Merit Jumbo, a Big-Wheel 750d Carbon Gravel Bike You Didn’t Know You Needed: First Rides

This carbon Merit Jumbo is the first production gravel bike to embrace 750d wheels, and we got an exclusive chance to be the first to test-ride it. Yes, this is a new wheel size. Yes, the tire and wheel options are still quite limited. But especially for taller riders, 750d could make some sense. So we wanted to give it a closer look…

Merit Jumbo 750d big-wheeled carbon gravel bike

The driving factor of an all-new wheel size is tire and rim availability. WTB set this ball in motion when they rolled out their prototype 750d x 40mm Nano last summer before the MADE show, with alloy i25 750d wheels to match. Then at MADE, we got a closer look at the custom titanium Moots CRDD gravel bike that showcased the new wheel size. But 750d hasn’t quite taken the world by storm just yet, and that CRDD still hasn’t made it into the official production line-up in Steamboat.

Still, WTB has added a fast-rolling Byway 750d semi-slick now, too.

Bigger wheels mean better rolling over rough terrain, the ability to run lower tire pressure, and thus improved grip. We all know how 29″ wheels were a game-changer that made 26″ obsolete. (And WTB was the first to make a 29er production tire, a Nano too!) And for a gravel bike that also just means smoother riding over those same washboard gravel roads. Plus, for longer-distance riding, those larger diameter (and thus heavier) wheels should help maintain momentum, too.

But the other real big benefit here is a better fit for bigger riders. And not only because it looks more proportional.

And Merit has you covered now!

Geometry, not so different than we’re used to

The Merit Jumbo 750d may have much bigger wheels than we are used to. But the geometry here isn’t all that different. Merit did in fact design this big-wheeled bike for taller gravel cyclists, but it’s really not all that big. Design, and prototyped in titanium (which may also be offered down the road), now the carbon bike is ready. The L will fit a lot of medium to taller riders, the XL & XXL though are pretty exclusively for taller riders who might have trouble fitting on a conventional bike.

The smaller of the 3 sizes on offer – the Large that I tested – has a shorter frame Reach and lower Stack than the M Grail that I recently tested, but slightly longer/higher than the M Ruut or M Yasei. The Large Jumbo’s fit on paper is a bit between a M & L in my mind.

It gets quite short 435mm chainstays to manage those extra-large wheels. And relatively steep 70° head angle and 72° seattube, again to help give this extra-wagon-wheeled bike a snappy feel. The larger 750d wheels and extra rubber are invariably going to be heavier than 700c, so the quicker handling is there to prevent a sluggish feel.

Jumbo 750d – Tech details

Merit developed this all-new carbon Jumbo 750d frame from scratch with the same Carbon frame manufacturer that has been making their conventional 700c carbon gravel framesets since around 2015. But it’s also not so much bigger than an adventure-ready 700c gravel bike, so you could still run 700x50mm gravel/XC tires for a more conventional setup.

• 1100g frame (claimed, size L)
• full carbon 1.5″ tapered steerer fork
• 1.5″ IS headset with full internal cable routing
• universal derailleur hanger (UDH) with T-type direct mount compatibility
• T47 bottom bracket
• 27.2mm seatpost, with a 31.8 conventional seatpost clamp
• flat mount FM160 disc brakes, 180mm rotor possible in the front only
• Road Boost thru-axle spacing – 12x110mm front & 12x148mm rear
• 750d x 45mm max tire clearance, or 29×2″ / 700c x 50mm (+5mm clearance in the fork)
• 1x only, with a 46T max chainring (47.5mm chainline)
• 3-bolt downtube & 2-bolt seattube bottle cage mounts, plus toptube bag mounts

Merit Turbo 750d Carbon Gravel Wheels

A big part of making this 750d project make sense was lighter wheels. As soon as WTB was ready to announce their 750d Nano gravel tire to the world last summer, of course, they needed a rim to mount it to. Just making a slightly larger diameter i25 aluminum rim was easy enough. But the tires are already going to be about 10% heavier than 700c, and the wheels were going to be even heavier due to the need for more spokes and wider hubs.

So from day 1, Merit set out to make lighter carbon 750d rims, as well. Opening up their own new mold, Merit opted for a light 35mm deep carbon rim, with a 25mm internal hookless bead. That helped them shed a few hundred grams off the complete wheelset. The wide carbon rim provides good support to the WTB tires, originally designed over 7 years ago for narrower rims.

Merit says a big benefit to the larger diameter wheels is actually the wider Boost hubs and longer spokes, which do a good job at absorbing gravel road buzz while maintaining good lateral stiffness for predictable handling. Merit built the carbon wheels I tested with CX-Ray spokes (some of the best in the industry). But they also tested a new wheel build with carbon spokes that will be substantially lighter, while keeping the needed strength & stiffness.

• 25mm internal
• hookless tubeless bead – 660mm bead seat diameter
• 31mm external x 35mm deep with a classic blunt nose aero profile
• 495g per rim (claimed)
• complete wheelsets built up with alloy Bitex Road Boost hubs with 12mm thru-axles
• 28 straight-pull Sapim CX-Ray bladed spokes per wheel, expected to be lighter with carbon spokes
• complete wheelset weights of around 1650g now as I tested

750d vs. 700c sizing comparison

The Jumbo doesn’t actually look all that jumbo in reality. I might say proportion-wise that this Large with 750d wheels looks pretty similar to a normal Medium gravel bike with 700c wheels. So how does this big wheel size compare to the rollout or circumference of other wheels in our workshop?

