Why are bike rear rack weight limits so low?

[sdtr443w]

Consider the two racks in this picture.

The one on the right came with my Bolton Foxbat. Weight limit: 25kg/55lbs.
The one on the left is an Axiom Fatliner. Weight limit: 110lbs. Also, it doesn't actually fit on my bike and the hardware for the rear axle shims sheared while taking them off. So it's going back.

Just looking at these, I would think the one on the right is the chonky thing that'll hold anything. I just realized that I've picked the rear end of the bike up from the rack just fine and probably instantly violated the weight limit in the reverse direction. No problems. Is there a major variation in the metals used? Is the Axiom made from forged fairy moonbeam ingots while these default ones are made from compressed Chinese melamine?

Going into other bikes: I tried an Evelo Aurora Limited. Its rear rack is integrated into the frame. You couldn't replace it if you wanted to. Weight limit? 45 pounds. While looking at other bikes, I was looking at the Dost ones with the integrated rack. Those have a 100 pound limit, which seems more reasonable to me.

Some other things I considered:
1. I figured the actual weak points are the bolts. The fittings look identical. I don't think the Axiom is using, say, grade 9 fittings--or really any other kind of fitting different than the one of the right. I wouldn't be surprised if they came off the same assembly line.
2. The shims. The Axiom shim is something like half as thick as the ones on the right. It doesn't look that way in the picture.

So what's up with this? I have some gigantic Ortlieb panniers coming in soon and I'm hoping to just mount them on the ones on the right and load them suckers up at the supermarket. It won't be 110 pounds but with a few 12 packs of cans and some milk, I've exceeded 75 pounds of stuff before.

 

[jim6b]

Do you think it matters that Bolton, the bike manufacturer, is saying it is okay for the rack AND the bike?
Whereas a rack maker is only concerned with the rack and perhaps knows that to sell aftermarket racks he needs to have a high weight guarantee.

 

[Sierratim]

Specialized provides Racmtime tacks on kost of their Vado series ebikes. The racks have a higher rating than Specialized publishes. They explain this by referencing balance, braking power, frame strength, etc. So in this instance a higher rated rack won't help, the ebike manufacturer limits the cargo load.

There are of course racks that can handle high loads. They need to be paired with a bike that has equal capabilitieis.

 

[Nova Haibike]

I know that the rack manufacturer Tubus intentionally limits the weight capacity 26 kg. to prevent their racks from being automatically approved for use as a mount for a child seat: "ISO 11243:2016 requires that all luggage carriers with a carrying capacity of 27 kg or more automatically be approved for the attachment of child seats, too." But they test some of their racks up to a load of 40 kg.

 

[sed6]

I know that the rack manufacturer Tubus intentionally limits the weight capacity 26 kg. to prevent their racks from being automatically approved for use as a mount for a child seat: "ISO 11243:2016 requires that all luggage carriers with a carrying capacity of 27 kg or more automatically be approved for the attachment of child seats, too." But they test some of their racks up to a load of 40 kg.

This must be it, or some version there of. It regulation and lawyers. Can't go over 28 mph and cant load more 55 lbs on the rack, because you're stupid, and we're the government and we know what's best for you!

 

[sdtr443w]

That child seat thing has the right sound to it.

 

[Ready]

Other things to consider:

1. Rack as an extension to the bike. It's not how much it can carry but how it can affect the dynamic of the bike. It can affect the balance of the bike greatly-to a point where it might do a wheelie if you hit bump. Can the rear wheel handle the weight? Suspension? Brakes?
2. The low weight limit is to protect against extreme dynamic load. 25kg at rest is very different then if you hit a bump or a jump (look up dynamic load vs. static load).
3. The parts the rack connect to may be not be designed to handle the load. The weight be be straight down when things are going straight, but when you turn, torsional shear stress is introduced.

There are just so many variables to consider.

 

[Brian10956]

Like everything else these days they are afraid of the lawyers goin after them when someone has a 51 lb. load on a 50 lb. rack and has an accident. You see videos of a farmer in Asia riding his bike with 300lbs of cargo and it’s working fine

 

[rich c]

Like everything else these days they are afraid of the lawyers goin after them when someone has a 51 lb. load on a 50 lb. rack and has an accident. You see videos of a farmer in Asia riding his bike with 300lbs of cargo and it’s working fine
View attachment 70137

That is a trike and it would be odd to have a rack over the cargo bin. Must be really heavy styrofoam to equal 300 pounds.

 

[Brian10956]

I didn’t notice that it had that 3rd wheel at first. But here is another picture.

I know this doesn’t look like styrofoam

 

[kurt_s]

I have an Old Man Mountain which bolts to the through axel. Listed spec is 70 lbs which is 31.75 kg. Made in Oregon so either they did not get the baby carrier memo or are playing it fast and loose with 11 lbs. But they again 11 lbs is quite a bit of gear.

