nonhunner

How do you pick your frame size? I remember ages ago someone mentioned it was your inseam multiplied by something but I can't remember...

Iride01 

If you have no other experience, then go by the manufacturer's suggested sizing for that model of bike you are looking at. If you look at another model, then find the suggested sizing for it. As the recommended sizing sometimes is not the same if the other model is different enough in some aspect of it's geometry or the other things put on the bike such as bars and stem.

If you go to a bike shop, the sales person will have a good idea what size bike you should look at just by judging your height and maybe leg length. You'll fit a size or two up and down without big issues. At least that's true for the majority of people. Only your experience with bikes will tell you if you are in that majority or not.

There really isn't a perfect size that you can calculate or guess at. It really just comes down to trying them out and finding what you like. Understand that different bikes give different positions for the rider. Some you sit almost upright. Some you are in a very aggressive and aerodynamic position. Also know what kind of riding you will be doing with the bike. Try to get one that satisfies the riding you intend to do the most. IE: off road get a mountain bike. Paved roads and paved trails get a road bike. Gravel roads, get a gravel bike. Slow leisurely rides get a cruiser style bike.



Welcome to BF!

bruce19

I've been cycling for about 45 yrs. So, when I started it was before sloping TTs. I used the LeMond-Guimard method which is to measure your inseam in CM and multiply it by .665. This puts me in the 54-55 range of traditional frame size. With today's S-M-L-XL sizing you would have to take a virtual TT measurement in order to get BB to TT size. Simply using your height may or may not work since two people of the same height can have significantly different inseams. And, when it comes to measuring saddle height I would encourage you to avoid measuring from the center of the BB since crank lengths differ.

Turnin_Wrenches

Solicit assistance from a reputable local bike shop and/or bike fitter if you are totally unsure about frame geometry / sizing and what will fit you. Your style of riding will influence final fit, but the task of identifying frame size is largely based on your physical dimensions and level of flexibility. Also, don't gorget that saddle selection, saddle setback, stem length, handlebar width, and crank length will also have a significant influence on final fit and comfort. And after all that is said and done, you have shoe selection, cleat placement, and orthotics to figure out. There is a lot more to comfort and efficiency on the bike than most people think. Good luck! The process of getting a new bike is always exciting.

nonhunner

Very helpful thanks! I'm sort of looking at frames beforehand. I'm pretty flexible so I'm not worried about an aggressive position. It seems to be very expensive to get that level of fitting. Not saying it's not justified for a full fit just that for most budgets it's a lot. I reckon that's why most folk go for the ol' eyeball it method.

Turnin_Wrenches

I deal with folks on a daily basis that used the "ol' eyeball it" method. They are caught in an endless cycle of trying to turn the bike into something it was never intended to be... because they bought the wrong bike. A little professional assistance ahead of the purchase will make your riding experience more enjoyable. Just sayin' .

PromptCritical 

A good fit is way, way cheaper than multiple stems, seats, etc.....

cyclezen

You're not giving much info about yourself, cycling & bike equipment experience and intent/desire.
without that, the current suggestions pretty much cover the options.
go by manufacturer recommendations
talk to a local bike shop
do something else...
if you'd like more thoughts & conversation here, which actually might help - type in some info about yourself, cycling & bike equipment experience and intent/desire.
The more you give, the more you get...
Ride On
Yuri

nonhunner

Actually this is very helpful and one of these don't know what you don't knows. Perhaps I'm a silly sausage but hey ho. Live and learn?
So I usually go on 1-3 hour cycles. I've ridden steel bikes for a while now that in all honesty have probably been a bit big for me. I've never really had any back pain upper or lower. I'm pretty flexible and can fairly easily touch my palms on the ground in the morning when I get up. Point being I don't mind an aggressive position for periods of about 30 mins or so. Where I live is basically up hill all the time for some reason. Yes there are down hills of course but as you know 10 mins to climb is 1 min back down. I'm maybe a bit shorter leg and longer body. My current frame is 58 and I'm constantly pushing forward rather than down. Went for a preliminary fit and was told that they could see right away that my frame is too big from the saddle being so far forward and so steep and angle, the stem being 80m, the bars being short reach and angled up. I'm actually not too uncomfortable on that bike all things said. But as I do more cycling and want to progress my speed and endurance while maintaining a steel vintage I'm looking for a frame that fits me a bit more. Given my in seam is 800mm 55cm frame seems to be what I'm getting out of that.
From what I'm hearing here and elsewhere my stem and bars may need to increase in length but I'm also throwing into the mix now that I'm wanting SRAM double taps similar which again have more reach than your old school bar brake.
I reckon I can get away with swapping stems and bars a bit to make my ride more comfortable over longer distances and increase performance. My seat post will be more exposed but I don't mind that. It's a beautiful seat post so why not show it off a bit.
Hopefully this info is helpful to my riding style, what I'm currently doing and hoping to achieve. I realise that this is all probably pointing towards dropping 150gbp on a fit but in a world where that wasn't possible... Would you recommend sticking with my current frame or getting a smaller frame (55cm) ...
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cyclezen

