Sizing for a Steel bike.
 

I'm looking to get a Steel framed bike to use as a winter bike and take on some off road/ gravel paths. It doesn't seem I'll be able to test ride one as most shops I've talked to don't stock them. Comparing ones online has me concerned about fit. I'm 5'5" with a 30.5" inseam.

Here's my current road bike size small with a 75mm stem and about a 15mm drop from the saddle.
TCR® C2 (2007) | Giant Bicycles | United States

Here are some of the bikes I've been looking at
Straggler | Bikes | Surly Bikes
Masi Bikes - Cyclocross - CX Comp
Velo Orange

I test road these two. While the reach was OK on both the standover was close on the CAADX
Size S AnyRoad 1 (2015) | Giant Bicycles | United States
Size 48 CAADX 105 Disc - CAADX - CYCLOCROSS - ROAD - BIKES - 2015

Thanks
Dan

Just use a bike fit calculator:
Bike Fit Calculator | Find Your Bike Size | Competitive Cyclist

seat tube length is part of size, top tube length is the other..

I just test ride bikes , myself.. I sorted it out way back . now IT people want programs.

Get something with top tube/virtual top tube that is close to the well fitting bikes you own and the rest will sort itself out. Stand over doesn't mean much when you are riding

For road cycling, standover clearance really just needs to be > 0. However, for off-road, having no margin can make uneven, and especially off-camber situations a little more dicey. On bikes with "traditional" Cyclocross geometry, the high bottom bracket usually costs you some standover. Some newer CX frames as well as those in the "adventure bike" niche (or whatever it's called this week) like the Anyroad have lower bottom brackets and may be better suited to a shorter rider. However, for a winter "beater", a late 80's - early 90's steel frame full-rigid mountain bike is hard to top in terms of versatility and ruggedness (not to mention retro-cool). Throw on some trekking bars and the right tires and they're right at home on both paved and unpaved roads.

Thanks for the replies. I had a bike back in the '80s that was on the small side, 48cm, and I could not get my seat position where I wanted it. I realize we're talking mm here but...

I'm that height, have a PBH of 30.7" and comfortably ride 52/53cm (horizontal TT 53.5 to 55cm) steel frame road bikes with everything from 700c x 23 to 35c tires.

Frame material has nothing to do with sizing. I mean, I suppose it imposes certain design constraints, but the range is so great with any given material that it's really just academic.

Sounds about right. My pbh is 80.7 cm (yours converts to 78.0) and I like frames 53 to 55 cm c-t seat tube with TT from 53 to 56, depending on ST angle.

I checked the Geometry on the Gran Criterium, the 51 would be the size I would go for 51 ST 53 TT 74 SO. the Terraferma didn't show geometry but also runs 650b wheels so that would give a lower SO. Road bike aren't an issue it's the CX bikes which tend towards a higher BB.

My older road bikes had always been 50-51 bikes. I guess I was looking for comments on how a smaller CX frame felt to those who had them. I know I could use a longer stem but my main concern was KoP. I had a Bianchi Brava 48 ST back in the '80s and it was a tight fit.

Thanks

As far as matching your old bike, if you didn't keep bike measurements, it's just up to luck.

Have you ever measured yourself? It can help get you in the right direction.

My Masi is a classic from the old days, and I doubt there's any correlation to the current ones. Geometry was not published for the Masis of my era. And the Terraferma was a custom (for someone else) so it's no basis for you to analyze. Besides, it doesn't match me very well.

What does work for me is a 52 cm and a 54 cm Mondonico, and you can find those geometries on the Torelli website (torelli.com? you'll have to google it).

Also, no on the lower SO of a 650b. 650x42b has about the same diameter as a 700x23c: 584+42+42 = 668 mm, and 622+23+23 = 668! What is lower on my Terra is the BB, which is 8 cm versus a more typical 7 cm. That gains me a cm of clearance relative to a similar conventional bike, but it's really just a little too much seat tube for me.

What is your pbh? That's a good starting point. It really doesn't make sense to compare yourself to strangers on the Net bike-for-bike. That's not what fitting is really about.

sorry for asking, but is that your trouser inseam or your pbh?

Given that it's your pbh, it converts to 775 mm. That gives you a saddle height calculated starting point of 68.9 cm measured from the center of the BB axle to the top of the saddle along the seat tube. If you straddle the bike in bare feet, you will be touching the top tube solidly if this is the SOH of the bike. Let's assume your shoe thickness is 15 mm, so then your "ground clearance" goes up to 790 when you wear shoes. If we now say you want 30 mm SO clearance, your target bike SOH is 760 mm.

Now let's see about a seat tube length. If you have 700x28c tires, the radius is 340 mm. If you have a (now common) BB drop of 70 mm, the bb height is 270 mm. Subtracting from 760, the frame rise from BB center to top of top tube is 490 mm.

If your seat tube angle is 73 degrees, we can divide the rise by the sine of 73 to get your center-to-top seat tube length = 512 mm.

So in a c-t measurement you need a frame size of 512 mm. In a c-c measurement you need 1/2" lower for a 50.0 cm frame. That's your center-top frame size. If you get a frame like my Terraferma with 8 cm BB drop, your frame size will be about 11 mm larger to get the same standover, for a c-t size of 511 mm = 51.1 cm.

This is only an estimate, people have some latitude and it really depends on how much stand-over clearance you feel you need. If for example you have a 53 cm frame that is simply a joy to ride, don't take this calculation as a strong reason to throw it over and go out on a new bike search.

If your 30.5" stated pbh was rounded and not reported accurately (Velo-Orange for one says to measure it to the millimeter), there could be a tolerance in frame size from about 50.1 cm to 52.1 cm.

This all says nothing and implies nothing about top tube length or reach in any of its definitions. That can be estimated as well, but it takes some knowledge of your torso and arm lengths. Pro fitters will also look at your flexibility to decide your target handlebar height.

Thanks for reply. I guess with an "off the rack" bike the goal would be to get as close a possible with ST & TT then adjust with stem leghth and angle. Seems like there will be some more test rides in the future just to get a better feel for the whole thing.

Remeasured myself tonight and came up with 76 for PBH (did the whole Competitive cyclist thing)

Thanks again I appreciate the time you took.

Most road steel frames that I know build with horizontal top-tube, so standover height is really important
Very different with modern race bikes like specialized or giant, etc. They offer sloping top tube, therefore the inseam length is almost not needed, you can determine size from eff. top tube length alone

I rode specialized secteur size 54 comfortably
Now I ride surly pacer size 50, because I have short length long torso
I stand over size 52 pacer, and my n*ts start to touch the top tube, which is never a good thing..

This happens to you a lot while riding? :lol: