lots of suspension questions...

[79-GS550-L]

Ok, I don't know a whole lot about suspension... yet I'm planning the rear end of my project bike and have lots and lots of questions. I'm not entirely sure what I'm going for yet, still coming up with ideas, but I would like the rear lowered somewhat and would like less total wheel travel so I can fit the fender closer to the wheel. Not too extreme, just a bit. I know this means I will end up with a stiffer ride, but that's ok. I intend to plan everything out and make sure it's mathematically sound.

So, questions:

1. My shocks look like this:
I've seen pictures of some people's shocks where the windings look more even (same amount of space between each, whereas mine are closer together at one end). Does this indicate I have progressive rate springs fitted already?

2. I've read about shortening shocks by cutting the spring and screwing in the spring retainer further (cutting some threads if needed). Is that something that can be done with progressive springs too, or is that a bad idea? I would assume the softer portion (wider spacing) would need to be cut.

3. Somebody suggested raking the shocks in order to lower the rear. I know that will give me more wheel travel though, so I'd need to shorten the shock stroke by a whole lot in order to have a lower rear AND less wheel travel. How short can I make the shock stroke, practically speaking? I know after a while sloppy tolerances will catch up and make it unpredictable.

4. I really like the way the harley softail looks, and I think the horizontal shocks are a neat idea. Does anybody know whether they put the shocks at the top, right under the seat, or at the bottom, right above the road? I've read conflicting information on this. Maybe they changed it at a certain point?

5. Is this something feasible for a GS? The "Monoshock, older style, regular swingarm" from http://www.carbibles.com/suspension_bible_bikes.html - only I think I'd do it with dual shocks, but same kind of shape.

6. Where can I find specs for my stock springs (I guess I could measure extended length and stroke but I don't know how I'd measure the spring rate)? I've looked in the Haynes manual but can't find it. Sure would be helpful when shopping around for new shocks.

 

[Dave8338]

Those are progressive springs that you have on there right now. Old school with how they are dampened, but progressive none the less. I'm not sure on the "shorten shock" thing/idea but whenever possible and for sure with suspension pieces, use manufactured parts (shock, springs(though they can be cut) and ball joints / tierod ends ect.) You can do almost whatever you want with the swing arm. If you rake the shocks, you need to keep in mind that you're going to need stiffer springs if you rake them much (a little thing called leverage).

As far as the mono shock set up, it can be done both ways...above or below the rear axle. Again keeping in mind your spring ratios.

 

[catbed]

ooooooooh look at my sig!!

post pics in a few.

well the softail shocks are underneath the bike and obviously below the back axle so unless the engineers at harley davidson made a huge flaw, you should be safe.:-D:-D

 

[79-GS550-L]

wow that's some very informative stuff. Thanks guys.

Dave, what would I use ball joints and tierod ends for on a motorcycle? It's nice to know I've got the progressive springs on, in that case I don't think I'll try to cut them. One more question, if I rake the shocks do I have to change the torque on the shock mounting point? Reason being that now they will pivot more as they compress, and the way they are torqued down now they are pretty stiff and don't rotate too easily.

Catbed, can you send a slightly more zoomed-out picture of the back end? I'm having trouble visualizing how the two frame pieces connect. I thought they were connected in the middle, but it looks like they're connected at the bottom, behind the shocks. Also is the foot peg on the swingarm? I assume that since the shocks are on the bottom that they work in reverse, where they stretch instead of compress? Also I can't seem to find the leaf in any other diagrams. Is that an aftermarket leaf?

 

[trippivot]

those are good questions you have. let's clear up where spring rates vary:

the wide rings of the spring are the stiff part and the narrow rings are the soft part of your spring. that is a progressive spring/ spring combo on your shock.

as a rule the progressive end of a spring (narrow winding end) should be mounted to the stationary side of any moving assy. the spring is springing. (valve springs, fork springs,rear shock springs) just like the rear shocks are on your bike --the frame is stationary while the swing arm is swinging etc... you get the picture.

lowering the rear end by raking the shock--moving the lower mount rearward will 1.Reduce the suspension travel AND stiffen the suspension movement mechanically. There used to be brackets available to do this without welding.

