bicyclepost

Hey everyone, so I recently bought a touring bike that was built with a mountain bike frame but am confused about the sizing. When I was in the shop the employee measured the seat tube to be 54 cm which fits me and I test rode the bike and was comfortable. I later noticed the receipt said 19" bike and found the bike online (showing a friend as I haven't picked it up yet because they're making modifications for me) and it said it was a 49 cm frame. I tried researching this sizing discrepancy but haven't quite found the answer I'm looking for. But apparently my mountain bike size is 19 inches but my road bike size is 54 cm which are not the same. Can someone explain this to me? Will this converted mountain bike be big enough for me to tour with comfortably? Thanks in advance.

MarcusT

Bike sizing has become confusing as frame geometry has made it so. If you tried the bike out and it is comfortable, then you should be fine after some tweaking.

maybe this article will help clear it up

The confusing world of bike sizing ? https://www.ten-point.co.uk/

LesterOfPuppets

I ride 53-54cm road bikes and have toured on a 19" MTB. My 19" mtb's seattube measures 45 to the top of the top tube, about 51 to the top of the seat tube. Most folks who ride 54cm roadies would probably want 17"-18" for actual mountain biking, but I like a big frame for touring. It depends what kinda fit you like.

Here's pics of the 19" KHS I like tour on.

BobG

I agree with Marcus.

Many touring and mountain bikes now have some degree of a slope to their top tube, others are level. This makes seat tube length relatively meaningless for sizing. A sloped TT will result from either a taller HT, a shorter ST or both. If the ST has been shortened to produce the slope then that dimension is no longer a constant that can be used for frame fitting.

For example my 16" (41 cm) seat tube touring frame with a sloped TT is equivalent in fit to my previous 20" (51 cm) frame with a level TT. They each have the same equivalent TT reach. They each have the same saddle height from the pedal...

current sloped frame... 16" seat tube + 8" seat post (24" BB to saddle rails)
old level frame............ 20" seat tube + 4" seat post (24" BB to saddle rails)

djb

this is a very common source of confusion, I remember clearly not understanding the stated size numbers thing.

as said by others, the main distance that is important is the top tube dimension, and if that will work for the types of bars, flat bars or dropbars.
It very much helps if you already have a reference of a bike that works well for you, as you can measure the toptube, or specifically the ETT, the estimated top tube, because of the diff types of top tube slant and all that.

within reason, different handlebar stem lengths that can be changed out to shorten or lengthen the distance of bars to seat, can compensate for reasonable needs, and make all the difference for rider comfort.

As another example to add to what others have written here, I have one bike made for dropbars and I use a 90mm stem on the dropbars, and could even have a 100mm on it and it would be fine. It is officially a 54cm frame, toptube is about 54 or a bit more.

another bike is a sort of mountain bike frame, setup for mtb bars that sweep back a certain amount, so while its also a medium, the top tube is much longer than the other bike, so when I changed this bike to dropbars, I needed to put a short stem on it, about a 50mm stem, and the bike works great for me fit wise, similar to the other bike in terms of "seat to dropbars" distance.

yes, you have stem lengths that come into play, but also different dropbars have diff shapes, diff lengths of the "tops" of the bars to where the hoods are, and then you also get into the actual height of where the bars are, which makes a difference for comfort also.

than of course with mtb bars, you get into a lot of actual hand position differences from bar to bar, some are more straight, some angle back a lot and so bring the hands much closer to the seat......

lots of variables, but knowing the top tube and ETT estimated top tube , length, is the main important thing to know and to at least be aware of when looking at a new bike--and like I said, hopefully you have a reference of a bike that works for you or close to it, that you can compare a new bike to.

also, in general, for touring, its nicer to have a more relaxed position within reason, ie bars not too far forward, not too far down--but this is personal of course, but long days riding at an easy pace generally is more comfortable with a reasonable rider position--but its up to you to decide what is more comfortable for you and that only comes with riding, riding and more riding....

good luck with new bike and having it setup well for you as you ride it more and become more atune to how it fits you.

djb

what is the bike by the way?
photo?

cyccommute 

Bike sizing isn’t nearly as confusing as many people make it out to be. A 54cm bike is still a 54cm bike even if the seat tube doesn’t measure exactly 54 cm. The proportions for a bike of any size are such that the various parts of the geometry work together. If a 54cm bike fits you, you won’t find a 58cm or 60cm bike to be all that comfortable. The reach to the handle bars would be too long on larger bike and you wouldn’t be able to stand over it as comfortably.

