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Surly's Way of Seat Tube Measurement

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Surly's Way of Seat Tube Measurement

Old 06-06-19, 01:03 PM
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Surly's Way of Seat Tube Measurement

Hi
I think I uncovered something worth noting.
Below is from Surly's website for the LHT.
Their "frame size" is from center of BB to the top of the top-tube.

This is not the standardized way of measurement.
One could have missed this minor difference and order one size too large or too small.

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Old 06-06-19, 01:15 PM
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That is the common method for showing "effective" seat tube length, here in the era of sloping top tubes. It would be nice if Surly were to point that out, though.

Though I guess so long as they provide reach/stack and standover, it all works out.

Meanwhile, my bikes have like 8" of seatpost showing because of sloping top tubes.
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Old 06-06-19, 01:22 PM
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Originally Posted by DrIsotope View Post
Though I guess so long as they provide reach/stack and standover, it all works out.

Meanwhile, my bikes have like 8" of seatpost showing because of sloping top tubes.
Yeah for sloping top tubes.

But the LHT is a flat top tube bike.
If I pick the right size LHT for me, the seat post would only show about 3cm.
And if I pick one size larger, the saddle would be slammed on the seat tube.

I like to pick larger size so I can get higher stack and compensate with shorter stem.

Last edited by mtb_addict; 06-06-19 at 01:27 PM.
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Old 06-06-19, 01:24 PM
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I would think that too small/too large would be determined by stack/reach before seat tube length, unless you have wee little kickers. I have stick legs like a stick person, so I dunno.
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Old 06-06-19, 01:28 PM
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Considering frame sizes based on seat tube length died a long time ago. With modern frame design it's all about the effective top tube length and stack/reach dimensions. Heck, even when frame sizing was seat tube based, there was little consensus over where to measure point-to-point. Center of crank to center of top tube/seat tube junction? Center of crank to top of seat tube? Measuring from the top of the bottom bracket housing? Nobody agreed on a standard.


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Old 06-06-19, 01:34 PM
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All that matters is the height from the seat to the centre of the BB. Things like seat stays or top tubes vary on frame design and aren't relevant to saddle height. Stand-over height depends not only on the type of bike but also the specification of any one example, so that should always be specified optionally.

So the relevant measurement for seat tube length is from the centre of the BB to the highest part of the seat tube - i.e. the part which stops the seat travelling any lower.

Surly have got it wrong.
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Old 06-06-19, 03:15 PM
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Kona still designates their frame sizes based on seat tube length -- even with sloping top tube frames. Imagine ordering a size 54 Sutra only to realize after delivery that the top tube is 57cm long? I doubt something like that happens a lot, but I think they'd be better off going with a S, M, L, XL scheme instead.

"Reach" only addresses a portion of the saddle-to-bars length and completely disregards the length associated with seat tube angle. Frame sizing is still pretty much a "buyer beware" situation.


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Old 06-06-19, 05:47 PM
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There are several different methods for measuring even traditional horizontal top tube bikes. This can lead to confusion about what a frame size is all about. Even then, top tube length can change the way a bike fits. With sloping top tube frames, most of that goes out the window, so you have to learn about such arcane fitting methods as reach and stack to get a good fit. Thank heavens that I own a couple of great well fitted bikes that I am content with for now. For Dave Moulton, Surly's frame measuring system is spot on.
Dave Moulton's Blog - Dave Moulton's Bike Blog - Measuring Frames
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Old 06-06-19, 06:59 PM
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So what size do the Europeans call this, 5ins?!

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Old 06-06-19, 08:10 PM
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One way plumb line to BB.. divides reach & setback on either side of a horizontal line..

know the seat tube bb to top you can calculate the angle..
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Old 06-06-19, 09:09 PM
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Originally Posted by mtb_addict View Post
Hi
I think I uncovered something worth noting.
Below is from Surly's website for the LHT.
Their "frame size" is from center of BB to the top of the top-tube.

This is not the standardized way of measurement.
One could have missed this minor difference and order one size too large or too small.

C to T is really common. The other was/is C to C.

