Tubus Tara different?

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gregoryoftours
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Re: Tubus Tara different?

Post by gregoryoftours »

cycle tramp wrote: 31 Jan 2023, 4:07pm Good Lord! That's a might spacer- are you using carbon steel bolts or stainless? Any more photos of your bike, please :-)
Hmm, I thought I remembered using grade 12.9 bolts for that reason, but they're actually A2-70 stainless :/

Nevertheless I actually think they're pretty secure, there's a decent flat area on the fork mount, the bolt passes through the fork which has a threaded insert the whole way through. I have them dogged up pretty tight with thread lock applied and a nut on the inside.

The spacers are pretty stable too, they are the heavy steel 8mm hex nuts you get on some really cheap v brake pads that have quite a lot of surface area on each end to contact and provide stability and friction. Consequently I don't think that the bolts see as much shear force as one might think. I have changed the bolts periodically and they've never been even slightly bent.

I can't really bend the u-bar of the rack due to the design of the dropout mounts and clearance. But I am satisfied with the strength and support as I have it fitted.

Here are some photos of the bike on tour:
DSC00930.JPG
DSC00362_edited (1).jpeg
P1180744.JPG
DSC00297_edited.jpeg
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531colin
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Location: North Yorkshire

Re: Tubus Tara different?

Post by 531colin »

cycle tramp wrote: 31 Jan 2023, 6:04pm Thanks for the update - I'd be interested in their reply..

531 Colin - would the strength of the m5 bolt increase if the spacer had a m5 thread and had to be threaded onto the mounting bolt?
I'm no engineer!!
My post is based on my recollection of what Brucey said on the subject of mounting rear panniers and mudguards.

Generally, its recommended to fit the carrier next to the frame, and the mudguard on the outside if they have to share the same bolt.

My recollection of Brucey's "counsel of perfection" is as follows...
Fit a bolt with its head on the wheel side of the dropout.
Remove paint from the dropout where the carrier will go, so the carrier and frame meet "metal to metal"
Fit the carrier, then tighten a nut against the carrier.
If the mudguard needs to share the same bolt, secure the mudguard with a second nut.

So, I think the Tara side rails should be fitted tight to the forks.
Putting a bolt through from the wheel side of the fork and threading and tightening as many M5 nuts as you need as spacers before fitting the rails secured by another nut I think would be inferior.

I'm afraid I don't have the patience (or searching skills?) to dig out Brucey's original stuff.....anybody?

Having said all that, Gregory seems to carry some stuff!
gregoryoftours
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Re: Tubus Tara different?

Post by gregoryoftours »

cycle tramp wrote: 31 Jan 2023, 6:04pm Thanks for the update - I'd be interested in their reply..

531 Colin - would the strength of the m5 bolt increase if the spacer had a m5 thread and had to be threaded onto the mounting bolt?
I'd say maybe,
If the bolt was threaded completely through the fork with the head on the inside, and if the spacer had flats on it so that it could be tightened into place (it would have to be basically a fat flat-ended nut), then the rack and then a washer and nut on the outside.

But not if the bolt head was on the outside because a threaded spacer in that case would not allow everything to fully clamp up together.
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531colin
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Location: North Yorkshire

Re: Tubus Tara different?

Post by 531colin »

PT1029 wrote: 31 Jan 2023, 5:12pm I had to use 1 set (concave + convex) of V brake pad spacers (the thicker ones) to fit my Cro Mo Tara rack onto my 1980's touring forks - I wasn't worried about bolt shear as it was only a short term/handling test/comparison exercise.
Mechanically of course spacing out bolts is not good. On the plus side, you are less likely to damage your paint with the pannier hooks.

I have sent a query to Tubus to see what they say, including my wide arms photo, and a link to this thread.
https://www.tubus.com/fileadmin/user_up ... ra_5.0.pdf
............Dimensions for Tara "loop"

Is your Tara "loop" the same dimensions as this drawing?

If it is, I would assemble the rails to the loop and bend the rails inwards until their ends are the right distance apart for the forks. I guess the bolts will bend, and the tubes maybe ding a bit. Having bent the bolts, don't turn the bolts to tighten.....tighten the nuts, holding the bolt head with an Allen key. Bend the slotted brackets so they fit flat to the mid- fork mounting points.
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gaz
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Location: Kent

Re: Tubus Tara different?

