XL rates tyres?

-Mike- · 13 May 2015 at 23:13

Hey all,

Looking to get some tyres fitted at the weekend, but I'm at a loss as to whether the car needs XL tyres or not. Putting the registration into Kwik-fit as an example brings up both XL and non XL tyres in the correct size.

Camskill offer both versions of the Eagle F1 AS2 and the XL is cheaper than the regular one.

Can anyone offer any advice? The car in question is your typical average VW blunderbus saloon!

Thanks

swinnie · 13 May 2015 at 23:17

Are there XL tyres currently fitted to the car?

delta0 · 13 May 2015 at 23:21

Cars that require XL tyres must only use these. Lighter cars can use either.

-Mike- · 13 May 2015 at 23:26

swinnie said:
Are there XL tyres currently fitted to the car?

There are currently four XL tyres fitted to the car and all are being replaced. All are ditchfinder 3000's and need to go! Two look to be almost new and the front two are in need of change anyway.

delta0 said:
Cars that require XL tyres must only use these. Lighter cars can use either.

I can find nothing in the owners manual regarding XL tyres or anything mentioning their size actually!

[TW]Fox · 13 May 2015 at 23:34

Purchase the correct load index for your car. Sometimes that'll happen to be an XL tyre, sometimes it won't. It doesn't matter.

-Mike- · 13 May 2015 at 23:37

[TW]Fox;28036356 said:
Purchase the correct load index for your car. Sometimes that'll happen to be an XL tyre, sometimes it won't. It doesn't matter.

Where might I find out this information Fox? Kwik-fit etc list both XL and non Xl and not always 94.

[TW]Fox · 13 May 2015 at 23:43

Look inside your drivers door usually, lists the tyre sizes and pressures for your car. Will also show correct load rating.

DB_SamX · 13 May 2015 at 23:52

-Mike- said:
Where might I find out this information Fox? Kwik-fit etc list both XL and non Xl and not always 94.

Did your car come with a manual? Will be in there too.

-Mike- · 13 May 2015 at 23:54

[TW]Fox;28036379 said:
Look inside your drivers door usually, lists the tyre sizes and pressures for your car. Will also show correct load rating.

Shows tyre pressures in fuel cap but not sizes :/

DB_SamX said:
Did your car come with a manual? Will be in there too.

It does have a manual but I can't see it in there at all.

Akagi · 13 May 2015 at 23:56

Don't XL tyres have thicker side walls? Wouldn't this make the ride a little less forgiving? Not as much as runflats do, but in a similar fashion?

-Mike- · 14 May 2015 at 00:00

Acme said:
Don't XL tyres have thicker side walls? Wouldn't this make the ride a little less forgiving? Not as much as runflats do, but in a similar fashion?

This is what I'm trying to avoid if it doesn't need them! Unfortunately I can find no info whatsoever anywhere! I rang VW UK today when I got back from work but their tech team leave at 5pm so I missed them!

Akagi · 14 May 2015 at 00:06

What passat is it? B5/B5.5/B6/B7? Saloon? What engine? (the 1.9TDI might be heavy enough to tip it over to XL, I dont know)

http://en.wikipedia.org/wiki/Volkswagen_Passat

-Mike- · 14 May 2015 at 00:20

Acme said:
What passat is it? B5/B5.5/B6/B7? Saloon? What engine? (the 1.9TDI might be heavy enough to tip it over to XL, I dont know)

http://en.wikipedia.org/wiki/Volkswagen_Passat

2007 Jetta 2.0 tdi (not sure if trim makes any difference to weight but is a sport)

Thanks for all the help!

Akagi · 14 May 2015 at 03:10

My apologies, I assumed it was a Passat when you said it was a typical VW Blunderbus.

Okay so from a quick bit of digging, the curb weight of your car is 1402KG which isn't particularly hefty at all (103KG less than a 2007 BMW 320d for example) - the Jetta is basically a Golf saloon on all accounts - so you certainly don't need XL rated tyres.

The total admissable load on the front axle is 1080KG, so 540KG per tyre, so any load rating over 87 should be fine.

That said, 87 isn't the OFFICIAL load rating for your car, just what I've calculated. So any typical tyres with 91V ratings or whatever will be more than enough/perfect.

As a side note, could somebody tell me how the admissable weight over the axle is calculated? I assumed you would take the weight distribution (which is 57F:43R on the Jetta) then divide the kerb weight accordingly, but 1402KG * 0.57 is just under 800KG which doesn't work at all... Is it the kerb weight + the maximum load weight, then divided according to the weight distribution?

Dandle · 14 May 2015 at 12:11

Acme said:
Don't XL tyres have thicker side walls? Wouldn't this make the ride a little less forgiving? Not as much as runflats do, but in a similar fashion?

That's not how they work. They have the ability to hold higher pressure which when under those higher pressures have a higher load capacity. They don't necessarily have a thicker sidewall just a different construction. When under a lower pressure (below 2.5 bar) their load ability is reduced below that of a non XL tyre at the same pressure. Unless you car requires XL tyres I wouldn't bother fitting them, they bring no benefit and offer reduced load capacity.

bJN · 14 May 2015 at 12:14

Dandle said:
That's not how they work. They have the ability to hold higher pressure which when under those higher pressures have a higher load capacity. They don't necessarily have a thicker sidewall just a different construction. When under a lower pressure (below 2.5 bar) their load ability is reduced below that of a non XL tyre at the same pressure. Unless you car requires XL tyres I wouldn't bother fitting them, they bring no benefit and offer reduced load capacity.

Stiffer sidewalls, so less roll whilst cornering hard.

Dandle · 14 May 2015 at 12:27

bJN said:
Stiffer sidewalls, so less roll whilst cornering hard.

Only if they are inflated to higher pressures.

tlrBeta · 14 May 2015 at 15:07

When you say "higher pressures" What are you thinking?

My EXEO Estate (basically an A4) on the fuel cap recommends 42psi all round for full car + luggage.

Dandle · 14 May 2015 at 15:19

2.5 bar is about the cut over point so 36psi.

Dr Who · 14 May 2015 at 17:08

Dandle said:
Only if they are inflated to higher pressures.

Tyre pressure depends on the weight of the vehicle not the type of tyre used.

XL (also referred to as RF for reinforced) tyres are reinforced to flex less so they build up less heat but any tyre underinflated for the weight of the vehicle is a liability as the excessive flex will cause a breakdown on the synthetic cords.

Lower profile tyres often use XL tyres so they flex less and maintain a more consistent profile when cornering hard, if you overinflate these tyres they can then have a lot less grip in wet or slippery conditions as the blocks no longer move enough to bite into the road. Any tyre underinflated will flex excessively but a reinforced tyre obviously flexes less.

In a nutshell, XL tyres used at the correct pressure for the vehicle weight have no dangers over non-xl tyres at the same pressure, but they may have a harsher ride (due to the stiffer sidewalls) and grip might be reduced slightly under cornering due to less compliance in the tread.

Cars that require XL tyres generally need them due to their increased weight which REQUIRES higher pressures.

You can always run a higher load index than required but you should never run a lower load index than specified. If you run a higher load index you do NOT increase the pressures over the manufacturers specifications to gain XL reinforcement.