Mk8 St Line tyres - PS4 speed rating?

[Jonson]

I'm trying to replace the Michelin Pilot Sport 4 tyres on my Fiesta. Currently fitted are 205/45ZR17 88W XL.

It seems to be quite hard to find stock of this exact spec. - the 205/45ZR17 88Y XL seem more common, am I correct to assume that this small difference in speed rating (higher) will make no difference?

[Cal844]

Speed rating is simply a safe working limit the tyre manufacturer knows the tyre will be safe at, a higher speed rating will not affect your car in any way. 

 

Hope this helps 

[MarksST]

Yes it’s fine to go up a speed rating but not down.

[TomsFocus]

Why not down?  He could even drop to a H rating perfectly safely unless he's going to spend large amounts of time above 130mph...   

[Eric Bloodaxe]

26 minutes ago, TomsFocus said:

Why not down? 

In the back of my mind I have an idea that dropping from the oe speed rating (which is based on the theoretical top speed of the vehicle, irrespective of legal limits), would give problems with insurance, etc.

 

 

 

 

[TomsFocus]

7 minutes ago, Eric Bloodaxe said:

In the back of my mind I have an idea that dropping from the oe speed rating (which is based on the theoretical top speed of the vehicle, irrespective of legal limits), would give problems with insurance, etc.

Technically, using any brand of tyre other than the original fitment 'can' void your insurance.  But it depends what the crash circumstances are, I think they'd struggle to claim a H rating (130mph) was inadequate when investigating a 60mph crash.

The only reason these tyres have such a high rating is because low profile, extra load tyres are generally fitted to sporty cars so they're not made in 'slow' specs...  The book top speed of 1.0EB in question is 125mph so you couldn't even exceed a H rating, let alone a V rating...  W is 170mph, even the ST won't top that!!  

[Eric Bloodaxe]

 Just illustrates the silliness of fitting tyres for "sporty" looks rather than necessity, I suppose, though if an ST-L could pull max revs in top gear (downhill autobahn, perhaps?) in theory it would just top 170.

Trouble is, once you start messing with oe tyre specs, where do you stop? Skinny crossplies on your F40?😀

[alexp999]

3 minutes ago, Eric Bloodaxe said:

 Just illustrates the silliness of fitting tyres for "sporty" looks rather than necessity, I suppose, though if an ST-L could pull max revs in top gear (downhill autobahn, perhaps?) in theory it would just top 170.

Trouble is, once you start messing with oe tyre specs, where do you stop? Skinny crossplies on your F40?😀

It would need to be a steep hill with a tail wind, or maybe one of those Tesla vacuum tunnels.

I can tell you from experience that the Fiesta is not very aerodynamic at 130 mph 😅

[Eric Bloodaxe]

11 minutes ago, alexp999 said:

I can tell you from experience that the Fiesta is not very aerodynamic at 130 mph 😅

Naughty!😀

[alexp999]

1 minute ago, Eric Bloodaxe said:

Naughty!😀

Autobahn. It's like jumping on the brakes when you lift off the throttle at that speed in a Fiesta.

[Eric Bloodaxe]

Just now, alexp999 said:

Autobahn. It's like jumping on the brakes when you lift off the throttle at that speed in a Fiesta.

Lol. I thought you'd have a good excuse!😀

[TomsFocus]

1 hour ago, Eric Bloodaxe said:

 Just illustrates the silliness of fitting tyres for "sporty" looks rather than necessity, I suppose, though if an ST-L could pull max revs in top gear (downhill autobahn, perhaps?) in theory it would just top 170.

Trouble is, once you start messing with oe tyre specs, where do you stop? Skinny crossplies on your F40?😀

There's no way a 1.0 EB will get anywhere near 170mph unless you drop it off a cliff!  

As Alex says, the aerodynamics make it an impossibility on the road, there are very few cars that will hit max revs in top gear.  I am a bit surprised at the 125mph book speed for the 140ps STL though...I've done more than that in a PD130 Golf!    

