B9 Berlingo tyre modify

[IKUN]

I bought a B9 for long distance motorway travel. After tyre pressure adjusted to 32, it can be handled stably on 70mph or 60mph with side wind. But I think I would still upgrade it for higher speed travel in EU motorways commonly with a speed limit for 130 or 140 kmh. My original wheel size is 215/55R16, and I want to upgrade it to 225/50 R16 P ZERO Rosso or Pilot Sport 4 or Potenza. Also there is Eagle F1 for 225/55 R16. I checked that my wheel is 6.5J, sounds not good for 225, but the original 215/55 R16 also recommend 7J wheel and can range from 6-7.5. And I checked online the 225/50 R16 P ZERO Rosso and PS4 also recommend 7J but can fit 6-8. My car in China is also 6.5J wheel with 225 tyre but its 225/60R17, so I wonder whether a 50 or 55 tyre can do this? Thank you.

[deejay_xb]

you cannot alter the tyre size, if you do this you will get a police reward, at least here in Romania.

[ItsGreen]

Totally legal here in the UK. First step would be get your fingers behind the back wheel and feel how much clearance you have between the tyre sidewall and the plastic trim.

[Sol]

Remember if you change the tyre size where it affects the rolling circumference significantly, it throws your speedo reading out.

[Gryffindor]

I have no personal experience of changing wheel sizes but have read a lot of threads on this forum about it. So I hope my thoughts are not unwelcome, or incorrect.

Your research looks good so far; you have identified which tyre brands you prefer, which wheel sizes they fit, and what wheel sizes you have.

Zion's advice that changing wheel diameter (including tyre) will alter the speedo accuracy is correct. Legally, speedos must be accurate to within a small percentage either way, so I would say that you must stick to the R16 number if at all possible (which you have done in your examples).

ItsGreen's advice is also correct - going from 215 to 225 will add 10mm to the thickness of your tyre, and it could therefore become too wide for the space inside your wheelarch. I don't know where the extra thickness would be - 1cm on the inner face of your tyres or 1cm on the other face, or 5mm on both; but to be sure, feel how much space you have between your tyre inner face and the wheel arch lining, and between the tyre outer face and the edge or lip of your wheelarch, and assume that you need at least 1cm in both cases.

I think that here, under the law, tyres cannot protrude further out than the wheel arch and must be inside it, so if 225 tyres will extend like this, you might need to mod your wheelarches or your wheel hubs.

Last of course is the stud or bolt pattern - your new wheels must fit onto the studs on your wheel hubs! I have seen other threads on that subject here recently. I think you can get adapters, but they will push your wheels further out, leading to the wheelarch issue I just mentioned.

If I am wrong on anything, others will point it out quickly and I apologise. They are right, not me!

[deejay_xb]

Totally legal here in the UK. First step would be get your fingers behind the back wheel and feel how much clearance you have between the tyre sidewall and the plastic trim.

OP sayd he wants to travel in EU motorways, so not UK only, and he needs to check all EU country's tyre policy, at least here in Ro we are not allowed to have different tyre sizes than the ones in the cars manual and paperwork. If you are stopped by the road police and they find out you have other tyre size then you get a ticket and the car's certificate paper gets retained until you fix the problem.

[RattyCortina]

https://tiresize.com/calculator/

If you click on 'more size tools' there is an offset calculator as well.

[Gryffindor]

OP sayd he wants to travel in EU motorways... other tyre size...

Good point deejay_xb. But what does other tyre size mean? Can you keep to the R number (wheel diameter) but change other numbers, or must you keep all numbers the same?

[deejay_xb]

all numbers need to be as they are in the manual or cars paperwork.

[Sol]

Remember too the R16 is the steel wheel diameter but the 215/55 R16 and 225/55 R16 are different outer diameters, as is a 215/65 R16 different again.

225/55R16 means 225mm width tyre, with sidewall height 55% of 225 and wheel core 16" diameter. So 123.75mm sidewall height, x 2 and added to wheel diameter gives 16x22.5 (convert R16 to mm) + 2x123.75 (double sidewall) x Pi (3.1412)

225/55R16 = 360 mm wheel + 247.5 mm (sidewall of 2x123.75) X 3.1412 (Pi) = 1908.5 mm rolling circumference. 523 turns per 1km

215/55R16 = 360 mm wheel + 236.5 mm (sidewall of 2x118.25) X 3.1412 (Pi) = 1873.9 mm rolling circumference. 533 turns per 1km

So at 100km/h or 60 mph the smaller tyre (215/55/R16) makes 967 more rotations per hour, to cover the same distance. Or rough cut would have been 10 turns per km / 1000 turns per 100km more. Calculator says 967 to be exact.

Changing from a 215/55R16 to a 225/55R16 then, puts your speedo out by another +2% on top of the legal limit of +/-10%. Could make it better or worse depending on where it was on that +/- 10% scale, if already at the top, you're now at +12% (so doing 12% more speed than you are seeing on the speedometer) and if it was at -10% then you would now be at -8%

Hard to tell beforehand, whether it results in a problem then. Until the speed camera decides for you! At an indicated 70 mph, with a +12% speedo, you are actually doing 78.4 mph. Enough for a ticket? (yes, your Honor)