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Tandem BB size for 160mm dropouts?(13 posts)

Tandem BB size for 160mm dropouts?yfoiler
Jul 23, 2002 7:45 PM
I have 68mm bottom bracket shell widths (English thread) for the triple crankset on a tendem I'm building up.
I plan to use the Ultegra splined BB which will mate up with my FSA Gossemer triple crankset.

The Ultegra BB comes in 68X109 and 68X118.5 splined spindle widths.

Obviously I use the 68mm x 118.5mm spindle width for the triple cranks and the standard 68mm X 109mm for the front timing cranks, but---can anyone confirm that these will line up with my tandems 160mm rear drop out width? I've never done a bike set up with such wide rear dropouts.

Thanks in advance.

Marty
Interesting question.Spoke Wrench
Jul 24, 2002 8:09 AM
I've got 25 years experience working on tandems, but I've never thought about the subject before. That alone is a good sign that you will be OK, but I really don't know for sure.

The first thing I would do would be to check with FSA to see what spindle length they recommend. The other thing I might do would be to call Santana and ask what the spindle length of their Hadley bottom brackets is.

So what kind of tandem are you building? Good luck.
Interesting question.yfoiler
Jul 24, 2002 9:17 PM
Thanks for the input.
The guy at FSA wasn't much help. Basically he said when I get the cranks try it out. If it doesn't work call back! Uh, OK...

The bike is a KHS built by accord in Taiwan. It's the same as the KHS "Roma" frameset. Sort of an entry level road tandem. 7005 Al tubes with rough welds. It's brand new and I got it pretty cheap. ($374)including the "un-badged" Santana CF fork with Al steerer.

I took a chance on it because my wife (the stoker) is only 4'11" and this frame is a 20.5/16 inch. The only other way for us to get into the tandem thing with her being so small was to go custom... she saw the price tags with "custom" and that was the end of it---until I found this thing. So the 16 inch stoker was a real "find" for us.

I'm fixing my wife up with a rock-shox 27.2 suspension post and the Selle "pro-link" saddle with the CF/Ti rails with a bit of give to them for the little bumps---the post can grab the big bumps. I'm trying to make it as easy as possible on her because she's not a cyclist, and I don't want to scare her off of the tandem idea---so cushy, (within limits, like No fat lady saddles!), is what I'm going for. I'm using a profile aero bull horn for her bars instead of drops and a deminsion adjustable stoker stem so I can gradually get her down to where she needs to be in time. Slowly...very slowly...
So there you have it... Now if I can only score some Ultegra STI's cheap and gently break it to the wife what a set of tandem wheels will cost... we'll be ready to roll.

Thanks for you help.

Marty
Tandem adviceSpoke Wrench
Jul 25, 2002 5:02 AM
You sound to me like an ideal tandem couple. The fact that she is a non-rider means she doesn't have any cadence habits yet. She will just learn to pedal at your cadence.

Learn to say "Bump" just before you hit every single one. She'll love you for it.

Don't worry about getting her acclimated to a low handlebar position. It won't matter. She is already in the perfect drafting position behind you.

I hope your stoker handlebars are wide enough that your legs won't rub them and wear out your shorts.

People who don't ride tandems often hold the opinion that the stoker's view is limited to the captain's butt. That's not true. Since the stoker doesn't have to drive, she is free to look off to the scenery on both sides. My wife is constantly advising me of pretty views that I would have otherwise missed.

Good luck.
Great point!yfoiler
Jul 25, 2002 8:32 AM
Great point about the "view" for the stoker. I believe she's going to have a lot of fun once she realizes she doesn't have to actually drive.

Good point about the profile bullhorn bars too. I had thought 44cm was going to be wide enough but now I'm not so sure. They are already on order so I'll just slip them on my rear when they arrive and see if my rear is bigger than I think! I noticed after more searching that there is a bullhorn type stoker bar available. They didn't list the width on it but I'll bet it's darn wide---to cover the problem you brought up about rubbing.

Thanks again for your knowledge and help.
where did you get it at?Bobha8
Jul 25, 2002 3:50 PM
I saw some on chucksbikes.com. I am looking to build one up for my wife and myself. Also do most frames come with the tension insert for the bb or do you have to buy them somewhere?

thanx,
Bob
where did you get it at?yfoiler
Jul 26, 2002 8:43 AM
Hi Bob,

Yes, I bought it at Chucks Bikes in Sante Fe Springs, CA.
He had the CF fork in stock also. It's an incredible price for what I would classify as sort of an excellent entry level tandem. The frame is very strong, 7005 Al, not to heavy, and best of all for my wife and I it was a 20.5/16 inch. Most off the shelf tandems are to big on the stoker seat for my 4' 11" 90 lb. wife.

If you get one I don't think you will regret it one bit.
Expect to hunt for a deal, or pay big $$ for the 160mm rear undished wheel. Or you could just use spacers---your choice.

Good luck,

Marty
Probably not an issueKerry
Jul 24, 2002 4:11 PM
While the rear end will be moving over in a 160 mm spacing, you also will have (typically) much longer chain stays in a tandem, so the chain line will not be nearly so critical. I expect you will also have a triple chain ring, so you won't be seeing the big tooth jump like in a double - minimal chance of chain rub on the next larger ring. With the triple, you also will not likely ever use the smallest 3-4 cogs with the granny, so that chain line issue is moot. IOW, a number of reasons not to worry. Just go with the "standard" triple BB. A spacer on the right side would fix any egregious problems.
Probably not an issueyfoiler
Jul 24, 2002 9:20 PM
Thanks for the positive input Kerry. Yea, I'm going to plow ahead and see how is goes. The parts will start trickling in next week.

If you're curious about the bike see my reply to spoke wrench one message up.

Thanks again,

Marty
Totally not an issuegrzy
Jul 25, 2002 4:25 PM
Even with 160 mm rear wheel spacing the rear wheel/freehub is still going to in the same place on the centerline. All you're going to do is effectively add spacers on both sides of the axle. Net effect is zero.
Not quiteKerry
Jul 25, 2002 5:23 PM
Your analysis went through my mind too, but it's wrong. Picture a wheel spaced to 130 mm - now we want to space it to 160 mm. The rim stays in the same place but the right chain stay moves right to allow the hub to be centered on the rim. That moves the FW to the right as well. If your analysis was correct, then the wheel would remain dished and just have 15mm of spacers added to each side.
Hmmmmgrzy
Jul 26, 2002 9:38 AM
So what's the point of blowing the right chainstay out 30 mm - unless you're doing this to remove the dish from the wheel. Which would make sense given that you have roughly twice the average torque available due to two riders. Seems obvious the with a 30 mm adjustment to the chain line something has to give and that the better solution would be to make the adjustment in the location of the BB shell/spindle length. But given the design of a tandem you can't ignore this. I guess I'm left wondering how the guy can be using standard components on a tandem in the first place.The front BB mounts the single chainwheel on the LHS and the rear BB has chainwheels on both sides - not exactly standard stuff.
WellKerry
Jul 26, 2002 5:23 PM
It is really all OK due to the typical long chainstays on a tandem. Plus, with the standard triple on the tandem, you never expect to use the small cogs with the small ring, or the big cogs with the big ring. The whole point of the wide rear end IS to eliminate dish in the wheel. When it's all said and done, the tradeoff of a stronger wheel is more than worth any minor chain line issues.