How To Reduce Tire Noise/Road Noise

Road noise/Tire noise: This droning and rumbling noise is mostly produced by the tire tread's interaction with the road surface, and the noise is mostly low-frequency in nature. Your typical damping sheet (Dynamat etc) will never block or absorb such low-freq noise. It was never designed for these purposes. Neither will any closed-cell or open celled foam. For effective absorption of low-freq noises, you'll need at least a few inches thick of fluffy materials (such as jute, rockwool, fiberglass etc).

This common complaint (tire noise) should be your 1st target to attack in most modern vehicles. The strategy below gives the best Bang for the Buck results.

 Step 1: Wheel arches 
This area is the closest to the tire...the source of this noise. The shape of the wheel arch's interior and the air space within will amplify certain frequencies, and these will easily penetrate the metal into your interior. Spray each wheel arch with few layers of rubberized undercoating (3M,Bondo, Duplicolour, Sikagard etc). You can also use the brush-on type from many soundproofing materials manufacturers (eg StP's Mastic, Secondskin etc). Get this coating as thick as possible. Treat your wheel arch liners with the same product, attach a damping sheet to the underside of the liner, and stick a piece of 3M Thinsulate on top).

Step 2: Undercarriage 
Do the same thing as per your 4 wheel arches. The above Wheel Arch and Undercarriage treatment should always be your 1st soundproofing activity as you are addressing the areas closest to the NOISE SOURCE. The above will give you a significantly noticeable result without stripping any of your interior bits. Once you have done the above, and if you feel you want to improve it further, and you're on a tight budget... 

Step 3: Door hinge area
Open your front doors and look at the top and bottom door hinges. Look at the area between the 2 hinges and BEHIND them...there's usually a gap that leads into the front fender. This is a critical area, and hence, many car mftrs (especially VW) pay special attention to this gap. Squeeze any closed-cell, non-water absorbent material to totally seal this gap. Makes a huge difference in tire noise intrusion into cabin. VW uses foam blocks and even then, there's still some small gaps around these foam blocks. You can use silicone etc to ensure a good seal as lots of noise easily penetrates through the smallest hole.  Remember...we're on a tight budget and addressing the main critical areas pertaining to irritating road/tire noise.

Step 4: A, B and C pillars. 
Tire noise comes from the lowest part of the car, enters the hollow door sill, penetrates into the pillar's bottom and the noise shoots upwards to the interior roof. Hence, certain vehicle's A, B and C pillars are fully foamed or partially foamed at the assembly plant or have some kind of fluffy materials stuffed into them. Foaming the pillars is often recommended by retailers who're heavily into offering foaming services. The foam cannot block all frequencies and because its closed-cell nature, it can't absorb most low frequencies well either. Foaming can produce respectable results but bearing in mind the cost of foaming, you can stuff the A, B and C pillars with fluffy polyfill (used to stuff speaker enclosures) or even the new 3M Thinsulate which is light, highly sound absorbent and hydroscopic). Treating your pillars, especially the A pillar makes a significant difference in lowering tire and engine noise. Why? Engine noise easily penetrates your hood, and the oncoming wind carries this blanket of noise, and slamming it onto your windscreen (which transfers the sound vibrations onto the A pillars), and the external noises also penetrates the pillars and amplified by the hollow space within the pillars.

 The above 4 steps are the first few things you must do when addressing tire noise, and once done, anything else will be really labour intensive and could start getting expensive cos you might end up following the others who're doing the wrong things and using materials in the wrong manner. I will get elaborate on Step 5 a while later as its late now...Yawnnnn!