Megamo Reason Coil conversion question

[Emilio-Megamo Reason]

Hi Greg!

I recently installed a new Fox DHX2 coil shock on my Megamo Reason AL ( 160 mm travel) . The bike shop recommended a 650–700 lb spring because I weigh around 103 kg (227 lbs) fully geared up.

After installing the 700 lbs shock, I checked the sag and measured approximately 22 mm. Since the shock has a 55 mm stroke, that works out to about 40% sag, which is much higher than the 28–30% range I'm targeting.

I've used several online spring calculators, and most of them suggest either a 700 lb or 750 lb spring for my weight and bike setup. However, based on the sag I'm seeing, there seems to be a large gap between the recommended spring rates and the sag I want to achieve.

Because of this, I ordered the stiffest spring Fox offers, an 800 lb coil. What I'm trying to understand is why my bike appears to require such a heavy spring rate. On other bikes I've owned, a 650 lb spring was typically sufficient for my weight and riding style.

Is there something about the Megamo Reason AL's suspension kinematics or leverage ratio that would explain why I need a significantly stiffer spring than expected?

 

[Greg Watts]

Hi Greg! I recently installed a new Fox DHX2 coil shock on my Megamo Reason AL ( 160 mm travel) . The bike shop recommended a 650–700 lb spring because I weigh around 103 kg (227 lbs) fully geared up. After installing the 700 lbs shock, I checked the sag and measured approximately 22 mm. Since the s...

Hi @Emilio-Trek rail 9.7 - before we chase spring rates, let's sanity-check the maths, because I think that's where the mystery is.

You measured

22mm of sag on a 55mm-stroke shock.

That's actually 22/55 =

Something isn't adding up, and jumping to an 800lb spring may be treating the symptom, not the cause.

A few things worth checking before that 800lb spring goes anywhere near the bike:

1.

Are you measuring sag at the shock, or at the axle?

This is the classic trap.

Sag should be measured at the shock shaft - how much of the 55mm stroke is used when you sit on the bike in riding gear.

If you measured 22mm of shock shaft movement, that's genuinely 40%.

But if you measured wheel travel at the axle and divided by shock stroke, the numbers don't relate - the leverage ratio sits between them.

Our data has the Reason's ASP linkage running around a 21% progression with a fairly sensitive early stroke, so the wheel moves far more than the shaft.

2.

Preload. On the DHX2, has the spring got the correct baseline preload - turns from first contact, not cranked in to fake a rate?

Too little preload reads as excess sag.

3.

All pumps and rulers lie a bit. Re-measure a couple of times, bounce and settle, feet on pedals, weight centred, someone else reading it.

On the leverage question directly: the Reason isn't wildly heavy on spring rate.

But going from a 700 that gives 40% sag straight to an 800 is a big jump; an 800 would normally land you around 35% if 700 gave 40%, which still isn't your 28 - 30% target.

That gap is the tell that the measurement is off, not that you need an even stiffer spring.

Quick question that changes the answer: your dossier shows a 2022 Trek Rail 9.7, but this thread's about a

Megamo Reason AL with a coil - is the Megamo the bike you're setting up here?

Nail those two and the spring choice falls out cleanly.

---

Hola @Emilio-Trek rail 9.7 - antes de cambiar de muelle, revisemos las cuentas, porque ahí creo que está el misterio.

Saltar a un 800lb puede atacar el síntoma, no la causa.

Comprueba antes:

•

¿Mides el sag en el vástago del amortiguador o en el eje? Debe medirse en el vástago (los 55mm).

Si mediste el recorrido en la rueda, los números no se corresponden - la relación de palanca va entre medias.

La suspensión ASP de la Reason ronda un 21% de progresión, así que la rueda se mueve mucho más que el vástago.

•

Precarga: vueltas desde el primer contacto, sin apretar de más.

•

Todas las bombas y reglas mienten un poco - repite la medida varias veces, centrado y con los pies en los pedales.

Si un 700 da 40%, un 800 te dejaría sobre 35% - sigue sin llegar a tu 28 - 30%.

Ese hueco indica que la medición está mal, no que necesites un muelle aún más duro.

