What It’s Like Trying To Fit GR Corolla Suspension and Brakes Onto A Toyota Prius

When I last shared my Toyota Prius project with you, it had received some wheels and lowering springs and since then has been a blast to drive, but I am on the path of adapting OEM Toyota parts wherever possible and attempting to drop some weight from the car. Our latest test digs into both.

Installing new wheels with Michelin all-season tires was probably the largest improvement from a handling perspective, but it also came at a slight cost on the efficiency side due to the wider contact patch. One of the reasons that the Toyota Prius Prime is so efficient is the fact that every piece of the car is engineered for the task at hand, which means that the OEM 17×6.5 wheel and 195/60R17 Bridgestone Ecopia tire only weigh in at 36.5 pounds per corner, and even though I found forged 19-inch wheels as replacements, the added width of the wheel plus the added rubber of the wider tire meant that I increased the weight to 47.5 pounds per corner. This was a reasonable compromise for me, as the handling was still significantly better than stock, but I saw an efficiency drop and knew that handling could be further improved with lighter wheels.

New Wheels and Tires

I lucked out and found a set of take-off wheels from a Mitsubishi Lancer Evolution on eBay and decided to match them with a set of the new Michelin Pilot Sport 5 tires. The Evo wheels are an inch wider than the Lexus wheels but are only 18-inches in diameter, and combined with the efficient build of the new Pilot Sport 5 tire, that meant I was able to drop down to 42 pounds per corner compared to the Lexus wheels, potentially improving handling not only from a weight perspective and also from a tire compound/construction perspective.

The handling improvement from the Michelin PS5s isn’t a surprise as they are summer tires, but they also implement a lot of tech from the brand’s most extreme performance tires and borrow their “Wavy Summit” construction from Sport Cup 2 tire. The name of the architecture comes from the fact that there is a wavy layer of rubber in the plies underneath the structural cables in the tire, theoretically improving cornering and steering response due to increased stiffness.

Testing Brake Upgrades

Moving to a new wheel and tire also opened opportunities to chase another project because the spoke design of the Evo wheels allowed for a larger brake caliper to fit on the front. I had previously acquired a set of GR Corolla 4-piston calipers but put the project on hold after doing some measurements and realizing that the spokes of the previous wheel did not have enough clearance to the face of the caliper. Another stumbling block that came up was the fact that the GR Corolla uses a larger rotor which would mean more weight added to each corner. Fortunately, I learned that Toyota had combined the GR Corolla caliper with a smaller bracket that matches the Prius rotor already and used it on the JDM GR Yaris RC in order to fit a more rally suited wheel.

I ordered bracket part number 47751-52020 from Japan and it bolted right up to the caliper and the knuckle on the Prius as expected. The big benefit here is that the GR Corolla caliper is four pounds lighter than the single piston stock caliper on the Prius which should not only improve braking performance but also help with handling. Standard GR Corolla brake pads don’t fit this combination due to how close they are to the rotor hat so I’ll be working with Carbotech to see if they can build me a customized version of the GR Corolla brake pads for the application.

More Suspension Upgrades

Lowering springs gave me a slight improvement in handling due to an increase in spring rate, but I was still convinced I should level up the entire suspension, so I decided to grab some components from a GR Corolla on eBay.

I was able to find a complete right front strut assembly with the knuckle and hub for a very reasonable price, allowing me to measure and test. Right out of the box, I was pleasantly surprised to see that the components were visually similar except for a few small details. The stud spacing on the top mount was exactly the same, and the plate looked to be similar as well, with the primary difference being the shape below, which wouldn’t impact how it mounts to the car. As shown by measurements in the video above, the flanges that mount to the knuckle also had the same spacing and even used the same nuts and bolts for the mounting, which gave me confidence for my test fit.

Installing the GR Corolla strut assembly was no different than installing the Prius strut assembly, as everything bolted up easily, and even things like brake line and speed sensor mounts were in the same position. One of the notable differences was that the anti-roll bar link mounts slightly farther away from the strut body, but attaching it did not cause any issues. I’ll do some math there to see if I need to make changes and swap to GR Corolla links if necessary.

Now that I have confirmed fitment, my next move will be to make use of the GR Performance struts and shocks from Toyota that are intended for the GR Corolla; deciding on springs will be a tougher question. From my testing, using the OEM GR Corolla springs would increase my ride height back to where the Prius was from the factory, and I prefer the look and handling of the lowered car. The Tein lowering springs currently on the car have a spring rate of 145 lbf/in for the front and 200 lbf/in for the rear. OEM GR Corolla springs are rated at 285 lbf/in in the front and 340 lbf/in for the rear.

Toyota offers a GR Performance lowering spring kit under part number PTR63-12232 that is listed as matching the GR Performance shocks and struts, but no spring rates are listed, and GR Corolla owners have reported a drop of around an inch or so, which would be slightly higher than my current combination. The other option would be to chase aftermarket springs; something like RS-R SUS Down springs would offer a drop just over an inch with a spring rate of 340 lbf/in for the front and 400 lbf/in for the rear. I will likely start with the GR springs, since they are tuned for that strut and shock set, and then if I don’t like the ride height, I may chase some aftermarket options.

More to come!