question on rear tyre size help plz!

[Alpha Trion]

Hi guys,

i'm due for rear tyres and i will be going PSS again. My supplier tells me he can't get them in my current 255/35/18 but he can get them in 255/40/18 or 265/35/18

QUESTIONS..

Are there any issues with running 265's on the stock wheel (rubbing etc)?

Will the difference between 35 and 40 (on the 255's) profile affect my speedo or anything?

Thanks for the help

[OzJustin]

I'm not sure whether 265 will fit the stock rim (will be mighty close to max I'd think) but 40 profile will have a mild impact on your speedo.

Head to willtheyfit.com & input your stock & desired tyre sizes & it will calculate your % speed difference at 100kph.

[flinchy]

265 on the stock wheel is a bit too wide

not sure on rubbing, check how close you are now and measure out 5mm more each side, and a fair bit taller too.

[BMW86]

I ran a 265/30/19 in PSS when they first came out because they didn't come out with 255/30/19 initially.

I rubbed in the rear with my guards rolled but I was quite low. The PSS in 265 is the equivalent of a 275 in some other brands. It's square and wide.

[135]

The measured rim for a 265 tyre is 9.5", while the permitted rim range is 9.0-10.5", therefore, a 265 tyre is not permitted to be fitted to the OE rear wheel, which is 18x8.5". That's not to say that you can't physically fit it on. A PSS 265 should clear the lip, although, depending on the section width (and PSS do run wide and square), you may need a slight roll. The difference between a PSS 255 and 265 is 0.5" / ~13mm, so you'd want to ensure you have at least 7mm additional clearance on the inside and outside.

The 255/40 is not an option since its 1" taller than a 255/35 (and 1.2-1.3" taller than the OE 245/35) so you'd have height clearance issues, not to mention speedo inaccuracies being amplified.

[Alpha Trion]

Thanks for the replies.

ok so where else can i get PSS in NSW? Gotta be 255/35/18.

[martymil]

I ran 255 40 18 for a long time no issues as it gives more grip with the slightly taller side wall.

[Alpha Trion]

speedo was ok martymil?

totally agree with the taller profile and more grip! If you're saying no issues with speedo and rubbing i'll go for them.

[martymil]

Standard speedo is out by 4 to 5 km from factory when you put the 40 series tyre on it will only be 2 km out so more accurate with less safety margin for cameras

[Alpha Trion]

255/40's coming in tomorrow. Mate at Bob Jane hooked it up for $375 each.

Happy days and thanks for the help martymil

[135]

A 255/40 is ~5% taller than the OE 245/35, which translates to almost 6km/h at 110km/h, i.e. you really travelling at 116km/h even though your speedo indicates 110km/h. My speedo currently reads 3km/h under, so, if I were to fit these tyres, then this difference would mean that I'm now travelling 3km/h faster than the 110km/h indicated by the speedo. I'm not sure what it is like in Sydney but I've heard of people getting fined for travelling 1 or 2km/h over the limit in Melbourne/Victoria.

Apart from the speedo differences, a more important factor in determining which tyres to fit is the Vehicle Standards Bulletin (VSB 14), NCOP10, Section LS (Tyres, Rims, Suspension and Steering), Paragraph 4.2.4 Overall Nominal Diameter, which states:
The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

A 255/40 tyre (and 245/40 and practically every 235/40) does not satisfy this requirement, therefore, it is not permitted to be fitted to your vehicle.

I'm extremely surprised that Bob Jane didn't point this out to you. If it was me, I'd be cancelling the order at their expense and finding suitable tyres.

Paragraph 4.2.12 regarding load rating and speed rating is equally important, for which the PSS 255/40 tyres do satisfy.

[PG]

sorry to Hijack the thread
I am running 255/40 PSS rear and 225/40 fronts.
Speed at 110kmh set on cruise control, on P3 Guage is around 102kmh, and around 106kmh via GPS on phone.
... which should I trust?
I do loads of long distance driving and havn't been pulled over yet with Cruise set at 121kmh, with P3 showing around 114kmh....
any insights?

[martymil]

Trust the phone it's dead accurate

[Superdaws]

Isn't the max 15mm larger tyre limitation on the tyre width? I.e. 255 only 10mm more than 245 standards...

[Alpha Trion]

had them fitted today. turned the tomtom on to see what the difference is and it is telling me that i am spot on 100 when my speedo says 100.

my speedo (according the tomtom) before said 97 when speedo said 100.


I'll try the phone next time and update.

