Does 650B reduce toe overlap?

[NHAero]

My Anderson wears 700x37 tires plus Velo Orange fenders. I have MTB flats on there too, so kinda worst case for toe overlap (588mm front center, 170mm cranks) - the flat pedals themselves hit the fender strut. I realize looking at this carefully that I could re-bend the fender struts and rotate them down, helping out with this.

I'm wondering, would a 650B bike be designed to have less toe overlap, given 37mm tires? Maybe a different way to ask the question is, would the front center be the same, and with the reduced wheel diameter, have less toe overlap?

I know the issue is only at low speeds, but it is real at those speeds.

[robt57]

Smaller diameter tires reduce toe-verlap.

a 47x650b and a 23x700 should be about the same IIRC.

[NHAero]

In theory the same size tire on the 650B rim is 19mm lower radius. My question is more about whether the frame design stays essentially the same.

Originally Posted by robt57

Smaller diameter tires reduce toe-verlap.

a 47x650b and a 23x700 should be about the same IIRC.

[robt57]

Originally Posted by NHAero

In theory the same size tire on the 650B rim is 19mm lower radius. My question is more about whether the frame design stays essentially the same.

I'd assume any changes in trail are for diameter changes, although I seem to recall fat tires also change trail.

[happycampyer]

For wide tires and fenders, 650B is the way to go. If you look through Firefly's flicker or other feeds for examples, you will see plenty of bikes—even smaller ones—with wide tires, fenders, and plenty of room to avoid toe overlap. Here's just one example:



https://www.flickr.com/photos/firefl...h/49029300647/

The narrowest I would go on a bike like yours would be 650B x 42mm. The bike above has wider tires than that (650B x 47mm Switchback Hills).

[Ed-B]

In addition to the clearance gained using a wheel and tire that have a 19mm smaller radius, some 650B wheeled bikes will have a front end geometry that improves handling with a front load. These "low trail" bikes typically have more fork offset which increases the front center dimension and reduces toe overlap.

[Hilltopperny]

I swap wheels on my Drifter between 35mm, 36mm 700c and 42mm on 650b. It definitely decreases toe overlap, but drops the bb down about 1.3cm which changes the handling a bit. A 42mm 650b is basically the same diameter as 23mm 700c, but adds more pneumatic suspension because of the extra tire volume.


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[NHAero]

It's interesting that you experience the lower BB as changing the handling. I wouldn't have expected that, since the whole bike drops the same amount. Can you explain further please?

Originally Posted by Hilltopperny

I swap wheels on my Drifter between 35mm, 36mm 700c and 42mm on 650b. It definitely decreases toe overlap, but drops the bb down about 1.3cm which changes the handling a bit. A 42mm 650b is basically the same diameter as 23mm 700c, but adds more pneumatic suspension because of the extra tire volume.


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[John H.]

I also notice different handling and feel when I move to 650b.
One of my bike has a low bb- 75mm of bb drop. I do not love how this bike feels with 650b wheels and tires on it.

With respect to a bike with fenders- you need to look at the entire geometry package. Was the bike designed to work well with fenders? Or was the bike a copy of a road design that just added fenders to it.
I have had fender bikes both ways. The bikes that were copies of non-fender bikes tended to have more of these overlap type issues.

True story. A buddy of mine had a new Firefly that took Honjo fenders. But it was a 100% road design with clearance for fenders. It was even a rim brake bike.
He pulls up to meet for a ride- Track stands it. Foot goes into the back of the front fender and puts a big dent in it.
"Guess that is a limitation on this bike"?

[happycampyer]

The bike designer needs to take into account (or design with the assumption, if it’s not a commission) that the owner is going to switch between different wheel sizes. There are two considerations—first, that there is an optimal wheel/tire combo size, and second, that the geometry needs to be able to accommodate the intended extremes.

To give an example, before I got an all-road bike with disc brakes, I worked with Steve Hampsten on a Strada Bianca ti. Since it’s a rim brake frame, it is limited to 700c wheels, and can take tires up to 35mm wide (it’s quaint to think that that was a super wide tire bitd!). I can run skinny (23 - 25mm) tires on it, but the geometry was optimized for 30 - 33mm tires. I can fit up to 28mm tires with fenders. Steve really knows what he is doing in this genre.

With the widespread move to disc brakes, this exercise gets way more complicated. Just because one can swap different sized wheels (no longer constrained by brake caliper length), doesn’t mean that the bike will work with those different wheels, and tires. As noted above, bottom bracket drop needs to take into account the extreme case (e.g., 650b x 42mm, etc.). The frame needs to be optimized for some specific wheel diameter/tire width. Other combinations are possible within limits (e.g., chainstay length and width for max tire size), but the handling of the bike will not be as good as with the optimal wheel/tire combo. Fenders add another layer of complexity. I personally have come to the conclusion that a bike that was designed for fenders is best designed to always have fenders (like a Weigle, Chapman, etc.).

[robt57]

Originally Posted by happycampyer

The narrowest I would go on a bike like yours would be 650B x 42mm. The bike above has wider tires than that (650B x 47mm Switchback Hills).

Are you saying that based on width alone, or do you know specifically what the BB drop on his frame is as part of your comment/equation? And I say equation as BB drop and tire diameter as it pertains to pedal strikes is all math. Q factor also come into the pedal strike equation as well.

And folks that just can't seem to not pedal thru in turns and noticeable leans, etc [like me]

[Waldo62]

I run my cleats at mid-foot and have significant and unavoidable toe overlap on every bike. After overlapping and rubbing a few times, I learned to avoid it, and when it does happen I don't freak out anymore.

[happycampyer]

Originally Posted by robt57

Are you saying that based on width alone, or do you know specifically what the BB drop on his frame is as part of your comment/equation? And I say equation as BB drop and tire diameter as it pertains to pedal strikes is all math. Q factor also come into the pedal strike equation as well.

And folks that jua was st can't seem to not pedal thru in turns and noticeable leans, etc [like me]

Sorry, what I was referring to is a bike like his, i.e., with fenders, a front rack, etc., basically a randonneuring-style bike. 650b x 37 is a pretty small tire—the OD is shorter than a 700c x 23mm tire, and it sort of defeats the purpose of going for 650b.

[NHAero]

To clarify - I'm not asking about a bike that interchangeably works with 650B and 700C wheels. I'm asking if one isn't interested in more than a 38mm tire, and is clear that fenders are part of the mix, would a bike designed as a 650B road bike have less toe overlap? It seems to me that it would, because the radius of the wheel/tire is nominally 19mm less. I want to ensure I'm not missing something.

Originally Posted by happycampyer

Sorry, what I was referring to is a bike like his, i.e., with fenders, a front rack, etc., basically a randonneuring-style bike. 650b x 37 is a pretty small tire—the OD is shorter than a 700c x 23mm tire, and it sort of defeats the purpose of going for 650b.

[happycampyer]

The thing is, once you step down to 650b, a 42mm tire is as narrow as I would go unless you were building a wide-tire aero road bike. 42mm sounds wide, but I would compare it to a 700c wheel with 32mm tires.

Either way, yes, a bike with 650b wheels with either 38 or 42mm tires and fenders should have less toe overap than a 700c wheeled bike with fenders. I'll measure the pedal-to-wheel distances on my all-road bikes and let you know what the differences are.