Sizing vs reach

[beeb]

Help, so confused by this new school sizing!
I'm 176cm

Current trail bike: Medium, 435mm reach, seated top tube 610mm
Also a large XC bike with seated top tube 630mm. Both ride great, but obviously feel quite different to ride.
Probably prefer seated position on the XC, but happy to do big k's on both. Cant really compare standing position as bikes are used for very different riding.

Bike I'm looking at: Medium, 455mm reach, top tube 593mm. Large, 485mm reach, top tube 621mm.
I'm more concerned about standing performance with this one, is a more descent focused bike.
Manufacturer has me on the lower end of a large in their size chart.

Large felt great for seated and not bad standing, but was only a flat carpark test. Did feel long.
Medium, definitely felt a bit cramped seated, but felt almost the same as current trail bike standing.

To get the best out of this new long geometry, should I be sacrificing seated position or taking a leap to the super long reach.
Is a jump from 435mm to 485mm reach too much?

I thought riding the bikes would give me a clear direction, has just made me even more confused lol.
Any other in between size riders, what did you go with. Did you make the right decision?

I’ll have a bit more of a think about this tomorrow, but a couple of points to start:

• ETT only effects seated fit. If you’re sizing a bike predominantly for descending you can largely ignore it. Unless the STA is super steep or super slack, you can generally find the ETT you want by sliding the saddle back or forth on the rails.
• Don’t forget to compare stack and reach dimensions as a combo. A bike with 5mm longer Reach but 20mm less Stack is actually going to have a shorter overall reach (to the bars/grips) once the handlebars are positioned at the same relative height to the BB.
• IMO, unless the bike you’re looking at has longer chainstays to balance the package out, yes - jumping from 435mm to 485mm reach is too much. If you want to ride something with those kinds of measurements let me know and you can take one of my bikes for a spin. A little longer would probably give you that stability you’re (I suspect) looking for, but too long and bikes just get unwieldy. I’m sure you could ride it, but you’re so active on the bike I’m not sure being stretched to the max between two wheels will suit your style and abilities unless you just want to straight line everything.

 

[ozzybmx]

but honestly it sounds like the main difference has been the focus on technique.

100% It was my fault. If I had the Hightower back again I could probably make it work.

Many near misses seated. I know that bike felt very far in front, nearly like I was hanging off the back.

Hightower was a 150mm CC IL DB coil rear, 160mm front Fox Factory with Push coil.

My previous bike was a Med Evil Following and I rode everything on that bike without any issues, near misses or crashes. It might be a better one to run numbers on.

 

[fjohn860]

That was quiet the jump John!

Yes it was. The biggest change I noticed first ride out was initiating turns with the 29" wheels. They just want to go straight, where as the 26" you could be lazy and the bike would almost fall into the corner. The 29er wants to keen going straight. Didn't take me long to sort that out.

 

[Chriso_29er]

I’ll have a bit more of a think about this tomorrow, but a couple of points to start:

• ETT only effects seated fit. If you’re sizing a bike predominantly for descending you can largely ignore it. Unless the STA is super steep or super slack, you can generally find the ETT you want by sliding the saddle back or forth on the rails.
• Don’t forget to compare stack and reach dimensions as a combo. A bike with 5mm longer Reach but 20mm less Stack is actually going to have a shorter overall reach (to the bars/grips) once the handlebars are positioned at the same relative height to the BB.
• IMO, unless the bike you’re looking at has longer chainstays to balance the package out, yes - jumping from 435mm to 485mm reach is too much. If you want to ride something with those kinds of measurements let me know and you can take one of my bikes for a spin. A little longer would probably give you that stability you’re (I suspect) looking for, but too long and bikes just get unwieldy. I’m sure you could ride it, but you’re so active on the bike I’m not sure being stretched to the max between two wheels will suit your style and abilities unless you just want to straight line everything.

Thanks Beeb, excellent info.
Yeah, I've been thinking about the stack numbers as well and also got onto a sizing theory using lever distance between your feet (bb) and hands.
Interestingly with that theory the Trance is too short and my XC bike spot on. I have always thought a L Trance might have been a little better.