[MrBlonde]

Originally Posted by 135

..
Apart from the speedo differences, a more important factor in determining which tyres to fit is the Vehicle Standards Bulletin (VSB 14), NCOP10, Section LS (Tyres, Rims, Suspension and Steering), Paragraph 4.2.4 Overall Nominal Diameter, which states:
The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model...

So what?

[BMW86]

If you've got the P3 gauge and set it to the Speed menu it will tell you your real speed too. I think I'm doing 94 when my speedo says 100.

[ALLSHW]

didn't want to start a new thread

having trouble deciding on rear tyre size

i have a 19x10 ET45 wheel. i have done some measurements and a trial fit without tyre, i believe the setup is possible with:

235/35/19 or
245/30/19

since a 10 inch wide wheel is 254mm they will be some stretch on the tyre.

235*0.35=82.25mm sidewall
245*0.30=73.50mm sidewall

i have never purchased a 30 profile tyre so my question is which option should i go for?
do i chase 10mm width and lose some sidewall or go with the narrow option and gain some sidewall?

[PeteA]

Could always get a 1M tyre place card and do a swap.

[135]

Originally Posted by ALLSHW

i have a 19x10 ET45 wheel. i have done some measurements and a trial fit without tyre, i believe the setup is possible with:

235/35/19 or
245/30/19

since a 10 inch wide wheel is 254mm they will be some stretch on the tyre.

A "10in wide" wheel is actually ~11in wide.

The quoted wheel width (10" in your case) is the measurement between the bead seats (inside the flange).
Each flange adds an addition ~0.5", therefore, the overall/full/actual wheel width measured from the outermost extremities of the rim's flanges is very close to 11" (279mm).
The overall wheel width is used to calculate backspace [and frontspace], which in turn determines the wheel offset.

Unless your right into that whole stretch craze, you don't want to be fitting 235 or 245 tyres on an as-advertised 10" wheel.

The ideal tyre to use would be something with a section width of 280mm or more when fitted on a 10" wheel.
Note that if the Measured Rim for a particular tyre is less than 10" then you need to increase the section width by 0.2" (5mm) per 0.5" increase in wheel width difference between the Measured Rim and the target wheel width, e.g. 10". This means the section width would:
- increase by 10mm for a 255 tyre
- increase by 5mm for a 265 or 275 tyre
- remain unchanged for a 285 tyre

Rarely, a tyre manufacturer specifies an extended wheel width range, although the Measured Rim always stays the same (industry standard).

Semi-slick / R-comp tyres can run wider, even exceptionally so, but the above still applies. An example is the Hoosier R6/R7 twin-groove semi-slick, which, among other sizes, is available in a 255/35/18 (which runs extemely wide) and 275/35/18, although, the tread width of both is 262mm! Here are their other keys specs:

255/35/18
- 9.0" Measured Rim
- 275mm Section width when fitted on the Measured Rim
- 285mm (+10mm) - Section width when fitted on a 10" wheel (1.0" wider)

275/35/18
- 9.5" Measured Rim
- 277mm Section width when fitted on the Measured Rim
- 282mm (+5mm) - Section width when fitted on a 10" wheel (0.5" wider)

This is all theory but, in my experience, it matches in practice (or at least within 0-2mm).

Here's another post where I discussed the same topic.

[martymil]

Originally Posted by ALLSHW

didn't want to start a new thread

having trouble deciding on rear tyre size

i have a 19x10 ET45 wheel. i have done some measurements and a trial fit without tyre, i believe the setup is possible with:

235/35/19 or
245/30/19

since a 10 inch wide wheel is 254mm they will be some stretch on the tyre.

235*0.35=82.25mm sidewall
245*0.30=73.50mm sidewall

i have never purchased a 30 profile tyre so my question is which option should i go for?
do i chase 10mm width and lose some sidewall or go with the narrow option and gain some sidewall?

There is no way that wheel will fit a 135 without major fender work.

Been there done that, even with a stretched tyre you are going to rub hard.

[135]

Originally Posted by martymil

There is no way that wheel will fit a 135 without major fender work.

Been there done that, even with a stretched tyre you are going to rub hard.

It looks like ALLSHW has an E87 hatch so, if it's a 123d or 130i, it will have 10mm narrower hubs, which help with wheel offsets, so a 10" wide wheel with +45 offset will fit, as long as its guards are similarly shaped to a 135i.
I would still fit a wider tyre that's suited to a 10" wheel though, e.g. 265/30/19.