Don't forget to insulate your rear hatch

I recently did a massive sound insulation of my 2015 Toyota Prius Two. I had a real issue with terrible road noise and so I started attacking that problem.

First up was tires. The Goodyear tires that were from the factory were terrible tires. Hard riding and very noisy. Replaced those with Michelin Energy Savers....not the all season version. Made a huuuuuuuge difference.

Then it was the interior floor. Took out the seats and added Boom Mat sound deadening product to the floor first. I then added a sound deadening fiber mat and finally a rubber membrane. I then reinstalled the factory foam and mat. That made a big difference. Not as much as the tires but still a big improvement.

I then went after the wheel wells. I added Boom Mat to the plastic wheel well liner and any non insulated areas of the wheel wells. I then coated them with spray truck bed liner and finally a coat of spray undercoating.
Made a big difference.

Finally, I went after the rear hatch. The hatch is one of the biggest noise conduits in a Prius. Taking the plastic liner off was easy. The hatch is nothing more than stamped steel that sounds like a drum. Adding Boom Mat to that....inside the hatch and also on the plastic liner, really made this Prius every bit as quiet as my Lexus LS430 or 2017 Lincoln MKZ. It is just so much nicer. Averaging 58 MPG overall.

Recent trip through the Metro Park system of Cleveland got me 92.7 MPG on a trip of 37 miles. Most of it was on electric....under 47 MPH. It seems that the extra weight had no effect on mileage so far. Cruising on the highway is so much better. Heavier, it is more stable behind trucks.

Boom Mat is similar to Dynamat and is a bit less expensive. Works just as good.
Total cost to sound insulate......$535. $625 for the tires. Was it worth it? Well......I was going to turn in this Prius because of the noise. I am now going to buy it.....I saved over 10 grand over new and I know the history of this used car as I have been driving it since new. It is now way better than it was when I first got it.

 

The floor insulation was next after the tires. It was very evident that the floor was not well insulated when I took the carpeting out.
It is hard to put numbers on the differences of noise suppression that each made. If I were to rank the best improvements....it would be tires first. Then floor insulation. The floor has 4 layers of sound deadening insulation. First Boom Mat. Then I had a fiber mat insulation. Then I had a rubber mat type insulation and finally the factory sound deadening materials.

Then rear hatch insulation which has two layers of Boom Mat. The first layer on the metal of the hatch and the second layer is on the plastic liner. The wheel well insulation was I would say not as effective as the other areas but should be done anyways. I cannot hear the tires going through the wet road like I did before. The rear wheel wells were a big source of noise and so I did the interior of the wheel wells with boom mat and then sprayed the plastic interior pieces with spray adhesive and then put on them some fiber mat sound insulation.

All the areas mentioned made a huge difference in the comfort of the car. Long drives are way less tiring. The stereo sounds so much better. (I did replace all 6 of the factory speakers with better units. Amazing how light and how bad the factory speakers really are with almost no magnets in them). I also replaced the factory stereo with an Alpine Halo9 head unit. I can now see the screen when the sun is out! Better reverse camera and I added cameras under each side view mirrors and have those running all the time the car is on.

If you are going to sound insulate your Prius, I recommend getting the plastic trim removal tools that come in a 3 piece kit available almost anywhere.

I test drove the new 2018 Prius Prime and while it is a great car, I cannot justify buying it with the price of close to $34K. I really did not love the Prius I have until I changed the tires and started to modify it for more comfort. Nothing like shutting your doors and getting that quality solid noise when you close your doors. I don't get the slapping as bad when running over expansion joints in the pavement. The car just sounds more luxurious and is way more comfortable. It seems that Toyota feels that less weight is helpful with mileage targets. But, so far I have not found that the added weight of the sound insulation has had any effect on mileage. I would say that doing sound insulation with new tires is the way to go. Makes the Gen 3 Prius a way better car.

Speaking of comfort. I also added a power lumbar support to the drivers seat. Makes my back really happy and makes long trips more comfortable. I put that on while having the seats out to install the sound insulation. Remember......if you do any interior electrical work, disconnect the negative terminal of the battery and wait about 5 minutes before you start. You don't want an air bag to pop....expensive!

 

Oh yeah...I did do the doors. (Forgot to mention that)
That made a big difference....very quiet and the sound of the door closing is Lexus like. The Boom mat was applied inside the door on the exterior panels. I then covered the inside of the door frame with Boom Mat. I then did the interior trim with Boom Mat and then sprayed the interior trim with spray adhesive and then applied fiber mat sound insulation. I got all the products from Summit Racing as they are right down the road from me.

The spray products work but not as well as the self adhesive mat and the fiber mat. It should be used as part of at least a three part sound insulation system. You do have to have a special spray gun to use it and from what I hear, it can be rolled on also.

I talked to a local stereo shop and they said that the spray products have a smell for a few days and then it goes away. He told me my Prius is the quietest Prius he's seen so far and he's installed dozens of stereos in Prius cars.