Bigger Riders and 650b

[pakora]

I'm sniffing around the possibility of 650b wheels on a custom all road bike (instead of the 32s and fenders that I've already considered and been running on other bikes) and I'm 90% sure I can digest the Kool Aid. But:

At my weight (220 kitted and shod) on a big bike (say 63 c-c) I'm not sure about the pressures people talk about riding on the road or mixed surfaces. With super high volume tires that are nice, can heavier riders on big bikes still benefit in the same ways? I haven't seen many 650b bikes either in the wild or online that approach that size except super burly extreme bikepacking/mountain bike/monster cross things.

I run 30 pounds in my cross race tires, and e.g. 20-22 psi in 2.4" tires on my mountain bike, but descending at 40mph is different. I've ridden tires with the pressure too low (unintentionally of course) and felt my contact patch change as the bike navigates a turn. As a result I have trouble thinking about running a road tire at like 40 psi (or less) even if it's 42-47c. I totally get that car tires are like 28 psi but... maybe I just need help getting my brain to accept it?

[mhespenheide]

I have no experience in this, but my gut feeling (as someone 6'4") is that you might want to stick with 700c. That's just a feeling that it should scale, not any deep reasoning.

But really, I'd recommend heading over to the 650b google mailing list, https://groups.google.com/forum/#!forum/650b and ask around over there.

[echelon_john]

I agree with this. If you're going full custom, and are open to discs, there are lots of good options for 700xBIG tires that would give you the same benefit as the Littles (as I call them) enjoy with 650B.

To me, the main reason for 650B on a gravel bike is to swap wheels with bigger meat when you don't want to run 700xrelatively skinny. If the bike is built for it, no reason you couldn't run both on a 700c setup. Maybe not as fat as a 650x2.X, but still large.

Originally Posted by mhespenheide

I have no experience in this, but my gut feeling (as someone 6'4") is that you might want to stick with 700c. That's just a feeling that it should scale, not any deep reasoning.

But really, I'd recommend heading over to the 650b google mailing list, https://groups.google.com/forum/#!forum/650b and ask around over there.

[ColonelJLloyd]

Originally Posted by pakora

With super high volume tires that are nice, can heavier riders on big bikes still benefit in the same ways?

Yes.

At 220# I would suggest 35f/40r psi in a tubeless Switchback Hill to start and then let air out to experiment. I'd think you'd want to end up a little lower than that on pavement and lower still off pavement.

Tire volume is not the only reason to consider 650b. You have to consider the overall diameter of the tire and how that will affect the handling, TCO, etc.

[ripvanrando]

Originally Posted by pakora

.........I'm 90% sure I can digest the Kool Aid. But:

...............maybe I just need help getting my brain to accept it?

Seattle?

The Kool aid is strong up there.

I have 650b x 38 and also 42 tires and am almost your weight. No problems but I only really taste a benefit on really bad roads or gravel.

[donevwil]

IMO, big riders (I'm 6' 5" & 240#) have more to gain from greater tire volume. Just realize, if you're open minded and not a racer there's no turning back.

As far as 700c vs 650b it's certainly a personal thing, Kool-Aid or not. As has already been posted, some prefer 700c even at 40mm+. I personally prefer 650b at that size, but I also prefer 26" to 29" on an MTB.

Edit: I currently run Compass Snoqualmies (700c x 44 actually more like 41) on a Monstercross at 40f/45r. Any less on paved roads and it feels too squirrely in fast turns.

[seajaye]

this thread makes me smile verrrrrryyyyyy broadly

[keevon]

Originally Posted by pakora

*snip* I haven't seen many 650b bikes either in the wild or online that approach that size except super burly extreme bikepacking/mountain bike/monster cross things.

Here's one - it's an XL NFE. For reference, I'm 6'-5" and roughly 190#.

On smooth roads with 650bx42 tires at 45 front / 50 rear, it feels like a good road bike. On rougher roads I'll drop 10 psi.

Lately I've been putting the majority of my miles on this bike - it's great. Average speed seems to be about the same as my other steel bike with 700x32's.

[DRZRM]

So I have not ridden these yet, but my plan for my incoming ti gravel bike is 47mm 650b tires for trails and dirt, and a pair of 700 that I'll put 35-40mm smoother tires. I'm 6'3" 220 and folks seem to think I'd never run tires much over 40 psi, I'll start at 50 and go down. Given that I never really run my tubeless road tires much over 60 psi I think you will be fine.

