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Post by lastvagn8 » Sat Jun 08, 2019 12:12 pm

Hi All,

beginner at NVH (and picoscope), so searching for some guidance.
This is a heavy truck, suddenly got some vibrations between 73kmh to 80kmh. the whole cabin was vibrating heavily. Problem identified as tire-related.
New tires were mounted first at the 1st axel, then 3rd axle finally 2nd axle.
no difference.
They removed the tires and balanced them again. No difference.
We checked the propshaft, bearings and bushings, no problems.

So I bought the NVH-kit.
very quickly I understood the problem was related to the frequency of the wheels.
It misses T1 and T2 but i think its a diff, since I dont have a OBD-adapter, bought a ELM327 Bluetooth adapter but it dont seem to work on Trucks (1939 protocoll)

So inserted the RPM of the engine at 1250 rpm and ratio of rearaxle at 3,1 (as it is) and ratio of the highest gear (12) at 1,0.
But tires arent possible to enter 295/80r22.5 is says its no valid dimension. So entered 22 and a correction factor. Maybe I should measure the real circumference. But I didnt.

Anyway. looking at the wave form I a vibration at T1 6,31Hz/17mg then at 12,6Hz/over 40mg!
What can it be producing such reinforced(?) vibration. Thinking of an eggshaped rim/tire/wheel?

Sending the files i have...

Next up is raising axles and removing driveshafts.

Thanks for help in advance!
HRD136 KÖRNING.pddata
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Joined: Mon May 27, 2019 2:55 pm

Re: VOLVO FH 2012

Post by Iver » Sun Jun 16, 2019 1:13 pm

But tires arent possible to enter 295/80r22.5 is says its no valid dimension. So entered 22 and a correction factor.

that post suggests that the half sizes in commercial tyres is in the latest software (perhaps in the beta) as of January 2019.

Below added 07-01-19
Tyre sizes can now be added in multiple formats and can also include half sizes for commercial vehicles.
For example you can enter your tyre size as:

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