650b or 700 Bombadil frame question

[maxcr]

Hi Everyone,

I recently teased my new Bombadil project in another thread and now I'm reaching out to all of you with a question. As I was deciding on parts for my build, I was inspired by John's post on The Radavist and ordered some Ultradynamico Mars Race tires.

Based on the sale copy, measurements from the seller and the geo posted on Cyclofiend, I was certain this frame was a 56 (L) and had 650b, so I ordered those tires in 2.2".

To my dismay, I went to installed them only to realize the wheels are 700c. Of course, I felt like an idiot for not double checking my wheels before ordering, but now I'm wondering whether the wheels that came with the bike were the originally intended by Grant/Riv for this frame?

It could be that this is a prototype, so perhaps it's an odd one. It can also be that I was mistaken and it's not a 56 but a 60 (XL) frame which would explain the 700 wheel size. 

At this point this doesn't matter (if you're curious, I re-measured the top tube is around 61cm and the seattube is around 59cm so it's probably a 60) but this got me wondering, if I buy a frame, how do I know if the design is made for 700c or 650b? 

Is there a measurement around the canti posts or something one could check to figure that out?

Thanks in advance for your help.

Max

PS. Now, I'm not even sure the frame would fit the 700 mars race 2.2 tires - I was hoping it would. The geo says 50's are the max tire for the XL (it's weird, the smaller frames fit a wider tire because they are 650b). The 650 Mars Race seemed huge when I presented them next to the fork (I didn't mount them, because I didn't have the right wheels for them) so maybe once inflated they would fit? Anyway, I ended up installing my Schwalbe Marathon Supreme 700x50 which went in with room to spare, so maybe the 2.2 fit...

[Garth]

Max, Your frame pictured appears to be a 60cm, which is measured center-BB to the top of the seat tube( C-T for short ).

The TT be measured center seat tube to center head tube ( C-C ). If measured along the top tube, regardless of angle, that's called the "actual TT". If the measured horizontally from the center-head tube horizontally to where it "would" meet the center seat tube(if it was that high), that's the effective TT( ETT ). The ETT is a virtual figure, it's "virtually" there but not actually !  Your TT ought to measure 63cm actual, 64cm effective. The effective can be a bit tricky, if you have a long straight edge with a level on it it's easy-er. 

For the canti wheel distance, just measure from the center dropout to the center canti post (where it meets the frame, not it's extension), along the seat stay. On the photo for example, you'd just draw a line along the chain stay between those two points, c-c.  Any way you do it will work as long as you're consistent. 

By your photo I assume you are referring to the fitting of tires with the fenders installed ? If so, well it's not sized for that, the max tire size is for no fenders. You have to take in account the actual tire shape/type itself also, a Marathon Supreme is more like a slick tire. Knobbies need more room. Your Supreme with "room to spare" to you, doesn't appear to have any room to spare to me. I assume the fenders are P50's ?  Fenders do need room for debris to pass. I have P50's and Big Ben's on my 60 Bomba and despite the tire being actually 46mm wide, it does rub very slightly against the mounting bracket rod inner hardware every so often when shaken hard. It's also a relatively tall tire, so that has to be accounted for also. So the clearance is just not vertical, it's also horizontal, the inner hardware, notably on SKS fenders. 

[maxcr]

Thanks Garth, I think you're right and this is a 60cm. What confused me is that the geo chart shows 64cm for top tube which is much more than what I'm seeing - perhaps it changed from 2TT to diagotube?

This is the C-C that I have:

As for the tires, apologies for not being explicit but I meant without fenders. I took everything apart to clean the bike and treat some rust in the chainstay area. I think my fenders are either P55 or B65 or something bigger than P50 but I haven't tried installing them back yet.

Here are some photos to clarify and I will measure the tire width and fork space with calipers and report back

Best

Max

[Garth]

Oh sheesh, now I was confused too because the linked chart is wrong. I just measure mine, and it's the same as your, 62cm c-c along the TT, 63cm effective. I never used that chart anyways, it's either a preliminary version or it's simply a misprint, I'm guessing a misprint as the ETT jump from 56 to 60 frame should be 60.5 to 63, respectively. Every geo chart ever printed by Riv, and I've kept most if not all, show the 60cm Bomba @63cm ETT.

As for the tire clearance, those Supremes are what, in the 46-48cm range ? Yes, there's lots of room between the stays, and on the front you can fit a 2.2 without a fender. Between the blades is 63-64mm I think, where the fender would go. The chainstays and bridge however I'm not so sure, you'd have to either apply some widened calipers to guestimate the width and how forward, or just put a mounted tire in there. How much room is enough ? Enough that you don't crash and burn if caught in a "jam" ! ((( laughing ))).

