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Should ETT be considered when sizing bikes, or is it all Reach with modern geo bikes?

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Discussion starter · #1 ·
Should ETT be considered when sizing bikes, or is it all Reach with modern geo bikes?

Keen to hear what everyone thinks about Effective Top Tube Length vs Reach when sizing modern geo bikes?

I'm 176cm tall and typically fall in between M and L in sizing calculators, more typically in the M side.

I have a Scott Spark in M, which isn't modern geo, that feels ok with a reach of 432 and a ETT of 605, but I suspect a longer stem is playing a part in the size feeling ok.

I have also spent some good time riding a GT Sensor 29 in M, which is a more modern geo, with a reach of 445 and a ETT of 593. This feels really cramped when seated. Especially climbing.

This has got me thinking that while the Reach will help determine how long the bike feels when in attack position, the ETT is important to indicate if it will feel cramped when seated. Does everyone agree?

I'm starting to think about a new frame, and not sure how to approach sizing. Ideally I'd demo a bunch of different bikes, but it's not that easy to organise a demo where I am, and I find short rides don't really provide enough time to get a good understanding about how I might adjust to the size in the long run, since both will be ok... but I want more than ok :)
 
#2 ·
you need to consider both. I wonder if "effective seat tube angle" plays into this. a steeper seat tube angle, theoretically, changes the ETT less with height than a slack one.

as a person who's only about 1cm shorter than you, I'd size down and stick to medium frames. modern bikes are huge. that's my personal preference for how and where I ride, though. I prefer to be more in control of a smaller bike for wrangling over the terrain than a bigger bike that just plows over everything. YMMV.
 
#3 ·
Yes ETT plus stem length and bar width determines your climbing fit. Most bike manufacturers take these weird steps in bike design, currently rarely adding enough reach to compensate for the steepening seat tube angles.
 
#4 · (Edited)
An excellent question.
ETT is an absolutely critical factor in how well you fit the bike when seated and pedalling. However, ETT It is a direct result of reach, stack and seat tube angle.

Factors that impact how well you fit a bike in standing and descending positions:
  1. Reach
  2. Stem length
  3. Handlebar width and rearwards sweep - very wide bars can make the bike feel longer unless they have a good rearwards sweep angle
  4. How many spacers - more spacers on a slack head angle will mean the handlebars are further back and make the bike feel shorter
Additional factors which impact how well you fit a bike when seated/climbing only.
  1. Seat tube angle
  2. Saddle fore/aft position
  3. ETT - a product of reach and seat tube angle.
 
#5 ·
Reach matters when you’re out of the seat, ETT matters when you’re seated.

You can tweak ETT by sliding the seat fore/aft
You can tweak reach and ETT by running a shorter or longer stem.

A slack or steep seat tube can skew the numbers… I’m facing that problem now as I size for a Zerode Taniwha which has a slack seat tube and an odd reach; it’s partly due to building around a Pinion gearbox.

Buying a bike based on geo alone can work out, but not always. Best bet is to get something similar to what you already ride and like… unless you’re trying to make some changes in your set up.
 
#6 · (Edited)
Further to my comment above, when I was looking for a new bike, I was temporarily riding my ancient 26er hardtail. It was only 380mm reach but it had a 610mm ETT, a 100mm stem, skinny handlebars and a 68 degree seat angle. I now have a bike with 470mm reach, 644mm ETT, 50mm stem, 750mm bars and 74.5 degree seat angle.

In comparing the ETT's of old and new: If you allow for the 50mm shorter stem and wider bars on the new bike, the effective ETT's of old and new bikes are actually quite similar! 😮
 
Discussion starter · #7 ·
Great discussion! Thanks for helping validate my thoughts.

@Sanchofula - I am trying to make some changes... looking for something that's not as cramped seated as the medium GT Sensor, but also something a little more capable than the Spark. The Spark I think is more of a shock thing than a geo thing, something more plush but less pedal bob.. I'm thinking that's more the linkage and the Scott Twinloc shock tune.

I really feel to be comfortable seated I need an ETT of at least 605, probably more like 625 once I account for a short stem. I guess from here I need to ride some bikes to see if the associated reach makes me feel too stretched out.

For the plush / bob aspect, hoping to demo a Revel bike. I'm not in any rush so this is a bit of a long term project :)
 
#8 · (Edited)
If you plan to pedal your bike around, then yes ETT is still very important. To me reach tells how the bike feels standing up, ETT tells me how it feels sitting down.
I tend to do long rides and I tend to get neck pain pretty easily, so ETT and stack is very important, because I want an upright and not super stretched out positon. I also have long legs, so I look closely at the seat tube design. I tend to avoid bikes with a very slack actual ST angle, because at my seat height the actual ST angle will be very different, which again is important because I don't want a super long ETT (and I don't want to sit on the rear axle).
 
Discussion starter · #10 ·
HollyBoni said:
I want an upright and not super stretched out positon
Click to expand...
100% with you there... in fact I just got some new bars with more rise to get a little more upright to see if it reduces the impact on my shoulder... getting old is rough :ROFLMAO:

weeksy950 said:
just find what you like, what suits you.
Click to expand...
Totally agree... I guess its hard to do this sometimes when looking at high end bikes where there aren't many around and demos are rare. It kind of makes me want to travel to a trade fair to ride a bunch and try and sort out this problem.
 
#11 ·
SideSwip said:
Totally agree... I guess its hard to do this sometimes when looking at high end bikes where there aren't many around and demos are rare. It kind of makes me want to travel to a trade fair to ride a bunch and try and sort out this problem.
Click to expand...
Yeah of course, but time and experience will tell you, it just takes a bit of time potentially to get the knowledge.

