Newbie sizing issues and how to get a bike fit without bike

Hi All,

I'm looking for a new quiver killer and am having trouble with sizing.  I'm 170 cm (5'7") and am right at the small-medium threshold for most bikes. Most of the LBS are out of bikes in my size due to the Great Bike Buying of 2020. I'm interested in higher-end bikes, so I want to make sure the fit is correct before I spend the money. In other threads, people have recommended getting a bike fit. I've asked several bike fitters if they would do a fit without a bike and they've all said no.

Any suggestions on how to get a fit without a bike? Thanks.

You don't have any existing bike to create base reference point for fit?

The GURU fit system is what you want to find. 
It is a robotic device that will fit you to a virtual bike or a virtual bike to you.
http://www.gurucycling.com/the-experience/

@Alex_C perfect. Thanks!

@smoothmoose good point. I don't think my existing bike fits me that well. I talked to a couple of fitters in town (I live in Austin) and it was pretty expensive (~300) to get a fit for my existing bike. I really didn't want to get a fitting on a bike that I'm not going to have much longer. 

Some of the better places have these bucks you sit on so they can adjust everything and get you dialed in without constraints of a specific frame.

Bike shops that do fits would certainly have a bike to fit you on.  At least that is how it works around here.

Sometimes I'm a Canyon fanboy ;-) but if you get one of their bikes and it doesn't fit, you can just send it back in.  Nothing out of pocket for you (although re-boxing a bike is fairly tedious).  I did that (bought two sizes, kept the one that fit best).

Even without that, I think buying a high end bike, trying it out, and finding it doesn't fit, spending the $50 bucks to send it back would be a good investment if you are going to plunk down significant $$$.

Personally, I think cockpit length is the critical factor as you can't change that too much without changing the handing of the bike.  Other dimensions are more adjustable.  

You could also try online calculators

Easy method:

For people 5’ 6” to 5’ 10” frame size = Height divide by 3.2
Reach = frame size (center to top) + 10cm.

or for more details:  https://www.competitivecyclist.com/Store/catalog/fitCalculatorBike.jsp

Specialized Retailers use RETÜL

Basic fit is $99

I'd think one of those guys would have a bike in your size.

Here is a list in Austin:
https://scheduler.retul.com/search?country=US&state=TX&city=Austin

@chas @bearlyfinish This is great information. I really appreciate it. Thank you. I called one LBS today and they said they aren't doing fittings right now bc of COVID (and normally only do them if you're buying a new bike from them). I'll check with the others in town. 

I'm doing the same as @TSwan.  I can't find any fitters that are open during Covid.  I do have road bike.  I've been using geometrygeeks.bike to compare geometries
with candidate gravel bikes against my current road bike.

 

I've read from a few places that the Stack and Reach should be the primary metrics for sizing.

Are there any rules-of-thumb from sizing a gravel bike from an existing road bike?

Thanks.

@Alf

Interesting question.

Ultimately it matters what you are after.
Personally, I don't often have time for all day rides, so I want something agile and fast to get the most out of a 1-2 hour ride. My goal is to get something close to a fat tired road bike (an I was successful).

But, if you are doing long hills, more endurance rides, less sprinting and high speed, your needs will be a lot different.

IMHO - cockpit length is the critical thing, although its height can be important if it can't be adjusted to your liking (rare but it happens).

That kinda is stack and reach (although you have to take into account seat angle, stem length/angle, and handle bar properties to really get a cockpit set up).


The other measurements can often be trivial
my bike has a long top tube (and short stem) to give the same cockpit as it is mimicking the stability modern mountain bikes are going after - but that certainly isn't a requirement.
Seat tube - the more exposed set tube, the better - as this will allow flex (if you are using a good flex seat post). This is huge for me as some of my carbon posts flex a lot when exposed, but don't flex at all with a tall seat tube.

Head angle - that is one of the key factors determining trail (stability) vs agility. A gravel only bike will want a lot of trail, a race bike or mixed paved/gravel bike may want to be more agile.

Chain-stay is going to be longer to accommodate larger tires, and a long wheel base will allow the bike to drift better - but shorter ones tend to accelerate a lot better.

BB drop. I power out of turns and hate smacking my pedal, but if you are doing solo or non competitive rides and are happy coasting through a turn, then a lower center of gravity may feel better. Realize that if you have 40mm+ tires on your bike, you can have more bb drop with the same clearance compared to a bike designed for 25mm tires.

Good points @chas

I hadn't even considered the seat tube length in relation to flex.

Thanks!

@Alf

The rule of thumb os +1cm stack, -1cm reach. But thats just a starting point. It depends on what gravel means to you and how your current road bike fits. If you have a crit racing position on your road bike and want a bike thats a pseudo rigid mountain bike, then you're going to need more stack and less reach. If you have and endurance fit and want a bike to ride on smooth dirt roads, I'd match the road bike for s/r.