shock angles

[wera racer]

I?ve found a nice GS1100 aluminum swingarm to replace my GS1000 stock steel one and I?m reading through the Yoshimura build specs about reinforcing the rear frame section with 22mm O/D mild steel tubing ??to handle the increased loading caused by the (54.5 degree) laydown shock position.?

So I have a few questions for you vintage sages:

• What benefit is derived by increasing the shock angle and why is more better? (WERA and/or AHRMA limit it to 45 degrees.)
• How would one calculate the additional load put on the shocks when ordering new shocks? (I suppose the shock company could do that math.)
• Should I consider bridging the aluminum swingarm? The Yosh specs note that they ran an unbridged steel swingarm in an eight-our endurance race and noted no difference compare to the bridged one.

Thanks, guys!
Rick

 

[GregT]

Longer travel rear suspension was seen at the time as a good thing. To fit the longer shocks required, they were laid down.
With the better damped/more adjustable shocks now available the need for longer travel is debatable.Slightly longer shocks in stock position are all I'd do.

The positives are - the trick factor which may just intimidate the oppositon....and laying down reduces the effective spring rate due to the geometry. As it is often difficult to find soft enough springs for the rear in race trim this can be a major plus.

 

[trippivot]

exactly how good are you at advanced math?

the more aggressive the angle (away from 90 degrees) the more force required to compress the same shock/spring the same length.

I have formulas if you actually have exact specifications. the angle is only the beginning. as the material thickness, total weights, and lever length are all important factors to answer your last question about bracing, welding,and spring rate.

supposing and guessing is a bad habit because the shock vendor probably has a teenager at the counter not an engineer.

 

[posplayr]

http://www.thegsresources.com/_forum/showthread.php?p=1260145&highlight=shock+angle#post1260145


% Leverage Change = Cos (45 deg) / Cos (54.5 deg) x 100 = .707/.580 x 100 = 121%


So a 54.5 degree angle increases the leverage against the shock, which means the same shock travel cooresponds to more swing arm travel at 54.5 deg.


The issue of frame reinforcement is primarily because the stock frames are beefed up at the upper shock mount. Moving the upper mount to below that point would require reinforement.

However, it is not clear why the forces would be alot more (after getting the shock properly sprung), I would think it is has mostly to do with the strength of the new upper mount compared to the lower mount. (see the pic in the link above)

I have no experience with this just the physics of the matter.

 

[wera racer]

http://www.thegsresources.com/_forum/showthread.php?p=1260145&highlight=shock+angle#post1260145


% Leverage Change = Cos (45 deg) / Cos (54.5 deg) x 100 = .707/.580 x 100 = 121%


So a 54.5 degree angle increases the leverage against the shock, which means the same shock travel cooresponds to more swing arm travel at 54.5 deg.


The issue of frame reinforcement is primarily because the stock frames are beefed up at the upper shock mount. Moving the upper mount to below that point would require reinforement.

However, it is not clear why the forces would be alot more (after getting the shock properly sprung), I would think it is has mostly to do with the strength of the new upper mount compared to the lower mount. (see the pic in the link above)

I have no experience with this just the physics of the matter.

Thank you. And that link was very helpful.

 

[wera racer]

exactly how good are you at advanced math?

the more aggressive the angle (away from 90 degrees) the more force required to compress the same shock/spring the same length.

I have formulas if you actually have exact specifications. the angle is only the beginning. as the material thickness, total weights, and lever length are all important factors to answer your last question about bracing, welding,and spring rate.

supposing and guessing is a bad habit because the shock vendor probably has a teenager at the counter not an engineer.

I'm more than a few years removed from trig, but still know my way around a calculator, so I'd love to get the formulas. I'm not sure moving the mounts forward adds much given the improved shock technology today, but I'd love to hear from people that have experimented with this to see if it's worth messing with. Thanks! Rick

 

[sharpy]

This is the current setup of the fastest Suzuki in australia so judge for your self if you want your shocks layed down and a swing arm unbraced. And this is one of the other bikes and my mates.....http://motoaus.com/news/latest/2010-shannons-australian-historic-road-race-championship.html

 

[posplayr]

This is the current setup of the fastest Suzuki in australia so judge for your self if you want your shocks layed down and a swing arm unbraced. And this is one of the other bikes and my mates.....http://motoaus.com/news/latest/2010-shannons-australian-historic-road-race-championship.html

In the attached pic, looks like Ohlins with clevis mount raised a bit as part of the overbracing.

