensors).
Porsche, BMW, Mercedes, etc. all have 4-channels at most. No more. |
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| presten |
| I find it hard to fathom the logic that says that bigger calipers/bigger brakes will improve the stopping distances on the MDX or any car for that matter. For a one time panic stop...if you can lock up the wheels or activate the ABS, what further improvement can you ask for that can be gained by "bigger brakes"? Now if you want to talk repeated stops or hard driving use such as racing or perhaps heavy towing, then there is definitely something to be gained by upgrading the capacity of the brakes. If you want to reduce the stopping distance in a panic stop (and I sure hope these are one time events), then tires, tires, tires are the only answer. Fatter or softer are the way to go. If you want to demonstrate this to anyones satisfaction, put a full set of NASCAR style racing slicks on your car and try a panic stop....be prepared to have the fillings pulled from your teeth!! Unfortunately, this only works on absolutely dry pavement and the slightest hint of water makes racing slicks into true "slicks". One other factor that effects stopping distance is "control" of the vehicle. If the driver is having trouble keeping the car under control in a panic stop situation...there definitely will be an increase in stopping distance. My evaluation of the MDX in those types of stops is that it truly a "hands off" vehicle. Just stand on the brakes and hold on, no corrections were necessary! |
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| tigmd99 |
quote:
Originally posted by presten
For a one time panic stop...if you can lock up the wheels or activate the ABS, what further improvement can you ask for that can be gained by "bigger brakes"?
That's the whole point! If you have bigger discs and more pistons, you can lock up your wheels faster (more contact area). Remember, the weight of the vehicle is going forward.
MORE CONTACT area between your piston/caliper and the disc = faster more powerful stop.
Yes, tires do make a lot of difference...but you canNOT discount the piston/caliper and disc roles.
Thanks. |
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| DaleB |
Yes, but wider contact patch, generally means more tendency to hydroplane. Plus, a bigger patch is more friction when you are NOT braking also.
But all things considered, there are nice compromises that can be made. I think "Harry" with his 19" wheels and Scorpion tires obtained a wonderful balance of better handling, likely better braking, with very few trade-offs, except maybe a little less agility in the snow. |
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| ardvarkus |
quote:
Originally posted by tigmd99
That's the whole point! If you have bigger discs and more pistons, you can lock up your wheels faster (more contact area). Remember, the weight of the vehicle is going forward.
MORE CONTACT area between your piston/caliper and the disc = faster more powerful stop.
Yes, tires do make a lot of difference...but you canNOT discount the piston/caliper and disc roles.
Thanks.
Thai-
Methinks you are wrong here.. and there is A LOT of info available to prove it.
It takes MILLISECONDS for pads to grip and lock. Bigger pads/bigger rotors/20 cylinders doesn't turn a 5 millisecond loc into zero... the speed to LOCK is of no consequence in determining stopping dstance
This is PROVIDED THE EXISITING BRAKES CAN LOCK THE WHEEL ON DRY ASPHALT...
There are several reasons to "upgrade" brakes:
1. In repeated, heavy braking, tremendous heat is generated... larger pads control temperatur...larger pads allow use of friction material than can handle heat yet stop. Larger rotors will disperse heat better..larger rotors will not warp as quickly.
2. More cylinders can generate more force with better uniformity across a larger pad...they can also be packaged easier out at the outer geometric rim of a large diameter rotor..they can also disperse heat better....yes, the calipers get hot, the brake fluid boils..the brakes fade.
3. Here is the most important reason on this forum: they look cool.
On any vehicle there is a lot of engineering done to match all components of the system to generate proper pedal feel... unless I was prepared to spend $4k per axle, I'm not going to mess with brake system design.
Ard
Ard |
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| harmonr1 |
quote:
Originally posted by ardvarkus
...Stopped 5 feet from his bumper. Had I installed twin cylinders up front, plus better pad material, I'd have had AT LEAST 10 feet. :)
If you had looked up a second later, it wouldn't matter.:awais: |
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| tigmd99 |
Also, wider tires = more weight (unsprung weight). Therefore, it is not a total win-win situation when you get wider tires.
