Sizing considerations when choosing an MTB for drop bar conversion?
 

I'm interested in finding a mtb to add drop bars to, but I was wondering about sizing.. do you want to go with a slightly larger than normal MTB side, like how road bike sizing is bigger than mtbs? i'm talking about traditional horizontal top tubes, not slanted ones.

i've been seeing this one bike on CL.. it's a 22.5 which is on the larger side but still in my size range for me at 5'11". I'm thinking it might be better suited for a drop bar conversion compared to a 19" frame i've been eyeing. The DB Apex I ride now is 20" and overall the sizing is good, though i feel like i could stretch out a tiny bit more when going all out. the larger frame will give me the longer top tube so that's why i'm thinking it woud be more suited for a drop bar conversion.

any thoughts from people who've actually done the conversion?

Check the TT length, that is the biggest challenge to me. My next conversion will be the 20 inch Cimarron I picked up. I usually ride a 18 t0 19 inch mtb, and a 22 inch road bike. Road bike stem, or are you planning to use the MTB stem? MTB stems tend to stretch you out even more.

I am thinking the 20 inch Cimarron will put me between the two sizes.


Assuming you get the MTB at a reasonable cost, I would try it out regardless.

I second the effective top tube begin he most critical measurement.

80's mountain bikes were closer to a Touring bike geometry. As time went on that changed. The top tube got longer making the reach longer to make more room for knees when standing and climbing steep hills when off the saddle. The BB also came up for ground clearance and the top tube dropped to make a shorter stand-over so you didn't hurt yourself on uneven terrain when you dismounted.

If you tried to go for a french fit on a modern mountain bike you would have one heck of a reach even with a short stem.

I was able to find the catalog.. the 22.5" has a 59cm TT. My current mtb is 56cm with another ~10cm reach on the stem. When I'm tucked in a more aero position, my arms end up underneath me and it's hard to hold the position long. i'm not sure how much farther out i need to stretch but in the drops woudl help i'm sure.

looks like the 19" bike's TT is right around the same length as the one i've got now.. 56cm

head tube angle is 70, 73 for seat tube on both bikes i'm looking at. my current mtb has a 68 head tube angle which is why the TT is shorter even though the seat tube is longer

i hadn't gotten that far.. probably a mtb one if i'm gonna run cantis since mtb stems have a center hole for the brake cable, but im thinking bout swapping in vbrakes and getting those tektro vbrake levers

yeah.. i've been waiting out this guy for a while as his price has finally dropped into reasonable range hahaha. still not 100% set on getting the one i'm looking at.. wish it were one size smaller and diff color. the 19" has better paint but might still be too small.. though looking at the TT sizes doe make me think that the 19" could work with the right stem.. could potentially get the 19" for cheaper than the 22.5 as well... hmm

yeah i'm talking about "traditional" geometry with horizontal TT :)

Frame size is also going to be dependent on the intented use. If the bike is going to stay on the road such a beater or gravel road bike, a taller frame will be more comfortable, off road trail riding you'll want a shorter frame. Some of the TT's can be longish, but as you plan to use a MTB stem that will bring the bars up and not stretch you out too much. I ride a 62-65cm Road bike and am happy on a 60cm MTB frame with drops. My conversion is a '81 Giant Iguana

cool thanks for your insight. the intent would be almost excursively as a road rider. i was thinking a frame closer to my road bike size would make more sense for that application. why are taller frames more comfortable?

I did a mock up on the Cimmarron tonight. Cockpit definitely too long with the MTB stem. I may try a road stem on it instead.

+1 I will have the same problem on front brake routing, as the current route goes through the center of the stem. I will need to squeeze in one of those HS mounted cable stops instead.

Evening the bars with the saddle results in less saddle to bar drop and less reach.

