New Tyres for Octavia VRS, slightly bigger on profile size??

[Donweather]

5 minutes ago, zeta said:

You’re talking about fitting tyres with 9mm greater horizontal diameter … and the vertical diameter is unchanged? Are you re-inventing the wheel?

 

And all those SUV’s have the extra clearances you’re trying to fill. – It’s a fashion thing.

 

PS. I don’t need to know what a flush guard is.

Never mind. 

[SurreyJohn]

8 hours ago, Donweather said:

I’m no expert so I could be missing something but how does circumference affect ABS. Doesn’t ABS measure whether the wheel is moving or not moving. If it’s not moving then it reduces the braking pressure. I don’t understand how circumference would affect this?

Doesn’t the ABS sensors also affect the traction control.  If it detects different size wheels front and back, I thought it assumes you have a temporary spare and limits revs and speed.

 

 

[nta16]

11 hours ago, Donweather said:

It’s a fashion thing with the 20 inch rims and wider tyres trying to fill out the huge distance left by the stock rims and tyres to the guard edges.

The designers already oversized the wheels for fashion, fashion often has less regard to function.  They could fill out the wings to reduce the gaps also or as was once the fashion put covers (spats) over them.  Under the wheel arch is a gap distance from the arch to the tyre this is obviously is to allow for movement from the suspension and body, this is for loading and travelling the vehicle.  The more you fil that gap in height and width the less the range of movement available.  The Superb is a big car so potentially could be filled with people and luggage perhaps a roof rack too and/or towing.  Lots for the engineers to consider, not all of the considerations of course apply to all of the end users.

 

The use may include going over humps, over rough road surfaces or those with potholes, getting mud or snow build up under the arches and other stuff I can't think of now.

 

 

11 hours ago, Donweather said:

I have a Sportline which is a 4x4

I'm not an expert in anything but I thought 4x4 or is it (all-wheel-drive) you want tyres that are matched to in size and type to help maintain the drive system.  And I too thought the ABS interacts with the traction control, the VW computer programs in general seem very intertwined.

 

Some people find the larger wheels with ribbon tyres not only less practical but also a lot less comfortable, of course tyre selection would be a part of this, some even consider going to, or back to, the smaller sized wheels (Mk2 not 3). -

  

Edited 7 September, 2022 by nta16

[KenONeill]

9 hours ago, nta16 said:

I thought 4x4 or is it (all-wheel-drive) you want tyres that are matched to in size and type to help maintain the drive system.

You do, unless the drive system is specifically engineered to deal with the different rolling radii.

[zeta]

22 hours ago, Donweather said:

Never mind. 

OK it’s bugging me now. What is a flush guard?

[Donweather]

5 hours ago, KenONeill said:

You do, unless the drive system is specifically engineered to deal with the different rolling radii.

So a no go for different tyre sizes front and rear then in the 4x4 superb sportline?  How do they do it in the Audi S3s, RS3's etc because I've seen staggered wheels (and hence presumably different tyres) on these.

[Donweather]

1 hour ago, zeta said:

OK it’s bugging me now. What is a flush guard?

Ok, it's where the tyre wall sits vertically flush with the edge of the guard.  You know what the guard is yeah?  ie the tyre is not recessed (horizontal offset) into the wheel well.  Also known as a flush fitment.

 

https://www.fitmentindustries.com/blogs/161/4-different-styles-of-fitment

[KenONeill]

6 hours ago, Donweather said:

So a no go for different tyre sizes front and rear then in the 4x4 superb sportline?  How do they do it in the Audi S3s, RS3

I don't know the detail engineering of specific fitments; just that it's usual to stick to OEM wheel and tyre sizes all round.

[Carlston]

10 hours ago, Donweather said:

So a no go for different tyre sizes front and rear then in the 4x4 superb sportline?  How do they do it in the Audi S3s, RS3's etc because I've seen staggered wheels (and hence presumably different tyres) on these.

 

Cars that fit staggered tyres, usually have a similar outside diameter.

 

Even if the staggered tyres don't have the same outside diameter, the manufacturer would have programmed the car's electronics accordingly.

 

Edited 8 September, 2022 by Carlston

[nta16]

10 hours ago, Donweather said:

How do they do it in the Audi S3s, RS3's etc because I've seen staggered wheels (and hence presumably different tyres) on these.

Were those factory standard or modified cars?

[zeta]

13 hours ago, Donweather said:

Ok, it's where the tyre wall sits vertically flush with the edge of the guard.  You know what the guard is yeah?  ie the tyre is not recessed (horizontal offset) into the wheel well.  Also known as a flush fitment.

 

https://www.fitmentindustries.com/blogs/161/4-different-styles-of-fitment

Thanks Donweather, for the link at least (definitely not what Google found) – your description however is less illuminating.

So,

• What you call the guard, is what the link calls the fender – and everybody else calls a wheel arch.
• Your (horizontal offset) should be (no horizontal offset) – and ‘not recessed’ doesn’t really need clarification
• Vertically flush should be horizontally flush – ie, the movement to make it not flush, is horizontal cf. horizontal offset

This is apparently (according to your link) flush fitting;-

  Maybe they were aiming for flush – what they got is poke!

 

Still, the gap from tyre to arch is greater than the poke.

Good luck with the ride and handling, if you want to minimise that gap.

 

[Ootohere]

^^^ That is a good example of what is not legal in the UK if you can see the tyre when looking down from directly above.

 

[nta16]

2 hours ago, zeta said:

the fender – and everybody else calls a wheel arch

😁 Not so I'm afraid, what we called the wing those over the pond call a fender, the wheel arch is part of the wing - we'll that's how it is with old folk like myself.