I think the point is that the increased angle in and of itself does nothing unless it is matched to the travel limits and spring rates of the shock itself.

 

[Mindless]

First and foremost I'd brace the swingarm. They aren't very strong in contrary to popular belief.

As for the shocks: sharper angle -> more progressive -> harder to fully compress the shocks. So you could use softer springs which initially are just that, soft. But as they start to bottom out more and more they get harder.

 

[BentRod]

If I may toss in my 2 cents:

oh-man.. suspension design.. where to I start. I don't know what your prior knowledge is, so I say sorry now if it appears that I am talking down to anyone. Folks of all ages and abilities read these forums.

First off, I need to recommend that any suspension work, welding, designing etc be done be a professional. I would hate for anyone to have a crash on their bike because i either gave bad info or it was not read as I intended.

However, if you are determined, better you be informed.
Basic trig really isn't good enough. It is needed to figure out static forces, for example, give a swing arm angle A, and is the force applied by the spring in the vertical direction. Trig is used here to related the angular displacement of the swing arm to the compression of the spring. Trig should also be used to relate the angular velocity of the swing arm to the velocity of the damper. finally you will also have some angular acceleration of the masses in your system, the most significant of which will be your rear wheel and swing arm. the basic equation of motion is:
Mass(i)*Acc.(i)+C(i)*Vel.(i)+K(i)*Disp.(i)=F(i) where i represents any given component numbered 1 to n, and Acc=acceleration of that component with a given Mass, C is the equivalent Damping co-eff for a damper moving at velocity Vel., and K is the equivalent spring constant, for a spring compressed some distance Disp.
Each component of your rear suspension should be discribed mathematically in this way, to determined and ensure the dynamic stability of your rear suspention, and to give you the best performance.
You also need to consider the effects of the rear wheel, given the spring-damper system posed by the tire it self, and that you have a large rotation mass driven by some power P, and torque T in the horizontal direction.
The math should not be too too complicated, as you really only have two spring-damper systems, the tire and the shocks, and two masses, the rear suspension and the bike. Howeever for an accurate model you also need to include the front suspension and the rider, as the load of the bike and rider will likely not be equal front and back. so perform previous steps for front suspension.

you then need to consider the system under acceleration, braking, and cornering where the load fraction carried by the front and rear will change from the neutral, or static situation. Also be sure to include the fact that the wheel base of the bike changes when you turn, as does the location of your contact patches with respect to the centerline of the bike's frame.

once you have built such a model and run the numbers, you can start changing things like the incline of the rear shocks. Only then can you tell what if any significant benifits might be attained.

In the immidiate assessment, the angle of your shocks really makes little to no difference to the confort of your ride or the bike's performance in corners, when compared to the effect of say the temperature of your tires, or the compound, or your riding position, or..etc..

The only justification I can think of off hand to incease the distance of travel for rear suspension springs and dampers is that with greater distance the range in which the assumption of spring-damper system behaving as a linear system is increased, and therefore made designing those systems to behave linearly was made easier, as the expense of heavier and more costly parts.


If any of the above analysis sounded like a bunch of mush, then I would recommend further readings be undertaken, from sources more reliable than a web forum. (and I haven't even touched on the bracing yet, or the possibility of building this at home). to do the job right you will need some knowledge of dynamic equations of motion and stability. A working knowledge of a simulation program such as MatLab would help, and a knowledge of needed manufacturing and measurement techniques is required.


And so no one thinks this is a lot of rubbish

K. Tanaka
B.Eng, M.A.Sc. Candidate
Dept. of Mechanical Engineering
McMaster University


If anyone really plans to modify their own suspension in the hopes of 'tuning' it, please look me up, and may be I can help you.

 

[BentRod]

First and foremost I'd brace the swingarm. They aren't very strong in contrary to popular belief.

As for the shocks: sharper angle -> more progressive -> harder to fully compress the shocks. So you could use softer springs which initially are just that, soft. But as they start to bottom out more and more they get harder.

this observation about the extreme compression of springs can be correct, in that any spring will become non-linear once outside a certain range of travel. However, as the inclide of the spring becomes more horizontal the spring is put at a mechanical disadvantage and further upward travel of the swing arm can result in a decrease in the immidiate rate of compression.

Also, stressing any spring to it's extreme is how you break them

all metals, spring or otherwise have a range of loads in which they are elastic, and anything beyond that range they deform plastically. In other words a portion of the deformation becomes perminent.

Also not that even in steel, high loads can trigger cyclic fatigue.

