C5X soundproofing

[xf1ref]

One thing where I might have gone wrong on this car vs my previous DS9 is under the hood. Here I've put 2 layers of butyl stickon under the bonnet felt pad, but on the DS9 I put a liner across the whole bonnet and that seemed quieter.

Please drop a link with that "liner", I don't know exactly what is it.
Today I tested with some foam tape, I think 1mm thickness sticked under the door frame seal and that sound almost disappeared.
I'm thinking instead buying new seal to stick tape all around.

[DS9]

This is it, apologies in advance to the mods if it's deemed advertising. "Dodo Bonnet Liner - 10mm Engine Sound Proofing Hoodliner Heat Shield 1m x 1.5m"...normally retails at £40.

I'll post some pics in the next post with explanations just in case this post gets pulled.

[DS9]

Hope this comes out ok with all the pics in a haphazard order. These were on the DS9.
1) Get the mat which comes as a roll, unroll and leave on the back seat of the car for a few days flat just to straighten it out.
2) Take off the clips for the felt and clean the area.
3) Peel the back off the mat and then affix to the car as a rectangle and get a roller or similar to push down and make it stick to all the parts including recesses.
4) Trim to size around the edges (as you can see I did this badly)
5) Fish for the felt clip holes with a ferrule or similar, and then affix the felt back over the liner.

Maybe took me an hour or so, but it's not a job I rushed.

Like I say this is probably far better than just going behind the felt with denser stuff like I have on the C5X. In fact I need to swap mine out for this solution.

[DS9]

I've just ordered one but delivery didnt come cheap, they are really hard to find now and OOS at most places. They have a pro version for 80 quid which is a little thicker but hasnt got a heat reflective side and I didn't want that.

[Windowlicker]

Hi all,

I’m new to this forum.
I’ve had a C5 X Hypnos, built in October 2024, for about a month now. The car came with brand-new Michelin Primacy 5 tyres in 205/55 R19 99V, which I was obviously very pleased with.

But here’s my question: I was on holiday in France, and on some sections of the smaller country roads, the noise coming from the tyres was almost literally deafening, even though these tyres are known for being quiet.

What are your experiences, and which tyres have you found to be particularly quiet?

I’m also planning to switch to the 17-inch Vector wheels with 215/65 R17 tyres, mainly to improve the secondary ride comfort even further, and hopefully, reduce the road noise coming into the cabin at the same time.

[DS9]

Welcome to the forum!

I looked at tyres in some detail because mine just needed changing. To decide I looked at reviews of not just noise but comfort. I could have perhaps got quieter tyres like the Michelin eprimacy 2 ACO but these arent as apparently as comfortable. So when choosing I bought on a mix of noise, comfort and price, and for me the Primacy 5 came out on top. Some of the crossclimates maybe £200 more expensive would haave won it it was money no object as they ahve more tread depth apparently. One other thing I found is dont choose for noise on the A B C rating, its meaningless, its just passer by noise and has no impact on how loud the tyres sound in the car.

As for general noise coming up from the road, theres a few things to note. The acoustic glass makes things quieter, the engine at a cruise isnt particularly noisy, not much comes from the wing mirrors, so anything noticeable seems to come from below. In this regard it's not as quiet as my previous DS9 and I think it's just been made with far less sound deadening. The other difference is the boot area isn't isolated like in a saloon so you get an extra maybe 30%-40% coming up through the boot floor into the back of the cabin.

I've tried a few ways to get it down, documented on here. There are a few easy quick wins such as sound deadening in the boot, thick mats on the floor with MLV underlays, sound deadening under the bonnet. Then theres more difficult ones like sound deadening behind the plastic wheelarches which takes a bit more time and cost. Ideally I'd have just liked it in the production stage if they'd put down a few mm of sound deadening across the entire floorplan underneath the carpet, I think it would have made a world of difference.

I'd love to know what the car is like on the 17 vector wheels, I think the ride would be far more sumptuous on these. I toyed with the idea but never did it myself. I don't think it'd make much difference to road noise though.

[Windowlicker]

Thanks!

I don't think going to 17" will make much difference to road noise either.
But I am sure secondary ride will improve, so before the end of the year I'll make the switch.

I've read good things about the interior noise of the GoodYear Efficientgrip 2 SUV, but the SUV rating is putting me off a little.

[Sloppysod]

I have been popping in/out of this thread as my 5X is quiet, especially around town and on most A roads.
However, I've just got back from a 1,100 mile trip to Belgium and back and the road noise on UK motorways at 70(+/-) was bad.
What I don't understand is as the boot WAS FULL of luggage this surely would have provided some sound deadening, but it didn't!
It can't all be tires, ½ worn Michelin Primacy all round, can it?
My last car was an X7, and I think that was quieter at motorway speeds.. However, I'm thinking wheel arches, doing something with those plastic inserts and behind.
Also, would adding expanding foam to those hard to get areas, between inner and outer panels in the boot help as it would definitely stop panel vibration - not sure about the heat generated when cureing though.

