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Sizing for Trek 750 Multitack w/ drops

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Sizing for Trek 750 Multitack w/ drops

Old 02-10-21, 01:04 AM
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Sizing for Trek 750 Multitack w/ drops

For my winter is project I am wanting to find an old steel straight bar hybrid like a Trek Multitrack and convert it to a drop bar bike. I believe the straight bar hybrids and drop bar road bikes are use different sizing. I plan to use this mostly as a gravel bike and do an occasional loaded camping tour.. Like many of you here, I do have other bikes both road and mtn. So, I want this bike to be more of relaxed fit compared to my road bikes. (Raleigh International and Professional)

My inseam is measured at 31 inches from the floor. I usually ride 56 cm bike Trek 750s come in sizes 17, 19, 21 and 23 inches. I guessing that 21 inches (53.4 cm) would be optimal for me. Any thoughts. I may be buying on ebay or drive a long distance to purchase so I would like to have the sizing squared away.

Thanks in advance
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Old 02-10-21, 06:29 AM
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I'm still keeping my eye out for a 750, and there are a couple details about the geometry that changed over the years this bike was offered. Basically the earlier lugged frames have a shorter top tube and a higher bottom bracket. At some point Trek decided that most people were riding the Multitrack bikes on pavement than off road, so they dropped the bottom bracket on the later tig welded bikes. I got that trivia from a Trek sales brochure. I think its on vintage-trek.com. The top tubes also got longer, I guess because all the mountain bikes of the era did. I would check out vintage-trek.com and all the geometry charts and compare the fit to your road bike.

I ride a similar 23" Koga-Miyata Cityliner Hybrid that's realy a bigger bike than a 23" road bike, primarily because of the higher bottom bracket. I've got 40mm Schwalbe Little Big Bens under fenders that put me higher up and add to the already high trail feeling. This bike was designed around a 35mm max tire, which is different than the Treks.

Moral of my rambling is that for this kind of bike; would be to decide what kind of riding you want to do and how the bottom bracket height will effect that, and also consider sizing down to a 19" if you can get the saddle and bars where you want them.

Last edited by bark_eater; 02-10-21 at 06:36 AM.
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Old 02-10-21, 06:58 AM
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I think sizing was intended to be more inline with MTB sizing of the day. That is, size down from your road sizing.
The 23” is almost certainly going to be too big.

A local buddy here just finished the kind of build you speak of. He’s 6’ on a good day, but with short legs.
He’s happy with his 21” (53cm ST, 56 TT)
There’s no shortage of different stem ideas to find one that’ll suit you. Especially some of the whacky hybrid stems from that era.

Here is his build...

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Old 02-10-21, 07:08 AM
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I'd worry about the top tube length mainly. You can get a longer seatpost and you can get the stem up high enough but you can't do anything about the top tube length.

I think Sheldon Brown is right on this,


This is my '92 Stumpjumper that I recently converted to drops. The top tube length is 22.5 which is right around the length of my road bikes. The frame is a 20 inch frame which is smaller since I ride a 22-23 inch road frame.

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Old 02-10-21, 08:08 AM
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Well..certainly a 19 or 21, but that doesn't help much.

You'll never know how a drop bar conversion really feels until you're done with it..again, not much help.

I've done a couple conversions..a pic of the first can be found in the Hybrid forum "Show your Multitrack" thread
Show your Trek Multitrack!

Your biggest issue will the drop bar handlebar reach, which goes right back to the top tube length.

1) Google how to make frame and handlebar stack and reach measurements. You'll need to do this in making estimates on how to do the conversion.

2) Measure c-c the top tubes, frame, & h-bar stack and reach of your other (comfortable) bikes to get an idea of what stack/reach range works for you.

