New wheel size?


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There has been some press in the bike world recently about a new wheel standard that was developed by WTB and recently showcased at the made bike show in Portland by Moots of Steamboat Springs, CO that have been making Ti bikes for decades now. It has spawned quite a bit of angst amongst the bike faithful that all seem to get up in arms whenever any new standard is introduced but when I becomes accepted they are more than happy to fight to the death over them.

A friend was in on the development and sent me a frame/fork, rims/tires and component group back in the fall of 2019. I have had several whacks at using the wheels specifically since then and was unable to really say much about them. But now that the cat is out of the bag here is where the bike is at today with a Grin All Axle DD hub, CA3 display, Schlumpf High Speed Drive and 52v 17.5Ah 21700 cell shrink wrap battery/baserunner controller set to 25A in the top tube bag for the clean look I was going for. A Shimano drive train and hydraulic brakes as well as a dropper post that is activated by the left brifter lever rounds out the build. The bike operates without PAS and instead a throttle with cruise control as the use of the Schlumpf doesn't allow for PAS. I have had drop bar bikes now set up like this and actually prefer it for primarily road use although I like torque assist PAS on my MTB in addition to having a throttle on board for the moments I feel the need for one.

EAR driveside.jpg

Here is the Moots version:

Screenshot 2023-09-03 at 8.29.25 PM.png

Because of the diameter of the wheel being the equivalent of a 2.4 tire mounted on a 700c rim, commonly known as a 29"er that WTB also developed back in '99, a frame and fork must be made specifically to fit them as above, although there are 29" frames that will fit them also truth be told. Here is one I trialed with a TSDZ2 back in 2020 and posted up here:
So we're talking about 750d's?

What benefit does a slightly larger wheel diameter have on an ebike that's (respectfully) less than optimal gravel bike? I can see a benefit of having a slightly softer wheel (that doesn't transmit quite as much harshness to the handlebars) from the longer spokes but the larger tires are probably taking care of most of that. I also regularly ride a front hub setup (Grin-Shengyi) with a nice rigid straight arm front fork so I'm familiar with this issue.

For the mainstream gravel bike users I'm guessing the 750d wheels will have a similar benefit as the 700c does over 650s but with the addition of wider rubber choices (with frames designed for the wider rubber). Very small weight gain, but slightly better rolling efficiency over obstacles and gravel surfaces and wider rubber choices. Anything else?
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WTB's designation is 750d which is based on the diameter of the wheel overall. However there are standards in the bike industry in regards to wheel size that are a bit nebulous and depends on how companies feel they can best market them? A decent explanation here of the current popular wheel sizes: that addresses ETRTO Bead Seat Diameter which addresses the rim diameter without a tire:

650B actually meant 650 outer diameter and a 32mm tire height, which got pretty close to the ETRTO Bead Seat Diameter of 589, but using the B for MTB tires was just stupid, because they're all closer to 60mm in height/width. 700C was the same idea with 700mm outer diameter and a 39mm tire height, which again is pretty close to the 622mm BSD of road wheel and 29ers, but the actual C height/width is only just now being used on road bikes. 750D should mean an outer _tire_ diameter of 750mm and close to 45mm of tire _height_, which does get close to the BSD of 660, and will probably represent a fairly common actual tire height/width, but it still adds the complication of 750 not always being the actual tire diameter and D not always being the actual tire width.

Here is an explanation of what drew Moots to try this I took from PinkBike:

I got to see this bike in the flesh yesterday at MADE and I spent some time talking to Moots about why they're experimenting with this. Here's the gist of their "why":

- It's still an experiment and may evolve into something different.

- The reason they aren't just using a larger MTB/Gravel tire pertains to aerodynamics, ride quality, and contact area: Moots says that a 40c 750D tire effectively has the contact area of a larger 48-52mm 650B tire, but in a longer and narrower contact patch. They say this is more aerodynamic for the same level of float, and the ride quality at higher speeds is better/more controllable than 650B in their experiments so far.

