Rear Tyre Width - Michelin PS5

[Patchy]

Apologies I know the subject of tyres has been worked extensively. But I have 3-4 very specific questions and think I've made a mistake.

I have a 3.0si Coupe (2008) with BM Autosport 18" CSL copies (18" Veemann VC359 M359 5x120 9.5"et45 Quartz Silver 72.6cb). I had Bridgestone Ponza's 255/35R18 - 94Y – VRT5 P3H 0218 that I moved from my old rims and they looked fine.


I needed to replace my tyres this year and as the rims could take a wider tyres, But after reading a number of discussions wider tyres creating more tramline effect. So I decided to stay with this size of tyre but move to Michelin PS5's (I had PS4's on my mini cooper s and they were superb and again positive feedback in the discussion groups for Z's).

But the more I look at the tyres they look to narrow for the rims... I had someone round yesterday and without prompting suggested the tyres looked a bit narrow.

Questions :

- Has anyone had a similar experience?
- Too narrow tyres on the rims - What is the impact is it just more chance of scraping allows?
- What size of tyre have you fitted to the back of your Z4 Coupe and not had an issue with rubbing etc?
- If I decided to swallow my pride, take a loss and switch tyres is eBay the best option to sell the almost new PS5's?

Any feedback appreciated, I've asked BM Autosport and they would normally match a 265 PS5 to this rim.

Nick

 

[TheDan]

Tyre widths table (very useful to have lying around or saved somewhere on your computer):



In terms of why the 255s might look narrow is probably because they are a low profile tyre (35). This can make tyres that are on the stretch side of the widths table (in your case 245 and 255) look even more stretched because there isn't much sidewall to account for the stretch.

If you have any pictures that would be helpful to see how stretched they look.

If you want to sell tyres the forum is a pretty good place for standard sizes such as the 255/35/18. Alternatively, if they're priced well, FB marketplace is also a good shout.

 

[Patchy]

This is superb and really helps, I'll take a photo and post but this really gives some comfort that it's not way way off..

Thanks for the feedback.

Nick

 

[Pondrew]

Tyre widths table (very useful to have lying around or saved somewhere on your computer):

according to one member that is a 'very basic' table, though! I have used it a lot and it seems fine to me. :idunno:

 

[plenty]

There can be variation in actual width between tyre variants. Some tyres advertised as 255 might actually be closer to 245 and others 265.

A slight stretch won't be an issue from a handling or safety perspective although you may lose some of the protection afforded by the rim protector.

 

[axelleveau]

I like to use the chart from that link as it has different values depending on tyre profile: https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart

 

[Z4Mariner]

Thanks for the table, TheDan. I recently went through a similar tire decision. Plenty's comment on variation in sizing by manufacturer is quite true.

Since I'm in the US, I used TireRack's web site to find specs for each tire model in multiple sizes - I imagine that one or more UK vendors have similar spec lookups. It took a little time, but I spread-sheeted: total width, tread width, diameter, and recommended wheel width upper-lower limits for each tire model I was considering. Seeing those data side-by-side helped my decision.

 

[Patchy]

As promised here are some photos... (The first on his just because... 2009, 65k miles, ex demo so all the gadgets except sat nav... black leather seats)

 

[Pondrew]

Sorry but they look too narrow for the wheel IMO.

 

[warmasice]

That looks wrong tbh. I agree with @pondrew

 

[Pondrew]

I agree with @pondrew

I think that may be officially against the rules now. :wink:

 

[Z4Mariner]

Hi Patchy, nice coupe !

I agree with others, the tire seems too small for the wheel width. I checked a US vendor and their data (from Michelin) says a Pilot Sport 4S in size 255/35R18 should be fine on up to a 10 inch wide wheel. I can read the tire sidewall on your tire, and it seems correct.

Some almost silly questions: 1) Does the inside (toward center of the car) of the wheel and tire look the same as the outside ? 2) Have you ever measured the wheel width to be sure it's really 9.5 inches ? (and tricky part is that the actual measurement is on the inside of the wheel sealing surface) 3) how much have you driven on the new tires ? and 4) Have you had a conversation with tire installers about this ?

Q's 3 & 4 are in case the tire is not fully seated onto the outer sealing surface of the wheel 'barrel'. I don't know the geometry of your wheels, but if the barrel design allowed the tire to seal and hold moderate pressure without pushing the bead all the way to the edge of the rim, maybe you could get this effect? Seems very unlikely, but . . . If the tire installer didn't use any soap or tire "slime", maybe this could actually happen ?

I'm hoping you get to the bottom of this ! Very curious how all the numbers can seem right, but the result isn't.

PS Editing to add that the PS4S data say a cross-section width of 10.2 inches. This might be a clue, because the 9.5 inch wheel width is inside, and if the wheel lip is more than 0.35 inch per side, the wheel would stick out. Can you get data on your old tires to see whether they had a larger cross section width ?