Jackontheroad

Lets say, just an example: 20.5" is the size for a road bike; I understand that 18.5" should be the size of a MTB and that 19.5" of an hybrid. But, on my research I have not found a concrete answer on how to choose the size frame for a touring bike or how to compare it to a road bike?
Thanks.

MassiveD

Classic road touring bikes are road bike frame type. Position can vary depending on the exact use, like cross vs, time trial. So if you are nicely in the mid range of a size, you are probably OK. That said, if you have a frame that you currently ride, that you are happy with, it is well worth your while to document it. Position wise, this means seat tube angle; a reference point from the saddle to the BB, which can be the nose down if you will use the same basic saddle for the touring bike; and the top tube length and angle; the head tube angle; and a reference point for the bars, like saddle nose and from wheel bolt. With this info in CAD, or a drawing, you can compare the geometry of bikes you are looking at, because they can vary a lot for the same frame number.

seeker333

Short answer: if your 20.5" road bike fits like most peoples' road bikes, then you probably need a 21-22" touring bike. You'll want the bars higher and closer, thus you need a bigger frame.

Here's the longer, better answer -

A touring fit is usually a more relaxed version of a road bike fit - higher handlebar, shorter reach.

Don't assume the bike you have now is sized exactly right - if it's not, then the next bike will be wrong too. Take measurements to more objectively determine if your bike is fit properly. Odds are good that it is not fit optimally, and perhaps not even fit well.

Start out by measuring your PBH. From PBH you can accurately determine optimum saddle height and frame size. If your physical dimensions are within 2 sigma of normal (95% of population) you should be able to fit a std sized frame by adjusting handlebar height and reach. About 5% truly require custom frames.

Take your time and get good measurements, especially with PBH, since it's a critical dimension. Get someone to help you make these measurements, especially if you use the CC and WS fit calculators linked at the bottom.

There are some simple, popular formulas that originated with actual measurements of professional racers, promoted by Greg Lemond in a book, and these have been adopted by various bike makers and bike shops, and proven to be pretty accurate. The most useful ones I recall are:

saddle height = PBH x 0.883

frame size (CTT) = PBH x 0.67

There is a goggle users group for the Surly LHT. The group maintains an excel spreadsheet where users submit data such as PBH, frame size, etc. I took the data and calculated a linear regression on PBH vs frame size for sizes 46-60cm, and the equation surprisingly came out to

FS(cm) = PBH (cm) x 0.667 - 1.0; R^2= 0.76

This means for the included 113 data sets, these 113 people on average managed to buy a frame that was about 0.67 times their PBH (Surly frames are measured CTT), minus 1 cm - which is nearly identical to the aforementioned simple equation used widely for sizing frames. This result really surprised me, since surely some of these people didn't measure PBH exactly right, some probably measured it in thick socks or even shoes. R Squared of 0.76 surprisingly good too (indicates pretty good correlation, considering the data).


https://www.rivbike.com/kb_results.asp?ID=38

https://www.rivbike.com/kb_results.asp?ID=39

https://www.nettally.com/palmk/BikeFit.html

https://www.competitivecyclist.com/za...LCULATOR_INTRO

https://www.wrenchscience.com/Login....%2fHeight.aspx

fietsbob

One measure is stand over .. bare foot, level top tube, planning Paved roads..
an inch of clearance will do ... but then your arms and torso need to be considered
for reach..

rougher roads where you may have to leap off.. foot in a chuck/gopher hole, ?
add a bit more stand-over clearance..