I put more grocery trip weight than camping gear I reckon. When I am loaded with groceries; think beer, I worry more about the rear wheel than the rack.

 

[Explorer-1]

Broken bolts can definitely happen, but the general reason must be more involved. Some of the Disc-Brake compatible ones are designed such that there is a lot of leverage on the bolts so it's probably a complex thing and maybe some designs just are not tested to maximum. I would not doubt in some cases there are regulation issues involved as mentioned above.

 

[Terry777]

I have the one on the right on my bike. I don't know what weight it is safe for carrying but it makes a rare wee handle for hauling the bikes heavy as hell ar5e end around while wrestling it out my flat!

 

[sc00ter]

On my motor scooters 3 things come into play for weight limits. 1: When the rack breaks from to much weight. It always destroys something else when it fails. 2: When the rack actually breaks off the mounting points! You suddenly become very creative in rigging stuff or face a large specialist repair bill. 3: When you have the rack overloaded and hit the perfect bump at speed, or just as bad doing a slow turn. You get a quick physics lesson that usually ends with you on the ground. I guess a 4th issue would be if you had a baby seat on the back and something failed. That would be super horrible! I try to follow the weight limits because I've personally experienced the first 3! But racks make riding so much better.

 

[kmccune]

I have an Old Man Mountain which bolts to the through axel. Listed spec is 70 lbs which is 31.75 kg. Made in Oregon so either they did not get the baby carrier memo or are playing it fast and loose with 11 lbs. But they again 11 lbs is quite a bit of gear.

I put more grocery trip weight than camping gear I reckon. When I am loaded with groceries; think beer, I worry more about the rear wheel than the rack.

Right ! You have to consider whats holding up the load.Some of these Bicycle wheels look awful spindly.The Emotorcycle wheels look a whole lot better than the Bicycle wheels.'
Get a "cargo" bike if you want to haul a lot of weight,Tern, etc. Consider CYA also as a safety device, These "Bikes" in the pictures are not supporting a lot of weight, on the other hand the trike with the styrofoam boxes would tip in a strong breeze, the empty cooking oil cans are not extremely heavy either.

 

[Kayakguy]

Right ! You have to consider whats holding up the load.Some of these Bicycle wheels look awful spindly.The Emotorcycle wheels look a whole lot better than the Bicycle wheels.'
Get a "cargo" bike if you want to haul a lot of weight,Tern, etc. Consider CYA also as a safety device, These "Bikes" in the pictures are not supporting a lot of weight, on the other hand the trike with the styrofoam boxes would tip in a strong breeze, the empty cooking oil cans are not extremely heavy either.

The beefier looking rack on the right likely is make with hollow aluminum tubing, so it may not be as strong as it looks. The one on the left appears to be solid aluminum rod, rather than tubing (can't tell for sure). My Ariel Rider C-class has a built-in rack, with thick tubing. It is rated at 60 lbs, and Ariel specifies that it can carry a child's seat.

 

[Asher]

If you're selling a third party single item product, then there's much more incentive to give an optimistic figure. (Others have said the converse about manufacturers, esp. wrt warranties.)

Ebike manufacturers of course are happy to inflate range estimates.

I had an Axiom rack, and it was fine, but I don't think it was much different than other racks such that it should have wildly higher capacity, unless it's markedly heavier.

 

[john peck]

Like everything else these days they are afraid of the lawyers goin after them when someone has a 51 lb. load on a 50 lb. rack and has an accident. You see videos of a farmer in Asia riding his bike with 300lbs of cargo and it’s working fine
View attachment 70137

I´d love to see a video of that guy loading up, musta bin like genga on steroids

 

[FlatSix911]

I know that the rack manufacturer Tubus intentionally limits the weight capacity 26 kg. to prevent their racks from being automatically approved for use as a mount for a child seat:
"ISO 11243:2016 requires that all luggage carriers with a carrying capacity of 27 kg or more automatically be approved for the attachment of child seats, too." But they test some of their racks up to a load of 40 kg.

This is the correct answer.

Tubus has artificially limited the rated capacity to reduce their liability with child seats. The actual capacity is much higher and listed in parentheses for each rack.

This must be it, or some version there of. It regulation and lawyers. Can't go over 28 mph and cant load more 55 lbs on the rack, because you're stupid, and we're the government and we know what's best for you!

Company - Tubus

* ISO 11243:2016 requires that all luggage carriers with a carrying capacity of 27 kg or more automatically be approved for the attachment of child seats, too. In our opinion, transporting children on luggage carriers is dangerous, so we voluntarily restrict the carrying capacity of tubus luggage carriers to max. 26 kg, thus excluding the attachment of child seats and/or the transport of children on our carriers.
This restriction has only the legal reasons mentioned above. tubus carriers are still tested with considerably higher luggage loads (which are specified for each product in brackets).

 

[PatriciaK]

My mechanical engineer spouse says most major-brand hitch-type bike carriers are over engineered.