I looked through past threads and didn’t see anything that touched on this. I want to know what the crucial measurements are for xc mountain bikes.
I am looking at going from a Kona Honzo (Trail) to an XC bike. I found a nice used Specialized Epic, however, its a size larger (XL) than my Honzo. I am looking at the geometry charts for both bikes and I’m not sure which measurements are the most important with mountain bikes. I am 6’1" (~185 cm) and typically ride a Giant M/L frame on the road/CX. In some other research I did I see people saying stack and reach are the most important on MTB.
Here’s a comparison of the bikes geometry (L Honzo, XL Epic)
Stack 642, 636
Reach 475, 480
Top Tube 647, 662
Seat Tube 470, 520
Standover 750, 847
Front Center 769, 753
Taking into account these are different styles of bikes, do you think these compare well? Are there other measurements I want to look at? I don’t want to waste my time driving 1.5 hours both ways to find out it doesn’t come to to fitting.
Take a look at the seat tube angle of both bikes too, effective top tube measurement is pointless with out STA. When people size their bikes on stack and reach alone they’re basically ignoring a pretty important fact; we spend most of the time on our bikes in the seated and pedaling position, not the attack position.
If I’m sizing a XC bike, I’d prioritize ETT, and STA - just to get a starting point. Then I compare stack, reach, stand over… before that I’ve already looked at head angle, and BB drop, those two variables alone can be deal breakers before going any further.
@mcneese.chad The numbers are for a 2019 Honzo and a 2020? Epic. One is a trail bike the other an xc bike so I think that has something to do with it.
@iamholland To be honest, I have no idea why I’m on a large either. It was my first mountain bike and I just bought based of their sizing chart and knowing that I liked smaller road bikes. My honzo feels fine, however, I have no idea what a XC bike is supposed to be like.
Hi, I’m thinking about buying an epic and trade my epic evo but I have some dubs on the size.
I’m 183cm riding at 77,2 (saddle) but it looks like I got slightly short arms. That’s why a bike fitter fitted me on a 54 super six evo 2021 road bike with a 11cm stem. Also the epic evo fits me in L but I didn’t have any bike fitting on it.
Watching the two videos posted about the RAD and the reach for the mtb, I don’t know if it is worth buying an epic M. It’s 2,5 shorter reach.
I measured a RAD of 80,5 cm.
Any suggestions? Are these measure so important for Xc bikes?
Thanks
Try them both. And remember that you can always get a longer stem. If you have a fitter you trust, work with them! Many fitters can simulate the fit of any bike if they have the dimensions. I (personally) prefer the smaller of two frames if it fits. I don’t understand the appeal of going big. Unless you are a teenager, it’s not like you are going to grow into it!! They all have the same size wheels and gears…
Thanks for these!
I have the stepladders to do the RAD measurement, but the pencil-on-the-wall method is so much easier and faster!
And this gives me some for issues to clear up - ones that I didn’t know I had, but explain the challenges I’ve had with certain kinds of bike handling!
Just calculate it. Take the square root of (Reach X Reach)+(stack X stack). Sorry, don’t know how and don’t feel like looking up typing equations properly.
I think you mean Gen 6 (since 8 doesn’t exist yet)? This assumes you mean the Fuel EX and not the Top Fuel (since you didn’t include the other half of either name so it’s ambiguous).
For one example though, you just use the geo chart and online calculator to get the Frame RAD as shown below:
Any time i switch bikes i automatically use this site… https://geometrygeeks.bike/
you can geek out to all sorts of different combos. It wont necessary tell ya how it will ride but if you know how your past frames felt/rode then its a good comparison
Also one thing that looks at is BB height, wheelbase and fork offset. HTA is really important but don’t forget that those adjustable headsets work really well once dialed in.
I used to love Geometry Geeks and still use it if I need to directly compare 3 or more bikes, or this next options is lacking the model I need to research… but Bike Insights sort of rules with it’s actual geo overlays:
It also has more info overall (with some calculated) including the Stack & Reach Ratio that can be useful here. But it still lacks the RAD measurements so you have to do that as I showed above.
Thanks, I do mean the fuel ex8 gen 6. I’m wondering though how you account for the stem and bar bend.
It seems that the method Lee McCormack is suggesting tries to get to the center of the grip line not necessarily the distance from the center of the BB to the top of the head tube. Am I missing something?
I just can’t find a shop near me with a bike to measure.
Thanks
Since MTB stem sizing has sort of been refined down to a choice of Short or Really Short (not to mention restrictions from stuff like 35mm clamps or even integrated bar/stem combos), there is a mixed bag there.
As ever, having live samples on hand help.
Next step is to look at the full bike specs, where Trek in particular will list the sizes of components like Stems & Handlebars with respect to each frame size. So cross check those per bike size and then consider what you have at the moment.
I personally record similar info where I have the straight distance from the saddle to handlebar/stem center (reach & drop) but also the diagonal from the saddle nose to middle of grip. I do this for road bikes too since it is more closely related to the real rider reach and effectively includes stuff like handlebar width, roll angle and such.
Not sure if you are missing something, other than the fact that this rolls into the 3D sizing and fit that is not really addressed directly in the bike world at present. They have good 2D stuff like covered above, but the “width” aspect is more hand waving and general comparison to prior experience to nail down.
I have run a few CAD sketches for riders wondering about stem/handlebar swaps, but each one is a special case at the moment. Until one of those great 2D geometry tools adds this other plane, we have to do the extra work ourselves on top of those tools data.
So in your case, starting with the full data set of your current bike (hoping you have at least something on hand), and then coupling the 2D stuff above with the bar/stem info relative to your current bike is the key.
