Tyre Stretch - 3.0si

[craigbeal]

These are the tyres that came with the car when I bought it.

Front tyre seems to have a lot more stretch on it than the rear but under closer inspection the front should have a 40 side wall and these have a 35 side wall.

I’m guessing this would cause the visual stretch maybe or could it be the case I’ve got rear sizes alloys on the front or is it normal to have a little more stretch on the fronts over the rear in a staggered alloy size.

Any thoughts?

FRONTS:




REAR:

 

[mjennings23]

Yes it's normal. The front wheels are 8" wide and the rears 8.5" wide, but the rear tyres are 30mm (about 1.2") wider so they will always look different. You are correct that the fronts should be 225/40, but the 40 is sidewall height only and has no bearing on the width.

225 wide is an ideal width for an 8" rim.
255 is the absolute maximum width for an 8.5" rim
A lot of people run 245/40 rears for this reason, plus the extra bit of sidewall.

 

[craigbeal]

Great thanks for the reply.

Sounds like I need to go with a 245 rear in that case.

Could I run a 245/35 rear on a 8.5?

 

[mjennings23]

Great thanks for the reply.

Sounds like I need to go with a 245 rear in that case.

Could I run a 245/35 rear on a 8.5?

You don't need to change, a 255 rear is absolutely fine and is factory spec. The incorrect one on your car is the front, which should be a 225/40. Not a big difference but adds a bit more sidewall.

There isn't any benefit to a 245/35 rear. You'll end up with a smaller tread area and a smaller sidewall than factory. The idea of people using 245/40 is due to it adding a bit of sidewall height, as well as typically being cheaper and more readily available than 255/35

 

[craigbeal]

Would having standard widths of 255 & 225 but having a 40/40 side wall improve my ride over the current 35/35 as I will be honest with the car already lowered as it is the ride is HARD at the moment :?

 

[mmm-five]

Is it on standard suspension, or aftermarket?

That may be making the ride worse is it’s not set up right, or not designed for road use - most aftermarket non-adjustable suspension tens to just lower & stiffen to make a car more (sporty). This is great for the odd track day & smooth motorways, but not much good for suburban/country roads.


You shouldn’t have the same profile front & back...so you’d either got to the standard 225/40 front and 255/35 rear, or go up a profile on both to 225/45 front and 255/40 rear (which are the M sizes).


I notice that you’ve got XL (extra load) tyres too...that will also be contributing to the harsher ride.

Final question, are they runflats, or normal tyres?

 

[ben g]

Not all brands are created equally. I'd assume these are WANLI's or some other obscure Chinese ditch finder rubbish.

Most of the cheaper tyres aren't the same width as more expensive brands. Thats why they look stretched.

 

[Bertz4]

Might be worth checking you have actually got 8” wide on the front and not 8.5”. When I bought my car the wheels were on the wrong ends of the car and also had the wrong tyres on, so they were stretched at they front and a bit flabby at the back.

 

[craigbeal]

Thanks for the input,

The suspension is adjustable aftermarket shocks and springs but havnt messed with dampening rates yet.

The tyres are s**t ditch finders and non run flats but yes XLoad won’t be helping.

 

[mjennings23]

I notice that you’ve got XL (extra load) tyres too...that will also be contributing to the harsher ride.

On this note, good luck finding tyres in the correct sizes that AREN'T rated XL. It's very common that sports cars have XL tyres, as they can take more abuse and hard driving than a standard tyre can, it's not just about the weight of the vehicle but the purpose of the vehicle too. After a quick look on blackcircles using the reg number, every single tyre in both sizes is designated XL, a 92 load rating on the fronts and 94 rears.

I know you can get lower load rating, yes. However, they tend to be the older styles of tyre only i.e. Goodyear Eagle F1A3 is 92 load only, if you want 88 you're going back a generation to the F1A2. The michelin PS4 doesn't come in 88 load, only the Supersport does (again, an older tyre)

Basically, XL is irrelevant. If you're adamant that you don't want an XL tyre, then you're buying old designs and compromise on grip, wear etc that new tyre designs improve upon.

 

[mmm-five]

I notice that you’ve got XL (extra load) tyres too...that will also be contributing to the harsher ride.

On this note, good luck finding tyres in the correct sizes that AREN'T rated XL. It's very common that sports cars have XL tyres, as they can take more abuse and hard driving than a standard tyre can, it's not just about the weight of the vehicle but the purpose of the vehicle too. After a quick look on blackcircles using the reg number, every single tyre in both sizes is designated XL, a 92 load rating on the fronts and 94 rears.