[mickthemaverick]

It would be a lot easier and cheaper to invest in these Stu !!

https://www.ebay.co.uk/itm/820050098298

[Windowlicker]

Thanks!

I don't think going to 17" will make much difference to road noise either.
But I am sure secondary ride will improve, so before the end of the year I'll make the switch.

I've read good things about the interior noise of the GoodYear Efficientgrip 2 SUV, but the SUV rating is putting me off a little.

I’ve really sat down and looked into this properly, and I’ve now found out the following:

The 205/55 R19 97V Michelin Primacy 5 that Michelin specifies for the C5 X PHEV is an Extra Load (XL) version, with a reinforced carcass and heavier steel belts. This probably explains why I’m finding the tyres rather disappointing.

I’ve also discovered that the 17-inch version of the Primacy 5 that Michelin specifies has a load index of 99, but is nevertheless not an Extra Load, but simply a Standard Load tyre (215/65 R17 99V SL).

So now I’m absolutely certain that I’m going to fit 17-inch wheels.
Lower unsprung mass, taller sidewalls and a more compliant carcass.

I’m expecting significantly better ride comfort and less noise inside the cabin.

[DS9]

Thanks!

I don't think going to 17" will make much difference to road noise either.
But I am sure secondary ride will improve, so before the end of the year I'll make the switch.

I've read good things about the interior noise of the GoodYear Efficientgrip 2 SUV, but the SUV rating is putting me off a little.

I’ve really sat down and looked into this properly, and I’ve now found out the following:

The 205/55 R19 97V Michelin Primacy 5 that Michelin specifies for the C5 X PHEV is an Extra Load (XL) version, with a reinforced carcass and heavier steel belts. This probably explains why I’m finding the tyres rather disappointing.

I’ve also discovered that the 17-inch version of the Primacy 5 that Michelin specifies has a load index of 99, but is nevertheless not an Extra Load, but simply a Standard Load tyre (215/65 R17 99V SL).

So now I’m absolutely certain that I’m going to fit 17-inch wheels.
Lower unsprung mass, taller sidewalls and a more compliant carcass.

I’m expecting significantly better ride comfort and less noise inside the cabin.

This is something I discovered when I was seeking new options, all the 19s have to be XL, its because of the weight of the car. I am surprised the 17s don't have to be but I didn't research this so will take your word for it.

Stu - the wheel wells i did on the c5x and also on the ds9 before it, think it makes some difference but i still think a lot is just coming up from the floorplan. I think the gauge of body steel in the C5X is a bit thinner than the DS9, well it feels that way. I've posted some pics while I was doing it. essentially I get a butyl layer (or 2) first and then overlay with black closed cell foam.....not only on the wheelarch but up in the wing too as you can see. Doesn't have to be neat by any means. The only thing i will say is the front is snugger than the back so if you put too much on you cant get the liner back on.

Like i said a few days ago I've got the new bonnet liner and will fit sometime soon, and will report back. I don't think it'll be as silent as the DS( was at tickover but we'll see. I've also got more door deal stuff coming today and I'll fit that soon and report back.

[Sloppysod]

Cheers, I see you added to the arch cowling as well as the inner wing.........note understood about thicknesses.

Now back to read the whole thread.

[Windowlicker]

"I am surprised the 17s don't have to be but I didn't research this so will take your word for it."

I was really surprised myself, but I’ve checked and double-checked, and it really is the way it is.

[DS9]

That's really good about the 17s, I now wish I'd have been a bit more brave and done it myself but I spent up all my "political capital" just convincing the missus tyres with 6.5mm on them needed swapping. Unless I can now get a grand or so for my existing rims and tyres with a few hundred miles on them I can't justify it.

If you do go ahead I'd be very interested to see how it pans out. Looking around a bit I do think it will reduce road noise and the comfort will improve a lot. The vortex are currently 25% off on the EU site.

Stu - the front and backs are different as you'd expect, seems to be a lot of clearance all around on the rears and you can pack the stuff in layers thick but the front's you have to be a lot more careful. I actually packed too much in on the fronts at first, couldnt get the fixings back on so had to take some out and then I strained my arm trying to force it back. I had to laugh at what was in there factory fitted which is one of the pics, its like 2 very thin tampons, I can't see them making any difference.

Like i say there are other quick wins tho, the boot floor under the platic polystyrene where the charging cable is takes no time, slip the surround out and you can cover half the boot floor in 15 mins. I didn't do the battery half in case there's any issues with the battery down the line and they claim it's because it's too hot or something. Here i just put some unaffixed stuff over the top and a thick rug around the sides.

I still keep tinkering here and there a year after owning, like i say the door seals and bonnet liner are the latest.

As said before what I do think would make a massive difference is just a bit of deadening behind the door panels, but I haven't got the confidence due to lack of instructions about how to remove the door cards. If you tap the doors in the middle they just sound like big drums. Because the doors wrap around under the car instead of sitting on a sill I think they throw up a lot of noise from below.

[Windowlicker]

"If you do go ahead I'd be very interested to see how it pans out."

I'll let you know my first impressions once I have the 17s on and have put a few miles on them.