Dogbones length and design

[broken neck]

Hell-O there,

After scoring an almost brand new GSX-R 600 shock, it's time to think about its installation.

From what I've read here, the length is a tad smaller than the OEM one, it should lower the rear by about 15 mm. I know it's not a big thing, but I'd like to keep the same height in the back. I've looked around and I couldn't find one that would raise about that height, except the "threaded ones", and the Rexbo ones go too high for me.

So I guess I could designed then and have them machined here at my work.

To make a story short, since my bike is parked at a friend's garage and I don't have access very often, about once a month, I ask for your help for some of the dimensions and design concerns.

For the length, what is the OEM one? Do I have simply to shorten the eye to eye distance by 15 mm to get the height back? Or is there more calculations involved?
For the hole diameter, since it uses 12 mm bolts, I guess about 12.1 mm should be good. Just to have a little play to move freely.
For the material and thickness, I would go with 6061T6 and a thickness of 1/4". Is that would be enough?

As usual, everyone's comments or opinions are welcome.

Thanks.

[Somchai]

Thomas, I wonder that nobody answers your questions since so many guys here already did this mod, so let me give you an answer about the OEM length what's measured eye-to-eye 165mm.
Maybe you'll think about a softer spring (depends on the year) since many guys in Germany riding the 600 and 750 Gixxer have probs with a to stiff setup and please keep in mind that shorter dogbones could also make your setup more stiff.
Good luck

[csmith12]

@Rexbo can you help here? If I remember right, you had some math on this.

[broken neck]

Thanks Roland for the dimension. I've checked with Racetech and the spring rate of the GSX-R spring is 9.4 and the one recommended for my weight and riding type is 9.328, so it should be fine, but I'll keep an eye on it, even more if the shorter suspension link can make it a bit stiffer.

As for the answers, I'm in no hurry, and we're less than week from the Christmas Holidays, so it's better to get tings going on that side instead of trying to find where were those little steel tings and where did i put that napkin with the good length. Some put Rexbo's ones which lift the rear 1.25 inches, others might have kept the OEM ones.

I know the answers will show up sooner or later...

Thanks csmith12 for thinking about Rexbo. I've seen his post in the market place, some asked them, not long ago, for any leftover... I was waiting for him to answer back before asking him personally if I could help me out.

Tchou!

[DCMoney]

Tagged for interest at well.

[Somchai]

Thomas and Andrew, maybe this information could give you some good insight about the theme: http://www.promecha.com.au/leverage_linkages.htm
I did a quick calculation about leverage (pi times thumb like we say in Germany, so it's not very accurate) of the Ninjette and it should be around 2.1 to 1 (in the above weblink it says the 2004 R1 has a nearly exactly 2:1 leverage ratio).
So in case of your shock the question is the year and when it's a K6/K7 the length is 315mm what means its 5mm shorter then the Ninjette's and therefore your dogbones should be 160mm to keep it on the same level.
But for a better behavior in curves Wilbers says it's a good way to turn the bike around the center what means lower the front (not to much) and raise the rear for the same amount or maybe a lil bit more.
In case I'd miss anything or misunderstood I hope someone will jump in and correct me, thx.

[broken neck]

Thanks Rolland for the link... Quite interesting

As for the ratio of 2.1:1... Can you just explain to me how do you end up with a length of 160 mm for the dogbones? Same thing for your ratio? That could help me understand a bit more


I've read in Roxbo's topic Ninja Race Prep here http://www.ninjette.org/forums/showthread.php?t=59486 that, post #12.
According to him, the suspension ratio would be more 3.5:1.

That's where I am now...

[alex.s]

the ratio is determined by taking the distance of the dogbone mount on the swing arm to the swing arm pivot (its like 8" or something), dividing that by the distance between the shock knuckle mount on the frame and the mount for the shock itself on the knuckle (the ninja is like 4" stock), that gives you the difference in swing arm movement to shock movement. so say the shock is one inch shorter you would divide 1" by (8/4ish), or 0.5". it's actually like 0.55 or something. so one inch difference on shock would be 0.5" difference on dogbone length. but then if you want to figure out the actual rear wheel height change, you multiply that by the ratio between the full swing arm length and the distance from the swing arm pivot to the dog bone attachment, which is something like 22/8, so 1" shock / (8/4) = 0.5 dogbone * (22/8) = 1.375" axle height. note this doesn't take the sinusoidal curve into account which is small but would get bigger with more rotation