Neither was right or wrong. It differed based on brands and areas of manufacture.


Sure, one could have missed what you mention...but then they didn't try very hard to find the frame that fits since Surly lists complete frame geometry, of which seat tube length is but a minor part.

How do you want them to measure it?
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Old 06-08-19, 09:58 PM
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Are you buying a Surly or is this just another I just want to complain about companies that aren't my Magna or Huffy or whatever you have. In the span of a month I have bought 3 frames in the span of 2 years you have done nothing. The old phrase poop or get off the pot always reigns true for you.

Now I am not saying one should buy 3 frames in that span (or that they need to buy them all at once) but the Salsa Timberjack Ti was planned for a year and I have all the parts, the vintage Proteus road frame (with Tange Prestige tubing and Campy dropouts) was going to be turned into a cheap single speed so I had to save it (and happen to have almost enough bits to make a complete bike without having to spend much more than the initial $200) and the Specialized Sequoia Pro Module was at such a deal I couldn't with all good conscious let that go. Luckily though I am planning on the Sequoia for a good fall/winter project or maybe something for next year and have a few people interested in a bike I am selling so will recover most of the money from buy of the Proteus and Sequoia and hopefully will sell another bike as well and make a little more.

For those interested some manufacturers measure CTC some to CTT either way you still want to test ride a bike if you can especially if you are unsure about geometry but also ride quality. I test rode the Sequoia a bunch and that is why I got it, I really really liked it almost instantly. Surly makes some excellent bikes that may not be flashy or blingy but super durable and reliable and excellent platforms to get started cycling. My first bike I purchased was a Disc Trucker and I loved it.
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Old 06-08-19, 10:39 PM
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If you choose your size based on seat tube length, you are doing it wrong, anyway.
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Old 06-09-19, 06:19 AM
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Originally Posted by fietsbob View Post
One way plumb line to BB.. divides reach & setback on either side of a horizontal line..

know the seat tube bb to top you can calculate the angle..
This suggests a new critical point - one can focus on reach, but you also need to understand how far behind the BB the saddle can be placed. This is limited by seat tube angle, setback of available seatposts, and saddle rail design. Ultimately this is a point where frame fitting puts limits on frame sizing. Two frames of identical stack and reach might fit totally differently, and some might not be acceptable.

Perfect reach from the BB does not help you if you cannot place the saddle to satisfy your natural pedaling geometry or get good weight distribution. And the top tube length or ETT of a perfect-fitting bike does not by itself determine that another bike with the same spec will fit as well, or at all.
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Old 06-09-19, 06:25 AM
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Originally Posted by fietsbob View Post
One way plumb line to BB.. divides reach & setback on either side of a horizontal line..

know the seat tube bb to top you can calculate the angle..
Or just use the reach and seat tube angle numbers they list on their website.
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Old 06-09-19, 07:32 PM
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I don't see what's wrong with measuring to the top of the TT.

Surly's are the STUPIDEST fitting bike ever made, seriously. Plus 90% of their buyers are also when fitting. Pffft
The TT is a cm longer, the TT is level, 100 mm stem and they have a setback seat post.
All of this screams made to use a comfort bar, but NO they mostly have drops.
So the customer gets on and cries, I CAN'T REACH, WHaaaa. LOL So then they get a size or TWO smaller, heaven forbid they do the SENSIBLE thing like switch in a 80 cm stem maybe with rise too. The 2 cm lower front actually makes the reach FARTHER, but nobody seems to figure that out. WTF. So the average Surly goes home with 4+" seat post and 3" giraffe steerer..... For a PERFECT fit. hahahahahaha

A month ago I found on CGOAB a 6'3" old guy riding a brand new 56 cm. LOL 6" seat post and 4"+ steerer. He also had a blurry 6 sec YT video. I called him a Moron. LOL... Then 6 days into his TransAm trip westward in PA, his crummy derailleur snapped into his spokes. Awwww

I'm 5'8" and have ridden 4 slammed seat 23"/ 58cm bikes, but none with drops. They have 35,000 miles total.

Last edited by GamblerGORD53; 06-09-19 at 07:47 PM.
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