[maxcr]

Thanks for sending that geo chart Garth! That makes more sense.

You were close! I measured my Schwalbe tires and they are 44-45mm as installed on the velocity synergy rims. It's hard to gauge the true clearance of the frame without actually trying the wider tire, but I think 2.1 is ideal and anything beyond would be pushing it, particularly in the rear - maybe I can go 2.2 or even 2.3 in the front and 2.1 in the rear. It gets close as you approach the kickstand plate where the stays narrow, I'll play with it some more but my guestimate is that I'll have around 60mm of clearance with the wider/taller tire, so if I want at least 3mm on each side, that means 2.1 is the way to go in the rear, which means the 700c UD MARS Race probably won't work for me on this frame.

Thanks again

Max

*All of the above is without fenders

[lconley]

I have 650B x 57 Schwalbe G-Ones on my Bombadil 52, but my chainstays are longer than the 45 shown on the chart.

Laing

[Leslie]

I built up my 56 Bomba w/ NeoMotos originally; then I swapped and was running my Ram's 700c wheelset (I am using Motolite brakes, so I could slide the pads up to fit the 700c wheel).   I did go back to 650b on the Bomba, built a 650b wheelset for the Ram (and am running the 700c wheelset on the canti-Rom... )   

It's crazy what all you can do w/ these....

[maxcr]

Thanks Leslie!

About brakes, what do you all think for the Bombadil? V-Brakes or Cantis?

I'm wondering if not using the built in hanger would be a waste

ideas?

Max

[lconley]

Mine doesn't have a built in hanger.

I went with cantilevers - easier to put bigger tires on with fenders and also I am using drop bars. I have Paul Motolite V-brakes on my Gus ( and other V-brakes on other bikes) and I don't see any advantage in braking for V-brakes (nor discs for that matter) over cantilevers, but I do live in Florida.

Laing

[maxcr]

Here's mine - wouldn't it look odd just hanging there? 

Max

[Garth]

I use only cantilevers and basically will always ! Good ol' smooth post cantilevers that clear the frame as opened and open all the way. No silly overly long and offset pads that add nothing to the braking performance. I take a certain delight(albeit comical and always good for a laugh in just thinking it), in denigrating v-brakes and certain cantilever designs, including making/selling/defending frames without rear cable stop bridges. Call it what you will, as so have I. ((( laughing )))  Nevertheless, it stands. I could also speak about how "the industry" is their own worst enemy, in fact, their only enemy and the customer but a witness.

I remember not long ago before the Clem Riv couldn't give a v-brake away. Then with disc brakes becoming the thing, and dwindling proper canti manufacture and design , it didn't leave them much choice as the frame was a sales hit. It's like drinking a brand of beer you really don't like, but because the wife loves it, and you love the wife's company, you swallow your taste buds,    one   bitter   chug    at    a    time.   "Ain't this beer great ?   said with crooked broken smile and whose eyes betold another story.

What's life without a couple of good ol' stories ?  .... teeheehee .

So sure Max, Anything but a cantilever on your Bombadil would leave you without any brake at all :-)

[Leslie]

I've cantis on the canti-Rom, Motolites on the Bomba, like 'em both.   Have to admit:  I'm running 700-40 MSO's on the Rom, and I have to deflate to get that fat tire into the cantis on that frame (I'm running a tire seriously over what is spec'd on it).     The Motolites are easier to get really fat tires in and out of....    

[maxcr]

Something else I have now started to realize is that cantilevers are more likely to rub against a handlebar bag. Are V-Brakes preferred for this reason?

Laing, what stem are you using with the towel racks on the bombadil? Also, how wide did you go?

I'm reconsidering my Riv Bullmoose choice and wondering whether towel racks (660) or a spank flare 25 bar is a better way to go. 

I plan on running a BXB goldback bag in the front

Thoughts?

Max

On Thursday, February 16, 2023 at 2:47:11 PM UTC-5 Garth wrote:

[Garth]

That totally depends on the location and type or rack, bag, and cable run. You don't have to have a drop down cable stop in your headset stack, you can use a Tektro 1277A fork mounted cable stop w/adjuster which allows a solid cable run just like a caliper brake. V-brakes are no more a solution than cantilevers are a problem. 

[lconley]

The stem is the Nitto DirtDrop 100mm.

I went with the widest 660mm Towel Racks.

Big tires, big fenders with clearance to the tires and V-brakes tend not to play well together. I have V-brakes on several of my bikes and I don't really see any real advantage to them over cantilevers, unless you consider ugly an advantage. The cantilevers work just as well and have all the fender clearance that you could want. I am waiting for Rene Herse to get their cable hangers back in stock to get one for the Bombadil.

