Hot stuff!

bigredduke · 17-12-2018, 04:11 PM

Now that the weather has turned traditionally British, I was thinking back to riding in Italy this summer.

It was seriously hot, but I have a mesh jacket & also wore Kevlar jeans with short boots so I was prepared, to a degree (pun intended). I have also ridden many times in Southern France over the years.

Obviously, it is much worse at a standstill, the heat from the engine & exhaust is especially uncomfortable in the inner-thigh region. I suppose the engine configuration of a Ducati adds to this, sitting directly over the rear pot.

Anyway, my question is (at last I hear you say), why is it we suffer from the engine heat in hot weather but don't appear to benefit from it at all when it is cold?

350TSS · 17-12-2018, 05:45 PM

Cold air in winter is denser and stays nearer the ground?

Mossleymonster · 17-12-2018, 06:04 PM

Because the bike stays in the garage?

bigredduke · 17-12-2018, 06:12 PM

Quote:

Originally Posted by Mossleymonster

Because the bike stays in the garage?

If below 10degC, definitely!

Nickj · 17-12-2018, 07:48 PM

Quote:

Originally Posted by bigredduke

Anyway, my question is (at last I hear you say), why is it we suffer from the engine heat in hot weather but don't appear to benefit from it at all when it is cold?

EFI ... The engine does run better sucking in cold slightly damp air but you notice it more with carbs, fuel injection changes the mapping when it's cold so you loose that leaning off of the mix (natural compensation for running hotter by sucking in more volume of cold air).

And of course who really wants to hammer the throttle wide open when it's cold, wet and slippery. Even worse here in Cheltenham, the roads are littered with drifts of wet sludgy leaves, makes the wilds of the countryside seem tidier!!

Mr Gazza · 17-12-2018, 08:17 PM

You will probably be wearing thinner clothing and less of it when it's hot, so you will feel the engine heat more. Especially when the air flow slows when you stop. Instead of the engine heat being taken away behind the bike, it rises up round the rider and also begins to get hotter compounding the effect.

In the cold you will be wearing better insulation if you have any sense! So the heat won't penetrate your clothes so well. The engine is far better cooled, and indeed the air cooled Monsters are renowned for over-cooling, so there is less heat to be had. For the most part the engine heat is being swept away from your body as it is not in the same airstream.

To feel any benefit you need a faired and water cooled bike. Then the rad is at the front and you sit in the lee of the fairing where the warm air is exiting, with hopefully most of the cold air slipping past on the outside.

A very eccentric fellow from my way once had a Twin pipe Panther which he used to commute in the Winter.
He slid some larger pipe over the lower run of each exhaust pipe and closed the rear ends.
He then attached short flexible hoses to branches at the rear end of the pipes and then plugged the other ends into adapters in the ankles of a flying suit.
Basically he had made two heat exchangers connected into his suit, which apparently worked so well that it inflated the suit with warm air and he was able to commute happily looking like some sort of Michelin Man with a big cheesy grin...

bigredduke · 17-12-2018, 09:05 PM

Quote:

Originally Posted by Mr Gazza

…...A very eccentric fellow from my way once had a Twin pipe Panther which he used to commute in the Winter...….

I do hope it was pink!

Explanation makes sense, I did wonder about clothing & how much or little insulation made a difference.

Slight deviation everyone, what would be your perfect ambient riding temperature?

jerry · 18-12-2018, 06:19 AM

In thailand I really feel the engine heat especially in traffic and slow speeds before i even start the bike its 90f

Char · 18-12-2018, 10:18 AM

that's why I prefer leathers & merino whatever the weather - you're hot anyway and I find wearing textiles just means you suffer extra heat from the bike

just stuff on water laced cooling top and keep on the move - was fine in 36 degrees of heat a couple of years ago in France

I think 19-21 are perfect temps

utopia · 18-12-2018, 01:22 PM

Had a ponder.
As one does.

I decided that radiation could be discounted on the grounds that it would not be affected by the differing summer and winter conditions.
I also discounted forced convection, as I'm only considering a stationary bike (and perhaps to nit-pick, an aircooled one).
So that leaves us with conduction and natural convection as modes of heat transfer worthy of consideration.

So, at the instant that you stop, the engine first loses heat by conduction to the adjacent (film of) air.
The heat continues to dissipate further into the surrounding air mass until enough of it is warm enough to set up a natural convection current.

Then I got to thinking about the huge difference in the temperature gradient between the engine and the ambient air in winter, compared to that in summer.
ie .. Summer = Hot engine in Hot air .. Winter = Hot engine in Cold air.
Could we say something like .. In winter the heat of the engine would be dissipated rapidly by conduction into the adjacent film and nearby cold air, whereas in summer the effects of conduction would spread faster and more widely.....?

I'm going to suggest that in winter, heat is lost by conduction so rapidly across the steep temp gradient that it is dissipated before a natural convection current can be set up.
On the other hand in summer, a greater relative mass of air is heated in a shorter time, so the natural convection currents get set up faster.
And the rider sits directly above, in full blast from it.

