I have on mine with no problems, they've been fitted since winter before last and have been through Europe and all over here I had some reservations myself when I wanted to do it so sought advise from various sources, my main concern was shearing the bolts due to them being a little further out but the lad at Racebolt where I got my slightly longer bolts from said it would take a huge amount of force to shear them if they were torqued up correctly (he did say what force was required but I can't remember what it was) To be fair though no-one recommended to do or not to do, so I guess you pays your money and takes a chance, I've taken the chance albeit a fairly educated chance due to my various sources The spacers I put in were 3mm thick
It looks like you had the same problem I've got. My Brembo M4's do not have enough clearance when used with my Dymag wheels. 3mm would cure it with no problems. It is on a trackbike and would be subject to more stress than even hard road ridding. I really am not sure which way to go - back to standard calipers or the spacer option.
I agree with your comment about there being more stress on a track bike than a road bike, my problem arose from wanting to fit my BSTs from my old R1 to my Blade, different spacing all over the shop but think it was worth the hassle in the end Unfortunately your problem although similar has the added stresses of track riding, I'd be tempted to go for it but that's easy for me to say seeing as I won't be riding it, but I have done it so at least you know it's a feasible option if you decide to go along that route
Hi are you talking disc width spacers or disc to caliper diameter spacers? The way I read it your talking caliper spacers as the M4s should have the same offset as standard calipers that is the disc will fit in the caliper but you may have to space it out or in. IMO spacers either way your talking about are fine just get bolts that screw in the same amount as standard.