Laing

On Monday, February 27, 2023 at 10:53:01 PM UTC-5 maxcr wrote:

[Jason Fuller]

I need to get Laing to set up my cantis for me :)  I have found V's to have significantly more power and tend to save my hands on hillier terrain as a result.  I run Motolites on my Bombadil (and I have the canti bridge just hanging there.. doesn't look too weird though) and while they do become a clearance limitation when you're trying to fit larger fenders, they'll clear anything that fits the Bombadil.  I wouldn't go more than 2.4 or 2.5 with V's although I see Riv and Crust promoting larger; and biggest fender combo I would try is a Flat 65 with 2.1 or 2.2. 

I will say, after running a couple sets of Motolites and most recently setting up and riding a pair of Avid V brakes ... the Avids work just as well and are even easier to set up. They just lack fanciness. 

Jason 

[esoterica etc]

> On Feb 28, 2023, at 12:50, Jason Fuller <jtf.f...@gmail.com> wrote:
>
> I will say, after running a couple sets of Motolites and most recently setting up and riding a pair of Avid V brakes ... the Avids work just as well and are even easier to set up. They just lack fanciness.

Jason, curious as to specifically which Avid V-brakes you were referring to here? Very interested in a brake that's comparable in function to the Motolites but without the price tag. Thanks,

~Mark
Raleigh, NC

[lconley]

I might just be really, really bad at setting up V-brakes.

Laing

What is hilly terrain?

Delray Beach FL

[Mackenzy Albright]

I was able to fit Avid SL V brakes with Honjo Flat 65's and 2.1 tires on my Clem Smith. The Flat 65's really give you a lot of height adjustability. They work really really well. 

[Patrick Moore]

1. Cantilevers too work better with tires no more than about 60 +/- mm wide; getting a 3" knobby between the canti bosses (unused; the Monocog 29er has disc brakes and is set up for both) is a hassle, even when they are soft at 13-15 psi.

2. While I can get decent (my definition may not be yours) braking from good cantilevers, at least I personally have found it much harder to get "powerful" -- = strong retardation with moderate hand pressure -- braking with cantis than with V brakes. I do like other things -- adjustability, modulation, looks -- better about cantis than Vs.

I recall the miserable power from Mafac cantis, both single-bike shorter-arm version and longer-arm tandem version, on my Herse, pulled by Mafac levers. I daresay I could have shortened the straddle cables, but sold the bike before I got around to doing so (sold, not because of the brakes).

Laing: How do you get strong cantilever braking, particularly with drop bar levers? I guess that one preliminary factor is to match the pull of your lever to the needs of the cantilever; my Dura Ace 7410-era drop levers probably don't have as much MA as my Paul Neo Retros and Touring cantis need for best operation, but I love the shape of those levers.

I'd be interested in others' apercus about this.

[lconley]

Geometry is all important with cantilevers. I will use Paul models for reference. Note that at a certain level, V-brakes are just optimized cantilevers, so much so that they have too much braking force that must be reduced at the levers. If maximizing braking force is the be-all, end all of braking, then why use levers that reduce the braking force? But there is something to be said for V-brakes having less tension (and therefore stretch) on the brake cable.

1. You want the straddle cable operating at, or as close as possible to a 90 degree angle to a line drawn from the brake arm pivot axis (the post brazed/welded to the frame) to the straddle cable connection to the arm. This is much easier on a Paul Touring than a Paul Neo-Retro. Motolites are basically taking the progression to it's conclusion (Neo-Retro -> Touring -> Motolite). Note that when working with Neo-Retros, this generally means rotating the arms as far towards the rim as possible, using the fewest, narrowest spacers between the pad and arm as possible (and that is allowed by your tires). This is where some "experts" get it all wrong, they seem to think that the rotation of the arm changes the direct of travel of the pad at the rim - i.e. the arm carrying the pad should be straight up, which is untrue. The direction of travel of the pad at the rim is fixed by where the relative location of the pivot is to the rim-pad interface - only a welder can be used to adjust this. The pivot is below and outside the rim -> the pad will ALWAYS be traveling in a downward arc relative to the rim. Note that because V-brakes use the same pivots as cantilevers, the cheapest POS cantilevers that you can find vs. Paul Motolites - on a given bike, the pads are traveling in exactly the same arc, this is a function of the frame and wheel, not the brakes nor the brake adjustment.

2. Ideally, you want the straddle cable as close to straight as possible where it goes through straddle cable carrier -> the straddle cable as short as possible. This is a very unappreciated part of the equation. When you apply a perpendicular pressure at the center of a straight cable, you would actually get an infinite tension in the cable if it did not stretch. This a very handy thing to use in many instances - you can move a car with only a rope and this principal. The cosine of 90 degrees is 0. When you divide by 0, you get infinity. If you want to prove this to yourself - make a straddle cable between the ends of a V-brake and use a straddle cable hanger connected to the brake cable cantilever/centerpull style.

