WTF Are Offset And Trail On An MTB And Why Should I Care? | #AskGMBNTech

Welcome back to another episode of Ask GMBN Tech, where we try to answer all of your complex, scary, niche, and technical questions about mountain bikes and MTB-related tech! This week Anna and Isaac tackle a range of topics, covering upgrades, bike washing, suspension compatibility, and more.

⏱️ Timestamps ⏱️
0:00 - Intro
0:28 - Fork offset still confuses me. I know it exists, but what does it do?
5:19 - Where should you set reach and bite point whilst bleeding your brakes?
6:04 - Most underrated and overrated tech upgrades for an MTB?
8:15 - When should I wash my bike? Am I damaging my bike by washing it so often?
9:51 - How do you decide on bar width?
11:15 - Are all full suspension bikes compatible with coil shocks? What exactly makes them compatible or not?

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[muzzarobbo]

offset is measure relative to the steerer tube and not the fork lowers, its common for the fork crown to provide some of the offset

[TheDustyShredder]

YESSS, I built my own wheels and I have never had to worry about them. They are amazing, and you can build some really good wheels for under $300 for the set.

For handlebar width, shoulder width also factors in. A bar that's too wide for your shoulders will give you less leverage than a more narrow bar that fits your shoulders.

Indeed, the topic of air vs coil compatibility of the frame is a fairly complex one, but the simple matter of it is this: a progressive frame will work with air and coil, but with air will feel bottomless. A linear frame is only compatible with air and can damage a coil shock or itself. How can you tell? If it's equipped with a coil shock at the shop or in the box, you can likely use either. If it's equipped with air, use extreme caution when installing a coil.

[ThunderStruckMTB]

I live in the SoCal high desert (always dust, never mud) and I use compressed air to blow off the dust then a damp Costco microfiber to finish it bearings last forever, no water near your fork seals and overall just way better than washing. In places with actual rain, you have no choice but to wash.

[netposerx]

GMBN can take a simple concept and ramble on forever about it to the point it gets more confusing then when you started. Should have shown the lines are the start and left them up there.

[mattkavanaugh]

Thank you Anna for the great explanation of fork offset and trail. I think I get it now! :)

[Mavrik-]

Some of these settings if changed can damage your frame.
I saw a Ti frame come into the shop with a broken frame. Snapped in two places at the end on the chain stay. Because he went from eighty mill fork to one twenty mill fork. Put to much strain on the frame. Ok good stuff as usual do keepemcoming wont you?

[mattiniemela]

I am pretty sure shorter offset is often for 29"/slack head angles and longer offset is for 27, 5"/steep angles. I think you mentioned this the other way around.

[floydblandston]

Re: bar width; when I was starting out, I asked an experienced rider why bars used to be narrower.
He told me it was because of the distance between the trees they rode in!😂🤣

[skymaracle]

Axis of steering is the steerer tube I believe, and not the fork legs.

[DirtRoadie]

Fun fact: Stanchions can be offset a bit too.

[stujm]

I’ve just gone from 680 to 760 on my hardtail, on my full sus it came with 780. I’m thinking of cutting them down to 760, it just seems to be the perfect size for me. I’ll have to spend a bit more time on the 760s to make a decision.

[tomvonderharr]

Only mentioning Shimano for the bleed bite point question? Would've thought you should at least add SRAM to that, where the reach is supposed to be from 75-80mm center of grips to tip of the lever, and contact adjust fully out opposite the arrow.

[jonathanlindup]

I always wondered what fork offset was, does it have the same affect when the fork crown differs like when the stachions are set back closer to the steerer tube?

[Bugle]

#Askgmbntech Hey Doddie and Anna great to have the gang together again, I have installed Magura MT5 brakes, they work great, but the front brake rotor has an annoying ring when I rolling at speed and rattles when you tap on the rotor, everything is torqued to spec and it’s driving me mad…what’s the cure?

[KP-oltc]

Would running a 46mm fork on a hardtail with a 47mm headtube angle risk cracking the frame? Would an angled headset help reduce the added stress?

[The_One-Eyed_Undertaker]

#AskGMBNTech I understand the importance of a correct saddle width according to your sit bones to achieve adequate support. But what's the difference between a MTB saddle and one intended for road cycling? Even within MTB saddles there are different models intended for XC, trail, Enduro or DH. Is there any valid point to these subtle design differences or they are just trying to sell us N+1?

[miyui]

one should never really worried about trail, just make your body stronger and by then you can ride better than almost everyone who can afford dentist's bikes.

[DennisKhaye]

#askgmbntech
Is the trail measurement shorter when you switch to mullet? Lower back hub would decrease the trail measurement, wouldn't it?

[tomhopkins]

#AskGMBNTech I have a new bike with a 100mm rockshox recon gold fork, my weight is 100kg and I have had to add 140psi to get the correct sag with compression fully open. This is way higher than I have set on longer travel forks and they don't feel as plush. Should I reduce the pressure but add in some clicks of compression? What is the difference between more psi and fully open compression vs lower psi and compression added on? Thanks.

[thebeaglebeat]

Love the WTF lol, & nice long hair today, well done, thank you for explaning the trail.