^ but doesn't a riser stem accomplish the same thing?

earlier today i was thinking maybe the 19" would be an ok choice, now i'm back to thinking the 22.5" would be better... or... *gasp* getting neither and waiting longer lol

Since a lot of vintage MTBs were measured by the (short in relation to everything else) seat tube, you'll probably want to use a "smaller" size. Here's an old picture of my 20.5" Diamondback next to my 23" Bianchi, which have the same TT length, and are set up roughly the same (the bars have come down a little on the DB):

http://s36.photobucket.com/albums/e2...k/IMG_2679.jpg

As one example, I ride most often a 22" road bike, in a mtb. I ride an 18" most often. I would not want to set that frame up with drop bars, for that I would want a 20" most probably, but as has been mentioned, the top tube length really plays a significant influence.

You probably know this but if the HS stack height won't allow the cable stop(not enough thread engagement) there are others that mount on the fork crown brake hole(assuming there is a brake hole).

nice ascent.. 88? and you've got two brake levers but only one brake huh? :D

the two bikes i'm looking at are both 1989 diamondbacks actually :) i think the 20.5" size would be ideal but not sure if going smaller or bigger is best if not going with the ideal size.

Why wait? Mid 80's Kuwahara with 20" seat tube and 57cm TT. Seems right in the middle for you.

http://i246.photobucket.com/albums/g...Sale2110-1.jpg

Also, this one could be fun.

http://i246.photobucket.com/albums/g...0/DSC08218.jpg

^ hah i've been thinking bout hitting u up, but i'm cheap and u drive a hard bargain ;) but u got a pic of the kuwahara?

The first pic is the Kuwahara. The second is a '84 Cannondale SM500. It was Cannondale's first MTB. It has Deerhead mechs, side pull BMX rear brake and 24"/26" wheels.

oh the 1st pic wasn't loading the 1st time. what's the tubing on the Kuwahara? looks pretty damn nice actually.. is that a repaint?

and just realized the smaller wheel on the cannondale.. that does look fun.

I don't really need a new bike, but my apex doesn't handle too well at high speeds. most mtbs don't, i know.. but a lil steeper head tube would go a long way. I'm used to being able to ride where ever i want on an mtb too, and fat tires are way more comfy

It's the original paint but the stickers are long gone. It has more relaxed geometry and I'm guessing it to be Tange chromo.

Many MTB's will have a seat tube angle similar to a road bike's, but the older one's will have a more layed-back angle, which will definitely steal from the frame's effective top tube length unless the saddle is situated radically rearward as compared to a road bike.

As far as the head tube angle though, the MTB frame will just about always have a slacker head tube angle than a road bike, something that can make the handling quite floppy when using road bars with anything but a shorter horiz stem extension.

So, for both of the above reasons, I find that larger MTB frames with modest stem extension are the only good candidates for road-bar conversion, not that these actually make so much of a good all-around road bike.

Compared to a build-up using a proper road frame, the MTB framed bike will typically have a high bb, a stiff ride and will tend to be heavy.
If ridden in a brisk road biking group, the steering may also have a different response than the bikes that surround you.

The advantage would be added durability of the frame and wheels, plus the generous tire clearances which can accomodate fenders with ease.

Thanks! I've since deleted the right brake hood -- the fixed-gear conversion allowed me to do without a lot of things, including those limited-time-only U-brakes. ;)

Very cool. Unless you've got particularly short arms for your height, I'd spring for the 22". Diamondbacks are tanks! To my surprise, it's become my daily driver.

I'd venture to guess that the Kuwahara is Tange.

http://i246.photobucket.com/albums/g...Sale2115-1.jpg

I've got this Norco I'm about to sell, too. I realized I can't keep them all. :(

http://i246.photobucket.com/albums/g...r_Sale2137.jpg

My Scott seems to have a more aggressive head tube.

http://i246.photobucket.com/albums/g...r_Sale2138.jpg

Hey frantik, if you decide to go the larger route, I've got this frame, too. ;)

http://i246.photobucket.com/albums/g...r_Sale2126.jpg

The bars you choose will have an impact on the geometry as well. If you pick something with a lot of reach, a longer top tube might be problematic.

I'm currently putting some Midge (dirtdrop) bars on my Stumpjumper. The word on those is to set them up to ride mainly in the drops. So you have to get the stem pretty high, which would be more difficult with a smaller frame.

Thanks, I may have to consider that option.