Stronger rack mounts!

[jon_norstog]

Last year I had a repair job referred to me by Dave Bohm - R, a big, strong rider from Utah, was going on a cross-continent tour and had broken off an allen screw in his lower rear rack mount. I did the repair, relining what was left of the original mounting boss with a piece of canti stud. And I made sure he had a steel 6mm screw in it when he left. I told him if he had any problems with the repair, get it fixed and send me the bill.

The tour went fine, he included me in his daily postings. Very entertaining. Anyway, I heard from him again last month. he said the 6mm mount held up fine, but he had broken off the 5mm bolt on the other, unrepaired side.

R is a big guy who looks like he could pull a heavy load on a bike. And who probably doesn't slow down when the road gets rough.

My take on it is that a 5mm mount for the rear rack is just a failure waiting to happen, and one that will happen in the middle of an otherwise great ride.

My own take from this is that 5mm rack mounts are marginal, at least on the rear of the bike. From now on, unless the client is the size of Tinkerbelle and never carries more than her gym bag on the rack, I'll use 6mm rack mount bosses on all my bikes.

jn

"Thursday"

jn

[Andrew R Stewart]

I understand the issue is the rack bolt and not the eyelet. Agreed that 6mm bolts will be much more durable then 5mm. A few comments though.

The thread engagement amount will lessen with a 6mm bolt (.8mmpt for M5, 1mmpt for M6, that's 25% less thread overlap) so a longer/thicker eyelet might be a good idea. Many racks are built around the M5 size bolts, so the strut tab size might not support a larger hole. Will the 6mm hole be too big for the rack? The only times I have seen broken off bolts is when the bolt loosened and the bolt was in a bending mode, not a shear one. This includes when the fender braces have been mounted on the same bolt as the rack strut. Unless care in mounting and maintaining the bolts' tightness the added length and changeable nature of poorly installed fender braces the bolts can often suffer and bend/loosen. Andy.

[steve garro]

IMG_1674.JPGIMG_1667.JPGIMG_1665.JPGIMG_1669.JPGHaving toured all over on the suckyest roads I could find here is how I do it now - the Coco-Moto dropouts have a mirror image eyelet to the upper disc mount for thru-bolts of 6mm or 1/4-20 or whatever will fit through, and here is the upper mount which is attached to the thickest part of the bike = ST, sleeve, and post - if stripped, it can simply be rotated and tapped to whatever is at hand.

I also ditched the Old Man Mountain's aluminum lowers for disc brake/QR and made these more minimal lowers as direct mount out of steel.

The bike also uses two identical wheels F&R for redundancy in BFE & the racks are both the same.

Good to Go.
- Garro.

[Jonathan]

Good idea for a seat collar.

[steve garro]

Good idea for a seat collar.

Won't tear off with a piece of your SS for company = availible in steel or alloy from Mc Master-Carr.
You do the tapping.
- Garro.

[blasdelf]

My take on it is that M5 is more than strong enough for the job, but that people dramatically compromise it with misguided attempts to improve on a simple system.

Adding separate washers dramatically increases the tendency to self-loosen in this scenario. That may seem far-fetched and unintuitive, but it's what happens in reality: Vibration Loosening of Bolts and Threaded Fasteners

Stainless fasteners are often the devil, generally under half the strength and far more brittle than a proper high-strength alloy steel bolt in a black oxide finish. When loaded perpendicularly like in most rack installations, once vibrated loose they're much more likely to break.


I'm also pretty sour on waterbottle bosses for any major load-bearing application, hourglass mounts on the surface or tunnels all the way through the tube are much stronger especially against fatigue.

And to hell with aluminum racks, it's simply the wrong material for a job needing such small ODs. 4130 tubing is far stiffer / stronger / lighter in the dimensions required for such things without even trying.

[surlypud]

Thank you for that link to vibration bolt loosening. Based on what I read there, it would seem like loctite would be the best bet for rack mounts.

[Mark Kelly]

Dazza swears by studs and nylock nuts.

[steve garro]

IMG_1088.JPG

Dazza swears by studs and nylock nuts.

If you use "regular" hourglass rack mounts the best thing to do is run the buttonhead bolt from the inside of the frame with washers on both sides & then put a nylock on the outside so if the bolt does shear then you can back it out with the head and flip it and still use the same bolt if needed.

This is shit I had to learn the hard way from 1000's of miles of off road touring.

Here is a pretty good Baja route........that IS the road.
- Garro.

[shiggy]

IMG_1088.JPG

If you use "regular" hourglass rack mounts the best thing to do is run the buttonhead bolt from the inside of the frame with washers on both sides & then put a nylock on the outside so if the bolt does shear then you can back it out with the head and flip it and still use the same bolt if needed.

This is shit I had to learn the hard way from 1000's of miles of off road touring.

Here is a pretty good Baja route........that IS the road.
- Garro.

Is that Eugene?

[steve garro]

Is that Eugene?

Nope - it's Yod
Euge was in diapers when this was taken.....
- Garro.

