Top down driving in rain

[bcworkz]

Almost everyone has at least heard, or had first hand experience, that one can drive in the rain with the top down and stay reasonably dry, provided a particular speed is maintained. This has been my experience as well, until now. A few days ago, I attempted to drive through a sudden thunderstorm while on the interstate/motorway. There was no chance I would have to slow, and I was certainly going fast enough, at the legal limit of 80 mph. So I gave it a go. Unfortunately, everything in the passenger area received a heavy misting, quite unlike my previous experiences. Fortunately, I had a small towel on hand to immediately dry off all the electrical bits, and so far have suffered no serious consequences.

Is it possible to drive too fast to stay dry? So much turbulence (no wind deflector installed) that the water drops were carried by the strong wind back wash into the cockpit? Or maybe different turbulence? This was the only time I did this with the windows fully up, raised due to significant water coming off the windscreen flowing over the A pillar and into the cockpit.

Or is it possible to rain so hard that the drops fall through the protective wind stream, even though broken up into smaller droplets by the wind? It was raining quite heavily for a couple minutes. The small droplets that got in were fairly uniformly distributed, no particular area seemed to get wetter than another.

I'd like to determine just what caused this so I can avoid the same situation in the future. And please don't tell me it is caused by rain and that I need to avoid it. Anybody have any idea about just what caused this uniform, heavy misting to occur? When driving in the rain, should I drive slower? Keep the windows down? Drive around the heaviest part of the storm?

 

[Bing]

In my experience...

There is a point at which the rain becomes too heavy, even at high speed, for you to stay dry. Leaving the windows down makes it worse because the water comes straight off the screen round the A pillar, but in heavy rain I find the water travels along the top of the window and then down inside anyway. I think the lack of a wind deflector will add to the problem because of the Venturi effect that draws air back into the cabin... Which the wind deflector reduces, but does not eliminate.

Just a quick thought before going back to work

 

[nick_z4]

I find that you can travel in most rain storms with the wind deflector in place and windows up at 60 mph+ and not get "rained on", of course you'll get the odd splash from water running along and off the window tops etc. I can remember once driving on the motorway at about 80mph in a Thunder and Hail storm and as soon as you cant see the road in front of you for water and the wipers are going crazy, thats when you really start to get wet - i had hail bouncing throughout the interior. It wasnt the best roof down experience ive ever had :roll:

 

[buzyg]

I drove through most of Northern Belgium last year in a heavy rain storm with the roof down. Very little came in to the cabin.

Quite sadly I have just Googled the velocity of rain & it's only between 20-25mph depending on droplet size and other atmospheric conditions. So I can see why it is generally deflected up and over the passenger cell. At higher speeds there is a lower pressure in the cabin area, due to Bernoulli' effect ,so I would expect less rain the faster you go. Certainly not having the wind deflector in place will be worse.

It would be interesting to know if there is an optimum speed for staying dry but I doubt it myself. Other than go a little faster.

Edited due to Mr Bernoulli' not being called Venturi

 

[Bing]

It would seem 90mph should do it...

http://mythbustersresults.com/car-vs-rain

I knew all those hours watching Discovery would come in useful, and I also got to watch a lot of Kari Byron, who I adore :wub:

 

[Jembo]

It would seem 90mph should do it...

http://mythbustersresults.com/car-vs-rain

I knew all those hours watching Discovery would come in useful, and I also got to watch a lot of Kari Byron, who I adore :wub:

Thanks Bing, will save this as the excuse why I'm doing 90 in the rain if I get stopped

 

[RichardG]

I also got to watch a lot of Kari Byron, who I adore :wub:

Does this moving to the guilty pleasures thread?
But I know what you mean.......

 

[Anonymous]

Kari Byron is just sex on legs, everytime she opens her mouth I melt at the thought of what I would ...........................

 

[deka]

no guilty pleasure there she is top tottie

 

[bcworkz]

If not for Kari, Mythbusters would be only marginally worth watching. While they have some good topics, others are quite silly and hardly worth my time.