Post by gaz »

531colin wrote: 31 Jan 2023, 8:40pm I'm afraid I don't have the patience (or searching skills?) to dig out Brucey's original stuff.....anybody?
A few other possibilities but these look the most likely.

viewtopic.php?p=516126#p516126

viewtopic.php?p=915579#p915579
High on a cocktail of flossy teacakes and marmalade
slowster
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Joined: 7 Jul 2017, 10:37am

Re: Tubus Tara different?

Post by slowster »

gaz wrote: 1 Feb 2023, 12:05am
531colin wrote: 31 Jan 2023, 8:40pm I'm afraid I don't have the patience (or searching skills?) to dig out Brucey's original stuff.....anybody?
A few other possibilities but these look the most likely.

viewtopic.php?p=516126#p516126

viewtopic.php?p=915579#p915579
Also (albeit pithy) viewtopic.php?p=1443860#p1443860
PT1029
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Re: Tubus Tara different?

Post by PT1029 »

I sent this e mail to Tubus: -
Dear Sir/Madam,

I have a new Tubus Tara rack in stanless steel, I have a question about the width.

The instructions say the forks must be 130 - 140mm wide (top mount measurement [b1] in the instructions).
My forks are 120mm wide - no problem, I can add a 5mm spacer each side.
The problem is, when I assemble the Tara rack before putting it on the bike, the horizontal bars are about 155mm wide (see attached photo).
I assume the best option is to cold set the horizontal bars (well, tubes) a little to narrow the width. Obviously I would need to check if this affects pannier bag fitment, and to not dent/buckle/crimp the tube being bent.
I raised this on the Cycling UK Forum, a few comments made, viewtopic.php?t=154800

NB. The horizontal bars on my older (~1993) Tubus rack measure 138mm.
Many thanks,


The reply I received was this: -

thank you for your feedback. I just checked in our stock, and they have 135 mm width at this point.

I’m not sure if I understand your assumption correct. Cold set = bending? You should not try to bend the arms, you will get a kink, which weakens the rack more than mounting under a little stress.

The 14 mm U-tube is really stable and the rack itself can carry much more than the admitted 18 kg. The limitation to 18 kg for front racks is given from the ISO 11243 standard.

I recommend to use the included 8 mm spacer on both sides and mount it under stress.

Mit freundlichen Grüßen
Best Regar
ds

The response it a bit disappointing,
2 X 8mm spacers means I fit a 155mm wide rack to forks/spacers 136mm wide (120 + 16mm).
I think a "spring" of 10mm each side would be too much.
He refers to "... and mount it under stress" I did try to move the arms in a bit (with the bolts I think). I didn't move then far as the stress felt is was going to be much more than "a little".
The rack at his end was 135mm, nothing stated as to why mine is 155mm wide.


I might investigate the "bent bolt" option that 531 Colin suggested, though I have slight reservations on this as I have to remember in future maintenance the bolts, like Mrs Thatcher are not for turning.
Tubus's concern over cold setting/bending the roads seems to be getting a kink. I think with some care/big vice/something curved (akin to a pipe bender) I might achieve a better result by careful cold setting/bending. If I bend near the front U bar (but not at the weld) the amount of bend should not be that much. I could always try it on some bit of similarly dimensioned metal just to see how much bend is needed.
cycle tramp
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Re: Tubus Tara different?

Post by cycle tramp »

PT1029 wrote: 1 Feb 2023, 8:26pm I sent this e mail to Tubus: -
Dear Sir/Madam,

I have a new Tubus Tara rack in stanless steel, I have a question about the width.

The instructions say the forks must be 130 - 140mm wide (top mount measurement [b1] in the instructions).
My forks are 120mm wide - no problem, I can add a 5mm spacer each side.
The problem is, when I assemble the Tara rack before putting it on the bike, the horizontal bars are about 155mm wide (see attached photo).
I assume the best option is to cold set the horizontal bars (well, tubes) a little to narrow the width.

NB. The horizontal bars on my older (~1993) Tubus rack measure 138mm.
Many thanks,


The reply I received was this: -

thank you for your feedback. I just checked in our stock, and they have 135 mm width at this point.

The 14 mm U-tube is really stable and the rack itself can carry much more than the admitted 18 kg. The limitation to 18 kg for front racks is given from the ISO 11243 standard.

I recommend to use the included 8 mm spacer on both sides and mount it under stress.

Mit freundlichen Grüßen
Best Regar
ds

The response it a bit disappointing,
The rack at his end was 135mm, nothing stated as to why mine is 155mm wide.
Ah, thanks for the update. It might be just me but does anyone else feel that perhaps occasionally a very small amount of tubus tara racks are released onto the market which haven't been correctly set at the factory?

