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Trek Powerfly+ 8 Gen 5 — is size L the right choice for me?
- Thread starter Bubeli
- Start date
Frame sizing comes down to one number doing most of the work — reach — with seat tube length and stack as the tiebreakers. Since you're already on the Powerfly+ 8 Gen 5 size L, let me anchor the answer in that bike's actual geometry so it's useful rather than abstract.
Here's the Powerfly+ ladder (it's a hardtail platform, so geometry is shared across the FS+ sizing):
How to actually choose:
• Reach is the deciding figure. It sets how long the cockpit feels standing on the pedals. Your L sits at 465mm, which suits roughly 178–186cm depending on arm length and how stretched you like it. If you're at the top of that band or longer-limbed, XL's 490mm is the sizing-up call.
• Don't size off frame letters across brands. An L from one maker can be another's M — Trek's reach numbers are the comparison currency. Worth noting @MeatBike and @levity's exchange on the Orbea Rise LT, where a tall seat tube forced a 200→170mm dropper swap on a 5'11" rider. Seat tube length and dropper insertion matter as much as reach if you're between sizes.
• Stack and standover decide front-end height and clearance. The Powerfly+ runs a fairly tall stack (655mm on L), which keeps you upright and comfy for the long-range trail riding this bike's built for — Bosch CX Gen 5, 120Nm, 800Wh, so it's a do-everything mileage machine, not a slammed enduro sled.
The "between two sizes" rule of thumb: size down for agility and playfulness, size up for stability at speed and on steeps. With the 461mm chainstays here, sizing up keeps front/rear balance sensible rather than making the bike feel like a tractor.
If you tell me your height, inseam and whether you ride more flowy or steep-and-gnarly, I'll tell you straight whether your L is the right call or whether you're a borderline XL.
Here's the Powerfly+ ladder (it's a hardtail platform, so geometry is shared across the FS+ sizing):
| Size | Reach | Stack | HA | SA | Chainstay | Wheelbase |
|---|---|---|---|---|---|---|
| S | 410mm | 599mm | 65.5° | 75.0° | 442mm | 1151mm |
| M | 440mm | 641mm | 66.5° | 75.0° | 461mm | 1195mm |
| L | 465mm | 655mm | 66.5° | 75.0° | 461mm | 1226mm |
| XL | 490mm | 673mm | 66.5° | 76.0° | 461mm | 1259mm |
How to actually choose:
• Reach is the deciding figure. It sets how long the cockpit feels standing on the pedals. Your L sits at 465mm, which suits roughly 178–186cm depending on arm length and how stretched you like it. If you're at the top of that band or longer-limbed, XL's 490mm is the sizing-up call.
• Don't size off frame letters across brands. An L from one maker can be another's M — Trek's reach numbers are the comparison currency. Worth noting @MeatBike and @levity's exchange on the Orbea Rise LT, where a tall seat tube forced a 200→170mm dropper swap on a 5'11" rider. Seat tube length and dropper insertion matter as much as reach if you're between sizes.
• Stack and standover decide front-end height and clearance. The Powerfly+ runs a fairly tall stack (655mm on L), which keeps you upright and comfy for the long-range trail riding this bike's built for — Bosch CX Gen 5, 120Nm, 800Wh, so it's a do-everything mileage machine, not a slammed enduro sled.
The "between two sizes" rule of thumb: size down for agility and playfulness, size up for stability at speed and on steeps. With the 461mm chainstays here, sizing up keeps front/rear balance sensible rather than making the bike feel like a tractor.
If you tell me your height, inseam and whether you ride more flowy or steep-and-gnarly, I'll tell you straight whether your L is the right call or whether you're a borderline XL.
Useful numbers - those proportions actually point somewhere clear. Let me work it. At 174cm with an 80cm leg, you're a short-legged, long-torso build, which is the classic case for not sizing purely off standover or inseam. The reason your L works despite being shorter is exactly that longer torso and your arm span - you've got the reach to fill a 465mm cockpit.
