Tyre pressures - the figures on the tyre are not the recommended pressures but the maximum. The starting point with tubeless is: your weight in pounds / 7 then add 1psi for the rear and subtract 1psi for the front. That’s just a start, the benefit of tubeless is that you can run low pressures, keep lowering the pressure until the tyre feels like it’s squirming and going to come off the rim then add 1 or 2 psi. It’s an easy thing to play around with.
Rotor sizes, generally the bigger the better assuming your fork/frame can take them, a smaller rotor tends to cause the pads to glaze as there’s more heat. I weigh 86kg and run with 200mm up front
Looks like most/all your questions were answered above. I’ve had a Spark RC 900 World Cup for 3 years and do most of my own mechanics work. I’ve taken that XC bike around the Midwest, East Coast, Colorado and a MTB vacation all over Scotland. I’ve put my Spark through terrain where most others are on trail and enduro bikes. The Spark can handle quite a bit very well. Additionally, I race XCO expert class and MTB 100s.
So, you have a great and very capable bike, now it’s just dialing in the fit, settings, pressures and components as others have mentioned above. Which will change depending on where you’re riding and if the conditions are significantly different than where you’ve been riding. If you have any specific questions along the way let me know and I’d be glad to help. Also, I’ve found this forum to be the best on the internet and possibly MTBR if you’re looking for a specific technical issue. However, MTBR can have a quite different culture so carful with advice given.
Since you asked about gloves for hot weather, I really like the POC Tectal Race Spin helmet for XC. It’s light and breaths well. The downside is that it doesn’t play nice with some sunglasses.
Over time, air gets into the hydraulic lines and your brakes/levers are less response. Your levers should feel crisp and actuate with little effort/pull. Indicator that you need a bleed: your brakes feel less responsive and you have to pull the lever closer to the handlebar to get any braking action.
I disagree with this. I am about 202 and I run carbon rims on my XC rig. I run Enve rims on my Nomad, too, FWIW. I’ve raced XC at 198-205ish and the only rim I’ve ever tacoed was an aluminum one. But that crash would’ve destroyed anything.
I ride 25mm Berd rims/spokes with I9 Hydra hubs. Been very happy with them. I’m on 2.25 in tires normally. - Utah racing mostly.
I second having a proper brake bleed kit. Not something you do all the time, but having the proper tools to do this procedure makes it 1000% easier in my opinion. I find that I end up bleeding my brakes at least once a year, sometimes more if issues arise (has happened from riding in bad conditions).
Love it. That’s what I was hoping we’d find with the Sparks.
I’ve decided against joining any other forum. This thread has been immensely helpful so far.
Will consider! Especially for me. @michelleihowe is likely to be a little less rough on things.
Okay what’s with MTB helmets having “bills” (the sun blocker thing on forehead)? Every time I see that I think “that looks non-aero and not light.” but enlighten me!
Good to know. I’ll probably end up on 2.35-2.4 at least, and will keep the carbon rims for now.
Are these universal? Got a link?
Awesome. Thank you!!
What are multi-grips? Safe / useful for me to use? Got a link for clarity? Never heard of them and would love to understand the application to my front wheel. Here’s the front wheel that I’ll actually be taking the rotors off of, and replacing with 180’s.
Helpful when riding on a trail into the sun (sunrise or sunset). Without something blocking the sun, you can end up slowing to a crawl cause you can see anything.
I ride west facing descents in the evening, and this problem is very noticeable.
You can get various kits based on if your brakes use mineral oil or DOT. I believe your model has Shimano XTR brakes, so you’re looking for the mineral oil kits. Large collection based on what tools you need to get the job done. There are plenty of kits like this on Amazon, might search around if you don’t need all the tools (like the allen keys and wrench) https://www.amazon.com/SHIMANO-Hydraulic-Brakes-Stopper-Silicone/dp/B07VXS6ZWJ
I’ve not personally used this kit, I originally just purchased the kit Shimano offers and the mineral oil separately (could definitely save money buying a different brand on Amazon) Shimano Tl-BT03-S Disc Brake Bleed Tool | Jenson USA
+1 for the POC tectal race spin. It’s a comfy fit on my melon and the ventilation is pretty good for my climate. (POC Ventral for really hot days).
The visor is for more than simply blocking the sun. It’ll also help with getting whipped in the face by low hanging branches. It’s a simple tilt of the head with a visor most times.
Once you hit less ridden trails (or it rains) there can be loads of low hanging branches and you can get scratched up before you know it.
In regards to bleeding your brakes, my Spark is a 2018 model and the brakes still work perfectly. My other MTB is from 2017 and only the rear brake has started to go spongy if I flip it upside down. YMMV.
You had way too much pressure in the tires. (For reference, I weigh 190 lb and run 24 psi) Tubeless tires (setup tubeless) generally blow off the rim at 45-60 psi. The actual number depends on tire and rim. You’re lucky they didn’t blow off the rim while pumping them up or riding. The failure was at a weak point in the casing that gave way. Make sure you use tires and rims that are both tubeless ready.
