david.clement@verizon.net wrote:
: IMHO, unless you are consistently carrying a load the cost of doing the swap is
: going to be a waste of money. In an empty or lightly loaded truck there is so
: little traction out back that the rear wheels provide little in the way of
: stopping power. That's why they all have anti-lock brakes on the back wheels.
: Your money would better spent upgrading the fronts.
Agreed. Rear disc brakes are practically a religious topic so
I hesitate to even post this :-) but I will do so anyway. :-)
The fact is that around 80% of the braking is done by the front
wheels, so any improvements that you make in the rear are only going
to affect 20% of your total braking ability. I completely agree
with Dave in that if you want to put your money to the best use
as far as improving braking ability goes, improve the front brakes
first.
By way of example, lets assign arbitrary values which represent
braking power to the front and rear brakes. The front brakes have
80% of the power, and the rear have 20%, so lets break it into
fifths and assume that each fifth of the braking system, as it
currently stands, contributes our arbirtrary number "10" to
the system as a whole. So, the current braking system would
look something like this:
Front brakes: 10 10 10 10 (= 40)
Rear brakes: 10 (= 10)
So, the front brakes have a stopping power of 40 and the rear
brakes have a stopping power of 10. The total power of your braking
system is 50. Now, double the power of the rear brakes:
Front brakes: 10 10 10 10 (= 40)
Rear brakes: 20 (= 20)
The power of the front brakes remains at 40, but the rear brakes
have doubled to 20. This means the power of your braking system
as a whole has increased from the stock 50 to 60. Now lets see
what happens if we instead doubled the power of the front brakes:
Front brakes: 20 20 20 20 (= 80)
Rear brakes: 10 (= 10)
Now, the power of the braking system as a whole has increased
from the stock 50 to 90.
Doubling the power of the rear brakes increased the power of the
braking system by 20%. Doubling the power of the front brakes
increased the power of the braking system by 80%. In fact, in
order to equal the 20% overall increase we got by doubling the power
of the rear brakes, we would only need to increase the power of
the front brakes by 25%! Obviously, this will vary from vehicle
to vehicle, but I don't think it would be too farfetched to imagine
that it will cost less to increase the power of your front brakes
by only 25% than it would to double the power of your rear brakes.
Another aspect that ties into the above (which Dave already
mentioned) and which concerns our trucks especially, is that there
isn't a lot of weight on the rear wheels as compared to the front,
and when you brake, the rear of the truck gets lighter still!
Eventually, you get to a point where increasing the power of the rear
brakes won't make any difference, because they don't have enough
traction to apply any of this additional power to the ground. About
the only thing I still remember from my Econ 101 class is that they
refer to this phenomenon as the law of diminishing marginal returns,
and it applies to a whole lot more in life than just economics. :-)
IMHO, the VAST majority of the cars and trucks on the road
do not need rear disc brakes. Heck, my '70 Barracuda has drums
all the way around, and that will put your face in the windshield.
(That said, I *do* plan to swap to front discs on that car because it
is relatively easy and inexpensive to do so for that particular
vehicle, and there is certainly a stopping distance and maintenance
benefit.) The rears, however, will remain drums.
Unless you are road racing or autocrossing or something along
those lines, most people will not use the added benefit of rear disc
brakes. Don't get me wrong - I am not saying the vehicle will not
stop better, but how much better? Better enough to justify spending
$1,000? $3,000? $5,000?
Everybody has their own budgets and priorities so to each their
own; I'm just here to say that if you have other mods competing
for your vehicular budget, I'd skip the rear discs and do other
modifications first, which have a better bang for the buck.
--
-Jon-
.-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
| 1970 Barracuda - 1990 Dakota 'vert - 1992 Ram 4x4 - 1996 Dakota |
| 1996 Intruder 1400 - 1996 Kolb FireFly - 2001 Ram QC 3500 CTD |
`------------------------------------ http://www.jonsteiger.com --'
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