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Shock length and spring weight?

  • Thread starter Thread starter TwnsndWhln
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TwnsndWhln

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I have a 1984 GS1100GK and I'm replacing front springs to progressives and I want to replace the rear stockers as well. I want to go with Progressive 412 series shocks with heavy duty springs.

I believe the stock length of the rear shock is around 13 inches.

I called Progressive's tech line and the rep told me that they recomend a shock length of 12.5 inches for my bike. They also recomend a spring weight of 120/170 pounds.

I have read that some bike owners went to a longer shock, 13 or 13.5 inches to improve handling.

My question is can I simply get a Progressive series 412 shock that is 13 inches long instead of the 12.5 incher? The rep gave me a universal adapter part number for bushings if I needed it, but she did not recomend straying from the 12.5 inch length, saying that the engineers designed the shock in 12.5 inch for a reason.

What type of performance increase/decrease can I expect for getting a longer/shorter rear shock? I'm not an all out top end performance type rider, but I do enjoy spirited rides and would appreciate some better handling characteristics. Seeing as that I'm changing the shock I might as well get as much for my money as possible.

I'm 200 lbs and I have the stock shock on the highest dampner setting (#4) and I don't bottom out now, but I plan on doing some 2 up riding soon with loaded bags.

Thanks in advance, Steve.

Also, here is a website with progressive shock lengths. My recomended manufacture # is 4124207C for the 412 series 12.5 inch.

Down the page there are the 13 inch lengths. I tried to narrow down the closest match for the 12.5 stock number. I think it would be #4124212C. Not the most scientific match data but seemed reasonable from the groupings of the 12.5 incher group. Called that website and the rep could not recomend a match and echoed the progressive rep.

http://www.accwhse.com/progress.htm#Shocks

Let me know what you think!
 
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Come on,... Somebody?

Come on,... Somebody?

Keith Krause, PlaneCrazy, DaveDanger, AOD, Redman, Argonsagas, Billy Ricks, 83GK, Kalessin, Bwringer, ...Where are you guys????

Anyone!!!!
 
I think I would ask myself: Do you think the frame/suspension design engineers missed thinking of this, kinda simple don't you think? How is my bike going to handle if I change the front and rear geometry; who's idea of 'better' means what? Even the aftermarket suppliers don't recommend a change from stock shock length.

Heavier springs for two up, sure change 'em, but I wouldn't change shock length.
 
jimcor said:
I think I would ask myself: Do you think the frame/suspension design engineers missed thinking of this, kinda simple don't you think? How is my bike going to handle if I change the front and rear geometry; who's idea of 'better' means what? Even the aftermarket suppliers don't recommend a change from stock shock length.

Heavier springs for two up, sure change 'em, but I wouldn't change shock length.
Click to expand...
Awww, what do engineers know, anyway? \\:D/

Ignoring all their knowledge I went with one inch over stock, 13.5" off the top of my head, Ikon rear shocks on my '83 GS1100E. The ride is much better than stock, due to the quality of the shock, nothing to do with the length. The handling quickened up quite a bit due to the increased rear ride height. Lane changes take just a light push (or pull) on the handlebars and countersteering in general is much easier. The increased ride height helps keep stuff from dragging in corners. At the North Carolina Rally guys I was riding with were grinding pegs and centerstands while I was spark and pucker free. I also ride two-up a lot so I figure that when riding two-up my ride height will be the same as the engineers originally intended. As an added benefit, putting the bike on the centerstand is now almost effortless.

Thanks,
Joe
 
Jimcor and Joe thank you for the response.

Jimcor, I may have not worded my question properly. I agree with your setiments about stock length and why change from it. That is why I found Progrssive's decision to stray from a Suzuki stock length of 13 " for my 84 GS1100GK and make their shock 12.5" somewhat disconcerting.

I have heard they (Progressive) are a very good company and produce nice shocks so I'm tempted to take their recomendation for a 1/2" shorter shock, but when I see some aftermarket supply stores like Bike Bandit list a warning directly below their shock listing for my bike that the bike may handle somewhat slower due to the shorter length it leaves me puzzled as to why Progressive's engineers strayed from Suzuki's. http://www.bikebandit.com

Hmmm, I think its a decision of which engineers, Suzuki's or Progressives, to trust. (Or like Joe pointed out neither of them.) :)

Now when I want to order a shock for my bike and stay with Suzuki's recomended lentgh I have to order a shock for a plain GS1100G instead of one for my GK. Kinda weird. That is at least if I'm going to get a Progressive shock. I have yet to check out Ikons or other manufacturers lengths.

Joe, I like your reasoning. I think I'll either get the Progressive 13" thats close to my stock length or even a 13.5".

