# XC Mountain Bike Sizing - The Important Measurements **URL:** \ **Category:** Equipment\ **Created:** [April 20, 2021, 4:31pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583 "2021-04-20T16:31:40Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![wistoon33](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/wistoon33/32/79474_2.png) [@wistoon33](https://www.trainerroad.com/forum/u/wistoon33)\ **Post date:** [April 20, 2021, 4:31pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/1 "2021-04-20T16:31:40Z")
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) 1. Stack 642, 636 2. Reach 475, 480 3. Top Tube 647, 662 4. Seat Tube 470, 520 5. Standover 750, 847 6. 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. ---
**Author:** ![ibaldwin](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/ibaldwin/32/44413_2.png) [@ibaldwin](https://www.trainerroad.com/forum/u/ibaldwin)\ **Post date:** [April 20, 2021, 5:02pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/2 "2021-04-20T17:02:04Z")
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. ---
**Author:** ![mcneese.chad](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mcneese.chad/32/15056_2.png) [@mcneese.chad](https://www.trainerroad.com/forum/u/mcneese.chad)\ **Post date:** [April 20, 2021, 5:08pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/3 "2021-04-20T17:08:58Z")
> [@wistoon33](#): > > Standover 750, 847 - Pretty sure that you have a typo on the Epic Standover. Hard to picture 100+mm [4"] difference there. ---
**Author:** ![wistoon33](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/wistoon33/32/79474_2.png) [@wistoon33](https://www.trainerroad.com/forum/u/wistoon33)\ **Post date:** [April 20, 2021, 6:06pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/6 "2021-04-20T18:06:36Z")
@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. Here are the bikes: [https://www.konaworld.com/2019/honzo.cfm](https://www.konaworld.com/2019/honzo.cfm) > **[Epic Hardtail | Specialized.com](https://www.specialized.com/us/en/epic-hardtail/p/171127?color=264116-171127&searchText=91320-7003&fbclid=IwAR1m-TDAuLeSjE6UXty-Qv0MWquG-_8B_n3myoAh_zPPBF4F5pL3zx4kMy0)** > > Hands down, the best value in cross-country racing machines today. The Epic Hardtail now features the same featherweight carbon chassis as our Pro model. Complete with a smart component package and a ride quality that’s second to none, this bike is a... ---
**Author:** ![Madhavok](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/madhavok/32/7721_2.png) [@Madhavok](https://www.trainerroad.com/forum/u/Madhavok)\ **Post date:** [April 20, 2021, 6:28pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/7 "2021-04-20T18:28:42Z")
Please watch these videos: [![](https://global.discourse-cdn.com/trainerroad/original/3X/0/2/023234edccb5e602e1ed6e6d1fbf0b9838a547bd.jpeg "SIZING MY NEXT MOUNTAIN BIKE | How long is too long?") ](https://www.youtube.com/watch?v=HyppZOpHocM) [![](https://global.discourse-cdn.com/trainerroad/original/3X/d/e/de333cb15635d21d5788f8338d9985198b4dee7d.jpeg "HOW TO FIT A MOUNTAIN BIKE TO YOUR BODY | Free Fit Kit") ](https://www.youtube.com/watch?v=rHagRovHSYs) ---
**Author:** ![NikolajPelevin](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/nikolajpelevin/32/90120_2.png) [@NikolajPelevin](https://www.trainerroad.com/forum/u/NikolajPelevin)\ **Post date:** [October 16, 2021, 10:59am UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/8 "2021-10-16T10:59:27Z")
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 ---
**Author:** ![iceaxe](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/iceaxe/32/7746_2.png) [@iceaxe](https://www.trainerroad.com/forum/u/iceaxe)\ **Post date:** [October 16, 2021, 2:34pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/9 "2021-10-16T14:34:30Z")
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… ---
**Author:** ![wake](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/wake/32/83021_2.png) [@wake](https://www.trainerroad.com/forum/u/wake)\ **Post date:** [October 17, 2021, 1:26am UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/10 "2021-10-17T01:26:06Z")
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! ---
**Author:** ![TimG](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/timg/32/12908_2.png) [@TimG](https://www.trainerroad.com/forum/u/TimG)\ **Post date:** [September 18, 2023, 1:30pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/11 "2023-09-18T13:30:09Z")
Has anyone measured the RAD on a large or Extra larger Trek fuel Generation 8? ---
