wushaw
Elite Member
Soundguy, the rear brakes only accout for 30% braking for the vehicle no matter how good they work or what vehicle it is.
I rolled my tractor
- Thread starter davidseaquist
- Start date
- Views: 6843
Soundguy
Old Timer
- Joined
- Mar 11, 2002
- Messages
- 51,575
- Location
- Central florida
- Tractor
- RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
Um.. logically thinking out what you said.. it seems incorrect.
If you have a vehicle with ONLY rear brakes.. and you apply them.. those brakes account for 100% of that vehicles breaking power.... even if they are ineficient.. they are accounting for 100% of the braking occouring on that vehicle.. less wind resistance, rolling resistance and mechanical drag, and engine compression braking.. etc...
I think you might revise that statement to preface it with: for vehicles with front disc and rear drum.. and possibly 4 wheel drum.. the rear brakes only account for X % of the total braking of the vehicle.. no matter how good they work.
The "no matter what vehicle it is in" is the falacy... there are plenty of rear brake only vehicles, with those brakes being drum brakes....
For instance.. my bycicle.. has only rear brakes.. yet they are the 100% sum total of the braking force on that vehicle.. I.e. no front brakes.. etc.. same with a rear brake only truck.. like an oldie/antique... PLENTY of those still in service..
Soundguy
If you have a vehicle with ONLY rear brakes.. and you apply them.. those brakes account for 100% of that vehicles breaking power.... even if they are ineficient.. they are accounting for 100% of the braking occouring on that vehicle.. less wind resistance, rolling resistance and mechanical drag, and engine compression braking.. etc...
I think you might revise that statement to preface it with: for vehicles with front disc and rear drum.. and possibly 4 wheel drum.. the rear brakes only account for X % of the total braking of the vehicle.. no matter how good they work.
The "no matter what vehicle it is in" is the falacy... there are plenty of rear brake only vehicles, with those brakes being drum brakes....
For instance.. my bycicle.. has only rear brakes.. yet they are the 100% sum total of the braking force on that vehicle.. I.e. no front brakes.. etc.. same with a rear brake only truck.. like an oldie/antique... PLENTY of those still in service..
Soundguy
ultrarunner
Epic Contributor
- Joined
- Apr 6, 2004
- Messages
- 24,398
- Tractor
- Cat D3, Deere 110 TLB, Kubota BX23 and L3800 and RTV900 with restored 1948 Deere M, 1949 Farmall Cub, 1953 Ford Jubliee and 1957 Ford 740 Row Crop, Craftsman Mower, Deere 350C Dozer 50 assorted vehicles from 1905 to 2006
I would have to agree...Both my 1912 Model T and 1905 Oldsmobile only brake the rear wheels. The T has external contracting bands and the Olds has a single band that slows the flywheel (You need to be in neutral to stop!!)
tjkadar
Platinum Member
- Joined
- Apr 18, 2005
- Messages
- 712
- Location
- Sumter, SC
- Tractor
- Massey Ferguson 5609, Kubota GS1800, eXmark LazerZ XP
On the flip side of that, some vehicles have 100% of their braking force on the front wheel. A modern sportbike can generate enough stopping power to lift the rear tire off of the ground. So, 100% of braking power is on the front wheel. It all depends on the vehicle and its use at the time of braking.
Soundguy
Old Timer
- Joined
- Mar 11, 2002
- Messages
- 51,575
- Location
- Central florida
- Tractor
- RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
Yep.. good point. The previous blanket statement about rear brakes accounting for 30% of breaking on a vechicle no matter the make/model/efficiency was just too all-encompassing to be very correct. Plenty of exceptions exist..
Heck.. my new CUV has rear brakes only.. some sort of small cable actuated 'canister' style breakes situated on either side of the axle ends.. just inboard of the tires.... I'd wager they are 100% of the vehicles brakeing.. since no other brakes exist /forums/images/graemlins/smirk.gif
Soundguy
Heck.. my new CUV has rear brakes only.. some sort of small cable actuated 'canister' style breakes situated on either side of the axle ends.. just inboard of the tires.... I'd wager they are 100% of the vehicles brakeing.. since no other brakes exist /forums/images/graemlins/smirk.gif
Soundguy
RedRocker
Veteran Member
It may be more accurate to say that 70% of your stopping power comes from your front brakes. This would assume you have brakes on both ends. If you lift your rear wheel off the ground then you've eleminated 30% of your stopping power. If you only have rear brakes, you only have 30% of the stopping power you'd have with fronts added.
Soundguy
Old Timer
- Joined
- Mar 11, 2002
- Messages
- 51,575
- Location
- Central florida
- Tractor
- RK 55HC,ym1700, NH7610S, Ford 8N, 2N, NAA, 660, 850 x2, 541, 950, 941D, 951, 2000, 3000, 4000, 4600, 5000, 740, IH 'C' 'H', CUB, John Deere 'B', allis 'G', case VAC
I'd say that is a more acurate way to present it than the statement that was mentioned earlier.
Soundguy
Soundguy
tjkadar
Platinum Member
- Joined
- Apr 18, 2005
- Messages
- 712
- Location
- Sumter, SC
- Tractor
- Massey Ferguson 5609, Kubota GS1800, eXmark LazerZ XP
That would totally negate the physics at hand. Stopping a vehicle is the act of taking the energy of forward motion and translating it into heat energy. How fast you can do that depends on a variety of factors, including weight shift, available traction, the ability of your brakes to dissipate heat, etc.
