Welcome to the North American Subaru Impreza Owners Club Tuesday May 5, 2015
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC General > Newbies & FAQs

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 04-08-2014, 07:22 PM   #601
boost-o-matic
Scooby Specialist
 
Member#: 248364
Join Date: Jun 2010
Chapter/Region: SCIC
Location: SoCal
Vehicle:
2010 Huevos grandes
WRX Dom 1.5XTR E85 silver

Default

Yes, great post. For those that actually track their car...they will want a brake upgrade to combat fluid fade, pad fade, and rotor heat fade. But like the OP said, sticky gummy tires is what shortens your braking distance. =)

Regardless, I just purchased some stop tech drilled rotors. Why? Because they look cool, were cheap, and have somewhat better fade resistance due to the cross drilling. Simple matter of increasing surface area for cooling.

There have been cars out there with insufficient brakes. One of them was the Eclipse turbo Spyder (convertible). With they're crappy calipers and 10.25" brake rotors on a 3,050lb car...they were severely overloaded. One panic stop from 60...fine. 2nd panic stop...double the stopping distance! It was really bad.

Anyway, my 2010 WRX I believe has an 11.8" rotor and sufficient calipers for auto-x and of course street duty. SInce I don't intend to "track" my car, I should do just fine.

Again, thanks to the OP who was posting this the day I bought my car almost 4 years ago! He just convinced me and validated my recent decision to buy sticky tires on wide 17x9 rims. =)
* Registered users of the site do not see these ads.
boost-o-matic is offline   Reply With Quote
Old 04-13-2014, 03:21 PM   #602
Awilson
Scooby Newbie
 
Member#: 387624
Join Date: Apr 2014
Default

Interesting read. Made me realize my thought process was illogical.
Awilson is offline   Reply With Quote
Old 04-22-2014, 07:20 PM   #603
diverescue0
Scooby Newbie
 
Member#: 388526
Join Date: Apr 2014
Chapter/Region: South East
Location: SC
Vehicle:
2004 subaru
blue

Default

Quote:
Originally Posted by kevosnowsti View Post
While I completely agree with everything your saying, and tires/pads have alot to do with stopping distance, if you track your car and have significantly more horsepower than stock, wouldn't it make sense to have better performing brakes since you will be reaching higher speeds?



these cars are set for the weight of the car and your brakes should be fine unless adding weight to the vehicle thats when you have issues with braking the reason the older cars brakes where changed was due to better disc brakes to eliminate drums but weight is a issue not speed just some info most of these cars are also standard that also gives you better braking with tranny
diverescue0 is offline   Reply With Quote
Old 04-22-2014, 07:29 PM   #604
diverescue0
Scooby Newbie
 
Member#: 388526
Join Date: Apr 2014
Chapter/Region: South East
Location: SC
Vehicle:
2004 subaru
blue

Default

Quote:
Originally Posted by Smoblikat View Post
Very informative post, though im not sure I understand it yet (ive read it 3 times already).

So I know that the tires are what technically stops the car, but if the brakes stop the tires, it would stand to reason that the brakes stop the car (A=B, B=C, A=C). Wouldnt larger breaks help if the car is heavier though? What I dont understand is that you cant just get a car to be an 800hp fire breathing, alcohol drinking monolith without adding more weight. So say my stock 2002 WRX with 200hp weighs 3500lbs (guessing), but if I add more parts to it, it will weigh more and be harder to stop due to inertia. So dont larger brakes actually help a car stop if it weighs more than a stock car with stock brakes?
usually when you make a upgrade change pipes you put a new item in and take the old one out. let say stock headers,they are made from cast iron very heavy stainless or steel alot lighter most upgrades mean you replace item most cases making car lighter unless its stereo equipment or towing good luck
diverescue0 is offline   Reply With Quote
Old 04-22-2014, 07:50 PM   #605
diverescue0
Scooby Newbie
 
Member#: 388526
Join Date: Apr 2014
Chapter/Region: South East
Location: SC
Vehicle:
2004 subaru
blue

