sweetspot

Or there are other limitations aparat from bb drop?

Spoonrobot 

Bottom bracket height isn't a limitation. Any production frame designed to take 700x40mm tires is going to have a sky high bottom bracket so going to a slightly smaller wheel/tire combo will only lower it to a more reasonable level.

I have seen a frame that would fit 700x40 fine but would only take 650bx47 slicks and not knobbies, I can't recall what it was but it appears to have been an unusual design. Regardless most bikes that fit such a large 700c tire will be fine for that size 650b.

JayNYC

The Orbea Terra has a max size of 40mm whether it's 700C or 650b. So it's not safe to assume you can go bigger with 650b.

wheelsmcgee

Spoonrobot 

It's obvious looking at pictures online 650bx47 would fit in the fork and I suspect in the rear as well.

The issue here is "fit" CPSC requires a certain amount of space between the tire and frame/fork. I think it's 8mm but I don't remember offhand. Anyway, point is that a company will say only X size tire fits because that's the CPSC requirement. Reality is that it's usually X+5/6/7mm or whatever. Reducing the wheel size by an inch and a half allows a much larger tire in the vast majority of frames. That was the whole point of WTB road plus: https://www.wtb.com/pages/road-plus

650b bare rim is a full 1.5 inches smaller than 700c. This opens up a huge amount of clearance for the tire. There's no way the stock AWOL only has 3.5mm of clearance per side on a 700x40mm tire. I bet it's closer to 5-7mm per side to give a total chainstay width of 50-53mm - that's a pretty common width on the OEM frames I've measured. Which means a 650bx47mm slick will fit and most likely be fine if there's no mud.

As I said earlier:

We can pick nits about this frame or that frame but the statement stands. As always it would behoove anyone working on a project to independently verify max tire size for their frame and fork using actual measurements when available.

JayNYC

Well, my information comes from a LBS that talked to a guy at Orbea who had the Terra with 650b wheels on it and said you can't go higher than 40. I'd call that pretty definitive.

Point is, there are bikes where you can't go wider with 650b. The Orbea Terra is one of them. Always ask. Don't assume.

chas58

I'm going 650b in the front only. a 54mm 650b will have roughly the same diameter as the 40mm 700c I use in the rear.

Personally, I have no use for a 650b on the rear. Between tire pressure and a good seat post, its plenty smooth for me in the back. A wider front tire will give me more cush, better rough trail ability, and flotation over sand.

OP: Chain stay clearance in the rear often won't take a wider tire unless the bike was specifically designed for it by useing extra wide mountain bike bottom brackets, design only for 1x and drop the chain stay.

Spoonrobot 

Look I know you're new at this and don't have a lot of hands on experience. Third hand information that is sourced from the company is worse than useless. Read this section of my earlier post again:

Look at the pictures here:

https://cdn-cyclingtips.pressidium.c...6-1280x854.jpg
https://cdn-cyclingtips.pressidium.c...a-Terra-18.jpg
https://cdn-cyclingtips.pressidium.c...a-Terra-15.jpg

Read the captions too, they list the measurements. That's a 700cx40mm tire. I 100% guarantee a 650bx47 slick will fit and ride fine.

It is exceedingly hard to design a bike that will fit 700x40 tires that will also not fit 650bx47 tires.The math and design choices that would allow this to occur just do not happen except for all but the most uncommon frames. 99% of production bikes that will take a 700x40 tire will take a 650bx47 tire.

ETA: Next time don't ask for tire clearance, ask for the width of the chainstays, seatstays and fork blades 323mm from the dropouts. This will give you the correct answer you seek.

chas58

You are assuming the chain stays flair. my bikes don't have chain stays that flair much behind the tire. It fits a 40mm 700c or 650b. Going to a 650b doesn't give me any more clearance width wise. I see frame builders doing a lot of tricks near the chain ring to get the bike to work with wider 650b tires.

If the frame was designed for 2x, it is even more likely that the chain stay does not flair. You are going to have better luck with a frame that is designed 1x only.

Spoonrobot 

I am not assuming anything. Even if the chainstays are parallel as long as possible the clearance required to fit a 700x40 tire and go to market require there to be enough room for a 650bx47 tire. No production frame is shipping with less than 5mm between each side of the tire on a 700x40 tire combo. The vast majority of "parallel" chainstays are not actually such either, they almost always flare directly behind where a 700x40 tire would fit, just extremely shallow flare. Enough to get an additional 1-2mm at 650b diameter.

I'm not speculating here, I see several different gravel bikes every week and have mocked up dozens of designs in bikeCAD. The math the would make a frame fit 700x40 and not 650bx47 does not work except in the more uncommon edge cases.

sweetspot

The interesting case is with Jamis renegade bikes. They all have 700x40c tire clearance but Jamis says that only Alu and Steel versions will fit 47c 650b tire and carbon not. The question is why? Limited space between shorter seatstays?

Spoonrobot 

Find a pic of the chain stays and you'll see why they only recommend a 40mm tire. Same as the Orbea a 650x47 will fit but is "not recommended".

sweetspot

https://goo.gl/images/UGcW9v this is a photo of aluminum orbea gain chainstays. In your opinion will it work with 47 650b tire?

unterhausen

do you know what size tire is on that Orbea? Looks like plenty of room for bigger tires

sweetspot

28 mm but this bike comes with 40c tire.

Garfield Cat

Yes, there is. But do you want to pay a lot of $$$$$ for it?

47c tire size . The 47 mm is equivalent to 1.85 inches.

