Bicycle Mechanics - 700c to 650?

I wasn't sure how to search the databases for this info, but whatever. here it is:

I've got a 58cm klein quantum. it's a pretty tight frame as far as tire clearance goes, and i've been wanting to start using a slightly wider tire to be able to cover a wider range of terrain, maybe even some cross stuff. Can i rebuild the rims with a smaller hoop, change the brakes to some long reach/wider clearance calipers, and just lose maybe a cm or cm and half in stand-over?

My wife has a older touring bike with 650's with 35c tires, so i instinctively slid them into place before i even asked this and things looked like they might work. But what am i missing? Crank length problems if i lower the overall height of the bike?

I realize i might be better off with a different bike, solving many of my problems from the frame POV, but i just sorta love my klein too much.

The only real issue is the added 19mm of brake reach. That's quite a bit and you'll find there some loss of brake arm rigidity, and overall brake performance. How much depends on what you have vs. what you but, but it is a big difference, and there's not much you can do about it.

You'll also lower pedal clearance, but not by as much since the wider tires will make up for it somewhat. Pedal ground clearance isn't super critical since most people coast through tight corners inside pedal up.

Before you spend the dough, you might seek out a bike with brakes of the reach you're considering and test ride it just to see if brake performance is acceptable. Of course bikes vary, but it'll give you an idea.

IMO it's a shame that most decent road bikes are built as if they were going to be raced, when in fact they're not. Even if they don't have fender clearance or eyes, tire clearance of at least 28mm would be nice.

BTW- if your brakes and rear bridge clearance will allow for it, you can gain a few (very few) millimeters of added tire clearance by mounting your front wheel a bit lower in the dropouts. Make sure you are still clearly on the parallel faces for everything but the slot itself. If you have the room and it makes the critical difference, you can make this semi-permanent with a bit of fill at the top of the slot. This is what I did so I could mount road tires on my track bike 45 years ago, and I've been riding it that way ever since.

An option for dealing with the potential brake reach issue is to go to drum brakes. It is a great option in instances like this.

as for the brake issue, i did a little hw, and found rivendell with an possible solution: http://www.rivbike.com/product-p/brsr559allen.htm

And yeah, tire clearance is my main grief with the klein. the thing won't accommodate even a 28c front.

I think this might happen if those are my two main concerns.

Good luck.

May I suggest that you don't cut your wheels apart, but buy a fresh set. That way you preserve the option of switching back at any time. If you're willing to do the work, you can even switch back and forth as the situation warrant.

good point.

I realize i might be better off with a different bike, solving many of my problems from the frame POV, but i just sorta love my klein too much.

I have a Klein too and I love it because of the way it feels on the road. I don't think putting on wider tires is going to make it handle like a cyclocross bike. I predict you'll be sorry if you do this.

Be careful you get the "right" 650. 650C is only used for triathlon and small-framed bikes, and there aren't a lot of fat tire options.

650B is the size that has been on the rise for conversions and "rando"-style bikes. Pricey, but worth it by many accounts.

650A is the old and lonely size used on the old English 3-speeds. You can still get new aluminum rims and some decent tires (usually 35-38mm wide). Since they're not as high-zoot, and you wouldn't need to extend the brake reach as much, you may consider this size for the conversion.

It would cost a lot less and be far less hassle to just get a different frame, like a touring or cyclocross frame. You could then move all your components over with no "hacking", though you'd likely need new brakes.

650B tire sits on a 584 rim 700c is 622 .. that is bead seat diameter..

do the math..

NB there are 650abc & 700abc.

French sizing scheme, basically, rim smaller tire fatter and rim bigger tire thinner
similar overall outside combined

my wife's bike is 650a, i should have specified that. On a 35mm tire i liked the minimal difference in height. i'm aware of the popularity in "b" which would increase my rim selection. That warrants some investigation. I'll check the usual places...

And, yeah, while i agree with the general consensus that i am making my life needlessly harder that is sort of the point. I've got a 29er mtb which i could easily turn into some sort of salsa fargo knock-off, but thats no fun. from my pov.

The other possibility is to make a brake drop bolt (see Sheldon Brown) so that you can use normal-reach brakes.

The drop bolt shown on the SB website is kind of ugly. I saw a much nicer one somewhere here, it was made with a double ferrule for steel cable. Of course, it would also be a simple thing for a machine shop to make.

Ah, here is it, see post #10.

http://www.bikeforums.net/showthread.php/819004-Is-there-anywhere-to-get-brake-caliper-drop-bolts?highlight=brake+drop+bolt

And, yeah, while i agree with the general consensus that i am making my life needlessly harder that is sort of the point. I've got a 29er mtb which i could easily turn into some sort of salsa fargo knock-off, but thats no fun. from my pov.

I understand. :thumb: I go back and forth over converting one of my Bianchis to 650A or 650B so I can run fenders, but then I think about it more and wonder if it would be worth it.

If you go from 622 mm to 584 mm and use similar size tires, the bike will drop by 19mm.

If you change from 23mm wide tires to 35 mm wide tires, the bike will only drop about 7 mm (~1/4 inch) - this is a pretty small change: you can make this change on a touring or road-sport bike by switching from a 23mm tire to a 30mm tire.

650A is an EA3 in English schemes , a commonly used 3 speed bike
wheel size.. 590
You could improve the rim and leave it as is for size, a 1 3/8 tire, 37
should suit most uses.

The other possibility is to make a brake drop bolt (see Sheldon Brown) so that you can use normal-reach brakes.

The drop bolt shown on the SB website is kind of ugly. I saw a much nicer one somewhere here, it was made with a double ferrule for steel cable. Of course, it would also be a simple thing for a machine shop to make.

Ah, here is it, see post #10.

http://www.bikeforums.net/showthread.php/819004-Is-there-anywhere-to-get-brake-caliper-drop-bolts?highlight=brake+drop+bolt

This option may also limit the OP's tire size choices too much.

Brad

This option may also limit the OP's tire size choices too much.

Brad

Not may most likely will. Since he started with a tight frame, it's safe to assume it cam with short reach brakes, These generally don't clear much over 28-32mm tires, even if mounted very low. There's also the issue that there will be severe loss in rigidity with the brake hanging out in space 15mm or so below the crown. It would need a sizable well braced chunk of metal between the bolts, not to cause vibration and chattering when braking.

I'm not a fan of longer reach brakes than necessary, but that would be the best bet if the OP goes to 650b

Yeah, you want to keep the brake-arms as short as possible to keep clamping-leverage high. Standard-reach brakes should clear the largest tyres he'll want to use and that would only require around a 10mm drop-bolt. Would also look nicer than long-reach brakes with all that air-space above the tyre.

Yeah, you want to keep the brake-arms as short as possible to keep clamping-leverage high. Standard-reach brakes should clear the largest tyres he'll want to use and that would only require around a 10mm drop-bolt. Would also look nicer than long-reach brakes with all that air-space above the tyre.

Length of the arms has nothing to do with leverage. Brakes with longer pad arms also have longer cable arms, and so leverage ratio is preserved.
And added flex has little to no effect on braking power - makes the brakes feel worse, but not actually stop worse.

I've a 27" bike converted to 650A. Tire choices are pretty slim for 650A though, and the bike has a little bit higher chance of pedal strike now. Fenders and fatter tires is awesome though.

Another good option is building a drop bar conversion of a vintage 26" MTB.

I totally agree that it's stupid how much racing aesthetics influence bicycle design. A bike with more clearance for fenders and fat tires as an option is only losing a hair of aerodynamic advantage.