[zeta]

16 minutes ago, nta16 said:

😁 Not so I'm afraid, what we called the wing those over the pond call a fender, the wheel arch is part of the wing - we'll that's how it is with old folk like myself.

Actually, we were both talking about the guard. The link Donweather provided, used the term fender. But I wasn't trying to find an English equivalent for fender, I was trying to find an English equivalent for guard.

I understand fender is usually reserved for front wings, in cars at least, with the rear wing called a quarter panel.

I think wheel arch is best in this context, especially as my Octy III has three panels around the front wheel; wing, bumper & outer sill. Even our American cousins on first encounter, would understand wheel arch.

None of these terms are exact equivalents. I chose the closest to ‘edge of the guard’.

PS. I did think flush guards were guards for the flushes. And yes, there are such things, just not in this context.

[nta16]

1 hour ago, zeta said:

Actually, we were both talking about the guard. The link Donweather provided, used the term fender. But I wasn't trying to find an English equivalent for fender, I was trying to find an English equivalent for guard.

Oh, OK, fairy snuff.

 

1 hour ago, zeta said:

I understand fender is usually reserved for front wings, in cars at least, with the rear wing called a quarter panel.

Ah, yes, sorry I forgot, I'm old, and I'm no good at English let alone American, no wonder the spellcheck can't understand my speelings.

 

I was trying to lighten things a little, but I've probably heated you up more, another fail. 🙁

 

 

[zeta]

Thanks nta16, your efforts are not unappreciated.

39 minutes ago, nta16 said:

Ah, yes, sorry I forgot, I'm old, and I'm no good at English let alone American, no wonder the spellcheck can't understand my speelings.

I’m not exactly young myself, and I thought a fender was a bumper (to fend off other cars 😁) so I had to Wikipedia it. My reference vehicle for such Americanisms, is Chitty Chitty Bang Bang! which IIRC had four fenders, so … just can’t rely on anything these days.

39 minutes ago, nta16 said:

I was trying to lighten things a little, but I've probably heated you up more, another fail. 🙁

Don't worry; very chilled here. Just can’t help being a pedant 🙁

[Donweather]

8 hours ago, zeta said:

Thanks Donweather, for the link at least (definitely not what Google found) – your description however is less illuminating.

So,

• What you call the guard, is what the link calls the fender – and everybody else calls a wheel arch.
• Your (horizontal offset) should be (no horizontal offset) – and ‘not recessed’ doesn’t really need clarification
• Vertically flush should be horizontally flush – ie, the movement to make it not flush, is horizontal cf. horizontal offset

This is apparently (according to your link) flush fitting;-

  Maybe they were aiming for flush – what they got is poke!

 

Still, the gap from tyre to arch is greater than the poke.

Good luck with the ride and handling, if you want to minimise that gap.

 

Thanks so much for the impressive inordinate response.

[nta16]

3 hours ago, zeta said:

Just can’t help being a pedant

I used to put I was a pedent and that would keep the Spelling and Grammar Police, pedants and the offended happy - you can have that to use, I'm always willing to serve. 😁

 

ETA: yes I keep thinking of a bumper when the American say or put fender - but remember bumper cars are/were actually supposed to be dodge-'ems.

Edited 9 September, 2022 by nta16

[EnterName]

On 06/09/2022 at 23:50, Donweather said:

I think that’s exactly why he was asking the question as I’m suggesting using different rolling radius tyres front and rear. 

Bingo!

 

On 06/09/2022 at 22:28, Donweather said:

I’m no expert so I could be missing something but how does circumference affect ABS. Doesn’t ABS measure whether the wheel is moving or not moving. If it’s not moving then it reduces the braking pressure. I don’t understand how circumference would affect this?

Hang on, I'll dust off MS Paint...

Right, there we are.

So this image is based on how I understand ABS works. I've exaggerated the wheel size difference and only put 4 ABS markers on each wheel, but the principle is sound.

The ABS system gets a regular "tick" from each ABS wheel sensor as the ABS marker passes the ABS sensor. When braking, the frequency of the ticks should reduce, because the wheels are rotating more slowly as the car slows down. However, the ABS ticks from each wheel should all come in at roughly the same frequency. (Note, there may well be a speed difference on an axle due to the cornering and the outside wheel rotating faster than the inside wheel. I'm going to disregard that in this example.)

The next bit depends on the sophistication of the ABS system, but for this purpose, I'll assume the ABS system is thick as pudding and very basic.

If one of the ABS wheel sensors doesn't send a "tick" to the ABS unit, the ABS unit says "Ah ha! That wheel is locked, I'll loose off the brakes a bit until it regains traction. I'll know when it's got traction, as I'll get a tick from the ABS wheel sensor."

So it releases the brakes on the locked wheel, get's the "tick" from the now rotating wheel, and then thinks "There we go! All good now, I'll re-apply the brakes."

 

All this happens very quickly.

 

The problem I'm highlighting, is that the extra time between ABS ticks on the larger diameter wheel & tyre combo MAY be enough to cause the ABS to think "I haven't had my ABS wheel sensor tick, the wheel must be locked. I'll release the brakes on that wheel."

 

Now it might not be a problem at all. But also it might be, which is why I mentioned it.

Edited 9 September, 2022 by EnterName
More explanation added for clarity.

[nta16]

Another way to squint at it. -

 

235/40 R19 - Revolutions per mile = 764

 

245/35 R20 - Revolutions per mile = 754

 

255/30 R20 - Revolutions per mile = 775

 

Info from - https://tiresize.com/tyre-size-calculator/