Pompiere

Same here, my road bike has a 50 chainring, so I'm not losing much with a 48. Even bikes with 42-32-22 compact gearing, when coupled with an 11 or 12 cog, have a reasonably high gear, considering the terrain and weight of the bike.

Shinkers

The bike I'm getting has that same 42/32/22 triple currently.

What I was hoping to do is use a double crank and throw something around that 42t on the out outside position with maybe a 32 or something on the inner position and use a single ss cog with a Melvin tensioner in the back.

This would give me the all purpose gearing I've been looking for.

My concern is moving the outer 42 on a triple to the outer of a double. Shifting inboard a couple millimeters, I'm not sure what clearance would look like.

due ruote 

So 2 x 1 gearing? I have never tried that. Doesn't really sound like most people's idea of all purpose gearing, but maybe it will work for you.

What I have done is a single ring and a 6 speed rear. I don't have hills to speak of so I used 44 x 13-21. That worked out great.

(Edit) aren't most tensioners meant for a straight chainline? Not sure how that's going to work out. Maybe someone has tried it.

Shinkers

Here's part of my inspiration from this very thread:

https://www.bikeforums.net/15547548-post1704.html

The melvin has floating pulleys that can move with your chainline.

due ruote 

OK I do remember neo pop's post now that you mention it. So at least you know it will work. I would set up the rear wheel and then select a BB length for the best chainline you can get. Pls post pics!

Loose Chain

Yeah, I like that one. If my 52 tooth big wheel "drop bar" conversion does not work I may convert to a three speed like that bike. Why 52 teeth, well, I am still pretty strong and the Kansas wind can get behind and push me along at ridiculous speeds. I had, and it is not terribly unusual, to have a 30 plus MPH tail wind. I bet people did not know old MTBs could do 40 MPH! Well, not sure, but my new GT (roadie) nearly melted its tires I was being pushed so fast. Yeah, I call my wife to come get me, when it blows like that, I go one way and cheat on the return. My point is, a big gear range might be needed for me for my conversions mission profile. I am using an Origin 8 Tikki mustache type bar. It has a nine speed cluster. Probably going to use Tektro levers and a Shimano 9 speed bar end with Velo Orange thumb converters.



A 52X13 on a 26 inch MTB cannot be too much higher than a 48/11 on a 700C, I guess, not bothered to calculate it, suppose I should.

Where can chainrings be (reliably) ordered for older Shimano cranksets?

HTupolev

52-13 is a lower gear than 48-11, even with same-size wheels.

Shinkers

See if I could fit up to a 52 that'd make me even happier but it's just too hard to tell. I know the double single system will work, it's come down to how large of an outside ring I can squeeze on with the chainstays.

I had actually intended to run this with a 52/36 mid compact and an 11/34 cassette as that'd be a ton of range. But with some compatibility issues, it was getting too complicated.

So I settled on the double single idea (or even just ss).

tiredhands 

Maybe the drops aren't appropriately deep, but here's a GT Tequesta I've recently put together with Origin8 mustache bars. I like it. Those bars offer great leverage for grinding up climbs.

Lascauxcaveman 

I did a 3x1 using the Paul tensioner I picked up in a box of parts, and it was good for yuks but not nearly as useful as a 1xWhatever with a regular derailleur, of course. With a flip-flop hub, it worked well enough as a "tringlespeed" but when I flopped it over the fixie side, I realized right away I'd have to be extremely careful riding it as a "trixie" or I'd break the tensioner.

It was fun to try, but decided if I'm going to have something hanging off my hanger, it might as well be fully functional.

NocoRider

I'm not fully understanding your goals but as for the calculating the diameter of a chainring use this equation. It's an approximation but will be very close:
Diameter = s* N/pi
Radius = Diameter/2

s=12.75mm
N=Number of Teeth
pi=3.14

So a 52t chainring will have a diameter of about 105.5mm
52 => 105.5mm
48 => 97.4mm

With your current setup, measure the clearance between the chainring and chainstay.
Calculate the Radius of the current chainring

Since the bicycle flexes when it is pedaled you'll want some clearance between the new chainring and the chainstay.

Typically the middle chainring is aligned to the middle of the cassette/freewheel, so in theory this would be a better location for a single chainring. But the clearance between the middle ring and the chainstay is much less so you won't be able to fit as large of a chainring in the middle position.

As for calculating your maximum gear...

