Author Topic: Frame size - seat height  (Read 1144 times)

Frame size - seat height
« on: 12 August, 2022, 01:19:12 pm »
I've been riding recumbents for years, but was a fairly experienced cyclist before that. 

I've been thinking I might get back to riding a normal bike, and yesterday I was in a city a few hundred miles away from me where a bike shop selling an Italian brand of frames is located.  I'd arranged for them to measure me up for a frame so that if I decided to buy one I could simply order without having to go back and see them.

The looked me up and down then sat me on a customer's bike (they said the customer was about my height).  I was wearing office shoes.  The saddle seemed really low, but they got me to sit with one foot at the bottom of the pedal stroke then dip my heel really low before saying the size was good and that I'd need a 55cm frame. 

I remembered that my normal saddle height is around 780mm (BB to top of saddle), but they said that would be far too high, and sat me on one of their own (larger) bikes and got me to repeat the heel-dipping process.  I couldn't dip my heel very far, and they confirmed I'd need a 55cm frame.

The measured the saddle height of the first bike at something around 720mm. They did say I might need to raise it by 10mm or so.  After getting home I looked up some old bike-fitting notes, and saw my saddle height was 783mm (that would obviously change depending on cleat position, crank length and pedal\cleat stack height etc). 

I'm open-minded, and realise common knowledge changes over time, so perhaps their fitting advice would be better for me.  However, it does seem like a massive change, and because I wasn't able to pedal the customer's bike I'm not sure how it would feel.  I suspect my leg position might feel a bit too closed at the top of the pedal stroke.

I know the old advice to roughly set saddle height was to extend a leg with the heel on the pedal, which would then give a bend in the knee when pedaling.  However, I'm curious about the heel-dipping 'test' - is it a new thing, and what does it do?   

robgul

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Re: Frame size - seat height
« Reply #1 on: 12 August, 2022, 02:06:26 pm »
Two immediate questions: 
1 What "shape" was the frame for the earlier measurements - sloping top tubes make measurements (even more) confusing.
2 What size of bike did the shop have in stock/on order?  . . . . was it a 55  :demon:

Re: Frame size - seat height
« Reply #2 on: 12 August, 2022, 02:42:29 pm »
I'm guessing that the frame you tried was a modern 'compact' frame design, i.e. sloping top tube. In this case, frame size as measured by seat tube length is almost irrelevant as the point where the top tube and seat tube meet can be wherever the maker wants to put it. If this is the case, the 'effective" seat tube length is more useful, in that it's the point where a virtual horizontal top tube running from the head tube would meet the seat tube if it was extended beyond where it actually meets the top tube.

In practice, seat tube length on compact frames is practically irrelevant. I just look to see if the BB to top of saddle height looks reasonably aesthetic to me, not too high or too low (but it is subjective). In any case, frame sizing is somewhat arbitrary between manufacturers. All you can say is that a 55cm frame is bigger than a 54 and smaller than a 56 from the same range.

So if the size of the frame is determined purely by the actual seat tube length then its not a very useful number.

What is far more important is the reach of the frame - governed by a number of measurements but the one I find the most useful when looking at frame geometry charts is our old friend, above, the virtual top tube length, which tells me what length of stem I'll need.

There are a number of ways to determine saddle height, none of them absolute. Placing your heel on the pedal at the bottom and raising the saddle until your knee is just slightly bent is a reasonable starting point.
I am often asked, what does YOAV stand for? It stands for Yoav On A Velo

Re: Frame size - seat height
« Reply #3 on: 12 August, 2022, 03:22:07 pm »
Thanks very much.  I don't think it was about the frames he had in stock or on order, as each is a custom order (size and paint design).  It would be a classic steel frame with horizontal top tube.

I don't know what sizes the bikes I sat on were, and they were both gravel bikes anyhow.  He somehow extrapolated what he saw when I sat on the customer's gravel bike to the road frame I was interested in.

I know seat tube length isn't that important to a certain extent, but I've had bikes which ranged from 57.5cm to 60cm, nearly all with horizontal top tubes.  I was fitted to the 57.5cm one with the 783mm saddle height, and the seat post was quite a bit (from vague memory , around 30mm) above its minimum insertion line (classic aero seat post).

So, if the suggested 720 - 735mm saddle height with the 55cm frame ends up being too low for me, then I might end up with an extended seat post and maybe the reach and handlebar height will also be sub-optimal!

Re: Frame size - seat height
« Reply #4 on: 13 August, 2022, 08:20:34 am »
Ah right. Traditional horizontal top tube frames were always sized by the seat tube length. But there are 2 ways to measure. British built frames tend to use CTT, centre of BB to top of seat out whereas continental frames use CTC, centre of BB to centre of seat lug. CTC gives you a frame about 2cm bigger than the same labelled size CTT frame.
I am often asked, what does YOAV stand for? It stands for Yoav On A Velo

Re: Frame size - seat height
« Reply #5 on: 13 August, 2022, 08:50:14 am »
Not enough information about the bike and it's geometry, that along with the range of sizing ought to give a better idea than one measurement.
if your saddle to BB is 780, which size of that model would be most suitable to achieve it and how would the reach be?
720 and 780  is a huge difference, it's hard to see how a rider, or bike shop, could get it that far wrong, you'd either look like you were riding a BMX or not be able to reach the pedals. On a really compact frame it might be possible to achieve both, but both would be at the extremes for the size.   I'd put aside what the shop has said and what you remember, then start from scratch with an online fitting guide.

citoyen

  • Occasionally rides a bike
Re: Frame size - seat height
« Reply #6 on: 13 August, 2022, 01:12:42 pm »
I know the old advice to roughly set saddle height was to extend a leg with the heel on the pedal, which would then give a bend in the knee when pedaling.  However, I'm curious about the heel-dipping 'test' - is it a new thing, and what does it do?

