Urgent disc related help needed
 

Hi Guys,

Someone on another forum tells me that i have have ordered the wrong brake discs for my bike. I've got a 2002 748s with Showa forks and p34 calipers. I recently got some new disks which were for a 748r. I thought i'd need them when changing to p34's, but I'm told the offset will be wrong.



I hope the photo shows offset. The question is do i need to get them sent back and exchanged?

Cheers

Chris

You only need 748R specific discs if you are using 748R specific forks.

If you are using "standard" 748BP/S or 996/998 Showa forks (65mm caliper bolt spacing) and P34 4 pad calipers (like on 748R/996R/999/749 etc) then you should use "standard" 748/9*6 disc offsets.

I have a 916SPS with P34 calipers and use standard offset discs.

Hope this helps,

R

The confusing point is not all 748R's run the 15mm offset discs, only the ones with the Ohlins forks, my 2000 model 748RS came with Showa forks and 10mm offset discs same as the 748R of that year

Your pic does indeed show a disc with the 15mm offset for use with the Ohlins forks, when bolted to the wheel they will measure 130mm from outer edge of one disc to the outer edge of the other disc, where as for the standard setup that goes with most 748/916/996 and the Showa forks that same measurement will be 120mm
Note the standard Hub width is 100mm

Not wishing to confuse things, but in the picture above there is 10mm from the work surface to the lower edge of the disc, so surely the discs have a 10mm offset ?

I guess that begs the question, does Chris have the right discs for use with showa forks or not...
;)

Offset must be the distance from the surface to the outer edge of the disc. I mocked up the front end today and they're def the wrong part. Oh well time to get an exchange i guess. Thanks for the help guys

Yep for some reason thats how they measure it,

and although what John W says also makes as much sense especially for flat discs without a carrier as they would be zero offset

For me I would have have thought from mounting face of the hub to the centre line of the disc would be the way to measure it, that way all discs would have a positive offset even a flat one dependent on the thickness of the rotor.
One thing I have wanted to setup many times is the caliper spacing, where I want the distance between the centre track of a pair of calipers to be the same as the distance between centres of a pair of discs or the centre track of a single caliper and the centre-line of the wheel to match the distance between the disc and the centre of the wheel.

I got the discs from www.bikedevils.co.uk who were selling them through ebay. They've been great about things and exchanged them no problem. The new ones arrived today and the difference is clear as soon as you look at them.



These are the correct offset for non ohlins models.

I hope this thread may help others who are unsure about what discs they need.

Cheers all for your help.

Chris