Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (November 2002, week 1)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Thu, 7 Nov 2002 21:02:22 +1300
Reply-To:     Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Andrew Grebneff <andrew.grebneff@STONEBOW.OTAGO.AC.NZ>
Subject:      Re: Drilled Rotors vs. Big Brake Kit  (long)
In-Reply-To:  <013601c285a8$4c760c80$392c6620@laptop>
Content-type: text/plain; format=flowed; charset=us-ascii

>If I were choosing between the ventilated brake kit and the Big Brake kit >.... I'd go for Big Brake. > >If I were choosing between Ventilated and Stock .... I'd stay stock. > >In theory the Ventilated just doesn't seem to me to be that much of an >improvement, if any.

The big South African brakes are the ventilated ones. Drilled discs are NOT ventilated... unless someone drills a set of ventilated discs!

Ventilated discs are basically 2 discs with RADIAL vents running from the hub to the edge... making the disc a fan, which draws cooling air into the hub center and blows it out the edge slots.

DRILLED discs are merely discs which someone has used a drillpress or mill to drill holes ACROSS the disc, from side to side. These holes are useless for anything but causing accidents... when the holes hold water and prevent the brakes working effectively, or when the disc breaks, locking the wheel with a bang when the calipers pinch into the missing bit (or breaking the caliper off and ripping the hose, resulting in no brakes at all on that circuit. The holes will not dissipate much heat, as there will be no real flow through them.

Taller wheel/tire combinations will have greater leverage on the brakes, thereby decreasing the brakes' ability to work effectively than smaller-diameter tires. When fitting tires/wheels of larger overall diameter, just to keep the preexisting level of braking larger-diameter discs must be fitted to gain mechanical advantage. Fitting larger discs without increasing tire diameter will increasing braking force available. Think of the thing as a lever. The axle is the fulcrum point; the crowbar is the tire. With the hub held stationary by the brake, push on the crowbar (which is levering against the axle) at a point one foot out from the axle (about one normal tire diameter). Then shift your grip outward 6" along the crowbar, simulating a much larger tire (exagerrating here, but it illustrates the point) and push again. You now have much greater leverage against the brake, therefore to slow a tire of the same diameter it will take a lot more braking force than for the smaller-diameter tire. have I confused anyone?

>That's pretty much what I would expect. The stock brakes can lock the >wheels, so the stopping power is being limited by the tires, not the >brakes.

It would take quite an effort to lock the stock brakes with decent tires on a hard dry surface. And to hold them just a flysh*t short of lockup, where braking is at its maximum, it would be near-impossible to modulate them to hold them at this point in an emergency stop. Bigger brakes have more bite, and are in theory easier to modulate. My old 1972 Honda CB740/900 Four K2 had an extra disc added. A stock 750 Four can lock its front wheel, but not controllably. On mine I could, using 2 fingers, howl the front tire from 80mph all the way down to zero. That is, more powerful brakes make for better control. Now, these discs were stainless and had been drilled by a PO (OK, they LOOKED good), and in the wet the holes would retain water, which the pads would then sweep a film of from the holes across the disc surface, thereby reducing braking to virtually zero.

>Drilling rotors actually has very little effect in terms of increasing >braking force. It does allow slightly better cooling over the solid rotors and slightly bettter wet performance.

The very opposite, in fact, as my bike showed so well.

> Any better cooling going on is offset by the mass >lost to holes. It is mostly just a claim blown out of proportion to sell the drillings.

Actually, drilling increases the surface area of the disc. As cololing rate is a function of surface area to volume, the drilling in theory would INCREASE cooling, but only in a passive way. Not actively, as with venting.

> Does a Vanagon need cross drilled rotors? - >NO. Not gonna feel any benefit unless you are a brake pad manufacturer. >Eats pads.

My old 900 didn't eat pads. And I rode it hard... it would easily do 140mph.

>Slotted/vented

Ventilated. Slotted is a gimmick on street cars, like crossdrilling.

>Suffice to say that since I often carry a ton or more of earth/sand/ballast >in my Syncro, which has 15" wheels, regardless of the debate, I know a set >of solid ventilated SA discs and calipers I've ordered are going to make a

Ventilated discs are NOT solid... the have chanels within them. UNVENTILATED discs are solid eg early T3s.

>rotors are the highest performance rotor you should go with >on a street vehicle IMHO. Quality brake pads like Mintex or Ferodo along >with quality brake fluid like ATE or Pentosin will make a bigger difference >on stock rotors than any big brake kit. Unless of course you are adding >more pucks (pistons) to your calipers which I don't think is available for >the Vanagon. I'm sure if one spent enough money though you could get a 4 >piston StopTech or Bembro system with 11" slotted/crossdrilled rotors fitted to the Vanagon. But what's the point.

Well, I for one WILL be fitting Porsche 993 brakes all round. For these I need at LEAST 17" wheels.

>the limitations on braking in a westy are pure physics...you still have >to stop a massive amount of weight with an awesome kinetic energy >storage for something that size. the bigger disk sets i have seen >mounted just help lock the brakes up and the braking distance is still >the same except you now have a worn out set of tires as well as loss of control.

What proportion of Vanagons are Westies?

Go for ventilated discs. AVOID drilled discs.

Metallic pads such as Bendix Metal King are good for long pad life and work very well when hot (so olong as the fluid doesn't boil, thereby fading the brakes by another means!). All of our cars (including taxis) are running Metal Kings.

>I don't know how you are getting that kind of stopping performance, >but my '84 westy has *never* been able to do that (and i've been >riding in it since day 1). Within the last several months, i've had >my entire brake system overhauled (pads, all cylinders, etc.) and >still can merely "slow down". I've checked if my brake booster is >working (according to bently method, it is...), but still i come no >where near locking up any tires... dry or wet (as wet as california >gets, anyway). >So maybe i should just get some cheap, *really* hard tires? :-)

Same for my 84 Caravelle, and that's empty and not a camper!

Another way to increase braking is to fit calipers with more swept area; this often means a caliper with more and/or larger pistons, up to 6 per caliper. Combine this with larger disc diameter... -- Andrew Grebneff 165 Evans St, Dunedin 9001, New Zealand <andrew.grebneff@stonebow.otago.ac.nz> Seashell, Macintosh, VW/Toyota van nut


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.