Default

i agree completely sticky tires and mods don't usually add weight because you remove the stock item that is in most applications heavier unless stereo equipment or towing i have seen people with the bigger brakes with a 50000mile tire which is a harder tire to last probably should own two sets of tires 1 set sticky for play and the other hard for travel just a thought. old school brake changes for added power was due to poor drum brakes maybe this has stuck in peoples mind like the old chevelles,camaros,nova,charger well you get the idea
diverescue0 is offline   Reply With Quote
Old 04-22-2014, 08:13 PM   #606
diverescue0
Scooby Newbie
 
Member#: 388526
Join Date: Apr 2014
Chapter/Region: South East
Location: SC
Vehicle:
2004 subaru
blue

Default

Quote:
Originally Posted by prncnhorse View Post
I didn't read anything in the otherwise brilliant post about ABS brakes. We aren't talking about systems that lock up so there might still be something to the increased surface areas of larger rotors.

But, with that said, I once made a full pass in an 11 second Chevy II with original drum brakes on all 4 corners. Very Scary and dodgy but I didn't die!
yes drum brakes scary to drive they had to be set perfect or brake steer was crazy really had to learn to use transmission for braking or slowing car more control glad to see most cars have drums just for parking brake fun fun
diverescue0 is offline   Reply With Quote
Old 04-24-2014, 04:13 AM   #607
kboehme
Scooby Newbie
 
Member#: 362558
Join Date: Jul 2013
Chapter/Region: HIIC
Location: Honolulu, HI
Vehicle:
2013 Impreza WRX
Silver

Default

i think the reason most people swap brembos in their wrx's is because they look badass. and hell...its only money. bright red, blue, green, etc stock floating calipers look stupid and makes you look cheap. but bright painted brembos look so nice.
kboehme is offline   Reply With Quote
Old 04-24-2014, 11:06 PM   #608
kryptea
Scooby Newbie
 
Member#: 388765
Join Date: Apr 2014
Chapter/Region: SCIC
Location: SOCAL
Vehicle:
2012 STI sedan
DMG

Default

great read
kryptea is offline   Reply With Quote
Old 04-25-2014, 03:53 PM   #609
boost-o-matic
Scooby Specialist
 
Member#: 248364
Join Date: Jun 2010
Chapter/Region: SCIC
Location: SoCal
Vehicle:
2010 Huevos grandes
WRX Dom 1.5XTR E85 silver

Default

I threw some drilled Stop Tech's on my WRX for improved fade resistance. For $80 a piece, WTH not? Drilled = increased surface area, which = increased cooling. It may be minor, but every bit helps. =)
boost-o-matic is offline   Reply With Quote
Old 04-26-2014, 08:47 PM   #610
inelement207
Scooby Newbie
 
Member#: 389114
Join Date: Apr 2014
Chapter/Region: NESIC
Location: Brunswick, Maine
Vehicle:
2010 Impreza WRX 5dr
Satin White Pearl

Default

Very Informative! new to NASIOC and am planning to begin DIY's for 2010 WRX's as I work on mine. Of coarse first maintenance for the car is brakes (slotted/drilled Cough Cough) Will certainly reference this post. specifically this part:

Quote:
Originally Posted by Davenow View Post
"BUT MY BUDDY PUT BREMBOS ON HIS WRX WITH WTFBBQ ALLOY PADS, SUPERBUTTSEKS INCREDITAINIUM LINES AND CHUCK NORRIS BRAND FLUID AND IT STOPS WAY HARDER."


No, it doesnt. It has a lot more INITIAL BITE.
95% of people will mistake initial bite and/or decreased pedal travel, for the ability to stop shorter.

