pillows_

I have an aluminum alloy frame without eyelets for a bike rack. Is it a good idea to use one of those racks that clamps to the seat post and seat stays? Im looking to haul 10-20 lbs on groceries regularly and concerned I might damage the seat stays

PaulRivers

Hauling groceries is pretty intense work for a bike rack, totally fine on a regular rack but no way would I try to do it with one of those seatpost-mount racks. Groceries would be way over their weight limit.

There are ways to get a rack on your bike though.

Here's one example, the Axiom Streamliner, it attaches at the bottom to by the wheel quick release:
https://www.amazon.com/Axiom-Streaml...dp/B004094HY2/

For the top mounting point I'd use a rack seatpost collar similar to this:
https://www.amazon.com/Axiom-Trekk-C...dp/B0025UQ3I6/

I know there are other racks designed for a bike without mounts as well, they all use similar designs to this one to get mounted to the bike. The only drawback is it's more hassle to fix a flat on the rear tire as you have to take both the rack and the wheel tire of, rather than just the rear tire.

pillows_

Oh thats right! I've seen ones like that in the past but completely forgot they existed.

As for the top mounting, these should be good right?

indyfabz

That's what they are there for.

rumrunn6

& for the bottom you can use rubber lined compression clamps instead of the skewer type

https://velo-orange.com/products/p-c...der-attachment

that's what I use on one of my bikes. I don't carry groceries, just way too much stuff anyway

PaulRivers

Note that the description says they're meant for fenders - not racks..it's not going to have the same ability to handle weight like the skewer type does.

rumrunn6

ah, gotcha. funny a bike co. would provide those mounting holes up top, but not down below

but wutz the difference mounting a rack on a bolt in the dropout vs a bolt on a p-clamp. I really can't see the bolt in the dropout being any stronger. I must be missing something

base2 

cuz peeclampz aint that strong, yo.

autonomy

Second this post. I own both of the items mentioned and can recommend both. The Streamliner comes with a metal bracket which will also mount to the central brake mount bolt (it might also come with a couple P-clamps, I don't quite remember). I used to commute with it on a road bike, frequently loading both panniers. I've also hauled things like a gallon of milk, a sixpack of beer, or 2 bottles of wine in a single pannier using this rack (not all at the same time).
I used the seat post collar on a bike on which I stripped one of the rack eyelets. I used it to mount a rack and a kid seat. Worked just fine.

PaulRivers

The way bolts work is complicated, and involves putting pressure on 2 other pieces so those 2 pieces bear the weight, not the bolt. Used as fasteners, bolts can hold a lot more weight than they could if all the weight was applied to the bolt sticking out by itself. P-clamps don't work the same way they bear all of the weight themselves. P-clamps would need to be a lot stronger than a fastener bolt would be to bear the weight.

You also have an issue of putting weight on the rear seat stays in a way they weren't designed to handle. Seat stays are thin. They're designed to handle weight coming down from the seat in a certain direction, if you attach a rack with clamps rather than applying force where the seat stay is the strongest (between the seat and the wheel) you're throwing weight at it from a totally different angle where it's much much weaker. Just look at how thin a typical seat stay is - it's not designed to have 50 pounds bouncing up and down pushing down onto it any direction other than coming from the seat.

In contrast the rear dropout is designed to have about half the riders weight (min: 100lbs) push down on it, and push down on it hard - bouncing, hit bumps, getting on and off the saddle, etc. The weight from the rack should act exactly like your bodyweight does...the bike is designed and engineered to handle a substantial amount of weight at the bottom bracket pushing, bouncing, etc.

If you have aluminum seat stays and you're just carrying like a rain jacket and a pair of gloves I wouldn't worry about it. But once you're carrying groceries, you could be carrying 2 gallons of water and a gallon of milk home, that's getting to be a lot of weight. The bottom bracket can handle it fine (it's designed to handle a large portion of your bodyweight) but a cheap p-clamp is not and a rear seatstay is not designed to handle that kind of weight from an odd angle either.

Like here's a race bike, look how skinny the seat stay tube is compared to any of the other tubes on the frame:


Now contrast this with a mountain bike rear seat stay that's designed to handle some weight, bumps, etc:


And then you're also exerting weight on the frame at a weird angle it's not designed for..it's just a bad idea. In contrast if your rack attaches via the rear dropout, it's putting weight on the bike in the same way the rider is so it's basically like you gained the weight yourself on your body.

