Pros and Cons of Two Possible 650B Conversions

[cachagua]

In a nutshell: put a pair of 650B wheels either on a road frame, or on a mountain bike frame, as a quick and dirty method of seeing how wheels like that behave.

I have both frames, a 56cm pre-Colorado Serotta and an early-90s Stumpjumper. Either way, I've got to re-do the brakes -- longer-reach calipers on the roadie, maybe that or maybe something different on the Spec. And I need a few other parts for each, naturally.

I'm impressed with the reports of how the big, juicy Grand Bois tires (and others similar) ride, and I'm thinking of having a bike built that will accommodate that size. And I figure this could be a way to get at least a partial sense of what that'd be like, and whether I'd enjoy it enough to justify the cost of a new bike.

Of course the two frames have different wheelbases, and one would end up with its BB a little higher than designed and the other a little lower, but beyond the obvious, what will the advantages and disadvantages of each option be?

[palincss]

What are the chances that there's room between the chain stays and at the fork for a 42mm tire on that Serotta frame? Many of the recent ones don't even have clearance for a 25mm tire.

[JAGI410]

Follow this and measure them up and find which one will work best:
http://www.bikeman.com/bikeman-blogs/650blog/1771-650b-conversion-guidlines

That said...I drank the 650B Kool Aid last year and converted my beloved sport touring bike into a 650B rando-esque bike and found that the Kool aid was just as delicious and refreshing as advertised. I now harbor anger towards my other 700C roadie.

[cachagua]

That page has some great information, thanks. It tends strongly toward converting the road frame, rather than the mountain. . .

Any arguments on the other side?

[roydyates]

That page has some great information, thanks. It tends strongly toward converting the road frame, rather than the mountain. . .

Any arguments on the other side?

What palincss said: It seems unlikely that the serotta will fit 42mm hetres. My personal feeling us that if you can't fit hetres, the 650b road conversion is not worth the trouble. On the other hand, I converted a 26in Riv Allrounder to 650b, and I like the conversion a lot. However, that may or may not have any significance relative to a stumpjumper conversion.

[pinkshogun]

what Royyates said. i would only convert a frame if Hetres or Pari Moto tires fit the frame.

[cachagua]

...If you can't fit hetres, the 650b road conversion is not worth the trouble..

Interesting. . . according to the measuring method on the Compass Cycles page, I could probably fit as big as a 38 in the chainstays (which is by far the narrowest place). But that won't yield enough difference from the 700X25s I'm using to be worth it, huh?

Guess I could build the wheels, go ahead and get enormous tires, try them in the road frame, and if they don't fit then I've got the mountain bike for back-up. But am I wrong to think of this as a way to split the difference between road wheels and really fat fat tires? If I wanted to use a tire bigger than 40mm, wouldn't I just ride a 29er?

[JAGI410]

I disagree, there are still some great tires in 650Bx38 if the Hetre doesn't quite fit. I'm running the Grand Bois Lierre in 38 and it's fantastic.

[cachagua]

Come on, y'all are betraying y'all's Paceline membership. A subject like tire size? How fat is fat? Controversy, hah, I thought there'd be fistfights, death threats by now! Six or eight pages of responses, at least! Is everybody still in a turkey coma?

I was looking at the Lierres too. Could be tasty. Even going from a 25C to a 35 is roughly doubling your air volume, according to my cocktail-napkin approximation. . . wouldn't you be able to feel that difference?

[keevon]

...I could probably fit as big as a 38 in the chainstays (which is by far the narrowest place). But that won't yield enough difference from the 700X25s I'm using to be worth it, huh?
You'll feel a huge difference with 650bx38. I recently converted a Surly Pacer with 700x28's to 650b with 38mm Soma B-Line tires. The difference in ride quality is astonishing - the Pacer now floats over just about anything. On the flip side, the bike feels like it might be a little slower, but it could be in my head.

If you're thinking about having a 650b custom built, I would recommend converting your road bike. The MTB will have too many other variables - geometry, tubing, etc.

