2018 Sworks Crux Tire Size 650B - Need Help

9 replies · 143 views

JeremiahJohnson
5 posts
#1May 22, 2024, 4:37 PM
I have a 2018 Sworks Crux I have been using for a cross over road and gravel bike for a few years. I am wanting to upgrade the tires but there is no direction on width. It says 38mm is the absolute largest you can put on with 700 rims.

I have 650B rims i wanted to outfit on this bike. What size tires are yall using? Can i fit 40s or should I stick with 38s? Specialized had no information for 650B wheels. Looking at Pathfinder Pros or like tire. Going to be using it for races like Unbound (not this year) and other similar style rides.

I appreciate the help.
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stu
646 posts
#2May 22, 2024, 7:07 PM
I can't comment on your particular bike but with any bike you can measure the clearances. I measure by finding the largest hex wrench I can slip between the tire and the closest part of the frame or fork (usually the chainstays). Keep in mind 650B rims are 19 mm less in radius than 700C rims so the widest point on the tire will be 19 mm closer to the axle, where the frame or fork may be wider. Most sources I've seen recommend 3 or 4 mm minimum clearance, you might want more if you expect to encounter mud.
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Eisbaer
27 posts
#3May 23, 2024, 12:05 AM
And you should consider that the idicated tire width is not always the real tire width. The manufacturer may not be accurate, tire and rim interact etc.

Did you ask Specialized or a local dealer for support?
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JeremiahJohnson
5 posts
#4May 23, 2024, 8:47 AM
And you should consider that the idicated tire width is not always the real tire width. The manufacturer may not be accurate, tire and rim interact etc.

Did you ask Specialized or a local dealer for support?
Specialized said they didn't have any info for 650B. I have no Specialized dealers in my area anymore. Just trying to see if any one has experience so i don't have to order several sets and have some not work. I will be in Dallas today, hopefully I can find a shop with a little knowledge.

Saw this article but goes totally against what Specialized said for 700. They went wider.

https://www.cxmagazine.com/bike-review-2018-s-works-crux-cyclocross-specialized-shimano-dura-ace
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JeremiahJohnson
5 posts
#5May 23, 2024, 5:27 PMedited
Looks like gap is only 2" so likely 40 is max. 42 is likely pushing it. What do yall think? I am having trouble finding many smoother 650B tires in these sizes. Three are quite a lot more 27.5 tires. Since these are technically the same size would they fit? Most are mud style grips in narrow 650B.
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stu
646 posts
#6May 23, 2024, 11:19 PM
Is that a 650B rim in the picture? If so it looks like clearance for 650B wouldn't be much if any better than for 700C. As you have noticed there's a better selection in 700C.

650B and 27.5" tires use the same rim with 584 mm bead seat diameter, like 700C and 29" tires use the same rim with 622 mm bead seat diameter.

Actual and marked tire widths can very significantly. Some tires run larger or smaller than advertised and rim width affects all of them. I recommend mounting a tire on your rim, keeping it inflated a couple of days to stretch, then measuring the width.
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JeremiahJohnson
5 posts
#7May 24, 2024, 9:36 AMedited
Is that a 650B rim in the picture? If so it looks like clearance for 650B wouldn't be much if any better than for 700C. As you have noticed there's a better selection in 700C.

650B and 27.5" tires use the same rim with 584 mm bead seat diameter, like 700C and 29" tires use the same rim with 622 mm bead seat diameter.

Actual and marked tire widths can very significantly. Some tires run larger or smaller than advertised and rim width affects all of them. I recommend mounting a tire on your rim, keeping it inflated a couple of days to stretch, then measuring the width.
Yes thats a 650B rim. They arrived yesterday. Unfortunately it has the same clearance on this bike as my 700s.

I bought the 650B rim with the intentions of building another bike with wider clearances down the road. Since I already have 2 other decent sets of 700 wheels, I wanted something different.

It looks like the Panaracer SK has a 650B 43mm. That would give me 3.5mm on either side of clearance if they don't balloon too much. That would give me a similar diameter wheel and tire combo as a 700C wheel with 23mm tires. A 38 or 40mm tire might be a better option on this bike if they expand much past listed width.
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stu
646 posts
#8May 24, 2024, 2:32 PM
What is the inside width of your 650B rim? BRR measured the 40-622 GK SK at 36.8 mm on a 17.8 mm rim so that one would be about right on a 25 mm rim, a little over on a 30 mm rim.
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JeremiahJohnson
5 posts
#9May 24, 2024, 4:39 PM
What is the inside width of your 650B rim? BRR measured the 40-622 GK SK at 36.8 mm on a 17.8 mm rim so that one would be about right on a 25 mm rim, a little over on a 30 mm rim.
Its actually a 21mm internal width rim. Its a 303 Firecrest hooked rim.
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stu
646 posts
#10May 25, 2024, 6:22 PM
21 mm is on the narrow side for today's gravel rims so I doubt any new tires in the 40 mm range will measure larger than marked. Tires measured by BRR on 17.8 mm rims should measure roughly 1 to 1.5 mm wider on 21 mm rims.
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