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Undertail vs Side Exhaust

19K views 42 replies 22 participants last post by  TheX 
#1 ·
Was reading on another thread about how under tail exhausts put way to much weight up high and how this lessens the flick-ability of the bike.

If this is the case then why does Honda still do this on the CBR600RR? Does having the tank lower help with this?

Personally I prefer an under tail exhaust (I think a bike looks better this way) and I feel they handle better. Though this might just be my mind playing tricks or it might just be my riding style.
 
#3 ·
That's what I was thinking. I know the logistics behind doing a side exhaust. I just prefer the symmetry of the under tail.

Most bike makers are going to a side exhaust again, which limits me on bikes when it comes time to get another one.
 
#4 ·
Man idk, ive heard arguments from both sides.

Mainly about how much extra weight undertail exhaust adds.

Apparently some exit exhaust interferes with ground clearance ect ect.

At the end of the day its what you like, honestly.
 
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#8 · (Edited)
FWIW...you can feel that the bike is "lighter" when you change to an aftermarket exhaust system ( 1/2 the weight, about 20lbs.) on a cbr w/center exh..and you can barely feel the change from a lead/acid to Li Po battery. (7lbs+ to 2lbs)

personally, i do not "flick" my bike much..slow rider.

A gentle re arrangement of weight works good.....for canyon riding...at my reduced pace.
 
#9 ·
Funny, almost every single shootout I watch comparing bikes in the 600 class points to the CBR as being the most nimble and easy to flick into corners.

How many of you get to ride the latest models around the track from all manufacturers for a day?
 
#16 ·
An low mout exhaust is a bit lighter due to a shorter overall pipe length. It also helps a bit in mass centralization. But motorcycle engineers use thousands of tricks for mass centralization. Exhaust is just one of them.

I prefer under tail because it's out of the way and looks a little sleeker. The only thing I don't lik about the undertail exhasut is that is reduces underseat storage.
 
#17 ·
It's funny how few bikes had under tail exhausts about 15-20 years ago. GP bikes (and a couple street 2 strokes) did it because in their V engine layouts they'd separately route the rear head through the tail and the front head into a stubby side exit or under engine config. As for mass produced bikes only a couple exotics like the iconic Ducati 916, MV Agusta F4, and the Honda NR750 to mind. Then everybody was doing it. The 600RR, then Kawasaki, a BMW sport tourer, the R1, a whole slew of side exit bikes custom modified with under tails. It wasn't novel anymore and in many instances didn't add anything but weight and the problem of heat management under people's asses. Following Buell in chronology if not literally the hot setup was the under engine or stubby side exit behind the right rearset. Funny how trends go. The 600RR underseat doesn't bug me but doesn't turn me on in any way. I would welcome the trend to an under engine or stubby side for the 600RR. Looks wise you'll ditch the surfboard sized rear seat cowl, a bunch of weight in the extra pipe routing, and all the heat shielding. I would be surprised if a new design 600RR retained the under tail. The 1000RR didn't.
 
#20 ·
I'm big into symmetry. So I obviously enjoy the looks of the under tail and that is the reason I went with the year of CBR that I did. I've read others debate pros and cons. One good pro, not on the CBR, would be on a sport-touring bike, an under tail might allow for bigger saddle bags. On a street bike application, I don't see much advantage performance wise, more just fashion wise.
 
#22 ·
Generally speaking though, bikes aren't symmetrical. It's not like there's a chain and sprocket on both sides of the bike, nor is there a caliper and rotor on both sides of the rear.
Putting all symmetry aside, I think as long as it's designed well, a side-exit exhaust can look great. -Although aesthetics are in the eye of the beholder.
 
#24 ·
The RC213v Moto GP bike is the fastest, best handling, road racing motorcycle in the world at the moment. It has both undertail and sidemount exhaust. Although that exhuast system is made from exotic materials and probably costs more than an entire production CBR600RR.


 
#27 · (Edited)
Personally I think if this were 10 years ago and the then-new fashion was under tail exhausts you'd be having the same argument that the previous generation side mount exhaust was the way to go. It's not as much about performance but about what's fashionable at the moment.

