Comments on: Vehicle Braking Tests = Misinformation Everywhere

By: how brakes work

how brakes work — Sat, 24 May 2008 17:01:33 +0000

[...] reality of how brakes work. This is a short and succinct description of the reality of car brakes.http://www.pansypatrol.com/brakes/How Brakes Work? : How Car Stuff WorksFeb 22, 2006 … The modern automotive brake system has been [...]

By: Chris

Chris — Wed, 10 Oct 2007 08:42:19 +0000

You certainly do your research. I’d have trouble refuting any of that as the facts certainly seem quite clearly laid out. The one exception I’d like to raise is that these are ABS-controlled stops. In the same way that we established brake modulation is improved through increased brake leverage, ABS performance might also improve.

Because threshold braking only involves the initial ramp-up to maximum, and very little modulation thereafter, transients are a minimum factor. ABS is all about transients. ABS is oscillating between full lock (if you applied enough pedal to trigger ABS, you have enough hydraulic pressure to lock the brakes), and full release. A more “modulatable” braking system will achieve lock faster and release quicker also. Without any elaborate simulation, it strikes me that this could improve braking distances and that the effect would be somewhat magnified compared to a stop by threshold braking.

The Mustang article sounds of interest if you can find it on the web somewhere. While I believe most cars can brake at the threshold of lockup on normal rubber in a single-stop situation, exceptions could and probably do exist. Is a Mustang underbraked from the factory? Perhaps. I think a first-generation 3000GT VR4 violates this assumption also — at least my old Stealth was resistent to locking the brakes when that was my intent.

I’ll finish with a counterpoint: for each brake upgrade that stands to potentially improve single-stop performance, I bet there are five more that change bias enough to worsen performance slightly.

By: Fraser Elliott

Fraser Elliott — Mon, 08 Oct 2007 19:05:46 +0000

Here’s one pertaining to Grand Prix’s.
The Grand Prix shares platform and most of its suspension with the Monte Carlo and the Impala. But inexplicably, the highest-performance version of the Grand Prix, the GTP, is saddled with the puny 10.9 inch front brakes of its less powerful brethren, whereas the Monte Carlo and the Impala got 11.9 inch, much heavier front rotors. Everything else about the cars’ brakes (with the possible exception of ABS calibration) is exactly the same, including the calipers and pads. The only difference is the size of the rotor and the caliper bracket which spaces it further from the hub.

This makes the junkyard parts-bin 12-inch upgrade a very popular and cost-effective upgrade for GTP’s..for $100 and 30 minutes work you can really make a substantial improvement to the car. They’ll take substantially more abuse before overheating, thanks to the much higher capacity heat sink provided by the heavy rotors, and an instrumented test bore out an actual stopping distance improvement as well. The results can safely be pinpointed to pretty much the size of the rotors only, because everything else about the brakes including the very pads themselves remained constant: http://www.thrashercharged.com/tech_htm/brake_test.shtm

Real testing of this stuff is hard to come by, but this is one I could put my hands on.

A car magazine (might have been Hot Rod) did instrumented testing of several high-performance and track brake pad compounds on a Mustang a few years ago and showed a huge improvement was possible not only in hot durability and high-speed braking distance, but also in lower-speed, lower-temperature situations where coefficient of friction was the prevailing factor. The tires remained the same throughout the test, which again shows that there may be more power to be had through a given tire than a given braking setup is letting it produce.

By: Chris

Chris — Fri, 28 Sep 2007 00:01:49 +0000

Thanks very much for this addition Fraser; there is plenty of truth there. It’s excellent that you point out properly balanced as well, because many brake upgrades change a car’s braking bias for the worse and can hurt braking efficiency. Few people will look at brake balance very critically, and almost nobody (’cept the serious road racers) would go to the trouble of fine-tuning bias with a dual tandem master or proportioning valve.

I would love to do a real before-after brake upgrade comparison between several cars to get some real numbers to play with. Whatever the findings, it would be really interesting to see.

By: Fraser Elliott

Fraser Elliott — Thu, 27 Sep 2007 20:41:07 +0000

While it is true that tires are what stops the car, which as you’ve pointed out is revelation enough in itself to many people, braking modulation is key. The better modulation afforded by larger-diamter rotors allows a greater force to be imparted by the tires before lockup than would be possible with smaller-diamter rotors, and this alone is why bigger brakes, properly balanced, CAN in fact reduce stopping distances. In plain english, nearly any car, even one with undersized brakes, can lock its tires. A car with properly sized brakes can actually get more work out of the tires before forcing them to lock, thereby resulting in shorter stops.

I don’t drive a VR4 but you’ve done a good job with the tech I see around here.

By: Chris

Chris — Wed, 14 Feb 2007 00:52:16 +0000

While not all cars are equipped with adequate brakes, it seems to be the case more often than not. Obviously I haven’t driven everything with four wheels, but in my experience from sportscars to econoboxes, everything made in the last 20 years usually stops well once. Thanks for the reply Andrew!

By: Andrew

Andrew — Tue, 13 Feb 2007 23:17:06 +0000

I’m sure you taken this into consideration, but a lot of the time, brake upgrade kits are being reviewed for older cars. 2nd gen RX7’s , base model 240’s, etc , which really didn’t have spectacular brakes, both due to aging and old design. New cars are, well, better by design, in my experience.

By: Wider tyres - Will they increase braking efficiency-Modifications & Accessories-Team-BHP

Tue, 13 Feb 2007 18:42:35 +0000

[...] First, take a look at this informative link, which I found pretty enlightening: The Pansy Patrol - Info for the 3000GT / Stealth Community To summarize, brake upgrades (i.e. bigger discs, grooves, drills, etc.) are mostly for heat dissipation to reduce brake fade when brakes are being used repeatedly. It is the tyres’ contact patch area (and compound I guess) that are crucial in the actual slow-down of a vehicle once the wheels lock (or modulate at that level without locking, in the case of ABS). Rear discs may help some, but on most Indian cars, esp. with front-wheel drive (viva?), this won’t make a big difference. And it’s probably not worth the hassle and price. This option makes sense if you’re adding vast amounts of power to your car, i.e. with a turbo/supercharger or constant NOS. Which I don’t gather is the case here. The one option that IS worth trying though (in addition to bigger tyres), is upgrading the front-discs system and any parts thereof. Hope that helps! __________________ "We’re all riders on the Storm!" - Raoul Duke [...]

By: Chris

Chris — Tue, 23 Jan 2007 22:05:02 +0000

Good points yourself. I meant to refer to those vehicles which have been modified for performance, however slightly or extravagantly, and reviewed in comparison to other cars — sometimes the other cars are also modified, but often new cars are used as the benchmarks. Yes, in short, enthusiast publications.

By: Dan

Dan — Tue, 23 Jan 2007 12:36:49 +0000

Good points. But you fail to mention whether the magazines you’re reading are comparing cars (as in the buff books) or doing before-and-after tech testing (as in the enthusiast mags). If the latter, your points are well taken. If the former, then it’s a legitimate test pitting the stock tires, the stock brakes and the stock weight distribution of various competing cars.