Lowering forks

I have been doing research about lowering 36mm forks internally (on the cheap, that is) and I have realised that the progressive springs I use are about 4" shorter than the stock they replaced, the instructions had me make spacers for it all to fit.
Would making the spacers shorter lower the forks effectively?

Sure, if you don't mind violent, teeth jarring bottoming out and a wallowing front end that dives miserably when braking.

Saggy forks are not lowered forks, they are just dysfunctional forks.

The correct way to do it is to add a spacer, or more rebound spring on the underside of the damper rod. Some people will cut and weld the damper rod to make it shorter, but a spacer will accomplish the same thing. This allows you to have the proper pre-load on the springs so that your front end works properly.

Hoosier Daddy said:

http://honda-cb750-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html

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I did exactly the same thing with a set of cb650 forks last week. I used 3/4" PVC. I had to ream out the ID just a tiny bit because it was a little too tight. I was also limited to about 1 1/4" because there were holes about that distance from the damper piston that oil has to flow through. I didn't cut the main spring, because they were already saggy and if I wasn't lowerin the bike, I would have added 1 1/4" preload spacer to them. The guy who rides the bike is a short fuck, so I lowered the forks, carved the seat foam, and I am trying to talk him into spending the money for 12" shocks.

Yeah I know about the spacer at the bottom. My question is, since my new springs are short, do I need to trim the spring anyway?

Strange that a set of springs designated for a particular bike would be shorter, usually just heavier spring or progressively wound at the top end. I would definitely confirm they are the correct springs.
Correct way to do it if your using them springs would be to add the spacer on the damper rod then fit the springs and work out what size spacer you need at the top between the spring and cap to get the correct peload. 20mm of spring preload is usually a good starting starting point for an average guy.

Adjust the length of the spacer until you get 30-35mm of compression when you sit on the bike. Then you need to adjust the oil gap to suit the damping you require.

notlob said:

Strange that a set of springs designated for a particular bike would be shorter

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Progressive springs are generally shorter than the stock springs. A piece of PVC comes with them to add preload to your preference.

notlob said:

Adjust the length of the spacer until you get 30-35mm of compression when you sit on the bike. Then you need to adjust the oil gap to suit the damping you require.

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Not sure what you mean by "oil gap." If you are talking about adjusting the quantity of oil in the fork, that does not change damping. Damping is changed by using different viscosity oil. With higher pre-loads, you need more damping to balance out the rebound speed.

Varying the amount of oil in a fork has a different effect. More oil means a smaller airspace inside the fork. Therefore, as the fork compresses, the internal pressure rises faster. This gives more of a progressive effect, making the forks more resistant to bottoming out without making the ride harsher. The limit is that you do not want to add enough extra oil that that the forks bottom out on oil. That can blow fork seals. You certainly want enough oil in the forks so that at full extension, the damper rod is not sucking air.

AlphaDogChoppers said:

Progressive springs are generally shorter than the stock springs. A piece of PVC comes with them to add preload to your preference.

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I presume you mean Progressive as in the company. Over here they are not that common, usually Hagon or Wurth. Of those I have used are the same length as the stock springs and a straight swap over.

AlphaDogChoppers said:

Not sure what you mean by "oil gap." If you are talking about adjusting the quantity of oil in the fork, that does not change damping. Damping is changed by using different viscosity oil. With higher pre-loads, you need more damping to balance out the rebound speed.

Varying the amount of oil in a fork has a different effect. More oil means a smaller airspace inside the fork. Therefore, as the fork compresses, the internal pressure rises faster. This gives more of a progressive effect, making the forks more resistant to bottoming out without making the ride harsher. The limit is that you do not want to add enough extra oil that that the forks bottom out on oil. That can blow fork seals. You certainly want enough oil in the forks so that at full extension, the damper rod is not sucking air.

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Agreed ADC I should of said Compression characteristics not Damping.

Yes, I was referring to Progressive Suspension, the company.

thanks for all the info guys! Yes, this is Progressive Suspension springs, they are about 4-5" shorter than stock. i'll use the advice and relocate part of the spacer to the valve.

Picture's worth a thousand words......

Heres a tutorial

http://www.xs650chopper.com/2009/06/mulligan-machine-lower-your-xs650-forks-low-buck-garage-tech/

But dont forget your progressive spacer is part of your total spring length.