Thanks. |
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| ardvarkus |
quote:
Originally posted by harmonr1
If you had looked up a second later, it wouldn't matter.:awais:
Either way a change of underwear was called for... |
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| DaleB |
quote:
Originally posted by tigmd99
Also, wider tires = more weight (unsprung weight). Therefore, it is not a total win-win situation when you get wider tires.
Thanks.
For the same size wheel, yes, but:
Wider means more rubber, but remember the sidewalls of lower profile tires have shorter sidewalls.
In addition, high quality (as in expensive) after-market wheels, can weigh the same or even less than the smaller stock wheels. |
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| frostyra |
quote:
Originally posted by tigmd99
MORE CONTACT area between your piston/caliper and the disc = faster more powerful stop.
Nada. More contact area ONLY helps with heat dissipation. The old (and still accurate) friction formula says that Friction = coefficient of friction between the two materials [pads and rotors] X applied force [pounds of force that the pads are applying to the rotors].
And I fully agree with DaleB's assertion that wide tires are more prone to hydroplaning. If it doesn't rain hard where you live and drive, no problem; if it does, you may be floating off into oblivion with those wide tires.
Also remember that the training phrase for ABS brakes is "Stomp and Steer"; one without the other isn't too useful. |
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| ardvarkus |
quote:
Originally posted by frostyra
Nada. More contact area ONLY helps with heat dissipation.
I'll quibble a bit- larger pads (ie more contact area) reduce the heat density- this can prevent the formation of gas, which can cause sponginess (this is why rotors are slotted or drilled- to release trapped gas from the intense surface heating of the pad material...
so, same diff- lower heat denisty versus better dissipation. I agree wit your post-
Interestingly, increased drilling can lower the mass of the rotor and actually decrease the heat dissipation. Not much air flows through the holes- dual wall rotors with internal vanes to direct airflow are ideal- as are vents to direct airflow into the wheel wells... even wheels wich will 'suck' heat from the rotor/wheel will help in race applications.
Ard |
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| donsev |
I found this quote from an article in the May 2003 issue of Popular Science titled "My 1,500-Horsepower Brake Job" somewhat amusing;
quote:
...The 1989 Turbo rotors that he rehabilitated were originally cast by Porsche with the myriad holes for gas venting and rapid water dissipation that also look so cool. (Here's how cool: I remember asking a Ferrari PR guy why the full-race 360 Modenas at a Ferrrari Challenge race had channeled but solid rotors while the ordinary road 360's rotors were cross-drilled. "Cosmetics," he said.)
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| DaleB |
| The holes for some cooling, but the slots for routing excessive debris out of the contact area, right? The slots are probably more useful. |
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| peterb |
quote:
Originally posted by ardvarkus
Yep, from a simplistic view you'd think so.
But you need to recognize the system is not static: in a dynamic process things get pretty complex. For example, as a wheel starts to lock, the ABS computer 'releases' the brake.
OK, fine-
It then waits a certain period of time, then applies the brakes again- all it knows is that when it was designed at the factory, if it simply waited 27 milliseconds (for example) between those two actions, the system would work properly- if you have more volume in the caliper (and perhaps a larger diameter piston) it takes longer for sufficient brake fluid to enter the caliper and apply brake force... All of a sudden, your big brake kit seems to just squash away when you you stop on it- not enough dynamic anticipation in the fluid management.
Keep in mind that the time constant between actions may in fact vary based on speed, how much slippage was detected, pressures, etc. In fact, the system may change the pressure applied to the caliper so it is DIFFERENT than 'so pushing on one end of the system (the pedal) will push on the other end (the caliper piston)'....
I've done a bit of research on this for another vehicle (which really does need bigger brakes) - you can find some pretty interesting info on this on-line...I could find the bookmarks I had otherwise I'd have posted them.
If you find a reputable vendor- (A company who has enough financial resources that they won't risk marketing an unsafe product)- you have a better chance of buying a kit that has been tailored to you vehicle.