[pinkshogun]

i've never used the Lierres but the tread, compared to Hetres, just looks slower....my non-scientific judgement

for real world evaluation, Hetres proved flat-free for over 500 miles of dirt, crushed limestone and gravel.....as well as smooth and fast on pavement

[palincss]

What palincss said: It seems unlikely that the serotta will fit 42mm hetres. My personal feeling us that if you can't fit hetres, the 650b road conversion is not worth the trouble.

There are some pretty nice 36-38mm wide 650B tires, you know: the Pari Moto is one outstanding example. The difference in plushness between a 23mm racing tire at 100+ psi compared to a 38mm tire of equal suppleness inflated to 50 psi is simply astounding.

It's not like swapping wheels and brakes is all that much trouble: we see plenty here replacing their brakes (and spending simply breathtaking amounts of money doing so, too) solely to save a few grams; and if it weren't for Lawyer Lips, removing & replacing wheels would be entirely trivial.

[palincss]

Interesting. . . according to the measuring method on the Compass Cycles page, I could probably fit as big as a 38 in the chainstays (which is by far the narrowest place). But that won't yield enough difference from the 700X25s I'm using to be worth it, huh?



The hell it wouldn't.

[pinkshogun]

here is another option...

http://www.somafab.com/archives/product/b-line

[palincss]

here is another option...

http://www.somafab.com/archives/product/b-line

Definitely one of the nice 38mm tires I had in mind. The Grand Bois Lierre is another.

[pinkshogun]

all this talk reminded me of an old set of 650b wheels i have and how nice it would be to put back into service a frame, for lack of adequate tire clearance, i dont use anymore

[ColonelJLloyd]

Don't forget to consider BB height after conversion. I believe 700Cx23 is roughly equivalent to 650Bx42. So, if you can't fit a Hetre you're BB is going to be lower.

[roydyates]

Interesting. . . according to the measuring method on the Compass Cycles page, I could probably fit as big as a 38 in the chainstays (which is by far the narrowest place). But that won't yield enough difference from the 700X25s I'm using to be worth it, huh?



If you fit a 650bx38mm tire, and you like to experiment, you should probably try a parimoto. The ride is quite similar to a hetre. My personal experience is that the parimoto is less durable, so I wouldn't recomend switching just to use a parimoto. Moreover, if you fit a 650bx38mm, you proabably also fit a 32mm 700c tire like a grand bois cypres, and that makes the value of switching to 650b is not so clear. However all of these options are likely to be quite different from a 25mm tire.

[bfd]

The hell it wouldn't.

Steve,

We all know you have ridden wheels with 584x38 and 700x25 tires. You stated that a 584x38 is more "comfortable" than a 700x25. That makes sense - more air volume = more comfort. But what about performance? Do you feel you can go "as fast" on 650b wheels as a bike with 700x25s?

Others have said that the 650b wheels, while more comfortable, felt slower. As someone who has ridden both, it would be good to get your impression. Thanks! :eek::butt::banana:

[umami]

The Spring 2013 issue of Bicycle Quarterly has a lengthy and detailed article on tire sizes, rolling resistance, and the effect of width on ride quality. A 25mm tire has 18% more air volume than a 23mm in the same rim diameter. 18% for a mere 2mm increase in width. A 41mm tire has 218% more volume. 38mm comes in a mere 16% lower.

I converted my Bridgestone RB-2 to 650b with 38mm tires (the largest that would fit in the chainstays) and the difference is significant. The decrease in trail is small but noticeable, and the fat tires roll over the rough stuff much more smoothly. I'd call it "different" rather than "better."

By contrast, I swapped my 700c 38mm wheels with a friend's set of 650b Hetres on my Rawland dSogn and the ride is hands-down better. The frame just feels like it was made for the smaller wheel size. Takes less effort to accelerate, steers better, rides super smooth. Those Hetres are really great tires.