I know you can get lower load rating, yes. However, they tend to be the older styles of tyre only i.e. Goodyear Eagle F1A3 is 92 load only, if you want 88 you're going back a generation to the F1A2. The michelin PS4 doesn't come in 88 load, only the Supersport does (again, an older tyre)

Basically, XL is irrelevant. If you're adamant that you don't want an XL tyre, then you're buying old designs and compromise on grip, wear etc that new tyre designs improve upon.

Owners are free to fit what they want, as long as it meets or exceeds the OE spec.

I was just pointing out anything that might contribute to the OPs ‘harsh ride’.

You don’t have to find an 88 rating, but on the other hand you also don’t need to find the stiffest tyre you can find. There are plenty on non-XL tyres around - im sure you know a higher load rating does not make it an XL tyre - only the labelling will tell you that.

It might be more common to find XL (extra load) now, but XL tends to be for heavier cars, not specifically sportier cars, and XL has nothing to do with being a new or old design, so I’ve no idea where you’ve got that from.

Too high a rating and you may get more understeer and a twitcher ride/tramlining.

When I bought my last set of Supersports for the Z4M the rears were available in 97 or 101 ratings and the front were available in 91 or 95 ratings. Both meet/exceed what is specified for the car (91 front / 95 rear), yet only one of them is XL (the 101) - and that was intended for a mich heavier Mercedes saloon.

Maybe they’re making everything XL now as a marketing exercise - or just because cars are becoming a bit heavier :wink:

 

[mjennings23]

Owners are free to fit what they want, as long as it meets or exceeds the OE spec.

I was just pointing out anything that might contribute to the OPs ‘harsh ride’.

You don’t have to find an 88 rating, but on the other hand you also don’t need to find the stiffest tyre you can find. There are plenty on non-XL tyres around - im sure you know a higher load rating does not make it an XL tyre - only the labelling will tell you that.

It might be more common to find XL (extra load) now, but XL tends to be for heavier cars, not specifically sportier cars, and XL has nothing to do with being a new or old design, so I’ve no idea where you’ve got that from.

Too high a rating and you may get more understeer and a twitcher ride/tramlining.

When I bought my last set of Supersports for the Z4M the rears were available in 97 or 101 ratings and the front were available in 91 or 95 ratings. Both meet/exceed what is specified for the car (91 front / 95 rear), yet only one of them is XL (the 101) - and that was intended for a mich heavier Mercedes saloon.

Maybe they’re making everything XL now as a marketing exercise - or just because cars are becoming a bit heavier :wink:

Perhaps it is, but I was just stating the newer tyre releases, in 225/40/18 at least, all seem to be a 92 load rating which is XL, whereas the only tyres in 88 load are the older ones (i.e. Goodyear haven't released an AS3/AS5 in 88 load, only 92. Same as the Michelin PS4 etc)

It's also very dependant on tyre size. The rears on mine are 245/40 (so 10mm narrower than the M) and a load rating of 97. This is XL in that size, yet up the tread profile 10mm and it becomes the normal tyre. So the load ratings on my car right now are 92/97, both of which are classed as XL, yet they're nearly identical to the M 'non-xl' spec.

Take this extract from an article on the subject:

The advantages of reinforced tyres resulting from their increased load capacity are:

When normal and reinforced tyres are used in the same way, the latter will last longer. XL tyres can travel for a greater total distance without suffering internal damage, even when under intensive use. This applies as long as the vehicle manufacturer’s recommended pressure is being adhered to.

Reinforcement of the tyre improves resistance to mechanical damage caused by, for example, driving at high speeds into the curb.

Better traction and adhesion properties. The tyre’s greater rigidity ensures stability, more effective transmission of the vehicle’s power to the road surface, better handling on corners, a faster reaction to turns and a greater resistance to additional loads and forces (acceleration, braking, centrifugal forces on turns).

Of course, there is no such thing as a perfect tyre. All models are a designed and calculated compromise between various parameters and this still applies to reinforced tyres. The more important drawbacks to reinforced tyres are:

Higher noise levels. The tyre certification requirements permit reinforced tyres to produce 1 dB (decibel) more noise than normal tyres.

The use of reinforcement may involve increasing the thickness of the face (under the tread) and shoulder of the tyre. This, in turn, can cause increased rolling resistance and greater fuel consumption.

Reinforcement usually involves an increase in the tyre’s weight and mass, which again leads to higher fuel consumption.

Modifications may lead to a lowering of driving comfort, when compared to using normal tyres, although such differences will be minimal and rarely felt by the driver.

So basically, a stiffer tyre improves the driving dynamics of a sports car by ensuring the tyre makes better contact, at the price of a bit more noise and a bit more resistance - hardly elements considered when choosing UHP tyres for a sports car. I'd also expect you'd have to be a pretty skilled and experienced driver to notice the difference in a tyre thats a few hundred grams heavier, hell my wheels are about 5kg lighter each than the 108s it had on and the difference is negligible.