Invictus35

So I just acquired a Bianchi Piaggio from the early 80's made in japan. I measured the bottom bracket and it's 68mm for the shell width and the full length is about 150-155mm. I couldn't quite get an accurate measurement with the crankset still on. I think that's probably a wrong measurement though because when i was looking at sheldon's site on bottom bracket length it doesn't go more than 136mm. Now I'm ordering formula hubs that are 120-130mm. The rear drop out spacing is 130mm but again I don't have access to wrenches at my dorm room to take the rear wheel off. Questions for those who can help is with my current bottom bracket will I be able to use the 130mm formula hubs and a new crankset to get a straight chain line? What I'm trying to say is that with this hub, spacing, and bottom bracket can I achieve a fixed gear with a good chain line? I feel like the overall length of the BB is too long and when I add a crankset it'll be too far out. I measured the inner most ring to the center of the seat post and it comes out to about 45mm give or take 2mm so it could very easily work I think. If I'm missing data or measurements or something else let me know so I can reply and add it.

Thanks

dbg

If the bottom bracket has a threaded end (so you can bolt on the cranks) then you don't count the threaded part in your BB spindle length measurement.
And anyway you can't measure it with the cranks in place.
Could you use the existing crankset and just substitute the appropriate chainring on the inside (presuming it was a double). That way you have a BB and crankset that already matches.

Invictus35

It is threaded and the crankset bolts on. That said, when I got the bike, some idiot swapped crank arms and one is longer than the other so no I can't use the crank arms. That means I need new crank arms. I want to get shorter ones anyway because I tend to wreak havoc when I bike. I'm reckless as hell and aggressive, not in the sense dangerous to people, but like on turns I'll corner it over speed by a lot and lean in. I expect the 170mm that I have now to hit the ground. I'd rather get 165mm and a new ring. That said I was reading more on sheldon's site and now I have more to understand. I was thinking of going 44-16 but now with all this combined I have no idea what to get since I'd have to get the chain length right too. It doesn't bother me that there's a lot to it but i'd rather get it right now and not have to return parts.

Invictus35

and also can someone tell me if these are Machined Side Wall. I'm trying to stay away from them.
https://www.velomine.com/index.php?ma...roducts_id=462

Thanks

Spoonrobot 

Before you do anything you need to have a concrete idea of what's going on.

The chainline for a fixed gear is fixed and is what you work to. It's going to be 42mm with the Formula hub. This is regardless of the 120/130mm spacing. 120/130 refers to the over-locknut dimension and is not a measurement of the actual hub, as such it can be changed with spacers. This measurement tells you what spacing between the rear dropouts the hub is designed for.

Now, the Bianchi Piaggio appears to have a rear spacing of 126mm. This is the over-locknut dimension you want your formula hub to measure to. This is done using spacers on each side of the hub. You generally want buy wheelsets or hubsets already assembled with the O.L.D. you want. For example; if you order from Velomine, you generally specificy during checkout and they pull the right spacing for you.

See here for a better O.L.D. and spacing explanation. https://sheldonbrown.com/frame-spacing.html

As for chain-length, when you buy a chain it comes with excess links. You feed it around your drive-train and then remove the excess links. Taking up the final tension by sliding the rear wheel back in the dropouts.

Invictus35

Thanks for the explanation. I understand this part, but what about with my bottom bracket? If I purchase a new crankset which I have to, with my current bottom bracket will I still be able to run that 42 mmm line?

Bill Kapaun

You buy the BB specified for the crank you buy.
IF you are real lucky, you already have that length and don't have to buy a new one.

Is this a cup & cone or a cartridge BB?

Invictus35

It's a cup and cone.