Why does the C5 have W-rated tyres?

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pete_wood_uk
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Why does the C5 have W-rated tyres?

Post by pete_wood_uk » 24 Apr 2008, 14:19

My much-travelled Xantia TD has parked me at the side of the road once too often, so it's departing this life and a much newer C5 HDI 2.0 16v joins the fleet at the weekend.

I was just looking at the likely tyre replacement costs for the new toy. 215/55/16W. Ouch. Does anyone know *why* the C5 runs on W-rated tyres? I thought that Citroen claimed 124mph or something, why does it need a tyre capable of 168mph? H or V would do just fine.

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Pete

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np
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Post by np » 24 Apr 2008, 19:44

My 406 Hdi tyres are 205/55/16 W.Although when i needed new tyres got Goodyears at £55 each on a H,which is rated at 150mph.
I`m sure someone will come along with the correct answer,but it does seem to be over kill on speed ratings on todays newer cars.

MikeT
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Post by MikeT » 24 Apr 2008, 20:13

It's been argued on here before but I am confident that it is perfectly legal and safe to use the lowest rated (86mph?) tyres on UK roads (assuming you observe speed limits).

deian
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Post by deian » 24 Apr 2008, 20:47

That is an interesting thought MikeT.... how-ever:

Me 'personally', I would not think that 100%, the size, width, acceleration (torque), cornering forces (especially on a hydropneumatic cars) are all factors to take into account.

I think it's all a balancing act of top speed vs. safety characteristics for a specific car. Meaning, the top speed rating is based on many factors, not just the stresses imposed on the tyre at top speed, it is a ballpark figure derived to achieve a theoretical top speed based on characteristics.

In saying that, my theory goes out of the window comparing the C5 to a 406.

My old Xantia V6 had V rated tyres even though the top speed is around 145mph. So a H would have done, which I did.

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xantia_v6
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Post by xantia_v6 » 24 Apr 2008, 22:15

Note that H rating is 130 MPH, and V rating is 149 MPH.

Tyres with higher speed rating tend to have stiffer sidewalls, so maybe the car manufacturer though that the sidewall stiffness helped the handling.

elma
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Post by elma » 24 Apr 2008, 23:11

Why does everyone only look at speed rating?
It is only half the picture, tyres have a load rating as well.

You may well find that a V rated tyre will not support the mass of the car safely when fully loaded.

Check the load rating before you make any decisions on tyres based upon the speed rating.

To emphasise the point there are almost no H rated tyres with a load rating which is great enough for a laden 1.9Td Xantia

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Post by elma » 24 Apr 2008, 23:32

Just re read your first post, they are w rated because they are a 55 profile, load rating reduces with profile. I'm fairly certain that the load rating of the tyre is correct for the car although the speed rating is excessive.

If you had a 65 profile then you could probably use v rated tyres

Heres a little table to show the load ratings
http://www.tyresave.co.uk/tyreload.html

note most tyres will say something like 81H or 88V, not just H or V.

Another point about tyres that really gets to me, when you have new tyres fitted insist that the red dot on the tyre alligns with the valve, it is the lightest part of the tyre and as such putting it by the valve will minimise the amount of weights needed to balance the wheel. I've only seen one pair of tyres fitted like this (correctly) in the last year or so.
It's amazing what a fitter won't bother doing despite the fact that it is very basic stuff that ultimately makes their job easier.

MikeT
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Post by MikeT » 24 Apr 2008, 23:47

elma wrote:To emphasise the point there are almost no H rated tyres with a load rating which is great enough for a laden 1.9Td Xantia
Almost. I like the odds :lol:

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Post by elma » 25 Apr 2008, 00:45

What I meant was I couldn't find any I could afford 2 years ago.
I swapped to 195/50/15 after that set of tyres so have no idea whats available in standard sizes at the moment.