But the problem I see here is that the mountain bike you bought is too big for you given your road bike frame size. A 54cm road bike is 21”. Mountain bikes should have sized about 3” to 4” smaller than road bikes. That’s so that you have more room to bail off on uneven ground so that you don’t hit the sensitive bits on the top tube.

Because of the smaller frame size, mountain bike proportions are different from road bikes. For example, the top tube on a smaller mountain bike is proportionally longer to fit a larger person. It’s actually even a bit longer so that the rider is better centered on the bike for off-road use. A 19” mountain bike is meant to fit someone who rides a 58cm or 23” frame. For a 54cm bike, you should be riding a 17” mountain bike to have a similar proportionality to your 54cm road bike. I hate to say this but your bike is too big. If you use drop bars on it, you will have a really long stretch to the handlebar. It won’t be all that comfortable for riding all day on tour.

Tourist in MSN

Agree with everything Djb said.

Also, stems can be bought in different angles. I have one bike with a 17 degree stem angled down, so the stem is nearly horizontal, but I have two bikes with 35 degree stems angled upwards, and other bikes in between.

Some bikes only have a few stem spacers (or I call them steerer tube spacers), but some bikes have more giving you more up and down adjustment.

If the standover height is high enough that you can stand with both feet firmly on the ground while over the top tube, plus a bit of extra contingency might be useful if standing on uneven ground, as long as reasonable tweaks to stem length and angle, plus some spacers on the steerer tube to adjust height, you should be able to do the fine tuning you need.

But, you did not say if you have a quill stem. If you do, it is harder to adjust fit by changing stems. It can be done, but it is more work and takes more time to do so.

seeker333

Your basic question may have been answered with the link in post #2 , but if you doubt the LBS salesperson and want a better understanding of the comparative geometry and fit of your bicycles, then take measurements, collect bike/frame geometry data and complete the first two columns of this table:

Stack and reach calculator

Even with stack / reach figured, you still have to make some inferences with regard to bike-specific posture and usage. For example, a drop handlebar offers three standard grip positions which significantly change posture/fit, which is hard to measure and represent numerically, graphically, or extrapolate to how it "feels" when actually riding a bike for several hours a day, day after day. Plain ole "flat" MTB bars are simpler to figure with their only-one-grip math.

fietsbob

Years ago I saw a post by a Canadian Machinist who rook a full suspension frame

somewhat , like this and turned it into a hardtail , that came apart
so as to make it a smaller package, to fly, to where they wanted to go tour..







....

bicyclepost

It's a Bianchi Blizzard. I haven't been able to find anything about it online.

LesterOfPuppets

Looks nice. I think it's an Ibex. From 1991 or so. That Blizzard sticker is not stock.

LesterOfPuppets

Traditionally Italians measured bikes from the center of the bottom bracket spindle to the point where the center of the top tube and the center of the seat tube meet. I think Bianchi measured their MTBs in centimeters at that time.

djb

good spot, thats certainly what it appears to be.

hope it fits you and that you are happy with it. The most important thing is that you are comfortable riding it.
I'm originally from there, and one day will ride by that place if I am visiting and have a bike and time to go by, always like to visit a bike store.

LesterOfPuppets

I think that may be a 19". This guy says he measured this Grizzly from the same era as being 19" and certainly looks the same size.

Keep in mind that back in the day, MTBs often had shorter front center dimensions but had super long stems installed. So sizing isn't the same as a modern MTB. Replacing flat bars with a 140mm 10° stem with drops and a high-rise 90mm stem can often get you into a similar fit.

Tourist in MSN

A few thoughts on the photo. Looks like an older friction bar end shifter (not a indexed one). Front fender looks a bit odd where I am not sure if it is attached at the fork crown or how. But the upper fender stays are much closer to the fork crown than is normal which is what caught my attention. These are not important issues, just a few things that drew my eyes to them as being unexpected.

djb

good spot, now that you say, yes that is odd.
I suspect that given how high up the mudflap is, and the fact that the front part of the fender is by no means overly long, I suspect these are fenders for a smaller sized wheelsize. The water coming off the wheel is certainly going to go all over the front chainring area, given the the fender bottom is so high up.....

