Maelochs

No .... because the measurment You are s=describing is not "Actual" reach.

Taken to the ridiculous (Reductio ad absurdum) only works in some cases ... but because the real measurement "reach," on real bicycles, Can be used to give real information .... your showing that it can be distorted to have no meaning doesn't mean it is wrong, just that you like to quibble.

All measurements on a bike are information. and can be used by a knowledgeable person to help him or her understand a frame. Sorry if you cannot.

I have bought several bikes online based on their geometry sheets and every one has fit perfectly with the exception of the latest, where I didn't precisely measure my spacer stack and am now about to install some bars with 13 mm less reach to compensate. That's what I get for cutting corners ... I get new, lighter bars.

I hope you don't get confused by that use of the word 'reach."

And if you ever have trouble again figuring out what all those words and numbers on the geometry chart mean, drop me a line.

Kontact 

This post has zero content applicable to this thread. Ddub is trying to compare frames of different stack height using Reach numbers, and didn't understand why that doesn't work. You post, like all the rest, does nothing to make anything clearer, and is just your attempt to sound superior.

You didn't sound superior when you mouthed off all the other times, and you don't now. You just sound like someone who likes to (attempt) to insult people.

Seattle Forrest

The previous model is marked down. It has better paint and better wheels. I got mine just before this one came out, they gave me Di2 for the price of mechanical.

Maelochs

jealousy is a sin ... why do you tempt me ....

Seattle Forrest

I'm an enabler.

Drew Eckhardt 

They're better, with room for a larger seat tube water bottle and full-size frame pump stowing beneath the top tube.

Or at least enough people feel that way you're losing share in a commodity market with companies fighting for slivers with model variations like gravel and all-road (versus disc brake road with clearance for wide tires, or cyclocross).

Samuel D

Going back to the original premise:

I have never heard a convincing explanation for why a compact frame would be stiffer or lighter. The one above is no exception: the extra seatpost length weighs more than the tubing it replaces (these tiny weights being insignificant anyway); and I don’t know what is meant by “smaller triangle reduces lateral torsion”.

A structure is strongest when forces act exactly along the axes of its tubes, as they do in a space frame, since in that arrangement the tubes need not resist bending or torsion but only tension and compression. Most bicycles are not space frames (although Pedersens and some Moultons get close), but the principle applies.

It follows that each tube should be supported at only two points. You cannot bend a tube by applying force only to the two points of its ends.

Seat tubes along with their posts diverge from this ideal because the saddle is not at the seat cluster. Therefore the seat tube + post has force applied at the saddle, at the seat cluster, and at the bottom bracket. Unnecessary bending results, and this can be minimised by putting the seat cluster as close as possible to the saddle, i.e. exactly the opposite of the compact frame idea.

In the early days of the bicycle, many bad designs were attempted with braced frames (the braces supposedly strengthening the frame but doing the opposite by inducing bending) or frames with curved tubes. Curved tubes of course cannot resist tension or compression as well as straight ones, so they must be heavier.

With carbon fibre easily allowing any shape, it seems we’re back to mechanically bad designs with non-straight tubes and compact-like shapes. Maybe these can be justified by comfort or aerodynamics although I doubt it.

Racing Dan

Maybe someone else mentioned it, but compact frames are better if you want to reduce SKUs and only have a few frame sizes, because the seat height can be varied more. Some, even expensive bikes now only come in t-shirt sizes, S, M, L, XL. Then there is the stand over height that for the same size frame is lower.

https://www.liv-cycling.com/gb/langm...ced-pro-0-2018

Racing Dan

Im betting most of the "advanced" geometry is purely for marketing and cool looks.

ddub

Reread your post and see how utterly ridiculous it sounds. Reach most certainly impacts how a rider fits a bike. You are trying to school a bike fitter? I'll not pursue this topic with you further as it's off topic and I would rather refrain from returning the personal insults you seem all too eager to offer.

Kontact 

To be clear, "Reach" with a capital R is the horizontal distance from a vertical line through the BB to a point on an angled head tube. That distance is entirely dependent on the height of the head tube at a ratio of 3mm less Reach for every 10mm of additional head tube. That 3:10 ratio means that Reach is only meaningful at the same head tube height - AKA Stack.

The other "reach" is the distance a rider has to reach from their saddle to the bar, horizontally (little "r"). This is most easily expressed as Effective Top Tube, because the head tube and seat tube are roughly parallel, so head tube height is not a factor. The only problem with this number is that you have to correct for different seat tube angles because people set their set back without reference to the seat tube angle so correcting for the difference zeros it out. The head tube may not be perfectly parallel to the seat tube, but the difference of even 3° is not going to have any real difference on ETT reach within a foot of head tube height.


It sounds like you are insulted that I felt the need to explain these things to you because you are a fitter. But as a fitter you should be aware that if you are going to fit someone to a bike that has a different stack, you can't use the reach number to determine things like stem length. And that's what your post comparing Endurance bikes sounds like.

If you wanted to duplicate the fit of a 56cm Cervelo C3 on an R3, you'd want the same frame size because they have the same ETT. Once you add the spacers to the R3 to make up for the head tube difference, your will find the post-spacer Reach to be identical between them. If you try to go by Reach alone, you would choose a 54 R3 because it has a closer Reach number to the 56 C3. But once you add enough spacers to make the R3 stack high enough, you'll find that the reach is 16mm shorter on the R3, requiring a longer stem. If you had just used the ETT, you would have selected the 56 R3, added 20mm of spacers and used the exact same stem.

