| As you saw mate i run now the std 15 front and 40 rear. I was on 15/38 rear, but struggled to pull top gear even on hanger straight!
I have to say first impressions of this combination at Oulton were quite impressive. its not too fierce even over the rise and down to hizzys!
I have 2 extra links in my chain this works with both the 38 and 40 rear and puts the rear wheel in the centre of the adjustments on the 40 and 10mm longer on the 38.
go for it! | 
Threaded Mode