 

With regards to tyre specs...I wouldn't go crossply, but skinny tyres are pretty common for the current trend of stance & fitment!  All well and good until they pop off on a slight bend. 🤦‍♂️

[Jonson]

Thanks, all, I assumed that was case. Booked in for Y rating option. Seems weird that Michelin have so many different speed ratings for this tyre (mostly beyod the cars they are going on), all apparently the same price? Why not just do one at the max?

[Jonson]

And in case anyone is interested, I've been mightily impressed with these Michelin PS4 - enormous grip both wet and dry, consistent all the way down to the wear indicators at 38000 miles.

[TomsFocus]

1 minute ago, Jonson said:

Why not just do one at the max?

The tyre is made stronger to cope with the higher speed, you'll probably find the fuel efficiency and noise figures are worse on the max rating.  They'll also lose some ride comfort, but with very little sidewall anyway and being XL it's unlikely you'll notice in that particular size.

[Kental]

3 minutes ago, Jonson said:

Thanks, all, I assumed that was case. Booked in for Y rating option. Seems weird that Michelin have so many different speed ratings for this tyre (mostly beyod the cars they are going on), all apparently the same price? Why not just do one at the max?

The volumes the manufacturer are buying makes it viable for them to have more specific tyres for each car.

A tyre wholesaler has to have available tyres for a myriad of different cars it is easier for them to stock the highest rating as it fits more cars.

To my knowledge the tyre pressure sticker in the door shut shows what speed rating for each tyre size is acceptable.  Any speed rating above that is allowed.  If you have winter tyres fitted, if you have a sticker or an electronic limiter you can sometimes fit one grade below the manufacturers specified tyres.

[Kental]

7 minutes ago, Jonson said:

And in case anyone is interested, I've been mightily impressed with these Michelin PS4 - enormous grip both wet and dry, consistent all the way down to the wear indicators at 38000 miles.

Michelin do state that their tyres are specifically designed to perform well all the way to the wear limiters.  Especially with winter & all season tyres they are far better in tests compared to rival manufacturers when less than 3mm

[Eric Bloodaxe]

22 minutes ago, TomsFocus said:

There's no way a 1.0 EB will get anywhere near 170mph unless you drop it off a cliff!  

Lol well I did say "downhill"!😀

[TomsFocus]

8 minutes ago, Jonson said:

And in case anyone is interested, I've been mightily impressed with these Michelin PS4 - enormous grip both wet and dry, consistent all the way down to the wear indicators at 38000 miles.

If you're near a Home Bargains, 49p can get you a cool air freshener to show your Michelin appreciation!  

[TomsFocus]

2 minutes ago, Eric Bloodaxe said:

Lol well I did say "downhill"!😀

Good point!!   Now I'm wondering what the terminal velocity of a Fiesta would be...  

 

[Jonson]

16 minutes ago, TomsFocus said:

The tyre is made stronger to cope with the higher speed, you'll probably find the fuel efficiency and noise figures are worse on the max rating.  They'll also lose some ride comfort, but with very little sidewall anyway and being XL it's unlikely you'll notice in that particular size.

The W and Y variants have identical figures according to Michelin...? I'm hoping for no discernable difference.

[TomsFocus]

22 minutes ago, Jonson said:

The W and Y variants have identical figures according to Michelin...? I'm hoping for no discernable difference.

I really don't think you'll notice a difference in the real world.  

The figures are the same on those 2 by chance, but if you look at the others (G1 & DT1) you'll note the figures are different.  It's all to do with manufacturer emissions and fuel consumption figures essentially.  It makes little to no difference to the customer in reality.  Just means that if they can get away with a slightly slower rated tyre, that may reduce the emissions to get into a lower tax band and reduce the manufacturers average CO2 output...that's why there are so many choices instead of just making everything to maximum spec.

I did note a slight difference in ride quality going from a V to W on a 205/55 (identical tyres but the W was cheaper at the time) but I'm very sensitive to ride, I honestly don't think anyone else would have noticed.