Considering the Bernoulli principle and eddy effects, it's remarkable we stay dry at all. On further reflection, I think minimising chaotic cockpit turbulence is the most effective measure after maintaining a reasonable speed. Avoiding rain is still not an option. With no wind deflector and windows down, there is a strong eddy current, but it is not chaotic. But then you get water ingress over the A pillar. Windows up, less current but more chaos. Wind deflector also introduces chaos, but greatly decreases volume.

I'm normally quite content with wind levels without a deflector, I can't see getting one for the rare heavy rain storm. I think my strategy will be to leave the windows down until the water coming over the A pillar gets to be too much, at which time raising the windows and enduring the heavy mist is preferable. And grudgingly, if the storm looks particularly nasty, maybe consider stopping and raising the roof.

 

[buzyg]

If not for Kari, Mythbusters would be only marginally worth watching.

And grudgingly, if the storm looks particularly nasty, maybe consider stopping and raising the roof.

N E V E R .!. D O N ' T D O I T .!.

 

[Mangozac]

This thread is hilarious! And here I was thinking I was badass driving through a light shower at highway speed and not getting wet

The biggest problem is that once you reach the point where the rain is too heavy to be deflected by the wind, coming to a standstill in order to raise the top is going to result in a drenching!

 

[mcbeee]

The problem I face is when the rain turns into hail and the stones start to hurt ... ouch! :x

 

[bcworkz]

I must be rather self-centred, it just occurred to me that the other drivers must have thought me to be completely mad. I should have liked to see a video of me driving through this downpour. It must have been unapparent to others that I was actually staying rather dry.

The biggest problem is that once you reach the point where the rain is too heavy to be deflected by the wind, coming to a standstill in order to raise the top is going to result in a drenching!

That's exactly how this all came about:
"Should we pull off and put the roof up?" "Doesn't look too bad, we can get through." "This is a bit much, but I don't want to get wet by stopping now." "Well, this ridiculous, we're getting wet anyway." "We're going to get far more wet if we stop now, keep going."

 

[paulgs1000]

I have a perspex wind deflector but the wind (and rain) still comes down the middle of the seats and lifts my wifes coat off her legs (which I quite like!) but the tickets and papers flying about the cockpit are a bit much. Anyone find a way of getting rid of this central draught?

And - when you absolutely have to stop having the electric roof is a big help but is there a speed when it can be lifted and lowered or has the Zed got to be completely stopped?

I wouldn't worry about others thinking you're mad in the rain - I often think other drivers have that in mind whenever I ride in all weathers and in the dark with the roof down - they don't know what they're missing

 

[Bing]

You have to be stationary for the opening or closing process to start, though you can move off slowly - under 5mph I think - after it has. Without a Gaptech module for one-touch operation driving would be hard whilst having your finger on the button. Guess your passenger could do it for you though...

I am not convinced by the perspex deflector - I am sure the OEM is mesh for a reason, to let some of the draught that does come in over the top out the back :?

 

[buzyg]

And - when you absolutely have to stop having the electric roof is a big help but is there a speed when it can be lifted and lowered or has the Zed got to be completely stopped?

You have to be stopped to start the roof moving. But I also think you can then drive slowly away and it will continue to change position, but it's so long since I tried that I'm not certain.

The only place mine is normaly raised is when parked up.

 

[Mangozac]

Should we pull off and put the roof up?" "Doesn't look too bad, we can get through." "This is a bit much, but I don't want to get wet by stopping now." "Well, this ridiculous, we're getting wet anyway." "We're going to get far more wet if we stop now, keep going."

I can just imagine (and totally relate to) this conversation

You have to be stopped to start the roof moving. But I also think you can then drive slowly away and it will continue to change position, but it's so long since I tried that I'm not certain.

That's correct, but the time it takes to pull over and slow down enough for the roof operation to start is still going to be enough to get pretty wet in a downpour.

 

[paulgs1000]

I've made a post about the perspex wind deflector being creaky due to the pressure build up before - for that reason I would think the mesh is more appropriate (but much more expensive)

 

[buzyg]

I've made a post about the perspex wind deflector being creaky due to the pressure build up before - for that reason I would think the mesh is more appropriate (but much more expensive)

Cost less than a decent pair of tyres. :?

The mesh one certainly works well. I leave mine in place at all times these days. The few times I used to removed it, the extra buffeting was very noticeable.