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  #1  
Old 11-24-2020, 03:11 PM
Smitty2k1 Smitty2k1 is offline
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Quick question on stack and reach

I've been professionally fit on a frame of one size, but am looking at another frame that has +20 stack and +15 reach.

Is stack/reach an apples to apples comparison across frame styles and brands and could I assume that I'd use 20mm less spacers under the stem and a 15mm shorter stem (of the same angle)? Currently have quite a few spacers and a 110mm stem at +6 degrees.

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  #2  
Old 11-24-2020, 07:04 PM
mhespenheide mhespenheide is offline
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In theory and as long as the two head tube angles are close to each other, yes.
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  #3  
Old 11-24-2020, 11:13 PM
joevers joevers is online now
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If you're going for within half a cm or a cm then yes. More specifically though the frame with 15mm longer reach actually has a few mm more than that- each spacer on your current frame shortens the effective reach the slightest bit while also having the tiniest bit less stack (really negligible). Round down 2cm on the stem instead of 1.5cm and maybe take out 1-3mm of spacers at most if you care.

http://www.bikegeo.net/

This site is also really useful for playing around with things like stem length and angle between multiple bikes.
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  #4  
Old 11-25-2020, 03:58 PM
SPOKE SPOKE is offline
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Seat tube angle matters too.....
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Life's too short to ride cheap bikes!
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  #5  
Old 11-25-2020, 11:29 PM
joevers joevers is online now
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Originally Posted by SPOKE View Post
Seat tube angle matters too.....
Noo
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  #6  
Old 11-28-2020, 02:21 PM
Imaking20 Imaking20 is offline
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Yes, stack and reach is apples to apples no matter the frame style or shape. Stack and reach are the result of things like head tube length, top tube length, ST and HT angles. This is why I roll my eyes every time someone just asks the top tube or head tube length - because those figures on their own do not matter.

With that said, changing stack and reach to the tune of 20 and 15mm is significant. That's a different bike size.
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  #7  
Old 11-28-2020, 02:28 PM
Clean39T Clean39T is online now
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Originally Posted by joevers View Post
Noo
Yes. But not necessarily for your reach/drop to the bars - it matters for other things..

There are no independent variables in bike design - move one thing and it impacts something else.

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  #8  
Old 11-28-2020, 02:49 PM
Smitty2k1 Smitty2k1 is offline
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Quote:
Originally Posted by Imaking20 View Post
Yes, stack and reach is apples to apples no matter the frame style or shape. Stack and reach are the result of things like head tube length, top tube length, ST and HT angles. This is why I roll my eyes every time someone just asks the top tube or head tube length - because those figures on their own do not matter.



With that said, changing stack and reach to the tune of 20 and 15mm is significant. That's a different bike size.
Thanks, it *is* a different bike size. My current size M bike has about 30mm of stem spacers and a 110mm stem at +6deg. So a larger sizes bike with a 90mm stem and fewer spacers should fit just fine?

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  #9  
Old 11-28-2020, 02:57 PM
Imaking20 Imaking20 is offline
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Seat angle matters when you're focused on top tube length. Seat angle does not matter so much if you're looking at stack and reach figures.

In the attached comparison, notice how the the TT length is the same (seemingly the only measurement most folks here use to determine if a frame will fit), but the STA means a cm difference in reach. That's not a small change. This means that, if your fit is dialed, you need to change your stem (to the tune of +/- 1cm if swapping from one of these frames to the other).

Notice I didn't say move your saddle. Your saddle fore/aft position is a static thing - which means your body composition needs your saddle to be in one spot so you don't torque your knees or dip your knees in at the top of your stroke - that means these two frames also necessitate different seatpost offsets in addition to the stem change. If you're already running a 0-10* offset post on the bike with a 74* STA, the 73* STA bike is not for you because you won't be able to get your saddle far enough back.

But that's a lot of nerdy details you can largely shut out if you're focused on stack and reach figures instead of TT length. Because reach is determined from the vertical centerline of your BB - reaching forward on the bike. STA is how far the saddle is setback from that vertical line.
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File Type: png STA Comparison.png (54.1 KB, 114 views)
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  #10  
Old 11-28-2020, 03:03 PM
Imaking20 Imaking20 is offline
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Quote:
Originally Posted by Smitty2k1 View Post
Thanks, it *is* a different bike size. My current size M bike has about 30mm of stem spacers and a 110mm stem at +6deg. So a larger sizes bike with a 90mm stem and fewer spacers should fit just fine?

