If you looking at size M, the Topcarbon TCSF046/Lexon Riot in M or L (reach brackets the Epic Evo M) is essentially identical in geometry (BB drop, head angle, seat angle, chainstays) using a -1.5 degree angle headset (68 to 66.5) like the Works Components Angle Headset and going 110/120 travel. You could even go with a -2.0 headset if you want to go a tad slacker.

Quote from: looksee on July 15, 2021, 02:18:14 AM
A hardtail will be and feel longer in reach than a same spec reach/stack full suspension bike because it will only ever compresses in the front. You disagree? This isn't my original idea, I got it from some youtube video that I can't remember at the moment.

Found it. This is what I'm talking about. This guy had to go to 40mm shorter on his hardtail compared to his full suspension to have a comparable real world riding reach, and he explains why - basically what I've written above. Give me your thoughts if you watch it.

Another serious consideration when choosing between frame sizes on a carbon frame is do your shifters clear the top tube when the bars swing towards the top tube, especially if you are using flat bars. On my (stolen) 19", 625mm stack hardtail, there was a big/deep scratch in the top tube from the previous owner. It was an aluminum frame, so little harm done, though I did consider that a crack might initiate there. A carbon frame probably would have cracked. I also smacked the top tube with the shifter myself a few times over the years. I was reminded of this when I read this review on the Specialized site:

QuoteI LOVE the Epic Evo, but seriously, DO NOT ride this bike before ensuring the handlebar controls clear the top tube. I spent $1,000+ to repair the frame after the bike fell over leaning against my car - The bar controls hit and cracked the top tube when the bars spun. A seemingly common occurrence turned into a costly repair. I currently use the ENVE M6 25mm rider bars with the 50mm ENVE aluminum stem to ensure the controls clear the top tube. The repair company, Ruckus Composites, and my LBS were fantastic handling the repair.

I'm certainly not compromising my bar position to make the shifters clear the top tube. Without being able to have the actual frame in hand, I think the size 19 frame might possibly have clearance issues for me with the 619mm stack, while the 17.5 should definitely avoid the issue.

There's reach as a bike spec, which you are talking about, and reach as you ride, which varies. Yes, a bike's instantaneous reach will be shorter on an upslope. That's obvious when you ride up a steep hill, the bars come closer to you when you are standing.

You asked me how reach changes with suspension movement, so I talked about reach as you ride, or instantaneous reach. I answered that it is different for a hardtail vs. full suspension. A hardtail will be and feel longer in reach than a same spec reach/stack full suspension bike because it will only ever compresses in the front. You disagree? This isn't my original idea, I got it from some youtube video that I can't remember at the moment. I hadn't considered it in my initial post in this thread, but then remembered that factor and brought it up.

I mentioned it the first place because that is a consideration for me coming from hardtails. I know the exact distance and angle between bottom bracket and grips that works for me on a hardtail. That exact spatial relationship between bottom bracket and stem transferred to a full suspension bike will be and feel a bit shorter when actually riding and doing things like getting the front wheel up in manuals/hops/etc. where weight will be only on the rear. The 25mm reach+stem difference between my bikes is huge in terms of getting that front wheel up. It basically felt impossible on the longer bike because it was over my RAD number, while it is really easy on the shorter bike. That's what I'm keeping in mind while I'm doing pre-calculations on fit/frame size preference/stem choice to less than 5mm. Why shouldn't I try to be that precise as someone on the border between M and L on many frames, and coming from a technical/engineering background and able to analyze it closely?

Nope, reach is defined by the distance to the vertical line through the bottom bracket. That vertical line does change relative to the frame when the frame is tilted back. Same thing for the stack. The horizontal line to the top of the steerer changes relative to the frame. The only side of the reach/stack/diagonal triangle that is fixed is the diagonal (except in the Slingshot). If you have a picture of a frame geometry diagram on a sheet of paper and put it on the wall, and tilt the picture slightly to simulate a longer or shorter fork for example, the vertical and horizontal lines on the paper are no longer vertical and horizontal, and need to be redrawn to actual vertical and horizontal, changing the shape of that right triangle. There's no debate on this.

