rEdDeViL

hey u techie guys cud u plzz tell me the diff b/w single downtube frame and double cradle frame
which one is better and wat is +ve and -ve points of both

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Ricci

Single downtube frame - CBZ , Karizma
Double downtube cradle frame - Pulsars , RX series , KB100 , KB125 , Fiero

There are 2 tubes that support the engine from below thus taking the weight of the engine . In Shogun/Shaolin , the single downtube splits into 2 tubes again to suppport the engine from below .

In Bullet ,CBZ and ZMA , the engine is not supported from below , the engine is the load-bearing member of the chassis .

Modern foreign bikes also have the engine as stressed member .

Overall its the stiffness and strength that matter , however you get it .

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madmax

Hey rEd, I've read that double cradle frames are better than single downtubes as far as the stiffness and rigidity are concerned. But I don't want to sound like a typical Pulsar guy yet again and state something like "yes, double cradle frame is much better than single downtube. That's why Pulsar has it and most others dont!". Just kidding!

As Ricci said, if even modern foreign bikes can use single downtubes with the engine as a stressed member, both configurations should have their own plus and minus points. Waiting for a real tech guy to put down all the points though! - MAX.

crazydiablo

Cant really say which is better. Some say Cbz is a better handler than the pulsar and along with they say that double down tube is better in handling, so you see the conflict?

Single downtube has the adv of less weight and using the engine as a stressed member gives the weight advantage.

Double cradle chassis gives more rigidity but compromises in weight.

But the anomaly still remains between CBZ and Pulsar. The doulbe cradle chassis of the RX series has been proved to be one of the best on indian bikes in terms of handling.

Guys what do you think?

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Rare-Devil

Teknically speaking, if u get 2 bike models (1 each of single tube nd double dwn tube), hold the steering part in one hand and rest of d body in the other and give it a twist, a double dwn tube wud prove 2 b much stiffer nd wud budge d least, wen compared 2 d single tube model. Thats'll abt handling (influenced by rigidity) , wen confronted with torsional forces. As regards handling many other parameters play an important role. Pulsar has a dbl dwntube, ZMA single, but ZMA is the better of d two in handling. But put a CBZ (SDTube) thru some quick left-right turns nd u might notice it lacking in rigidity (even though CBZ is still s'posed 2 b the better handler of the two). So d +ve point of DDTube is rigidity, -ve is higher power 2 weight ratio. Vice-Versa 4 SDtube cradle. Handling characterisitics depends on the rest of the chasis, suspension design etc.

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racinglord

i have heard double cradle chassis r better than ddtube.more flexible

Ricci

I don't think that unwilingness in left-right turns is a sign of less rigidity , rather it indicates more directionals stability .

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Man will occasionally stumble over the truth, but most of the time he will pick himself up and continue on.

Cutcrank

When comparing double cradle and singe downtube the double cradle frames are more stiffer and stable. Other than the type of frame handling depends on like rake,trail, wheelbase etc.

Nowadays racing bikes use a different kinds of frame other than these two, like twinspar, deltabox, trellis etc. But during the 70s and early eighties, when doublecradle/singlecradle types where in use, most of the racing machinery had double cradle frame rather than single. And that makes sense.

During the hundred cc brigade of yore the bike with the best stability was KB100/125. RX is also a good handling and more nimble than the KB. And the Suzukis were the ones i didn't like in handling dept.

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rajnish

LOL tell this to nav tht kb/rx have good handling.as per him rx is wobbley and unstable.

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Glifford

R U guys sure that the ZMA (and all Single Downtube bikes) use the engine as a stressed member?

I don't think so. Agreed that the Bullet uses its engine (more so Gearbox) as the stressed member, but all other bikes don't do that. All other bikes have the mass of the engine so small that stressing it will be crazy. And then U have the Rubbed mounted engines to cut out the vibes ..can't be stressed.

I guess the ZMA (like other single downtube bikes) like the Caliber 115 as well has a normal (and not stressed engine).

On the other hand...the Bajaj Byk, is neither a single or a double downtube bike. It has no Downtube at all. The Sheet metal chassis takes all the stress and holds up that horizontally mounted engine. And so that the byks don't look something like bikes with a cut off chassis, they have 2 dummy downrod tubes goin down. Interesting stuff.

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