This thing RIPS

[maxtog]

The limit on braking when a bike has enough brakes to lock both wheels at speed, is the wheelbase.  The longer the wheelbase, the less weight shifts to the front.  The Roadmaster has a wheelbase of 65" almost 6 inches longer than a Concours, which is very significant (the only one I have seen longer is the Gold Wing at an amazing 66.6).  That will allow the rear brakes to do more in the stopping equation.  That long wheelbase will also make the ride more comfortable (which is why the Concours has a longer-than-sport-bike wheelbase) but it will hurt cornering in two ways- it will be slow to respond and it will not have good clearance for lean.

This is how the 900 pound Gold Wing can still beat even both, with a braking distance of 121.1 feet.

[mikeyw64]

Isn't it true to say that sometimes more weight (+where it is) can shorten braking distances (given everything else is identical)  due to the improved mechanical grip on the road ?

[maxtog]

Isn't it true to say that sometimes more weight (+where it is) can shorten braking distances (given everything else is identical)  due to the improved mechanical grip on the road ?

I haven't heard that before.  To me, that doesn't make sense.  The function of braking is to slow mass in motion, the more mass, the more difficult it will be to slow it down because it will have more inertia.  Grip might increase with weight, but with more weight you also need more grip to slow down without spin/sliding.

[kzz1king]

[If weigjt does not matter your argument about weight shigting to the front which results in more braking front, less in rear has no merit

quote author=maxtog link=topic=22769.msg283628#msg283628 date=1507378935]
I haven't heard that before.  To me, that doesn't make sense.  The function of braking is to slow mass in motion, the more mass, the more difficult it will be to slow it down because it will have more inertia.  Grip might increase with weight, but with more weight you also need more grip to slow down without spin/sliding.
[/quote]

[B.D.F.]

Interesting question Mike but I think the answer is no.

If it were just a case of friction, then the answer would be no. But tires on road surfaces do not operate on pure friction (the easiest proof that given a max. friction of 100%, then the best any vehicle could ever do would be to accelerate at 1g, and that would yield drag race elapsed times of ~10 seconds and we know that ain't right). Tires and road surfaces are both rough surfaces, with one digging into the other.

At any rate, the rear brake on any road vehicle does very little of the braking, at least when the brakes are used with some force. In fact, at some point in an 100% braking effort, assuming the brakes are powerful to lock the wheel (the case on all modern vehicles I think), then all downward force (what some are calling 'weight') is transferred to the front wheel(s) alone; this is what we see in a stoppie when the rear wheel lifts off the ground. The same thing happens at any application of any brakes on any vehicle but of course not so severely almost all the time.

I cannot speak for him but I think what Jim meant by the rear brake working so well on his cruiser is that it is much more responsive than the C-14's rear brake. And certainly I can believe that as the C-14's rear brake is pretty close to inert under any kind of moderate pedal pressure. So probably in normal, day- to- day, relatively relaxed riding, Jim's new bike has a more effective rear brake than the C-14 did, at least given the same, relatively light, pedal pressure.  But speaking in global terms, all road vehicles rely on the front brakes to stop it as the braking becomes more aggressive and in any hard stopping, the front brakes will do the majority of the braking; if the front brakes failed on a vehicle (or were not used on a motorcycle that did not have linked brakes) then the rear tire(s) would lock and drag under no more than moderate braking.

BTW- this is the failure mode of tractor- trailers under extreme braking; the rear wheel- sets simply lock and drag without doing much to slow the vehicle down quickly. And if the tractor tires are doing the majority of the braking, the trailer would desperately like to 'whip around that decelerating place'.... this is what causes them to 'jackknife'.

Brian

Isn't it true to say that sometimes more weight (+where it is) can shorten braking distances (given everything else is identical)  due to the improved mechanical grip on the road ?

[mikeyw64]

In the case of a bike the more weight put onto the front tyre , the more it squishes & the larger the contact patch becomes so surely (^& don't call me Shirley) there is a point at which for a given setup and increase in overall weight may actually allow more braking force to be applied die to the increased mechanical (my comment was based on Ssomething fro a Gu Martin program where he did a callenge against an F1 car and was around the downforces (which effectively increases the weight) helping in increasing the braking effieiciency (initially)

[gPink]

I think the  Bugatti Veyron used the same braking technique. Computer adjusted  ground effects to increase braking.

[B.D.F.]

That might be the case. Again, it is tricky because it is not a pure friction problem but one of two rough surfaces and one gripping or biting into the other. So maybe it does work better with more weight?

Lots of ways to look at this one but basically, I would take the angle of the pressure, which is always less than 45 degrees (meaning the direction of sum of all forces on the front tire cannot be more than 45 degrees, raised from the horizontal). So while increasing the mass of the vehicle absolutely would increase the down force, it would also increase the forward force and if the force is always less than 45 degrees, increasing mass would decrease stopping ability.

Now the problem is that my model above may not fit in this situation. A classic case of a perfect formula miss- applied to the wrong model. :-)  I believe it does fit but cannot be sure. Which brings us all the way back to.... I am not sure. ?? ??

Brian

In the case of a bike the more weight put onto the front tyre , the more it squishes & the larger the contact patch becomes so surely (^& don't call me Shirley) there is a point at which for a given setup and increase in overall weight may actually allow more braking force to be applied die to the increased mechanical (my comment was based on Ssomething fro a Gu Martin program where he did a callenge against an F1 car and was around the downforces (which effectively increases the weight) helping in increasing the braking effieiciency (initially)

[B.D.F.]

Virtually all autos with hydraulic brakes, and all with disc brakes, use a balance valve to adjust the braking pressure on the front and rear end of the car. As more braking pressure is applied, more of it is moved forward until eventually the front brakes are past the 90% point (the percentage of braking force applied) at which point it really does not matter if the rears lock or not anyway.

And of course with today's ABS systems, each wheel is kept turning almost all of the time, so the entire system becomes self- compensating.

Brian

I think the  Bugatti Veyron used the same braking technique. Computer adjusted  ground effects to increase braking.

[VirginiaJim]

I cannot speak for him but I think what Jim meant by the rear brake working so well on his cruiser is that it is much more responsive than the C-14's rear brake. And certainly I can believe that as the C-14's rear brake is pretty close to inert under any kind of moderate pedal pressure. So probably in normal, day- to- day, relatively relaxed riding, Jim's new bike has a more effective rear brake than the C-14 did, at least given the same, relatively light, pedal pressure.
 
Brian

I've done some pretty quick stops at lights turning red (using both brakes of course) and it basically stops on a dime.  You can tell the difference in the braking with just using the front vs the rear as well.   Rear (easy boys) braking is better on this bike.  Coming from a C14 where the front braking is superb, using the Indian brakes were quite a surprise (in a very good way).

[Conniesaki]

When I brake hard with just the back brake on my ZX14R, the rear wheel locks up easily ... as in, I would certainly not want to have to rely on only the back brake. I'm not sure how the Indian could be that different, unless it has linked brakes.

[maxtog]

Many of us misinterpreted what Jim was saying, originally.  He doesn't/wouldn't rely only on the rear brake, he was just saying [at least my interpretation] that he noticed it was more powerful than expected and contributed more to total braking than expected.  And it doesn't have linked brakes.