Just on this particular frame alone, you see confirmation of that in the reach/stack specs. The Lexon's reach/stack, which is spec'd at 100/100 travel is different from the Topcarbon, which is spec'd at 120/110, and therefore slightly slackened. They are the same frame, but reach/stack on the Lexon 17.5 is 432mm/603mm, while the Topcarbon 17.5 is 430mm/609mm. Those different numbers for reach and stack are there not because the frame is different, but because the Topcarbon's reach/stack is calculated with a fork that has 10mm longer travel than the rear travel vs. equal travel. Furthermore, the main purpose of that https://bikegeo.muha.cc/ website that I linked to earlier is in fact to see how reach and stack changes with changes in fork length. That's why they have fork selections at the top, and reach/stack at the bottom where you are looking for the results of the fork change.

On a hardtail, when you compress the suspension, only the front end lowers, and the bike only moves in the direction of getting steeper frame angles. The hypotenuse between reach and stack, the distance between the bottom bracket and the top of head tube is a fixed dimension, but the triangle formed by the hypotenuse, reach, and stack changes shape such that the stack gets lower, and the reach gets longer as the suspension is compressed. The sagged reach is going to be longer than spec sheet number.

You can see the exact amount reach (and stack) changes with fork compression using https://bikegeo.muha.cc/ . For example, using the default numbers in that calculator, the reach is 407.2 with a fork length of 470 (close in length to a 26" 100mm Manitou fork). If you change fork length to 455, using 25mm travel (about sag), reach increases to 412.4. At 50mm travel (enter 420 for the fork, changing nothing else) reach is 424.7mm (+17.5mm reach). At 100mm travel, reach becomes 442.2mm (+35mm reach).

On a full suspension bike, the rear is going to compress too (maybe more since more of your weight is in the back), so the bike's attitude will stay level on average, meaning the reach is relatively stable with suspension compression.

Quote from: bruto on July 14, 2021, 01:16:14 AM
when comparing older and newer frames by reach only, remember that steeper seat tube reduces effective length so the same reach won't mean the same feel
and with a slacker headtube each spacer under your bars reduces effective reach more

I bought cf7-213 in the smaller size, judging mostly by reach (if 430 feels fine on my hardtail with 69 HT/74 ST, why would it feel wrong on 65 HT/77 ST frame, right?) and it's short AF I'd really like to have those 25mm from the next size

Maybe you are feeling the effect of suspension on reach, or do you not try to equalize saddle to bar distance on your bikes? On a hardtail, when the suspension is compressed, the reach only gets longer. On a full suspension bike, it stays about the same on average? I should consider that aspect more, since I've never had a full suspension bike.

I'm using reach to help decide on what the standing feel would be on a frame. It's a figure that helps locate the bars relative to the bottom bracket. And not just reach, reach at a comparable stack, which you can calculate using trig/CAD/or geometryCalc website, or carefully measure with the help of a level and plumb line. Reach at different stack heights are not comparable obviously because as you go higher up the steerer, the reach gets shorter. For my '93 bike, I measured and calculated reach at a stack above the 40mm spacer stack instead of at the top of the frame's headtube just to make it comparable to more modern bikes. For the record, reach on my '93 is only 377mm above the 40mm spacer stack at a stack of 586mm with the swapped longer fork. Reach calculated at the top of the headtube, the "actual" frame reach with this fork is 399mm at a stack of 532.5mm, but that stack is so low it's not comparable to any modern mountain bike frame, so I measure stack/reach where it's comparable, right under the stem.

