W16W to W21W - is it a straight swap?

[silver1011]

My Superb (Twindoor) uses a W16W single filament capless bulb for the dual function brake and tail light.

 

I've always been critical of the Superb's poor brake lights, they aren't very bright in my opinion.

 

Can I swap them for W21W bulbs? These are bigger so they might not physically fit.

 

However I also wonder if the CANBUS will pick up on the different bulb and flag up a warning on the dash?

 

W16W (955)...

 

 

 

W21W (582)...

 

[adamal]

I presume it's a 21w bulb vs a 16w bulb. If so the resistance difference is probably enough to register a bulb warning. Maybe worth a try though if it fits?

[mannyo]

The bulb will have a lower resistance than the original one and this may fool the canbus into thinking something is wrong, of course adding resistance will just make the bulb dimmer again.

I never had a problem with the Superb2 brake light brightness when I had my 2008 one, they seemed no different to any other car with filament bulbs.

edit. beaten to it.

[silver1011]

Yes, the OEM is 16W, I was thinking of trying a 21W. I'm not too sure how the blown-bulb system works. I appreciate it measures resistance across the bulb, but would a higher watt bulb create more or less resistance?

 

There aren't many Superb's out there so it is rare I get to travel behind another one, but each time I do it always strikes me that the brake lights are dimmer than other cars. When refitting the standard clusters to my car today (used to have the LED clusters) I checked the bulb and noticed it was only 16W, which kind of supported my observation of them being a little less bright than normal.

[mannyo]

Higher wattage bulbs need more power, to get more power you lower resistance.

[silver1011]

That makes sense thanks.

 

So a blown bulb means the resistance is increased? I wonder then if I'd get away with the reduced resistance of a 21W bulb?

 

I did notice on VCDS that there is an option to increase the bulb brightness, but looking at this the choice is either headlights or tail lights, not brake lights...

 

 

[LasseTheDude]

Taillight is every function in tail I think

[adamal]

I think in practice it's a change rather than simply an increase in resistance that is picked up.

[100andthirty]

The detection system puts a small current though the bulb to detemine whether the circuit is complete. Clearly a blown bulb is an open circuit so is easily detected. Some people who have fitted LEDs have noticed that the bulb flashes momentarily on start up because of this current. LEDs take a lot less current than a normal bulb so often trigger the blown bulb detection. This is because they have a much higher resistance than normal bulbs, and, based on all the experience reported in these forums is roughly at the threshold of being detected as faulty by the car.

Compared with LEDs, we are talking about a lower resistance, and in any event, the difference between the 16W and 21W bulb is quite small (compared with a normal bulb and LEDs) and I would be surprised if it's a problem. As the cost is likely to be only a £ or so, I think best thing would be try it.

PS. On my estate, which I have followed, the brake lights seem plenty bright enough

[langers2k]

I don't think the car will notice the difference but I think the connector on a w21w (T20 ?) is much wider than a w16w (T10) which will probably cause you problems.

[silver1011]

I think you are right Rob, after a little more research the base fitment of the W16W is described as W2 1x9 5T, whereas the W21W is W3 x 16d.

 

Presumably the W2 and W3 represent different size bases.

 

Never mind, I might try the brightness setting in VCDS instead.