- Part of their initial prompt to explore wheel sizing was with difficulties optimizing the range of 1x drivetrains for gravel riding around a desired speed range and tire size, and the larger wheel size helps them optimize a gear range for the desired speed range with a desired tire size, while also claiming the benefits above.

- They see this tire optimized for a certain speed range. They said that generally for gravel, they see 650B as a 14-18 mph tire, 700C as a 15-25 mph tire, and 750D as a 17-30 mph tire.

- Because of the speed range, It's ultimately optimized for racing or higher speed riding.

For my purposes the last two bullet points have the most significance. As you might guess a 1000w front hub with the range of high gearing that the Schlumpf provides on the human side the bike above can be ridden pretty fast on level ground? Although I don't all the time and certainly only on open roads, when I do the bike is extremely stable, more so than my other ones that had 700c wheels. There is some compliance also afforded to the longer spoke lenghth also as you suggest and I have been getting away with low 30 psi that helps keep road chatter down.

Overall I don't see this wheel size blowing up the industry but it has been fun to build it up and mess around with and am sure that others will also if made available. My preferred mode of transport here is my FS eMTB because it adapts itself better to the surface variations that range from pavement to roots an rocks to sandy beaches that I encounter on any given ride. The term "gravel bike" seems to be more about a new marketing moniker and racing genre. Where I live the variety of gravel, from chunk to champagne, happens in spurts that can cause too much flat anxiety. The attraction is that it is primarily available behind locked gates with no traffic that makes it safer than highways I find.
Not paying enough attention and saw "b" instead of "d" in the online info - correcting my post above. Thanks for the background as I'm now cluing into the reason for the b, c, d designations to go with wheel diameter. The imperial vs. metric labels (and the end users who don't pay attention) must also drive many in the industry crazy.

Interesting about the concept of an optimal "speed range" for a tire/wheel combination.

I have an ongoing issue with the gearing of my front hub setup (SRAM 32 x 11-52) with a regular wind hub motor and a 52v battery. There's lots of top end speed so I really need more high (gear inches) to keep from spinning out. I put a similar Grin kit (same motor/battery) on a 700c bike with a 52 x12 top end. It's much more enjoyable to ride on roads and hard paths over longer distances.
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It turns into a bit of a nerd out for sure trying to follow all that has gone on in relation to wheel sizes over the years and what has stuck around. 700c is the outright winner IMHO and in use world wide for adult bicycles. The fact that it is the stock size for both road and mtb, since it's inception in 1999 at least, makes it so. I think on Sheldon Brown's site there is a list of all the different diameters that have been recorded and it is pretty lengthy.

The trick for me using a hub motor over a mid drive is that you need to separate the motor drive from the pedal drive due to the higher cadence that is generally in use? It removes the "magic leg" feel of a mid drive's attachment to the final drive and allows you to pedal at the cadence/force you desire while the motor can be set to operate at a consistent wattage. I liken it to if you had a row boat with a trolling motor giving you a constant forward momentum that takes up the slack when you are at a dead spot in your stroke. As I said it works for me on primarily road but a well tuned PAS and a selection of modes works better for mtb use when at a lower cadence and dodging obstacles and variations in elevation.

The Schlumpf High Speed drive on the above solves the higher gear inch issue in that it provides the equivalent of a 60t chainring (27t x 2.25od) with an 11t and 750d is a 160" gear. It makes it able to pedal effectively up to the mid 30's which in turn helps to get the bike to maintain that speed. As I said not that it is done often but is capable. Mostly the bike is used in 500w max mode through my digi aux control and average speeds in the low to mid 20's which it will do on level ground at 250-300w with a decent wh/mi in the high teens. Also when in 1:1 the 27t and 11/28 provides low enough gearing to go up about anything easily without straining the DD motor albeit not fast.