Cannondale BB30a and SiSl SRMs- bottom bracket choice

[ultyguy]

Hi Weenies,

Looking to pick up a Synapse HM with the BB30a bottom bracket and use my SiSl SRM with it. I know for the usual PF30 or BB30 you needed a special BB to use the SRM. What's the score with the BB30a?

Thanks!

[nemeseri]

Are you absolutely sure? Srm offers a spider for cannondale cranks and pro teams use it with third party rings. The only reason I see would be spacing, but with BB30/PF30 there is plenty. I guess you can ask srm support about it.

If you wanted to run shimano srm, you would definitely need a special BB. I'm also interested in jumping on the BB30a train with srm so please post your findings.

[micky]

I've been trying to find info about this for a friend as he's considering a Supersix with BB30a, and as far as I understood he would need to purchase a 109mm spindle, and then "play" with spacers for find the best setup.

[Calnago]

Go straight to the 109mm spindle for sure if you can. I had no end of grief trying to set up a Shimano 9000 mechanical drive train using the 104mm spindle of the sisl crank. It's just too inboard with nothing you can do because of the shoulder on the non-drive side. I sourced one of "SRM spindles (I "think" that's what @nemerseri is referring to above). But this is still a 104mm spindle except the shoulder has been machined down a bit to allow the SRM spider to clear the drive side BB. Still, the spindle on the Sisl II is 109mm and there is no shoulder plus the wavy washer is on the non drive side. It's a much better design but I'm not 100% sure it's works perfectly with the old spider and cranks (may be a q-factor issue so if that's all it is then you can either live with it or not). Not sure if that helps. I did get it working and my friend thinks it's ok but it's not really perfect by any means. I know I just set up a new Cannondale with the new sisl II crank not long ago which had the spacer (about 5mm) on the non drive side along with the wavy washer and if I recall a 2.5mm spacer on the drive side. I can't even remember what the bb30"a" is at this point (5mm more BB on the non drive side?) but I would think the shoulder on the 104mm spindle of the Sisl crank could pose a problem here. I don't get why people like Cannondale cranks, apart from their lightness.

[ultyguy]

I also sent an email to 'Dr.Cannondale' the german site and he recommended the 109 spindle as well. I think it might still need an extra wave washer on the side of the crank, but should work. For sure there's been plenty of SRM's on BB30a's on pro bikes (Synapse and new SS).

[ms6073]

I think it might still need an extra wave washer on the side of the crank, but should work.

As you can see in the image below, the newer 109mm road spindle is smooth and while spacers can be added on the drive side to adjust chainline, preload spacers & wave spring washer are moved to the non-drive side.