For those of us who rode sportbikes bike then it wasn't even something you noticed, thought about or even mattered. Manufactures simply placed parts differently on the bike to counteract the pipe (the batteries were usually placed towards the opposite side of the pipe) and when we went down on the right side we had to replace the muffler as well.

Hate to break it down to you but it's really current trends that makes it one way or the other. While under tail pipes do have some advantages, it's by far the heaviest style system out there and has the most weight up high. While side to side weight may be "even" you still have excess heat and heat shielding under the seat you have to deal with not to mention an asymmetrical swingarm to make room for the upwards pipe which have 2-3' extra length to it. And it runs that heat right by the shock.

Not a huge advantage other than looks if you honestly break it down.

My biggest beef with them is the exhaust gets all over you and your passenger far more than a side or under exit exhaust. I don't mind exhaust smell at the track but having to sit in it for 8 hours while at work is annoying compared to when I take the NC700X which is almost nothing.

Mike
 
#28 ·
While under tail pipes do have some advantages, it's by far the heaviest style system out there and has the most weight up high.
While what you are saying about the exhaust is correct, there are more things to consider when talking about mass centralization.

Consider the Buell systems (I've owned 3 of them) that are completely under the motor. The exhaust is low, but the motor has to be mounted a couple inches higher to allow ground clearance for the exhaust. Which affects mass cetralization more... the motor or the exhaust?

There are lot's of engineering solutions for mass centralization. The exhaust, which isn't the heaviest component of the motorcycle, is just one of the concerns.
 
#35 · (Edited)
Interestingly enough; lowering the cg can have a negative effect.

Honda experimented with NS500 in 1984
http://www.pinterest.com/pin/302093087478069313/

The result was a bike that understeer; he still won the championship but it wasn't an easy win

Re: suspension yea or nay
Postby rgn » Sat Apr 19, 2014 7:00 pm

The 1984 Honda NS500 of Freddie Spencer had the experimental underslung tank, it handled well enough to achieve forth in the championship out of a field of 27 riders, but it did have some problems changing direction, and with understeer. Next year honda turned the bike the right way around and Freddie won both the 250 and 500 titles in 1985. Here's a fun vid of the bike and Freddie in action.




I'm sorry for going off topic but here's some nice pictures
http://www.deejay51.com/honda_racebikes_pg_4.htm

There was a documentary about the NS and NSR500 history that talked about the issue with the underslung tank; I just can't find it anymore.
*Edit*
Not documentary but some webpage with words
http://www.superbikeplanet.com/NSR500.htm

The '84 NSR's problem wasn't lack of speed - the bike was a wheelspin-crazy rocketship, 140 horses was a big number back then. No, its downfall was the willfully innovative 'upside-down' chassis design - fuel tank mounted below the engine with expansion chambers sweeping back above the engine, for a low center of gravity. But motorcycle dynamics aren't that simple - the NSR's center of g was too low so the bike wouldn't transfer weight into and out of corners to aid front and rear traction. The low-slung fuel load also sloshed forward under brakes, pushing the front like crazy, causing major understeer. And the NSR was a mechanic's nightmare - imagine trying to change plugs or jets beneath those burning hot pipes. So much for superior engineering.
 
#36 ·
Honestly when you have a 150lb+ rider on top of a bike, a few extra pounds mounted a foot lower or higher really won't make much of a difference. I like the CBR's undertail for its aesthetics and helps to know that when I do go down, I won't have to worry so much about replacing exhausts. Unless of course it's a massive flop and the sub-frame gets twisted. But by then there are other issues to worry about than if an exhaust pipe is screwed.
 
#37 ·
It is more fashion than function. Ducati realized this and tried to go back to lower exhast and non single sided swingarm but the consumers all complained so the went back. (not forever but still).

Motogp uses underbelly which Eric Buell knew already. Lower wieght is always better but have you seen the VFR1200 or 800? Honda as of late have made some real butterball fat bikes.

Maybe its too many committees or groups of engineers?
 
#38 ·
Lower weight is not always better. The raciest bikes have the engines mounted high in the frames. Having a slightly higher cg will allow for lower lean angles and also help with weight transfer.


Erik buell did some absolutely retarded stuff with his bikes, he was trying to be different, not necessarily better.
 
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