The bikes I'm looking at are all long slack enduro rigs, so they do have a very steep seat angles. Hence my problem with the very short climbing position.
Numbers in my post are for the Norco Sight 29. While this bike will by my more descent focused machine, I do like to ride up as well so don't want to stuff up that side of things too much with my size choice either. The Norco does change chainstays with size so I should still be centered on the large with the huge reach.
The Sight gets great reviews for both up and down, but I just worry I fall into a spot where neither size is really suitable for my height, so I should just look at something else.

 

[Chriso_29er]

Also 175-176 and these are the numbers I look at on bikes, ETT, Reach and Stack.

My Deviate and Spur.

View attachment 390715

Still leaves me questioning my decision each time I buy a bike. Saying this, every bike I have bought in the past ~10yrs (since bothering to look at geo) has been round the 600mm ETT.

I had a large Santa Cruz Hightower LT before these around 2019 and looked at the numbers between the Large and Med, decided bikes were getting smaller and bought a large then ran a 33mm stem. This bike felt great, the longer ETT with shorter stem was perfect.

What I didn't realise was I was pushing the front wheel further away from my weight centre, also not helped by a 51mm offset fork. The 33mm stem then moved me back.

After 3 big crashes involving losing the front wheel, I sold the bike and my painful analysis over the Deviate frame size made me realise that with the longer reach on these bikes, I needed me to modify my attack stance as the standing over the pedals as I did on older bikes and this was putting all my weight over the back wheel.
The SC was a longer ETT and I was not compensating by moving forward a little bit to get more grip on the front.

These days I have got used to leaning forward more, knees bent, arms bent, getting my weight distribution more balanced and grip on that front. I was slower at first until I got used to it... haven't hit the ground since.

Thanks mate, great info.
You do some bigger k's so obviously get on quite well with the shorter seated position on the medium rigs.

I can see where you're coming from with the SC, we would generally gravitate to center our legs over the saddle for stability. So without the steeper seat tube to give us that reference it would be easy to find yourself too far back, even on a bike with similar reach numbers.

 

[yuley95]

Thanks Beeb, excellent info.
Yeah, I've been thinking about the stack numbers as well and also got onto a sizing theory using lever distance between your feet (bb) and hands.
Interestingly with that theory the Trance is too short and my XC bike spot on. I have always thought a L Trance might have been a little better.

The bikes I'm looking at are all long slack enduro rigs, so they do have a very steep seat angles. Hence my problem with the very short climbing position.
Numbers in my post are for the Norco Sight 29. While this bike will by my more descent focused machine, I do like to ride up as well so don't want to stuff up that side of things too much with my size choice either.
The Sight gets great reviews for both up and down, but I just worry I fall into a spot where neither size is really suitable for my height, so I should just look at something else.

It's an interesting dilemma for you as you do a lot of K's in the saddle but seem to also love a really active bike you can jump easily and throw around.

I would be tempted to say don't upsize. The relationship between reach and stack becomes really important when you want to be able to use body strength and movement to throw the bike around. There is an interesting video on it here:

Keeping it smaller in reach will make it cramped for climbing though so there is still an argument for going longer...

 

[kten]

I’ll have a bit more of a think about this tomorrow, but a couple of points to start:

• ETT only effects seated fit. If you’re sizing a bike predominantly for descending you can largely ignore it. Unless the STA is super steep or super slack, you can generally find the ETT you want by sliding the saddle back or forth on the rails.
• Don’t forget to compare stack and reach dimensions as a combo. A bike with 5mm longer Reach but 20mm less Stack is actually going to have a shorter overall reach (to the bars/grips) once the handlebars are positioned at the same relative height to the BB.
• IMO, unless the bike you’re looking at has longer chainstays to balance the package out, yes - jumping from 435mm to 485mm reach is too much. If you want to ride something with those kinds of measurements let me know and you can take one of my bikes for a spin. A little longer would probably give you that stability you’re (I suspect) looking for, but too long and bikes just get unwieldy. I’m sure you could ride it, but you’re so active on the bike I’m not sure being stretched to the max between two wheels will suit your style and abilities unless you just want to straight line everything.

