[toyosuprablue]

I have a 1982 Honda CB900F that I am trying to fit a ducati 748 SSSA on (dimensions are on CF somewhere)... With the swing arm I also got the stock shock from the ducati. I figured on it being on the soft side since the 748 is a lighter bike but when i mocked up a mount quick and took the bike off the stand it instantly sagged to where the shock was almost maxed out. My quick trial didn't use the accompanying linkage that the stock 748 setup uses. Does that make the rear shock stiffer? I had the shock at 90 degrees to the swing arm which is the angle that would make the shock most effective. Any suggestions that I could try would be appreciated. Also if you know how to calculate the necessary spring rate I'll try and find a different oem shock that is stiffer. Im a 200lb rider

 

[Problomatic]

Race tech article on linkage :http://www.racetech.com/page/id/44

 

[toyosuprablue]

I understand the concepts in that article. What im having trouble with is getting the spring rate and shock force for my current shock or any other oem shocks to know which one should work for me

 

[Problomatic]

http://www.hypercoils.com/spring-rate-calculator/

Try this.

 

[toyosuprablue]

THANKS!

 

[toyosuprablue]

Assuming a force of 360 lbs (half the weight of the bike plus me) and using the measurements for the swing arm i got the following data.
Values are for shock angle of 90, 45, and 35
motion ratio .219, .155, .126
static load 1527, 2160, 2663 lbs
spring rate 545.7, 771.7, 951.38 lbs/in
effective wheel rate 26.2, 18.5, 15.1 lbs/in

Time to find me a perfect donor shock

 

[Problomatic]

Why not just swap out the spring?

http://www.racetech.com/page/title/SRSP-RT Shock Spring List

 

[toyosuprablue]

I figured it would be cheaper to find a used complete shock on ebay... but those prices arent bad, i'll try and cross reference it now to see if they have one the right size

 

[toyosuprablue]

I found one that should work. I read else where that by upping the spring rate so much the shock needs to be revalved. How bad would it ride if I didnt do that?

 

[Problomatic]

Do you set your sag front and rear?

 

[toyosuprablue]

Not quite sure what you mean

 

[Problomatic]

Then I doubt you'll notice the difference in valving, especially since you're not adjusting the spring rate due to weight issues, but because you changed the shock position. You could adjust your dampening to try and compensate if the ride feels rough. On a side note, you should look up setting sag on your suspension. It'll improve handling and feel.

 

[toyosuprablue]

Ok, yea the spring rates that I calculated using that link you provided were for a shock ride height of 2.8" I think thats a safe estimate since its a 6" shock and the valving will be off. Im thinking i should leave the shock adjustment on the stiffest setting since I'm increasing the spring by almost double. Im also going to make an upper mount with three mounting locations so that I can try the shock at different angles and see what works best. Thanks for all your help!

 

[toyosuprablue]

Shock I ordered was on backorder. hopefully it arrives this week sometime so that I can keep going on this project