I haven't read anything of the sort. He's simply saying without good tires, what kind of brakes you have really doesn't matter. At least that's the point "I" see.
9in drum brakes
- Thread starter Plymouth72
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ultimatejay
Well-Known Member
He said above, " Tires stop the car not the brakes."
Yeah, I saw that. Only a fool would think he meant it literally.
ultimatejay
Well-Known Member
HE DOES
Bighead440
Well-Known Member
I'm fixing a '66 Valiant for off road (drag) use, with a peppy 360, and I'm determined to at least TRY the 9" front drums (it's a /6 no A/C car). I have some 10" drums/spindles off my '71 Demon that I can upgrade (some) with if it's scary. My '66 Coronet 500 with a 440 stopped pretty damn good with the factory 10x3" drums it came with, and I know it was much heavier than the Valiant. The rearend I'm using in the Valiant is a Ford (uggh, but it's 4.62 geared and spooled) unit from a Maverick that I THINK has 10x2.5" drums, which may help bolster it a little. I may need an adjustable prop. valve, and I'm prepared to add that if needed. There used to be a Super Gas '68 notch Barracuda that ran at tracks near me, and it had a series of progressively meaner 440/451/474/499 engines in it over the years, and the owner kept the 9" brakes!!! He also amazed everyone by running old cast iron Prestolite dual point distributors with only one points set, triggering a MSD7 box. Car was very competitive, and eventually before he sold the car, he temporarily installed a friend's 627" B1TS wedge and a 727 I built with all the A&A goodies and I sold him a 1450 QuickFuel dominator for it. With insane wheelstands and squirrely handling, I think they got a low 5 second 1/8mi time out of it, N/A and with 9" brakes, before the motor got sold to someone in Europe.
cudamark
Well-Known Member
I have the stock 9" front brakes on my '66 Barracuda 360/727/ 8 3/4 4.56 geared drag car too. It stops good enough IMO. I have the stock 10" A-body brakes in the rear also. I even drive this car on the street from time to time and haven't had any issues with fade or poor stopping so far. I'd probably go with disc brakes if I drove it on the street more often, or, if it had more of a freeway gear in the back. On a purely drag car, you just need to stop that once at the end of the track. Fading is not a big issue in that case, as the brakes will cool down fine before the next run. If you have a short gate for the return road, you might want something with a shorter braking distance, but, otherwise, I think the nice, light, weight-saving 9" brakes are good enough.
Owen 340+6
Bang em till it breaks
The real lesson here folks is, can you drive with no brakes disc or drums. Dont Matter then they fail... I've had disc fail and drums fail completely and still managed 30 miles home keeping my distance and unfortunately relying on that TCI streetfighter to help slow me down when need be.... I have much experience with both as well as everyone else on here but my drums on my 67 R/T after I fixed them this last time. Stops amazing. Locks all 4 up gracefully and dead straight if you really need. (Had to test it after fixing) my non power disc brakes from a 73 dart sport on a 71.. not super great but no complaints it's a 4 speed car will slow down that way if ever in a pinch . Power discs especially modern cars well I mean you really cant beat the ease and the power of modern braking
Locking up the wheels is the least useful measurement of braking performance that there is. It literally tells you almost nothing about the braking capability of the car, and it is the worst way to stop quickly.
When the wheels are locked, the brakes are effectively useless and all the stopping is being done by the sliding tire. The coefficient of friction for a sliding tire is lower than for a rolling tire. So even the tire is providing less stopping force than it could be, you can stop the car faster with a still rolling tire because there is more friction force available to the rolling tire. Not to mention all the kinetic energy that will be dissipated by the brakes because the rotor is still turning. The entire point of ABS is to keep the wheels from locking up and staying that way. If locking up the wheels was best, there’d be no reason for ABS- anyone can stomp on the brakes and lock them up.
Keeping the wheels rolling maximizes both the friction you get from the tires and the heat you can dissipate with the brakes, which is why that’s the fastest way to stop. And the safest, because if you’re not locked up you can still steer.
Brakes are really simple. They convert kinetic energy into heat. The faster they can generate and dissipate heat, the faster you will stop. Disk brakes are more efficient at both, and are especially better at dissipating heat.
None of these cars with factory brakes stop “amazing”. The factory disk/drum cars do ok, and they’re a significant improvement over the drum/drum cars. But even a basic modern eco-box can stop dozens of feet shorter than one of these cars with a factory disk/drum set up, even equipped with better radial tires. The articles I’ve already posted show that easily.
When the wheels are locked, the brakes are effectively useless and all the stopping is being done by the sliding tire. The coefficient of friction for a sliding tire is lower than for a rolling tire. So even the tire is providing less stopping force than it could be, you can stop the car faster with a still rolling tire because there is more friction force available to the rolling tire. Not to mention all the kinetic energy that will be dissipated by the brakes because the rotor is still turning. The entire point of ABS is to keep the wheels from locking up and staying that way. If locking up the wheels was best, there’d be no reason for ABS- anyone can stomp on the brakes and lock them up.
Keeping the wheels rolling maximizes both the friction you get from the tires and the heat you can dissipate with the brakes, which is why that’s the fastest way to stop. And the safest, because if you’re not locked up you can still steer.
Brakes are really simple. They convert kinetic energy into heat. The faster they can generate and dissipate heat, the faster you will stop. Disk brakes are more efficient at both, and are especially better at dissipating heat.