It could be that the only simple way forward is to return the rack you do have (perhaps even citing not sold as described) for another Tara rack which meets Tubus' design specifications.
It's time to go :-)
PT1029
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Re: Tubus Tara different?

Post by PT1029 »

Yes, I could send it back of course. Fudge it or return it, either way it is a bit of a faff.
slowster
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Re: Tubus Tara different?

Post by slowster »

I have a stainless Tara rack which I have not yet fitted. The spacing when assembled off the bike and the bolts tightened is similarly ~150mm.

Have you tried fitting the rack to the fork?

There is some slop/play designed into the fastening between the hoop and the horizontal struts, i.e. the holes for the bolts are a little over 6mm, allowing the M5 bolts quite a bit of wiggle room in the holes.

I presume that when fitted to a fork within the range of permitted b1 dimensions, final tightening of the hoop/horizontal strut bolts is best done after the bolts securing the rack to the fork have been tightened. The bolts will then be suitably offset at an angle inside the fastening holes through the hoop, and can then be tightened. Presumably staying within the permitted b1 dimensions should ensure that the bolt is merely offset at an angle inside the fastening hole, without being bent, and likewise that the horizontal struts are not subjected to inappropriate stress, i.e. excessive bending force.

I presume that spherical washers could have been included by Tubus, but that the small amount of angle of movement and the nature of the loads/forces on the bolts etc. were not such that they were considered necessary.
pwa
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Re: Tubus Tara different?

Post by pwa »

It's steel. So if it were me, I'd probably persuade it to be narrower. Call it "cold setting" if you like. Probably at the main bend at the front.
gregoryoftours
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Re: Tubus Tara different?

Post by gregoryoftours »

Have you already tried fitting the main u tube to the fork at the dropouts, using whatever spacers are necessary for it to clear the step out from the dropouts to the bottom of the fork blades? For mine a fair amount of spacing is unavoidable to clear the cast dropout:
IMG_20230202_204656.jpg
Once this is done and the rails bolted to the u tube, what is the gap you're looking at each side between the mounting plates of the rails and the mid fork mounts? It may have closed up to an acceptable amount more than when assembled off the fork.
If the latter is the case then you could cold set the bend in the main u tube, but I wouldn't bother personally, I don't think that the main tube is stressed in a harmful way if it's sprung in a bit.

Could you assemble the rack like this and post photos of the gap? I think it would be easier to get an idea of the extent of the problem visually with it near fully assembled.
PT1029
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Re: Tubus Tara different?

Post by PT1029 »

To answer a much earlier question, the U bar isn't the "Big Apple" version (a friend has one of these, it looks very different with the bigger radius curve at the top).
On my forks the U bar does not need spacing out (holes on top of drop out/in front of the fork blade).
With the U bar bolted on (I think it was as good as by the drop outs(?)) and the horizontal rods tight enough to eliminate play (I could swivel the rods round/up and down a round the bolt), there was a big gap at the fork blade.
The forks are in the post (separate issue from the rack mounts), so I can't fiddle any more for now. The rack is getting ready to go back - after all, the rack assembles well out of the technical drawing spec. My 1993 CroMo Tara assembles as per technical drawing spec.

I don't think suggestions of the horizontal bar mounting at an angle in the U bar due to the (radially) loose fit of the bolts through the U bar works. Although there is slop/wiggle room for the bolt, the rod will tighten flat to the mounting surface of teh U bar, which places them wide at the fork again. It would take curved a la V brake washers to permit this. It did cross my mind to try, but I though I'd aim to send it back in the hope it's replacement was better.

U bar plus rods tightened so there is no play: -
Tubus Tara width.jpg
gregoryoftours
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Re: Tubus Tara different?

Post by gregoryoftours »

Hmm, frustrating. Maybe they've re-jigged the design to better fit a more modern style of fork. Many of these have blades that stay wide further up the fork to give greater clearance at the crown to take wider tyres. I mean this kind of thing:
IMG_20230202_221129.jpg

It doesn't conform to the specs but it could be just that they haven't updated the specs to match the design. In the bike industry stuff like that happens all of the time, although I'd expect Tubus to be better about that sort of thing.
gregoryoftours
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Re: Tubus Tara different?

Post by gregoryoftours »

It might look a real messy bodge but if you really wanted to use this rack and that fork could it work to use the Tubus fork mount clamps? These are already spaced 12mm, and I think that you could even safely add an additional spacer.
IMG_20230202_222132.jpg
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