braindead

greetings fellow travelers!

i am talking as much of the evolution of my mind and opinions as my rd.

at the onset, let me make it clear that i have no intentions of keeping my bike stock. As i say, there are a lot of great people around doing a top notch job of keeping theirs stock.

The story start with a great RDD rebuild.
I already had an eliminator disk installed and the so called 'ace' handlebar.
After a month of riding around, the brain gets a twitch one morning that i want to make the bike better in the handling aspect.


so i spend a coupla months working on rearsets, two miserably failed attempts and then i finally get it right. and they work brilliantly! they are lighter than stock and bloody strong.




the brake arm had to be lengthened as the brake pedal had to be shortned in order to maintain braking effectiveness.

this pic is an old one where you can see my trial and error of getting the linkage length just right. it looks much better now.


ride around for a month on this setup.

then cought the weight reduction bug. had done a post here as slingshot but couldnt find it now. (can anyone who stumbles on it please post a link of it here)
the concept is lower weight improves speed, handling, braking... everything. the rd manual says the rd weighs something like 138 kgs. but i weighed it mine as stock and weighs 154 kg. now thats a lot!
so after the weight reduction i got the weight down to 134 kg. and it was still street legal.






then the last incarnation was small...



trust me... the pulsar tank was actually a bid to keep my stock tank unmolested. i was facing fuel starvation issues at full throttle, high rpms. so went for the big momma solution and got a low pressure lpg tap. to save the stock tank from the cutting, welding used this tank i had lying around. this setup flows 2 liters per minute from both the outlets with filters on compared to 400ml / minute from the stock tap.
annother advantade of the pulsar tank is it makes the bike get lost in a public parking so less chance of idiots playing with it.




the cowl was a pain... literally as i cut and bent the cold rolled steel by hand. my hands were bleeding and sore at the end of it. it works as a bum-stop and also hides the battery. i have grown to like bikes you can see through.



NOW!


i go like... this is not enough...
i want even better handling!

so i spend months going through dozens of sbk workshop manuals to see how the technology has progressed in the 40 years since the rd was designed.

[dont know if putting up links like this is allowed here, so please let me know so i will remove it if its frowned upon or you can remove it yourself.
]Bike Chat Forums : Workshop/Service manuals !!

i started trying to figure out how i can make the frame better by identifying the frame's weak points. but then realized a few things:

weaknesses of the rd chassis: (or most indian bikes for that matter)
1. forks
they are ancient. i can elaborate on that later but unless you have a metal guide bushes in them, they will behave like pigs during trail braking... if you know what i mean.

2. swingarm
its too short. but the wheelbase cannot be lengthened. it will be counter productive.
also, its too flexy. the axle to swingarm junction is hopeless. even a pulsar's rectangular swingarm is much better in that aspect.

3. steering stem bearings.
rd uses horizontal ball bearings race. the world is using taper roller bearings or angular contact ball bearings for donkey years.

4. swingarm pivot
most indian bikes use rubber bushes there. in the 80s bronze bushings became popular. now, everuone is on needle roller bearings. so we are two generations behind.

5. rake angle of the steering head
rd is 27 deg. its now being proven thats too much. most bikes use 23 to 25 deg rake. more the rake, harder it is to turn and survive a tank-slapper...


these are just a few of my observations in brief.
if you really want to know what i am talking about, please read "motorcycle handling and chassis design" by Tony Foale. its a easy to read book and very informative. highly recommended.


the conclusion i derived from this is that the rd chassis is hopeless and awesome at the same time. it is hopeless because it fails miserably when critically analyzed in the 2009 context. but because i see no significant advantage in any 'band aid' modifications to it, its a well rounded and adequate frame for 1970's. mind you, most current bikes are no better.

and by band aid mods, i mean sbk forks and stuff. you can put a rs250 fork on it, but whats the point if the frame will flex like a noodle.


Now i cant live with it and i love the sensory involvement of the rd engine.
so...





working on it.

dont measure anything in the pics cos the pipe is arbitrary.

as you can see, i intend to make a new frame which can in principle accept any engine... upto say 600 cc.
would probably use some 600 sbk USD forks and rear suspension unit. going to make my own swingarm.


fabrication starts in december.
the aim it to have a stiff frame in torsion and under longitudinal loading. and the operational weight under 120kgs. the chunk of blue you see at the seat is actually the fuel tank which i intend to make structural. that means the bodywork shown is purely indicative and i would much appreciate if the discussion will stay away from the cosmetics and appearance of it.

comfort is not my priority. that said, what sets high quality suspension apart from the old units we currently run is not hardness. its response time and damping quality. a sbk suspension will react much faster to all the tiny bumps in the road. the main motive is road holding but the same quality also improves the ride quality. the frame i am going to make has absolutely no rubber in it.

i think enough rant for today...
i am open to constructive criticism and i have put this up on this site basically to judge public reaction and some knowledgeable inputs as well.
would love to discuss anything i have mentioned in greater detail.

cheers
abhi

Sunny

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jd666

neato. great to see someone give an unbiased view on the bike. Yes there is scope for a lot of improvement, but the chassis has been proven to take a lot more power than necessary. Wont it be easier to experiment with different rake angles on a stock chassis first???

