916 Anyone Running Fg43 Forks??

There are 2 disc offsets on Ducatis of that era, 10mm and 15mm. 916 as standard is 10mm, 748R and (I believe) 996R are 15mm. Do you know what offset discs you have fitted ? Andy

 

What diameter do you have ? Andy

 

Is it something to do with old-school 'narrow band' discs as used on some race bikes?

Looks like the caliper brackets are bolt-on so could be swapped.

 

330mm discs instead of 220mm?

 

Dougie, the discs you have are brembo Racing discs, they have 12 bobbins instead of 10 and the minimum rotor thickness is 6mm.

Im guessing you have the 6mm rotor by the look of it.

Theoreticals:
Offset: 10mm and 15mm are numbers for the layman. They are only true when the rotor is 5mm thick as on a roadbike.
The OEM discs on a road bike are semi floating so you can get away with measuring from the disc mounting face on the hub to the outside face of the rotor, as a wave washer behind the press formed bobbin pretty much holds everything tight.

Everyone does it, but it's dirty when you're using anything outside of stock OEM parts.
Brembo Superport discs for instance are 5.5mm, so again would throw the accepted conventional 10 /15mm offset measurement out.

For your application you're thinking about centrelines. - In engineering terms, it's the only true constant when you consider those discs came in 6, 6.5 and 7mm thicknesses.
therefore your discs are a 12.5mm centreline offset with probably a 6mm rotor (which would make it's true mounting face to outboard face measurement 15.5mm were you to measure it the layman way).

Practical:
Looking at your images, I'd guess that you need a 300mm disc, not a 320.
If your caliper isn't fouling and just hitting the outer diameter edge of the disc then your disc is too large a diameter.
It wasn't uncommon to run 300mm discs as well as 290 depending on circuit, with the thickness increasing as size decreased in order to compensate for the reduction in rotor diameter.

Your FG43's are the final generation of FG43 R&T fork before Ohlins changed to FGRT forks.
Your biggest challenge is finding the caliper mounting for a 320mm disc, they do exist, but those 6 bolt items were stupid expensive to buy separately when they were available.
The two bolt axial mountings are easier to source. The advantage for you is that those 6 bolt radial mounting hardpoints were designed around the potential for radial caliper fitments as well.

You have two options, get smaller discs, or alternatively get different caliper mounts.

300 mm discs do come up for sale and are relatively cheap for what they are as the common size was 320.

You've more chance of finding a pair of those than getting those caliper mounts if I'm honest unless you get some drawn up and machined. For new discs I'd recommend you call Mode Performance (Brembo Racing Uk distributor), or Giles at HPS (who will order from mode), but is a throughly nice chap to deal with and understands pontificating layman road bike yap speak.

Mode are great guys, always balls deep with proper race teams both car and bike, so don't be offended if they're a bit short and to the point, there's only two of them there and they're always flat out.

@Dukedesmo The narrow band stuff was pretty much an AP racing and Nissin factory racing preserve, and you could only use their calipers for it. BSB used a lot of AP Narrowband stuff espcially as they did a caliper to fit the 90mm japanese mounting pitch, and the works GP bikes used the sublime Nissin factory racing components for the most part.

The Caliper our Dougie has the capacity to run with a disc rotor height of 37mm.

@Dougie durrand take the wheel out and bolt the caliper up. Measure from the centreline of the axle hole if you can to the centre of the round brembo logo on the caliper.

As you can see below in the image, the centreline of the rotor runs slightly below it, so that's your optimal position that the hanger is designed around. Your caliper can accept a maximum rotor depth of 37mm.

Roughly speaking - If you get a measurement around the 131-133mm mark then you need a 300mm disc.
For a 320mm disc you'd be looking at a measurement upwards of 141mm
For a 290mm disc you'd see a measurement of circa 126-128mm

Failing that measure to the nearest threaded portion of the axle if it's easier. Same thing applies, but your measurement will be around the 119-122mm mark. (above measurements just with 12.5mm axle radius subtracted.

Brembo logo to nearest part of Axle will give you a number, add 12.5mm to that number and you get the centreline axis line of the axle.



Sorry for the long winded post, but it was better that you had all the info to hand from the outset.

There is one final option to you but it's horrifically dirty - slacken off the six mounting bolts till you have desired clearance and then make a spacer plate to the desired thickness.
LIke I said, it's dirty - very dirty, but it gets you out of a hole.

To do it right you'd need to go up and out, but that's major ballache as you're working around accommodating a radius of disc as opposed to a given linear measurement, but you won't have the range to do that and get safe bolt engagement.

 

Ive been searching for 100mm 6bolt ohlins brackets for fg43 for 15yrs. I have the 108 on mine and 748R discs and a spacer. I put gold coloured gsxr radial calipers on. Mainly coz same colour my old 40mm brembos are. Works great (comparitively speaking)

 

I have these , 40mm bolt centres on 320mm discs.

 

@Dougie durrand Another thing I forgot to mention...

Without the caliper, see if you can measure the distance from the inboard(inside face of the caliper mounting bracket to the centreline of the disc.
It should be 26.5mm give or take 0.5-1mm.

Bootsam, if you feel like taking one off and trusting me with it for a couple of weeks over the winter I can reverse engineer one for you with the 100mm bolt pitch, then it's a matter of getting a quote from a tame machinist to get a pair made up.

 

When you bought them Dougie, did you get to see this, even in picture form, all assembled or did you buy them as an already dismantled lot?

The reason I ask is because if all this came off a running bike as one complete kit then it should all fit without issue.

Looking at the bolt spacing and geometry, @ducati dad has the same caliper mounting plates, the only difference being the disc.

Bear in mind that the 12.5 centreline offset disc (15mm) works with the 65mm mounting pitch calipers, which have a different mounting offset to the 40mm calipers.

40mm Calipers have a mounting face to disc centreline offset of 26.5mm
65mm Calipers have a mounting face to disc centreline offset of 32mm (both 2 and 4 pad variants)

The corresponding disc face offset from the centreline of the fork is also different as a result.

 

Dougie, give Mode a phone call. They will have the centres for your Racing discs with the shallower offset, then it's just a case of you swapping over the bobbins and the rotor.

You need to ask for the rotor centre for disc part number : Brembo 08670311 - (Racing SBK disc 320mm.)
(Offset is 7.5mm to centreline or 10.5mm to outside face if you factor in a 6mm rotor thickness)

 

@Sev. After reading this thread, it motivated me to write an email to Ohlins asking if they have drawings. Dont ask, dont get kinda thing.
Sure, the bikes not going anywhere for a while. Be nice to use my oem 916 discs as all I could get were galfer wavey things for 748r and I dislike wavey discs. Plus the carrier is black.

 

They do have the drawings, whether they'll release them to you is another matter.
They used to be great with releasing the drawings for out of production parts, but recently they seem to have gone a bit tight with all that sort of information.

 

The 40mm caliper whether billet or OEM has a 26.5mm offset from the caliper mounting face, so it should make no difference.