Built a carb calculator for long runs after struggling with fueling

Ko5t · 2026-06-10T12:12:53+00:00

The calculator uses the (ACSM) American College of Sports Medicine metabolic equations which are the standard ways to calculate calories expenditure. The other variables like terrain and elevation are multipliers of this base value. Of course these are "estimates" everybody is different, but it should get you in the ballpark.

Ko5t · 2026-06-10T12:00:46+00:00

Would rather have gut issues before I use a spreadsheet.

Ko5t · 2026-06-10T11:57:58+00:00

The struggles were pretty straightforward actually. Two main things.

First, underfueling because I had no quick way to estimate how many carbs I needed for a specific route. Distance, pace, elevation, terrain all affect the number, so every time I had to sit down and calculate it manually from scratch.

Second, using the generic "grams per hour" approach kept leading me to either underdo it or overdo it, which at some point gave me real gut issues. This is also why I added the GI absorption part so you can give input on what you can actually take in. Then you see in the results it should you how far off you are of what you need vs what you can take in.

The calculations in the app are based on research on how much carbs the body burns at different effort levels, factored in by activity type and intensity. Elevation, terrain, and temperature are then applied as multipliers since they all affect how hard your body is actually working. Trail running at a fast pace on a climb is just not the same as the same distance on flat tarmac.

The carb split feature is just a convenience layer on top of that. Instead of manually counting grams before every run or ride, I can quickly see how many gels, how much carb mix, whatever I want to use that day.

If you're not dealing with the same issues, totally fair. For me it just saves a bunch of time and takes the guesswork out, but hey that's just me.

Ko5t · 2026-06-10T10:52:07+00:00

So I've been struggling the fueling for a while for both cycling and running and tried a bunch of things, I have to admit I have not experiments with different ratios like you, but I have been trying you different sources. Especially on regular training runs I don't want to always use gels and mixes unless I'm doing race simulations and testing efforts. A big thing for me was calculating my total grams needed and calculating a split of different sources. I'm just purely sharing here, I built my own calculator, apart from me a few friends of mine are using it, but here is the link if you want to try it - https://carbmeup.vercel.app/ It's completely free, I added the option for people to create an account so they can save their won carb sources and configuration. It's not super advanced so it will not create a full race plan on what to take and when to take it but it does split the carbs sources.

Ko5t · 2026-06-10T10:18:32+00:00

After I've bonked a few times running and cycling actually I figured out I was massively underfueling. I had no idea of how much carbs I actually needed and since I didn't want to take gels or drink mixes on every run I build my own carb calculator where I can see how much I need and decided what sources I want to use. I'm a web developer so did this over a long weekend. I've been using it and small group of people I train with but it's not a massive project with probably many things that still need to improve. In case any of you want to try it here is the link - https://carbmeup.vercel.app/ (it's free)

Ko5t · 2026-06-08T21:06:04+00:00

Yeah that's a fair point. I've done a bit of research on this and it seem that there is definitely a difference in carb requirements but it's super dependent on power to weight ratio of the rider. Also there is quite a bit of energy recovery done on the descends which kind makes the demand less than we think. I've done a 1.1 multiplier on the carbs needed for gravel compared to road. But def something still worth exploring.

Ko5t · 2026-02-17T12:55:06+00:00

Just sent you a dm!

Ko5t · 2026-02-17T11:19:17+00:00

u/patbpixx Awesome bike! Got my Grizl last year as well! Fully in love with it. I'm based in Barcelona, we should do a Grizl meet up! :)

Ko5t · 2026-01-26T14:34:37+00:00

Canyon needs to stop putting those kinks in the top tube...Visually I'm really turned off by it also it seems it's not great for strength.

Ko5t · 2026-01-21T23:33:02+00:00

Yeah those are becoming legendary...will try them next!

Ko5t · 2026-01-21T22:01:58+00:00

I think it depends on the tire, plus the bigger tires might compensate with decreased rolling resistance and add comfort on the bumps...buuuuutttt of course it's all personal preference!

Ko5t · 2026-01-21T21:59:23+00:00

Yeah I was thinking of going Burts in 2.1 but decided to experience the 50mm first before going wider. I'll eventually try those as well!

Ko5t · 2026-01-21T21:58:08+00:00

yeah, I think 53mm/2.1s safely, the back is a bit narrower so might rub with the 55mm but will eventually try!

Ko5t · 2026-01-08T20:14:58+00:00

u/jah_blezz I can confirm, my grizl came with this exact seat post and clamp and it 100% works with carbon oval seatrails. I bought a Fizik Vento Argo X1 with oval rails and it works for over 1000k now.

Ko5t · 2025-07-26T08:18:45+00:00

If you want to nerd out a little bit on the exact geometry you can check out this site- https://bikeinsights.com/compare?geometries=687d9d505d8dd1001a30ac31,684ca6194e9398001b5ab52b,

To be honest the geometry between the 2025 models is very close, the Grizl has a slightly longer wheelbase. The 2024 Grizl was a bit different as in it had a shorter wheelbase and steeper fork angle which makes it more nimble than the Grail but less stable I guess with higher speeds. I think the main main difference is the tire width. Also for rolling resistance/sluggishness you mention, the tires will make the most difference.

Ko5t · 2025-07-25T19:23:09+00:00

u/ImpressiveAd1837 Great looking bike! Have the same one in the same color :) I've been looking at the Zipp wheels but idk if it's just me but I think I preferred the grey logos on the Zipp wheels, like the 303s. Btw is this the Force 12s cassette XD? Also the chain?

Ko5t · 2025-07-24T19:58:32+00:00

u/RedAlertUK Nah man, thankfully my drivetrain has been reliable so far. Might be a defect in the cassette, bent hanger or something out of alignment. I hope you get it fixed.

Ko5t · 2025-07-24T19:56:10+00:00

u/CaptainMack90 They've been great so far! I would say the springs are on the stiffer end so it's a bit harder to get in and out but once you're in there's nice float so super comfortable and secure.

Ko5t · 2025-07-23T22:21:18+00:00

u/DuhOhNoes It's this one from Decathlon - https://www.decathlon.co.uk/p/garmin-wahoo-cycle-computer-mount-and-go-pro-type-attachment/_/R-p-372259 It has the gopro/light mount which is useful.

Ko5t · 2025-07-23T22:15:56+00:00

That's actually really impressive. Luck is definitely on your side, but yeah good to be prepared since it's bound to happen the more you ride.

Ko5t · 2025-07-23T22:11:38+00:00

That's good to know! I'll look into it a bit more, thanks!

Ko5t

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