1975 FXE build

[Garry in AZ]

One of these days I'll get the current emergency off the lift and begin my FXE build.
I'm aiming for a low, minimalistic bobber style of bike, but with modern brakes and reasonable shovelhead reliability.
One of the ideas I'm toying with is to use an inverted sportbike front fork, for the better brakes, and frankly I just like the look.
I'm interested to hear from those who have done this, especially if you did most of the engineering yourself rather than buying a pre-made kit.
Also interested in hearing from anyone who has modified the frame to put a drop seat on, something like the kit from speedking.

Garry

[turboprop]

I have done a couple of inverted forks on FXRs that used legs from an '07-'08 GSXR-1000 (Friend had a set in his shed). Regardless of what anyone's friend of a friend says, the oem GSXR trees do not have the correct offset to work with a 19" wheel. Other issue are:

1. Length - almost every sport bike fork is about three inches too short (Axle centerline to top of the top tree).
2. Spring rate and valving - The forks on a sport bike will most likely not have the correct spring rate or valving for your unique application. Aftermarket can easily correct this. Unless you know what you are doing best to leave this a a shop that specializes in suspension.
3. Fender mounts - Custom mounts required to run a harley style fender. A 19" wheel will not fit under a sport bike fender
4. Offset Trees. A set of custom trees with the correct spread (tube to tube) and offset will be required.

Fun fact - Many sport bikes have 207mm fork spacing. An OEM harley narrow glide wheel with sealed bearing will have the correct flange width for the brake rotors to align with the calipers. The problem is most sport bikes have larger rotors than even the Harley/Brembo rotors. A real easy solution is to source a set of 320mm rotors for the harley hub. Then add spacers as needed between the radial mounts on the foot and the brake caliper(s).

I made my own trees (Three prototypes) to get the correct offset for the amount of trail I wanted. I also lengthened the legs at the bottom between the shoe and the lower tube (I really dont like dropped trees - gay).

A couple companies make turn-key kits for this. Giga Cycle comes to mind but there are others. Google. IME, the chopper crowd is typically more concerned with looks and does some really stupid and expensive stuff (ie open belts drives, dual magnetos, etc). Looks aside, The new dyna fork legs are pretty good, have the correct length and have oem and aftermarket trees available with the correct offset.

Of course, I get asked this pretty often. Most that ask will never actually do it, or if they do they will cut corners. I hope you are not like most. Looking forward to seeing pics of your inverted fork on that FXE. 

For reference, there are countless pics of my bikes with the inverted forks on this forum. Beware the arm chair crowd that has ideas have not done anything. Unfortunately there are too many of them.

Best fo luck with your project. 

[Garry in AZ]

Turboprop, thanks very much for an excellent reply. I understand and agree with you that the GSXR trees do not have the right offset for a 19" wheel. 100% on the same page there.
Good point on the fork length - I need to measure that to see if the idea is worth doing. Spring rate and valving is no problem, I'm an old motocrosser and have friends at Progressive and Ohlins.
Fender mounts are something I have thought about - probably fab my own.
Not planning to cut corners, I'd rather build it right the first time and be done. No deadline for it either, so time is not a factor. It'll be done when it's done.

Thanks again for the expertise. Much appreciated.

[turboprop]

Turboprop, thanks very much for an excellent reply. I understand and agree with you that the GSXR trees do not have the right offset for a 19" wheel. 100% on the same page there.
Good point on the fork length - I need to measure that to see if the idea is worth doing. Spring rate and valving is no problem, I'm an old motocrosser and have friends at Progressive and Ohlins.
Fender mounts are something I have thought about - probably fab my own.
Not planning to cut corners, I'd rather build it right the first time and be done. No deadline for it either, so time is not a factor. It'll be done when it's done.

Thanks again for the expertise. Much appreciated.

I lengthened my forks at the bottom. All of the arm chair crowd here said it should not be done. Software and known physical characteristics of the materials used said other wise. Over 30k hard miles latter and the sky has not fallen. PM me if you are interested in knowing more about lengthening an inverted fork from the bottom.