3. There is an interaction between 1 and 2 - as you make the straddle cable straighter (#2), you lose the 90 degree angle (#1). On top of that as the cables, straddle hanger, and brake arms move, and the cables stretch; the geometry changes. With Neo-Retros, getting the arm as close to the rim as possible also raises the straddle cable arm interface up, getting the arm-cable angle closer to 90 degrees. Note that means having your wheels extremely true and minimizing the pad gap and toe-in. As the brake arm rotates under application of the brake, this angle improves - gets closer to 90 degrees again. As the straddle hanger rises under brake application, this also gets the brake arm - straddle cable angle closer to 90 degrees and increasing your braking force. But as all of this is going on, the straddle cable at the straddle hanger is getting less straight, reducing your braking force. With precise measurements of the actual relative geometries on your bike, you can calculate all of this, or you can experiment with lengthening and shortening the straddle cable.

4. I think that a far bigger item with braking is the pad interface with the rim. Getting the pad centered on the rim, or actually just a little bit above centerline of the braking surface is advised (remember that the pad is traveling in a downward arc with the pivot below the rim with cantilevers - with centerpulls, the pad is traveling in an upward arc). You also want the pad flat to the rim (up-down flat when it contacts). If you don't want squealing brakes, you must toe them in. The better your pads, the more you must toe them in. The more you toe your pads in, the worse your braking is because less of your pad is is touching the rim. I think the long pads in fashion at the moment make this worse. I prefer shorter pads with less toe-in. I have not experimented with cutting/filing/grinding a bevel on the leading edge of the brake pads, yet, but I think that hold promise.

I spend a lot more time adjusting brake pads than anything else in the braking system (that goes for discs also). The location of the brakes makes it hard to observe the pad-rim interface which is where everything important happens.

I use bent pieces of old credit and business cards of different thicknesses at the leading edge of the pads to set toe-in (this does not apply to the Rene Herse centerpulls).  A velcro strap at the brake lever on non-Paul brakes to apply tension. My almost half-century old 3rd hand brake tool is too narrow for todays brakes - still works on the Campagnolo side pulls though. 

Laing

[Patrick Moore]

Laing: Thanks for this detailed and informing overview; I have read it through and will read it again slowly, but I think I get it: 90* to brake arm pivots + as flat as possible at straddle, as little toe-in as you can get by with to prevent squeal, and make sure that the pads meet the rim brake tracks squarely. I've already done the last 2, must go back and look at the first 2. The single rear rack strut to seatstay bridge may limit my options in the rear. My pads are old Kool Stop salmons, the short, blocky sort. I did make various shim tools for toe in, must seek those out again.

Thanks again!

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

[lconley]

Remember that flat at the straddle and 90 deg at the arms fight each other - it is always a compromise.

Laing

[maxcr]

I found this Path Less Pedaled video useful when I installed the Paul Touring Cantis on my Atlantis: https://www.youtube.com/watch?v=CDdWIq4cLLo

Thanks everyone for your responses and particularly to  Laing for that masterclass on how to set up cantis!

Max who's still rethinking handlebar and drivetrain choices for the upcoming Bombadil

[lconley]

That is a pretty good video - he uses the tool to show the 90 degree angle. He points out that lowering the straddle (making the straddle cable flatter) results in better braking. He even talks about getting the pads as close to the arm as possible with the Neo-Retro (wide profile) style cantilevers. To steal a phrase from someone - Approve!

Laing

[JohnS]

I agree with Laing, I spend way too much time setting up canti brakes. I usually remove the tires and even the fenders when installing them. This allows me to see how well aligned the brake pad is to the rim as Laing has noted. I prefer to use brake pad holders for this reason, set them up once and when the pads wear out, slide out the old pads and slide in the new. No adjustments necessary.

JohnS

[lconley]

Uh-oh. I am going to have to remove the tires when I reassemble the Bombadil to adjust the brakes now!

Laing

[JohnS]

Another trick that I recently learned while installing the Paul mini-mottos and touring cantis on my Crust Lighting Bolt Cant (was going to install them on my QB but decided the LB-C would benefit from them more) is to loosen the return springs so that I didn't have to work against them. I did have the cable adjuster turned out most of the way so that I could turn it in once I all the adjustments are done. I was able to do the same thing with the Tektro 720's on my QB since the spring can be unhooked from the brake arm easily. I don't recall if other canti brakes have this option or not.

JohnS