[Somchai]

Thomas, my guess about the length of the dogbones was that it should be the same amount like the difference in the shock. So when your shock is 5mm shorter then in my (wrong) guess the dogbones should be also by 5mm shorter.
But the first let me tell you that I'd read the post from Rexbo and with that I made my adjustment to my shock since I'd like to have my rear 10mm raised. But since I would like to understand the things better and I have sadly learned it's better to trust in nobody (what's not to understand going against anybody here, but that's the way it is) I did many research in the web and found some websites in Germany and the one I'd link in the last post and ALL of them talk about a standard linkage leverage of 2:1 ratio. So why should the Ninjette have that big 3.5 to 1 ratio, that's what I didn't understand?
About the post from Alex, maybe bc of my weak understanding of the technical english I at least don't understand nothing and I see his numbers are not the same what I'd measure and also I don't understand his talk about the spring rate in this case (even when I didn't measure by correctly mm's).
Also what I don't understand is that so many of the guys here now did this mod and it seems that NOBODY did a measurement before and after - very strange especially for racers???
My change of the rear shock was done by the Kwaki-Canter and even after I told them they'd forget to take the measurement - so it has to be and for me there always was the word from Rexbo and my believe I'd raise my rear by 10mm.
Now after you'd question here and I saw nobody is answering what I realize is new here since up to one year ago it took not 24 hours until you'd get many and all answers. It feels like the forum is on a way to fall in sleep...

So to understand my numbers you should now that I did a quickshot in calculation and came up with a 2.1 to 1 ratio.
But since a picture is better to understand than one thousand words, now I did a quick drawing and it looks like the ratio should be 2.3 to one. At least to be correct this has to be done with a tool like Solidworks or/and the correct measurement.
In my drawing (the scale is 2:1 and the numbers are in mm) I'd calculate a 10mm shorter shock and end up with the axle raised by 23mm but at least that's not very exactly since it's more an estimate - so please take it for that only.

So again, for me if someone could jump in and declare this I would appreciate, so I could really understand that theme bc the more I think about that the less I see the wood because of too many trees.

PS: What I forgot is the suspension travel, this is calculated by wheel travel divided by the shock travel with the values: 130 mm / 60 mm = 2.17 as result and different shocks can have different values.

[JohnnyBravo]

E=MC*

[alex.s]

your technical drawing looks correct to me

[choneofakind]

4-bar linkage. Position analysis. Alex is right with his method. Sorta.

He only solved for small angles. Like he said, sine wave. What he means was if you assume a negligible change in theta due to different length bars, you can make some assumptions that get the trig out of the problem and get just the x and y lengths.




The other way you could do that is solve for an equation of motion (f=ma, then do sum of the forces in the x and y direction (small angle approximation comes in here).

I have no numbers for dogbone length because mine are adjustable and I just changed length until my tail was the height I wanted. I let someone else do the hard work for me.

[broken neck]

Woahhhhhh...

Even better than I expected... Instead of giving the man his fish, you tried to teach the man how to fish...

I remember why I didn't like math and physics in my youth, now they're striking back...

Rolland, are your numbers quite accurate? The different lengths in your drawing? If so, I make a mock up in Creo, that should give me the right length for the dogbones.

Thanks for all you inputs, as usual, it's very helpful and informative...

Tchou!

Thomas

[choneofakind]

Play with this a bit, it's just something I found on a quick Google search, but it looks like it has the basics down:
http://www.softintegration.com/chhtm...ourbarpos.html

• Link 1 is your frame. Link 1 is always the 'ground' or however you'd like to interpret that.
• Link 2 is your swingarm, that's the input to the system. It's what takes the ground's 'motion'
• Link 3 is your dogbones. They transmit the motion to the output.
• Link 4 is your Unitrack linkage. This is the 'output' since it is was connects directly to the shock. It also pivots on the 'ground' and one side is stationary.

Redraw as necessary. Re-designate the angles from the horizontal to keep the math consistent and you should be okay. Might be easier to orient the drawing from Roland so that link 1 is horizontal. Idk, up to you. The math should work out, the trick is getting your angles drawn the same way as the link so its equations work correctly.

