M6 Rack Bolts - Overkill?

[horizon]

Thanks Brucey and PH.

I've solved the problem by switching another Tubus cargo from another bike which does have a 6 mm hole. However it wasn't really what I wanted (faff and colour) so I had considered 5 mm bolt through from behind with nut. Brucey: is this what you suggested is a better solution than a 6 mm bolt only in a 6 mm eyelet?

I didn't want to cut a wider hole but it isn't now necessary. I think the 5 mm Tubus is a much older model. The amount of metal around the two holes (5 and 6) BTW is the same.

PS CJ liked the 6 mm eyelets on the Spa in his review but I've got them for better or worse.

[Brucey]

... I had considered 5 mm bolt through from behind with nut. Brucey: is this what you suggested is a better solution than a 6 mm bolt only in a 6 mm eyelet?...

swings and roundabouts really.

cheers

[NATURAL ANKLING]

Hi,
One of the important factors as already said is to make sure that when the rack eyelets meet the frame they are parallel to each other.......perfectly.
And the rack legs do not spring in or out when fitted to the frame..............not stressed at all.
That applies to any bracket rack to frame too.

[horizon]

Two further points on this then as I often do find some stress in rack legs: should the lower mounting points be done up first? That has been my way, loosely and then tightened when the upper ones are done.

Secondly, what I appreciate about the Spa is that it has separate mounting eyelets for mudguards and rack. The Thorn Club Tour does not and I don't think this helps in lining up the rack to the frame while the mudguards are swishing about. Any views on that?

[Brucey]

if you only have one eye on the dropout then

a) put the rack against the dropout and have the stays outside of that
b) be sure that the mudguard stays will accept a tight bolt without deforming unevenly
c) consider using a separate bracket for either the stays or the rack, such that the rack can be bolted securely

IME you should at least nip the bottom bolts up and check that the rack mounts line up correctly without strain at the top. By all means tighten the lower bolts last, but if the rack is strained in any way when mounted, this is usually a bad thing.

cheers

[NATURAL ANKLING]

Hi,
Rocks by their very nature are Wiery things and always made symmetrical or true.
This is especially true of the mounting points.
I normally start by turning the rock upside down on a flat surface and looking at it to see if the legs on either side or symmetrically slanted.
If not clamp the rack body Or put it on the ground on a piece of wood and put your foot on it.
Straighten up the legs.
When you mount the rock the rock eyes and brackets should be perfectly parallel to the mounting points on the frame, you don't want any springing whatsoever when you do the bolts up!
it be very common for me to fit a rack on a bike and for it to take me least an hour to get everything nice and lined up.
The top brackets need careful bending if you're using separate brackets that is.

[NATURAL ANKLING]

Hi,
Racks by their very nature are Wiery things and aren't always made symmetrical or true.
This is especially true of the mounting points.
I normally start by turning the rack upside down on a flat surface and looking at it to see if the legs on either side or symmetrically slanted.
If not clamp the rack body Or put it on the ground on a piece of wood and put your foot on it.
Straighten up the legs.
When you mount the rack eyes and brackets should be perfectly parallel to the mounting points on the frame, you don't want any springing whatsoever when you do the bolts up!
it be very common for me to fit a rack on a bike and for it to take me least an hour to get everything nice and lined up.
The top brackets need careful bending if you're using separate brackets that is.
If you offer the rack up onto the frame it should fit just so touching the mounting points or a few millimetres of clearance, if not do it again!

[horizon]

Hi,

When you mount the rack eyes and brackets should be perfectly parallel to the mounting points on the frame, you don't want any springing whatsoever when you do the bolts up!
it be very common for me to fit a rack on a bike and for it to take me least an hour to get everything nice and lined up.

+ 1 on both these points. I'm not convinced I succeed on the first and most often exceed the latter!

[horizon]

If you use a full-threaded set screw from the inside of the dropout (clearance for head permitting, reduced head size is a good idea) such that it becomes a captive stud, and then use a good washer and nylock on the outside, this arrangement

1) is immune from b) above; at worst the stud bends once and once only, since it doesn't turn
2) the nut won't be lost
3) the threads in the dropout don't see a turning bolt under load so are unlikely to be damaged
4) the threads in the dropout are not loaded (the fastener head sees the load) and are therefore unlikely to be damaged
5) the loaded length of the bolt is made longer so there is more 'stretch' in the bolt and the tension is less likely to be lost
6) should the bolt ever break the remains can always be unscrewed from the inside.

