I had a custom MTB Rohlof Tandem built by a well Known frame builder in the UK.
I have been a bit concerned about the alignment of the frame. Both wheels are are aligned and tracking in a straight line, however the front bottom bracket is out of alignment by 4 to 5 mm.
Is this an acceptable tolorance?.
See attached image.
I forgot to mention that this Tandem cost me in excess of £3500, I expected a mm perfect Tandem for this price or is this to be expected for a custom hand built frame.
I would greatly appreciate any advice before I contact the builder.
I have enclosed another image, I hope this makes things clearer.
While it should all be spot-on with a new build, it's hard to say what you may have going on there just based on the photos and what I assume to be plumlines running from front to rear drop-outs. Does this bike have rear suspension or is it a hardtail?
It could easily be the fork that's a bit off, the frame, the rear rocker if it's a full-suspension rig, or a little bit of each. The more complex the frame becomes, the more likely some deviations become.
If you have a good relationship with your builder I'd simply share your observations with him and see what he says. Clearly, you're unhappy... and I can't think of anything we might offer up that will address your concern one way or the other: only your builder will be able to do that.
Best of luck with it. If you get a chance, please share a larger photo of the bike so we can gain a full appreciation for your new ride. If you're concerned about the builder's identity, a little photoshop action will take care of the branding.
Last edited by TandemGeek; 10-16-07 at 05:17 PM.
The Tandem is a hardtail and the plumbline was run around the front rim and round the rear rim to ensure both wheels were square and running true and aligned in the frame.
The bottom tube when standing from behind can be seen to be running out to the right.
Also if you study the bottom bracket it can be seen that bottom tube is not in the center of the bottom bracket this can be seen quite clearly.
The wheels however track in a straight line.
When I first collected the Tandem in June I mentioned to the builder that I thought the bottom tube may be out of line he became quite aggresive on the phone and stated I did'nt know what was talking about.
I have since used the Tandem in the Dolomites and France and it seems fine.
I have spent a considerable amount of time measuring and re-measuring using various methods and I am now without a doubt tht the frame is "out" by 4/5mm which may not seem much but it is visable.
My question is- Can that be classed as an acceptable tolorence.
If I go back to the builder I know what sort of reception I will get.
Last edited by Geordies; 10-17-07 at 02:22 AM.
I've bolded the pertinent comment in my 1st reply. Please note, I'm not a frame builder and don't pretend to be but this is what I've come to expect from any frame that was checked using an alignment table or jig before final finishing. The fork -- unless it too was fabricated by the builder -- remains a wild card, particularly if it's a suspension fork.
Originally Posted by Geordies
I'll defer to any of the frame builders who may offer a different perspective who will hopefully weigh in on this one.
Thanks for the reply, I am going to turn the forks through 180 degrees and re-measure.
I want to be certain before I return to the builder as its a long car journey.
Ideally I would like a second opinion from another builder.
You could try sending a private message to dbohemian. He is a tandem frame builder and participates in this forum. Good luck
Last edited by cornucopia72; 10-17-07 at 10:41 AM.
I should point out I am very pleased with the Tandem ,it does everything I expected ,I am just not happy about the missaligment.
Originally Posted by Geordies
Alignment discussions are common amongst framebuilders and there is no one right answer. Tandems due to their nature (being very long and having many welded or brazed joints) have a much greater tendency to have alignment issue than singles. Because of this fact, one has to be very diligent in maintaining alignment during the build. Even with this though, small misalignments which would lead to sub 1mm variations on singles can, on a tandems lead to 2 or 3mm deviations.
The reasons for it can also be varied. Maybe it is a tube off center but maybe it is a head tube twist issue that puts the fork out of plumb with the frame and shows that deviation with the string in your pictures? I can only guess without being able to measure it in person.
I would say this. If the front and rear wheels are true to one another and the tandem rides well with no apparent issues and you can let this part go, then just enjoy it.
Most tandems if measured would probably not come under 2mm, 2-4mm would be most likely average. and anything above than less than ideal.
Hope that helps, for what its worth.
I should point out I am very pleased with the Tandem ,it does everything I expected