The ABS does not wait any preset period of time-it applies brake again as soon as it detects that wheel is spinning freely,i.e. got "unlocked".It knows that by comparing the speed of each wheel and it acts when difference is detected.
Ard
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| peterb |
quote:
Originally posted by tigmd99
I was just reading on the MDX when i read that the '03 MDX has twin-piston front calipers, which is apparently new this year. So, i assume the '01-'02 had SINGLE piston calipers. I will also assume the rear calipers are also SINGLE-piston for all years.
Not to be a prick, but that braking system on MDX is certainly substandard. MDX is about 4500 lbs. Just for comparison, my lowly 2002 4Runner (weighs about 4100 lbs) has FOUR-piston 13" front v-disc calipers on each side. My 4runner weighs less, yet has MORE piston on the front calipers. (My rear brakes are 11.6" drums.) The GX470 has four-piston front calipers and two-piston rear calipers (same for 2003 4Runner Ltd.). I am sure the VW is just as well equipped.
Changing pads will not improve braking distance that much. Nor changing to wider tires (which weighs MORE than OEM-sized tires; thus, somewhat offsetting the greater contact area). The equipment is not up to standard set by the class. With an SUV weighing that much, you need more than just twin-piston front calipers on 11.8" discs...certainly, you need more than single-piston calipers in '01 and '02 models.
Thanks.
Actually changing tires to narrower would improve braking-friction is proportional to the force pushing the two surfaces together but not dependent on the surface area.Kind of counterintuitive. |
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| renov8r |
quote:
Originally posted by peterb
Actually changing tires to narrower would improve braking-friction is proportional to the force pushing the two surfaces together but not dependent on the surface area.Kind of counterintuitive.
no-- simple material science says tat coefficent of friction is independant of contact area. Wider tires empiraclly do improve stop distance, so some ot_er factor is at work. Best explanation used to be t_at micro-surface of tire is acutually deformin_ into road surface BUT t_en you would be correct t_at force distributed over wider area results in less PSI a_ainst surface--_mmmm
So t_at leaves materials properties & you know w_at? Tire makes do use softer (more sticky/more friction) rubber compounds in wider tires...
I dont t_ink you can _et a narrow tire in a sticky compound.
{btw t_e keys between F & J stopped workin_ sorry} |
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| ardvarkus |
(Disclaimer: this is based on simplistic, first order approximations)
The COEFFICIENT of friction is independent of area. It is the ration of force perpendicular to the surfact to the force along the surface. The force perpendicular is the weight, and the force along is the stopping force.
HOWEVER, as the surface are goes up, the force per sq inch goes down, so the overall result (the weight) remains the same.
So then you get into dynamic coefficients, surface deformation of the contact patch, non-linearity of coefficients, etc.
End result: more rubber increases road holding ability....
duh. |
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| ndahbar |
quote:
Originally posted by tigmd99
Nad,
4-channel is the most you can have! You have 4-wheels. All cars nowadays have 4-sensors. High end cars have 4-channels to INDIVIDUALLY control each wheel...you have 4-wheels and you have 4-channels (along with 4-sensors).
Porsche, BMW, Mercedes, etc. all have 4-channels at most. No more.
Oops. I mixed that up with something else (electronic), sorry. :D |
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| ndahbar |
quote:
Originally posted by renov8r
no-- simple material science says tat coefficent of friction is independant of contact area. Wider tires empiraclly do improve stop distance, so some ot_er factor is at work. Best explanation used to be t_at micro-surface of tire is acutually deformin_ into road surface BUT t_en you would be correct t_at force distributed over wider area results in less PSI a_ainst surface--_mmmm
So t_at leaves materials properties & you know w_at? Tire makes do use softer (more sticky/more friction) rubber compounds in wider tires...
I dont t_ink you can _et a narrow tire in a sticky compound.
{btw t_e keys between F & J stopped workin_ sorry}
LMAO now that was the funniest post on this site for 2004. I was wondering WHAT ON EARTH is he typing and then I read the last sentence, hahahah. :2:
Ok fine, it wasn't that funny. :1: And his only problem were the G and H keys. |
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