So after sticking 8.5kg of sound mat throughout my boot, bonnet, wheel arches, mud guards, underbody protection panels and skid pan in an effort to reduce road noise on Australian coarse chip surfaces I was a bit down hearted, the road noise had gone from being impossible to live with to a much better, less harsh, boominess. Better but not as good as I had hoped.

So today I changed the wheels and tyres from 225/40r18 (7.5") to 225/50r17

I got an excellent deal on the 17" wheels from a 2020 Octavia buyer - 17x7" for AU$200 (EURO140-ish) - and went up from the recommended 215/50 to 225/50 (the VW Passat uses this size as standard)

This was my last throw of the dice.

First impression is "OMG!!!! HOW BLOODY GOOD!!!!":

I am yet to do some Australian coarse chip freeway running, but on a couple of local roads the difference is incredible. I should have started with this change.

It is soaking up the road imperfections with a soft bump, rather than a hard knock. And the while there is still a rumble on the coarse chip it seems much more muted. Only a true Highway run on the coarse stuff will show the worst.

 

I'm very, very happy. The sound mat will also be helping no doubt, so no regret in the time and effort spent. 

I'll update when I have done a freeway run. I have 650km to drive tomorrow. Not dreading it now.

Think I can live with the difference to speed and ODO. I know the speed reads fast anyway. 

The arch gap loss is not noticeable. I guess its  0.5cm either side.

 

Edited 16 November, 20205 yr by Rkdee

650km highway run completed on variety of surfaces.

Very very Happy.

225/50r17's should be the standard tyre on this car. It is on the VW Passat in this country.

According to GPS, the speedo is now showing the exact speed. (GPS and speedo show same)

What tyres did you have on the 18" wheels? Did you change make as well as wheel size?

I had Continental Sport Contact once and they were very noisy.

1 hour ago, 26DIPP said:

What tyres did you have on the 18" wheels? Did you change make as well as wheel size?

I had Continental Sport Contact once and they were very noisy.

Pirelli Dragons 225/40r18

changed to

Pace PC10 225/50r17  - they seem quite soft in the sidewall and are rated at 72db from what I could find.

Just cheapies because I didn't want to spend too much money for no return. Instead got great return for minimal expense. Wheels and tyres combined AU$650. I would normally spend at least that amount on tyres alone. And very easy to recoup the expense by selling the 18" as the tyres and wheels are virtually new.

72 dB is quite loud. Michelin Cross Climate in 225/40/R18 is only 69 dB.

That may be so. However, the ride quality is amazing compared to the 18” and road noise on coarse chip is amazingly better. I can look forward to further improvements at my next tyre change.

the 8.5kg of sound dampening I added prior to changing the wheels is probably helping keep the actual tyre noise from penetrating the cabin. The new wheels and tyres are soaking up the coarse chip road vibrations

 

Edited 19 November, 20205 yr by Rkdee

My poverty spec Superb has 205 55 R16 Michelin Crossclimates and it's very refined indeed 

 

 

 

 

 

19 hours ago, bigjohn said:

My poverty spec Superb has 205 55 R16 Michelin Crossclimates and it's very refined indeed 

 

 

 

 

 

Snap.

Given mine is a 4x4 “Outdoor” the 40 profile tyre seemed a really strange choice, only confirmed by the 50 profile ride.
In Australia you would expect this model to be capable of taking on rough dirt roads.
Subaru Outback’s of similar vintage have 55 profiles. Other SUV types also have more tyre wall.

This is how it looks with the new wheels and tyres. You can see the gap between the tyres and guards is smaller. There is about 2cm when the wheels are fully turned