All other factors aside, I think one of the advantages of 650b is that at large (40mm+) tire sizes, it keeps the rolling diameter fairly close to a 700c race wheel/tire setup. I have never liked the feel of 29" mtb tires--they feel huge and heavy and slow to steer. 26" feels much more manageable, and I suspect that 27.5 comes in as a nice compromise between the two for bump absorption and nimbleness.

The downside is that tire selection is fairly limited (but growing thanks to the 27.5 mtb scene--less so for road tires, but once you get Grand Bois you won't want for much else), frame clearance is usually a hassle, and long reach brakes are necessary. I suspect you'll want a frame built for the right size wheels, eventually.

[HillDancer]

Tire shapes are not uniform when mounted, most volume quotes are based on a circle. Any deviation from a perfect circle (circumference of a tube) will reduce volume. A rim with a deep center channel will provide greater volume than a rim with mildly concave shaped channel.

Internal rim width will also have an effect on air volume. Rolling circumference is determined by the cords, but internal volume can be altered by moving the beads. Just as a 23mm tire feels and performs differently when mounted on a rim with 18mm between the bead hooks compared to an internal width of 14-16mm, a 38-42mm (nominal) tire will feel and perform differently when mounted on a rim with 27-34mm internal width. While Cypres, Hetre, and Pari-Moto tires were designer/manufacturer intended to be mounted on narrow rim brake rims, much of their performance potential is unrealized when mounted on rim brake limited rim widths. When rim width is proportional to tire width, slip angle is reduced. A 67 TPI Pari-Moto at 33psi (tubeless), with adequate sidewall support (29-34mm internal rim width), can nearly match the steering response prowess of a low volume/high pressure tire with the same trail numbers. There is a small penalty for high volume/low pressure tires when climbing out of the saddle, but it is an acceptable trade-off for an increase in cornering grip and pneumatic suspension, and both of those attributes improve with appropriate width rims.

Except for the tread pattern, I like Hetre tires a lot; more so when tubeless and mounted on wide rims. I'm looking forward to Soma's soon to be released Panaracer Slick for many of the reasons I like the high volume Hetre. In its preproduction examples it was slightly wider than the Hetre, and is purported to have a super supple casing. I also like the lower 67 TPI version of the Pari-Moto a bunch when mounted tubeless on a wide (34mm internal width) rim. A standard Hetre with Michelin tube was 552 grams, the black & tan Pari-Moto with tubeless sealant is 340 grams. The weight reduction alone has a positive effect on performance, and its file pattern tread when new grips much better than the grooved tread Hetre. Hetre's grooved tread does seem to slough potential damaging debris well though. Both the 127 and 67 TPI Pari-Moto models feel more supple in the hand than the Hetre.

[palincss]

Steve,

We all know you have ridden wheels with 584x38 and 700x25 tires. You stated that a 584x38 is more "comfortable" than a 700x25. That makes sense - more air volume = more comfort. But what about performance? Do you feel you can go "as fast" on 650b wheels as a bike with 700x25s?

Others have said that the 650b wheels, while more comfortable, felt slower. As someone who has ridden both, it would be good to get your impression. Thanks! :eek::butt::banana:

There's a difference between feeling fast and being fast. Vibration and harsh ride are often interpreted by riders as feeling fast, while plushness feels slow. Only way to tell for sure is by timing comparison runs on an identical course. All that said, based on my observed average speeds on numerous rides in the same area and on the same roads, I'm not any faster on my Ti Spectrum w/25mm tires than I am on 28mm, 32mm or 42mm. But then, I'm not a very fast rider regardless.

[cachagua]

Many thanks to all of you who offered good ideas! I'm now totally sold on converting the road frame instead of the Stumpjumper.

And so, that glorious pink Shogun up there -- do we get to see if once you've built it? I'll show you mine if you show me yours--

By the way -- good places to buy these tires? Selection's kind of spotty on eBay, and sadly, I don't know where else to look.

[JAGI410]

Harris Cyclery. They have sales or free shipping deals fairly often.