3) I also generally ride a 56cm road bike and around a 20 inch mtn bike(hybrid and mtn bike sizing is the same). When I did my second conversion (Trek 970 mtn bike to a drop bar touring bike) I bought an 18 inch 970(shorter top tube compared to my usual size) to see how it felt when riding it straight-bar. Since the drop bar conversion adds about 75mm of reach (beyond the h-bar reach of the straight bar, using compact drop bars) I figured starting with an abnormally short top tube made sense. I rode the 18 inch 970 as a mtn bike...yikes..it felt really claustrophobic. After comparing the frame and h-bar stack reach of this bike to what I needed in a conversion (or road bike)..the 18 just wouldn't work for me. I sold the 18 inch bike for what I had into it. Fortunately, the day after I bought the 18 inch 970 (1990 version), I fell into a near showroom 1993 20 inch 970..that one fit much better.
It's raining Trek 970's

4) Look at the vintage catalog/spec manuals for the Trek Multitracks and note the top tube lengths of various years and sizes.
Trek, Fisher, Klein, Lemond bike catalogs, bicycle brochures

5) Use this stem angle/length calculator to (virtually) adjust and compare potential stem lengths and heights. This will help you bridge the gap between what you need in your conversion vs what is available in the market. The stem can be the hardest part of a conversion.
Stem Comparison Tool | yojimg.net

6) Make some estimates on the hybrid/mtn bike regarding your needed seat post extension/saddle height and how much of a rise you'll need in your converted h-bar stack to get your saddle to bar drop where you want it. The Yojimg calcualtor helps here. There may be a difference in what you need vs what's available to buy.

I assume you're familiar with the mtn bike drop bar conversion thread..if not..settle in for some extensive reading.
Show Your Vintage MTB Drop Bar Conversions

If you take everything I've mentioned above and think about it, you can pretty much know what you'll end up with before you start a conversion. After reading the mtn bike conversion thread, I think many folks(some/many with more extensive back ground than mine) just eyeball a frame and do a conversion. If it doesn't fit..rinse and repeat. I went the numbers-estimation route as I'm more comfortable there.

A Multitrack will make a decent touring-gravel conversion. You can easily mount 38mm tires, and probably larger. The frame geometry of the 90's Multitracks are very similar to identical to the Trek 520 touring bike. The 750 & 790 have the same, better tubing than the 730 and below. My GF's 750 has worked fine for our tours. She carries about a 30 pound load. Sure, the aesthetics of the bike don't equal a new bike designed for such things, but her 750 in near showroom condition ran me $100...and I wasn't sure she'd enjoy touring as much as she does now that we're out there doing it. She LOVES the bike...and has other much nicer road bikes to compare it to.

You might consider a Trek 950 or 970 conversion also. The 970 ('93 at least) had a Shimano XT drive train. The XT front & rear derailleurs are fully compatible with brifters. Most conversions use bar-end shifters as it's less expensive and offers fewer compatibility issues. My 970 conversion turned out great. I completed it last spring and got in about 1000 miles on it (600 miles fully loaded touring) over the summer/fall. Very comfortable bike and handles 35 pounds of gear like a breeze. I run Schwalbe Big Ben tires..the bike rolls super easy. I used Tourney 3x7 brifters and Ritchey Ergomax bars(same dimensions as the Salsa Cowbells at much lower cost). All the conversion needed was bars, shifters, cables, and stem. The rest of the bike is stock. Took about 90 minutes to convert, with final adustments..no brainer. Also..the geometry of the early 90s 950 & 970 is the same as the Multitrack, which is the same as the 520. 73* seat post, 71* head tube angle. After '93, the 950-970 top tubes got 1-2cms longer.

You'll need to think hard about gearing. The Touring forum discusses this quite a bit. You'll need 18-ish to 100-ish gear inches readily available.

Last edited by fishboat; 02-10-21 at 08:30 AM.
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Old 02-10-21, 09:01 AM
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I have one of the last lugged 750's (1993) in default flat bar configuration, so if you need measurements for a 21" frame, let me know. The stand-over's just shy of 32." The TT is ~22.5" center-to-center. I'm 5'8" and it's a bit snug, but TT clearance is fine for road or gravel. Good luck in your search!
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Old 02-10-21, 05:57 PM
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Like this?

I built this, it's a 21" frame. This is a '91 I think.
Couple things, max tire size is 700x45c, rear axle width is 135mm which is mtb spacing, and the top tube is basically at the same height as most 56cm bikes, because the bottom bracket height is higher. This year and '90 as well for this 750 frame is basically the same spec as the 520 frame (within a cm here and there on most specs). Rides nice.

The full TIG welded frames instead of the lugged frames have a different geometry and maybe even a 19" would be okay for what you want to do.
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Old 02-10-21, 06:09 PM
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Also go here to see a bunch of Multitracks redone.

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