**Author:** ![rbean01](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/rbean01/32/7746_2.png) [@rbean01](https://www.trainerroad.com/forum/u/rbean01)\ **Post date:** [September 18, 2023, 5:27pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/12 "2023-09-18T17:27:43Z")
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. ---
**Author:** ![mcneese.chad](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mcneese.chad/32/15056_2.png) [@mcneese.chad](https://www.trainerroad.com/forum/u/mcneese.chad)\ **Post date:** [September 18, 2023, 5:34pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/13 "2023-09-18T17:34:43Z")
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: - [https://www.trekbikes.com/us/en\_US/bikes/mountain-bikes/trail-mountain-bikes/fuel-ex/fuel-ex-9-8-gx-axs-t-type-gen-6/p/41572/?colorCode=red](https://www.trekbikes.com/us/en_US/bikes/mountain-bikes/trail-mountain-bikes/fuel-ex/fuel-ex-9-8-gx-axs-t-type-gen-6/p/41572/?colorCode=red) - Large Frame RAD = 788.2mm - ![image](https://global.discourse-cdn.com/trainerroad/original/3X/3/5/354269c12a740f6d771eae8cacbf9d61db5a3eb1.png) Extra Large Frame RAD = 817.5mm - ![image](https://global.discourse-cdn.com/trainerroad/original/3X/d/3/d352921d7233e5fe314c1a7db8a07f97c1e6981c.png) Per: [https://www.google.com/search?q=right+triangle+calculator&rlz=1C1CAFA\_enUS700US700&oq=right+tr&aqs=chrome.2.69i57j0i131i433i512l2j0i433i512j0i131i433i512j69i60l3.3687j0j7&sourceid=chrome&ie=UTF-8](https://www.google.com/search?q=right+triangle+calculator&rlz=1C1CAFA_enUS700US700&oq=right+tr&aqs=chrome.2.69i57j0i131i433i512l2j0i433i512j0i131i433i512j69i60l3.3687j0j7&sourceid=chrome&ie=UTF-8) ---
**Author:** ![mackdhagen](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mackdhagen/32/28733_2.png) [@mackdhagen](https://www.trainerroad.com/forum/u/mackdhagen)\ **Post date:** [September 18, 2023, 5:36pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/14 "2023-09-18T17:36:26Z")
Any time i switch bikes i automatically use this site… [https://geometrygeeks.bike/](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. ---
**Author:** ![mcneese.chad](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mcneese.chad/32/15056_2.png) [@mcneese.chad](https://www.trainerroad.com/forum/u/mcneese.chad)\ **Post date:** [September 18, 2023, 5:42pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/15 "2023-09-18T17:42:36Z")
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: [Compare: 2023 (Gen 6) - Neutral / Low Trek Bikes Fuel EX 9.8 L vs 2023 (Gen 6) - Neutral / Low Trek Bikes Fuel EX 9.8 XL - Bike Insights](https://bikeinsights.com/compare?geometries=6480690942ef31001af865d7,6480690942ef31001af865d8), 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. ---
**Author:** ![mailman](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mailman/32/101794_2.png) [@mailman](https://www.trainerroad.com/forum/u/mailman)\ **Post date:** [September 18, 2023, 6:34pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/16 "2023-09-18T18:34:24Z")
> **[Bike Geometry Calculator - MAD SCIENTIST MTB](https://madscientistmtb.com/bike-geometry-compare/)** > > A mountain bike geometry calculator for mullet bikes, fork changes, anglesets, etc. Visually compare multiple bikes. Calculate your bike's RAD. This and Geometry Geeks is a great combo for working out RaD. Changes with stem length and height etc too ---
**Author:** ![TimG](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/timg/32/12908_2.png) [@TimG](https://www.trainerroad.com/forum/u/TimG)\ **Post date:** [September 18, 2023, 8:18pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/17 "2023-09-18T20:18:09Z")
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 ---
**Author:** ![mcneese.chad](https://sea2.discourse-cdn.com/trainerroad/forum/user_avatar/www.trainerroad.com/mcneese.chad/32/15056_2.png) [@mcneese.chad](https://www.trainerroad.com/forum/u/mcneese.chad)\ **Post date:** [September 18, 2023, 8:36pm UTC](https://www.trainerroad.com/forum/t/xc-mountain-bike-sizing-the-important-measurements/57583/18 "2023-09-18T20:36:39Z")
> [@TimG](#): > > I’m wondering though how you account for the stem and bar bend. 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. > [@TimG](#): > > 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 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.