A locked tire is a locked tire. And while big brakes can lock a tire without having to push the pedal as hard, stock brakes can still lock the tires instantly if you nail the pedal. Therefor, stopping distance and rate of slowing down, is unchanged.
inelement207 is offline   Reply With Quote
Old 05-10-2014, 03:27 PM   #611
Suby nation
Scooby Newbie
 
Member#: 388350
Join Date: Apr 2014
Chapter/Region: SWIC
Default

I couldn't agree more with this thread. I'm glad others out there understand how traction and friction play a factor into stopping distance. I'm pretty sure there isn't alot of time attack setups here and if off road use brakes are least of concerns when going sideways, believe it or not traction helps control drifts not brakes bigger than stock. I myself have fried stock brakes at 185 mph not 70 or 75 mph on my 02 bug eye! Before the Cosworth build I don't think I could get over 150 mph and honestly didn't want to try. I don't have big brakes but plan to get them to not fried them on the circuit. My car is setup for time attack with tracks that have high speed swiping curves and high speed entry into hairpins. I doubt 75 percent of people on here will ever drive at those speeds and leap into corners at over 150 mph. But I'm not just putting bigger brakes, I'm reinforcing the chassis, caging it, and using a upgraded sedan suspension with adjustability for drive to and from the track (my car is not street legal in most states, mind you). This won't be your normal wagon when it is finished and honestly probably won't look like a wagon anymore. So unless your gonna spend 100k to build a time attack style car, brakes won't help! I've had my WRX since 02 and before the Cosworth insertion I never found the stock brakes incapable of doing there job and doing it well. Thanks for posting this, it sadly needed to be said.

Last edited by Suby nation; 05-10-2014 at 03:33 PM.
Suby nation is offline   Reply With Quote
Old 05-29-2014, 07:34 PM   #612
kclank
Scooby Newbie
 
Member#: 391870
Join Date: May 2014
Default

Very good points that I will take to heart and also save some money. great points
kclank is offline   Reply With Quote
Old 06-26-2014, 12:13 PM   #613
nossliw
Scooby Newbie
 
Member#: 394656
Join Date: Jun 2014
Default

Excellent points, great read!
nossliw is offline   Reply With Quote
Old 06-29-2014, 03:55 PM   #614
zkhennings
Scooby Newbie
 
Member#: 393895
Join Date: Jun 2014
Chapter/Region: NESIC
Location: Boston Massachusetts
Vehicle:
2002 Impreza WRX
Blue

Default

I have been through brake upgrades with my other car, and choosing good pads is by far the biggest change you can make to the stock brakes.

I honestly don't think that cross drilling is ever worth it, to get rotors done correctly (cast holes) it is expensive. The slotting is not terrible because it does not cause stress concentrations like the holes will, and they help deglaze the pads.

If you upgrade your pads to a race pad, well they are not going to work unless they are hot. Which is never during normal driving. I have performance friction pads that are made for the street and high performance applications. When they are cold, they grab about as hard as the stock pads, but for the times on the highway when I have needed to panic stop, the second they get hot from the hard braking they grab so hard, and twisty road spirited driving when they stay hot they are great. I feel this is the best of both worlds unless you have a dedicated track car.

I would not upgrade fluid unless it was noticed that your lines need to be bled randomly, which is a good indication you are boiling the brake fluid releasing gas.

I have ss braided hoses, and they do improve brake feel by feeling very solid when you have your brakes to the floor. They seem to hit a point where it is impossible to push them farther which gives great pedal feel. This is the secondary issue they help however. With the stock rubber lines, one came loose once from its bracket, and I drove it that way for maybe 10 minutes with it rubbing on the inside of the tire. When I got home, the line had been worn through all the way to the inner braid, in seriously 10 minutes. The SS braided ones are way tougher, but you have to inspect them often for cracks and wear. The nicest ones in my opinion have a clear coating over the SS braid to stop sand and other small particles getting in the braid and wearing through the inner line from articulation of the wheels. It is also important to note that the inner line of SS braided hoses is generally a teflon hose which can crack if bent too sharply. So make sure your lines are plenty long to prevent that from happening.
zkhennings is offline   Reply With Quote
Old 07-19-2014, 03:16 PM   #615
sukwoo21c
Scooby Newbie
 
Member#: 352452
Join Date: Apr 2013
Default

I should have got the STI first place thinking of upgrading brakes intercoolers and everything
sukwoo21c is offline   Reply With Quote
Old 08-27-2014, 10:15 AM   #616
blueRex11
Scooby Newbie
 
