BackLoader X 15L
Where to Buy
How much room does it need?
This pack measures 51cm long and 24cm deep. Length is how far it reaches behind your saddle, and it's what drives sway — a long pack is a longer lever on the seatpost. Depth is what competes with your rear tire once the pack sags under load.
Across the 17 seat packs we hold dimensions for — which run from 31.8cm to 67cm — this one reaches further back than 12 of them, and hangs deeper than 14.
The other number that decides this — how much seatpost you have showing above the collar — depends on your leg length rather than your frame, and makers almost never publish a minimum. So measure from the top of your seat collar to the bottom of your saddle rails, then check it against the mounting hardware on the product page. If you run a dropper post, look for a pack that mounts to the saddle rails alone.
Check against your measurementsTopeak BackLoader X 15L— Specs & Analysis
Manufacturer specifications, compared against every other seat bags in our database. We do not test gear in the field — we measure, verify, and compare.
The same 15 liters as the standard BackLoader packed into 51cm instead of 67cm, by going fatter — 22cm wide against 18cm. If the regular BackLoader is too long for your frame, this is the answer to that exact problem.
This is a genuinely clever bit of packaging. Topeak took the 15-liter BackLoader, cut 16cm off the length and put the volume back in as width, and the result is a big pack that fits bikes the long one won't.
The numbers: 51 x 24 x 22cm. That 51cm length sits just above the 48cm median for seat packs in our database, so it fits like a normal pack. The 22cm width is joint-widest among the seat packs we hold dimensions for, tied with the Ortlieb Seat-Pack QR 7.5L — the field median is 16cm.
Width has its own consequences. A wide pack catches more wind, and on a narrow trail it's a slightly bigger target for brush. But a short pack sways less than a long one at the same volume, because the load sits closer to the seatpost. For most riders that trade is worth taking.
The X uses a holster design rather than a strap-only mount — hook-and-loop and buckle fasteners hold a carry bag in a support structure. That's more hardware and it shows in the weight: 605g, 40g more than the standard BackLoader, and heavier than most 15L packs. The payoff is that the load is supported rather than hanging.
Water-repellent outer, 10,000mm waterproof carry bag inside.
Who Is the Topeak BackLoader X 15L Best For?
Riders who want 15L but don't have the seatpost or tire clearance for a 67cm pack. If that describes your riding style, the BackLoader X 15L should be at the top of your shortlist. It sits in the Seat Bags category alongside 17other products we've reviewed.
How It Compares
At 605g and $130, the BackLoader X 15L is 463g heavier than the lightest option in this category (the Revelate Designs ECOPAK Shrew Seat Bag at 142g). The most budget-friendly option is the Topeak BackLoader 10L at $70.
The price-to-weight ratio comes in at $21 per 100g — a reasonable middle ground between performance and value.
What We Like
- +15L in only 51cm — fits frames the standard BackLoader won't
- +Holster mount supports the load instead of letting it hang
- +10,000mm waterproof inner carry bag
Watch Out For
- −22cm wide — joint-widest seat pack in our database
- −605g is heavy even for 15L
- −More hardware means more to go wrong
The Bottom Line
We haven't scored the Topeak BackLoader X 15Lyet. It's here for its verified specifications and dimensions, which is what the fit tools run on — a score is an editorial judgement and we don't hand one out until someone has a basis for it.
Specifications and dimensions come from the sources listed above. Where a page draws on first-hand riding, it says so.
How it compares
Against the 18 seat bags we hold published specs for.
At 605g the BackLoader X 15L is lighter than 1 of 17 alternatives we track, which makes it among the heaviest we track. The category median is 428g.
At $130 it undercuts 12 of 17 of them, against a median of $158. That works out at $21 per 100g — below the $39 median for seat bags.
Weight and price come from published specifications. Cost per 100g is a blunt measure — it rewards light gear and says nothing about durability or whether the thing works — so treat it as one input, not a verdict.
More in Seat Bags
Seat bags extend behind the saddle, carrying gear without the need for a rear rack.