bikeinxs

I'm looking at using Middleburn cranks with a 24 mm diameter external BB. I'm having trouble sorting out what axle length I need for my shimano double shifting. Can anyone out there tell me what length Middleburn axle they have and what the resulting chainline is? Chainline is measured halfway between the chainrings for a double and at the center of the center chainring for a triple, from the centerline of the seat tube.

Thanks.

bakerjw

IIRC, there are a couple of different shaft lengths available.
A year or so ago, I put some Middleburn cranks on our Curtlo custom mountain tandem. We used the external BBs with 24mm axles.
With the current "road" triple on the rear cranks, we needed a wider axle to keep the chain rings from rubbing the chain stays. This gave us a wide Q factor and a larger chain line. It shifts great and runs well. I can get more exact measurements when I get home though. but I do think that they have a couple of different axle lengths.

I would recommend contacting Alex Nutt at MTB Tandems as he imports Middleburn and is quite knowledgeable about their product lines.

bakerjw

One thing to add. One of the things that I like about Middleburn is that they have multiple spider options available. We picked up a couple of different ones so that we can change up our front chain rings if needed. For mountain usage, we're going to run a 22/36 up front.

bikeinxs

So I've received my Middleburn cranks. They look great. The problem is that the axle is way too long. My tandem has a standard 68 mm BB shell and with the bearings the outer width is 90 mm. When I put all this together with the Middleburn cranks I get a gap of about 18 mm when it's fully torqued with the cranks bottomed out on the axle. Also, my chainline ends up at about 51 mm instead of the standard 43.5 for road. So, logic would dictate that I need an axle that is about 20 mm shorter. Since they shipped a set of 132 mm axles I just need a set of 112 mm axles. However I am told that the standard axles are 125 mm which would still leave me with a 10 mm gap and a chainline that is 5 mm out of whack. The shortest axles they have are 121 mm which will still leave me with an odd chainline.

The Q factor is also about 18 mm wider than any other crankset I have. Something really doesn't add up here.

Anyone have experience with this? What am I missing?

bakerjw

Our Curtlo has standard 68mm BB shell and we needed the wide axle so we used spacers. IIRC, Middleburn has different shaft lengths.

When we built our tandem, we had 2 different spiders with different chainrings. One set was large (38-52) for road use and the other was small (36-22) for mountain use. The smaller chainring on the large set interfered with the chainstay so we needed the wider axle in order for a larger chainline. Hence the need for spacers.
The Q factor is a bit more than my other bikes but it has never presented any big issues. In fact, it works well because we will have frame bags in there and a wider Q factor helps to keep legs from rubbing the bags.

Is this for a road or mountain tandem? The thing that I love about tandems is that you can make enormous frame bags for them. I can already carry a lot of gear in my front frame bag but that bake area. OMG, there is room there.

I can post more specific pictures of "Lolly" on my gallery if that will help. You can PM me too for other questions.
Biking and Hiking / Lolly | Beth and John Baker's Photo Gallery

akexpress 

Steve
There are couple of things at play here., mostly it is that the crank is going to go a lot further on the spindle when you tighten it down. I have attached a picture of one sucked all the way down. Two you are not looking to achieve road bike chainline unless you have 130 mm spacing on the rear . I have 142x12 spacing (135) on mine and achieve a chainlink of about 44 mm and it

shifts great. The q factor is 110mm as set up with the double chainring setup with a 132 spindle. Hope this helps