Determine your maximum cadence (say 115 rpm)
Determine (measure or calculate) the circumference of your wheel in inches
- Example for 26" wheel: pi*Diameter = 3.14*26 = 81.64"

Convert inches to miles: 12 inches in a foot, 5280 feet in a mile
81.64/12 = 6.8 feet
6.8ft/5280 = 0.001289 miles

So every revolution of the wheel is 0.001289 miles

With a 52/11 top gear, every revolution of the cranks results in 4.727 revolutions of the wheel.

A cadence of 115 revolutions per minute, or 60*115= 6900 revolutions per hour

6900*4.727 = 32,616 revolutions of the rear wheel

32616*0.001289 = 42 miles per hour

So with a 52/11 top gear, if your maximum cadence is 115 RPM then you'll spin out at 42 mph.

All of this math is linear, so if you can spin at 120 RPM, that is 4.35% faster so you'll spin out at a 4.35% higher speed (43.8 mph). Similarly if the chainring is only a 48 (7.7% smaller), then you'll spin out at about 38.8 mph.

Hope this helps,
Greg

Dale Alan

I'm sure that uncomplicated it for him.

due ruote 

Ha! Alternatively you could take a 52 ring of any bcd and lay it on top of your current ring, and then with a China marker or piece of tape mark where it landed on the stay. Sight down your current ring and see how it looks. Maybe you could add a BB spacer.

Edit-easier still, and more accurate, forget the overlay thing; just measure the diameter of a 52 ring and go half the distance from the crank bolt; mark the same way.
Fwiw I have roughly 1/4" clearance from the large ring (46t) to the stay on my Stumpjumper. I bet it would be close, but it's going to depend on your frame.

Smlitz12

[IMG][/IMG]
This Is my khs Montana summit I built up. It has 26 1/38 rims, a 52t chainring, and a 7 speed freewheel. All the brake stuff is off an old ross Eurosport until I save the cash for something a bit better.

Shinkers

Thanks for the info and help, you've answered my question.

Smlitz12

[IMG][/IMG]
It clears just barly though with the bb I have. The spindle length is 108mm, but with a 113mm spindle length I had room for the double chain ring set up 52/39t, but that bb went bad and I had the 108 laying around. It's a truvative powerspline set up.

Eace

Nice bike, love the green.

Eace

I was hoping to see something like this GT here, nice bike.

Shinkers

I'm seeing a lot of Moustache bars in this thread aand am seriously considering them for my build.

What types are you guys running? Nittos primarily I'd assume?

smtesta

Took this for its first ride today. Rides amazingly well. This was designed to be a mountain bike touring rig. Awesome for paved roads, dirt roads, gravel, and single track.

https://goo.gl/photos/wy7fzKmBedhe1DB87

Squeeze

I happened to see this on craigslist today. I do not know the seller and am certainly not shilling for him by posting this here.

What caught my eye, other than seeing a drop bar MTB conversion on craigslist in the first place, and beyond the delightfully mis-matched handlebar tape, are downtube shifters. I've seen someone's orange Stumpjumper posted here with DT shifters, but this is the only other MTB I remember seeing with them.

Is this some kind of aftermarket clamp-on DT shifter mount that I've never heard of or seen before? I'm not looking to buy them, but just thought it might make for good discussion.

Or were those original equipment from the manufacturer? I'm guessing not.

Classic 90's Steel MTB Turned Gravel Grinder

romperrr 

@Squeeze, it's likely an aftermarket add on as I'm certain Miyata didn't offer MTBs with DT bosses. Origin 8 makes such a clamp.

Squeeze

Thanks, @romperrr. Hey, I learned something today!

Here's a picture from a quick search... and that sure looks like a vintage MTB to me!

Jeff Neese

My understanding is that those clamp-on shifter bosses almost always slide down the tube without some sort of braze-on or "nub" (like the one that holds cable stops in the same position). I was going to do something like that on one of my bikes, but my research at the time showed that a lot of people seem to have problems with them. I went with bar-ends instead.

Jeff Neese

I have run:

WTB Dirt Drops
Soma Portola
Nitto Noodle
Nitto Randonneur
Trekking bars

I eventually "settled on" the two Nitto bars on two of my bikes and a set of Trekking bars on a third.

Despite their legendary awesomeness, I didn't care for WTB Dirt Drops, but that's just because of the kind of riding I do. I did feel like I had the most control with those, though.