I might even go further and suggest that this fits quite well with the sensation of a sudden rush of hot air that you often feel when you stop on a hot day.

Somewhere along the line I was considering, for reference, how it is harder to light a fire if the chimney is cold.

Whaddya think ....?

Anyhow, the trick is .......
Switch the engine off.
I do it all the time in summer, and especially in Italy.
With the bike left in first gear, it also means I can put both feet down and fold my arms or flap the blood back while I wait .. no brakes are needed.

Though I admit, it did catch me once on the WDW trip, when I thumbed the starter and got nothing (as you may well remember, Paul).
Fortunately I've bumped her before so I wasn't too phased (and perhaps more importantly on the day .. I also caused no delay

).
.... and we were on a slight downhill anyway.
And if I'm perfectly honest, it felt kinda cool to bump a monster on the cobbled streets of an old Italian town.
Ok, and if I'm even more honest, it also felt kinda cool to fix her, without fuss, by searching the gutter for a twig to poke home the loosened starter solenoid connection, next time we stopped (it pops off about once every 4 yrs and it was overdue).

But I digress.

As for the perfect riding temperature .. well I guess I remember more good hot rides than good cold ones, but I can't discount the Dragon Rally in freezing february, or trail-riding in the snow, or feeling the chill as you drop into a river valley on a summer night.

bigredduke · 18-12-2018, 02:42 PM

Oooooh! There are some reet clever folks on 'ere.

I think I understood that

In summary then, in hot weather, the air rushes up from the engine towards the gentleman vegetables area (or lady garden if female) whereas in cold weather it lacks the oomph to rise up to the same extent or with the same force?

Bit of a bugger really, just when you need it.

As someone once said "ye ca'nee change the laws of physics Captain"!

Perfect riding temperature for me would be 22 degC, but if I waited for that I would hardly ever get out on the bike. I think I rode more miles in Italy this year than in England!

350TSS · 18-12-2018, 07:37 PM

I think there is something also in the ambient road temperature , summer and winter vs the ambient air temperature. In summer the road can be/is likely to be hotter than the ambient air temperature so air will be rising naturally before you park your bike with 80 to 100kgs of 90 to 100 degree c radiating aluminium.

Darkness · 18-12-2018, 07:55 PM

I reckon you are onto something there Richard.

bigredduke · 18-12-2018, 08:44 PM

Quote:

Originally Posted by 350TSS

I think there is something also in the ambient road temperature , summer and winter vs the ambient air temperature. In summer the road can be/is likely to be hotter than the ambient air temperature so air will be rising naturally before you park your bike with 80 to 100kgs of 90 to 100 degree c radiating aluminium.

Good point. I know from experience when we have parked the car in a French supermarket car park, the heat coming off the car park surface can be stifling!

Doesn't happen in Yorkshire. Strange that!

utopia · 19-12-2018, 12:56 PM

Excellent point.

So, can we say that in summer, the convection current coming off the bike is not only more easily established than in winter but is also boosted/kickstarted by that coming off the road ?
Sounds like a plausible explaination to me.

17-12-2018, 04:11 PM	#1
bigredduke Nothing to see here Join Date: May 2005 Location: brough Bike: M1100evo Posts: 1,546	Hot stuff! Now that the weather has turned traditionally British, I was thinking back to riding in Italy this summer. It was seriously hot, but I have a mesh jacket & also wore Kevlar jeans with short boots so I was prepared, to a degree (pun intended). I have also ridden many times in Southern France over the years. Obviously, it is much worse at a standstill, the heat from the engine & exhaust is especially uncomfortable in the inner-thigh region. I suppose the engine configuration of a Ducati adds to this, sitting directly over the rear pot. Anyway, my question is (at last I hear you say), why is it we suffer from the engine heat in hot weather but don't appear to benefit from it at all when it is cold?

17-12-2018, 06:04 PM	#3
Mossleymonster Registered User Join Date: Nov 2017 Location: Barnsley Bike: M1100s Posts: 238	Because the bike stays in the garage? __________________ Always remember. Your home is at risk if you set fire to it.

17-12-2018, 08:17 PM	#6
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,804	You will probably be wearing thinner clothing and less of it when it's hot, so you will feel the engine heat more. Especially when the air flow slows when you stop. Instead of the engine heat being taken away behind the bike, it rises up round the rider and also begins to get hotter compounding the effect. In the cold you will be wearing better insulation if you have any sense! So the heat won't penetrate your clothes so well. The engine is far better cooled, and indeed the air cooled Monsters are renowned for over-cooling, so there is less heat to be had. For the most part the engine heat is being swept away from your body as it is not in the same airstream. To feel any benefit you need a faired and water cooled bike. Then the rad is at the front and you sit in the lee of the fairing where the warm air is exiting, with hopefully most of the cold air slipping past on the outside. A very eccentric fellow from my way once had a Twin pipe Panther which he used to commute in the Winter. He slid some larger pipe over the lower run of each exhaust pipe and closed the rear ends. He then attached short flexible hoses to branches at the rear end of the pipes and then plugged the other ends into adapters in the ankles of a flying suit. Basically he had made two heat exchangers connected into his suit, which apparently worked so well that it inflated the suit with warm air and he was able to commute happily looking like some sort of Michelin Man with a big cheesy grin... __________________

