# Noise levels of Run-flat tires vs non-run-flats



## KAJ (Oct 12, 2012)

I disliked the run-flat tires from the moment I drove a car with them. The ride was harsh and loud, but I loved the car, so I bought the BMW Z4 35is in spite of the tires. Everything I read about RFTs was bad and numerous disadvantages outweighed the single advantage of not having to change a flat tire on the road. Run-flat tires are for sissies, I thought. So I decided to swap them out for conventional tires after only 200 miles. But since I am a scientist, before changing the tires, I made a sound level recording using the iphone app "SPL Graph." A 20 mile loop near my house provided a good mix of road surfaces: typical asphalt, smooth-as-glass new asphalt and a bad section of particularly rough chip-asphalt where the road had been re-surfaced tar and gravel a year ago. I then drove the car around the loop while recording the sound levels before and after changing the tires. The car had 18-inch wheels with 225/40/R18 in front and 255/35/R18 in the rear. The run-flat tires were the original Bridgestone Potenze, and were replaced with Michelin Pilot Super Sport. 
After the change there was an immediately noticeable improvement in the ride quality and noise level. Gone was the harsh feel-every-crack-in-the-road experience. And the car no longer bounced over bumps while turning. The noise level was definitely less harsh and tiresome. Then I compared the sound recording, as shown below. There was no significant difference seen in the level of the sound! :dunno:








The figure shows recordings of sound level while driving over the same road surface with run-flat (upper) and conventional tires (lower). The dip in noise shows when the car stopped at a light or to make a turn. The thing to note is the average intensity between stops, which define the transitions to different road surfaces and speed limits. With the meter I was using, a comfortable sound level for listening to music was about 70 dB. Most of the asphalt roads gave noise levels around 65 dB, but the chip-asphalt hit 78 dB.

How could this be that there was not difference in the sound level in comparing the run-flat tires with the conventional tires? There was definitely a difference in the quality of the sound in that it seemed less harsh with non-run-flat tires. In particular, the higher pitched whine was gone, which is especially notable on some sections of concrete. I still have to do some frequency analysis on the recordings made, but there is no doubt that the ride quality has improved, and I don't notice any negative affects on handling. I am not planning to race the car on a track (or on streets) so perhaps my standards for handling performance aren't as high as some. But overall, I think the switch was still a good idea. I posted another thread on why I ditched my run-flat tires.









2013 BMW Z4 35is, Melbourne Red Metallic on Beige Kansas leather, 18 inch wheels, Navigation, backup sensor.


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## vern (Apr 19, 2002)

I can only tell you my experience with the RF's MY 2005 530i had Dunlop RF"s I believe that was the first year BMW put them on there cars, I could be wrong. They were so noisy you could have them replaced before 20,000 miles. I had mine replaced at 18,000 +.I then had a MY 2010 535i 28,000+ miles on them very little noticeable noise. MY 2012 335i Sport Goodyear RF's 8,000+ miles no noise that I can speak of. I have never changed them out for other tires. It would help if you would tell us the year. Good luck
cheers
vern


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## Tom K. (May 10, 2008)

It seems to me that noise is more a function of tread design than sidewall stiffness. So comparing a go-flat RE 050A with your OEM RFT RE 050A might be more informative.

I've had RFTs which were noisy (RE 050) and others which were quiet (NCT5) - same with conentional tires.

Tom


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## KAJ (Oct 12, 2012)

*Reply to Vern*

In reply to your question, the Bridgestone Potenze tires were made in July 2012. The date code is 2812.


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