How would your tyre hit your crown?

On the thread about sticking a big wheel in a little fork people started saying the tyre could hit the crown. I have been jumping up and down on my handlebars while riding along to see if I acould make it happen and I can’t.

As you can see from the photo I have absolutely minimal tyre clearance but I still can’t see what is going to bend, twist, deflect or otherwise to make the tyre reach the crown.

Advice welcome as I am going to be riding this around Afan shortly and would like to know the likelyhood of needing an air ambulance.

your tyre wont hit the crown or deflect but it would not take much stuck in a tyre (mud , stone)to starting hitting/rubbing/grindign /blocking etc

I agree with that but was really amazed when riding around a really muddy Lordswood how there was no mub build up on the front even though the back end did get clogged.

I guess a stone might be more of an issue.

That’s not the crown, it’s the brace. The crown is the bit the steerer tube sprouts from.

Scientific theory clearly dictates that at high speeds centrifugal force will increase the tyre diameter, alos, higher altitudes with lower air pressure will cause the tyre to swell, however so will lots of pies.

I think you should let the air out of the tyre and turn the wheel upside down, then the flat spot will always be at the top – hence no problem.

to elaborate – if your brace overlaps with the crown at full travel you need a bit of clearance under the brace or the tyre will hit the crown.

Okay, how will my tyre hit the brace or anything hit the crown?

There is even enough clearance for the tyre to miss the frame when the fork is fully compressed.

i don;t really understand technology but someone was convinced that something would hit soemthing else on the front of the bike and I would die horribly.

Measure the distance from the tyre to the crown and if it is less than the amount of travel your forks have then there will be a problem at some point when you bottom out.

the only fork ive ever heard of that happening on was the first manitou nixon, which they sorted out fairly promptly by adding a spacer to expose more stanchion.

the allen key is between tyre and brace, not tyre and crown. what people mean by the crown (here) is the very bottom of the steerer tube

you’re right, the tyre can’t hit the brace but as the fork compresses the brace and tyre move upwards towards the crown. at full compression the brace will likely be above the level of the crown but that’s OK since the brace sits in front (or soemtimes behind) the crown. the tyre, on the other hand, is right under it.

If your chosen wheel and tyre has a bigger diameter than the fork was designed for then the tyre might foul the crown (or even the down tube). if it does, the wheel might stop dead and chuck you over the top, especially as this will be on a major compression so you’d be unbalanced

If you really want to know, try taking the spring (or air) out of the fork & see if you can get the tyre to make contact

As wwaswas said, it depends on the design of your fork.
If they’re air forks let the air and and see how close the tyre is to the crown at full compression. If it’s very close, you might get contact on big hits as there will usually be bump stops – either springs or elastomers, that could compress a bit more.

scaredypants – You have explained it in a way I understand. I now feel a bit stupid. I will go and have another try at crashing the wheel into the crown now I know what I am trying to achieve.

Thanks

PS Anyone see why it would be a bad idea at Afan (assuming it doesn;t hit the crown)

When using a 29″ wheel with Maverick (upside down) forks, the wheel will hit the crown, that’s why Maverick do a travel reduction kit for 29er’s.

You’d die instantly if this happened

(I had to let loads of air out of the tyre and remove the blummin’ wheel to get that one out…)

used to happen on very early forks. compress elastomer until it compressed no more. Sometimes with the right(?) tyre the fork wouldn’t bottom out before the tyre was buzzing the crown.

I managed to do it on some Judy XLC tipple clamp 100mm forks. I dropped the lower crown as much as possible to lower the front end and did my calculations wrong. Fortunately it wasnt that bad just buzzed a bit.

? wasn’t this something to do with discs, qrs and torsional whatever force ?

I **seem** (so I may be balking tollocks) to remember reading something about this and the way that a bigger wheel delivers torque to the qr may be different ?? – so it may impact the ability of the qr to hold – which could be a problem.

absolute nonsense! nevermind all this pseudo-science: if the wheel spins round, you can ride your bike

gus – I remember something like that but I thought it was to do with discs exerting more force and pully the wheels out of the QRs which is why they brought in the lawyer tabs at the bottom of forks to stop the wheel popping out

Oi! Who put that tag up there then?!?!?

I had lawer tabs on a bike in 1992 which is long before discs in fact it was before vees even.
They have brought in the angled dropout to counter act the whole disc thing (if its true as i have ride with a lose wheel and it didn’t get flung out).

Phiiil,

was that a message from the grave !?!

K

The drop outs and brakes have nothing to do with the fact WCI 😆 put a cross wheel on a fork intended to be used only with 26″ tyres.

Good tag. Well done.

Right then.

Given the minimal difference in over all diameter of the wheel and the fact the wheel/tyre is significantly lighter than the 26″ set I had before, why will this cause a problem for the fork.

The wheel doesn;t touch the crown BTW

wcA

it can happen when you lower the stantions so full travel cant be reached.
my mate did it on his monstert forks.i told him but he did nt listen.he hooned of the chicky ladder drop and folded his wheel etc…the bang was awesome.like a bomb 🙂

Hmmm this reminds me of a weird one on my wotans with a RRP mudguard thingie, on hard impacts (drop etc) the tyre definately buzzes the velcro straps around the brace (it makes a buzzing noise). However in normal use its fine.

Whys that?

My mate put a 2.5 Kenda on his bike with Revelations (older ones) for going to the Alps, it spun ok when fitted but in use it rubbed at the sides. I recon you’d be ok assuming you have enough sideways clearance which it looks like you do.

Personally if it were me I’d not chance it the way it is at the moment.

jedi – so even if it does go horribly wrong it will still be impressive. That’s good then

As long as you don’t ride somewhere with mud like this…..

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fact 🙂

Thing is though.. why? You just run out of wheels or something?

I reckon it would stop mud build up, cos the gap is too small.

Given the minimal difference in over all diameter of the wheel … The wheel doesn;t touch the crown BTW … , why will this cause a problem for the fork

If that’s right, then you should be OK (as long as it can’t hit the down tube either) – until phiiiil’s stick gets you !

(TBH, I reckon it’d be a fairly kack fork design that allowed a tyre to fit under the brace but still foul the crown. downtube fouling depends on frame AND fork so more variable)

the wheel/tyre is significantly lighter than the 26″ set I had before, why will this cause a problem for the fork

light is no worry, as long as it’s strong enough

dezB – actuall yes. I had a puncture and it was too cold tobe bothered to fix it. Mainly done out of curiosity rather than to prove anything. Just suprised how well it worked.

TBH, I reckon it’d be a fairly kack fork design that allowed a tyre to fit under the brace but still foul the crown.

I recon it’d be a good design to have the brace high enough to allow plenty of mud buildup on the tyre….. 😉

As said above measure the distance from the tyre to the crown then compare that to the length of travel. Or let the air out/take the springs out and see if it clears.

I can see how you chose your user name.

Even if it comes close and skims during extreme impacts the wheel wont lock, just slow, your knobbles will just deflect a little. But as said above, several times, its easy to find out.

If you see the air ambulance over Afan on the 7th you will know that it wasn;t such a good idea

😉

I’ve buzzed a michelin 2.2 on the crown of my float r 130s… crap landing off a fast drop… still didn’t catapult me over the bars. I wouldn’t imagine you’d be doing anything mental with a daft wheel like that on your bike anyway!

Those Bombers still going ok then ??

Can’t see what the fuss is all bout TBH.