[Somchai]

Sorry Thomas, but my numbers are not exactly so think about plus-minus 10 per cent and since I see that there's no way to get real help for this I'll do it by myself with changing the length of my shock and measure the difference in rear height.

@choneofakind - you said: 'I have no numbers for dogbone length because mine are adjustable and I just changed length until my tail was the height I wanted.'
So let me ask you if it would be possible for you to tell us (for me stupido also) the length (eye-to-eye) of your adjusted dogbones and the change in your rear height you wanted - that's the only question and since this would answer the question so why make it unnecessarily complicated by pointing to any website and let others invent the wheel from new again (by the way its not against you but that is one of the big problems nowadays, nobody is able or really willing to help only idiots like me, even when they don't know the answer, try to give some help or support).

[Motofool]

[choneofakind]

Originally Posted by Somchai

so why make it unnecessarily complicated by pointing to a website and let others invent the wheel from new again (by the way its not against you but that is one of the big problems nowadays, nobody is able or really willing to help only idiots like me, even when they don't know the answer, try to give some help or support).

No idea on how long my dogbones are exactly. I just went until the tail about about 1.5" higher than stock. And I adjust for tire height when I change tires.

Roland, calm down. My dogbone eye-eye length isn't applicable anyway. I ride a pregen. The pregen dogbones are shorter than the newgen dogbones, the unitrak linkage is different, as is the swingarm. It's pointless for me to give a number because it's not the same. The math is the same, but the link lengths aren't.

I gave some help for topics to research because no one else did. I do not know exact numbers for this application, but I have an idea how to solve the problem at hand. alex.s also has figured it out. Like said above, "give a man a fish and he'll eat for a day, teach a man to fish and he'll eat for life"

The way I see it, I helped. I have not given exact numbers, but with an hour or two of research and some measurements of their bike, one could do a position analysis of their rear suspension and determine the length of the dogbones needed for a given shock length.

I'm sorry you don't seem to like my answer. I'm not going to waste my time doing the math for a bike I don't own,but I'll gladly help someone learn something new.


EDIT: my bike is in storage. The best measurement I can get of my dogbones is completely an ESTIMATE. That's not good enough for someone planning to make their own, so I won't even waste anyone's time by posting. I'm certainly not taking the whole thing apart just for measurements.

[broken neck]

Thanks chone,

I'll try to give it a good look during the holidays... From the first look, it looks like a foreign language to me...

As for the numbers, it would be a big plus for me if someone had them... If not, no worries, I'll be able to get them when I'll go at my friend's house.

Nice animation Motofool... Is that by hand?

[Alex]

Neat thread.

[Motofool]

Originally Posted by broken neck

...........Nice animation Motofool... Is that by hand?

No idea, it is not mine

I wish I could help you, but I have a pre-gen.

[Somchai]

OK, I'd get the needed measurements and, still with an error code of app. 3%, I would say the progression is 1:2, what means when your shock is 5mm shorter it will lower the rear by 10mm.

I wish yall merry christmas, a happy new year (whatever it brings) and a safe ride always - stay healthy

[Motofool]

Originally Posted by Somchai

..........I wish yall merry christmas, a happy new year (whatever it brings) and a safe ride always - stay healthy

Same to you !!!

Note to the OP:
Consider the different rate of your new spring in order to calculate your riding height (which is what determines handling) rather than the height of the rear tire while unloaded.

[JohnnyBravo]

@choneofakind where you get fancy adjustable dogbones?
I wish I had some joke full of technical jargon so I could throw a bazinga in this thread sigh

[choneofakind]

I got them from Soupy's Performance. Iirc, the pregen bones work well but the newgen had some interference when used for lowering. Haven't heard about the 300 though.

[JohnnyBravo]

Goin to check out soupy and their performance

[choneofakind]

Their links are meant for a range of -2 to +0.5 inches I think. I contacted them ahead of time and ordered a set that were shorter with the intention of raising instead of lowering. Stock height is about as long as they get.

[old3]

I'm looking to get the ratio of DB length to ride height, anyone have an actual number,

i,e. 5mm shorter DB = 15mm ride height lift.

Even an estimate. I see the formulas but I'm not seeing the answers?