[Clean39T]

Originally Posted by DRZRM

So I have not ridden these yet, but my plan for my incoming ti gravel bike is 47mm 650b tires for trails and dirt, and a pair of 700 that I'll put 35-40mm smoother tires. I'm 6'3" 220 and folks seem to think I'd never run tires much over 40 psi, I'll start at 50 and go down. Given that I never really run my tubeless road tires much over 60 psi I think you will be fine.

Whatcha gettin?

[Clean39T]

Originally Posted by keevon

Here's one - it's an XL NFE. For reference, I'm 6'-5" and roughly 190#.



On smooth roads with 650bx42 tires at 45 front / 50 rear, it feels like a good road bike. On rougher roads I'll drop 10 psi.



Lately I've been putting the majority of my miles on this bike - it's great. Average speed seems to be about the same as my other steel bike with 700x32's.

Wow. Love the look of that bike!

[hollowgram5]

I've had a variety of both. I am currently running a Salsa Vaya Travel with 650x48s on 23 internal width rims. Salsa says the frame is designed around 700x40s, and I've ridden it with larger and smaller tires than that on a 700c rim.

I had it set up with some Quasi Moto 2.0s for a while, and it was fun as well.

My TwinSix RandoTitanium will also run both styles of wheels. As others have said, having a bike that can run either is a huge benefit. At this time, I've got one set up with 700s and one set up with 650s, mostly because I can.

For what its worth, I am 6'4" tall and am roughly 240lbs. I run a slightly higher pressure than most of the others, but i also lug around 20+ lbs more than them too.

Edit: one thing I was going to say and hit post too soon was that it feels slower but I can't validate that necessarily. Looks like nesteel has a similar opinion below..

[nesteel]

I ride a vintage factory built 650b bike with a true 41mm tire @ 40#'s and have had no issues on pavement or gravel. Rider weight is 220-230#'s. It FEELS a little slower on pavement than my narrow tired road bikes, but I have no actual data that says it is.

[Pastashop]

Ahma write all this in the hopes that nobody actually reads it, because... TLDR and all.

Pressure = Force / Area
Force = Mass x g
g = 9.8 m/s-s (constant)

Pressure = Mass x g / Area

Pressure 1 / Pressure 2 = Area 2 / Area 1

... all this to say that the size of the contact patch scales inversely with pressure. It doesn't really matter whether you're running a fat tire or a skinny tire, for a given rider weight, for a sufficiently supple casing and tread, the size of the contact patch depends basically on the pressure in the tire. If you're running a skinny tire, that contact patch area will have to be achieved by proportionately greater local deformation of the casing than for a fatter tire. Meaning that your casing is likely to get more damage over time. Or that your wheel will bottom out on an imperfection in the road deeper or taller than the tire. There are some considerations for the tire blowing off the rim or busting out the rim's sidewall at high pressures, but you'd have to be pumping your 38mm tires to > 80 psi to do that – not very pleasant ride quality.

For these reasons, for me, the tire width is dictated primarily by the type of surface I'll be riding. If the potholes and rocks I'm likely to encounter are larger than 1.5 inches, I'm gonna roll 38 mm tires. It doesn't even matter a whole lot if it's 26", 650b, or 700c. Where the wheel diameter does play a big practical role is when trying to eliminate toe-clip overlap with fenders.

In terms of wheel service life, you're likely to want 36 spokes per wheel. A 650b wheel will be marginally stronger laterally than 700c, but with 36 spokes and a proper build (including stress relief) you're fine either way.

By the way, the notion that fatter tires don't handle well at high speeds is probably just some artifact of what / how people ride. Motorcycles run wide tires – relatively speaking*– on small diameter rims and routinely achieve speeds far greater than what bicyclists do. And look at the lean angles on these things: Of course, they've got easy access to power to the rear wheel while cornering, which helps to some extent, but no issue with running fat tires at lower pressures than a typical road bike.

[pakora]

So I've now done some reading about 650b vs 700 for the same or similar tire width and there's a lot of disagreement, but a lot seems to come down to "hey, 650b in 42 is kind of the same size as 700x23 and lots of people agree about the geometry and handling for outside diameters of that size".

Does anyone have experience on tires of the same or similar width on 650b vs 700 wheels e.g. 700x42 vs 650x42? I'm starting to think the answer might be more like "if you think your bike in your size will look weird with 650b wheels, you should go 700; if at your weight you've had trouble with light wheels being strong enough in 700, consider 650 wheels"

Esp interested if you had experience with carbon wheels and tubeless.