Whilst I'm right on the cusp between sizes at 5'7 I've tried 3 different make/model mediums in shops and on all of them the staff had said I'be be better off with the small (nowhere's had one in stock to actually try) and the reach does feel that bit too much but I'm looking for a 2nd hand bike and smalls virtually never come up but there are loads of mediums available (one in particular at the moment).

If I take this bike as an example
https://www.halfords.com/cycling/bik...adventure-bike

the difference in reach is only 9mm ... is that the figure I should be looking at and if I swapped the stem for a 10mm shorter one will that in essence do the same thing or are there other differences I'd notice and would you just wait until the right size comes up .... that said I've been looking for months and have money burning a hole in my pocket at the moment.

Buying a bike that doesn't fit is a waste of money. Buying used takes patience, sometimes a lot of it.

A shorter stem extension is what I do, buy a new stem. you can change that.

you can't change the top tube length without changing the 'size' of the frame,

that, for you, is buying a different whole bike since you are, seemingly, unclear on which to buy..

do you know what size , (standover height) is best fit , yet?





...

Probably wrongly so but I've never thought about this .... I'm guessing though if I can sit on the bike and comfortably put both feet on the floor then it should be OK???

The one I tried today which was a medium I would have raised the saddle from where it was if I was actually out riding the bike so it'd be nowhere near it's lowest position and I could comfortably stand with clearance over the top tube ... is that all you look for???

Blah...blah...blah.

This is nonsensical. Stop talking about sizes and models and start measuring. Have a friend help you and use one of the on-line fit calculators (like the one on Competitive Cyclist, for example) to determine the dimensions that you want in your bike. Print out the results. Take those dimensions to the bike shops and have the shop set up a model to match what you need. That will be your starting point.

#BikeFitMatters

^ I agree. For me, at any rate. Any frame can be made to fit if the top tube and stem get me within 0.5 cm or so of my optimal.

The "reach" measurement is the horizontal distance from the bottom bracket to the top-center of the headset. Comparing the small and medium here, notice that they have different "stack" measurements as well with headtube lengths differing by 20mm. If you have the handlebars at the same stack height on the two bikes, the reach measurement difference will be 9mm (as you've noticed) plus 20mm*cos(70.5 degrees) = 6.7. Put another way, the stem would have to be 15.7mm shorter on the medium to fit like the small.

Anyway, bike fit is super important. Either get measured and fit properly, or test ride loads of bikes until one feels right. The size labels on bikes have little relation to how they actually fit .

[Diamond Frame] Straddling the top tube, ahead of the seat,standing

one hand on the saddle, in back , other on the bars , in front of you,

Pick the bike Up , how far off the ground are the tires?

if you feel you need a bike that you can put feet on the ground from the saddle ,
look for a crank forward / cruiser.

otherwise, the saddle height is in relation to the Pedals , for decent leg extension.

the staff of your favorite bike shop can assist you..





...

as 9th post suggests, reach is front ahead of a plumb line ,
down to the BB axis to your bars.

setback is from that line, back to the seat post center line.

It can be measured.. This was described in a classic book,
written for cycling coaches and riders for the 1960 Rome Olympics.

Plumb is straight down.. a vertical line.




...

if riding a biker matter to you, take the time to get a bike that fits.

If riding a bike doesn't matter, don't get a bike.

third option---get a wrong bike and regret it. Lots of people have tried that solution. Then they come here and advise against it.

Also----the Competitive Cycling fit guide (https://www.competitivecyclist.com/S...ulatorBike.jsp) is not always going to work. But ... it has worked really well for me. It can give you at least an idea of what yur body looks like to a bike.

Also ... if you think proper size involves being able to put both feet flat on the floor, you really need to research bike fit before you buy a bike.