What length raises the rear 25mm for example?

Thanks!

[old3]

Thanks to Alex S.

0.559 = 1"

[alex.s]

there is a post on this site somewhere that details how to arrive at the number by measuring the swingarm length, and the lengths of the two sides of the triangle knuckle along with the dogbones offset. but i'm too lazy to go and find it.

[alex.s]

it's something like
triangle ratio = (triangle side B (frame to shock) / triangle side A (frame to dogbones))
arm ratio = (dogbone mounts length to arm pivot / swingarm length)
final ratio wheel to shock = arm ratio * triangle ratio

so if the arm ratio is 0.5 and the triangle ratio is 0.5 also,
and if you swap a shock in that is one inch shorter without changing dogbones,
you would be left with a bike that was roughly 4 inches shorter at the wheel. in reality the arm ratio is closer to 0.56 and the triangle ratio is like 1.3 or some **** so final wheel to shock ratio is not what you would expect

[old3]

Well, I think the 250/300 are the same but here is what I tried and it totally failed.

I added a new hole, 3/4" from center of the original mounting hole on both of the arms. I got the arm mounted to the swingarm with the original, untouched end and started raising the bike to line up the new holes with the link. I got to 2" of lift over the originals and was only about halfway between the holes.

Sooo, I'm thinking when I make new link arms, the difference will be a few mm instead of even .559".

Thunderstorms just started, I guess I'll go mess with it again, try to get a clean spec to use for 1" via the ruler.

[old3]

1/2" pretty much gives me 3X at the rear end ride height, 1.5".

As a bonus, I need new link arms now, drilled too close to the edge for comfort.

I think I'll just make them about 1/4" shorter and see what it feels like when I can ride again.

Is there a member who has these already made ready to sell arms about 160mm center to center?

[old3]

I found this guy,

http://burkhartcycle.com/store/

Custom links at about $25 shipped. Increments of about 2-3mm.

[ForceofWill]

I wish he would put the raising links up on his site. I've called with no answer and emailed them. I want some dogbones lol.

[old3]

I decided to just order a set of 6925A20, 157.78mm O.C.

I might have to knock them down 1/8" at the holes or narrow my spacers as my bolts just clear the nuts now and the new link arms are thicker.

[alex.s]

why don't you just order a set of threaded rods and heim joints and make your own adjustable links? it only costs like $20 of parts and you can adjust them anytime you want

[old3]

I've seen that done, and the lowering kits like that too. I'd rather lock tite them in and forget them. It is my street bike, touring, 2 up, not a track weapon. If I want to go higher another set is cheap enough to buy.

I won't be changing it up and down between sessions, if I was I'd go that route and be under there enough I'd not worry about one coming apart.

[alex.s]

i'm just saying, its cheaper, easier (no machinist or CNC involved), you can fine tune it to exactly the height you want and if what you want changes, so can it. if you don't make one side reverse thread and instead make it so you have to unbolt them (all the same threads all the way around) then you wont ever worry about it coming undone. otherwise you can safetywire/locktite the nuts and not worry about it. i have done both directions and while you do have to order specific high pressure heim joints, everything is seriously much simpler and easier than trying to get some machinist to make some specific length that you tried to figure out and then it turns out to be just slightly off but its not off enough to bother having a new set cut out... you know where im going with this

[old3]

I hadn't though of reverse on either side. Hmmm, still, the arms I ordered are a standard thing at that guys site. I don't think he has to spool up the CNC to make them. Should be on the shelf.

The only glitch is maybe having to recess the holes 1/16" to keep my bolts as is, which is as easy as dropping my friend's house to use his mill. Not a big deal. In really thinking about it, I may have him spin 4 spacers from aluminum that are slightly shorter than the heavy steel nuts I'm using now. Saves a fraction of weight and I can leave the arms as is.

If I need to change it again, I'll price up the heims and thread and see how it stacks up. I think they will be more than $20 either way but they do offer many benefits.

[rojoracing53]

Took me about 30 mins to do this.

First we have stock height with 164.5mm spacing


Second we have 155mm spacing


Third we have 150mm spacing


Now those drilled blocks are 1-2-3 blocks as in 1"-2"-3" so you have a reference of the ride height change, Hope this helps.