I now know i want slacker and smaller than many would say i should want.. but it works for me, i'm 6'0 on a Medium RM Slayer, which the naysayers tell me is too small... but i really like it... As i've liked several other 'smaller' bikes i've owned too. I've tried bigger and not got on as well.
 
#13 ·
ETT is critically important on any bike you plan on climbing. The industry has shifted to reach as a fundamental measurement. For me, reach is about the third measurement I check, after stack and ETT. Hell, 10 years ago, I don’t even remember reach being a thing. Even today, it’s clear that most riders don’t actually know what it means.
 
#14 ·
Yes, I think you have it correct. ETL determines how roomy or cramped the cockpit will feel when seated. So, yes it's definitely important. If you compare older geo bikes with new geo bikes you'll find that the ETL are similar between sizes, even though the reach is longer due to the fact that the STA is steeper. Reach comes into play when you stand. The longer reach on the new GEO bikes simply means you don't have to lean so far back on the bike when descending. When you stand you can be in a more neutral position. It's a much more comfortable and controllable position. It doesn't necessarily mean the bike feels long or big, which would be more attributable to a longer wheelbase and slacker HTA.
 
#15 ·
To throw another angle:

www.leelikesbikes.com

Dialing in your bike setup step 1: Make it RAD - Lee Likes Bikes

This article is adapted from the book Dialed and ran on Pinkbike. It lays out the most important aspect of mountain bike fit and setup. I hope you find it helpful! When it comes to mountain bike setup, the most important measurement is the distance between your bottom bracket and your grips. I...
www.leelikesbikes.com www.leelikesbikes.com

I think the rad does a great job of encapsulating the bike handling while standing.

I’ve no idea if his fit equations work for everyone but I do know I found all my bikes were within millimeters of each other (including road bikes.) I’m still shocked that a bike fit number can remain so constant for 30 years and all the bike changes in that time.

Make sure your ‘rad’ is possible on your prospective bike (reach, stem, stack, bars) then make sure your seat can be positioned well (height,bow/stern).

worst thing about rad is the math to determine it from a geo table.
 
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#16 ·
What I'll say it's hard to optimize everything....

Reach optimizes out of the saddle weight balance and positioning
ETT optimizes mainly for flat/rolling terrain pedaling
STA optimizes for uphill climbing

Some are saying optimize ETT - but the problem is say you do bike fit, the ETT will be too long for steep/sustained climbing. That's why many people scoot up their saddle on long steep climbs. If ETT feel a bit cramp or short for flat pedaling, chances are it will feel better during climbs. The STA obviously place a huge part in the climbing position as well as to better center you on the bike when there is an incline. But my takeaway from switch to older and new geo bikes is, you can optimize ETT for either flat or uphill, but you can't do it for both.
 
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#17 ·
But if you're not timing things then does it matter?

If you make a climb in 6min or 6.04 or 6.30 who cares, unless training, racing etc, it's just a part to get out the way
Make your bike the best you can be for what you want to enjoy the most? If that's jumps, then jumps, if it's climbing, it'll be a different size, shape and geometry.

No bike is perfect for everything.
 
#18 ·
As it has been said already, seated position, ETT still matters a lot. There's a reason even modern XC bikes still have "steep" head angles and "slack" seat angles. Further, regionality plays a big role in what kind of bike rides well in a particular area. The problem is the bike industry is really more concerned with trends as of late, and if your bike company isn't on the latest and greatest, then you quickly become irrelevant.
 
#19 ·
mack_turtle said:
you need to consider both. I wonder if "effective seat tube angle" plays into this. a steeper seat tube angle, theoretically, changes the ETT less with height than a slack one.

as a person who's only about 1cm shorter than you, I'd size down and stick to medium frames. modern bikes are huge. that's my personal preference for how and where I ride, though. I prefer to be more in control of a smaller bike for wrangling over the terrain than a bigger bike that just plows over everything. YMMV.
Click to expand...
It’s funny you said you like a smaller frame. My old Turner was a medium frame I’m 5’11. While it was easy to maneuver it felt small. I had to get a longer stem and such. I looked big on it when watching vids and pics. Anyway I’m on a Large 29r now and no stem length. Bike felt huge going a frame up and 26 to 29. But damn only took me a couple rides and it feels so good. I keep telling myself I should have made the switch long ago, knowing that it may not have been the same since I’m on the latest geo. I am enjoying not have to wrangle the bike. I enjoy the rollover this bike has and the size just feels right.
 
#20 · (Edited)
+1 for RAD from me as well. With LLS (low long slack) bikes the old rules of thumb for reach are out of the window especially with steep seat tube angles.

I went from an M with old skool geo to a modern LLS in L-size and I am currently "overbiked" in terms of reach as well as the manufacturer's recommendation. However, the bike fits me because it matches my RAD (rider area distance or whatever who calls it) and M sizes now feel small to me.

RAD is the distance from the middle of the bottom bracket to the handlebars. RAD can be measured as the distance from the ground to your hands as if you were doing a deadlift with hands handlebar width apart.

For any bike it calculated from bike specs online as
RAD = SQRT(Reach^2 + Stack^2 ), where SQRT = square root .

Though this isn't perfect as it doesn't account for the stem and handlebar, maybe adding 2-3 cm to stack before squaring it would be a better approximation?

However, a long ETT puts more pressure on your hands thus getting the width, up- and backsweep right for your wrists is important in order to avoid hand pain or other issues.
 
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