E86 Changing rear tyre size to 255/40/18

[24057]

Hi all, I can’t see to source Michelin PS4 in 255/35/18 as they’ve been out of stock for ages on all websites (camskill, Openeo, black Circles etc)

So I was thinking of changing to 255/40/18 at the rear? Can’t see this being an issue, or am I overlooking something?

May even work better improving comfort? Plus PS4 sidewalls are plenty firm enough

Thanks!!!!

 

[mr wilks]

Guessing non ///M so assuming 8.5j (or even 9j) its worth considering 245 40 18

 

[24057]

Guessing non ///M so assuming 8.5j (or even 9j) its worth considering 245 40 18

Sorry, correct Andy.

E86 Sport 3.0 Coupe.

MV2 Alloys

So 245/40/18, that sounds like a good idea

 

[Homer]

I was discussing this with a couple of the guys at the Scottish breakfast meet the other week, seems to be a standard thing for Z4s to run a lower sidewall on the rear. I can only guess it’s to do with less sidewall flex so it makes the rear end more predictable when you start to slide?

 

[mmm-five]

I was discussing this with a couple of the guys at the Scottish breakfast meet the other week, seems to be a standard thing for Z4s to run a lower sidewall on the rear.

Lower sidewall on the rear compared to what, a John Deere?

The ratio is smaller, but the sidewall height is almost identical - as the height is a formula of width x ratio. So 225mm x 40 = 255mm x 35 = 90.0/89.7mm. On an ///M it would be 225mm x 45 = 255mm x 40 = 101.25/102.0mm.

If you run a staggered width set up, you have to lower the sidewall ratio in an effort to maintain THE SAME sidewall height (although some cars do have completely different front/rear overall diameters).

 

[Homer]

Lower side wall compared to the front is what I meant.

 

[mr wilks]

Lower side wall compared to the front is what I meant.

Much wider though assume the idea being to have wider rear for more grip but retain a similar rolling radius to a narrower front wheel

 

[ben g]

Lower side wall compared to the front is what I meant.

Not sure I understand what you're saying here.

The front sidewall is '40', which means 40% of 225mm (the standard width of the front 18'' tyre). This gives 90mm.

The rear sidewall is' 35', which means 35% of 255mm (the standard width of the rear 18'' tyre). This gives 89.25mm.

So the front and rear tyres have pretty much identical sidewalls.

 

[Homer]

Didn’t realize the 40 was a % and not mm

 

[ben g]

Didn’t realize the 40 was a % and not mm

Oh OK, that makes sense then :lol:

Yeah the sidewall number is the percentage of the width of the Tyre. I didn't know either until I read it somewhere a while ago.

 

[24057]

Hmmm. That’s certainly interesting! I also thought the 35/40 was mm, not a %. Every day is a school day!

Perhaps it would be best for me to wait for the PS4 to come into stock in the OEM size, meaning I will maintain the correct rolling radius. Obviously I was aware it was going to change, but thinking about it perhaps it would be best to leave it as per factory setup.

 

[Zedtastic]

Hi all, I can’t see to source Michelin PS4 in 255/35/18 as they’ve been out of stock for ages on all websites (camskill, Openeo, black Circles etc)

So I was thinking of changing to 255/40/18 at the rear? Can’t see this being an issue, or am I overlooking something?

May even work better improving comfort? Plus PS4 sidewalls are plenty firm enough

Thanks!!!!

Ive done exactly this. Michelin PS4 in 255×40×18 at the rear as well as PS4 225×45×18 at the front. It feels like a different car now. Not sure if its down to the tyre wall size, or coming away from run-flats, but its so much better. The sizes are effectively the same as the standard Z4M, theres no clearance issues, even with 5mm spacers on the front and 12mm ones at the rear. According to my GPS, the speedometer is reading almost perfect now (ie. Speedo says 59.5mph and GPS says 60mph).

 

[24057]

Hi all, I can’t see to source Michelin PS4 in 255/35/18 as they’ve been out of stock for ages on all websites (camskill, Openeo, black Circles etc)

So I was thinking of changing to 255/40/18 at the rear? Can’t see this being an issue, or am I overlooking something?

May even work better improving comfort? Plus PS4 sidewalls are plenty firm enough

Thanks!!!!

Ive done exactly this. Michelin PS4 in 255×40×18 at the rear as well as PS4 225×45×18 at the front. It feels like a different car now. Not sure if its down to the tyre wall size, or coming away from run-flats, but its so much better. The sizes are effectively the same as the standard Z4M, theres no clearance issues, even with 5mm spacers on the front and 12mm ones at the rear. According to my GPS, the speedometer is reading almost perfect now (ie. Speedo says 59.5mph and GPS says 60mph).

That’s good to know! Thank you!!

 

[Steve84N]

Definitely go for 245/40/18 rather than 255/40/18.

I chose to run a 245 when I had my 3.0si Coupe as it reduces the front to rear stagger and therefore takes out some of the understeer. 245 is still plenty for 265hp and it gives you a better balanced car.

BMW specced 255 on their M3 with 338hp so the same size on a 3.0si is mainly for looks. Even my C63 with over 500hp is also meant to run a 255 but that is under tyred and I run a 265.

 

[mr wilks]

Definitely go for 245/40/18 rather than 255/40/18.

I chose to run a 245 when I had my 3.0si Coupe as it reduces the front to rear stagger and therefore takes out some of the understeer. 245 is still plenty for 265hp and it gives you a better balanced car.

BMW specced 255 on their M3 with 338hp so the same size on a 3.0si is mainly for looks. Even my C63 with over 500hp is also meant to run a 255 but that is under tyred and I run a 265.

The M3 rears were 9j width same as style 224s.so you can understand the choice of 255,
On the non M rears 8.5j as you know the 245-40 is just better in every way & that's all there is to say

 

[Steve84N]

Yep.

Trend is the same on many BMW cars like e46, e90 and F30 all running 225/255 on 8 & 8.5" wheels as soon as you opt for the M Sport trim level, regardless of engine power.

 

[paullyjay]

I have 255/40/18 on my 2003 3.0 - they are great, I have no rubbing etc and the car drives really well, but I am running X1 style 322's 9j with a 41 offset - I don't know what the original fitment is...

 

[24057]

Massive bump

Could I alter just the rear size and keep the fronts the same?!

Thinking 245/40/18
Front: 225/40/18

Thanks chaps

 

[mr wilks]

Massive bump

Could I alter just the rear size and keep the fronts the same?!

Thinking 245/40/18
Front: 225/40/18

Thanks chaps

Yes

 

[Davz]

Why just Michelin? There are now some really good tyres that are equal or better. Goodyear f1 nct5, Hankook Evo 3, german mags that have tested these put them in front of the michelin. Falken fk510 is also highly rated. I bet if you drove a zed not knowing what tyres are on it you would be hard pressed to tell the difference.