24" over too long for 39mm tubes?

[AlbertaFarmer]

Hey everyone. I am in the early stages of planning an Evo build. Softail donor, going to have a custom frame built around the neck. I'd like to do a swedish style chopper with an OEM 2000+ 39mm dual disc fnarrow.glide. 19" 13 spoke front mag.

In a perfect world, I would swap 24" over tubes into a stock dyna / sportster front end. Hoping that with the correct frame geometry, I can get away with using the stock trees and not needing to purchase raked ones. I will be using a fork brace as well.

Has anybody gone super long with extended tubes in OEM trees? I've got 12" over 39's by Frank and they are great on a stock rake sportster.

Thanks in advance

[docmel]

Look good with the proper geometry, yes. Drivability? Questionable

[TriNortchopz]

What rake in the frame are you planning with those +24" 39mm tubes? Flexing may be an issue depending on your rake.

Long tubes are very common in Europe, through well known manufacturer Tolle:

Tolle Fork tubes Tolle/Showa

X-tra strong fork tubes in thicker material for improved stiffness, to Tolle / Showa sliders.
Recommended for choppers with long fork."

Up to +32 overstock available.



https://www.tolle-engineering.se/sto...e-showa-434519

Tolle Triple trees - 250 mm.
Available in three versions; 3°, 4° and 7° rake.
https://www.tolle-engineering.se/sto...-250-mm-335900

with a long set of forks and lots of rake in the frame, the trail will be high; raked trees are used in this application to reduce the trail

https://www.tolle-engineering.se/en-...%A5ng-24408943

"The term 'trail' is used to describe another variable that greatly affects the handling characteristics of our motorcycles and in fact proper trail is far more important than rake in determining how well any given frame and fork geometry combination handles on the road.Most authorities agree that the ideal situation is to keep trail somewhere between 2.0 to 4.5-inches regardless of the rake angle but in my opinion this generalization is far to broad and this dimensional range should be treated only as a starting point to be used in the development of your front end geometry. There are many bikes out there with trail measurements over five inches that still handle reasonably well at all speeds and conversely there are bikes out there with little or no trail that also handle well. One noted Springer designer sets his front-ends up for nearly zero trail and they handle superbly.

When a bike is running fairly large neck rakes and mounting telescopic forks it is extremely difficult to keep trail measurements within reason without resorting to what are called 'raked triple trees' that in effect move the axle of the front wheel forward thereby reducing trail while leaving the neck angle untouched.
These trees are typically available with 3, 5 and 7 degrees of rake and are intended to be used exclusively on modified frames that have neck rake angles in the range of 37 degrees and greater..."

https://chopperbuildershandbook.com/rake.html

[AlbertaFarmer]

Thank you both, fellas.

I would love to do a proper Tolle front end. But just the tubes and lowers would cost $2400 Canadian before shipping and taxes.

I see a few guys in Europe with long tubes that don't appear to use raked trees. I suppose what i'm trying to do is find out just how long I can reasonably go without needing raked trees.

[AlbertaFarmer]

To me, this is perfect. Just guessing, but looks somewhere around 24" over and no rake in the trees.

[AlbertaFarmer]

I spoke with the owner and this one is 24" over.

[drivermark]

From the Chopper builders Handbook article titled "FrontForks"

link to article
https://chopperbuildershandbook.com/forks.html



There are some facts and then there are also some myths about front-end systems that just don’t ever seem to die. One myth is that Springer’s are sloppy and ill handling and this is simply not the case unless the rocker bushings are shot. Another myth is that hydraulic forks don’t work to well on radically raked front ends and this is true. Once you get beyond a 38-degree rake angle or so the effectiveness of hydraulic forks starts to diminish rapidly and they start behaving more like a ‘flexible-beam’ system where the fork tubes are taking the entire load by flexing.


Food for thought

[AlbertaFarmer]

From the Chopper builders Handbook article titled "FrontForks"

link to article
https://chopperbuildershandbook.com/forks.html



There are some facts and then there are also some myths about front-end systems that just don’t ever seem to die. One myth is that Springer’s are sloppy and ill handling and this is simply not the case unless the rocker bushings are shot. Another myth is that hydraulic forks don’t work to well on radically raked front ends and this is true. Once you get beyond a 38-degree rake angle or so the effectiveness of hydraulic forks starts to diminish rapidly and they start behaving more like a ‘flexible-beam’ system where the fork tubes are taking the entire load by flexing.


Food for thought

Thank you for the info. I spoke with a Swedish builder and he basically said the same. He also said that he thought for a long (24"+) swedish bike, you need 41mm and 39mm would not handle the stress.

I have always like the 39mm stock front ends, and have one with forking by Frank's 12" over tubes. That one is on a stock rake sportster and rides great.

[AlbertaFarmer]

This bike belongs to a member here. I am thinking now that I should do something like this, but with a 39mm hydraulic front end.

Seems to me that if I stayed at a 37 or 38 degree rake, and lifted the neck until the bike sat level with an 18" over, I'd be pretty safe. What do you fellas think?

[drivermark]

That's a killer looking bike, and I've always been kind of partial to the look of springer forks.

[Smiley]

When it comes to custom fabrications 'safe' is a relative term and may have a lot more to do with the rider than any particular set of forks and rake/stretch/trail combinations. There are probably a fair number of folks who wouldn't feel comfortable handling the first two bikes you posted and others who would feel perfectly at home in the saddles. Same applies to the high neck Swedish styles. Wiih respect to the extended tubes you really need to be asking the various tube manufacturers and see what they are willing to stand behind with respect to rake and extension.

[AlbertaFarmer]

When it comes to custom fabrications 'safe' is a relative term and may have a lot more to do with the rider than any particular set of forks and rake/stretch/trail combinations. There are probably a fair number of folks who wouldn't feel comfortable handling the first two bikes you posted and others who would feel perfectly at home in the saddles. Same applies to the high neck Swedish styles. Wiih respect to the extended tubes you really need to be asking the various tube manufacturers and see what they are willing to stand behind with respect to rake and extension.

This is very true. I believe I have quite a high tolerance for squirrelly, just didn't want to do anything that everyone knows won't work.

Talking to the manufacturer is a great idea. I will ask franks and custom cycle engineering. See if there is much difference in strength between 41 and 39mm tubes.

[AlbertaFarmer]

In the end, I decided to go back to my original plan. Evo with a 30" over springer. I had talked myself into something cheaper with front brakes. But by the time you set up a 39mm dual disc properly, it's nearly the same cost. And then keeping the rake under 38 is very limiting.

Oh well. I learned a fair bit about long tubes. Thanks for the help everyone.