While unsure of the '08 Speed III, I have been researching steering head T/Bearing replacements for my own '02 Daytona 955i.
@oldndumb: You are correct. The top T/Roller Bearing 25x52x16.5 is a standard size in T/Roller terms. Unfortunately it will not allow the OEM top bearing cover/cup/seal to seat neatly, thereby preventing the ingress of water and dust. It is therefore important to buy a narrow section 15mm T/Roller bearing which will allow the OEM top bearing cover/cup/seal to seat completely. From what I have read, the http://www.allballsracing.com/
kit does not allow for this.
In similar fashion, the bottom T/Roller must seat on a 55mm dust seal. I believe such a seal is available from Triumph Part No. T3600234.
Alternatively, Koyo manufacture a suitable T/Roller Bearing with an Integrated oil seal.
Here are the Koyo part numbers:
Top T/Roller: Koyo 30205JR 25x52x15 Narrow Section T/Roller Bearing
Bottom T/Roller: Koyo 32006JRRS 30x55x17 T/Roller Bearing [Includes Integrated oil seal]
My attempts to obtain here in South Africa these exact Koyo Bearings have proved utterly fruitless. Hopefully you will have better luck. Have a look here:
Finally, I see that the UK-based http://www.triumph-online.co.uk
have a complete T/Roller Bearing Conversion kit and Seals kit available. The problem is they do not give the size of the top T/Roller bearing i.e., 25x52x16.5 or the correct 25x52x15! Here is the link:
Any reliable feedback on sizes and availability would be much appreciated!