Fork Tube Length?

[Broken_Mold]

I am beginning to mock up and measure for my VW-based trike. At present I plan to use a '79 HD Sportster frame since I have a clear title in my name for it. I've crudely set it up at about the height it will be when the torsion housing is added. The steering head rake can vary from about 29 degrees to about 35 degrees. I plan for the torsion housing to mount to the end of the swing arm and solid links will replace the Sportster shocks. My inquiry regards the fork tube length.I plan to use a HD Wide Glide 5 degree rake triple tree and 41mm tubes with a 21" front wheel. My question is how do I determine how long the fork tubes need to be other than by trial and error? Overall length from top of tube to center of axle is easy enough but how do I determine the length of just the tubes minus the lower legs?

 

[Sidecarbill]

Slide the lower leg off and measure it. shouldn't take long, then you will be sure.

 

[Broken_Mold]

Slide the lower leg off and measure it. shouldn't take long, then you will be sure.

Thanks Bill.

If I had a collection of tubes I could definitely do it that way, but alas, I don't. I'm really trying to determine what tube length I need (minus lower leg) to be able to purchase them.

 

[Sidecarbill]

Sorry I thought you had the front end in your possession. It would be simple to remove the lower in that case.:Shrug:

 

[vwbug72501]

First stop: https://www.triketalk.com/forum/threads/35579-Tech-Tech-Tech-or-So-you-want-to-build-a-trike

Lots of good info from Rex.

You are starting from scratch so you can make your trike any way you want. Remember that all suspension dimensions will change from unloaded (bare frame) to loaded (on the road). This goes for the rear torsion assembly as well as the front fork assembly. At this point I'd sugect that you start from the ream and mock up your torsion bar / Sporty assembly, add the engine and transmission weight and see how the frame lays out(concrete blocks/sandbags on the frog legs will work). Level out the frame and you will have an approximation of the finished fork length. Add some more weight to the front of the frame (simulate front forks, gas, battery, you, etc.) and measure the front wheel weight. With this info you should be able to calculate or measure the amount of compression on a stock front fork assembly and from there determine what length tubes you will need.

Good Luck with your build!

 

[stacebg]

View attachment 97060

I am beginning to mock up and measure for my VW-based trike. At present I plan to use a '79 HD Sportster frame since I have a clear title in my name for it. I've crudely set it up at about the height it will be when the torsion housing is added. The steering head rake can vary from about 29 degrees to about 35 degrees. I plan for the torsion housing to mount to the end of the swing arm and solid links will replace the Sportster shocks. My inquiry regards the fork tube length.I plan to use a HD Wide Glide 5 degree rake triple tree and 41mm tubes with a 21" front wheel. My question is how do I determine how long the fork tubes need to be other than by trial and error? Overall length from top of tube to center of axle is easy enough but how do I determine the length of just the tubes minus the lower legs?

get a wooden dowel or electrical tubing to use for a fake tube ..run it all the way to the floor so you have the right

angle,, from there you can go to the center of the wheel .. then you need to know how far the slider goes into the tube ..

probably could help you there