Front rack difficulties - any advice?

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roubaixtuesday
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Front rack difficulties - any advice?

Post by roubaixtuesday »

We need a front rack for the tandem.

I've a nice Tortec one, but it seems impossible to fit without fouling the QR lever - see pic.

I think you can get skewers which fasten with allen bolts? Which would solve the problem.

Any other ideas? Is this because of the braze on position on the tandem fork, or would a different rack likely solve the problem?

Screenshot_20230206_205414_Gallery.jpg
Last edited by roubaixtuesday on 6 Feb 2023, 8:54pm, edited 1 time in total.
slowster
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Re: Front rack difficulties - any advice?

Post by slowster »

Insert the skewer from the drive side instead?
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531colin
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Re: Front rack difficulties - any advice?

Post by 531colin »

Not what you asked, but I don't like sharing a carrier fixing with a plastic (squishy) mudguard release.
i would make up a set of stays to fit to the carrier with a P clip.....10mm stainless P clips available from westfield fasteners
roubaixtuesday
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Re: Front rack difficulties - any advice?

Post by roubaixtuesday »

531colin wrote: 6 Feb 2023, 9:39pm Not what you asked, but I don't like sharing a carrier fixing with a plastic (squishy) mudguard release.
Why not? The carrier attachment is inboard of the mudguard release, mounted directly against the braze on.

I don't understand why this is a problem.
gregoryoftours
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Re: Front rack difficulties - any advice?

Post by gregoryoftours »

Double post
Last edited by gregoryoftours on 6 Feb 2023, 11:04pm, edited 1 time in total.
gregoryoftours
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Re: Front rack difficulties - any advice?

Post by gregoryoftours »

roubaixtuesday wrote: 6 Feb 2023, 9:45pm
531colin wrote: 6 Feb 2023, 9:39pm Not what you asked, but I don't like sharing a carrier fixing with a plastic (squishy) mudguard release.
Why not? The carrier attachment is inboard of the mudguard release, mounted directly against the braze on.

I don't understand why this is a problem.
Because the plastic is somewhere in the equation between the bolt head and the braze on, the rack can only be clamped with as much force as the plastic can withstand without deforming, i.e not a lot. This means that there is not a whole lot of friction keeping the rack in place when loaded. This will put a lot of shear stress on the mounting bolt when the rack is carrying weight. It would be even worse if the mudguard mount was between the rack and the braze on. Better to fit a slightly longer bolt from the inside of the fork, then the rack onto the bolt, then a washer and a nut clamping them together properly tight. Then on top of that the plastic mudguard mount and finally another washer and nut to hold the mudguard mount in place on the bolt. This means that the squishy plastic does not dictate the limit of how tight the bolt securing the rack can be.

I'd say that an Allen skewer is probably the way to go for your front wheel, presuming that you'd have the same problem on the other side if you reversed the skewer.

The rack does actually look like it's pointing up a little - would it be possible to mount the rack on the lower hole (mudguard mounts can stay on the existing hole) and rotate the upper disc mount (and use the hole that's closer to the disc edge) that the rack can be mounted close to level? If so it would solve the problem as it looks like the qr would just about have clearance using the lower mounting hole at the fork dropout.
slowster
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Re: Front rack difficulties - any advice?

Post by slowster »

Regarding the mudguard plastic safety release fastening, would there be enough space to fit it to the rack using the rearmost unused mounting hole of the rack's three mid-fork mount holes? It looks like it might foul against the rear of the fork blade, but maybe not.
roubaixtuesday
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Re: Front rack difficulties - any advice?

Post by roubaixtuesday »

gregoryoftours wrote: 6 Feb 2023, 10:58pm
roubaixtuesday wrote: 6 Feb 2023, 9:45pm
531colin wrote: 6 Feb 2023, 9:39pm Not what you asked, but I don't like sharing a carrier fixing with a plastic (squishy) mudguard release.
Why not? The carrier attachment is inboard of the mudguard release, mounted directly against the braze on.

