Starting in the 2018 model year, the Subaru WRX STI comes with a 19x8.5" wheel and 245/35R19 tires. The STI is a supremely capable winter car, but not on the stock tires, which are made from a high-performance summer compound that becomes hard and slick below about 40 degrees F. Most of our customers like to switch to winter tires for the cold season, but 19" winter or all-season tires are very expensive, not to mention the super-low-profile tires are not ideal for snowy roads, potholes, and unseen curbs.
The solution for many customers is to downsize to an 18" wheel and tire package for the winter. Cheaper 18" tires save money, and the taller sidewalls of an 18" tire setup are better suited for rough winter roads. Our preferred tire size for an 18x8.5" wheel is 245/40R18, which is the same as the STI used to come with when 18" wheels were standard.
Of course, Subaru's switch to 19" wheels corresponded with the up-sizing of the STI brakes, and the six-piston front Brembo calipers won't fit under a lot of wheels. That's where we come in. We've selected together all the wheels that we sell that will fit over the 2018+ STI brakes, so you can easily shop for 18" winter wheels knowing that they'll fit on your car.
Note that like any modern car the STI comes with a tire pressure monitoring system (TPMS). There are a few different choices about what to do with the TPMS system when you switch to your winter wheels. You can install new factory-style TMPS sensors in the winter wheels, but then your installer will have to use a special tool to talk to the car and introduce it to the new sensors, and then that will have to happen again when you switch back to your summer wheels.
The second approach is to just not install TMPS sensors in the winter wheels. Hey, we survived for almost 100 years without them, we can manage for three months. Honestly, we don't recommend this option, because modern drivers (us included) are out of the habit of manually checking tire pressures, and you'll have a TPMS light on in the dash all the time, but this is the most economical option.
Our preferred way to handle TPMS for a second set of wheels is to install "cloneable" sensors in the new wheels. The sensor information from the original wheels will be copied onto the new sensors, so as far as the car is concerned, the same sensors are still on the car. No TPMS errors, and no need to reprogram the car. Ask your tire installer for more details on cloneable tire pressure sensors.
If you're wondering if we'll be having Black Friday/Cyber Monday specials this year, the answer is yes. Watch our home page for daily specials and deals starting now and going through Monday, December 2, 2019. We'll have individual featured products as well as entire product line discounts. Also keep an eye on our Facebook page for various updates and promotions.
Our retail showroom and service department will be closing early Wednesday, November 27. We'll be closed Thursday and Friday to give our hard-working staff some time off for Thanksgiving. The Mach V retail showroom WILL be open Saturday, November 30, from noon until at least 3pm.
Of course our web site is always open, and there's years of built-up knowledge in both the Q&A sections of the site and the product pages themselves.
Happy holiday shopping!
We had wondered if Cobb Tuning was going to support the new Subaru Ascent with an Accessport, and the answer is yes! Just released today, the Accessport for the 2019-2020 Ascent adds decent power even with just 87 octane, and yields even more benefits with 93 octane gas.
As with other Accessports, installation couldn't be easier, and the dedicated hardware device is simple to understand and use. Besides increased performance, the Accessport offers a slew of other features: You can keep it mounted on your dash for live gauge display and other ECU-related functions, or you can just store it away after the ECU programming is done; it's up to you.
Accessport for Subaru Ascent is available right now from Mach V Motorsports. Get one today.
In this post I'm going to address some limitations with the factory fuel system on the 2015-2020 Subaru WRX STI. In the old days, you could bolt an intake and a turbo-back exhaust (consisting of a downpipe and a cat-back exhaust) to an STI, and then install the Stage 2 map from your Cobb Accessport, and you'd be all set. The stock STI fuel pump and fuel injectors provided adequate fuel flow for the Stage 2 hardware.
The current STI (2015-2020) is closer to the edge in terms of fuel supply, and if you install both a turbo-back exhaust AND a high-flow intake system, the car will run out of fuel supply. We know this because we can watch the fuel injector duty cycle, and in this state the car will run 100% injector duty cycle even before red line in higher gears. If you run short of fuel supply you could find yourself with a lean fuel mixture in the combustion chamber under boost. That's a recipe for detonation and/or melted pistons -- either way it could destroy the engine.
So what should you do? You could run just a turbo-back exhaust, with no intake. On this car, that's what Cobb Tuning calls Stage 2. You can buy a complete kit for that setup HERE. Or, if you really want to do the full exhaust plus the intake, you'll need to add upgraded fuel injectors and fuel pump. We highly recommend the Injector Dynamics 1050x injectors, and the AEM 340 lph fuel pump. Finally, the Cobb fuel pressure regulator kit is a must. There's no off-the-shelf map for this exact setup, so custom tuning would be required.
If you want to go whole hog, there's a complete Cobb Tuning Stage 3 Power Package including all those upgrades -- including the intake, exhaust, and all the fuel upgrades mentioned above -- plus upgraded fuel rails and AN lines. Cobb offers an off-the-shelf Stage 3 Accessport map for this setup, so you would not need custom dyno tuning.
To review: Unlike with older Subarus, the 2015-2020 WRX STI is nearly tapped-out in terms of fuel supply, and if you install both a high-flow intake and a turbo-back exhaust, you will run out of fuel. In order do prevent that you can run an intake ONLY, or a turbo-back exhaust ONLY, but not both together on the stock fuel system. Or you can upgrade the fuel system with larger fuel injectors and fuel pump, and then you'll be free to install all the intake and exhaust upgrades you want.