 

[trippivot]

simple divisor scale for spring rate

simple divisor scale for spring rate

hooke's law is easy to find.
There are many other empirical equations that will help you design this project of yours on paper, but I'd guess you are going to have to fabricate something first to get in the general geometric ball park before crunching numbers.

deflection angle and divisor
10 deg .96
15 deg .93
20 deg .88
25 deg .82
30 deg .75
35 deg .66
40 deg .59
45 deg .50


I'll give an example for a 200 lb spring at 20 degrees

200 divided by .88 will equal 227 so you need a 227 lb spring to get 200 / inch at 20 degrees away from perpendicular.

don't forget the first 20% is weak and the last 20% is super stiff of any given coil spring.

you'll still need to determine the ride height, dynamic lever stroke(center 60% of working spring/shock stroke) length, ride height, compression/ rebound dampening rates etc....

sprocket ratios effect so much more than just the final drive the rear suspension is hugely effected too.

ocillation will be the last issue on the list after you get to test ride it

might just be easier to copy another race bike exactly and find out what the other guy would change about his chassis.

 

[wera racer]

Thanks, guys, for all the info. It is most helpful. Being a CPA, not an engineer, it would probably be foolish for me to try and design anything. Chances are I'd make it worse instead of better. I can definitely handle the fabrication and welding, though. I think the best advice out of it all is to find other GS1000 racers at the track and find out what worked for them. So for now, I think I'll leave the shock mounts where they are, bolt up the GS1100 aluminum swingarm, invest in a nice pair of Ikons, and run this next season and see how they work. Many thanks! Rick

 

[sharpy]

Thanks, guys, for all the info. It is most helpful. Being a CPA, not an engineer, it would probably be foolish for me to try and design anything. Chances are I'd make it worse instead of better. I can definitely handle the fabrication and welding, though. I think the best advice out of it all is to find other GS1000 racers at the track and find out what worked for them. So for now, I think I'll leave the shock mounts where they are, bolt up the GS1100 aluminum swingarm, invest in a nice pair of Ikons, and run this next season and see how they work. Many thanks! Rick

Havent really asked but if you a new racer just go out and ride the sucker and learn how to ride it before you strart modding it. I use to race a TZ350 and when i sold it the new owner couldnt go as fast so he modded what was a record holding bike for that class at that track. Went backwards when he already had the tool to do certain times. Just a tip. I know you want a trick bike but going fast on a "dunger" is always more pleasing

 

[wera racer]

Havent really asked but if you a new racer just go out and ride the sucker and learn how to ride it before you strart modding it. I use to race a TZ350 and when i sold it the new owner couldnt go as fast so he modded what was a record holding bike for that class at that track. Went backwards when he already had the tool to do certain times. Just a tip. I know you want a trick bike but going fast on a "dunger" is always more pleasing

Good advice, thank you. This was my first year racing: three outings on a very modified RD350 and one at the end of the season on the GS1000. I only decided to convert it to a track bike a couple months before the race, so it was stock except for a new 18" aluminum wheel, the salty_monk brake upgrade (sweet!), steering damper, jet kit, racing baffle and velocity stacks. The rear shocks were cheap aftermarket stockers. I was dragging the belly oil pan bad in left turns and the 4 into 1 in rights. This winter I'm installing Traxxion fork springs and emulators and having the motor gone through. New rear shocks and maybe some cams, but that will be it for season 2 prep. So you're right, no shock mods for now and see how it does. Many thanks to everyone on this thread for their advice! Rick

 

[Mindless]

this observation about the extreme compression of springs can be correct, in that any spring will become non-linear once outside a certain range of travel. However, as the inclide of the spring becomes more horizontal the spring is put at a mechanical disadvantage and further upward travel of the swing arm can result in a decrease in the immidiate rate of compression.

Also, stressing any spring to it's extreme is how you break them

all metals, spring or otherwise have a range of loads in which they are elastic, and anything beyond that range they deform plastically. In other words a portion of the deformation becomes perminent.

Also not that even in steel, high loads can trigger cyclic fatigue.

With everything in moderation of course. Putting too much of an angle to the shocks won't just damage the springs but the whole shock assembly. And as you say - if the springs are compressed enough - they will deform permanently.

When I built my bike, I did no real mathematics or calculations on how it would behave with X swingarm length, Y swingarm travel, Z shock length, etc. etc.

I used common sense and asked myself: will this work? Probably. So I went ahead and built it like that and lo and behold - it worked.

Of course I did some measuring and compared to working shock installations, then I figured out something inbetween that wouldn't compromise the look I wanted or the performance of the bike.