How to upgrade Scale 930 to reduce weight and gain speed?

Question

I need to upgrade Scott Scale 930 (2022) with the following properties:

• fork: FOX 32 Float Rhythm Grip 3 (100mm travel)
• bottom bracket: Shimano BB-MT500 / shell 41x92mm
• rear derailleur: Shimano XT RD-M8100 SGS; Shadow Plus / 12 Speed
• crank: Shimano FC-MT511-1; 32T
• shifters: Shimano Deore SL-M6100-R / Rapidfire Plus
• cassette: Shimano Deore CS-M6100-12 / 10-51 T
• brakes: Shimano MT401 Disc
• pedals: Shimano SPD PD-M520
• weight: 12 kg (size L with tubes and without pedals)

And the wheels:

• rims: Syncros X-25 / 32H / 25mm; Tubeless ready
• spokes: Stainless Black 15G / 1.8mm
• front hub: Formula CL-811 / 15x110mm
• rear hub: Shimano FH-MT410-B CL / Boost 12x148mm / Micro Spline
• rotors: Shimano SM-RT10 CL / 180/F and 160/R
• tires: WTB Ranger 2.25"

Riding style

• XCM (Cross Country Marathon)

What I need

• reduce weight to <11 kg or even <10kg
• gain more speed
• safety in mountains and difficult terrain

First thoughts

Brakes

MT401 are good in easy terrain but their braking power is too low in fast downhills in mountains when you need to brake fast and effectively. I would go for Shimano XT brakes but I have some doubts:

• what I really need to buy in total (to fit to the bike)?
• is it worth to buy 4-piston brakes instead of 2-piston ones?
• mechanic told he must cut cable housing - can anybody confirm this?
• need to upgrade rotors too?
• how about Magura brakes and can they be easily mounted on this bike?

Wheels

Current wheels weight (calculated) is 2080 gram. Most people agree that upgrading the wheels could reduce bike weight and decrease rotating mass. But not against safety. Hubs must be sealed and rims must be strong.

• how about alloy XR 1700 (DT350 Ratchet 36SL 25 mm)?
• 25 mm or 30 mm? how will switch to 30 mm affect uphills and overall speed?
• carbon or alloy? NO LIMITED produces carbon 30mm wheels with Microspline

Tires

WTB Ranger 2.25" are good in easy terrain but behave much worse on loosy terrain but much heavier than e.g. Racing Ralph, Vittoria Barzo, Maxxis Ikon... Looking for tyres that are fast but have good adhesion in both loosy and rocky terrain.

Is it a good idea to switch to 2.35" for better safety and speed on downhills? How does it affect uphills and overall speed?

Fork (?)

Current is Fox Rhytm 32 Float. Is it advisable to upgrade to some lighter fork? Also, can you put 110mm or 120mm travel to this bike in order to get better safety in rocky mountains and difficult terrain?

Other components

What else to upgrade to reduce bike weight at reasonably low cost?

TL;DR:

I need a list of items to buy for upgrade because mechanic could not tell me what will fit and what to buy but he told me to buy all on my own and bring him components and he will mount them to the bike.

Also local stores don't have parts because they are getting cheaper so on-line is an only option.

New bike?

Another option is to buy a new bike instead of upgrading Scale 930. Things that changed are:

• lower head tube angle (930 has 89.5° but newer bikes have 87°-88°)
• higher saddle tube angle (closer to the BB so more power to the crankset?)
• cables hidden inside stem

What can you recommend? Max budget for a new bike is 4000 USD.

Answer 1

If weight is your main focus, compute the g/$ per upgrade and prioritise upgrades over that. The crank and cassettes are also easy ones on that regard. If the cost of the upgrades is greater than the price of a new bike, take the new bike. It's the "technical answer" to the question, but it's not a good one.

I do think that focusing on weight is a mistake. If your focus is speed, overall fitness level, control and riding skills are more important. In XC, there's a trend towards full-sus bikes, that are heavier than hardtails for example.

A few thought on the components:

• You'd surprised on how a good fork can improve control and comfort, changing the travel is a bad idea.
• Brakes can be a good upgrade as well, but not for a reason you mention: higher-specs brakes can take pads with cooling fins and/or semi-metallic pads. Cooling and semi-metallic pads lower/mitigate the fading effect that you can have when brakes reach high temperature (but that's only critical if you experience fading, which seems to be the case) - and if your rotor are resin-pad only, you'd need to upgrade them as well.
• On tires, what matters is to have the right tread pattern, that must be suited for the conditions in which you are riding, more than the section.
• Tubeless is a must.
• All other upgrades will only you give you marginal or psychological gains. Lighter wheels are more reactive so feel faster, but not necessarily faster - sometimes having inertia is good. But if you ride often in different conditions (but the rides themselves are consistent), why not a second set of wheels with a different kind of tires for different conditions.

Your target of sub-10kg is not realistic, it's the weight of an high-end race-oriented cross-country hardtail, designed from the start to reach that target.

Answer 2

Scott Scale is not a slug of a bike, Scale is still reputed for its light weight no fuss pedigree. Shaving of weight in a way that makes a difference you are heading into $'s/gram territory. Current Scale 930 is specified at around 12.2kg, the Spark RC Pro 11.1kg. Nothing you do will get you bike 1kg lighter without compromise (I say this because you could put a rigid fork on it and save a lot of weight). You have to buy a new bike with a lighter frame as your starting point. If money is no object, go for it, I bet the Scale RC is a superb bike ride.

If just you want to go faster, there are things you can do that will return more speed for much less dollars. Ultimately 1kg bike is only adding about 1% weight to the riding equation, based on the 1kg/100kg (rider + bike + gear). (If you are already doing all of these, upgrading the bike may be sensible)

The need for safety also suggests you want a robust bike rather than a pure race-oriented bike. Fortunately, the things you can do to improve you speed also improve your safety.

Things to consider, if you have not already are:

• Body Weight - very few people cannot afford to lose 1kg of body weight without losing performance.
• Nutrition - Related to body weight, but more so, good nutrition will fuel you longer with more power.
• Coaching - a small amount of coaching will make a big difference to speed, especially with XC Moutain biking where something as simple as choosing a wrong line or braking a bit to early or late will cost you speed though a corner. That speed has to be regained....
• What you carry - do you arrive at the end of you ride with water in your water bottle, that is weight you did not need to carry. What otehr things could you leave behind? (without compromising safety, easy to go too far with this one).
• On bike training - do you just go out and ride (nothing wrong with that), or do you do structured training on the bike aiming to improve performance 
• Off bike training. - Bike specific gym training can pay off big time. Has to have the right focus - want to build strength and endurance rather than size, so have to have a program tailored for cycling (typically high rep/low weights to build strength/endurance, low rep/high weight builds bulk which you do not want.)
• Road/Gravel/Indoor cycling - Allows you to focus on building endurance and strength without having to worry about the technical aspects.