Widest tyre possible with Paul Racer calipers?

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satanas

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Jul 20, 2016, 4:05:32 AM7/20/16
to 650b
Does anyone know? It would be useful to be able to fit >42mm tyres without fenders, say something like the nominally 50mm Schwalbe Marathon, or the actually ~50mm SBHs or Thunder Burts. The various Marathons are most likely smaller than the nominal size, but if anyone has measurements of these on ~23mm external rims that would help, as would tyre height above the rim edge.

Currently thinking about a new frameset, primarily for randonnees (including PBP 2019) and touring. The big decision is what size tyres to run, and thus what brake calipers to use; I've decided to stick with rim brakes. Cantis are an option for wider tyres + fenders, but the Racers are a bit neater and I have a set I could use.

Note that I have MTBs so heavy offroad use isn't likely.

Any suggestions or data is welcome.

Later,
Stephen

Mark Bulgier

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Jul 20, 2016, 7:23:47 AM7/20/16
to 650b
I don't know the answers, sorry, but here are some thoughts.

If you're just in early stage musing, then crowdsourcing the answer in this way can be of some use, but before you commit to building your dream bike, you're going to need the actual tires on the actual wheels, for setting up the brakes and verifying it all works.  I wouldn't trust measurements, if you're pushing the limits.

To maximize the tire clearance, design the bike to put the pads at the bottom of the slot in the brake arms.  That's risky though; safer to design such that there's a little more slot below, so you can lower them a little.  Since the pads follow a rising arc as they move inward, they come up higher as the pads wear or when you switch to a narrower rim.  So you may need to lower them a bit someday from your initial conditions.

Pads all the way down is the minimal leverage setup (weakest braking power), but not all that different from, say, the same brake with the pads halfway down. Probably not a dealbreaker.  That can be mitigated by choosing a brake lever with higher than normal leverage, if such a thing exists. 

Back when I was a young mechanic, there were significant differences between the available levers (Mafac, Universal, Weinmann, Campy etc.), so you could tune the feel and leverage by choosing the correct lever.  I haven't paid attention to modern stuff though, so I don't know if there's still options like that.  Other than V-brake levers, which are too far off (and in the wrong direction), not usable at all on Racers.  I mean regular "non-V" levers that have slightly different cable-pull ratios.  Anyone know?  Probably moot if you're a brifter kinda guy, that decision will be made based on other requirements.

In flat-bar levers, there are some with an adjustable ratio, but I think all drop-bar levers have a fixed ratio.  Or to  be slightly more correct, they may have a variable ratio as you go through the stroke, but you can't change it.  The beginning and ending ratios are fixed.

There being no free lunches, any high-leverage lever risks running out of room to move (bottoming out) before you have enough stopping power, unless the pads are kept impossibly close to the rim.  So all levers probably fall within a narrow range of ratios.  But one made for big hands might have more leverage.  Anyway we're not talking about trying to get extremely high leverage, rather just taking a low-leverage brake back into the normal range.

Mark Bulgier
Seattle

satanas

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Jul 20, 2016, 8:37:11 AM7/20/16
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Thanks Mark. Levers will be 11 speed STI (sorry!), so leverage adjustments will be via caliper choice or straddle cable tweaking. FWIW, I have most of the parts likely to be used, except a Schwalbe Marathon Almotion/Mondial.

Most of the time BSPs or Hetres will be used, but it would be handy to be able to use something tougher in bad condutions (like the Marathons), or bigger for dirt - largely to lift the BB a bit.

Thinking aloud, it might be sensible to use a MTB crown + cantis for clearance and versatility. Seems like clearance at the rear may be easier to achieve, given the bike will be using 2x11 with small rings, probably 44x30 max.

Anyway, no need to decide until after trade show season, just in case something changes the rules again. :-)

Later,
Stephen

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Philip Kim

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Jul 20, 2016, 8:59:05 AM7/20/16
to 650b
Stephen,

I've done Switchback Hills on Velocity A23's on Paul Racers on my now sold Cheviot. Fit fine, with a few mm of clearance. The SBH were not 50mm on the A23, closer to 47mm. Paul states that clearance is 54mm between brake arms. I also thought about Thunder Burts, but decided against it as the side knobs would have probably rubbed against the brake arms.

I think Cantis is your best bet?

Stephen Poole

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Jul 20, 2016, 9:11:12 AM7/20/16
to Philip Kim, 650b

Thanks Philip, just the sort of info needed; I hadn't thought about the sides of the tyres rubbing on the calipers. Cantis are looking more likely all the time, and I could always repurpose the Racers (maybe for a conversion), or sell them.

Later,
Stephen

Max

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Jul 20, 2016, 9:57:25 AM7/20/16
to 650b, phili...@gmail.com
PSA: Word from Rivendell is that they've introduced 3 sizes of Hunqapillar using 650b tires, up to 56 cm frames, using cantis with a possibility of the Racer type bosses as well. No official word on geometry yet (trail, etc.), but I spoke to Grant in person last week while looking over a 54 cm x 700c demo Hunq, which was a size too small for me, at which point he spontaneously told me about the new 56 cm x 650b version. Given that the 700c model clears 52 mm tires, I'm guessing the 650b version will also. So, now I'm officially saving up for that one, as I don't have anything that can run >42 mm right now. :-) 

- Max

rob perks

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Jul 24, 2016, 3:15:10 PM7/24/16
to 650b, phili...@gmail.com
Stephen, 
Having handled a fair number of these and fielding the question often enough, the inside of the pivots is the most likely constraint.  That assumes you take care of the chain stays well.  The space between pivots measures 56mm.  The position of the narrow point is such that it is over the wide point of most tires.  Tires up to 47 fit fine with a decent safety margin.  If you go bigger, it can work depending on the cross sectional profile of the tire, relative to your tolerance for "safe clearance".  I have run the Soma Cazadero and BG Rock&Road with no concern at all, ant they have a wide squared off upper profile compared to something like a Pasella.

I love the feel and modulation of the Racer enough to design a line of bikes around it.  It is not perfect, but fit what I wanted it to be perfectly.  

Stephen Poole

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Jul 25, 2016, 1:11:29 AM7/25/16
to Ocean Air Cycles, Philip Kim, 65...@googlegroups.com

Thanks Rob,

It looks as if the only way to figure this out would be to obtain samples of all the potential tyres and check each one. That could get expensive very quickly, whereas cantis would definitely clear. They have their own set of problems though. Might be time for me to order a couple of tyres and find out for sure.

Later,
Stephen

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djm323

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Jul 25, 2016, 3:33:23 PM7/25/16
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Any suggestions or data is welcome.

You are probably are aware of this, but note that the Racers wont clear wide tires during installation or removal.  I need to deflate / inflate my BSPs to transport the bike with wheel(s) removed which means I need to bring along a floor pump.

:Dan

Stephen Poole

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Jul 25, 2016, 4:31:54 PM7/25/16
to djm323, 650b

Huh, that's interesting. Just checked and my Racers (centre mount, not braze-on) allow a Soma GL tyre through when the QR is undone, though the pads do touch. And that's with the thicker toe-in washers on the inside of the arms; if these are swapped around the pads clear the sidewalls by a mm or two.

As I don't have a car this wouldn't be much of an issue for me anyway, and no way I'd carry a floor pump on the bike.  :-)

Later,
Stephen

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Harry Watson

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Jul 26, 2016, 7:30:40 PM7/26/16
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Stephen,
My well used SBHs measure 47 on GB rims
Harry
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