[blasdelf]

If you use "regular" hourglass rack mounts the best thing to do is run the buttonhead bolt from the inside of the frame

I'm a fan of this, and much prefer it to thru-hole mounting that lets the bolt/nut assembly rotate under vibration

But don't use button heads! Hex-head bolts are by far the better low-profile fastener, and these are still available for ballers Campagnolo Bolts and Washers - set of 8 - Sale! (and you should already be carying one of these badasses: Park Tool Co. » MT-1 : Multi-Tool : Multi Tools )

with washers on both sides

No washers for shear loads! Watch the video: Video on a Junker Fastener Vibration Test

The added surface area helps, but you can get that with hex or flanged heads without the dramatic self-loosening under vibration

then put a nylock on the outside

Just as long as they get replaced every so often — they're much easier to put on the second time, and wear to nothing over many uses

Safety Wire is the big boy solution

Our recent racks have all used breezer dropouts at the attachment points, and the next step is to start drilling them for wire

If you look at the special hardware that Shimano includes with their disc calipers, caliper adapters, and XT 6-bolt rotors, you can find a LOT of inspiration there

so if the bolt does shear then you can back it out with the head and flip it and still use the same bolt if needed.

indeed, but if you avoid stainless and especially unrated fasteners, they really don't want to shear even under abuse

[steve garro]

I'm a fan of this, and much prefer it to thru-hole mounting that lets the bolt/nut assembly rotate under vibration

But don't use button heads! Hex-head bolts are by far the better low-profile fastener, and these are still available for ballers Campagnolo Bolts and Washers - set of 8 - Sale! (and you should already be carying one of these badasses: Park Tool Co. » MT-1 : Multi-Tool : Multi Tools )




No washers for shear loads! Watch the video: Video on a Junker Fastener Vibration Test

The added surface area helps, but you can get that with hex or flanged heads without the dramatic self-loosening under vibration




Just as long as they get replaced every so often — they're much easier to put on the second time, and wear to nothing over many uses

Safety Wire is the big boy solution

Our recent racks have all used breezer dropouts at the attachment points, and the next step is to start drilling them for wire

If you look at the special hardware that Shimano includes with their disc calipers, caliper adapters, and XT 6-bolt rotors, you can find a LOT of inspiration there




indeed, but if you avoid stainless and especially unrated fasteners, they really don't want to shear even under abuse

I guess I did it wrong all those 10's of thousands of miles - go figure.
How the hell did I ever make it through Bolivia?
- Garro.

PS - Breezer dropouts suck.......super soft, minimal eyelets, and the damn hanger is too far forward - & the hangers bend looking at them.

[blasdelf]

I guess I did it wrong all those 10's of thousands of miles - go figure.
How the hell did I ever make it through Bolivia?

people ride PBP on english roadsters and tour central asia on fucking pennyfarthings, miles are proof of the rider not the bike

but it is conclusively known that using washers when attaching racks makes the bolts self-loosen dramatically faster

PS - Breezer dropouts suck.......super soft, minimal eyelets, and the damn hanger is too far forward - & the hangers bend looking at them.

having just gotten a custom bike with them I agree about all of that in the strongest terms, my builder was complaining about how thin the hoods were for welding the Paragon Wrights, but next time I'm just gonna tell him to HTFU


in this case I wasn't talking about the frame dropouts, I was talking about our solution to what Paragon calls a "Rack Lug"

we've been calling them "breezer style" because they have a hood to braze to, they're made from 7/16" 4130 rod with a 5mm thru-hole and a deep 9mm countersink for the bolt head

is there a better name to use for that type of doodad?

[Matthew J]

Good discussion.

What of Tout's (and some others) approach - building the rack on the bike? If you know the bike is going to be toting luggage most of the time, is this a sensible approach? Are there drawbacks other than having the rack permanently part of the bike?

[steve garro]

people ride PBP on english roadsters and tour central asia on fucking pennyfarthings, miles are proof of the rider not the bike

but it is conclusively known that using washers when attaching racks makes the bolts self-loosen dramatically faster




having just gotten a custom bike with them I agree about all of that in the strongest terms, my builder was complaining about how thin the hoods were for welding the Paragon Wrights, but next time I'm just gonna tell him to HTFU


in this case I wasn't talking about the frame dropouts, I was talking about our solution to what Paragon calls a "Rack Lug"

we've been calling them "breezer style" because they have a hood to braze to, they're made from 7/16" 4130 rod with a 5mm thru-hole and a deep 9mm countersink for the bolt head

is there a better name to use for that type of doodad?

I've made racks from those.
They work fine with 3/8th x .035 if I remember right.
"rack lugs" best I can come up with, but they are not a lug or hooded but rather a plug.

Thanks for giving me the credit for touring, but months out it's YOU that are keeping the bike going & with what you got and what you can scrounge.

Best thing you can do is a nut & bolt check over coffee.

Usually the racks bust before a bolt - hell........axles bust out touring pretty frequently, freehub bodies as well.

Who are the "We" and "ours" you keep mentioning?

- Garro.

[shiggy]

Good discussion.

What of Tout's (and some others) approach - building the rack on the bike? If you know the bike is going to be toting luggage most of the time, is this a sensible approach? Are there drawbacks other than having the rack permanently part of the bike?

If the rack breaks it is a frame builder repair rather than just a bolt-on replacement.

[Matthew J]

If the rack breaks it is a frame builder repair rather than just a bolt-on replacement.

So then it would be a matter of weighing the odds between bolts breaking or rack itself versus ease of remedy.

[blasdelf]

Usually the racks bust before a bolt

Aluminum ones all the damn time (done several myself), but in 4130 it's way way harder though still possible if you crimp a tube somewhere and wiggle the shit out of it

I have had bolts self-loosen a number of times from the Jost Effect, with some falling out or shearing.

Who are the "We" and "ours" you keep mentioning?

Haulin' Colin Porteur Racks
Flickr: Haulin' Colin's Photostream
Flickr: Garth L'Esperance's Photostream

I'm not one of the main principals, but there's a new joint company for the shop being formed called "Cyclefab" with a number of existing and new products under that umbrella.

[Matthew J]

I'm not one of the main principals, but there's a new joint company for the shop being formed called "Cyclefab" with a number of existing and new products under that umbrella.

Please do keep the forum posted on this.