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drop bar mountain biking sizing question

Old 07-28-22, 02:57 PM
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Swimmingbulldog
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drop bar mountain biking sizing question

As a 5'9" individual with short-ish legs, I would imagine most mountain bike sizing charts would put me at a 17 inch frame. If I was to switch my handlebars to drop bars, do I need to alter frame size? Should I still be looking for a 17 inch frame? Back story: I am more of a road bicycle guy and I like the physical aspects of bicycling. I want a mountain bike for distance. I am not looking to do technical jumps or anything fancy as I am 51 yo and that just seems like a bad time to start. . I am looking at older models (90s or 2000s) of mountain bikes to convert to to drops. Most of the bikes for sale locally on FB or CL are in the 18-20 inch range.
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Old 07-30-22, 06:23 AM
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If anything, you would likely want to size down if you plan to run drops. Frames designed for drop bars have shorter top tubes than frames designed for flat bars.

Of course, this also means that youíre likely going to need a few spacers or a riser stem, as the stack will likely be a bit too short.

Also, older mtbs (like pre-early 2000s) tend to be better for conversion since top tubes have gotten even longer since then.

Be aware that these conversions can be tricky, as there can be compatibility issues when mixing Road and MTB brakes/levers and shifter/FDs. There is a ton of information out there about this, so Iím not gonna go into details here.
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Old 07-30-22, 08:05 AM
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You will need to size down for a shorter top tube when converting to drops. I have done the conversions and recomend just buying a medium Salsa Fargo or the new Surly drop bar mtb frame. It will save you headaches in the long run.
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Old 07-30-22, 09:13 AM
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Just measure the top tube length range you're comfortable with and look for a MTB that has a top tube length in that range. 1993 and older Trek 900 series had top tubes about 1.5cm shorter than 1994+. Also, measure the frame stack and reach of a bike you're comfortable on as well as the handlebar stack and reach(to the horizontal bars or hoods). With some measuring and a little ciphering you can pretty much know how a MTB/hybrid conversion will fit you before spending money on it. I've done three DB conversions (two on hybrids and one MTB) and they all fit close to well fitting road bikes. My MTB conversion ('93 Trek 970) is used as a touring bike. Very comfortable and fast ride with good street tires(Schwalbe Big Bens 26x2.1). Fit is close to my road bikes.


(edit..Realize that as you size down in frame size the seat post will have to be raised higher. This requires a higher and higher stem if you're not comfortable with excessive saddle to bar drop distances. Basically there's diminishing returns with smaller frames to yield shorter top tubes as other issues come in that need to be dealt with. The key is to find the balance between right-sized top tube and seat post/stem height.)

Last edited by fishboat; 07-30-22 at 09:18 AM.
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Old 07-30-22, 09:26 AM
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Also consider this to ease the conversion.

Surly Corner Bar | Drop Bar Handle Bar With Flat Bar Controls | Mountain Bike Handlebars | Surly Bikes
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Old 07-30-22, 09:35 AM
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Thereís a long running thread in the classic and vintage forum about converting old rigid mountain bikes to drop bars. There are special problems related to the cable pull needed by the shifters and brakes.

Youíre best off starting with a 7 or 8 speed Shimano bike from up to the mid 1990s that has cantilever brakes, not V or disc brakes, because cantis take the right amount of cable pull from drop bar brake levers. And then using bar end shifters, because an eight speed shifter on the right will also work on a seven speed giving you more options and the left side will be friction so the different mountain versus road front shifter cable pull is not a problem. You probably should not choose a SunTour bike because Shimano went on to become standard in the industry for this stuff while Suntour gave up on shifters and switched over to suspension forks.

