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C6 sound insulation
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Tjensen   
Mon Jun 01 2020, 10:53am
Joined: Jul 17 2012
Member No: #954
Location: Bergen
 There is a setting in Lexia to chose between 17" 225-55 and 18" 245-45 to tell the electronic systems (but I have not changed it each time)
ChrisW   
Mon Jun 01 2020, 10:56am
Joined: Jun 18 2013
Member No: #1335
Location: Surrey
 Thank you, Radox and gkirkov, for your replies. You have to be careful that you do not increase the tyre radius too much otherwise it will foul the wheel arch and the speedo reads too low. There are plenty of "tyre size calculator" sites on the web that calculate the radius from any combination of xxx/yyRzz tyre size. Before making any change, do check the clearance between the tyre and wheel arch

I changed things in two steps. First, several years ago, I put 245/50R18 tyres on my Atlantique wheels. Definite improvement and they did not cause a problem with speedo or fouling, but the clearance between the tyre and wheel arch was tight. I did not think to use 225/55R18's but, as they are slightly larger radius, I think they may be too big. 225/60R18's will definitely be too big.

My suggestion is to go to 245/50R18 on your Atlantiques at your next tyre change as it worked on mine and gives a benefit (but check first). I have been driving on non-standard tyres for at least 6 years now and have never had a problem with the suspension.
C6Dave   
Mon Jun 01 2020, 05:29pm

Joined: Oct 01 2009
Member No: #1
Location: Northumberland
ChrisW wrote ...

My suggestion is to go to 245/50R18 on your Atlantiques at your next tyre change as it worked on mine and gives a benefit (but check first). I have been driving on non-standard tyres for at least 6 years now and have never had a problem with the suspension.

Just to show the difference between 245 45 18 and 245 50 18:


Basically you just need to be careful and drive a couple of mph below the actual limits although it is within the 10% 'leeway' one is 'supposedly' allowed.
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gkirkov   
Thu Jun 04 2020, 11:22pm
Joined: Jul 12 2019
Member No: #3981
Location: Bulgaria, Sofia
ChrisW wrote ...

Thank you, Radox and gkirkov, for your replies. You have to be careful that you do not increase the tyre radius too much otherwise it will foul the wheel arch and the speedo reads too low. There are plenty of "tyre size calculator" sites on the web that calculate the radius from any combination of xxx/yyRzz tyre size. Before making any change, do check the clearance between the tyre and wheel arch

I changed things in two steps. First, several years ago, I put 245/50R18 tyres on my Atlantique wheels. Definite improvement and they did not cause a problem with speedo or fouling, but the clearance between the tyre and wheel arch was tight. I did not think to use 225/55R18's but, as they are slightly larger radius, I think they may be too big. 225/60R18's will definitely be too big.

My suggestion is to go to 245/50R18 on your Atlantiques at your next tyre change as it worked on mine and gives a benefit (but check first). I have been driving on non-standard tyres for at least 6 years now and have never had a problem with the suspension.


Could you please give me more details on the difference you felt going to 245 50 R18? How noticeable it was? Was it just felt with minor but sharp road imperfections or it was felt at handling too? Also, what brand and age were the 245 45 ones and the new 245 50 ones? I just bought a 245 45 r18 Primacy 4s but can exchange them if I'm confident it will be worth the "risk"
P.S. My main concern is that your improvement was mainly due to newer and better tyres, I'm a little skeptical I personally could feel just 11% increase in sidewall, but who knows...

Thanks

C6Dave, I'm using the exact same calculator, it's very convenient
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ChrisW   
Fri Jun 12 2020, 05:34pm
Joined: Jun 18 2013
Member No: #1335
Location: Surrey
 gkirkov - I am sorry for the delay in replying. The old tyres were the original Michelins and had done 18000 miles and needed replacing. The new ones were Nexen 7000. I chose Nexen (budget) tyres rather than the big names, like Michelin, because a tyre fitter told me that the cheaper tyres have thinner, more flexible side walls, which should be more comfortable. I want comfort and don't care about "performance".

I saw a significant improvement going from 245/45R18 to 245/50R18 and a bigger improvement going from 245/50R18 to 225/60R17. Essentially, the more rubber between rim and road the quieter and more comfortable. I saw no difference in handling but I am a "gentle" driver.
gkirkov   
Mon Jun 15 2020, 10:46pm
Joined: Jul 12 2019
Member No: #3981
Location: Bulgaria, Sofia
 You're welcome, but wife killed it all - she doesn't seem to be able to tell whether the ride height is set to normal or middle position... So the eventual 1/10th increase in comfort is out of the equation :D I'll be waiting to run into a fellow C6 driver with 50s and compare for myself
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bargi   
Wed Aug 05 2020, 08:56pm
Joined: Apr 10 2016
Member No: #2590
Location: London
 - Click Here -
Kaloteck   
Thu Aug 06 2020, 01:16pm
Joined: Apr 25 2013
Member No: #1271
Location: Warsaw
 Hey ppl, come on, why are you messing up with original manufacturer's tyre size?
That's just not kosher...
mtee   
Thu Aug 06 2020, 05:02pm
Joined: Oct 29 2014
Member No: #1924
Location: Kuopio
ChrisW wrote ...

a tyre fitter told me that the cheaper tyres have thinner, more flexible side walls, which should be more comfortable.

My tyre fitter told the same, so I bought such soft sidewall tyres. They are indeed more comfortable when using the normal tyre pressure, but the other side of the coin - or wheel in this context - is that they are also more fragile.
I destroyed one such front tyre by driving over a stone on a small dirt road, not high speed.
The fitter told that the tyre pressure recommended by Citroën is too low for such a soft tyre and heavy car.
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