Dirt bike fork shortening for LSR

[Travislee]

Hi everyone, I am starting on my build of taking a 2002 Honda CR250 and turning it into a land speed bike. I am ready to start the suspension work but was needing some recommendations on how to lower the bike as much as possible. I spoke with RaceTech suspension and they say they can cut the fork tubes down and machine the internals to lower it considerably but i was wondering if there is any other options. The only other option I have thought of is changing to a CBR600RR sport bike front end.

Any help is greatly appreciated.

Travis

[sofadriver]

Because of the huge amount of travel you'll probably have problems getting the bike as low as you want with the CR250 forks.
Go with the CBR600 front end.  It will be much easier to use a smaller wheel, too.

[wobblywalrus]

Sometimes a shorter set of compression springs can be used with spacers on the damper rods to prevent the forks from extending to their full length.

[55chevr]

Drag straps are a common solution.

Joe

[rgdavid]

Would using the 21 inch front wheel be better for stability ?

Smoother over the bumps and hollows as well.

[Stainless1]

Go with a wheel size that has available tires that exceed the record speed... 

[Milwaukee Midget]

Go with a wheel size that has available tires that exceed the record speed... 

Limitation engineering tip 101 from the master . . . 

[Marty]

What I did for my bike was quite easy and lowered it 3 inches. I used a set of 34mm RD 350 front forks, had my local machinist chop off the bottom of the tubes 3 inches then he mad the same cut on the remainder of the inner fork tube to duplicate stock, put back in the dampener rod and i cut a small section of the spring .Put new seals in a there you have it lowered forks.. Did the same to my GSXR drag bike too. Was very inexpensive. The CR forks look to be a little more complicated and they are quite large. I would find smaller front forks and adapt them to the neck, but thats my opinion

[Marty]

P.S Travis  What class are you gunning for? Two strokes are cool, like mine, but you need to make it last for miles, cooling is EVERYTHING to 2 cycles. I found out the hard way last year. I would like to talk more bout your project. shoot me an email, I will send you pix of my AAF 500CC RZ powered 496cc beast. Thanks and good luck!!

[BVCBR]

Shortening a cartridge type fork is not too difficult. Finding a short replacement spring can be tricky though.

Remove the cartridge from the fork assembly and then remove the plunger shaft from the cartridge tube. Look at the shop manual on how to get the cartridge apart.

Make a spacer the length you want to lower the forks that will slip over the plunger shaft and clear the inside of the cartridge tube.

Reassemble the cartridge and then reassemble the fork assembly just as you would normally. I use the same oil type and level (volume will be less) as specified in the shop manual.

You'll need to find a spring that is shorter with the spring rate you want. Eibach is a good source for springs.

If you don't have them already, you will need to get a couple of special tools to disassemble the forks and get them back together again. Look at the shop manual and see what they recommend. Some of them you can make yourself, other not so much. You shouldn't need to remove the inner fork tube from the outer tube. Just remove the cartridge.

The rear shock can be done in much the same way, by putting a spacer on the shock shaft, but they are a little more difficult to disassemble/reassemble.

JW

[tauruck]

If the forks are old school type and not upside down I have a solution.

Strip the forks, get the tubes in the lathe and part off the amount you need.
Tap the top end with the same pitch as original and shorten the spring by the same amount.

Worked for me on my Sporty. It's not like you're going motocross and you aren't shortening the forks by 10 inches.

[sofadriver]

Apparently everybody around here has a machine shop.
Travislee just look on e-bay..........

http://www.ebay.com/itm/like/261992803743?ul_noapp=true&ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F711-117182-37290-0%252F2%253Fmtid%253D1588%2526kwid%253D1%2526crlp%253D53601919689_324272%2526itemid%253D261992803743%2526targetid%253D87946131969%2526rpc%253D0.16%2526rpc_upld_id%253D57148%2526rlsatarget%253Dkwd-87946131969%2526device%253Dm%2526mpre%253Dhttp%25253A%25252F%25252Fwww.ebay.com%25252Fulk%25252Fitm%25252Flike%25252F261992803743%25253Flpid%25253D82%252526chn%25253Dps%2526adtype%253Dpla%2526loc%253D9033520%2526poi%253D%2526campaignid%253D239125209%2526adgroupid%253D14978428809%2526gclid%253DCJ-3qObX5cgCFdKGfgodVzYDuQ%2526srcrot%253D711-117182-37290-0%2526rvr_id%253D919703169163&chn=ps&lpid=82

[Travislee]

Thanks for all the replies everyone. I have a lot to think about with the front suspension. I know it is not the most cost effective route but I am leaning towards the front suspension from a newer sport bike. I figure if i want to make another bike in the future I can just swap over the suspension to the new frame. Plus as Stainless1 said there are numerous tires at multiple speed ratings well above what the class runs. For the rear I was thinking about a really short shock in the same location and a lowering link if need be. Plus a 17" rear rim and tire (again many more tire options).

Marty, I am looking to run in the modified frame 250cc class. I am not sure if i want to run gasoline or fuel. Any recommendations? I would love to see your setup if you dont mind sharing.

Travis

[wobblywalrus]

Travis, lately I run gasoline the first day 'cause it is a good fuel , gives predictable performance, and I can get a time on the books.  Then I switch over to fuel and run it for the grand finale. 

[tauruck]

Apparently everybody around here has a machine shop.
Travislee just look on e-bay..........

http://www.ebay.com/itm/like/261992803743?ul_noapp=true&ul_ref=http%253A%252F%252Frover.ebay.com%252Frover%252F1%252F711-117182-37290-0%252F2%253Fmtid%253D1588%2526kwid%253D1%2526crlp%253D53601919689_324272%2526itemid%253D261992803743%2526targetid%253D87946131969%2526rpc%253D0.16%2526rpc_upld_id%253D57148%2526rlsatarget%253Dkwd-87946131969%2526device%253Dm%2526mpre%253Dhttp%25253A%25252F%25252Fwww.ebay.com%25252Fulk%25252Fitm%25252Flike%25252F261992803743%25253Flpid%25253D82%252526chn%25253Dps%2526adtype%253Dpla%2526loc%253D9033520%2526poi%253D%2526campaignid%253D239125209%2526adgroupid%253D14978428809%2526gclid%253DCJ-3qObX5cgCFdKGfgodVzYDuQ%2526srcrot%253D711-117182-37290-0%2526rvr_id%253D919703169163&chn=ps&lpid=82

You wish. I have to fight, scratch and claw to get stuff machined. I even had to settle a score once just for lathe work. Semper Fi.