zucchiniboy

Hi there,

I'm considering converting a road bike from 700 to 650b. I can barely squeeze some skinny 32mm tires in the rear (they actually measure 30.9), and can probably do up to 35mm in the front. If I convert to 650b, I'd still only get enough clearance for 38mm in the rear. Would this be worth it to convert this into a gravel bike? I was thinking of putting on Maxxis Ramblers (650bx38) if I wanted knobs, or Panaracer Gravel King Slicks (650bx38). My thought is I'd still get some extra volume in the tires, lowered the overall height a bit, but overall I'd really be going from 32mm to 38mm in tire width.

Any thoughts? Is this worth the effort?

Elvo

Depends on your BB height. Going from 700x38C (686mm wheel diameter) to 650x1.5" (660mm) is over a 13mm drop in BB height.

shoota 

Depends on the surface you're riding and how attached to the bike you are. I would vote no.

chas58

I've thought the same, and decided no.

BB drop is a big issue. And, really, really make sure you have width all around the tire - brake bridge, chain stay, front derailer...

I do ride 32 and 38mm tires (ramblers). The difference is significant to me. but in the end, I got a bike that can comfortably take both sizes.

tangerineowl

You really need to try that tyre size first, or a bike with a 650b x 42 on it. Whether you like the rolling-diameter feel.

If I was strictly on smooth paved surfaces I would only do it. Anything above groomed mild gravel and I would give it a miss.
For me a 650b x 42 feels borderline acceptable but only over smooth stuff. Over heavier stuff the tyre just feels too small.

Spoonrobot 

I wouldn't bother. Every road-focused 650bx38ish tire fudges height to keep the weight low. Most are only going to be ~35mm tall. Since wide tire comfort comes from both height and width you are not gaining near as much as you expect.

700c tires are often more true to height and will have close to the same comfort as a wider but shorter 650b tire. Also the 650b gravel king sicks are probably worse than gatorskins as far as rolling resistance and suppleness are concerned. My pair of 650bx48 measured only 44mm tall on 21mm inside width rims. 700c gravel king slicks are a much better tire.

chas58

Phoo hoo on the naysayers for 38mm. The 38mm rambler is my do everything tire. Light, fast and very versatile. I do roll mine on a 700c though...

zucchiniboy

With 700x32mm tires right now I'm at 285mm BB height, so this would theoretically bring me down to 272mm, which I've read is still ok.

Yeah, I'm on the fence because I can only get to 38mm, but if it's a true 38mm, I'd still be getting something like 50% more air volume. But would it be worth it?

That's helpful to hear. What do your 38mm ramblers measure? If I did this, I'm thinking of building a set of wheels on A23 or Quill rims and the slightly wider internal width than my current 19mm outer rims.

Thanks all for your input thus far. I was hesitating, and most of the feedback here seems to be leaning toward no. I'm still pondering it though...

BluesDawg

I would consider going with a wider rim than that so that later you can use these wheels for 650B x 47 or wider tires when you eventually realize that what you really want is a bike that can take bigger tires.