Dos preguntas clave: tu perfil muestra una

Trek Rail 9.7 de 2022, pero aquí hablamos de una

Megamo Reason AL con coil - ¿es la Megamo la que estás montando?

¿Y mediste los 22mm en el vástago o en la rueda?

Con eso, la elección del muelle sale sola.

 

[Emilio-Megamo Reason]

Hi @Emilio-Trek rail 9.7 - before we chase spring rates, let's sanity-check the maths, because I think that's where the mystery is.

You measured

22mm of sag on a 55mm-stroke shock.

That's actually 22/55 =

Something isn't adding up, and jumping to an 800lb spring may be treating the symptom, not the cause.

A few things worth checking before that 800lb spring goes anywhere near the bike:

1.

Are you measuring sag at the shock, or at the axle?

This is the classic trap.

Sag should be measured at the shock shaft - how much of the 55mm stroke is used when you sit on the bike in riding gear.

If you measured 22mm of shock shaft movement, that's genuinely 40%.

But if you measured wheel travel at the axle and divided by shock stroke, the numbers don't relate - the leverage ratio sits between them.

Our data has the Reason's ASP linkage running around a 21% progression with a fairly sensitive early stroke, so the wheel moves far more than the shaft.

2.

Preload. On the DHX2, has the spring got the correct baseline preload - turns from first contact, not cranked in to fake a rate?

Too little preload reads as excess sag.

3.

All pumps and rulers lie a bit. Re-measure a couple of times, bounce and settle, feet on pedals, weight centred, someone else reading it.

On the leverage question directly: the Reason isn't wildly heavy on spring rate.

But going from a 700 that gives 40% sag straight to an 800 is a big jump; an 800 would normally land you around 35% if 700 gave 40%, which still isn't your 28 - 30% target.

That gap is the tell that the measurement is off, not that you need an even stiffer spring.

Quick question that changes the answer: your dossier shows a 2022 Trek Rail 9.7, but this thread's about a

Megamo Reason AL with a coil - is the Megamo the bike you're setting up here?

Nail those two and the spring choice falls out cleanly.

---

Hola @Emilio-Trek rail 9.7 - antes de cambiar de muelle, revisemos las cuentas, porque ahí creo que está el misterio.

Saltar a un 800lb puede atacar el síntoma, no la causa.

Comprueba antes:

•

¿Mides el sag en el vástago del amortiguador o en el eje? Debe medirse en el vástago (los 55mm).

Si mediste el recorrido en la rueda, los números no se corresponden - la relación de palanca va entre medias.

La suspensión ASP de la Reason ronda un 21% de progresión, así que la rueda se mueve mucho más que el vástago.

•

Precarga: vueltas desde el primer contacto, sin apretar de más.

•

Todas las bombas y reglas mienten un poco - repite la medida varias veces, centrado y con los pies en los pedales.

Si un 700 da 40%, un 800 te dejaría sobre 35% - sigue sin llegar a tu 28 - 30%.

Ese hueco indica que la medición está mal, no que necesites un muelle aún más duro.

Dos preguntas clave: tu perfil muestra una

Trek Rail 9.7 de 2022, pero aquí hablamos de una

Megamo Reason AL con coil - ¿es la Megamo la que estás montando?

¿Y mediste los 22mm en el vástago o en la rueda?

Con eso, la elección del muelle sale sola.

Hi Gregg here are my answers

Are you measuring sag at the shock, or at the axle-- Yes, I measured it at the axle how much the rubber bumper moved while I was on the bike.

Preload- one turn of preload

All pumps and rulers lie a bit-- I measured it 3 separate times.

And yes I just changed my bike form a Trek Rail to the Megamo Reason.

 

[Greg Watts]

Hi Gregg here are my answers Are you measuring sag at the shock, or at the axle-- Yes, I measured it at the axle how much the rubber bumper moved while I was on the bike. Preload- one turn of preload All pumps and rulers lie a bit-- I measured it 3 separate times. And yes I just changed my bike form...

Yes, I measured it at the axle

- that's it, that's the whole mystery solved, and it's actually the opposite problem to the one you've been chasing.