Tire clearance



The U.P. fits mountain bike tires up to 2.1” wide. But you can also fit a 40mm cross tire, or a 28mm road tire, or anything else in-between (exact tire sizes depend on manufacturing tolerances and rim width, so this is a guideline. Always make sure you have 6mm clearance between tire and frame).

How do we fit such a wide range of tires without affecting the handling? Let's start with the numbers; below is the outside radius for various wheel+tire combos:Radius
Rim
Tire
341mm
700c/29er
28mm road
344mm
700c/29er
32mm cross
350mm
700c/29er
40mm cross
342mm
650b/27.5"
2.1" mtb
365mm
700c/29er
2.1" mtb



As you can see, the top-4 wheel+tire combos (700c cross/road tires and 650b mountain bike tire) are very close in radius, the bottom one (the 29er mountain bike tire) is way off.

So you’ll hardly notice a difference in geometry swapping 700c cross/road and 650b mountain bike tires on the U.P., while 29er tires would make a total mess of the handling.

There is a second reason we designed for 650b and not 29er tires. They would require very long chainstays, while the U.P. now sports a very short 420mm rear end. Most gravel and cross bikes have longer chainstays than that yet they can't fit anywhere near the same size of tire.

Crank clearance

Behind the bottom bracket, the chainrings, frame and tire all fight for space. And with the need to fit big mountain bike tires and narrow Q-factor cross/road cranks & chainrings, the U.P. presents the toughest possible packaging problem.

Dropping the right chainstay moves it out of this crowded area, allowing it to be wider and therefore stiffer (a huge effect; with the same amount of material, twice the width will give you eight times the stiffness!).

chas58

It’s a good thing we stepped back from the claim that any bike that fits 700x40 would fit 650bx47. There are several problems I have run into in attempting this conversion:

1) Claim: If the frame fits 700x40 then it should fit 650x47 – "fit" does not equal "meets ISO standards." For the 700x40 ISO standard is a total of 12mm clearance (6mm/side) or 52mm. Yeah, you can "fit" a 47mm x 700c or 650b tire on a frame with 52mm clearance if you really want to. I have done stuff like that. I have to keep the tire very true, avoid sticky mud, and not put more than 500watts torque down, but it worked good as a deep winter rig. Not something I would recommend though. It is are correct that it may be marginally easier with a 650b.

2) Claim: Any frame that fits a 700c tire can take a wider 650b tire. Not in my experience – not on my bikes. Two problems: 1) my carbon frames are designed for a stiff bottom bracket and have no flare in the chainstay (untill it gets well away from the crank). Clearance is roughtly the same for 700c or 650b. 2) on my alloy frames, they are crimped so the 700c wheel has clearance. Moving the wide part of the tire backwards moves it out of the crimp spot and reduced the clearance for the tire.

3) That comment that the wheel is 1.5” smaller is misleading. I try to match the diameter of my 650 & 700 wheels, but the wide part of my tire certainly does not move back 1.5”.

Then there is the whole bottom bracket issue. I don’t know where the claim is that “Any production frame designed to take 700x40mm tires is going to have a sky high bottom bracket” comes from. Most gravel bikes I have looked at have a low drop of 70-80mm. Sky high to me is 50-60mm. Personally I find 75-80 too low already – dropping it down lower with 650b tires would just compound the problem.

I don’t want someone to go out and purchase a set of 650b wheels and tires assuming it will work on any bike then run into these problems.

Metieval

I can fit a 40c, but there is no way a 650 47 will fit as it would move the tire out of the Designed spot for the tire.
Matter of fact, the 40 is too big, but I don't run mud.

Spoonrobot 

The Open UP has a lot of design compromises in order to fit large tires and very short chainstays into their overall geometry. Most of the issues noted in the unquoted website advertorial disappear with chainstays closer to average 430mm+.

Nobody claimed any bike that fits 700x40 will fit 650bx47. I said the vast majority - 99% - will accommodate both size tires. ISO standards are overly cautious. 47mm tire in 52mm chainstays is perfectly fine. I broke a spoke on my rear wheel using this combo and didn't even have to make any adjustments to ride home and repair it.

There is nothing misleading about this comment. It is a true statement. On most bikes 1.5 inches less wheel diameter opens up a large amount of addition space to fill with tire.

A 700c bike with 70mm bb drop and 700x40 tires is going to have a bb height of 284mm. I consider anything over 269 to be high and anything above 280 to be very high. For a gravel bike.

Also, as I posted earlier as well:

Spoonrobot 

Have you tried a 650bx47?

That looks perfectly fine for the kind of mud we get down here. It's rare to see silt content high enough that it sticks and causes issues.

Metieval

I have not tired a 650x47, that is the bottom of a Trek Crossrip btw.

Garfield Cat

I looked at Giant Revolt chainstay 425 throughout its size chart. Canondale Slate chainstay 40.5 throughout. Specialized Diverge chainstay 419, then 421 throughout. Open cycle UP chainstay not listed but rear center 420 throughout.

It seems that these have the shorter stays than the 430+ average. Is this average a suggestion that its a more relaxed geometry?

Spoonrobot 

I should have said "very large" tires. The UP is essentially designed to take smaller 650b mountain bike tires without using a narrow band of carbon fiber or wide/narrow yoke for the chainstay. The others are more in line on the roadish side of gravel bikes and will not fit most mountain bike tires.

Garfield Cat

Woud it be reasonable to say that the UP is designed for both 650 and 700 in mind, and that the chain stay length is as short (wheelbase) as the others to come close to road bike handling and feel?

chas58

Yeah, if it is designed for wider tires (i.e. 650x2.1) it will have a dropped chain stay or something funky down there to allow tire clearance. It does sound like it handles as much like a road bike as it can.