Standover height really only matters to parents who are buying bikes for growing kids .... because they want to buy the biggest bike possible in hopes that it will last three years. Otherwise ... who stands over a bike? When i stop at a light i can put the ball of my foot (or actually the edge of the ball--I don;'t like to grind my cleats) and the ground to keep me upright. If the light is Really long, or it is after a long ride (when calf-cramps can be an issue) I can step down ... but so long as I am not cut in half by the top tube, I am fine. (As it happens, I have plenty of standover on all my bikes, but that is incidental .. I never bothered to care.)

You need to figure the distance from the bottom of the pedal stroke to the top of the seat, the stack and reach, the middle of the saddle to the stem/bars juncture .... you need to find the angle at which you naturally want to bend while riding. The most important thing is probably saddle location, both in height and setback---these might change marginally as your fitness changes, but pretty much you need to find where you sit on the bike with the right compromise of power and comfort.

If the seat height and location are correct, your legs can bear most of your weight . if not, you will either overstress or overextend your knees and surrounding muscles, you will use your arms to hold yourself up, and riding a bike will always be uncomfortable.

Anyway ... if you know all this, sorry to be pedantic. if you don't find out before you spend any money.

The guy at the LBS today that I have an awful lot of time for ... I asked if I were to mess around with shorter stem what would it need to be and without going and referring to anything instantly said off the top of his head it'd need to be 15mm shorter ... wonder if that was chance or he really knows his bananas.

The stems only 80mm to begin with, wonder if reducing it to 65mm would then have a negative effect on the handling / make it more sensitive.

It's funny that not one out of the 3 places I've been to have actually offered to measure me as they've all know I've been in to see what size fits best ... the bike fit person I saw at one whilst he was quite emphatic I'd be better off with a small I suggested getting a fit and he said not until you've had the bike for 6 weeks or so and know if you have any niggles / joint pain etc.

Just tried the competitive cyclist URL and because I#m outside of the US with recent GDPR regs I can't see it .... B**%$s

How do you find out what your optimal ETT distance is??

People at bike shops generally are there to sell bikes and accessories. That's how they survive. They know how to move a saddle up, down, back and forth - and they can sell you a different stem. Some people who work at bike shops know a thing or two about fit. A very, very small percentage of people who work at a bike shop are actually adept at fitting you to a bike. The shops around here generally refer customers to a professional fitter when the topic comes up.

The reality is that most people go in, buy a bike and ride it without worrying too much about fit. A lot of folks in this thread know their stuff (and they're not trying to sell a bike). So you have choices. Figure out this whole fit thing, get a professional fit or go in and buy a bike and ride it.

Witterings, keep in mind that in professional fitters terms, "fit" means a true fitting to find the best body position on a bike to start with and is very involved usually cost 150+ dollars. Many, many shops "fit" bikes, but are really only sizing the person to an existing bicycle. There is a big difference. One starts with body position to match a bike to, the other starts with a bike to figure out how to make it work for the body.
In summary, to have a fit done, it will cost you plenty. To have a "fit" done at no cost to you is simply having you swing a leg over the bike, ride it around and have the sales guy observe the body on the bike and make the call. Not the same method or outcome.

With that being said, myself and plenty of other fitters that have been trained in the subject and have fit many, many people, are able to observe and come close with a simple observation due to experience. Won't be perfect nor optimized, but will be close enough to present comfort on most rides.

With that having been said, spend the money and have a pro level fit done and then there will be no questioning. If you are unsure of the competency of the shop you are dealing with, find a different one and work with them.

Now I have to throw a wrench into things. Smaller frames mean shorter top tubes, but also mean a greater disparity between saddle height and handlebar height. Some of that difference can be made up with a riser stem, but if the difference is too great, then there is no where to go. A friend of mine has long legs and short torso and arms. Always had to ride a smaller frame to reach the bars, but the saddle to h-bar height difference always forced him into an unwanted position. After forty years he finally had a pro level fit done and a custom bike made. It has the reach of a medium and a stack of an XL. Kind of an odd looking bike, but he can sit on it for hours, which he was unable to do before.

