Off center pannier rack mounting (disc brakes)

[alexnharvey]

Hello all. I am considering mounting a pannier rack off centre to a Genesis Day One to clear the disc brake (older, seat stay mounting position). It would be approximately 20mm to the NDS. This would also reduce the spreading force on the aluminium rack, either bypassing (mounting inside the mount rather than outside if there's clearance), and/or removing the redundant welded extension on the drive side entirely. The rack is a Topeak super tourist dx disc rack. Having tried it, I think mounting inside the mount and removing the extension which would foul the freewheel sprocket is best.

Any thoughts?

[RickH]

If you remove the extension bit you will have a mahoosive bolt hole in that side (maybe 10mm at a guess without going out to the she to measure mine) which would be tricky to get a firm fix using a washer unless you have a suitable bolt with a really large head.

What is the problem with just using the rack as it is?

[alexnharvey]

Thanks for your reply. Maybe our racks are different or I have not explained myself very well because there will be no difference to the diameter of the hole because it is of constant diameter along its axis, which the cut is perpendicular to.

I am talking about making a vertical cut to remove the horizontal piece of the L shaped extension which is welded to the bottom of the pannier leg. This serves to space the rack out further from the mounting points, making it wider than a non-disc rack overall. I would be taking off the base of the L without reducing its height. The hole appears to be threaded and the same diameter along the whole length so no larger bolt needed.
On the NDS the L piece allows the rack to pass outside the brake. On the DS it serves no purpose, it appears to me, except that it makes the rack symmetrical. Do I need to worry about this symmetry? I would think not particularly, many people often use a single pannier or ride with loads that are not perfectly balanced on each side, The arms that attach to the seatstay mounting points are steel and I think will easily tolerate the deviation, but i'll check before cutting.

The rack mounts on the bike are spaced further apart than than the distance between the inside faces of the pannier rack by a fairly large margin, maybe 25-35mm. The rack must therefore be pulled apart to fit them. There would be a constant stress on the rack which might over time lead it to crack through fatigue as it's aluminium. I can reduce this stress by taking off the redundant piece as described above, and further by mounting inside rather than outside the fitting. I will also slightly reduce the overall width of the rack a little which is a bonus for both aerodynamics and negotiating obstacles. Obviously a risk of mounting inside is that if the bolts unscrews it hits the chain. I would mitigate this with threadlock and a split washer. Also I think I'd probably hear it before it became catastrophic.

[tim_f]

I have had this rack on my commuting bike for years and it has been fine in the supplied configuration.

I would just use it as it is.

Tim

[alexnharvey]

Did you have to spread it to fit the bike?

After another fit up, with the cut the rack will fit neatly on the outside of the drive side. It's quite hard to pull it apart enough to fit as it is currently.

[tim_f]

Did you have to spread it to fit the bike?

it was so many years ago that I can not remember. One of forum members with more expert engineering knowledge can probably advise on how much it is safe to spray the legs on an aluminum tubular rack. But I suspect if you do it once only and with care to make sure you do it evenly on both sides it will be ok.

Tubus racks (which are steel) come with instructions on safe spray amount, but TOPEAK racks instructions have no guidance on this.

I recall there was a mark one version of the rack which had a long narrow hole and a long bolt, and a mark two version with a wide hole which got narrow at the drop out end with a short bolt. Now there is a mark three version where the feet of the rack are separate allowing the length of the legs to be adjusted. Which version do you have ?

Mine is the mark two version.

That you are considering chopping down one of the feet, and think you can just use a shorter bolt makes me suspect you have the mark one version.

If you have a brand new mark three version it is probably defective.

When I now unscrew the bolts the legs spring out a bit.

[Brucey]

mounting the rack so that the top is off-centre offends my sensibilities somewhat. It ain't great for load carrying, either.

IME cold-setting racks to a new shape (once) is much preferable to 'springing them' to fit. The latter causes the rack to see high stresses all the time, and failure in service is made more likely.

cheers

[alexnharvey]

Can I cold set an aluminium rack?

[Brucey]

Can I cold set an aluminium rack?

yes; however if you are unlucky the welds will crack, often because they are already slightly cracked; examine them first if you are concerned about this.

When Jim Blackburn popularised the idea of welded aluminium racks (*) they were heat treated after welding and came with a lifetime warranty. They are not made like that any more, (not even by Blackburn I think).

[ (*) I am enough of a BOF to remember this, and still have such a rack that I bought in the early 1980s to boot....]

BTW one of the other things that knackers racks is hanging just one pannier off them. Breaks racks and even breaks framesets, that.

cheers

[alexnharvey]

I'll avoid single bagging then, it's just not worth the risk...

I'mm still tempted to cut it. I think it'll end up very slightly off center in the end. In fact, I might be able to cut down the NDS slightly yet still clear the brake, maximising symmetry, minimising overall width and eliminating splay.

[pga]

Fit aluminium or stainless steel spacers and precise length stainless steel bolts (online from China) to position the rack in the centre. Most recent bikes have recognised the problem and have made the effort to allow centre fitting racks. Alas the earlier Giant Liv models failed to do so, hence the challenge. Unless you are on a world tour this arrangement will be fine and probably for a world tour as well. The main problem with the Giant Liv was that the mudguard eyes were not through threaded, hence the need for the bolts to be of an exact length. We had the same problem at the front but in the end fitted front and rear mudguards as well as the rear rack. We should not have been forced to go through this long procedure to fit routine equipment.

[alexnharvey]

In the end I have taken the same amount from each side, probably seven or eight millimetres, to allow it to be central. I had to spread it about the same amount too.