I really like my bike. I put a Rick's RR and did the obligatory tune up when purchasing a second hand vehicle; i.e. Plugs, fluid changes and other small items that crop up. I also put a custom seat on it.

I spent a healthy sum on braided brake lines, kits to rebuild all calipers and both master cylinders, new pads and have new Progressive front fork springs ready to put in. The bike runs great and I'd like to see what the front springs, shocks, brake parts and braided lines do for handling and stopping. Right now it dips forward pretty good on hard stopping, actually any stopping for that matter.

Only three things stopping me from getting it done. I don't want to stop riding, I'd like to get my boat out of the garage for more space and the decision over shock length.
 
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My 850G called for and received 13 inch Progressives.

I don't have the foggiest idea why Progressive would list a 12.5 inch shock for the GK -- if I'm reading this correctly, the stock length on a GK is 13 inches.

I'm a great shambling galoot who rides way too damn fast, so I found that the heavy duty springs were still too light for any 2-up riding. After shuffling through the Dennis Kirk catalog, I found even heavier shock springs for the 12 series shocks, and ordered up a set.

Riding by myself and with light luggage, I have preload set at #2 out of five. With my wife, preload goes to #4 or #5 depending on the amount of luggage she's dragging along.

Anyway, on your GK, I personally would order up a 13 inch set of shocks with heavy duty springs and ignore the silly 12.5 inch recommendation. If anything, the slight amount of extra length will only improve handling, and with all the luggage and bodywork, the extra ground clearance will be welcome.

If you are also a huge galoot who rides too fast for decent people, you may wish to order up the super-heavy-duty springs. I think they may be listed under early Gold Wings or somesuch.

With these old bikes, you have to be very skeptical of catalog listings.
 
Thanks BW.

Whereas I probably don't ride as fast as you and Chef yet, I just may get there someday. :-D Still learnin' the ropes though. But, I'm definitely going to go with the 13 inchers on my GS GK.

Even though I probably don't eat as much as the Chef, I also like the idea of the heavy duty ones, which I believe are 120/170 rating. The highest for that shock.

Thanks for the setting info.
 
There may be 210/170 spring available for that shock.

Progressive will sell, if you ask, a 210/170 or in that range shock.
It's been a few years since I changed the rear shocks on my 1000S.
Doesn't matter if it's a G or S, shocks work the same.


I'm around 250 lbs and ride 2 up.
With the current Progressive shock/spring combo I can usually get away with the 2/nd setting for me.
With my wife on the back, usually the 3/rd setting, sometimes the 4/th.

Call them again and ask if the have any "special order" or extra heavy springs.

Oh and as to the length, see Joe Nardy's reply. Go with the 13 inchers
 
My Progressive shock springs have "1365 120/170" printed on them. That's probably the part number and the spring rate range. (On progressive-rate springs, the spring rate goes up as the spring is compressed.)

Hope this helps some other galoot...
 
BW, can you get a part #

BW, can you get a part #

BW, could you go to the first post on this thread and see my link to American Motorcycle Accesory Warehouse. If you have a minute can you go to that link and check out thier 412 series chrome shocks down the page and see the 13 inchers. They have the lowest prices I've seen for the 412's and they have quite the selection, only they don't label the pound ratings for each spring. I think they must expect one to know the ratings already. Dennis Kirk wants around $250 for their heavy duty shock which I believe is 120/170.

Bike Bandit is down to $217, but the site doesn't say what the spring rate is for their "Heavy Duty" application. Might be the same or might not.

I went to MAW and looked for something resembling the 1365 number on your 120/170 shock, which is the poundage I want to aim for. Nothing really matched definitively. Maybe I'm missing something.

KGB, I weigh in the low 190's when I keep my exercise regime and eating habits in check, which, as we all know is no easy task. I think the 120/170's may be the choice since I do mostly one up. That being said, I wasn't aware Progressive even made a spring that heavy (170/210) and if you would'nt mind checking that aforementioned link for a reference number it would be appreciated.

My only question now is about the shock I need fitting the eye bolt. BW, can I go with a shock made for a Gold Wing and would it fit my bolts or do I need an adapter kit or something? Basically is there a big size differential on UJM's for shock eye bolts? Also, if I did go with one of those after market supply stores, can they fit heavier springs to a shock that fits my bike?
 
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Hmmm, on that link to MAW there is a "Touring Magnum" shock made for BMW's and Gold Wings. Its a mechanical shock instead of air. One size listed is 13.25 inches, # (48862). Kind of an appealing size.

What are the benefits/drawbacks to mechanical vs air shocks? I've heard members say that they have disregarded the air adjustabilty with their front forks/springs when they installed Progressive springs up front. Would this logic work for the rears too?

Would these just bolt up to my bike?
 
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