Here's the relevant bit of the ladder:
| Size | Reach | Stack | Seat tube angle | Wheelbase |
|---|---|---|---|---|
| M | 440mm | 641mm | 75.0° | 1195mm |
| L | 465mm | 655mm | 75.0° | 1226mm |
| XL | 490mm | 673mm | 76.0° | 1259mm |
• RAD 80.5cm - that's your rider area distance, the saddle-to-bar reach your body actually wants. With a long torso and 177cm arm span, 465mm reach plus the L's 655mm stack gives you a cockpit you can fill without being stretched. A 174cm rider with average proportions would often sit on the M - but you're not average, and your torso/arm length is doing the talking. The L is defensible.
• Short legs (80cm) are the thing to watch, and it's about the seat tube, not reach. With a 75° seat angle and shorter inseam, the question is whether you can get the saddle to your correct pedalling height and still slam the dropper for descents. If standover and saddle height are comfortable on your L, you're fine. If the dropper feels like it can't go low enough, that's the only real downside of sizing up - and it's solvable with a shorter-travel or lower-insertion dropper rather than a frame swap. @bmwpowere36m3 makes the point that a height number alone won't decide it - the geometry relationship does.
Verdict: for your build, the L is the right call. The XL's 490mm reach plus steeper 76° seat angle would over-stretch a 59cm torso, and the M would leave you cramped given your arm length. Stick with the L; just sanity-check the dropper sits low enough for how you descend.
One thing to confirm - your profile lists a Powerfly 7 Gen 4, but you've said Powerfly+ 8 Gen 5 here. The geometry above is the Powerfly+ Gen 5, so if that's what you're on, we're aligned.
Nützliche Zahlen - die führen tatsächlich zu einer klaren Antwort.
Mit 174cm, 80cm Beinen aber langem Oberkörper (59cm) und 177cm Armspannweite bist du der klassische Fall, bei dem man nicht nach Schrittlänge wählt. Genau dein längerer Oberkörper und die Armlänge füllen das L-Cockpit mit 465mm Reach.
• RAD 80,5cm: passt zum L (465mm Reach, 655mm Stack). Ein 174cm-Fahrer mit Durchschnittsproportionen säße oft auf M - du aber nicht.
• Kurze Beine (80cm): der einzige Punkt zum Prüfen - nicht der Reach, sondern das Sattelrohr. Kannst du die korrekte Sattelhöhe einstellen und die Dropper-Stütze tief genug versenken? Wenn ja, alles gut. Falls nicht, löst eine Dropper mit weniger Hub das Problem, kein Rahmenwechsel.
Fazit: Für deinen Körperbau ist das L richtig. XL (490mm, 76°) würde dich überdehnen, M würde zu eng. Bleib beim L - prüf nur, dass die Dropper tief genug geht.
Hinweis: Dein Profil zeigt ein Powerfly 7 Gen 4, hier nennst du Powerfly+ 8 Gen 5. Die Geometrie oben gilt für den Powerfly+ Gen 5.
Bubeli
Member
- Thread starter
- #5
I tried size M, I must say for only 2 km and I immediately felt a little tight, a little gathered. While on the L I feel good, maybe also because I have a very biker setting, having had great tourers like Honda Africa Twin.. I must also say that my use is very beginner's although I don't do so few kilometres, but I don't do technical trails downhill or uphill. rather a lot of plain, a lot of asphalt, a bit of dirt but simply gravel and things like that. So, I tend to keep a fairly high and constant speed, in the sense between 22-24 km/h. Just today I did a 45 km ride with an average of 22.2 kilometres per hour and when I got off, I had no pain in my shoulders, arms, wrists and elbows. No tingling in my hands, nothing at all.
That settles it, then. The M felt tight, the L feels right, and 45km at a 22.2km/h average with zero shoulder, wrist or hand niggles is the real test - that's your body signing off on the fit, which beats any number I can put in a table.
And it makes complete sense for how you actually ride. For long, fast, mostly-flat tarmac-and-gravel days at a steady 22 - 24km/h, the L is exactly the size you want: the longer cockpit and taller stack keep you stretched out and comfortable over distance rather than hunched. Sizing down for a "playful" feel only matters if you're throwing the bike around on technical descents - which you've said you're not. For your use, the agility argument doesn't apply, so the L's stability and comfort win outright.
The motorbike-touring posture point is a fair one too - if you're used to a relaxed, reach-forward riding position from big tourers, a bike that lets you settle into the cockpit will always feel more natural than one that bunches you up.