Any vehicle equipped with brakes has a maximum braking capacity, which we shall call 100%. It doesn’t matter if the brakes are disc, drum, or Fred Flintstone’s feet. That 100% of braking capacity is not a static number. It is very dynamic. In this case, we shall use a motorcycle with disc brakes at the front and rear.
Braking is directly related to the amount of traction available at a given wheel. That traction is dependent on tire condition, road condition, and the forces being applied to the tire. To make things more interesting, we’ll have to discuss traction too. A tire has a certain level of grip before it will slide or skid. This is 100% of available traction.
If you are accelerating, part of this available traction will be given to forward motion. If you exceed the available traction limits of the tires, your wheel will start to spin and can reach the point where you have no forward motion at all. You have exceeded the limits of available traction.
Now, in this example, a motorcycle is approaching a corner at a high rate of speed. The rider wants to bleed off excessive speed at the last moment possible in the least amount of time. He begins his braking efforts while the machine is still upright.
For the first few milliseconds his available traction and braking force is distributed between the front and rear tires. However, as weight shifts forward more and more of his available traction and braking force is on the front wheel. In the space of a very short span of time, the rear wheel is off of the ground and the front wheel is at impending lock-up. One hundred percent of the available braking force is on the front wheel and the front wheel only. The rear tire at this point has 0% braking force and 0% traction.
As the rider enters the corner, he will slowly release the pressure on the front brakes. Now the tire is being asked to help slow the bike and turn at the same time. The available traction of the tires is now being tasked to do two different things, so the available traction is now divided between those two things. The rider is still at 100% braking, but that 100% is now dependent on only 50% of the traction.
If the rider exceeds his available braking force, he will also exceed his available traction and quickly wind up on his head. Braking and the forces at work during the act of braking are not static. You cannot simply say, 70% of your braking force is on the front and 30% is on the rear because those relationships are very dynamic. They change the instant you start applying brakes and change the forces at work on the machine.
Any vehicle equipped with brakes has a maximum braking capacity, which we shall call 100%. It doesn’t matter if the brakes are disc, drum, or Fred Flintstone’s feet. That 100% of braking capacity is not a static number. It is very dynamic. In this case, we shall use a motorcycle with disc brakes at the front and rear.
Braking is directly related to the amount of traction available at a given wheel. That traction is dependent on tire condition, road condition, and the forces being applied to the tire. To make things more interesting, we’ll have to discuss traction too. A tire has a certain level of grip before it will slide or skid. This is 100% of available traction.
If you are accelerating, part of this available traction will be given to forward motion. If you exceed the available traction limits of the tires, your wheel will start to spin and can reach the point where you have no forward motion at all. You have exceeded the limits of available traction.
Now, in this example, a motorcycle is approaching a corner at a high rate of speed. The rider wants to bleed off excessive speed at the last moment possible in the least amount of time. He begins his braking efforts while the machine is still upright.
For the first few milliseconds his available traction and braking force is distributed between the front and rear tires. However, as weight shifts forward more and more of his available traction and braking force is on the front wheel. In the space of a very short span of time, the rear wheel is off of the ground and the front wheel is at impending lock-up. One hundred percent of the available braking force is on the front wheel and the front wheel only. The rear tire at this point has 0% braking force and 0% traction.
As the rider enters the corner, he will slowly release the pressure on the front brakes. Now the tire is being asked to help slow the bike and turn at the same time. The available traction of the tires is now being tasked to do two different things, so the available traction is now divided between those two things. The rider is still at 100% braking, but that 100% is now dependent on only 50% of the traction.
If the rider exceeds his available braking force, he will also exceed his available traction and quickly wind up on his head. Braking and the forces at work during the act of braking are not static. You cannot simply say, 70% of your braking force is on the front and 30% is on the rear because those relationships are very dynamic. They change the instant you start applying brakes and change the forces at work on the machine.
RedRocker
Veteran Member
You'll have to argue all that with the really smart folks that came up with that ratio, it wasn't me. The way I understand it, 70% of your stopping power is on the front brakes, if you choose to not use them, use them a little bit, lock up the rear, lock up the front, whatever, that would be your choice. But, if you stop something as fast as possible with front and rear brakes, the majority of the power is up front. Maybe I'll get out my Keith Code book and we can talk cycle racing. /forums/images/graemlins/grin.gif
Tim_in_IA
Platinum Member
- Joined
- Feb 14, 2005
- Messages
- 840
- Location
- Eastern Iowa
- Tractor
- Kubota B7610HSD, Mahindra 6500 4WD, JD 440ic crawler, 2 560 farmalls.
Comparing motorcycles to cars to tractors might not be apples to apples to apples here. I think all soundguy was saying was that a machine with ONLY rear brakes would use them for 100% of it's stopping power, since it only has rear brakes to work with. Vehicles equipped with front brakes also might be a different matter altogether.
The only exception to this with tractors might be a unit that has 4wd engaged, which would still only use the rear brakes to stop, but distribute the braking force through the drivetrain to the front tires as well.
The only exception to this with tractors might be a unit that has 4wd engaged, which would still only use the rear brakes to stop, but distribute the braking force through the drivetrain to the front tires as well.
