STW braintrust, my question is, would the weight of getting a lower end, full Alu model make it more of a steamroller and less twitchy? Im sure this has been covered before and is deep in the STW archives…

Context:
I recently read a ‘Field test’ review on an unnamed website of the new Orbea Occam, a contender for my next bike. In the test they used the top of the range carbon everything model and kept banging on about how light the bike is and how light it felt on the trail but also how it felt less sure-footed/confidence inspiring at high speed. I know there’s more than weight at play here but as my question above says, in this instance, would a heavier bike feel more planted?
Im not a dentist carbon fanboy and hopefully I never will. My wallet thanks me for this.

A heavier bike, all other things being equal, will be a bit more planted, the frame will get the suspension moving more before you feel it.

This is of course not the whole story, and whether you want to be super planted is a questionable point anyway.

What we are talking about the sprung:unsprung ratio. It’s a thing in car suspension design and bikes work exactly the same. Unsprung weight is the weight of parts that move when the suspension compresses or extends. Sprung weight is the weight of everything else.

Basically the lower the unsprung weight is, as a percentage of the Sprung mass, the more sensitive the suspension and the better the ride and the grip will be.

A heavier Aluminium bike may feel better but it depends upon the weight of the suspension parts as much as the weight of the frame.

Ideal world; Alu’ frame (heavier) with Carbon rear triangle (lighter).

I think magazine tests are so subjective and full of the possibility to get free stuff that one really should take them with a pinch of salt. Race results are only possibly slightly better indicators of quality (I think there should be a ‘superbike’series on EWS where the riders have to ride a stock bike of their sponsors brand chosen from a dealer at random, but that’s a digression).

Personally what makes me feel more planted is:
a) My own bodyweight (it is part of the sprung weight)
2) heels down
iii) good weight distribution, at the right time (eg more front when turning in, more rear when descending in sandy loose stuff etc)
δ) correct damping, especially rebound

or get some coaching.

What we are talking about the sprung:unsprung ratio. It’s a thing in car suspension design and bikes work exactly the same. Unsprung weight is the weight of parts that move when the suspension compresses or extends. Sprung weight is the weight of everything else.

Basically the lower the unsprung weight is, as a percentage of the Sprung mass, the more sensitive the suspension and the better the ride and the grip will be.

This certainly applies to reducing the weight of the wheels and fork lowers/swingarms etc., but the difficulty on a bike is that the person on it is sprung mass that behaves differntly to the frame.

Watched the video of the same test and I have a feeling that their handling concerns might have had more to do with the DT carbon wheels (XMC1200 @ 1500g the pair). The emerging opinion seems to be that lightweight carbon wheels can make the bike more ‘skittery’ on rough terrain as the carbon rims don’t deform. If i remember rightly they were using Minion DHF/DHR 2.3 tyres as a control for the test which might excacerbate the problem over a 2.5 WT tyre.

I hope that’s the explanation anyway as my MyO M10 Occam will be here in February.! 😀

*gets engineering degree* kinematics makes sense

In reality I guess its similar to those bikes that really only come alive when going balls to the wall flat out, which is faster than 97% of us meer mortals ride. In this case, im guessing that 97% percent of us wouldn’t notice the Occams twitchiness

@H1ghland3r hopefully you wont be the only Occam north of the wall 😉

I think lighter wheels are more susceptible to being deflected.

I´ve ridden the new Occam a lot and am writing a few thoughts on it just now (it´ll take me a while to publish!). Did you guys not think that the Pinkbike write up was a bit weird? They said it was the most entertaining and it was twitchy and they all put up a really fast time on it. They also comment that they were popping off the trail features more on this bike. Basically what I read was that it was the best trail bike but for more gravity orientated stuff it lost out to other bikes. I don´t know if others read it like that? To be honest that is exactly my impression, it´s a great all day bike for 95% of the stuff I want to ride. I found it really confidence inspiring and the suspension works amazingly well, it was definitely more twitchy than my 170/160mm Rallon but on the flip side it was a lot more nimble. It´s a lot of fun to ride. Swapping from the Rallon it took a bit to get used to. In fact I crashed on the first corner on the press launch (ooops!) Once I got a feel for it I was really comfy on it. Igor my guide set a KOM on one of the well used descents in Zona Zero on his first ride on the bike so it definitely isn´t slow!

To answer about weight. I´ve been riding the Rallon and the new WildFS (an electric Rallon basically!) and the extra weight of the WildFS makes it a lot more planted. But it´s really planted and you could easily pop an eyeball trying to bunnyhop it or flip it over to a new line. I think that the thing i like about riding the new Occam is that lack of “plantedness”, it´s confidence inspiring, fast and the suspension works really well but it isn´t as planted, (i.e. fixed to the ground), as the Rallon which isn´t as planted as the WildFS. I don´t have the carbon wheels on any of my bikes, not a fan.

Not an engineer or dentist, but: often the difference between unsprung weight on a carbon and an alloy bike of the same model is probably about an extra spare inner tube, your packed lunch (including sausage roll) and not going for a poo before you ride.
As an example, the mk2 scandal was 200gm heavier than the carbon race thingy they offered (Can’t remember what it was called). That’s a bit less than four Mars bars, and it’s more likely you’d notice a difference in stiffness or geometry before you noticed weight.
Of course, the weight difference between a carbon vs alu FS frame is likely to be more significant as there’s more gubbins, but it’s probably worth figuring that out with the frame of your choice. As said above, tinkering with unsprung weight, in my experience, makes a massive difference. I can definitely feel the difference between a nice light pair of 29er hoops with conti trail 2.4s on compared to a pair of 27.5+ wheels, for example.
If I was buying or building up an FS bike today, I’d likely get the alloy version of the frame and spend the difference on a good pair of wheels and some fancier tyres.

https://www.bikeradar.com/news/add-weight-go-faster-orange-bucks-the-lightness-trend/

I think lighter wheels are more susceptible to being deflected.

Stepping away from the suspension theoreticals, yes I’ve found this, although it’s been due to lighter (and harder compound) tyres, which will contribute by having less damping.

I’d say they’re two completely different things.

My CX bike is ~20lb and feels planted, in that getting it airborne takes some body language even over rollers/jumps. It tends to want to keep the wheels on the ground owing to the proportion of the riders weight over the front wheel.

My fatbike on the other hand weighs 30lb and wants to take off a the slightest provocation, despite not having ‘nimble’ handling (short stem, slack-ish-for-xc, huge wheels). Probably because unweighting the front wheel only requires a small shift of bodyweight.

Then there’s twitchyness and flop, which is just a function of stem length, fork offset and heat angle (the shorter the stem, steeper the angle the twitchier it gets). The trick for designers there is to get the wheelbase and cockpit length they want coupled with decent ‘feel’. If you put a short stem on a steep angled bike it feels horrible for example, think BMX.

Then there’s weight, which just dulls the ride. A light bike shakes about more underneath you, but it doesn’t (within reason, a 2kg fatbike wheel Vs a 700g roadie wheel makes a difference once upto speed) turn into corners any quicker, that’s down to the other 90% of the weight being in the rider. That lack of shaking/feedback could be interpreted as confidence inspiring though. No one wants to think the bikes at it’s limits when it’s not.

So no. I don’t think adding weight will make it feel more planted, it will however feel heavier. Which is the same, but different.

Try running more downforce

Try running more downforce

I’ll try 5 more clicks of high speed downforce and only 2 more clicks of low speed downforce