Heel dipping is just a variant of heel on pedal - has the same effect, ie giving the leg a slight bend at the knee when the pedal is at its lowest point during normal riding.

As has already been said, stack is a far more useful/reliable/meaningful measurement than seat tube length for fitting purposes.

Also, the other customer may be the same height as you but they might have different proportions (ie different inside leg, arm length etc).
"The future's all yours, you lousy bicycles."

rogerzilla

  • When n+1 gets out of hand
Re: Frame size - seat height
« Reply #7 on: 14 August, 2022, 06:59:39 am »
You probably want a 23" or 23.5" frame if it has a level top tube.  There was a trend in the 90s to ride frames that were too small, meaning a severe drop to the bars.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Re: Frame size - seat height
« Reply #8 on: 14 August, 2022, 07:21:04 am »
If you are a fairly experienced cyclist, as you said above, you probably know better than anyone what seat height is best for you. Don't let marketing gobbish fools you. If they insist on selling you something you feel is wrong, then go somewhere else.

A

Re: Frame size - seat height
« Reply #9 on: 14 August, 2022, 07:32:51 am »
Thanks!  Yes, that's what I'm thinking too! 

Paul

  • L'enfer, c'est les autos.
Re: Frame size - seat height
« Reply #10 on: 14 August, 2022, 09:35:52 am »
Have I understood this correctly? Are you having a traditional steel frame custom built? And are you saying that the shop sized you up by having you sit on another customer’s gravel bike?
Whatever the measurements, the process sounds wrong to me.
I had a steel frame custom built for me once. They set up a jig to my preferred measurements, and then adjusted it a little here and there. Then they got me to pedal on the drops, the hoods are the flats, and tweaked it again until I was happy. I remember fitter wasn’t 100% happy: his instinct was to stretch me out further, but I told him what suited me, and he accepted that, saying “you’re the one riding it” OWTTE. It’s still the comfiest bike I have.

Even if you’re not getting a frame custom made, you want to be sure it suits you. Will you have the option of trying before you buy?
What's so funny about peace, love and understanding?

Re: Frame size - seat height
« Reply #11 on: 14 August, 2022, 10:25:22 am »
no expert here but regardless of frames and reach and stuff, the height between saddle and BB should be a fairly set distance for someone surely? Should I ever have a frame built, I would want them to measure or at least pretend to measure me all over all day.

a 60mm difference in saddle height is ludicrous surely.

Re: Frame size - seat height
« Reply #12 on: 14 August, 2022, 03:22:55 pm »
I've found a video clip of me pedaling with a 783mm saddle height, and I think it looks fine.  At the time I had someone checking me out, and they confirmed my hips weren't rocking, and that leg angles looked okay.  I'm fairly adaptable, so I could probably get away with a lower saddle height, but as you say, 60mm difference, or thereabouts is a joke. 

The frame I was interested in is from an Italian builder, and from what I can tell the dealer I visited is their main UK prescence.  I've sent them a copy of the video to see what they say, but I'll admit I was surprised by the fit they recommended, and the haphazard way in which they went about it.  I did explain twice that it was going to be difficult for me to return and that I wanted to get measured up so that I could have confidence when ordering.  They didn't have any bikes or frames from the Italian builder in stock, so there was no opportunity to try them.  I don't have my heart completely set on this particular brand, and it just seems too risky to buy one unseen!

vorsprung

  • Opposites Attract
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Re: Frame size - seat height
« Reply #13 on: 14 August, 2022, 03:41:50 pm »
Here is my so called bike fit guide

https://audaxing.wordpress.com/2011/03/07/long-distance-ride-bike-fit-tips/

I don't really believe in the Specialized take on bike fit where they measure everything and do science.  Get the bike approximately right (the shop are probably going to give you the right sized bike), make some minor adjustments and then get used to the bike.  Having good flexibilty and core strength seems to be the key to "bike fit"

Fit to be on a bike and the fitting of the bike are both important.  Don't stress about the initial parameters

Paul

  • L'enfer, c'est les autos.
Re: Frame size - seat height
« Reply #14 on: 14 August, 2022, 07:25:54 pm »
I've found a video clip of me pedaling with a 783mm saddle height, and I think it looks fine.  At the time I had someone checking me out, and they confirmed my hips weren't rocking, and that leg angles looked okay.  I'm fairly adaptable, so I could probably get away with a lower saddle height, but as you say, 60mm difference, or thereabouts is a joke. 

The frame I was interested in is from an Italian builder, and from what I can tell the dealer I visited is their main UK prescence.  I've sent them a copy of the video to see what they say, but I'll admit I was surprised by the fit they recommended, and the haphazard way in which they went about it.  I did explain twice that it was going to be difficult for me to return and that I wanted to get measured up so that I could have confidence when ordering.  They didn't have any bikes or frames from the Italian builder in stock, so there was no opportunity to try them.  I don't have my heart completely set on this particular brand, and it just seems too risky to buy one unseen!

If you haven't shrunk since then, 60mm shorter sounds too short to me.

How much is the frame? Have you paid a deposit? How are you going to know if it fits before you build it up and - once you have - will it be too late to return it for a full refund if it doesn't fit? And at whose expense (your additional journey)?

If it's not too late, you should get answers to all those questions before you commit. And if they won't answer, seriously consider pulling out. My custom build wasn't straightforward...
What's so funny about peace, love and understanding?

Re: Frame size - seat height
« Reply #15 on: 14 August, 2022, 09:47:08 pm »

If you haven't shrunk since then, 60mm shorter sounds too short to me.

Shrinking typically happens in the spine :(  legs remain largely static. DNAMHIKT.