The idea of going down a size to reduce the reach is on point, but the extra reach comes with not enough stack. So you also may want a taller stem. Thatís all right, you needed a new stem anyway to go with a different clamp diameter of the drop bars.

https://www.bikeforums.net/classic-v...nversions.html

if you are having trouble searching craigslist by inch sizes, try also looking for letter sizes. You are a medium and you are looking for a small. But to be fair in the price range youíre looking you are just as likely to find them listed as anything including ďold bike just needs airĒ

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Old 07-30-22, 09:54 AM
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Early 90s specialized Stumpjumpers are good for drop at conversions. They use a 1 inch headset so you can run a nitto technomic to raise the handlebars. Agree with the others to focus on top tube length. This is my drop bar conversion:


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Old 08-01-22, 08:46 AM
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Thank you for all your insight. I am surprised you all said go down a size. It makes sense to me now, No doubt that is what would be best for mountain bike riding. I failed to mention that I was thinking more along the lines of gravel riding/cyclocross. I did one cyclocross race last year and it was a 17 in vintage mountain bike with flat bars. I felt more stable on rocky terrain, but maybe the flat bars were not the best when on flat grass or gravel. Do you all think this would change the sizing to a bigger frame so as to be more forward riding posture?
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Old 08-01-22, 09:35 AM
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Originally Posted by Swimmingbulldog View Post
Thank you for all your insight. I am surprised you all said go down a size. It makes sense to me now, No doubt that is what would be best for mountain bike riding. I failed to mention that I was thinking more along the lines of gravel riding/cyclocross. I did one cyclocross race last year and it was a 17 in vintage mountain bike with flat bars. I felt more stable on rocky terrain, but maybe the flat bars were not the best when on flat grass or gravel. Do you all think this would change the sizing to a bigger frame so as to be more forward riding posture?
Do you have a road bike fit? A CX fit would be closest to a road fit, while gravel tends to favor slightly more upright postures and useful drops. If you have a fit analysis completed, use it, or even go back to the shop and ask their fitter what tweaks you could make. ATBs generally have a longer reach compared to a road frame, even with the long stems in use at the time, so getting a larger frame, combined with more relaxed ST and HT angles can make you very stretched out, or unbalance the bike by putting too much weight on the rear wheel, or force a short stem leading to floppy and twitchy steering.
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Old 08-01-22, 10:04 AM
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The hoods put your hands further forward, that is the reason for going down a size for the conversion. Your Overall cockpit length from saddle to primary contact points on the bars should be the same for both road and mountain bikes.
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Old 08-01-22, 10:37 AM
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You could instead consider a handlebar specifically intended for MTB gravel conversions like Surly Corner Bar | Drop Bar Handle Bar With Flat Bar Controls | Mountain Bike Handlebars | Surly Bikes
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Old 08-02-22, 07:55 AM
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My preferred road bike size is 21 inch. I know what you mean in regards to being to stretched out. I put drop bars on a 1990 22 inch Schwinn Crosspoint and it was too stretched out. My back got tired and I felt too much pressure on my hands.
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Old 08-02-22, 07:59 AM
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That Surly Corner bar looks like a nice option. Thx. I have not heard of it before. I have seen the Gator Bar and I see that it works with twist grips as well. I have considered that but the bar itself has gotten mixed reviews.
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Old 08-11-22, 11:26 AM
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Originally Posted by Swimmingbulldog View Post
My preferred road bike size is 21 inch. I know what you mean in regards to being to stretched out. I put drop bars on a 1990 22 inch Schwinn Crosspoint and it was too stretched out. My back got tired and I felt too much pressure on my hands.

Thats exactly what would happen with a drop bar MTB conversion --- top tubes are just too long for that and stack heights are generally pretty low -

thats why when you look at the conversions, a lot of them have a wonky looking long stem adapter (lot of rise) - with not much in the way of length

