What kind of shock should I use?

[cplcrawlerUSMC]

I have a 78 GS1000 that I am turning into a Monoshock similar to the one in this video http://www.youtube.com/watch?v=518N08mDM8I

What shock should I use. I'm not looking for a particular brand. Im looking for something that can take the load. What specs should I look for?

Thanks,
Colin

[Billy Ricks]

What swingarm are you using? An 1150 shock would probably have about the right spring rate, but that depends on the swingarm and linkage ratio. Works Performance still offers shocks for all the old mono-shock bikes.

[cplcrawlerUSMC]

I was going to have the fab shop in town take the original swing arm and frame and have them fab it up to look like this bike with the shock going under the seat. At least thats the plan.


Where the swing arm pivots would have to be lowered to get the look I want. I dont know if its possible or if they would have to fab up an entirely new back end.

[Billy Ricks]

I was going to have the fab shop in town take the original swing arm and frame and have them fab it up to look like this bike with the shock going under the seat. At least thats the plan.


Where the swing arm pivots would have to be lowered to get the look I want. I dont know if its possible or if they would have to fab up an entirely new back end.

That's much the way Yamaha does their rear suspension. If it's directly bolted to the frame and swingarm with no linkages that should make calcualting spring rate easier. Probably something in the 250-300 lb range depending on your weight.

BTW, thanks for your service.

[cplcrawlerUSMC]

You are very welcome! I am very proud of my service and am thankful to hear someone apperciate these days. It has been an unpopular time for our service men and women but has gotten better lately.

So pretty much any shock that is able to handle the load will work. I just hope it wont cost an arm and a leg to get it all fabbed up. Thanks for your help.

[posplayr]

I'll second that thought. Thanks for your service.

I looked at the video and that was a cool bike; I guess I have never seen a mono shocked bobber (that I knew what i was looking at).

I looked up these guys that apparently made the frame in the video. Might be a bit pricey for something like that but they might be able to steer you to a shock that works in this configuration. The frame in the video did not seem to use any linkage.

Without linkage I would suspect you need more shock travel than normal (almost the entire wheel travel). Stock the 750 has about 4.25" wheel travel and probably 2.5" (quickie measurement) of shock travel . With that type of bobber swing arm configuration the shock travel is probably a full 4.0" , so that would require a proportionately lower spring rate (after accounting for two vs. one shocks).

You mentioned load several times, and I'm not sure why the spring load would be higher. If anything given the leverage of the mono shock mounting point the spring load would seem to be lower. In other words there is no mechanical disadvantage between suspension height and shock compression.

You are likely to have to design the shock mounts around a specific shock. I would find that first before doing any welding.

Billy, is that configuration really old school (like from the 30's?); you mentioned seeing it before.

http://www.crazyhorsechoppers.com.au/parts/frames.htm

Good Luck and thanks again.

Jim

[Billy Ricks]

Jim, it's pretty much the way Yamaha mounted their shocks on many of their sportbikes. They laid down almost horizontal. Whether they used any type of linkage to change the ratio I couldn't say. I never took a close look.