18-12-2018, 06:19 AM	#8
jerry Old Git Join Date: May 2006 Location: Cricklade Bike: Multiple Monsters Posts: 2,814	In thailand I really feel the engine heat especially in traffic and slow speeds before i even start the bike its 90f __________________ MONSTERMAN

18-12-2018, 10:18 AM	#9
Char We're all mad here Join Date: Aug 2010 Location: Wiltshire Bike: Other Not a Ducati Posts: 1,536	that's why I prefer leathers & merino whatever the weather - you're hot anyway and I find wearing textiles just means you suffer extra heat from the bike just stuff on water laced cooling top and keep on the move - was fine in 36 degrees of heat a couple of years ago in France I think 19-21 are perfect temps __________________ If you don't know where you are going any road can take you there

17-12-2018, 05:45 PM	#2
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	Cold air in winter is denser and stays nearer the ground?

18-12-2018, 01:22 PM	#10
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	Had a ponder. As one does. I decided that radiation could be discounted on the grounds that it would not be affected by the differing summer and winter conditions. I also discounted forced convection, as I'm only considering a stationary bike (and perhaps to nit-pick, an aircooled one). So that leaves us with conduction and natural convection as modes of heat transfer worthy of consideration. So, at the instant that you stop, the engine first loses heat by conduction to the adjacent (film of) air. The heat continues to dissipate further into the surrounding air mass until enough of it is warm enough to set up a natural convection current. Then I got to thinking about the huge difference in the temperature gradient between the engine and the ambient air in winter, compared to that in summer. ie .. Summer = Hot engine in Hot air .. Winter = Hot engine in Cold air. Could we say something like .. In winter the heat of the engine would be dissipated rapidly by conduction into the adjacent film and nearby cold air, whereas in summer the effects of conduction would spread faster and more widely.....? I'm going to suggest that in winter, heat is lost by conduction so rapidly across the steep temp gradient that it is dissipated before a natural convection current can be set up. On the other hand in summer, a greater relative mass of air is heated in a shorter time, so the natural convection currents get set up faster. And the rider sits directly above, in full blast from it. I might even go further and suggest that this fits quite well with the sensation of a sudden rush of hot air that you often feel when you stop on a hot day. Somewhere along the line I was considering, for reference, how it is harder to light a fire if the chimney is cold. Whaddya think ....? Anyhow, the trick is ....... Switch the engine off. I do it all the time in summer, and especially in Italy. With the bike left in first gear, it also means I can put both feet down and fold my arms or flap the blood back while I wait .. no brakes are needed. Though I admit, it did catch me once on the WDW trip, when I thumbed the starter and got nothing (as you may well remember, Paul). Fortunately I've bumped her before so I wasn't too phased (and perhaps more importantly on the day .. I also caused no delay ). .... and we were on a slight downhill anyway. And if I'm perfectly honest, it felt kinda cool to bump a monster on the cobbled streets of an old Italian town. Ok, and if I'm even more honest, it also felt kinda cool to fix her, without fuss, by searching the gutter for a twig to poke home the loosened starter solenoid connection, next time we stopped (it pops off about once every 4 yrs and it was overdue). But I digress. As for the perfect riding temperature .. well I guess I remember more good hot rides than good cold ones, but I can't discount the Dragon Rally in freezing february, or trail-riding in the snow, or feeling the chill as you drop into a river valley on a summer night.

18-12-2018, 02:42 PM	#11
bigredduke Nothing to see here Join Date: May 2005 Location: brough Bike: M1100evo Posts: 1,546	Oooooh! There are some reet clever folks on 'ere. I think I understood that In summary then, in hot weather, the air rushes up from the engine towards the gentleman vegetables area (or lady garden if female) whereas in cold weather it lacks the oomph to rise up to the same extent or with the same force? Bit of a bugger really, just when you need it. As someone once said "ye ca'nee change the laws of physics Captain"! Perfect riding temperature for me would be 22 degC, but if I waited for that I would hardly ever get out on the bike. I think I rode more miles in Italy this year than in England!

18-12-2018, 07:37 PM	#12
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	I think there is something also in the ambient road temperature , summer and winter vs the ambient air temperature. In summer the road can be/is likely to be hotter than the ambient air temperature so air will be rising naturally before you park your bike with 80 to 100kgs of 90 to 100 degree c radiating aluminium.

18-12-2018, 07:55 PM	#13
Darkness . Join Date: May 2007 Location: Stockbridge Bike: M900 Posts: 1,984	I reckon you are onto something there Richard. __________________ Original and Best since 1993

19-12-2018, 12:56 PM	#15
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	Excellent point. So, can we say that in summer, the convection current coming off the bike is not only more easily established than in winter but is also boosted/kickstarted by that coming off the road ? Sounds like a plausible explaination to me.