I don't understand why this is a problem.
Because the plastic is somewhere in the equation between the bolt head and the braze on, the rack can only be clamped with as much force as the plastic can withstand without deforming, i.e not a lot. This means that there is not a whole lot of friction keeping the rack in place when loaded. This will put a lot of shear stress on the mounting bolt when the rack is carrying weight. It would be even worse if the mudguard mount was between the rack and the braze on. Better to fit a slightly longer bolt from the inside of the fork, then the rack onto the bolt, then a washer and a nut clamping them together properly tight. Then on top of that the plastic mudguard mount and finally another washer and nut to hold the mudguard mount in place on the bolt. This means that the squishy plastic does not dictate the limit of how tight the bolt securing the rack can be.

I'd say that an Allen skewer is probably the way to go for your front wheel, presuming that you'd have the same problem on the other side if you reversed the skewer.

The rack does actually look like it's pointing up a little - would it be possible to mount the rack on the lower hole (mudguard mounts can stay on the existing hole) and rotate the upper disc mount (and use the hole that's closer to the disc edge) that the rack can be mounted close to level? If so it would solve the problem as it looks like the qr would just about have clearance using the lower mounting hole at the fork dropout.
re top emboldened bit - how can it make any difference to shear stress? The fixing is directly butting the braze on. Unless the bolt comes loose there cannot be any difference in shear stress (though actually I think you mean bending moment?). And if anything, the plastic fixing makes it coming loose less likely imo - though the loctite on the bolt makes that really very unlikely anyway.

Re the bottom, unfortunately not, the top fixing is too high if the bottom hole is used.
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andrew_s
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Re: Front rack difficulties - any advice?

Post by andrew_s »

gregoryoftours wrote: 6 Feb 2023, 10:58pmBetter to fit a slightly longer bolt from the inside of the fork, then the rack onto the bolt, then a washer and a nut clamping them together properly tight. Then on top of that the plastic mudguard mount and finally another washer and nut to hold the mudguard mount in place on the bolt.
Don't forget that the end of the bolt must remain clear of the pannier. If it touches, you'll end up with a hole in the back of the pannier.
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foxyrider
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Re: Front rack difficulties - any advice?

Post by foxyrider »

I've got similar issues re qr when i fit my low rider to either of the suitable bikes i have, simple solution was to use some form of non qr retention system, oringinally pit locks bur latterly USE with either star or hex drive heads. Of course it takes slightly longer to remove the wheels but when you're unloading bags etc anyway, a few seconds is neither here nor there plus its a nod towards security from opportunist wheel thieves.
Convention? what's that then?
Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!
gregoryoftours
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Re: Front rack difficulties - any advice?

Post by gregoryoftours »

andrew_s wrote: 7 Feb 2023, 7:19am Don't forget that the end of the bolt must remain clear of the pannier. If it touches, you'll end up with a hole in the back of the pannier.
Oh yes, that's pretty important.
gregoryoftours
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Re: Front rack difficulties - any advice?

Post by gregoryoftours »

roubaixtuesday wrote: 7 Feb 2023, 7:11am re top emboldened bit - how can it make any difference to shear stress? The fixing is directly butting the braze on. Unless the bolt comes loose there cannot be any difference in shear stress (though actually I think you mean bending moment?). And if anything, the plastic fixing makes it coming loose less likely imo - though the loctite on the bolt makes that really very unlikely anyway.
The plastic in the assembly is the weakest link. Even though it's not located between the rack and the dropout, It nevertheless limits how tight the bolt can be torqued to clamp the rack to the dropout, because they are all sharing the same clamping force of the bolt. Either immediately or over time the plastic may deform or crack at the torque needed to reliably secure the rack to the dropout. I'd say this is quite a high likelihood.