Harley soft tail swing arm geometry is simple but labor intensive to create.

modern mono shock is commonly done But anything can be done if the budget will afford it.

a set of shorter shocks with a single rate spring is what I'd buy. Progressive 412 shocks they'll even swap your springs as a warranty if the rate is too soft. All you need to do is call the c s r line.
.
Don't try to cut the spring and reassemble it. I've done that on cars struts and it works. but these type of sealed shocks... you will squish it beyond the intended travel and it will pop and leak

 

[79-GS550-L]

the wide rings of the spring are the stiff part and the narrow rings are the soft part of your spring. that is a progressive spring/ spring combo on your shock.

Ah, had it backwards. That makes sense though now that I think about it more.

as a rule the progressive end of a spring (narrow winding end) should be mounted to the stationary side of any moving assy. the spring is springing.

Not sure why that would matter but I'll take your word for it

lowering the rear end by raking the shock--moving the lower mount rearward will 1.Reduce the suspension travel AND stiffen the suspension movement mechanically. There used to be brackets available to do this without welding.

Now this is the main thing I'm confused with. In my mind it should be the other way around. I'll have to mull that over a bit.

a set of shorter shocks with a single rate spring is what I'd buy. Progressive 412 shocks they'll even swap your springs as a warranty if the rate is too soft. All you need to do is call the c s r line.

Why do you recommend single rate springs over progressive?


Thanks,
Alex

 

[trippivot]

single rate rear springs are my own preference for "road feel"

laying down of the shock begins by using some of the available free travel(static lowering). it won't lift itself- that travel will be gone

now, the shock is only going to compress until it is stopped by hydrolock or spring pressure, and it will not expand beyond the static pre load height, determined by the action of laying down the shock and the weight on the rear half of the bike.

changing of the force angle (raking the shock) will make the spring you have now feel stronger/stiffer.

ever tried to compress a pogo stick?? it's easy straight up and down on it in line with the spring...you with me? take the same pogo stick and prop it in to a lower stair landing and try to compress it the same distance at say 15~20 deg. the force going downwards--- not at the same lean angle ... downward force compressing at an angle you'll see you need twice-3 times the force to compress the same spring the same distance.

it may take a while to sink in but you will have less travel and more stiffness the farther the shock is raked over. I would not go more than 3 inches from stock position. 1/2 inch ~ 2.5 inches rearward

the mounts will not suffer from over stress if they are welded with plenty of penetration.

 

[Dave8338]

I think Tripp sums it up quite well. As to your question of: "where would I use ball joints and tierod ends on a bike"...well, you wouldn't unless you were mounting a sidecar with partial bike travel / lean. They were only mentioned to bolster the point that when it comes to suspension...find the pieces that fit and use them, don't try to modify too much. I haven't got it sitting in front of me, but when it comes to controlling rotational force (torque) as it pertains to suspension geometry, unless you completely change the swingarm suspension type ie. mono-shock, dual tension (looks like what is used on the soft tail) or single compression like was on my Virago, you will be limited as to what your stock parts will allow you to do.

Also keep in mind...there is a limit to strength in the stock swing arm on the GS bikes. If you're thinking of changing to a mono shock setup, you'll need to change out the swinarm or do alot of clever mods.

 

[79-GS550-L]

it may take a while to sink in but you will have less travel and more stiffness the farther the shock is raked over. I would not go more than 3 inches from stock position. 1/2 inch ~ 2.5 inches rearward

Well I've been banging my head on the wall trying to figure out why that would be since you posted that. I think I finally see why we're on different pages - you're talking about moving the lower mount rearwards, and I'm thinking of moving the upper mount forwards. I believe that will give more travel and less stiffness. Does that make sense?

I was imagining moving the upper mount forward by 3 inches (just to the other side of the bar, making another little "web" between the bars to mount it on). If I did the math right, that would lower the bike by just over an inch with the shock extended all the way (no weight on it). Then I'd have to replace the shock with a shorter/stiffer one to limit travel.

Another question... the new mount, can it be a hardened steel bolt? Like a grade 7? Or will that not have enough shear strength? I want to make the new mount before cutting off the old mount so I can switch between them a few times to compare.

 

[trippivot]

top forward or bottom rearward exactly the same EXACTLY

a full 3" is too far in my professional opinion... but experimentation is allowed.
just remember Failure is painful or fatal

mild steel threaded bung mig welded is plenty strong

use 10-12mm bolt diameter and super hard material not required


I have to express welding different shock position mounting bungs is WAY EASIER to do and change on the swing arm.

 

[Dave8338]

A little more info.

A little more info.

Give these two a look and I think that your questions should be answered:

http://www.carbibles.com/suspension_bible_bikes.html

http://e30m3performance.com/tech_articles/susp-tech/eff_rate/eff_rate.htm