Who has the 700 / 650b Spectrum?

[BobbyJones]

Somewhere I saw a Spectrum (I think) that was built to run both 700 & 650 depending on need.

I've got a few questions if anyone can point me in the right direction.

Is anyone else doing this? Not as a one off, but built for dual purpose intent?

Thanks!

[ColonelJLloyd]

Is anyone else doing this?

Switching between 584 and 622 wheels on the same bike? Or specifically a Spectrum?

[Kirk007]

I can do it on my ti Spectrum but it wasn't purpose built for that hence the limit is around 38mm width on 650(b).

[zennmotion]

I may have mentioned my steel frame/fork Spectrum that Tom designed as an "all road" 700c for a 57mm brake reach. I originally built it with Shimano r650 mid-reach caliper brakes, then later found a deal on Paul Racer/center mounts (the longer ones, not Racer M). Although officially they accommodate 57-72mm reach, they work great with the thinline brake shoes at the top of the slots for 700c wheels and they're just barely long enough at the bottom of the slots to also use a set of 650b rims. In theory, this shouldn't work- the difference in rim radius is 19mm, but it does (just barely, on my bike). This was an "accidental" discovery, not an original intentional design request. Fitted with 700c wheels, the tire clearance (that I'm comfortable with) is 38mm, and the limit with 650b wheels is 40-42mm - so really just "one size" larger, not a huge difference functionally, but of course I can also run a 38mm 650b tire that's lighter and "feels" more like a narrow road tire. The clearance is limited by the chainstay width, I could go wider if the stay dimple were made longer but I am not going there on my favorite bike! In reality, I use 700c wheels almost exclusively, if I really want a bigger tire than 35-38mm I use another bike because the Spectrum was designed to ride like a road bike, not 'gravel' or 'offroad'. It just stretches nicely to my favorite mixed terrain type rides. I think the combination of Tom's design, using Paul Racers, with Thinline pads on adjustable posts on 25mm width rims (Pacenti with a fairly wide brake track) works as a happy combination, I'm not sure it would or wouldn't work with any other set of components on any bike with slightly different design elements. Hope this helps. While it works with some fiddling with my rim brakes, I think if you really want to have the option of switching between 700c and 650b wheels you need discs. IMHO, I also think that a bike design would be somewhat compromised with this feature- which may or may not be important to you. I wanted a bike that handles like a stable road bike, not a gravel bike, not a cross bike. Making the stays longer and other design features to optimize gravel and off-road would feel different, for me I would miss the lively feel of a road bike, because in reality, it's used on both pavement and maintained unpaved roads, not on the gnar stuff except for very short stretches.

[mistermo]

Somewhere I saw a Spectrum (I think) that was built to run both 700 & 650 depending on need.

I've got a few questions if anyone can point me in the right direction.

Is anyone else doing this? Not as a one off, but built for dual purpose intent?

Thanks!

I bought a tall, maybe 63cm, Rivendell Rambouillet, designed around 700c wheels. Previous owner put 650b wheels on it. It rode great with plump 650b Rene Herse tires. I've since redeployed the 650b wheels and have reverted back to 700c wheels. Rides great with 700c too.

[BobbyJones]

Thanks for all the replies.

I'm thinking it was a Spectrum with disc brakes that the owner had purpose built for this.

Looking to do a new custom and maybe a setup like this may get me closer to N+0

[ColonelJLloyd]

My bike was built to use up to 55-584 or 40-622. Using rotor shims on one of the wheelsets and the same range cassette on both it is truly plug and play.

[Kirk007]

Thanks for all the replies.

I'm thinking it was a Spectrum with disc brakes that the owner had purpose built for this.

Looking to do a new custom and maybe a setup like this may get me closer to N+0

Having both my Spectrum (designed around 700c x 28) and a 333Fab AirLandSea (designed for 650b x 48-50 but also accomodating 700c) I would offer this: It's hard, perhaps not impossible but hard, not to have a compromise somewhere in this type of bike if you are really looking for a large spread in tire size. My 333Fab is best, and to me noticeably so, with 650(b) wheels do to the relatively high bottom bracket. My Spectrum - probably could have had the chainstays dimpled a bit more or maybe spread a bit more to squeeze in a 42 diameter tire (they just take tires that measure out at 40mm) but I think trying to accomodate a 48-50 would have resulted in a different bike. It's hard to get to N+0. Sorta like having something like a BMW or Porsche SUV I would imagine; feels sporty until you drive a purpose built sportscare. Seems ok for light offroad duty until you get to a place where you were wishing you were in the land rover.