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outworldly maniac

Its great to see someone getting so much involved into something sincerely like this . And all these efforts shout out that the engine and the pipes are working beautifully and boy the feel must be like

Best of luck mate for whatever you do with the bike .

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wierd_san

beautiful piece u got there

braindead

Yes, the chassic can take more power without behaving like a noodle but thats not enough in 2009 in my opinion. Look at something like Cagivia Mito. its some 125cc 2 stroke 20~25bhp bike and even that has USD 40mm forks in the nose.
What i have observed in the dozens of modern bike repair manuals i have been through is that even bikes with little handling pretensions use much better details in their chassis. for example, rubber swingarm bushes are absolutely unacceptable in any modern bike... even a tourer.

As for modifying the stock frame to a diffrent rake... the reasons for not doing that are many...

1. i actually dont have the heart to cut my perfect rd frame.

2. the job is not as simple as cutting some tubing and welding it in a different place. you will need some sort of jig to keep the alignment true. because as some of you may know, welding shrinks the metal at the point of the weld, so you need some rigid structure to hold the components in place. if i am going to make a jig anyway, why not make the whole frame?

3. the rd frame is too heavy because of limitations due to mass production in the 1970s. there are too many little cleats, brackets, dowels stuck on it... its messy. anyway, the monoshock will render the rear part of the frame structurally redundant, and i cant sleep with that.

4. the down tube design itself has been all but discarded since 1990s. thats 20 years ago. the downtubes are an inheritance from the bicycles and dont work all that great for the immense forces a modern motorcycle generates.

5. and lastly, look at the evolution of the rd platform by yamaha. what did they do to the frame for the next model... the RD350 LC? they straightened out most of the tubing of course. then the TZR went the ali twinspar way.



its not just the frame i want to deal with... the small things like bearinds, bushes, axle diameters matter a lot as well.

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Abhishek

abhijeet080808

I am hooked to this thread. Would like to see the final outcome. Also have you thought about the materials to use to make the frame lightweight yet strong?

Also, any more book recommendations?

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jd666

^^ true, i was only suggesting the rake angle part. coz RD frames are the only thing IMO which are available in the market easily.

The RD needs better , stiffer suspension. Something like the R15. If only the frame of the R15 could be used! lol! that would totally transform the handling!

- the steering surely needed a damper, but i guess with a different rake you wont be going there.

- Disc brakes front and rear, and the biggies, like maybe the 280+ mm one of the bullet from pricol for the front.

- The frame is/was very heavy, agreed, but i remember someone very experienced with RDs telling me that it was designed with a certain amount of flex in mind. So are you looking at that as well?? ( incorporating flex in the chassis ?? )

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My offerings to the gods of speed -

- KTM Duke 200
- Yamaha RXZ 5 speed

braindead

abhijeet, i recommend "motorcycle handling and chassis design" by Tony Foale to everyone who is interested in motorcycle handling.
its a easy to read and understand book.

Also, take a look at this gentleman called John Britten from NZ. i am inspired by him big time!
born a dyslectic, he made a bike from scratch, including the engine with his friends in his garage. the bike had a carbon fiber chassis, girder forks, and electronics futuristic even today. and the bike was running way at the front at the daytona (or something) races in the us, matching and sometimes being better than the all all-winning factory backed ducatis.

there is a documentary on utube... 9 parts i think...



watch this if you have lesser patience or a slow connection...



its a must watch for any motorhead. i dont understand why we dont do things like this in india. the world attributes qualities of ingenuity and ability to work with limited resources to the people of both countries.




jd666, i suppose the r15 frame can easily be used to house the rd engine. i suppose you just need some interface plates and something to hold the front of the engine.
but thats not the point. the reason i am doing all this is to understand and learn how motorcycles and their chassi behave. and then create a solution that applies the knowledge. its a pride thing i guess. saying "i made the frame myself and it kicks the stock bikes hiney all over the place"

actually the steeper rake will really need a steering damper. the steep rake makes it easy to come out of a tank slapper but also makes it marginally more likely to enter one in the hands of an idiot. (me) hehe
actually there are many more factors influencing this and this is a rough statement. i need to learn more...

disk brakes... of course. i may be looking at the ninja 250 stuff if i cant land some sbk 600 fromt end.

about the flex, that is very important. still learning about it. i am in the process of entering the frame in a structural software to calculate the stresses and deflection for various situations. under any circumstance the torsional flex is never desirable in any frame. the required flex is built in this frame but i am not sure of it. the output from the software will verify it.

jd666,(or anyone for that matter) please do not think i am arguing with you. i am just discussing this.

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Abhishek

abhijeet080808

This is the point. Other people will never understand this. When something works exactly how you dreamt it will work, the pleasure is indeed immense.

I will try to read that book and add some points! Till then, I will watch you do it.

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