Fiberglass front fender: clearance and brace?

[NYSingh]

Replacing the front fender that the PO installed (which looks too chunky and I think is for a CB or some other larger bike) with a new Airtech one to keep the weight down.
(1) What's a good clearance between the tire and the fender? I've read anything between 3mm and 1", but figure 1/4-1/2" would give enough buffer for tire expansion and for pebbles that might get stuck in the treads.  Prefer to keep the clearance on the smaller side bc, you know, it looks cool. Any recs?
(2) Since a fiberglass fender doesn't provide the structural stability of the stock metal fender, is it recommended/necessary to use a fork brace to keep the forks from twisting?  Keep in mind this is a street bike, and I also plan to add a stabilizer, but watching too many tank slapper videos on youtube has me paranoid.

[Striker1423]

A fork brace is a must.

Mark has a good example of a fender he and a buddy fab'd up on an English wheel. I think that's on his lightweight? Looks awesome though.  Clearance wise, no idea. Someone else can chime in there. 

[m in sc]

I run the brace at 10.mm.  this is with a stock sized am26 . I run the fender above the brace. thanks for the compliments

[NYSingh]

Does anyone know of other Yamaha models with the same tube circumference and spacing between forks as an RD400C?  Tarozzi makes fork braces for 20 different Yam models but apparently nothing for RD400s.  Wondering if I can use one made for another model (RZ350?). http://www.fastfromthepast.com/fork-braces/yamaha 

[m in sc]

early xs650.

[NYSingh]

Looks like they have one for a 1976 XS650, which was before they changed the fork configuration in 1977 (according to Wikipedia).  Hopefully that works!

[SoCal250]

for reference here are some specs for the Tarozzi XS650 part:

Part #       Description                          Model Year             Tube Diam     Mounting Diam    C-C Distance
25-0046  Fork Brace Yamaha XS650    1975/1976                35                   55 x 58                185 Arched

The mounting diameter has 2 numbers because the clamping area is stepped. The OEM rubber dust boot must be slid up out of the way, and then it can be slid down over the lip on the brace after it is installed.

Not sure why the Tarozzi part states 35mm because the 74-76 XS650 is 34mm forks. The stock dust seals may not fit. The clamping dimension and centerline spread are the important specs.

[Seizer]

http://www.rswracing.com/rd350.htm

[rodneya]

Trachtech makes one as well.
Sizes to order for an RD are in the description section.

https://tractechmfg.com/product/universal-fork-brace/

[m in sc]

i have a yoshimura one that came off an xs, was on an rd, then was used on a GT550, and im back in possession of. it clamps where the dust boot is.

i don't run it because it -can- deform the fork enough to cause the seal to leak, never got that sorted on the gt till we took it off. was ok on the rd.  That's why i like the bolt on ones that go to the fender mounts. (hence the 1 i made).

[Dvsrd]

Even if the early XS also has 34 mm forks, XS fork braces won't bolt straight on, if the C-C is 185 mm. The RD fork is 175 mm.
These do look like a good RD350 brace:
https://www.fastec-racing.co.uk/products/yamaha-rd350-a-b-fork-brace

[m in sc]

ealry disc xs is same as RD, i have one on my r5

[Dvsrd]

ealry disc xs is same as RD, i have one on my r5

I just had to check. A set of 75 or 76 XS fork sliders I have, measured 50 mm where a brace is attached, same as RD350 sliders. I also have a 400 slider for 34 mm forks, but that has a larger diameter.
So that makes an XS brace suitable for 73-75 250 and 350, but not for a 400 without modifications.
My plan was to use the 400 RH slider, to get the caliper behind the fork. But that diameter difference is annoying. Wonder if turning it down to 50 mm is ok?

[NYSingh]

hey all - I ended up ordering a fork brace from TracTech Mfg.  The brace has a lip on one side of the clamp (rather than being the same diameter) so it doesn't fit on the lowers like most braces I've seen.  I e-mailed the company and they said I need to remove the dust boots so that the lip sits on top. This doesn't seem like an ideal setup and I'm hesitant to leave the fork seal exposed on my newly RaceTech-rebuilt forks. What do you guys think?

Here are photos the company sent me of the brace on an RD350.

[m in sc]

thats fairly standard fare for a fork brace of that style. I don't run the upper dust boots on my lightweight either. Not an issue really unless you plan on lots of dusty gravely roads or rain, which im guessing not so much. you can always fit fork gaitors i guess.