Someone mentioned just buying a frame from Surly or Salsa made for this and i would tend to agree ---- and Salsa Cutthroat is a great bike too that is nasically a drop bar MTB too
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Old 08-11-22, 12:31 PM
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Salsa makes Cutthroat (carbon, thru axle) and Fargo (steel or Ti, adjustable dropout) and they are both definitely drop bar mountain bikes, because they are short reach for drop bars and designed to receive suspension forks. Although for some reason the Cutty has road-bike seat tube length and brake mount while the Fargo has IS rear / post front like a MTB. They both have 27.2 seat tubes so they aren't going to take much of a dropper, but the Fargo with a 2" shorter seat tube will do better with the 4" droppers you can find.
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Old 08-14-22, 06:01 AM
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Originally Posted by Swimmingbulldog View Post
My preferred road bike size is 21 inch. I know what you mean in regards to being to stretched out. I put drop bars on a 1990 22 inch Schwinn Crosspoint and it was too stretched out. My back got tired and I felt too much pressure on my hands.
You do know that sizing a road bike and sizing a mtb are different? i.e. if you ride a 21" road bike, you won't be riding a 21 or 22" mtb..
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Old 08-14-22, 11:26 AM
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Originally Posted by fishboat View Post
You do know that sizing a road bike and sizing a mtb are different? i.e. if you ride a 21" road bike, you won't be riding a 21 or 22" mtb..
The OP is looking for advice converting a MTB to gravel and CX use, not necessarily for singletrack. So far the advice provided is to pay attention to TT lengths to avoid getting stretched out, and that stack heights might be short. Gravel and CX fit are likely not too far from a road bike fit.
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Old 08-14-22, 01:04 PM
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Originally Posted by Unca_Sam View Post
Gravel and CX fit are likely not too far from a road bike fit.
Oh man, donít poke THAT bear
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Old 08-14-22, 03:49 PM
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Originally Posted by Unca_Sam View Post
The OP is looking for advice converting a MTB to gravel and CX use, not necessarily for singletrack. So far the advice provided is to pay attention to TT lengths to avoid getting stretched out, and that stack heights might be short. Gravel and CX fit are likely not too far from a road bike fit.
Hybrid and mtb sizing are the same concept/approach relative to road bike sizing. Think about your statement and you should see where your logic blew up.
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Old 08-14-22, 07:30 PM
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Originally Posted by Unca_Sam View Post
The OP is looking for advice converting a MTB to gravel and CX use, not necessarily for singletrack. So far the advice provided is to pay attention to TT lengths to avoid getting stretched out, and that stack heights might be short. Gravel and CX fit are likely not too far from a road bike fit.
I am not clear whether or not you are agreeing with the advice given so far.
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Old 08-16-22, 02:32 AM
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Originally Posted by Kapusta View Post
I am not clear whether or not you are agreeing with the advice given so far.
We all seem to agree that the OP should keep the 17in frame, or potentially size down to get close to his reach, with stack becoming a problem due to the shorter head tube. The only unclear part is manufacturers continuing to use seat tube length as a proxy for bike size when 'square' bicycle geometry fell out of favor decades ago.
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Old 08-21-22, 04:16 AM
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If you donít need a 50ish tooth cassette then Rival will work fine with itís 11-42

youíll need to stack spacers unless you want a lot of saddle bar drop.
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Old 08-21-22, 04:58 AM
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Keep the same size frame a run a 50mm stem with riser drop bars, if you need more stack height. Gravel and CX bikes are not road bikes and should not be subject to the same aesthetic judgement you'd get with running a short stem on a road bike.

The long running myth that short stems cause "twitchy" handling are just myths supported by bike publications that keep repeating the same ridiculous argument that holding your bars next to the stem simulates having a short stem. The only thing that simulates is having really short handlebars.

I've designed and built a number of Gravel frames with "forward" geometry that run 50mm stems and they handle just fine. The forward geometry concept of stretching the front end and using a short stem is very similar to sizing up on a conventional frame and using a short stem. If he is using an older MTB that was designed around a 100-120mm stem, he can easily go with a 35 to 50mm stem and drop bars.
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Old 08-26-22, 11:16 AM
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Originally Posted by alikaka View Post
Virtually all models of modern bicycles, with the exception of folding bicycles, cruisers and children's bicycles, are available in several lengths. Each rosta is designed for a particular height of the cyclist. Growth bicycle is denoted by either a letter (s, m, l), or the size in inches (16", 17", 18", 20"), or the size in centimeters (52 cm, 54 cm, 56 cm). The actual length is the length of the seat tube.

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