Member#: 298691
Join Date: Oct 2011
Default

I would think also that SS braided brake lines would hold their shape better internally, and help decrease less air bubbles in the lines? What do you guys think?
blueRex11 is offline   Reply With Quote
Old 09-01-2014, 03:38 AM   #617
DivineStrike
Scooby Newbie
 
Member#: 162037
Join Date: Oct 2007
Location: Charleston, SC
Vehicle:
2007 VW GTI Black
2007 CBR600rr White

Default

I just want to point out that Bigger Brakes will stop a car faster than a car with smaller brakes, given all other variables are the same, IE cars and tires. Obviously tires are the biggest thing that help in improving stopping distances. But you can't deny the physics in how much faster a larger brake slows the wheel down vs the smaller brakes. In panic braking I can see your point but panic braking isn't where you will get your shortest stopping distances. If you can respond appropriately the bigger brakes will stop you in less distance. But even in panic braking and you have to rely on ABS, larger brakes will still stop you faster as long as the ABS system can handle the larger brakes. The instant lock up from OEM brakes isn't as instant as you would like to think. It still takes time although very minimal and as minimal as that time is, bigger brakes will get you to that point faster.
DivineStrike is offline   Reply With Quote
Old 09-05-2014, 10:13 AM   #618
speedshifter
Scooby Newbie
 
Member#: 400815
Join Date: Sep 2014
Location: Baton Rouge, La
Vehicle:
2015 STI
DGM

Default

Very Nice informative write up; thanks for taking the time to put this together.
speedshifter is offline   Reply With Quote
Old 09-05-2014, 11:25 AM   #619
Bluefoton
Scooby Specialist
 
Member#: 141373
Join Date: Feb 2007
Chapter/Region: E. Canada
Location: Quebec, QC
Vehicle:
2008 2.5i-hatch -
now with a HID retrofit

Default

Quote:
Originally Posted by DivineStrike
I just want to point out that Bigger Brakes will stop a car faster than a car with smaller brakes, given all other variables are the same, IE cars and tires.
Oh lord. NO THEY WILL NOT. What limits your stopping distance is tyre/asphalt TRACTION, not the brakes.

Quote:
Originally Posted by DivineStrike
But you can't deny the physics in how much faster a larger brake slows the wheel down vs the smaller brakes.
Physics > you

Quote:
Originally Posted by DivineStrike
In panic braking I can see your point but panic braking isn't where you will get your shortest stopping distances. If you can respond appropriately the bigger brakes will stop you in less distance.
Really. Define then "panic" properly please. And define "appropriately", if you make such claims.

Quote:
Originally Posted by DivineStrike
But even in panic braking and you have to rely on ABS, larger brakes will still stop you faster as long as the ABS system can handle the larger brakes.
No.

Quote:
Originally Posted by DivineStrike
The instant lock up from OEM brakes isn't as instant as you would like to think. It still takes time although very minimal and as minimal as that time is, bigger brakes will get you to that point faster.
Please provide us with PROOF that increasing the size of the brakes reduces the travel time of the pads towards the disks up until lock-up point. Really, I want to see see figures, and estimates with tangible results (i.e. not a 12 nanosecond improvement).


Bluefoton is offline   Reply With Quote
Old 09-05-2014, 01:15 PM   #620
DivineStrike
Scooby Newbie
 
Member#: 162037
Join Date: Oct 2007
Location: Charleston, SC
Vehicle:
2007 VW GTI Black
2007 CBR600rr White

Default

Sigh, I am not arguing tires create the ultimate limit in stopping distances. Because obviously you can't stop shorter than their grip allows. Larger brakes create more friction and have more leverage than smaller rotors. More friction and leverage means the faster a force can be applied. Also meaning it requires less hydraulic pressure to achieve the brake torque needed for wheel-skid or threshold braking. All of which reduces the time needed to induce wheel-skid or threshold brake.


and how is physics greater than me? are you trying to tell me a smaller rotor with less leverage and friction applies force at the same rate a larger rotor with more leverage and friction? If you do ya need to go back to school.

And if I really need to describe panic braking to you, then you should do more research yourself.

