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Under Tail Exhausts...


Snakebite68
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I'm relatively sure this is the place to post this, but I'm sure someone can move it if it isn't..! :D

 

This is probably a very 'n00b' question, but:

I've always wondered, under tail exhausts just (to me) look so cool! Neater, less visible, streamlining and hopefully cool...

So... Why aren't more bikes built with them???

 

There's obviously at least one major downside to them, or I couldn't see why more bikes aren't built with them.

So what is it? What makes them un popular to manufacturers?

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Packaging for one, takes a lot of thought routing pipework that could be a couple of hundred degrees through all the delicate parts of a motorcycle not to mention avoiding the rider. Especially with catalytic converters getting seriously hot.

Next one is a performance compromise, do you want to give away some horsepower putting the pipe there rather than the conventional position that needs minimal curves as opposed to the twisting and turning of pipe needed to get up under the tail.

Size, the amount of silencing and the cats in exhausts now mean they have to be big, you don't want big that high in the bike. Exhausts in the main now are actually completely under the bike to aid handling and lower the cog.

Handling, adding to the previous, high and heavy are not good, add that to taking weight off the front wheel is even worse. Cars are not like bikes, cars aim for 50/50, not so much with bikes. They want more on the nose, the rear can slide and skip to its hearts content you can deal with that. Skippy front end, yuk. My TDR by way of example, just the weight of a tank of fuel seriously changes the way she handles, that's 9 litres, 8kg maybe.

Lastly, its old hat, ducati did it long ago, cool on a 916, no not so much. Depends what the gp boys are doing, fikle really.

Personally i like it myself, on the right bike.

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Hmmm, well I had considered the insulation problems (not melting the seat/fairings/rider), and even the weight distribution problems.

But I didn't think about the performance problem...

 

Yeah, I've seen a few bikes with cans on the bottom of the bike, venting out either side of the rear wheel!
BMW are doing that, if they hid it behind the bottom fairing a bit more, that would REALLY clean up the lines!

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Realistically the performance difference is probably negligible.

Weight distribution probably makes the biggest difference. Getting the weight down low and near the centre of the bike is more desirable.

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I would go with packaging as the primary, with the silencing requirements and emission control required for engines dictate the size of a modern exhaust more than style, plus i think the temperatures needed for a cat to be efficient (so smaller) would be difficult that far from the engine.

 

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