Mismatched tyre size

DJ5831 · 17-11-2023 4:24pm #1

I've put new 19" alloys on my B8 A4 S-Line and sold the original 18" alloys. The correct tyre size for 19" alloys on my car is 255/35R19 however the tyres that came on these alloys is 255/40R19 so slightly bigger. Speedo is fine although 3-4km quicker reading, and no rubbing etc.

The tyres are coming up to needing to be changed so my question is whether or not it's okay to change the front 2 tyres to the correct 35 size and leave the 40 tyres on the rear until I can get them changed too in the near future, or do I have to wait until I can change all 4 tyres to the correct size? I'd never mismatch a size or tyre across any 1 axle but having slightly bigger tyres on the rear only shouldn't make any problems right?

Casati · 17-11-2023 4:28pm

Swap the fronts to rear and change all four together to the correct size. Having a larger wheel of 11.75mm is quite a lot

DJ5831 · 17-11-2023 4:37pm

https://www.boards.ie/discussion/comment/121380970#Comment_121380970

All 4 tyres need to be changed just as bad an each other and in an ideal world I'd change all 4 tyres or stop driving the car for now but I'm not in a position to change all 4 tyres at the moment, so would it be better to hold off until I can change all 4, and continue driving with the 4 worn tyres or to change 2 fronts to new 35 tyres and then change the rears in the near future?

artanevilla · 17-11-2023 4:48pm

Change all four, if they are in a bad enough state that you shouldn't be driving on them then you are in a position to change all four, because no matter the cost of that, the cost is much much less than pulling your car out of a ditch/having a blow out on the motorway and ending up under a truck/having your car seized by the guards/crashing/killing someone.

DJ5831 · 17-11-2023 4:55pm

https://www.boards.ie/discussion/comment/121381051#Comment_121381051

2 fronts are on 1.6mm exactly and the 2 rears are on about 1.4 or 1.5 just ever so slightly under the limit, they're actually Pirellis too. They aren't going to blow out or cause a crash but I do need to drive the car every day for 20km commute.

Padre_Pio · 17-11-2023 4:58pm

https://www.boards.ie/discussion/comment/121381079#Comment_121381079

Is the difference between the 35 to 40 that noticeable that you want to change it?

hoodie6029 · 17-11-2023 4:59pm

You need 4 new tyres.

1.6mm legal limit is from the 1960’s. 3mm is the real world minimum

Esel · 17-11-2023 5:02pm

The tyres are coming up to needing to be changed...

No, they need to be changed now!

User1998 · 17-11-2023 5:43pm

Just for clarification, having two different tyre sizes is perfectly fine as long as they are on separate axels. So the front two being different to the rear two is fine.

But because of your low thread depth you need to change all four

hoodie6029 · 17-11-2023 5:45pm

This thread seems strangely familiar. Like we had it a few months ago too. ‘My tyres are in sh1t. Should I change them?’ And lots of follow up posts from the OP on what they could ‘get away with for now’.

Or am I just having déja vu?

mikeecho · 17-11-2023 8:26pm

https://www.boards.ie/discussion/comment/121381313#Comment_121381313

This is exactly why we need the NCT.

Without it, we'd be back to the days of bald tyres, and exhausts held on with bail twine.

(And doors kept closed with seat belts)

.. those were the days

hoodie6029 · 17-11-2023 8:34pm

https://www.boards.ie/discussion/comment/121382044#Comment_121382044

Remember meeting a mk1 Jetta in West Clare in the mid 90’s. Heard it coming for miles. The exhaust and one front wing were on the back seat along with a very excitable dog.

The driver stopped to offer me a lift. I was about 11, I peered through the muddy windows and thought the better of it. If it was raining I probably would’ve gotten in. (eh, it was the 90’s)

Summitatem · 17-11-2023 9:42pm

I doubt 255/35R19 are correct for a b8 s line

mickdw · 17-11-2023 9:56pm

255 35 19 on the front of a b8 will be a pig ... it will pull all over the road I'd say.

I'd change to 245 35 max on the front and fit 255 35 on the rear if you want to for appearance. That set up is well within tolerance.

if its not a quattro, you should be fine to mix front to back. Worst that could happen is abs / traction control getting excited.

I'd change 2 tyres to 255 35 first then the 2 245 35 to.keep the variation as small as possible.

DJ5831 · 18-11-2023 10:38pm

https://www.boards.ie/discussion/comment/121382414#Comment_121382414

https://www.boards.ie/discussion/comment/121382512#Comment_121382512

255/35R19 is indeed the correct tyre size for the B8 S-Line according to all online sources + the sticker inside my door

What do you mean be 255/35 being a pig? I was under the impression that the correct tyre size would be the best for the car in every regard, 255/35 is the only tyre size for 19" wheels officially supported by Audi for the B8 S-Line.

Surely 245/35 would give less sidewall hence less protection for the larger rim against potholes... I don't want to crack it and go down the road of welding it, they're genuine original RS4 alloys. It isn't a Quattro it's just FWD but my question is why go to the smaller 245 tyres at all? It's still 35 profile anyway so what's the difference going to be? Apologies if I'm missing something, I'm not familiar with tyres and wheels etc.

mickdw · 18-11-2023 11:24pm

Just that width of tyre on the steering axle will be inclined to tramline and follow road unevenness.

I've an A5 of similar vintage and it's on 245 40 18.

I tried 255 (30 or 35) 19 at the time when buying and it was absolutely a pain in the hole on country roads.

The A5 has a more extreme wheel offset that the A4 I believe so maybe A4 not as bad.

I know we are talking front drive here but a ferrari 430 for example will typically have 225 35 19.

255 is too much tyre to be steering on anything bar motorway smooth roads.

DJ5831 · 19-11-2023 12:16am

https://www.boards.ie/discussion/comment/121386502#Comment_121386502

Thank you - I appreciate you sharing your knowledge. Forgive me if this is unrelated but I switched from normal S-Line 18s to the RS4 wheels (technically called S4s because they're 66.5mm bore so from the B8 S4 as opposed to the old B7 RS4 57.1mm bore) but when I measured them they're actually 9-9.5" wide which seems wider than the standard 18s were, does this matter?

Also, what about sidewall protection? Wouldn't 245 make the wheel more likely to crack on a bad pothole? I'm based in Wicklow/Carlow so not the worst roads ever but I do worry a lot about cracking them. They're genuine stamped and never been cracked or welded before, so am I overthinking it?

Summitatem · 21-11-2023 6:22pm

Apologies....for non quattro b9s 255 35 19s are larger circumference than the OE recommendation so though I was incorrect I'm surprised Audi recommend them for the b8.

I'd have no concerns about handling or tramlining etc though.