• 750d x 40mm on a 25mm internal rim measures 43mm wide and is 756 in diameter, for a calculated circumference of 2375mm.
• A 700c x 40mm tire is measured at 2190mm around at 697mm in diameter,
• a 29er (also 700c) x 2.4″ XC tire measures 2305mm in circumference for a 734mm height overall
• a 29 x 2.6″ enduro tire measures 2320mm around to come in at 738mm in diameter.

So yes, 750d is quite a bit bigger than classic 700c – and will make you 8% faster with the same gearing and tire size. But compared to a proper 29er mountain bike tire, you’re looking at a wheel that’s only about 1cm bigger in radius, or an axle that’s 1cm higher off the ground. It’s a big enough difference I couldn’t fit the 750d wheel in the gravel bike I have fitted with a 2.4″ mountain bike tire.

Putting the 29×2″ mountain bike tire that Merit says will fit in the Jumbo would only have about a 3% change on your top speed vs. the 40mm tire. In fact, it would be only 1.5% smaller than the 34mm WTB Byways that I test-rode.

Riding Impressions: A First Ride Review

OK, but how does it ride?

Last week, I took one of the first two pre-production Merit Jumbo 750d to familiar gravel roads and singletrack mountain bike trails on the outskirts of Prague to see how it handled. Without looking at geometry tables, I just set my saddle height and rode away. And my first impression, was wow, this bike is big. Then, I realized the saddle was slammed all the way back, and a bit too low. So, quickly putting the saddle in the right spot, immediately it felt like I was on the right-sized bike all of a sudden.

The bike is undeniably big, but it’s not really the geometry. The geo and fit of the bike were pretty close to what I might want in a modern gravel bike with a short stem and a relatively narrow bar. (I am 185cm tall, and sometimes ride a large gravel bike, but often size down to a medium.) I was comfortable on the Jumbo 750d, but at the start of the ride when I moved from doubletrack forest roads to singletrack, I could instantly feel that it was more work to maneuver those big wheels through twisty spots, and quick ups & downs

The Jumbo made smooth work of an otherwise bumpy field crossing. The big wheels rolled over roots in the trail like they weren’t there. They smoothed chunky rocks, too. Even with these relatively low-volume, 36mm wide (marked 34×750) WTB Byway semi-slicks. And yet, it was still manageable on tight sections.

But this is a bike that begs for fast open stretches…

Shining on open dirt & gravel roads

Yeah, this is a bike meant to rack up kilometers. On longer, straighter sections I could spin the big wheels up to speed, and they would effortlessly stay there. Maybe described as slightly sluggish on technical singletrack, on the gravel roads this bike was actually designed for, it was downright fast and stable. All-day comfort comes to mind.

My only real downside is that I would rather swap on an 80mm stem (vs. the 100mm Redshift) and a narrower handlebar (vs. Merit’s own 46cm wide carbon Rodla loop bar that’s 10cm wider in the drops.) But Merit expects they’ll sell most of these as framesets anyway.

These big wheels are always going to be a bit slower to turn, so a bit quicker handling cockpit setup would do wonders to balance that out. I was pleasantly surprised by how much grip I got out of the slick & narrow Byways. But unless you are riding more asphalt than gravel, the 40×750 Nano is the best tire choice for the Jumbo. Now, we just need more people to buy into the 750d concept, so more lightweight tire options will come to market!

At 9.1kg complete with 1650g wheels, it’s not much heavier than conventional gravel bikes, and none of the components here are ultra-fancy, weight weenie tech. So there is weight to be saved if you want. In any case, I had an easy time keeping up with a friend on an 8.5kg 700c gravel race bike with 1550g aero wheels that sells for about 10% more than the Jumbo.

Merit Jumbo 750d – Pricing, options & availability

So, it looks like the Czech gravel specialists at Merit Bikes are the first to bring a 750d production gravel bike to market. And really, it just looks like a normal, well-proportioned bike.

The new Merit Jumbo 759d carbon gravel bike is available to pre-order now here in all three sizes (L-XXL). Framesets retail for ~1600€ (40,000czk). But in reality, only the Large mold is already 100% finished and tested. So, pre-orders for those first L framesets will be the first available, with deliveries to start this October. Merit is finalizing the XL & XXL frame molds now, and those sizes are expected to ship to customers in January 2025.

Complete bike pre-orders are also possible now. The complete Merit Jumbo 750d Rival GX Mullet AXS bike build like I tested with carbon 750d wheels sells for ~4800€ (120,000czk). Merit will offer more complete bike builds, once the frames are available in stock. Merit regularly ships its frames, wheels, and complete bikes across the EU. And sometimes works with buyers further afield as well.

Merit has toyed with the design of a fourth Medium size that they may make available in the future if there is real consumer demand. They also talked about opening sales of their full carbon forks down the road – if custom steel, aluminum, or titanium frame builders want to offer a 750d option to their line-up. Merit even designed the Project 750d carbon fork to add 3-pack anything cage mounts in the future, if the 750d bikepacking scene takes off in a big way.

Are you ready for bigger wheels again? Let us know in the comments below!

Meritbikes.com