Anybody mount FZR600 forks on an RD350?

Anybody mount FZR600 forks on an RD350? Main question is shorten the 600 stem or replace with RD stem?

I guess I will adapt vintage legal brake and caliper and 18 wheel. Probably adapt 15 mm axle with simple hi-hat spacers in wheel bearings.

Also wondering about fork offset/trail.

Main reason is stiffening it up. Anybody done this?

 

Yes it has been done, Gruhn runs one on his 400. He runs the stock 600 stem, he made spacers that go between the top bearing and the upper triple clamp that take up the extra stem length. It does give a long trail number, can't say it has had a negative impact, he is F-500 champ last two years.

 

Yamaha Fan should also mention that Dick Gruhn was fast using OEM forks, as was (and is) Yamaha Fan...and Scott Reavis...and Mark Morrow...and Lyn Garland.. and Paul Garland...and Scott McPain...and Chris Spargo.. and a number of other guys who use modified RD forks or maybe old-school TZ forks (although i'm not sure of that by just a visual). The guys I mention here would be fast using solid-steel non-moving forks up front and rigid frames!!!

 

Hi, Thanks. Please check your messages, got a couple questions.

 

Well, Ebay and the USPS parcel post came through finally, think these got lost on a sled to the North Pole.

Anyway, I certainly see the point you made about trail. The stock RD 350 clamps appear to be about 47mm offset, while the FZR600 forks are about 36mm; equal for equal, changing only the triple clamp offset but using the same tires and wheels seems to result in about 1/2 inch extra trail. I use KR 124A front tire, and that has a fairly sharp contour that is not very sensitive to trail especially at turn in, so it should be okay. My 750 Triumph uses a little more offset with 38mm Marzocchi forks, and it is fine, so this should work.

Eyeballing the stem, I will have to turn the 25mm machined surface of the top bearing mount surface about 20mm farther down the stem, then space above that an equal amount to the lock rings. Center to center, the RD clamps space the forks 175mm apart, while the FZR are 195mm, making it an easy matter of spacing the caliper over 10mm, adding hi hat spacers for the wheel bearings 15 id, 17 od, with 10mm "brims", and the whole thing will bolt up.

Matt Wiley at Race Tech already has springs and Emulators for me, so I am going to go to LA next month and put this together, should just fly together.

 

Sounds like you have a handle on it, what are you planning on as far as spring rate?

 

Well, I use the standard RD forks this way and they work really well with minimal kick or chatter: 40 lb fork springs, 1 3/8 sag, 30 wt oil 5.5 inches from top, the lightest Emulator spring with zero preload, and an Emulator "adapter" (spacer on top of rod) with a piston ring in it. With the 38's I figured I would reproduce fork spring and sag and oil height and Emulator setting, I have no experience with these forks so I don't know oil weight, probably 20 or 30, and I am told no need for a piston ring or spacer. anyway, start there.

 

YOur setup numbers are different than what I use both in value and how you get to them. Forks I have setup use 20WT, you have a higher oil level which could make the forks stiffer.

FWIW, .85 or .9KG spring depending on your weight and riding, 5 - 10 mm preload, 20WT, emulator set to 3 - 4 turns from spring contact.

 

Different strokes, as they say. Interesting differences. My bike weighs 255 so maybe that is part of it. Race Techs recommended settings just didnt work for me--too heavy on the popoff, too much fork spring rate. Whatever. The 30 wt was per Paul Thede, and it calms down the rebound but makes the high speed compression sharp, thus the light settings on the popoff. I chased this for a while and eventually came to these settings at Willow with Matt Wiley of RT. It was still deflecting off the small sharp hits through turn 8, which unsettled the bike (and me) so we just kept lightening it til it stopped. Mo betta. No chatter no kick or deflection. But at the edge of traction with big tires it is still sort of vague and flexible so I am changing forks. I first roadraced in 1969, first rode RD's in 1975, I'm old and slow but I still get a kick out of getting these things working well.