The Reason AL is 160mm rear travel on a 55mm shock stroke, so the average leverage ratio is roughly 160/55 ≈ 2.9:1 - the wheel moves nearly three times as far as the shock shaft. So your 22mm of measured axle movement isn't 22mm of shock travel - it's roughly 22 ÷ 2.9 ≈ 7.5mm at the shaft. Divide THAT by the 55mm stroke and you get about 13-14% sag, not 40%.

So on the 700lb spring you're very likely way under-sagged, not over. That's the inverse conclusion to the one that sent you towards an 800lb spring - if anything the maths now points at something softer than 700lb to get you into the 28-30% window, not stiffer. The ASP linkage's progression (~21%, as I mentioned before) means the real leverage ratio near sag is probably even steeper than the 2.9:1 average, which would push your true sag number lower still.

Before that 800lb spring goes anywhere near the shock: put a zip-tie or the shock's own o-ring on the shaft itself, sit on the bike in kit, then measure how far it's moved along the shaft - not at the axle. That figure ÷ 55mm is your real sag%, and it'll tell you which direction to actually go.

 

[Emilio-Megamo Reason]

- that's it, that's the whole mystery solved, and it's actually the opposite problem to the one you've been chasing.

The Reason AL is 160mm rear travel on a 55mm shock stroke, so the average leverage ratio is roughly 160/55 ≈ 2.9:1 - the wheel moves nearly three times as far as the shock shaft. So your 22mm of measured axle movement isn't 22mm of shock travel - it's roughly 22 ÷ 2.9 ≈ 7.5mm at the shaft. Divide THAT by the 55mm stroke and you get about 13-14% sag, not 40%.

So on the 700lb spring you're very likely way under-sagged, not over. That's the inverse conclusion to the one that sent you towards an 800lb spring - if anything the maths now points at something softer than 700lb to get you into the 28-30% window, not stiffer. The ASP linkage's progression (~21%, as I mentioned before) means the real leverage ratio near sag is probably even steeper than the 2.9:1 average, which would push your true sag number lower still.

Before that 800lb spring goes anywhere near the shock: put a zip-tie or the shock's own o-ring on the shaft itself, sit on the bike in kit, then measure how far it's moved along the shaft - not at the axle. That figure ÷ 55mm is your real sag%, and it'll tell you which direction to actually go.

Sorry, I meant to say the oposite and did not use the correct word, I meant to say that I took the measurements at the shock shaft not at the bicycle axle.

Sorry for the confusion.

 

[Greg Watts]

Sorry, I meant to say the oposite and did not use the correct word, I meant to say that I took the measurements at the shock shaft not at the bicycle axle. Sorry for the confusion.

No bother, that clears it up - and it puts us right back to your original question, so let's answer it properly this time. Sorry for the detour, @Emilio-Megamo Reason.

So: 22mm at the shaft on a 55mm stroke genuinely is 40% sag on the 700lb spring. That's real, and it's higher than target. Here's the bit that actually answers your original question about kinematics: the Reason AL's average leverage ratio is around 160/55 ≈ 2.9:1, which is on the higher side for a 160mm bike. That matters because the spring rate needed at the shock scales with the leverage ratio squared, not linearly - so a bike running a 2.9:1 ratio needs a noticeably stiffer coil than one running, say, 2.4-2.5:1, for the exact same rider weight and the exact same feel at the wheel. If your old Rail had a lower average leverage ratio, that alone explains why 650lb worked there but doesn't get you close here - it's not that the Reason is "wrong", it's just leveraged differently.

Now the numbers: going from 700lb (40% sag) to 800lb should land you around 35% sag, using the rough inverse relationship between spring rate and sag for a linear coil at a roughly constant load point. That's progress, but it's still short of your 28-30% window.

Two things before you consider going stiffer still: • You're running only 1 turn of preload - nudge that up to 2-2.5 turns once the 800lb is in. It won't transform the number, but it'll claw back a mm or two without changing the rate.

• If 800lb still lands you mid-30s%, that's the point to look at aftermarket coils beyond Fox's own range (EXT, Vorsprung-style options) rather than assuming something's broken - the Reason's kinematics genuinely call for it at your weight.