This allows a few more thoughts and comments !
If that's your pants inseam preference, then I might suggest using 'cycling inseam' measurement - measurement more appropriate for considering frame size
use a sturdy book - at least 1.5 cm book spine, and barefoot...
would that put your overall height around 175cm + ?
your mention of SRAM doubletap seems to say you are looking for more 'modern' bike. There are differences in frame and how/which components will work on certain frames...
a bike/frame from the 20th century will be substantially different in workable components compared to a frame from the past 20 yrs (and more so for bikes 10 yrs and newer).
Given your flexibility which teamed with good core conditioning, will give you a much greater window on creating a 'position' on your bike, which is what 'fit' is all about.
SO given what you've noted - a 55 cm would be ok for a older frame (old steel/alu, maybe very early production CF).
A 54cm frame would be more preferable, especially if more modern design, with some riders even going to a 52 or 53... But 54 would put you in the middle of the design concept of most modern bikes, and also a real improvement over the 'older' designs - certainly for my 58+ yrs of riding performance bikes.
Given you have 58cm, I'd say very difficult to get a good 'fit/position' on...
Not knowing the finance elements, I would recommend selling/disposing the old bike, and looking for another more suitable bike, new or used.
As with all posts/info on BF, this is opinion - above is mine.
I think you can expect there will be others who present other points of view...
Keep your info coming, it goes a long way towards more directed conversation...
Ride On
Yuri

nonhunner

Really good guess on all of that so thanks for the response!
I'm basically building a vintage/modern. I've been checking like crazy and have made the modern components work on my current old frame. I'm about 183cm if that helps. I think that does put my closer to 55cm frame? I've got Morden wheels, a sram cassette with 11-28 which I'm fairly comfortable with. I think my current cranks are about 165mm. No idea if my weight factors in here but on a good year it's closer to 82kg on a bad year it's about 90kg. Big difference but I'm getting older and it's difficult to say no to a cookie!

nonhunner

P.s. I measured right up to the inside of my cycling short! So should be a good measurement.

Iride01 

Just to add some more food for thought to consider. I ride a 56cm Tarmac. I'm 180cm with a 87.6 cm inseam measured from the floor to snug in the crotch. (without bike shorts or heavy layers of clothing on.)

Since getting it new in 2020, I've put shorter 165 cranks on it and narrower bars from 42cm to 38cm. When I got it, Specialized showed me as being in the overlap of a 56cm and a 58cm frame. However I've always regretted not trying out a 54cm frame.

As far as you being flexible. I don't think that matters. I can't get my hands halfway down my shins on a good day. And I have long arms too. However I really like the large amount of saddle to bar drop that the low frame stack of the Tarmac allows me. While others use not being flexible as a excuse for sitting more upright, I think it's just more that you have to like the very head first position it puts you in.

My previous bikes were all old style bikes from the 70's. And way oversize for me. The one I rode for 35+ years was a 65cm bike. When I got rid of it, I went to a 59cm and a 60cm bike. They also like the other huge bike frame comfortable... to me. But they road like a luxury sedan on the road. Although the 59 cm Raleigh Competition was a little more sportier of them all. None have been as much fun to ride as my Tarmac.

Still wish I'd tried the 54cm model. However that might have given me too much drop from the saddle to bars.

cyclezen

Ok, so with the measurements you added, height and weight, I can visualize a shorter leg/longer torso rider. Arm length also has a part of the overall fit process.
But from current measurements, using most manfacturers chart might put you on a larger size frame than might provide a balanced riding 'position', and yes, you might find the need to move the saddle forward.
That depends on how upright vs forward lean you prefer for your torso lean angle. Riders carrying substantial torso weight, relative to core and back strength, might prefer a more upright posture, Riders with lower torso mass relative to overall body, might do well with and prefer more forward lean...
In any case, to balance the mass/load of the torso, the amount of pedal pressure (power) you apply contributes to helping balance torso mass... This helps counteract some of the torso mass...
And all this takes the mass/weight load off the hands contact... so a lighter touch and less pressure and weight applied means more comfort and control...
so the relationship of the saddle, your sitzbones contact point to the pedals, where you apply power, is a key, maybe The Key to finding the optimum balance between comfort and power.- For varied road riding.. There are times/riding type when max power supersedes comfort for consideration.

Smaller frame sizes usually have more upright seat tube angles, compensating for the shorter legs/femurs of shorter legs. Opposite for longer legs... and saddle placement may get 'funny' when that relationship becomes broken.
What this all points to, IMO, is that a 54 cm frame may be an optimum road frame size (considering other important frame geometry). 55 and maybe a 56 in older school frames (depending...) should also work.
These comments are for performance road bikes/riding. Loaded touring, townie, beach cruiser, etc.. riding other than mostly road have other/additional considerations.
Adjusting the cockpit is done AFTER you find or get close to your saddle position = Stem, bars, levers, and the info needed to set them optimally.
Since this is the 'Bike Fit forum', we can't and shouldn't assume that it's only 'road' riding, performance, and similar. But if not noted by the OP, then we often 'assume', and maybe not correctly.
There is large variation in how, why, overall intent of a person's ride...
Ride On
Yuri

nonhunner

Again thanks a lot for the details! Yes it's more road/performance based. I don't really have the time for touring though it's something I'd love to do one day. My rides are anywhere from 15-90km. There's a particularly big steep hill near me but then it's reasonably hilly all over here. Anyway this has been a really big help.

oldbobcat

The inseam method is almost as old as the days when the salesman would simply pull down the largest frame that didn't crush your nuts when you straddled it. These days, manufacturer recommendation is the best place to start if you're starting with an experienced, reputable brand. But it pays to understand your individual morphology. Are your proportions average or do they have eccentricities? They might limit your choices or indicate adjustments in size, stem, handlebars, and cranks.