On Thu, 13 Feb 2003, Navarrette, Vance wrote:
> Shane:
Hi All.
> Well, I have learned something. Disc brakes with no
> booster, eh? Has anyone driven one of them that cares to comment on
> the brake feel? I visited the Moss web page, and sure enough,
> no booster.
I have driven a TR4 with the stock single circuit TR4 MC and Toyota 4-pots
armed with fancy pads (I forget the brand, probably CarboTech or Hawk).
This was a race car with slick tires.
Pedal feel was _awesome_. You had complete control over lockup and the
front brakes grabbed so hard on heavy application, that the rear wheels
literally came off the ground. Not uncontrollably off the ground, but I
have video of me driving this particular car and braking hard, and I was
amazed when I watched the video for the first time. Damn that thing could
STOP!
This was the first "real race car" I'd driven at that point and I was
instantly converted to the idea of how important pedal feel is.
In contrast, my TR6 race car still runs the stock booster. It works fine,
but there is one fairly annoying problem. When the track temps are cold
(under 70 degrees), it is really easy to lock up the fronts -HARD-. This
makes for impressive clouds of tiresmoke and happy tire dealers.
Here's the deal - with the booster, you need less pressure on the brake
pedal to get a given amount of brake hydraulic pressure. So, the driver
input is _much less_ withthe booster. However, with the booster, there is
a much finer line between controlled braking and total lockup. When you
are at the limit, you really, really, really want to avoid lockup! So
racers tend to shy away from "boosted" brake systems.
> OK, here's another SWAG; Err...stopping distances will be
> shorter with a boosted system?
That might be true, but it might also be false. I can say with 100%
certainty that with the booster, you don't need to stamp on the pedal as
hard, so if you can control lockup with that setup you should be able to
stop at least as well. The key is controlling lockup, because once you
slide the tires, you're not slowing down nearly as much as you could be
with the tires not locked.
Now, the intial question was what ratio to use. I forget the numbers, but
I have seen folks on other lists mention them. If you are desperate for a
ratio number, contact me off-list and I will do a little digging. You are
on the right track - there's only two ways to get more hydraulic pressure
- a higher numerical ratio and playing with the volume of the MC.
Note: the TR6 MC will work okay without the vacuum boost, but the pedal
effort goes up considerably!
> Vance
regards,
rml
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