I ignore the seat tube angle or effective top tube length because the fore-aft adjustment of the saddle is sufficient to move it into the right position with just about any seat tube angle at my seat height. For example, the now longer fork on my '93 Stumpjumper slacked the original angles out by 2.5 degrees, resulting in an insanely slack 70.5 seat tube angle. Yet I am able to slam the seat forward on a non-setback seatpost, and have the seat in a "modern" position. It's literally in the same place in space that it would be if I had a 75 degree seat angle with a setback seatpost. I don't have to shift my butt forward onto the nose at all on even the steepest climbs. In fact, that was my criteria for determining the fore-aft seat location (very different from how I would do it on a road bike). Maybe a taller person would have to pay attention to seat tube angle, because most actual seat tube angles on the bent/kinked seat tubes are slacker than the "effective" angle, so the taller you have the saddle, the more it goes back than you expect for the "effective" angle with height. But at my seat height, it's a complete non-issue - I can make any seat angle from 70 to maybe 78 work to put the seat in the same, right place.

Quote from: bruto on July 08, 2021, 12:30:49 AM
19" Riot is only as large as the medium Merida 96, for example
compare reach, FC, wheelbase for yourself: https://www.merida-bikes.com/en/bike/1984/ninety-six-rc-9000?spm=a2700.12243863.0.0.38403e5fbrCKPv#w1

it would probably be fine for me at 178cm, with some 50mm stem (I ride a 430mm reach frame with 80mm stem currently)

TLDR below. Summary: I'm the same height, but I think I'd go for the 17.5, though both would work.

I've been browsing this forum for a couple months, and this is the frame that looks the best to me. I'm also 178cm, but I might go for the 17.5". The LCFS911 looks good too, but I'm more in between sizes on that one, preferring not an excessive reach.

I have had two mountain bikes, a 1993 Stumpjumper hardtail since new that is my current ride, and a 2015 29er Stumpjumper Elite M5 that was stolen late last year. My '93 Stumpjumper is surprisingly feeling really good with my current setup after messing with spacers, stems, and bars (and saddle slammed forward on straight post) since a large fork length increase after a swap. It fits and rides better than it ever has (came with 130 stem back in the day, and couldn't avoid a huge bar drop). I learned about the RAD fit theory last week, and it turns out my body measurement RAD of 790mm happens to be exactly the same as the 790mm bike RAD that was my final result after trial and error fitting by feel. That it feels right kind of validates the RAD theory for me, since I arrived at the same fit on my own before even hearing about RAD.

My stolen 2015 bike was a 19" that had a 437mm reach and a 70mm stem after trying some different stems, suggesting that the 19 frame here would work well with a 60mm stem for me. Although I didn't feel too stretched out on my 2015 hardtail, the extra reach to the bars (greater than RAD fit) meant that I did have a really hard time getting the front wheel up to practice manuals/wheelies/hops and things like that. I ride XC style, but don't currently race. My liking both fits, with a reach+stem difference of 25mm(!), for most riding shows how adaptable riders can be. But since I don't feel cramped or have difficulty at all with the RAD fit, even on the steepest climbs, I think I would choose that fit for my next XC style bike for the other benefits, even though I know most XC pros go longer.

Playing around in CAD, and I can duplicate the RAD fit of my '93 bike (including the angle of the RAD diagonal) with the 17.5 frame and a 50mm +6deg stem on a 10mm spacer, with the option of going lower and longer with a different stem if I want the XC racer fit (longer stem not at all out of place on XC pros bikes after all). The 19 frame would also work, but the seat tube is quite a bit taller. I had an issue with my legs rubbing the top tube when out of the saddle pedaling on my 19" 2015 bike, as well as basically having no standover clearance, so I like the lower top tube on the 17.5. I don't care about water bottle mounts, riding without water on my mountain bikes, so one cage is fine with me. Finally, I would likely be able to run a 140mm dropper on the 17.5 vs. 120mm on the 19. I haven't had a bike with a dropper, so 120mm it likely great already, but why not a bit more?