None of these cars with factory brakes stop “amazing”. The factory disk/drum cars do ok, and they’re a significant improvement over the drum/drum cars. But even a basic modern eco-box can stop dozens of feet shorter than one of these cars with a factory disk/drum set up, even equipped with better radial tires. The articles I’ve already posted show that easily.
Owen 340+6
Bang em till it breaks
Stops great for me. I don't care about yours as long as all my cars are good.
BillGrissom
Well-Known Member
I see you guys have gone off-Physics again. Maybe since I studied it, Physics seems so common-sense. Yes, "tires stop a car". What do brakes do then? They stop the wheel from rotating relative to the vehicle. Can you skid all 4 tires, and evenly, using your brakes? If so, your brakes can bring the tires to the max stopping ability, which is right before the tires skid.
Why are "big brakes" better then? They have more mass to absorb the braking energy better (less temperature rise) and disk brakes cool off faster, especially those with internal air channels which act like a fan, and even better if air ducts from the grill direct airflow at the rotors (i.e. big ugly black grills begun by Lexus). When does that matter? If the friction material temperature rises until it melts, you get "brake fade". When might that happen? Braking continuously down a long grade, aka clueless Florida drivers on the Blue Ridge Parkway (smell them a mile ahead). Trying to dissipate too much kinetic energy (mass times speed squared). If your 9" drum brakes don't fade when braking from 65 mph, then that is good enough for sane drivers. But, then they need to cool off, so don't keep doing that say in say twisty road-course racing. Use engine-braking on long downhill grades.
Why might drum brakes be worse? Neglect. Touchier about friction factor, due to the self-amplifying effect. Any gummy stuff on the shoes (even leaking glycol fluid) can make them self-jam. Above can make the 4 brakes unbalanced so one tire skids early. The amplifying effect makes them better if you lose power-assist and a weak-legged driver is at the wheel.
What about the data that 72BluNBlu presents? I see different tires in all tests. He has an engineering degree so should know that other factors need to be controlled between comparisons. Sure, your car may have spec'ed 170 ft stopping distance (0 to 60 mph) with the factory skinny bias-ply tires, but it might stop faster with say the kind of sticky tires current Mustangs ship with (95 ft stops). Typical sedans with modern tires stop in about 125 ft, pickup trucks in 150 ft, and sporty cars in <100 ft. Faster specs today may also be due to ABS since I think all they do is jam on the pedal and let ABS pulse the brakes. Interestingly, when the earliest Tesla Model 3 was first tested by Consumer Reports, it gave poor 150 ft stops. Tesla made software changes and it dropped to normal 125 ft. My guess is they fine-tuned the ABS pulse rate, though could have worked with the regen balance too. Why off initially? They had recently softened the suspension due to too-stiff complaints, so perhaps hadn't re-optimized the ABS settings. If you think tires don't matter, consider that tests were run stopping on ice with special snow tires vs All-Season tires and the former stopped in half the distance.
Why are "big brakes" better then? They have more mass to absorb the braking energy better (less temperature rise) and disk brakes cool off faster, especially those with internal air channels which act like a fan, and even better if air ducts from the grill direct airflow at the rotors (i.e. big ugly black grills begun by Lexus). When does that matter? If the friction material temperature rises until it melts, you get "brake fade". When might that happen? Braking continuously down a long grade, aka clueless Florida drivers on the Blue Ridge Parkway (smell them a mile ahead). Trying to dissipate too much kinetic energy (mass times speed squared). If your 9" drum brakes don't fade when braking from 65 mph, then that is good enough for sane drivers. But, then they need to cool off, so don't keep doing that say in say twisty road-course racing. Use engine-braking on long downhill grades.
Why might drum brakes be worse? Neglect. Touchier about friction factor, due to the self-amplifying effect. Any gummy stuff on the shoes (even leaking glycol fluid) can make them self-jam. Above can make the 4 brakes unbalanced so one tire skids early. The amplifying effect makes them better if you lose power-assist and a weak-legged driver is at the wheel.
What about the data that 72BluNBlu presents? I see different tires in all tests. He has an engineering degree so should know that other factors need to be controlled between comparisons. Sure, your car may have spec'ed 170 ft stopping distance (0 to 60 mph) with the factory skinny bias-ply tires, but it might stop faster with say the kind of sticky tires current Mustangs ship with (95 ft stops). Typical sedans with modern tires stop in about 125 ft, pickup trucks in 150 ft, and sporty cars in <100 ft. Faster specs today may also be due to ABS since I think all they do is jam on the pedal and let ABS pulse the brakes. Interestingly, when the earliest Tesla Model 3 was first tested by Consumer Reports, it gave poor 150 ft stops. Tesla made software changes and it dropped to normal 125 ft. My guess is they fine-tuned the ABS pulse rate, though could have worked with the regen balance too. Why off initially? They had recently softened the suspension due to too-stiff complaints, so perhaps hadn't re-optimized the ABS settings. If you think tires don't matter, consider that tests were run stopping on ice with special snow tires vs All-Season tires and the former stopped in half the distance.
BillGrissom
Well-Known Member
You have heard "where the rubber meets the road"? Did some fool start that expression? That "contact patch" is the only place where forces between the road and vehicle act. Brakes components don't touch the road. I'll let you tell us what they do (simple answer).
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