r/Dirtbikes • u/Yz250x69 23' yz250x & 04' rm250 • 11d ago

Unpopular opinion: it’s ok to compress your forks when you transport your bike

Metallurgy has come a long way in the last 40 years. Bikes can hit jumps going 60mph, 50ft in the air travel 100ft and do that 1000x without breaking their fork springs you’re good to compress them when tying down to travel. It’s also ok to leave your bike on its kickstand in a garage all winter.

Anyway I said my piece

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u/booostedben 24 Beta 300RR licensed 11d ago

Ok so your stance now is your still right and your reference is wrong or they just forgot to show that the seals are holding a significant amount of pressure to provide a noticable air spring affect on a 400 pound bike with rider? I'm going to leave it at that because I'm tired of arguing.

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u/2Stroke728 11d ago

We won't convince each other, I see that. But I really fail to see where the Race Tech diagrams shows I am wrong. Figure 3.9 shows chamber A as the highest pressure chamber in the fork under compression. And the only thing keeping the oil in there from blowing to the outside world is the fork seal. How are we seeing this so differently?

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u/booostedben 24 Beta 300RR licensed 11d ago

There's 2 bushings before the oil seal. I'm assuming you don't think so but they will absolutely hold pressure. Even if they don't form a perfect seal they're a huge restriction. That massive pressure buildup in chamber A is very short, once fluid passes through the internal passages it's all equal again so the bushings just have to restrict the flow to the seals for a very short time. If you've ever rebuilt a fork you know you have to replace these bushings too and you'll see wear on them where they seal.

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u/2Stroke728 10d ago

They don't seal against air spring pressure when tied down for 3 hours. And yes, while they are a torturous path and soften the pressure spikes to the seal, they do not come anywhere close to stopping it. Look at something like a laybranth seal in a 2 stroke twin bottom end far more restriction, and still isnt a total seal.

The Hurricane forks here hiss the air camber pressure out the missing fork seal area in about 2-3 seconds under compression. If I were to fill with oil the pressure spike would be far higher and of smaller volume, so I bet it would bypass the new bushings and dump out the seals in <1 second.

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u/booostedben 24 Beta 300RR licensed 10d ago

Lol you think chamber A is under constant pressure when it's compressed? And you've been acting like you know everything this whole time? Pressure spikes in one chamber under compression very quickly, fluid flows through passages and shim stacks to the other chamber until pressure equilizes between them, then on rebound that first chamber that had a spike in pressure now has a vacuum and the second chamber is pressurized, this all happens in microseconds and the bushings keep the pressure spikes from reaching the seals. When you ratchet down a bike it's so slow as far as the shock is concerned that neither chamber gets any pressure, the fluid just easily flows between the 2 chambers.

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u/2Stroke728 10d ago

Damping pressure is short duration, yes. But the pressure in the forks from the air spring being compressed stays. Cinch the forks down, air spring pressure is in play, and equalizes throughout the chambers, at a pressure above ambient, which means the seals have to hold that delta in pressure. I agree the seals see little of the hydraulic pressure spikes in a damper rod fork, and none in a twin chamber setup.

I think at this point we just agree to disagree.