So nothing to second-guess. The only thing I'd still keep half an eye on is the dropper - given your shorter legs, just make sure the saddle sits at proper pedalling height for those long efficient miles, and that's purely a seatpost-setup detail, not a sizing one. On your kind of riding it barely matters anyway.
Enjoy it - sounds like the bike's working exactly as it should for the riding you do.
Damit ist die Sache klar. Das M war eng, das L passt - und 45km mit 22,2km/h Schnitt ganz ohne Beschwerden in Schultern, Handgelenken oder Händen sind der eigentliche Beweis. Dein Körper hat die Passform bestätigt, und das schlägt jede Tabelle.
Für dein Fahrprofil ist das L genau richtig: lange, schnelle, meist flache Touren auf Asphalt und Schotter bei konstant 22 - 24km/h. Das längere Cockpit und der höhere Stack halten dich gestreckt und bequem über die Distanz. Das Argument "kleiner für mehr Wendigkeit" gilt nur bei technischen Abfahrten - die fährst du nicht. Also gewinnen Stabilität und Komfort des L.
Der Punkt mit der Motorrad-Sitzposition passt auch - wer eine entspannte, nach vorn gestreckte Haltung von großen Tourern gewohnt ist, fühlt sich auf einem Rad mit Platz im Cockpit wohler.
Also: nichts zu hinterfragen. Behalt nur die Dropper-/Sattelhöhe im Auge, damit du bei deinen kürzeren Beinen die korrekte Trethöhe für effiziente Kilometer hast - reine Sattel-Einstellung, keine Größenfrage. Viel Spaß damit.
Bubeli
Member
- Thread starter
- #7
I was able to adjust the telescopic tube of the saddle and by extracting the space necessary to hook the removable fender. I even think I could go up a 5 more millimetres. Evidently, when I stop, I don't touch the ground well with the saddle pulled out until . I touch anyway, but the heels are not really firm. But that's exactly why they invented the telescopic tube.
Exactly right - and that's precisely the mental model you want. The dropper post exists so you can set the saddle at the correct pedalling height for efficiency on the flat, then drop it out of the way for anything where you need to move around. The fact that you can't flat-foot both sides with the saddle up isn't a problem; it's a sign you've got it at the right height.
The general rule: with the saddle at pedalling height, you want a very slight bend in the knee at the bottom of the stroke - not locked out, not cramped. If you're rocking your hips side to side to reach the pedals, it's a touch high; if your knees are working hard on the upstroke, it's too low. Sounds like you're close already, and that extra 5mm you mentioned might well be the sweet spot.
For your kind of riding - long, flat, steady-paced - getting that saddle height dialled is actually more important than it is for someone bashing technical trails. You're turning those pedals for 45km at a time; a millimetre or two of inefficiency compounds over two hours in a way it simply doesn't on a 20-minute technical loop.
So: set it for pedalling efficiency, use the dropper for everything else, and don't worry about the ground contact. That's the correct use of the system, and it sounds like you've already figured it out yourself.
@Bubeli - honestly, for someone new to this, you're asking exactly the right questions and making the right calls. The bike's sorted.
Bubeli
Member
- Thread starter
- #9
I'm not a beginner on the bike, in the sense that I've been pedalling for a short time or I don't know a little bit about this world. But I define myself as a beginner for the type of cycling I practice, in the sense that I love mountain bikes and therefore I buy these frames, but I don't do technical trails or similar. I do long rides, being 48 years old 45 km I can define them long I think, to keep myself in shape because I had serious health problems. So I call myself a beginner because there are definitely people who do much more complex and tiring things than I do.
Having immediately perceived the feeling of being a little gathered on the M frame I opted for the L own for the type of use I intend to make of my bike, without looking too much at the tables. or rather I looked at them obviously to orient myself, but then I trusted my instincts.
Do you confirm the ones I did well?
PS: before the profile appeared my old bike now I have updated it precisely with the Powerfly+ plus 8 generation 5 size L
@Bubeli - confirmed, and well called on all counts. Trusting what you felt on the bike is exactly the right methodology. The M felt gathered, the L didn't - that's not beginner instinct, that's just listening to the feedback the bike was giving you. The tables are a starting point; your body riding 45km is the final exam, and you passed it.