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Unless you're a little person (let's say shorter than 5'7), running a 90mm stem is a mild indication that the frame is too large. Unless the bike was designed around a shorter stem (as some gravel bikes and mountain bikes do).

Since you're obviously not a little person, going from a M to L, I'd say this bike may be on the fence of not being the bike for you. Since you're running 30mm of spacers now, the extra stack is no bother - you'd still be running a 1cm spacer under the stem. Running a 90mm stem on a large/56cm bike isn't appropriate though. Your bike now either has a very short reach or the new bike a very long one.

If you've got a shorter stem laying around, I'd suggest you try that on your current bike and go for a short ride. Stem length has a noticeable impact on handling quickness. Any stability you'd gain with the (potentially) longer wheelbase of the larger frame may be cancelled out by the shorter stem. Additionally, with that short of a stem, you may end up with a bike that doesn't handle in a balanced way (i.e. the front turns faster than the rear wants to follow).
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  #11  
Old 11-28-2020, 03:09 PM
Smitty2k1 Smitty2k1 is offline
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Quote:
Originally Posted by Imaking20 View Post
Unless you're a little person (let's say shorter than 5'7), running a 90mm stem is a mild indication that the frame is too large. Unless the bike was designed around a shorter stem (as some gravel bikes and mountain bikes do).



Since you're obviously not a little person, going from a M to L, I'd say this bike may be on the fence of not being the bike for you. Since you're running 30mm of spacers now, the extra stack is no bother - you'd still be running a 1cm spacer under the stem. Running a 90mm stem on a large/56cm bike isn't appropriate though. Your bike now either has a very short reach or the new bike a very long one.



If you've got a shorter stem laying around, I'd suggest you try that on your current bike and go for a short ride. Stem length has a noticeable impact on handling quickness. Any stability you'd gain with the (potentially) longer wheelbase of the larger frame may be cancelled out by the shorter stem. Additionally, with that short of a stem, you may end up with a bike that doesn't handle in a balanced way (i.e. the front turns faster than the rear wants to follow).
Thank you

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  #12  
Old 11-29-2020, 08:34 PM
flying flying is offline
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Quote:
Originally Posted by Imaking20 View Post
If you're already running a 0-10* offset post on the bike with a 74* STA, the 73* STA bike is not for you because you won't be able to get your saddle far enough back.
Why is that sounding backwards to me?

73 is slacker than 74 so saddle is going to be further back (nose behind BB) already regardless of seatpost isn't it?

Last edited by flying; 11-29-2020 at 08:37 PM.
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  #13  
Old 11-29-2020, 08:40 PM
Imaking20 Imaking20 is offline
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Yeah, you're right. Too many beers or something.

I should have said that if you're running that little of a seatpost offset on 74* STA, you won't be able to get your saddle far enough forward on a 73* STA bike.

Whereas going from something like 25mm offset post on 74* STA may just mean a switch to a 15mm offset post on 73* STA (which is my reality and why I like 74* STA bikes)
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  #14  
Old 11-29-2020, 08:45 PM
flying flying is offline
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Quote:
Originally Posted by Imaking20 View Post
Yeah, you're right. Too many beers or something.

I should have said that if you're running that little of a seatpost offset on 74* STA, you won't be able to get your saddle far enough forward on a 73* STA bike.

Whereas going from something like 25mm offset post on 74* STA may just mean a switch to a 15mm offset post on 73* STA (which is my reality and why I like 74* STA bikes)
Hahah no prob I thought it might just be reversed.

Yes about not enough forward I always think of Valverde...He has a crazy amount of slammed forward seat & yet uses a large setback seatpost...Looks terrible IMO & I wonder why Canyon doesn't just give him a zero post?
Might not look as bad...or better yet give him a steeper STA
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  #15  
Old 12-02-2020, 09:19 AM
beartrapper beartrapper is offline
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I was hoping that stack was a simpler way of determining bike fit but the image above suggests that I still need to know every measurement.
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