So I went for this solution in the end rather than mess around with taking a rack off another bike. The head of the bolt fouled the 11T sprocket so I set the limit screw to avoid that. I won't miss the 11T but it isn't a perfect solution. Otherwise it was good and solid, fairly easy to do (rear wheel off of course) so I'm happy.

I had to replace the round stays with longer ones (and even these I had to cut down so the angle was right). There was enough bend in the ones I had in stock but ideally a little more curve would have prevented what tension there was.

I'm happy with the result - I like Tubus racks and it feels very strong. It was second-hand off this forum so while I didn't expect shop-bought perfection, it was still quite a saga to do. I also wonder how many people buy Tubus racks (and maybe other brands) where the round stays aren't right and they need either to be replaced, cut or bent and this doesn't get done.

[Jdsk]

... clearance for head permitting, reduced head size is a good idea...

The head of the bolt fouled the 11T sprocket so I set the limit screw to avoid that.

Was that a full height head, and how much extra clearance do you need?

Jonathan

[Carlton green]

I’ve never had rack bolts fail but then I’ve never loaded them to extremes - if you push anything hard enough then you’ll use up its safety margin and break it.

The one particular thing that I think is important is to have the rack legs flush to the frame and so if they are fitted (as they are on my bikes) the mudguard stays must be outside of them. Having a full length of thread engaged within the frame’s lug is essential. I like the idea of bolting through from the inside to create a stud in the frame but I understand that that is sometimes not possible. At times I’ve made and used a long grub screw to act as a stud (cut the head off of a bolt, cut a screwed slot in it, install stud with lock-tight) and held the rack in place with a plain washer, a spring washer, a plain nut and lock-tight. A similar trick - if not so neat looking - is to use a longer bolt as a virtual stud and secure the rack using washers and nut as above.

Historically racks were steel with thin plain ends but now they are alloy and with thicker mounting ends. I’d be inclined to check that the holes really were perpendicular to the rack mounting face and that the bolt seating wasn’t slightly tapered. There might be a case for counterboring an alloy rack to better control the (only) possible loading point. The bolt should see shear loads, tension loads but not (beyond minimal) bending loads; the arrangement was never intended for anything else.

[pwa]

Cool, I'll stick with the M5s.

I'll always have spares so it's no big deal if one breaks. And decent quality stainless bolts are a given. I use longish ones so there's a little bit poking out the other side of the eyelet - should make removal easier in case of one shearing off. I find it's possible to have a few mm excess on the drive-side without interfering with the cassette-chain.

Thanks for the replies.

I would prefer 6mm given the choice, but I have used 5mm with no issues simply because that is what the bike had. Take a spare screw and a tiny file so that if you had to (you probably won't) you can file flats onto the excess bit of screw and use pliers to remove it. That is always the snag, getting the remains out.

[NATURAL ANKLING]

Hi,
Horizon have you got a picture for us to goggle at

[horizon]

... clearance for head permitting, reduced head size is a good idea...

The head of the bolt fouled the 11T sprocket so I set the limit screw to avoid that.

Was that a full height head, and how much extra clearance do you need?

Jonathan

It was a full head height as it was the best screw I had. I reckon I needed only a millimetre or perhaps two extra but it wasn't there. I went very quickly for the no-11T solution as even under normal conditions I still have some unease about what happens when the chain reaches the outer limits!

I did try a flatter head screw for fit but although the screw was anyway too short, it still would not have provided clearance.

I also didn't (despite good advice to the contrary) use Nyloc nuts (I did try) as the rack legs didn't allow enough clearance to get a good grip - it was really fiddly. I'm happy with the soundness of the set up but will be checking for tightness on a very regular basis.

I'm a bit torn on this now as the nut-and-bolt method has merit (as Brucey explains) but my feeling now is to check for 5mm/6mm compatibility from the start and use the threading from the outside.

[horizon]

Hi,
Horizon have you got a picture for us to goggle at

I'll try!