I have heard similar stories to this, but I never really understood this. I also need a short reach and tall stack, and also end up on smaller frames. But all I have to do is use spacers and a riser stem to get the bars where I need them. Looks a little odd, but the fit is perfect.

I may go with a custom frame someday, but all I'll really be doing is replacing a bunch of my spacers with head tube.

Standover height is a means of sizing a bike makes no sense - sure, ideally you don't want to crack your nuts on the top tube, but its the fit when you're riding, not when you're standing, that matters. If you can get your feet on the ground while straddling the top tube, that's good enough - now work on proper fit.

This.

Also, one does not need to get a race-geometry frame. One of the big differences between endurance and race geometry tends to be head-tube length. People who for whatever reason want the bars higher can keep that in mind.

Once the frame is chosen, as Kapusta notes ....spacers and stems.

Everyone seems to want to imitate the pro-racer slammed, flat stem, but stems come in a lot of angles and spacers are about a dollar apiece. Build a bike that fits the rider.

For the money we spend on our bikes, and the time and energy we spend after we buy them .... it makes no sense at all not to buy a bike that fits and then to fine-tune that fit.

I would never pay the couple hundred dollars that a pro fitting costs. Some people have no clue on how to get their bikes to fit --for whatever reason---and seem to really benefit, but most of the people I know who have spent the money are very serious riders looking for that last little edge of efficiency

As I see it, a “bike fitting” is some thing to buy After you are used to your bike—after you have bought the right sized frame and have set it up pretty well.

Most people , when they get a new bike and start riding more, change their riding positions over a few months …. so getting a fiting for a brand new bike is a waste—as that one person at that shop suggested, get a fitting after six weeks on the bike—if you feel you really need one.

Two suggestions:

If you have a bike, does it fit? Can you ride it comfortably for a couple hours? If so, you can play with that bike a bit to get a really comfortable, functional fi. Then measure where all the contact points are relative to one another and reproduce that relationship on every bike you get from now on.

Or … if you don’t have a bike …. Consider buying a really cheap used bike that is pretty close to the right size …. And try a couple different stems, maybe play with seat post set-back …. Get that bike really dialed in for you, and then, measure where all the contact points are.

You can get perfectly good stems for about $15, a cheap but usable seat post for $20, spacers cost $1 each if you shop EBay …. Before you dump big bucks into a bike which is the wrong size, spend a little to figure out the right size. Once you know, with slight modifications, you can use those measurements for the rest of your life.

Cheers to everyone for their input some very useful information!!

One of the people that looked at me on the medium and said he thought I'd be better off with the small was a professional bike fitter so whilst it wasn't a full fit I guessed he's pretty used to evaluating people every day and has a reasonable idea to at least get the best size to start with.

Whilst it may be a shame to miss "the bargain" that's currently available and it awful tempting just to buy it and get a shorter stem especially as the longer head tube would give a more relaxed geometry, I think I may go and get a proper fit anyway with my 29er which is possibly a size too big although I do find it comfortable ... one of my replaced hips has started playing up recently so it's probably a good thing to do anyway and will make sure I do get the right size bike for the next one which as I'm hoping to keep it for many years is worth doing.

Yhanks again for everyone's help!!

Non technical here, but I'm shorter than you and I find small to be too small in most cases. Maybe I'm weird. What I was told by my local bike shop guy was that shortening the reach puts your wrists/weight behind the wheel hub, which is somehow less than ideal for handling. Also, depending on the angle of the seat tube, over extending can put your arse too far back, which can put your knee too far back, out of alignment with the pedal. Or some such. He simplified by saying, "get a bike that fits, don't try to make it fit". I think I lucked out buying online. I got a Bianchi in size 53, and it's just at the verge of being too big, but is actually just right. Other brands in "53" would be too big. So be careful out there, it's a minefield.