I'll be straightforward, I saw the ad for this bike, and I am assuming the person here has purchased it already, but I find $650 for a 80s or early 90s mtb bike with most likely 7speeds to be a bit high frankly. I know its from a bike shop, and it should be in excellent condition with everything regreased etc, but I would expect indexed shifters that work flawlessly and properly fitting fenders for that price, and heck, a rear rack.

BobG

Okay kids, don't try this at home as it is very approximate! Using high school arithmetic along with the posted photo it appears that the Bianchi has a 49cm (19") seat tube and a level 54cm (21") top tube.

I first expanded the photo on the screen until the crank measured with a ruler was 50mm. The seat tube measured 140mm and the top tube 155mm. Assuming a 175mm crank here's the arithmetic using cross multiplication...

50/175 = 140/X
50X = 24,500
X = 49cm seat tube length, center to top

50/175 = 155/X
50X = 27.125
X = 54.25cm top tube length, center to center

If it's a 170mm crank then each dimension is slightly shorter. Yes, I have nothing better to do on a boring cold drizzly day here in NH!

LesterOfPuppets

Those look like Suntour power shifters. They're kinda in between friction and indexed. They click but it's 2-3 clicks in between gears, IIRC. Feel a lot more solid than friction, and are less likely to slip out of gear than friction (when maladjusted or worn.).

Tourist in MSN

I mis-spoke, in that era when the Suntour bar ends that most people referred to as ratchet shifters, I was using Shimano bar end shifters that had a return spring and adjustable friction. So I was thinking of the word friction when I was also thinking Suntour.

bicyclepost

Picked up the bike yesterday and it's 9 speeds, looks to be in excellent condition. The shifters are friction but they work great. I'm not too concerned about the fenders and I have my own rack that they put on for me so overall I'm happy with it. Thanks for the input though!

bicyclepost

Picked up the bike yesterday and measured myself and those estimates were bang on. Impressive!

djb

that's great that it has a 9 speed rear wheel on it, and that it is in great shape and properly prepared. I started touring with 6speeds, so having more is always better, for the range of the gears at the back, and also having more manageable jumps between each shift. With bar end shifters and similar type shifters, there is a certain technique of shifting that helps with index shifting, so hopefully only a small adjustment is perhaps necessary, and or maybe just a bit more riding and getting used to the shifting "feel" for the shifters. One of my bikes has the same type of shifters, mounted in a diff spot, but even when everything is adjusted properly, when you shift you need to go a smidge past the click of the indexing and then back a bit , for a smooth proper shift. But its not a problem, and once you get the feel for it, its perfectly fine and Ive spent months riding that bike on trips.
I also ride sti "brifter" shifters, as well as mountain bike trigger shifters, but still find the type of shifters on your new bike to work great for touring.

on another positive note (apologies for the negative angle I wrote before) I have ridden a lot loaded up on frames very similar to this bike, my old 90s mtb and a 90s hybrid, and both behave very well with two heavy rear panniers--and looking at this frame, I am sure that it will be the same.

going the front rack and pannier route to spread out the weight really is a good idea though, the bike will ride and handle better, and it very much makes life easier on the rear wheels spokes, just cuz less weight is on it.

happy riding.

LesterOfPuppets

Yeah, those aren't really full coverage fenders but if they happened to put the L bracket in front of the fork, you could move it to the back of the fork to get a tad more coverage. Then add a mudflap for even more protection for your feet and drivetrain.

With a 54cm top tube that definitely can't be compared to modern MTBs, even MTBs that came out 5 years after that one. My 1996 16" Mongoose has a 56cm effective top tube. And 1997 19" KHS has a 60cm effective top tube.

djb

my mid late 90s Rockhopper and my medium Troll both have an effective tt length of about 590ish, so if this bikes tt is 54ish, which is close to what my 54cm Tricross has, then given this person rides a 54cm road bike, this is all in the ballpark.
I use a 90mm stem on the 54cm bike, and on the Troll, a short 50 or 60mm stem, and they both work for my 5'10ish" height.

the one reality of a quill stem is that its more time consuming to change to a diff length stem, quite a lot more, but hopefully this stem is going to work properly.
The upside of course on quill stems is the fast and easy height adjustment, but it is what it is.