That rambled on a lot, I'm not sure if my point is clear from all of that, lol, sorry for the wall of text...

fietsbob

Groceries, ? Consider an Extra Wheel trailer It uses a QR skewer mount & tow fork,

Somewhat like the BoB trailer, but its using a 2nd big front wheel like the bike uses,
and has racks for the Panniers on It..

I use My Touring bike Grocery getting .. Pop off the panniers and store check-out fills them ,
and I put them back on.. the bike, in the bike rack, it all works well ..

It worked better when Safeway was Still giving a nickel off the bill, credit,
for every carryout bag I did Not Need to use.


there are racks using the Axle QR, for the bottom mount..

from many companies..




...

rumrunn6

still don't get why a bike co. would supply bolt holes up top but not down below unless it's because they require us to use a skewer mount rack specifically. that must be it?

prathmann

I don't think you're missing anything. P-clips supporting a rack would be mounted down low on the seat stays where they are quite strong. I've used a child seat that was made to mount in that way without any problems and have toured with others who had their camping loads supported with such P-clips. Never seen any damage to the seat stays as a result.

indyfabz

Not all p-clamps are made the same, yo. This front rack is attached up top with p-clamps, and that was not the first (or last) time I carried a bundle of firewood.

dedhed

Over thinking. P clamps are fine. Get the size so that it is a tight fit to the stay.

MikeyMK

You want a seat-post mounted rack that also has reinforcement legs to bolt to your seat stays. Plenty of these on eBay, and they're cheap. The legs are best bolting to your dropouts though, if you're prepared to adapt them or likewise.

PaulRivers

It's...like you put all of internet arguing techniques in one post:

1. Emotional: Trigger emotional reactions by putting a small child in what may or may not be a dangerous situation. Effect: Some people will get very emotional at what may or may not be putting a child in a dangerous situation, you'll get emotional because you did it and need to defend it, endless flame war once someone wades into it.

2. There's a wide variety of bikes, an argument is sparked off that's basically one poster thinking of heavier bikes with thick seat stays while another thinks of lightweight road bikes with thin seat stays, the argument goes back and forth forever as at least 2 people argue over 2 different scenarios as if they're the same.

3. Situation where you often wouldn't find out if things went wrong, presented as proof that it worked fine. "I've never looked for damage, and had someone's seat stays had issues the person would leave the ride and I probably wouldn't hear about it...".

4. Say "P-clips supporting a rack would be mounted down low on the seat stays where they are quite strong" when you don't know where they will be mounted as it depends on the both the rack and the person installing them.

I'm not going to wade into one of these long and pointless internet arguing things...I tried to stop doing that after like, the 100th one I waded into, lol.

I personally think putting the weight on the seat stay in a way it's not designed to handle is a bad idea, though you could argue it depends on how sturdy the seat stay is, which varies from one bike to the next.

They sell racks that are well designed to go onto bikes without rack mounts that attach in ways that put weight on the bike where the frame is designed to take it. Going with p-clips which are both more hassle and more risk seems like a bad idea when an option is available that's both safer and easier.

steve0257

Try the plumbing section at your local hardware store. That's where I've picked up p-clips whenever I've needed them.

cyccommute 

MikeyMK

I'd rather use cable cleats than P-clips, as you won't damage the paint, and they're stiffer because they clamp all the way around the tube.

rumrunn6

oh yeah I remember seeing those. gosh I always get reminded of those AFTER I set up a new rack, ugh. those ARE sweet. I should take some measurements & slowly replace mine. do you know of any big enough for a front shock? (35mm) not that I need strength cuz my front fender stays get little to no stress. I couldn't find any p-clips at my hardware store & had to make my own w strapping

rumrunn6

oh. wonder how large they make them interesting

cyccommute 

The largest diameter is 24mm. You might be able to use spacers make them fit but it would be difficult.

On the other hand, if the load is light, you can get 32mm reflector mounts. You couldn't carry 30 lb loads but it could work for 10 to 15 lb.

dedhed

If you don't find them there they are in electrical

MikeyMK

I have 38mm P-clips but size 16 cable cleats are far better (Rockshox legs).