Your earlier response makes it sound like you didn't understand those facts. I don't know if you do or do not, but the reach (little r) of the Cervelos is consistant between sizes, while Reach is a number that is entirely dependent on Stack, and that means it can't be used independently, as in the comparison you made.

Dean V

Kontact is right on this. You can't directly compare reach with different stack heights.
A simple geometry equation has to be applied first to compensate for the steering head angles influence on the numbers.

Racing Dan

Why dont you just look at ETT and stack. Reach is largely meaningless because seat tube angles vary a lot between sizes and between models. That is you can have a number of bikes with the same or very similar Reach but wildly different ETT.

Sullalto

Define 'a lot'? Most bikes the variance is small enough that saddle adjustment has a greater effect.

Racing Dan

Yes of course you can compensate, to a degree, for different seat tube angles by moving the seat fore and aft. You can also put in an other seat post, with more or less set back. That however, does not negate the fact that bikes with the same or very similar Reach can vary a lot over ETT, because the seat tube angle is not a given. Because of that, the idea you can judge the "size" of a bike, or compare different models, just by looking at stack and reach, is simply wrong. You need to at least take ETT into account too.

Dean V

Stack and Reach as measured with the BB and top of headset as reference points is the most accurate way of comparing frames for fit. BUT you do need to factor in that a different Stack will have an effect on the Reach number.

Kontact 

If you want to use ETT, you have to add or subtract for the seat tube angle as I described above. We do that because people don't set their set back by anything related directly to the seat tube angle.

"Reach" is independant of seat tube angle, which is why it came about in the first place. But it is very dependent on Stack, so you can't use Reach without first ensuring the same Stack.

Stack and Reach were first used to compare Tri-bikes, many of which have nearly vertical seat posts. For those bikes Stack and Reach make a lot of sense. For road bikes that have roughly parallel head and seat tubes, it makes much less sense.

Fiery

Why would reach make more sense for triathlon bikes? The head tubes are not nearly vertical, so increasing stack still decreases reach.

Samuel D

My own view is that stack and reach are not very useful values taken in isolation, and yet their popularisation appears to be based on the idea that they tell you all you need to know. Not so.

Much the most important thing for me is how far behind the bottom bracket the saddle is positioned, i.e. the seat-tube angle in combination with whatever saddle and seatpost I hope to use. If the seat-tube angle is too steep, I can’t slide the saddle far enough back to get the weight off my hands, which leads to fussy handlebar placement (height, reach) in addition to hand and shoulder discomfort. The lower your position and the lower your pedalling force (whether by high cadence or low power), the slacker you need the seat-tube angle.

With less weight on the hands, the precise position of the handlebar becomes far less important, the reductio ad absurdum being riding no-hands.

If you’re struggling with hand pain or nerve compression, or if you think you need thick handlebar tape or padded gloves, that’s a sure sign your saddle is too far forward. It’s a common problem today because once-a-week cyclists often ride road bikes designed for racing, with racing seat-tube angles (e.g. 73° or even steeper). Yet they push the pedals half as hard as a racer.

Racing Dan

Lots (most) smaller road bikes even have seat tube angles in the 74+ degree range. 73* in size 52 for instance is far and few between.

Kontact 

Because the seat tubes are effectively near vertical. With a regular bike, if you raise the bar and stem at the same time absolutely nothing happens to the distance between them. Tri bikes don't have that relationship, and there really isn't an average set back being used by Tribike riders like there is with road bikes. So it made sense to look at the top of the head tube as a spot in space rather a point on a line.

Even then, you still wouldn't compare Reach without Stack.

Kontact 

Luckily, seat posts are relatively inexpensive and can be had in set backs greater than 25mm.

Some brands have used 73° STA across their entire size range. Cannondale used to do it and Cervelo does today.

Racing Dan

Yes that is what I said in #166, but now your 52 is more akin to a 54. Then you can put on a shorter stem to compensate, ect ... Lot of handles to pull on, but they are all interlinked. I have a 53* size 52, but as I said, most are much steeper. Im sure some prefer that, but I dont.

Kontact 

It really doesn't work that way. Once you correct ETT to whatever format you prefer, then that is the information you need without any sort of negative downside. And the correction is so simple you can do it quickly in your head - add 1cm for every degree above your preferred STA and you can compare them directly. And you only need to do that if the bikes you're comparing use different STAs for the size you're looking at.

The seat tube angle doesn't do anything but make the seat post stick up at a certain angle. If you add more set back via seat post you are extending the top tube to the rear, if you want to look at it that way. But you aren't changing the overall geometry of the bike.


Stack and Reach don't relate to seat tube angle or ETT at all, which is the point of S&R - they take all that stuff off the table. So while they don't relate to ETT, they strongly relate to each other. So we could just use S&R, but anyone trying to compare frames that don't have the same stack needs to understand that the math to compare different S&Rs is more complex - you have to do a Rise over Run conversion by subtracting 3mm of Reach for every 10mm of additional Stack. Easy to do on paper, not nearly as fast as you can do an ETT conversion.

The main issue is that people misunderstand Reach to be a number that directly relates to how someone sits on the bicycle, and it would be better to think of it as an arbitrary number that designates a point on a coordinate plane.

Dean V

Tri bikes and to a lesser degree TT bikes have some unusual layouts and tube shapes which makes traditional methods of measurement difficult or even impossible. Stack and Reach method based on BB and upper steering head makes sense for this. eg, how else would you measure a beam bike? Even a Cervelo P3 with its wiggly aero seat tube is problematic.