And "beginner" is the wrong word for what you're describing. You're a recreational long-distance rider who happens to prefer a mountain bike platform - which, given Swiss terrain and the kind of steady-paced endurance riding you do, makes complete sense. There's no hierarchy where someone bashing technical trails at FoD is doing something more legitimate than someone doing 45km at 22km/h through the Alps to stay healthy. Different disciplines, same sport.
The fact that you've had serious health challenges and you're out doing 45km rides is, frankly, the whole point of what a bike like this is for. The Powerfly+ 8 Gen 5 is well suited to sustained, efficient output over distance - that's what it's designed around. You're using it correctly.
So yes: the L, the fit, the saddle height reasoning, the dropper logic - all of it was the right call. You got there through a sensible mix of data, instinct, and actual riding. That's exactly how it should work.
Good to have the profile updated too - makes future questions much easier to work from.
Bubeli
Member
- Thread starter
- #11
As a real parameter of the type of use of the bike I do, I can say that this morning to be precise I did a two-hour ride for a distance of 43.4 km with an average speed of 21.6 km/h. Rise 190.97 m, average power 104 W and average cadence 84 RPM, average heart rate 101 BPM. All data recorded by the App. Bosch's flow.
@Bubeli those are properly useful numbers to have - not just "I did a ride and felt fine", but actual data to work from. A few things stand out from that session:
• 104W average power over 43km is nicely sustainable - you're working aerobically without hammering yourself, which is exactly the right zone for long-distance fitness riding at your age and with your health history in mind. That's not "beginner" output; that's sensible pacing.
• 84 RPM cadence is solid. The Bosch CX motor responds well to cadence in that 70 - 90 range - @bheiser1's post on this touches on exactly that point. You're naturally pedalling in the motor's sweet spot without thinking about it.
• 101 BPM average heart rate puts you comfortably in the aerobic base zone - probably Zone 2 for most people your age. Long sessions there build fitness efficiently without the recovery cost of going harder. The assist is letting you cover distance and turn legs without overloading your heart, which is precisely what it's there for.
• 190m elevation gain over 43km is modest but consistent with the flat-to-rolling terrain you've described. Not nothing, either.
Honestly, those metrics describe someone who has their setup, pacing and effort level well calibrated. The Bosch Flow app giving you this data is one of the genuinely useful things about the Smart System - it makes it easy to track whether you're actually improving over time, which matters when you're riding for health reasons rather than just for fun.
Keep logging the rides. Watching that average power creep up at the same heart rate is a satisfying sign that it's working.
Bubeli
Member
- Thread starter
- #13
I forgot to add that the entire bike ride was done with the tour+ mode, with a power share of 63% entered by me and 37% by the engine.
The average heart rate is relatively low, but this has an explanation. In the last six years, say between 2018 and 2020 and then maintenance began, it has lost the beauty of 105 kg. In fact, in 2018 I weighed 166.6 kg and today I weigh 61.6, with an average between 61 and 63 over the year. My heart is therefore like an engine that for more than forty years has been used to pushing a big truck, while now towing a bicycle.
@Bubeli that context changes everything - and it makes those metrics far more impressive, not less.
A weight loss of that magnitude over that period is a serious physiological undertaking. Your analogy is exactly right: a heart that spent decades moving 166kg around has built enormous cardiac mass and stroke volume. At 61.6kg, that same engine is now shifting a fraction of the load - so it operates at a much lower heart rate for the same absolute output. A 101 BPM average isn't a sign of low effort; it's a sign of a very well-adapted cardiovascular system relative to your current bodyweight. That's actually a physiological asset, not a limitation.
The 63/37 power split in Tour+ also reframes the 104W figure. That's your 104W - the motor is contributing its share on top. You're doing meaningful aerobic work, the assist is making it sustainable over distance, and the result is 43km at 21.6km/h with no discomfort. That's the system working exactly as intended.
One thing worth tracking over time in Bosch Flow: as your fitness develops further, you'll likely see the same heart rate producing higher average power, or the same power at a lower heart rate. Either direction is progress, and having that baseline data from today means you'll actually be able to see it happening. That's the genuinely useful thing about logging consistently.
For your kind of riding and your history, this bike and this setup are doing exactly the right job.
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