Jackontheroad

Thanks all. Because of budget, etc. now I am considering using a MTB like the Peugeot Orient Express for touring. And while I have not visited the links attached, yet. I would like to ask another question based on your experience: If I choose this bike, should it be 18.5" because it is a MTB or should it be taller because I am using it for touring? How tall, if taller is the answer? Going to work now, I'll do the calculator later. Thanks again.

cyccommute 

Stick with mountain bike fitting. If you ride an 21" road bike, you don't ride an 18.5" mountain bike. You probably ride more like a 17" mountain bike. The 18.5" mountain bike frame has a proportionally longer top tube to fit a much taller rider. They usually even have longer top tubes than road bikes. If you go too large in mountain bike frames you end up riding like Superman...which isn't comfortable for touring. I'd suggest not going too large in touring bike frames for the same reason. Fitwise, a touring frame is about the same as a road bike.

PartsMan

Ride a few.
I did the equations and came up with 58cm.
LBS thought that would be a little big for me so he put together a 58 and a 56.
The shorter top tube on the 56 was much more comfortable with my short arms.

fietsbob

A MTB , will tend to be Longer top tube, than a Road Frame.
though a straight bar hybrid will also tend to be similar to MTB

Drop Bar Frames will be shorter relative to seat tube length.

Collect data on both dimensions.

Yo Spiff

Agreed. When I converted my Trek 900 MTB to drop bars, I found the hoods were placed much further out than they are on my road bike. Took a couple of handlebar swaps and some experimenting to get things where I found them comfortable. Reach to the bars is far more important than standover height. My feeling is that the standover height rule-of-thumb is just to get you in the neighborhood of the correct size. I have shorter legs with more height in my upper body, so I tend to ride a slightly larger road frame than my height would dictate.

sstorkel

I'm not convinced this is correct... Most tourists seem to want a touring bike to have a more upright riding position than a standard road bike. A larger frame will usually have a longer top tube, which places the bars further from the saddle leading to a more stretched out position on the bike. For a more upright position, I would think you'd want some combination of: a longer head tube (to raise the bars), a shorter top tube (to bring the bars closer to the seat) and a shorter stem (again: bars closer to the seat). That's what I did for my touring frame anyway...

seeker333

Two things happen when you move to a larger frame:

1) The ETT is longer, but with a higher handlebar reach is reduced at a rate of ~1 cm for each 3 cm of bar height increase, due to HT angle {cosine (72degrees) = 0.31**. The net result is overall reach doesn't increase much, certainly not as much as one may expect from glancing at ETT specs in a frame geometry table. Higher handlebar and HT angle counter longer ETT when you move up on frame size. When you move from a road bike to a touring bike, you'll likely relocate the handlebar (to improve comfort for long hours on bike while touring) from a position 2" below the saddle to even with or perhaps 1" above the saddle (or more), which is a net 2-3" higher (5-7.5cm). 7.5/3 = 2.5cm of ETT length offset.

2) As your arms are raised with the handlebar height, arm length effectively increases. When your arms are at your sides (standing), their reach is zero; they are at maximum reach when they are extended horizontally. So you've got an arm length (the majority of your physical reach) that varies from 0 to ~80 cm depending on your size. If you raise your extended arm from a position 45 degrees from horizontal a couple inches in height, your physical reach is extended a couple inches (5 cm). This is approximately what happens when changing from a road bike fit to a touring bike fit. That 5 cm of arm reach "growth" will offset the longer ETT of a frame size increase of 2 to 4 cm.

The combination of 1) and 2) will result in a larger frame feeling and literally being shorter in reach than you would have originally imagined.

bradtx

Jackontheroad, Older mountain bikes like the one you mentioned have a pretty conservative frame compared to mountain bikes from the mid to late '90s when the top tube became longer and sloped downward at the seat tube. These older fully rigid mountain bike frames compare closely to modern touring bikes and many have been converted for touring. A difference that may or may not be important to you is the chainstays on these mountain bikes are a bit shorter than those on modern, expedition level tourers so there's a possibility of heel strike if you use a large rear pannier. There are several fixes if this is the case.

Test ride a few used bikes from bike shops, craigslist and local classifieds. I don't recommend an online purchase without having a good base of comparison.

Brad

Jackontheroad

Thanks all, I'll do a lot of test rides after doing some geometry calculations.