I think it’s important to know Chriso’s inside leg measurement and also arm span to make a recommendation.

@Chriso_29er could you put those numbers up too? Also what length cranks?

 

[beeb]

Thanks Beeb, excellent info.
Yeah, I've been thinking about the stack numbers as well and also got onto a sizing theory using lever distance between your feet (bb) and hands.
Interestingly with that theory the Trance is too short and my XC bike spot on. I have always thought a L Trance might have been a little better.

The bikes I'm looking at are all long slack enduro rigs, so they do have a very steep seat angles. Hence my problem with the very short climbing position.
Numbers in my post are for the Norco Sight 29. While this bike will by my more descent focused machine, I do like to ride up as well so don't want to stuff up that side of things too much with my size choice either. The Norco does change chainstays with size so I should still be centered on the large with the huge reach.
The Sight gets great reviews for both up and down, but I just worry I fall into a spot where neither size is really suitable for my height, so I should just look at something else.

The medium sight is reach/stack combined ~30mm longer than your trance (the extra stack height equates to roughly 9-10mm extra reach compared to your Trance).

Don't forget, you're not just increasing your reach distance with everything else staying constant - the Norco's geometry is radically different. Even if you slacked out the Trance 3 degrees to match the HA of the Sight, that would increase the front-centre of the Trance ~36mm. Then the Sight's a 29er, so fork axle-to-crown is longer than your 27.5 Trance, then it's got more travel, longer A2C again. So while you're reach will grow 30mm on a medium Sight, the front centre will be much longer again (the higher stack also increases front centre), all with the same chainstay length as your current Trance - meaning a notable rearward shift in weight-bias. So even on a medium, you'll want/need to ride in a more forward stance, so adding the extra 30mm to size up to a large sounds (IMO) like it'll be stretching things too far.

TL;DR - New geo bikes are big, you shouldn't need to size-up. (...and if you're seriously going to consider it, for the love of dogs - borrow/test-ride something that size first)

EDIT: It's only a 17mm difference in ETT between Trance and Sight in medium, probably within the range of most saddles adjustment, and you might like it positioned somewhat further forward with the more stretched out geo to weight the front a touch more on seated climbs anyway...)

 

[beeb]

I think it’s important to know Chriso’s inside leg measurement.

That's a bit personal isn't it?

 

[Chriso_29er]

It's an interesting dilemma for you as you do a lot of K's in the saddle but seem to also love a really active bike you can jump easily and throw around.

I would be tempted to say don't upsize. The relationship between reach and stack becomes really important when you want to be able to use body strength and movement to throw the bike around. There is an interesting video on it here:

Keeping it smaller in reach will make it cramped for climbing though so there is still an argument for going longer...

A dilemma it certainly is haha.

Thanks mate, that is a video I had seen and got the measurement of 83cm for me. Which actually matches my XC bike exactly, with the Trance being short by about 30mm

Thanks @kten
Wingspan 163cm, inseam 84cm in riding shoes. Crank length, what ever comes on the bike I guess, most seem to have 170mm factory. Current bikes are 175cm, but run shorter on my road bike.

Thanks @beeb, the long reach is concerning me. Luckily I have a mate who is on a large 27.5 sight I might get some mild trail time on this weekend. I know I will get along fine with the mediun on descents. The issue is Norco recommend large for me, so I would actually be sizing down if I go the medium. Yet very similar bike, Marin Alpine Trail recommends me Medium with almost identical numbers for both their medium and large bikes!

The bike shop guy must have thought I was a bit of a weirdo, throwing the bike around on the footpath yesterday lol.
Must say the huge reach on the large didn't seem bad for that, but cant compare flat concrete with trail. Your points are concerning me a lot, so agree I really need trail time to get a feel for the large before pulling the trigger.