Also, a word of advice. Bike setup and handling skills are far more important and complex on a mountain bike than any other type of bike. It’s best to build good habits from the start instead of trying to correct them later on. Lee McCormack (Lee Likes Bikes) is a great resource (used by TR guys) for proper bike setup and technique, via his website and books. There’s also lots of videos on YouTube, but quality of advice will vary greatly.
Lots of things could happen here. Did you pump your tires up inside and then go outside where it was warmer? How accurate was the pressure gauge that you were using? Heavy breaking equates to warming up the tire which increases the internal pressure. All of this is speculation but sounds like you were over maximum.
Ignore any minimum pressures indicated. You just need enough to not roll the tire off the rim or have rim strikes. Rim strikes can be partly mitigated with tire liners, but I wouldn’t bother with those yet. You have much bigger fish to Fry for now.
The force on a wide tire is much higher for the same pressure as a narrow tire. So it’s the max pressure that causes failure of either tire or rim (!). Don’t go above 35 psi with tubeless MTB tires, there’s no need and it’s generally not safe. Good tires and proper pressure are the most important bike setup item (second is suspension setup). The right tire pressure is usually as low as you can go without damaging your rim or burping your tires.
The tires of terrain you will encounter will vary greatly throughout the country (even within a given county). What tires and suspension setup works great one place might not be great in another. This is the problem with generic online advice.
Since I see you are living the nomad life, you will benefit greatly by finding the local mountain bike association, which you can usually find through the International Mountain Biking Association (IMBA). The local organization will have details on local trails and may have forums, a Facebook page, etc with trail conditions and where you can ask details for setup that works in the local area.
That was my first thought. But alas, no. Pumped outside in full sun, left bike in shade.
Within 2-3psi, I’d guess. Just cross-checked a Specialized AirTool, Dewalt compressor/guage, and Topeak gauge, and all registered 1.5psi of each other which is amazing. At least it’s likely I was under 57psi, and that the tire never exceeded 60psi.
No argument whatsoever that I don’t need that kind of PSI. Just alarming that a submax PSI would cause a burst, so I’m skeptical it was purely a psi thing.
Fascinating. You maybe right. Hard to imagine that I jumped up the PSI from probably 55psi, 57psi tops, to >60psi through maybe 3-4 hard brakes on asphalt, lasting no greater than 2 seconds each… and that the psi would remain elevated for 20+ minutes and then burst. I guess the combo of aggressive deformation of the tire and maybe damage to its internal fabric under high load, high psi braking on asphalt, followed by slight elevation in psi at rest might be sufficient to cause a blow-out.
Not saying your wrong, actually. Just thinking aloud… if heavy braking is responsible for >5-10% shifts in psi… do folks take that into consideration when setting psi numbers? Surely not… but I’m new here!
The only reason I continue to ponder this question is that I’m trying to answer the question:
Should I avoid super hard braking on asphalt in the future, regardless of proper psi settings? Or should I just plan to get beefier tires if I want to treat my bike like it’s indestructible?
I’ve previously inflated WTB Riddler 37mm tires which have a listed max of 55psi to 110-115 just to get them to seat (and to see what would happen). Did this on countless occasions actually. No ruptures. Those were with butyl tubes.
Question for the masses:
Are tubeless more more sensitive to higher-end pressure damage than tires with butyl tubes?
facepalm what?!? You’re saying Maxxis lists 35-60psi on tires that are easily damaged above 35psi?
Again, no debate… I’ll run lower psi for performance reasons anyway, but my mind is blown here.
So… it looks like both the front wheels, both 15mm axles, use shimano cassette lockring type. Both bikes were purchased from unrelated independent sellers and both wheelsets were custom additions to the bikes.
No, they won’t fail at 35 psi, but much higher will be bouncy and have poor traction, so they will be dangerous in that manner.
Tire blowout (tire and rim separating from each other, due to the tire bead escaping from the rim) is more likely to happen the higher the pressure is. Either your tire or rim may cause that number to be low (the lower number specified of the two). But that number also depends on tubes vs tubeless. A tube pushes the tire bead more securely against the rim wall, which results in a higher blowoff pressure than tubeless. Those numbers from Maxxis are probably based on tubes, because the ERTO standard is based on tubes.
What happened in your case is different. Part of the casing failed, as evidenced by the bigger section of tread vs casing that opened up. Since these are used tubeless tires, there may have been a casing cut there that was sealed by the sealant. The sealant stops the leak, but it is no way structural.
So this damaged area was ready to fail under high stress. Normally the casing is strong enough to keep going, but by pumping it way too high and braking really hard you caused a lot of stress. Sounds like you just got really lucky that you stressed it just enough to start the failure but stopped before the ultimate failure. I think temperature has nothing to do with it.
Quick numbers: a 2.4” tire has about 2.5 times the diameter and 2.5 times the force on it for every PSI of pressure compared to a 25mm tire. So your 60 psi on 2.4” is like 150 psi on a 25mm tire. It was doomed to end badly.