If the bolt isn't tight enough to clamp the rack and the dropout
adequately, the friction between the two surfaces can be overcome and they'll tend to slide against each other when the rack is loaded up/going over bumps etc. At this point the bolt will be under shear stress. It might look to be holding ok but it's likely that the assembly isn't tight enough not to put shear stress on the bolt through slippage.
Last edited by gregoryoftours on 7 Feb 2023, 7:25pm, edited 2 times in total.
roubaixtuesday
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Re: Front rack difficulties - any advice?

Post by roubaixtuesday »

gregoryoftours wrote: 7 Feb 2023, 7:16pm
roubaixtuesday wrote: 7 Feb 2023, 7:11am re top emboldened bit - how can it make any difference to shear stress? The fixing is directly butting the braze on. Unless the bolt comes loose there cannot be any difference in shear stress (though actually I think you mean bending moment?). And if anything, the plastic fixing makes it coming loose less likely imo - though the loctite on the bolt makes that really very unlikely anyway.
The plastic in the assembly is the weakest link. It limits how tight the bolt can be torqued to clamp the rack to the dropout, because the plastic will deform or crack at the torque needed to reliably secure the rack to the dropout.

If the bolt isn't tight enough to clamp the rack and the dropout
adequately, the friction between the two surfaces can be overcome and they'll tend to slide against each other when the rack is loaded up/going over bumps etc. At this point the bolt will be under shear stress. It might look to be holding ok but it's likely that the assembly isn't tight enough not to put shear stress on the bolt through slippage.
Ah, so you're arguing that the vertical load is transferred through friction, and the bolt isn't designed to take the vertical load at all?

I can see the argument, but are you sure? I'm pretty confident the bolt is there to take the load, and the clamping force only has to be sufficient to prevent movement?
gregoryoftours
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Re: Front rack difficulties - any advice?

Post by gregoryoftours »

roubaixtuesday wrote: 7 Feb 2023, 7:23pm
gregoryoftours wrote: 7 Feb 2023, 7:16pm
roubaixtuesday wrote: 7 Feb 2023, 7:11am re top emboldened bit - how can it make any difference to shear stress? The fixing is directly butting the braze on. Unless the bolt comes loose there cannot be any difference in shear stress (though actually I think you mean bending moment?). And if anything, the plastic fixing makes it coming loose less likely imo - though the loctite on the bolt makes that really very unlikely anyway.
The plastic in the assembly is the weakest link. It limits how tight the bolt can be torqued to clamp the rack to the dropout, because the plastic will deform or crack at the torque needed to reliably secure the rack to the dropout.

If the bolt isn't tight enough to clamp the rack and the dropout
adequately, the friction between the two surfaces can be overcome and they'll tend to slide against each other when the rack is loaded up/going over bumps etc. At this point the bolt will be under shear stress. It might look to be holding ok but it's likely that the assembly isn't tight enough not to put shear stress on the bolt through slippage.
Ah, so you're arguing that the vertical load is transferred through friction, and the bolt isn't designed to take the vertical load at all?

I can see the argument, but are you sure? I'm pretty confident the bolt is there to take the load, and the clamping force only has to be sufficient to prevent movement?
Yes that's what I think, especially with such a small bolt friction between the surfaces should take the load or as much of it as possible, while the bolt is under tensile stress or force which is what clamps the surfaces together to create the friction. Until there is slippage I don't think that the bolt is taking much bending/shear load. Where the surfaces that are being clamped are small or don't provide much friction then the bolt is taking the shear/bending load, but I think that this is to be avoided as much as possible.
Last edited by gregoryoftours on 7 Feb 2023, 7:41pm, edited 1 time in total.
nigelnightmare
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Re: Front rack difficulties - any advice?

Post by nigelnightmare »

The problem is caused be the forks.
They're straight! The rack was designed for forks with the curve at the bottom.
I had the same problem once and the allen bolt skewer solved it.
Also don't mount it to the same fixing as the mudguard fixing, IT WILL COME LOOSE! & if something jams the front wheel you WILL come off the bike.
DAHIK :roll:
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