There is a reason that new safety nannies are improving the reaction time of brake pressure to the brake. Things like Fords Brake assist or their version of Adaptive cruise control/crash avoidance system. The brake assist senses how fast you hit the pedal to amplify the pressure in the system to engage the brakes faster. Same thing for the crash avoidance system, it precharges the system to reduce stopping distances. Larger Rotors also improve the speed at which brakes engage. Although these new systems are greatly reducing the advantage of having larger brakes.

Braking appropriately is the same as optimal braking. Which is the amount of brake force required to get the best stopping distances. Other words called threshold braking.

Let me ask you something that is of a smaller scale.

What slows down a bicycle wheel faster; disk brakes or standard rim brakes?

There's a lot of info out there describing the benefit of larger brakes and how they help with stopping distances, not just heat dispersion. I will gladly link you my favorite article on the matter. But like I said there's a lot more info out there. And before you say anything, the article I am mentioning... I found it after previously having these little arguments with a couple people on another forum.
DivineStrike is offline   Reply With Quote
Old 09-06-2014, 03:24 PM   #621
Bluefoton
Scooby Specialist
 
Member#: 141373
Join Date: Feb 2007
Chapter/Region: E. Canada
Location: Quebec, QC
Vehicle:
2008 2.5i-hatch -
now with a HID retrofit

Default

Oh, I agree a substantial amount of time is lost in between the moment a driver touches the brake pedal, and full braking force. I just argue that it has nothing to do with disk/pad size. It's a compromise. The pedal needs to be progressive enough for the geriatric joe blow to be able to brake gently. The BA is supposed to detect a "slam" and apply full force even before the pedal reaches the bottom (don't 08+ Subarus have it actually?) - and the travel distance of the pedal itself is quite large.

Sorry, I was harsh, I was under the impression that after 13 posts, we went back to " igotmassivecrossdrilledferraribrakesandomgimstoppi ngonadime".

Also, my argument that bigger isnt better is only valid for the 1st braking, starting from cold conditions. When you have repeated sessions (lapping), it's a whole other story, as larger diameter = better heat dissipation = faster cooling.

Personally - on a track - I found the best upgrade to be a brand new brake fluid. Raising the boiling point, and running brand new juice with no water in it whatsoever made a hell of a difference.

No offence.
Bluefoton is offline   Reply With Quote
Old 09-06-2014, 05:06 PM   #622
DivineStrike
Scooby Newbie
 
Member#: 162037
Join Date: Oct 2007
Location: Charleston, SC
Vehicle:
2007 VW GTI Black
2007 CBR600rr White

Default

Quote:
Originally Posted by Bluefoton View Post
Oh, I agree a substantial amount of time is lost in between the moment a driver touches the brake pedal, and full braking force. I just argue that it has nothing to do with disk/pad size. It's a compromise. The pedal needs to be progressive enough for the geriatric joe blow to be able to brake gently. The BA is supposed to detect a "slam" and apply full force even before the pedal reaches the bottom (don't 08+ Subarus have it actually?) - and the travel distance of the pedal itself is quite large.

Sorry, I was harsh, I was under the impression that after 13 posts, we went back to " igotmassivecrossdrilledferraribrakesandomgimstoppi ngonadime".

Also, my argument that bigger isnt better is only valid for the 1st braking, starting from cold conditions. When you have repeated sessions (lapping), it's a whole other story, as larger diameter = better heat dissipation = faster cooling.

Personally - on a track - I found the best upgrade to be a brand new brake fluid. Raising the boiling point, and running brand new juice with no water in it whatsoever made a hell of a difference.

No offence.

No worries.

Everything you say in general is true. But the benefit of bigger brakes goes past heat dissipation. If I can explain this right, a bigger brake requires less brake pedal travel to achieve the point where you're threshold braking or skidding tires (due to the increased leverage and friction of the larger brakes). Less pedal travel is less hydraulic pressure. And less travel equals less time. Even in a single brake application. I don't have a quantitative measure for ya (mainly because if there are any comparison tests done on the exact same car with the exact same pad compound, just different brake sizes, then they are well hidden in the internet) but the advantage is there whether it is minimal or not. The advantage increases as speeds increase as well. There are also other variables that would enable or in-able larger brakes to have a slightly shorter stopping distance than a smaller rotor.

