After getting what looked like a piece of WW2 shrapnel in a pretty much new pilot sport 4 s yesterday (they think its actually a wheel weight from a steely, it was bloody massive I know that) and rocking the space saver look since then I have had no ACC. 

 

Question is does the car know that this is not the correct wheel and disable it? 

 

The manual says to try to turn the engine off and try again, so this morning I stored the tyre pressures as it was still showing the warning from the flat yesterday and it briefly worked at slow speed but as soon as I was over ~30mph it threw the error again saying that it wasn't available. My commute is mainly motorway which was fun on the space saver and halfway through that it threw another error in the tyre pressure monitoring system so I am not sure what that is about, my hope is again that it fixes itself when the proper wheel is back on. 

 

My main concern is the ACC as I use it all the time, if having the proper wheel back on there doesn't fix it does anyone have any other ideas? They're getting a new 4S in this morning so hopefully by the end of today it should feel better to drive at least. 

I'm sure I've read on here before that having the space saver on disables the acc. 

Yeah i've run with the space saver and ACC is disabled.

Thankfully the ACC is disabled when a slightly different size tyre (odd one out tyre)  on a spare wheel is fitted as the car should be kept to 50 mph max when on an emergency spare even if it has no warning sticker.

 

As to the TPMS. That can be reset when a Spare is put on so that the warning does not sound or show for the TPMS,

When the correct tyre / wheel is refitted and the pressures checked and set on the other 3 you then reset the TPMS again.

Cruise Control is disabled due huge diameter difference,

but that is only my guess, after replace tire on my 16" disc i haven't had to use it

 

On 14/04/2018 at 08:09, MartiniB said:

replaced stock 205/55r16 by full diameter 205/65r16
weren't easy put it in cause back side plastic

 

diameter comparison to 215/55r17 and 225/55r17:
205/55r16 _ -5.3% _ -6.7%, this huge size difference cancels usage of cruise control
205/65r16 _ +0.8% _ -0.7%, not tested yet

 

 

 

 

  

Sensibly, the speed limiter still works with an odd tyre on  It amazed me how quickly it's detected when you set off too.

Thanks for the replies everyone, has put my mind at rest that all should be well once the new tyre is on the car again. Makes sense that it is disabled as yes the diameter difference between the two is huge. So glad the Superb has a full size spare wheel though my last two cars haven't and I would have been stuck if this didn't. 

 

Is the wheel size that is fitted to the car hardcoded somewhere if its the case that it knows when a smaller wheel is fitted? Just wondering as you can get the wheels for the Superb in all sorts of sizes from the factory. 

 

 

You set the TPMS. 

The car knows what the Circumference / Rolling Diameter of tyres once the car starts rolling and that is what it remembers.

Then when a difference is noticed that will indicate a loss of pressure or a blow out that is what sounds / shows a warning. A change in Circumference / Rolling Diameter.

 

That is with systems that does not show actual pressures and sometimes the heat of the tyres.

couple different versions

 

2.0TSI    217hp    Diameter
215/55r17 -    26.3"    0%    ****
235/45r18 -    26.3"    0%
235/40r19 -    26.4"    +0.4%
255/35r19 -    26.0"    -1.1%
2.0TSI    276hp 4x4
255/30r20 -    26.0"    -1.1%
1.4TSI    123hp
215/60r16 -    26.2"    -0.4%
1.4TSI    148hp ACT
215/50r18 -    26.5"    +0.8%
1.8TSI    177hp
235/50r17 -    26.3"    0%
2.0TDI    188hp
235/35r20 -    26.5"    +0.8%

 

out of manufacturer approval
225/55r17 -    26.7"    +1.5% _ _ _ _ _ my choice
235/50r17 -    26.3"    0%
240/45r18 -    26.5"    +0.8%
245/45r18 -    26.7"    +1.5%
245/40r19 -    26.7"    +1.5%

245/35r20 -    26.8"    +1.9%
 

spare wheels
125/70r18 —    24.9" -5.3%    for 272/280ps 4x4
205/55r16 —    24.9" -5.3%
out of manufacturer approval
205/65r16 -    26.5" +0.8% _ _ _ _ _ my choice

 

https://tiresize.com/comparison/

 

Thanks, makes sense. 

 

New tyre is in and getting it fitted this afternoon, will reset the TPMS when its on and hopefully everything should be good afterwards 

Quick update on this to close it off...

 

New tyre on last night, all pressures checked and stored and all is well again, ACC and cruise working fine and no errors from the TPMS system. 

 

Just hope this tyre last longer than 1.5 months now! 

23 hours ago, Shaady said:

 Is the wheel size that is fitted to the car hardcoded somewhere if its the case that it knows when a smaller wheel is fitted? Just wondering as you can get the wheels for the Superb in all sorts of sizes from the factory. 

 

 

 

It (indirect TPMS) uses the ABS sensors to detect wheel rotational speeds.

If a tyre is running flat, or of a different size it will b picked up.

 

With direct TPMS, it has a parameter file in the tyre pressure module with different tyre size and associated pressures stored.

Edited 29 April, 20215 yr by JR RS