zandoval 

Sometimes it's a matter of "What Ya Got", rather than "What Ya Wanna Get..."

What ever the case if I were going for new stuff I would think about what wheel sizes and tiers will be available a few years from now.

FuelExnTCX

650s for more tire to absorb the road imperfections and faster take off. 700c to go fast in general

bamboobike4

I was working with what I had on hand:
1 Giant Liv Avail SL, 700C QR disc, 2x11 compact cranks.
1 Marin Bobcat, 650B QR disc, 2x9 mtb cranks
1 Felt VR40, can take 650 or 700, but is through-axle, crank is stuck due to stripped extractor threads.

The Liv fits my better half, but was a road bike. She has descent anxiety after her carbon rims/pads melted last year on a century.
I like the hydro discs, but the 700C did NOT have clearance beyond 28 Gatorskins, and it had road bike gearing, 11-28 and 50/34.

I bought the Marin for the 650B QR disc wheels. I figured I could use them on something.

With a wheel swap and tire change, the Liv is closer, with the 650B's working fine.
I've got an 11-34 rear cassette that will fit on the 8/9/10 freehub, and then I'll swap cranksets to a 46/33 or 44/30.
Once I tweak the fit and bar/stem/post/saddle, etc, I'm hoping it works as a gravel bike, by no means an MTB.

With the wheel swap, the Marin is a faux-29'er? I doubt I'd trust the wheels on MTB trails, but here's a thought:
I have a set of DA 7700 2x9 shifters, and with drop bars/gravel tires/crankset changes, perhaps this can become my gravel bike?
Or should I move all this to the Felt VR40 frame, and run it 2x9 as my gravel bike.

I'm a decent wrench, but no genius and no miracle maker.

Avail SL with 650B

Marin Bobcat with 700C..

mauricesnail 

I've got a 650b, a 700c, and even a 26" that all see gravel duty, and can't say any clearly jump ahead of the other. I suppose I just let the universe decide which wheel size I use for any given ride

Moisture

After snooping around on the Opus website, I noticed that out of the four Horizon models, the Apex version fitted with 650b wheels has an otherwise identical frame.

The geometry chart claims that the standover height is the same with both 700x45 and 650bx45. How is that even possible? Wouldn't the frame equipped with 700c wheels sit about 2cm higher?

Maybe I'll try it out with 700x45 wheels one day. I didn't know that these gravel bikes are optimized for both wheel sizes, despite the roughly 4cm difference in total diameter.

Chilepines

Believe it or not there are mistakes on the internet! It is possible that a 650bx45 is the same as a 700cx something smaller, but otherwise they cannot be the same. Charts of diameter show 700 x 25 being the same as 650 x 45.

Moisture

No doubt whatsoever that one of those charts are Incorrect .

I started doing a bit of research looking into gravel bikes with models especially designed for 700 or 650b and found that the differences between the two were mininal.. slightly shorter chainstays, wheelbase, a bit less trail, and a longer head tube to compensate for a shorter fork. It seems you can easily try different size wheels or tires if you wish to.

I find that 650b performs very well on gravel and pavement . a thicker than normal 650b would probably be the best choice. I imagine that 700 x 45 would most likely give you a better angle of attack on rough terrain such as singletrack.
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Chilepines

I know there is disagreement about the size of the effect, but I'm a believer in larger diameter wheels rolling over things better, so I'll stick with 700c x 38-42 mm tires. You would need a 650b x 2.4in tire to get the same diameter.
The main issue when putting a 650b tire in a 700c frame is going to be lowering the BB and being more prone to pedal strikes. The other effects on bike handling related to trail are going to be minimal.

dgodave

650b

x50 for road/gravel where pedal strikes arent much of an issue
x2.4" for rougher adventures.

Moisture

Agreed. I think a 2.4" can take on just about any terrain, especially with some suspension.

Generally I'd stick with 45mm tires for gravel or pavement, but id take it it up to 50mm to cushion some of the harder impacts.

dgodave

Yes, it all depends on the terrain we ride regularly. For me the 2.4" are important for stretches where the gravel is mushy or for long portions of more challenging single-track that get thrown into my rides. Heck even some of the Natl Forest or BLM roads are chunky enough.

So why not an MTB? Well, those sections might be only 40% of a ride thats otherwise pretty solid gravel or even some pavement. More "adventure" riding than sporty gravel.

Sooo 650b works well with 2.4" for me.

Moisture

My thoughts exactly...

Yet I still can't and won't let go of my carbon 29er XC Machine.

I've settled on a Cannondale Topstone Carbon 3 for my next gravel grinder; one day.

Interestingly enough, geometry between a Topstone optimized for 650b vs 700c is minimal. Slightly shorter chainstays, shorter fork, longer head tube to compensate, more BB drop only partially compensates the BB height ... Slightly less trail and wheelbase, etc. Can always swap wheelsets on most bikes. 700c is good for some riding conditions.

It seems like I have good tire clearance on my hybrid e bike. One day I'll try a 27.5 wheelset with fat tires on it.

Venturiano

700c, definitely.