Here's a good read if you're interested.

http://www.mgf.ultimatemg.com/group2...Big_Brakes.htm


Brake assist is probably a popular safety feature now, so I wouldn't doubt that Subaru has implemented it. I haven't really been following Subaru lately once I lost interest in hatches, oem 4cyl turbo cars, and the BRZ turned out to be way down on power. Got tired of turbo lag, even the lag a tiny turbo makes. Ready to go powerful NA and RWD. I have a truck now so I don't need a jack of all trades car. Which is generally what hatches are. While I still like them, there are just other cars I like more.

and agreed improving the whole braking system is best, if you're upgrading your brakes, you should invest in improving everything..not just getting bigger brakes. There's a reason they say you should improve brakes, suspension and power at the same time to optimize your performance upgrades. More importantly brakes, and suspension. Better tires are always important but they can hide a lot of mistakes if you just slap on some big sticky shoes.

Last edited by DivineStrike; 09-06-2014 at 05:11 PM.
DivineStrike is offline   Reply With Quote
Old 09-18-2014, 11:30 AM   #623
Loya1ty
Scooby Newbie
 
Member#: 383680
Join Date: Mar 2014
Chapter/Region: MAIC
Location: DC
Vehicle:
2008 Impreza 2.5i
Newport Blue Pearl

Default

I am glad I stumbled across this. Need new brake and rotors and was considering "upgrading" to better than OEM. As I don't think I will be pushing my car too hard (08' 2.5i), I will be able to save some cash now. However, I will still go with some aftermarket, slotted rotors (for looks) and slightly better pads just so I know I will never push them to their limits (I experienced 'slide' on my old Nissan Sentra once.. *chills down my back* uhhgg). And I do like to whip it around every now and then.

And although this post was very helpful from a vehicle and mechanical viewpoint, the physics was nothing new to me. This is high school stuff people.. you should have paid attention in class! Mind blowing physics --> Surface area doesn't increase friction!!! I still have a hard time wrapping my head around this, but you need to consider the other aspects of the system.

Tires: Wider tires are for control and stability (especially when cornering). If you need a reference point, think about bike tires on your car... The increased stopping power is in the composition of the tire material/rubber. This has to do with the friction coefficient of the specific composition of the tire (consider different season tires for reference). some compositions heat up faster to become softer and create that "stickiness" or in my mind, the coefficient of friction as related to the road/surface you are driving on.
Brakes: Larger brake pads aren't the cause for increased stopping distance... Size is more directly related to heat dissapation (a few other things for control), same goes for the rotor. If a brake pad gets too hot, you risk the "slide" effect I mentioned earlier, where the composition of the material breaks down and becomes too soft at high heats. And mentioned in the VERY FIRST POST in this thread, most of us will never get to that point of pushing our pads and rotors to that point on roads. That will only be achieved in race track or canyon performance.

And I'm not basing that off of high school physics, I also majored in Physics (it was hard) in college (your mom goes to college). I would be happy to link some equations if you're interested.. but based on some comments here, I don't think I could trust them with the math...
Loya1ty is offline   Reply With Quote
Old 09-25-2014, 09:00 AM   #624
DivineStrike
Scooby Newbie
 
Member#: 162037
Join Date: Oct 2007
Location: Charleston, SC
Vehicle:
2007 VW GTI Black
2007 CBR600rr White

Default

Surface area doesn't increase friction? then why does a tire of the same compound when increased in size (wider) stop a vehicle faster? Here's an idea, the larger contact patch IE surface area. Leverage is also part of it in regards to the brakes. Also, simply place your hand against the wall. Use the side of your hand then your palm. Which creates more friction? the palm of your hand. Maybe I'm misunderstanding your post or your not saying what your trying to say correctly. But seeing as you are a physics major, i find your post rather scary. A wider vehicle base creates stability, and maybe a wider tire helps a little but unless you increase the overall width of the vehicle at the tires you aren't increasing stability by that much given the same amount of stiffness in the tire remains the same (ie tire pressure or sidewall strength). Most of the advantage of a larger tire is in the increased grip it provides by increasing friction due to the tires increased contact patch. If you want, relate that tire contact patch to a brake pad increasing in size due to having a larger rotor. I agree a larger rotor by itself without increase pad size won't really help you any no matter the advantage in leverage. That is why, aside from heat dissipation advantages, pad size is also increased...to increase stopping power.

