Chromoly vs aluminum rear rack for battery packs?

alpharalpha

100 W
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Which is the better choice? Aluminum is rigid, strong and light but if it does crack it breaks while chromoly is heavier and maybe not as strong but it could bend and not break. I'm looking to upgrade my rear rack, I've never been comfortable using the stock blackburn mtn with my heavy battery pack. If you've got some under $100 suggestions on racks to consider that'd be great too.
 
Depends on the weight you will carry, and how rough the ride is.

The best rack is steel welded to the frame IMO, but that does not mean you cannot use alu. Look for alu racks specifically designed for cargo panniers for the strong ones. The typical Blackburn rack is fine for up to 15 pounds of battery, but if you want to put 15 pounds of battery in each pannier, it needs to be better for sure.

Don't carry 20 pounds of battery on top of a rear rack, at all, unless it is a cargo bike with a rack your girl can ride on.

If you are not worried about the looks, you can make a very strong rack with a seatpost type rack. Add home made legs to it with some kind of sturdy metal. 1/2 inch electric conduit for one example, bolting them to the beam on the rack.

Look for this type seatpost rack, with 2 or 4 bolts to attach to the seat post. not the one with a quick release lever.

https://www.walmart.com/ip/Bicycle-Bike-Alloy-Seatpost-Mount-Rear-Rack-Carrier/111640752
 
have you ever broken one?

I have had seat post attachment racks brake, but not the 4 point attachment racks. You can't accurately say steel is stronger than aluminum. It will bend more before it breaks than aluminum. If you are concerned about cracking/breaking - go for steel.
 
I had a topeak aluminium for years. I tried to load it under the top weight recommended and paíd special attention at bumps. I read people claiming to have broken the same rack I used within a week. Judging their comments I can assure they were really careless.
The metal is important, the quality of the welds and therefore the brand is also very important but do not forget about how you use it. That's crucial too.
 
rojitor said:
I had a topeak aluminium for years. I tried to load it under the top weight recommended and paíd special attention at bumps. I read people claiming to have broken the same rack I used within a week. Judging their comments I can assure they were really careless.
The metal is important, the quality of the welds and therefore the brand is also very important but do not forget about how you use it. That's crucial too.

Yes. I have a Topeak on my gravel grinder and just bought another for my e bike. It's rated for 55 pounds, as long as it's secured to the bike properly I don't see how there would be issues with any battery. I've had it loaded with maybe 25-30 lbs and tore down rutted gravel roads at 30 mph and the thing has stayed strong.
 
I never actually broke a rack. I have broke the seatpost from a rack, off road riding which is by definition careless. This is how I learned to brace up a seatpost rack.

But I have come to prefer some racks over others because they sway when loaded at or near capacity. This makes the tail wag the dog when you ride loaded with cargo or batteries for a 60-100 mile day.

Topeak yes, Axiom yes. The ubiquitous Blackburn, not for 50 pounds. The mount at the front is not stiff enough IMO. Fine for 20 pounds panniers, 10-15 pounds top.
 
alpharalpha said:
What type of Topeak rack do you have?
I do not have it anymore. I sold that bike time ago. I think it was this one:
http://www.chainreactioncycles.com/es/es/soporte-portaequipaje-tipo-vtopeak-mtx/rp-prod28820
The new owner of my ride still uses it. Still in good shape.
16m1thv.jpg
 
I would make the seatpost rack type but I don't have the room; I like a large frame bike so the seatpost is pretty far down, just enough room for the little shock it has. When you guys are talking about these different brands of racks are you referring to seatpost types only (I see the topeak pic is a seatpost type) because my mounts in front are like thisIMG_0087.JPG I have the battery pack on top of the rack, but it's a Trek Interchange Bontrager rackView attachment 1 I found these pics online, don't think they make it anymore, had them put it on when I bought the bike back in 2006, the listing with these pics state it's rated at 50 lbs, don't know but one of what I consider a weak point is this adjustable part down by the eyelettrek interchange bontrager2.jpg
 
It's a little expensive, but I haven't seen anything better than the Surly Nice Rack. It's Surly CroMoly and seems very tough -- advertised weight limit is 80 pounds. It's also a little on the heavy side, 1260 grams (over 2 1/2 pounds).

But if I ever go on a long trip, I will know I can count on it.
 
Aluminium suffers from metal fatigue. Most racks have bad design, so metal fatigue will be an issue sooner or later. With good design, they could be a lot more robust. The rack in the pictur above isn't too bad. They should have made the front strut like the rear one though. Beat would be to make each side in a complete loop without welds, then weld the platform on top. I've peronally had a few aluminium racks break.

Seatpost racks can be improved a lot by adding struts to stop tne bending loads. You can get steel seatpost racks as well that are much more resistant to fatigue failure.
 
I'd definitely go with the seatpost rack with added stuts but as you can see in the picture I don't have space for a seatpost rack to attach toIMG_0090.JPG That Surly Nice Rack is great, as are the Tubus racks, but too expensive. I haven't found a chromoly rack under $140.
 
Build a chromo rack yourself, whether you got a welder or not. Splurge on some metal epoxy, and bolts and hit up the metal store.
 
I've been using one of these for a couple of years now

https://www.filzer.com/products/pr-4-pannier-rack/#details

It carried my 16S A123 pack in a steel ammo box (probably a touch over 20 lbs) until recently, along with a pair of big panniers I use for getting groceries and stuff. In addition to that I've put a full 25lb propane cylinder on top of the battery box on more than one occasion, and rode the whole lot (camping gear included) down a bumpy gravel road to a camp site.

The whole rig has been airborne more times than I care to admit.

Last winter I hit a snow covered pothole at about 25mph while carrying the panniers full of food and the A123 battery, hit hard enough to dent both flanges of the rim and pull a couple of spokes out, and the rack is still fine. I replaced the mounting screws that time, just didn't have a good feeling about it. But I inspected the crap out of the rack and saw no damage, and it's still in service.

It's rated for 50lbs I think, but I've easily done 75+ on it, pretty impressive for something that maybe weighs 3lbs, I'd say closer to 2.

Anyways, highly recommend.
 
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