How These Strange Shims That Go Between Your Brake Pad And Caliper Promise To Improve Performance

What do you if your brakes regularly get too hot during spirited driving? You could upgrade to larger rotors and calipers as we’ve explored before, or you could build some ducting to get more air flowing to the area. What a company called CoolShims offers is a bit different; its thin metal shims promise to add additional heatsinks to your brake system. Here’s a look at the rather strange product.

The basic idea is simple. CoolShims are, at heart, steel shims—thin pieces of metal that you slide in between the back of your brake pads and the pistons in the calipers. The metal shims are designed with lots of cooling fins to help them dissipate heat, ideally helping to keep both brake fluid and friction surfaces cooler for better performance. At least, that’s the theory.

These striking automotive accessories promise to deal with a common problem for sports cars—excess heat in the brakes. If your brake pads get too hot, they tend to lose their stopping power. In extreme cases, your brake fluid can boil, too. Either way, excess temperatures can leave your brake pedal soggy and your car careening off into a gravel trap. The idea behind these wacky shims is to avoid brake fade by helping critical brake components shed more heat.

 

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The CoolShims come in two main variants. There’s the high-profile variant seen above and directly below, with big obvious fins sticking up directly above the caliper. While this design creates a lot of surface area for heat transfer, it’s not ideal if your brakes don’t have much clearance with your wheels.

To solve that problem, CoolShims also makes a low-profile variant, as seen below. These use fins that are bent down to lay almost flat on top of the caliper instead.

Either way, installation is simple. You simply slide them in behind your brake pads in place of any factory shim that might have been there to begin with. In the case of the low-profile shims, you also have to bend the fins flat to ensure they don’t scuff against the wheels. CoolShims sells its product primarily via eBay, offering variants to suit everything from Chevrolet Camaros to Porsche Boxsters, Honda Civic Type Rs to Subaru BRZs.

 

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It’s true that fins, in general, make sense when it comes to dissipating heat. It’s all about increasing surface area—the greater the area of a hot object in contact with air, the more heat it can transfer.

So do these work? Well, we could do an engineering analysis and a bunch of instrumented testing, but that would take a lot of time and money. Let’s first explore what the company says about its own technology. Then, we can just look to see if the smart people that know how to go fast are using this technique, because motorsports is the crucible of engineering innovation.

The CoolShims website lays out the basic concept. “It conducts heat from the caliper piston to a heat sink located externally to the brake caliper through a high thermal conductivity dual metal composite developed by Four Products specifically for the extreme thermal conditions found in a high performance brake system,” reads the explanation. “Testing has revealed a greater than 20% decrease in maximum caliper piston temperature as well as significantly faster cool down times for a caliper employing CoolShim technology.”

Per the graph above, CoolShims has run some real-world testing of its products. In this particular trial, the company measured the temperature of brake calipers on a 1970 Datsun 240Z during a long mountain descent. One was fitted with CoolShims, while the other was left stock. The testing reportedly showed that the CoolShims equipped caliper ran 115 F cooler—405 F versus 520 F for the stock setup. The company also noted that the CoolShim caliper cooled much faster after the test.

Another extreme test was performed on a Meritor Quadralic brake caliper used in heavy vehicles like garbage and fire trucks. The rotor was brought to 550 F before it was put through repeated stops from 60 mph to 10 mph. After 33 stops, the stock caliper suffered seal failure with brake fluid at a sustained temperature over 140 F. However, with CoolShims fitted, the fluid apparently remained much cooler at closer to 115 F and the caliper did not fail despite 60 stopping cycles.

Of course, seemingly simple solutions with outsized performance often draw suspicion from the automotive world. That’s very much the case with CoolShims; one thread on BimmerForums sees posters citing concerns around wheel fitment and whether the shims have any positive effects whatsoever unless something has been done to the brake airflow. “It looks to me that you’ve gotta install a dryer vent pipe behind each wheel to achieve their test results,” posted Blacklane. “I would guess there is more mass in the brake rotor than in the caliper anyway, so any additional investment in air cooling would be better spent being focused on the center of the rotor, not the caliper,” noted emoore924.

However, another user apparently representing himself as the founder came in to defend his product. Per the post:

I did not post the question about CoolShims nor do I know the poster. I don’t have plans to make CoolShims for BMWs anytime soon so I am not trolling. I did log on when I saw this thread. I have a 2011 335d, so I have had an account here for a couple of years.

To address some of the comments:
1) They are heatsinks and the have been proven to decrease brake fluid temperatures. Is this decrease dependent upon airflow? Of course. This is true with all heatsinks. Testing was done on a brake dynometer with a 15 mph breeze to simulate airport conditions (we were testing on an airport firetruck caliper). We have also done on vehicle testing with similar results. But, yes, they need airflow to be effective.
2) With the majority of vehicles there aren’t wheel clearance issues because with a floating style caliper the heatsinks don’t stick out the top, but are tucked under the caliper to the inside of the wheel. The video on our facebook feed for the FRS/BRZ/GT86 shows that particular design.

At the same time, someone who claims to be the founder later admits in a 2015 post that they haven’t been much use in performance vehicles—despite still selling them to this day. As per the forum:

 I obviously do care about CoolShims in general since it is my start-up manufacturing company, but I am not trying to make them for Z3s or any modern Bimmers. In the past I have made them for Porsche and there has been some success there. But what I have learned is that, generally speaking, the modern sports car has little need for them. Now I am mostly going to focus on pickups and RVs.

But back to our other theory—we can examine if this idea has any solid basis by seeing if it’s used in the world of motorsports. That’s because in motorsports, a good functional idea is typically either picked up by everybody or quickly banned by the relevant authorities. Indeed, we can see in Formula 1 that Brembo has used fins on its brake calipers. However, in this case, the fins are on the caliper body itself, rather than being a shim stuck behind the brake pad. There are titanium brake shims out there, and they’re meant for dealing with heat—but not dissipating it. Instead, they’re meant to act as a shield between your brake pads and the piston to help keep the brake fluid cooler.

Brembo fins its F1 brakes, but not with shims.

Ultimately,  I simply wasn’t able to find evidence of racing teams using brake pad shims as a little boost to brake cooling. It’s true that race cars often have tight wheel fitment, with little distance between the brake caliper and the inside of the rim. Still, you’d think we might have seen it somewhere if a small piece of stamped steel really made a difference.

It’s entirely possible that CoolShims do have an effect. They might help cool your brakes to some degree. However, whether or not it’s to a significant degree that might noticeably improve your performance is harder to prove.

Funnily enough though, this technique is sort of used in mountain biking. Shimano makes brake pads with integrated cooling fins that stick out above the caliper. SwissStop and a range of other brands do, too, and they actually look pretty cool. The basic idea is to allow the pads to shed heat more easily so they don’t fade and lose effectiveness on longer downhill runs. It’s not clear how effective these are in improving braking performance.

My back-of-the-brain’s envelope take is that a shim stuck behind your brake pads probably isn’t going to do much for cooling. You’re only adding a bit of surface area, after all. You’ll likely find far larger gains just by improving airflow to your brakes, through ducting or otherwise.  However, I’ll gladly be proven wrong if anyone does some independent instrumented testing to show us one way or another. In any case, as long you install them properly, they’re unlikely to do any real harm.

Image credits: CoolShims via eBay, via eBay