Last edited by DivineStrike; 09-25-2014 at 09:07 AM.
DivineStrike is offline   Reply With Quote
Old 09-26-2014, 05:54 AM   #625
JRCrutc
Scooby Newbie
 
Member#: 309978
Join Date: Feb 2012
Chapter/Region: NWIC
Location: Vancouver Wa/Portland, Or
Vehicle:
2012 WRX hatch
Ice Silver Metallic

Default

Here is your answer to why wider tires stop a car better.

Quote:
Originally Posted by JRCrutc View Post
Tires are a somewhat special case in the frictional force world. Here is an interesting article that explains why a wider tire (and therefore surface area) is better for stopping:

http://www.physics.sc.edu/~rjones/ph...efriction.html

The basic premise is that the tire road surface is not an idealized coefficient situation. The tire has the ability to shear at the contact point with the road and therefore the wider the tire the more shear resistance is available.

There are also deformation issues based on road conditions. If the road was extremely flat and the tire shear issue was solved then surface area wouldn't affect the situation as much (or at all).
(note the article above is no longer available, so here is a substitute: http://www.reddit.com/r/AskEngineers...and_car_tires/ )

As for the wider stance issue, the wider the car is the more stable it will be to lateral motion. The reason is that you are increasing the car's polar moment of inertia by widening the track (Sorry this is a Physics/engineering term, the math is complicated, see below for a better explanation).
You can test this by getting a friend to try to push you over (from the side) in two different positions. First try with your feet close together (like touching) and the second test try with your feet shoulder width (or farther) apart. Sure your height changes slightly (not much) with a wider stance, but your moment of inertia changes by a lot because it is calculated using the sum amount of weights and how they relate to a given axis (in this case a force from the side induced at your shoulder through your center of mass). I know the math and stuff is a pain, but this is the reality.

I am no brake pad or rotor guru, but the physics of surface area not effecting friction are valid as far as I know. Heat dissipation, sure, but braking force, no, not with simply putting bigger brakes on the car. From my understanding of braking systems, there is a maximum amount of system fluid force that can be applied through the brake fluid, and without a different brake master cylinder, this force can not be changed (to be accurate, it is pressure which is force over an area but the size of the lines aren't changing so the force of fluid power would be constant). This means that the same amount of force is being transmitted to the brakes no matter the size of the brakes. Therefore the changing the size of the brakes will change the pressure applied to them but not the actual force, thus no stopping distance changes (bigger brakes, lower pressure). Please let me know if you have any questions about this, or I need to go into more detail in sections.

As for your palm and side of the hand experiment, while this seems logical on the surface, the reality is that your palm is made of a different type of skin than the side of your hand, therefore the coefficient of friction would be different. In fact the coefficient of friction varies from finger to finger. You also may be feeling more of a difference than there really is because of the pressure force thing we just talked about in the last paragraph. When you push on the wall your body is measuring pressure (not force), so if you match the pressure between your palm and the side of your hand you are actually imparting way more force through the palm than the side of your hand, thus the friction force goes up with your palm.

Hope this helps you understand the physics involved a little better. Please feel free to ask questions.

Last edited by JRCrutc; 09-26-2014 at 06:27 AM.
JRCrutc is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Creepy cat is going to get you. aod Off-Topic 32 10-26-2011 03:00 AM
this is going to break a lot of hearts brentyloke General Community 5 10-25-2008 12:36 AM
this thing is going to get me fired dr_wheel Off-Topic 9 12-09-2004 06:43 PM
Do you think this is going to cause problems? AustinSTi Normally Aspirated Powertrain 7 11-27-2003 09:08 PM


All times are GMT -4. The time now is 12:22 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2015 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.