mwandaw

I recently bought a like-new 2009 Cannondale Road Tandem 2. It has disk brakes, but it also has lugs on the fork and stoker seat stays that are apparently for rim brakes. I want to use one of the lugs on the stoker seat stays to mount an accessory.

An 8mm-1.25mm bolt will screw easily into either of the lugs on the fork. However, that same bolt binds up if I try to screw it into either of the lugs on the stoker seat stays. The threads seem to be clean. It's hard to imagine that the fork lug threads would be different than the seat stay threads, but I really hesitate to force the bolt into the seat stay lug.

I would appreciate it if anyone has any experience or thoughts about this generation of Cannondale.

Thanks!

LV2TNDM

The picture you show is the cantilever post mounting spot. These are very coarse threads. I've never tried to find a bolt for these because canti posts always screws into those. I can't imagine you have matching bare holes on the fork you mention. The cantilever boss bolts that screw into the posts are finer machine threads. I assume you're easily screwing those into the fork cantilever bosses. (They're posts that stick out from the fork blades, right?)
If this is the case, you DEFINITELY need to find bolts for the frame's seat stays that match the thread count and pitch. I have no idea what it is. 8 X 1.25mm sounds about right, though.
OK, if that's the case and you do have bare holes on the fork blades that are 8 X 1.25mm and it doesn't match the frame, then I'd bet the frame threads are SAE. Cannondale's been making their frames like this for ever, so it wouldn't surprise me if they're standard thread and not metric. I would NOT try to tap these holes to match the bolts you have. Find bolts that thread in easily. Sorry I'm not more help, but that's probably what's going on.

cyccommute 

I didn’t check the fork (the tandem is hanging up and I’m too lazy to take it down) but the rear on mine takes a 5/16” x 18 TPI thread. I’ve seen some posts elsewhere that says an M8 is close but won’t fit. The 5/16” x 18 threads in nicely.

Nice tandem, by the way. Got one just like it. Small stoker?

Leisesturm

I could be wrong but the threaded hole shown should be the receiver for the cantilever (v-brake?) bosses. The bosses themselves are quite long and likewise threaded internally to receive the brake arm mounting bolts. Accessories meant to mount on v-brake bosses will not attach directly to the receiver threads in the frame. If this is a think outside of the box hack then all bets are off. I would contact Cannondale as perhaps the quickest way to determine what is threaded with what. It would have been nice to see the fork and how things are handled at that end of the bike.

jccaclimber

Assuming it isn’t one of the suggestions above, the easiest way to test this might be to ride down to the hardware store and see what fits smoothly by hand.
Alternatively, I agree that those look like where you would thread in the brake bosses, perhaps those are available as a part.

mwandaw

I tried several bolts and never could find one that fit. As others have mentioned, maybe the threads were compromised some time before I bought the bike.

Eventually I decided to take a different approach to mounting the accessory (a taillight). I used a bolt that was smaller than the hole in the lug. I put the head of the bolt on the bottom side of the lug and secured an adapter I made to the top of the lug with a nut. The taillight is so light that the clamping force from this set up will most likely be more than enough needed to keep everything in place.

Thanks for the help and suggestions!

Leisesturm

I've missed the threads saying that. It certainly isn't my take. Those threads are just fine. Here is how you find out for certain. Locate (no need to buy) some cantilever brake bosses and screw them in! Incidentally, when you have some genuine brake bosses in hand (that screw in) you will know exactly the diameter and thread pitch of the bolt you would need to use that mounting. But, to that point, and while I am still in curmudgeon mode, might I observe that putting a lasher in that spot wastes it's potential. Unless twinned, and that just adds extra weight and expense. The hot setup these days when the seatpost location is too passe is the seat itself. Or the back of the helmet. A location that is high and central is the best location for a flasher. FWIW.

Alcanbrad

This should be classified under “Hey Alcanbrad, get a life 😁”, however I believe you have the tire mounted backwards. The tread pattern should be oriented to drive captured water away from the wheel, not in towards the contact zone. There should be a rotation direction arrow on the sidewall, though it is always hard to find.

Also, great hack on mounting the rear light. Looks like it was meant to be that way.

mwandaw

Thanks for the tip. The bike is very new to us, and I haven't looked closely at the tires. I will now!

cyccommute 

Pssst! It doesn’t matter. It just drives the OCD people crazy. It won’t make any difference with regard to trapped water. Bicycles can’t hydroplane unless you get to really stupid speeds.

DangerousDanR

From Schwalbe: https://www.schwalbe.com/en/profil

cyccommute 

Tire direction makes a difference for mountain bikes. For road tires, not so much. The interaction of the tread with pavement is minimal and traction isn’t a problem. For mountain bikes, there is much more interaction with the riding surface and having directional tread helps…mostly with steering.

DangerousDanR

Stuart:
thanks for the input. I forgot to copy the other section in the link I pasted.

cyccommute 

Alcanbrad

I would tend to agree with your point of view for most riding conditions cyccommute. I would not expect a bike to hydroplane while going straight, but I would not be surprised if the point of loss of traction while turning at speed could vary based on tread orientation.

That said, I would ask, would you be willing to back up your claim by riding fast with a loaded tandem at high speeds on wet roads and recording the speed where the wheels lose grip while cornering to compare the loss of grip based on tread orientation? I am razzing you a bit here, but with the lack or real world data, I would give Continental's engineering the benefit of the doubt and follow their recommendation. It certainly wouldn't hurt. Hopefully, none of us will ever find out the real difference.