Help needed with the science of heat.

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Petebass
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Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 09:48

There are some pretty smart science types on here, so maybe you'll be able to answer a question. I've searched all the motorcycle forums and come up with not much at all .......

I just bought leather saddle bags for my bike. Occasionally, other owners of the same bike report that the heat from the exhaust burns a hole into their expensive saddle bags. No one seems to know if the problematic heat transfer is through the air, or through momentary direct contact when the rear suspension compresses and temporarily closes the gap between saddle bag and exhaust pipe. I suspect it's the former, but I'd like to address both scenarios if possible.

Others have addressed this by adding a heat shield to the exhaust pipe. I don't want to do this. It looks crap. The ones that look good cost a lot and reportedly don't do much heat shielding through the air. They are focusing on preventing anything touching the pipe - many have fancy holes cut into them so make them look nice which imo let's heat pass through.

So what I want to do is to add something to the bottom of the saddle bag to protect it. It'll look much better because you won't even be able to see it.

So what would you use? A piece of something with a high ignition point that won't transfer heat well through to the saddle bag. Ideas so far include:-
- a piece of plywood painted black to disguise the inevitable charring.
- a metal plate, but which metal? One that transfers heat poorly.
- layers of carbon fibre?

Any other suggestions?
Last edited by Petebass on 13 Aug 2018, 11:19, edited 1 time in total.
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packrat
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Re: Help needed with the science of heat.

Post by packrat » 13 Aug 2018, 10:35

Metal will transmit heat. They all do. Plywood or a really high temperature plastic would be better bets. Radiative heat is fast, contact is faster. Convection (hot air) is pretty slow. Carbon fiber isn’t heatproof last I checked. Ceramic would be great but is obviously brittle.

I’d actually suggest getting a couple of full thickness bits of cowhide and dying them and using them as sacrificial thingies.

B>

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david1234
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Re: Help needed with the science of heat.

Post by david1234 » 13 Aug 2018, 10:51

Is the heat damage caused by exhaust gas, or by proximity to the sides of the exhaust pipe? (Getting more air flow between the pipes and the bags might be handy, at least when you're moving).
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MrChameleon
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Re: Help needed with the science of heat.

Post by MrChameleon » 13 Aug 2018, 10:59

packrat wrote:
13 Aug 2018, 10:35

I’d actually suggest getting a couple of full thickness bits of cowhide and dying them and using them as sacrificial thingies.
This seems a sensible idea to me.
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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 11:22

david1234 wrote:
13 Aug 2018, 10:51
Is the heat damage caused by exhaust gas, or by proximity to the sides of the exhaust pipe? (Getting more air flow between the pipes and the bags might be handy, at least when you're moving).
It's from being in close proximity to the hot pipe. Airflow isn't a problem on a motorbike, which probably explains why not all Victory Hammer owners have this problem - they're the riders who are always moving at a decent clip. I don't want to have to worry about it whenever the conditions require me to be moving slowly or not at all.
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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 11:28

packrat wrote:
13 Aug 2018, 10:35
I’d actually suggest getting a couple of full thickness bits of cowhide and dying them and using them as sacrificial thingies.

B>
Good idea. I'll need to figure our how to attach it so it's also removable once it's time to "make the sacrifice". Plywood is easy, a few bolts through the bottom of the bag will do it. That won't work with leather hide.
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noplanb
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Re: Help needed with the science of heat.

Post by noplanb » 13 Aug 2018, 11:37

Sacrificial scrap leather (say from a saddler) is a good idea - I would add an outside pipe-facing layer of good quality sarking (silver side out). This will stop the radiant energy, and the scrap leather layer impedes any direct contact.
Radiant energy over time will progressively dry out the hottest spot which will then crack and tend to crumble away.
Regular inspections of the sarking will pick up when it needs replacing.
Leather can be attached with rivets (which conduct) or better still stitching - see your saddler.....
Put sarking on plywood if easier
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Re: Help needed with the science of heat.

Post by tearalong » 13 Aug 2018, 12:04

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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 12:57

Petebass wrote:
13 Aug 2018, 09:48
...
Others have addressed this by adding a heat shield to the exhaust pipe. I don't want to do this. It looks crap......
Not a fan of the look of those those wraps. But If I was to attach that sort of thing to the bottom of the saddle bag, what would be the best way to do that? Same question for this sort of thing:-
http://www.supercheapauto.com.au/Produc ... 0mm/121225
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BazzBass
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Re: Help needed with the science of heat.

Post by BazzBass » 13 Aug 2018, 13:25

a nice porterhouse steak wrapped in alfoil gaffa taped to the bottom of the bag
Looks ugly, but tastes good at the end of a ride :)
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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 14:15

BazzBass wrote:
13 Aug 2018, 13:25
a nice porterhouse steak wrapped in alfoil gaffa taped to the bottom of the bag
Looks ugly, but tastes good at the end of a ride :)
Best response yet. Add a custom shaped Billy and I can also have coffee on the go :)
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noplanb
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Re: Help needed with the science of heat.

Post by noplanb » 13 Aug 2018, 15:18

Remember there are 2 methods of heat reduction applicable to your bag:
1) radiant blocking - either the pipe goes highly shiny in a wrap (wont stay that way long) which lowers the pipe's emissivity; or you have a shiny surface on the bag - it becomes an effective reflector, it takes a lot longer to get hot, and doesn't get as hot
2) insulative blocking - the insulation itself gets hot, but conducts less heat through it
The combination of both gives you best bang for buck.
The platinum shield does this but is thick and maybe hard to cut nicely?
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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 18:27

OK so the saddlebag manufacturer assures me I'm worried about nothing. He's certain the incidents I mentioned involved PU Leather (i.e fake), or inferior quality leather. He's positive mine will be fine as long when I sit on the bike and compress the suspension under my weight, I leave an inch between the bag and the pipe. I will do this!

I decided to pop into Supercheap auto and pick their brain. They've seen this before. They suggested 6mm plywood from bunnings, painted with a special engine paint which is designed to withstand 280 degrees C ($28). The paint acts as a radiant shield, the wood acts as a insulative blocker. Then any adhesive with the ability to bond wood to leather that also has a high heat rating. They're pretty sure that side of the wood won't get all that hot, and they had a product for $13 which would do the job. Add a few bucks for plywood, I think this is worth a shot.
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
* Lots of DIY neo/lightweight cabs including one made from composites http://www.ozbassforum.com/viewtopic.php?f=5&t=2546

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NotTheFish
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Re: Help needed with the science of heat.

Post by NotTheFish » 13 Aug 2018, 21:38

What about a black silicone heat mat https://www.ebay.com.au/itm/Silicone-Ma ... Desc=0%7C0 ?

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Petebass
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Re: Help needed with the science of heat.

Post by Petebass » 13 Aug 2018, 23:09

NotTheFish wrote:
13 Aug 2018, 21:38
What about a black silicone heat mat https://www.ebay.com.au/itm/Silicone-Ma ... Desc=0%7C0 ?
That could work too! Certainly worth a try at that price.
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
* Lots of DIY neo/lightweight cabs including one made from composites http://www.ozbassforum.com/viewtopic.php?f=5&t=2546

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