[Closed] How would your tyre hit your crown?

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

[img] [/img]

(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

(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

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.

It's not very hard to take a ruler to them so I wouldn't risk it. A mate nearly spannered himself making that mistake when his tyre struck the crown bottoming out on a road gap.

Okay, I have now measured them. Can someone check I have measured the right bits.

The distance between the top of the tyre and the crwon is shown in green at 10.5cm.

The distance between the top of the fork bottom bits and the crown where they meet is 11cm.

[img] http://images.fotopic.net/?iid=yw9s4c&outx=800&quality=70 [/img]

I reckon this means that if I took all of the gubbins out of the forks the tyre would overlap with the crown by 0.5cm causing a load bang and projecting me in a graceful arc over the handlebars.

I also reckon that it is unlikely that all the gubbins inside the fork will get squashed to less than 0.5cm so I am probably safe. Remember I will not be doing road gaps or riding Jedi's wood work.

Biffer - Forks are fine. I replaced the star fangled nut thing after about a month of riding without a bolt in it. People kept giving me strange looks when they saw me riding without the top cap or tensioning bolt.

if they're 100mm travel you'll be ok, probably.

If your forks could travel the full length of your stanchions then yes, you'd have a tyre impact but I'll bet my bottom dollar the full length of the stanchions is not used. Fairly sure mine stop with about 10mm to spare, only way to find out for sure is to compress the fork fully, or measure from the top of you seal upwards by the number of mm travel your fork claims.

I can't get the forks within 1.5cm of the top regardless of how hard i jump up and down on them. I guess I am safe

More importantly, why on earth do you want that big wheel there in the first place?????? It'll be wheely crap at climbing for starters, and pretty vague descending....

South of England doesn't have hills. It is rollytastic round Swinley. Lordwood and the New Forest. I don't do climbs, I do walking if it gets steep and there is lock down on the forks if needed. Not sure what you mean about 'vague' on descents. It doesnlt seem to have slowed me.

tyre hits the crown?

shoot that fork designer!

let the springs loose,(or all the air out) and compress it all the way down.

strikes me the top of the Lowers should hit the crown/stantion joint first surely?
thats just sensible design?

I can't believe no one has commented about the state of my living room. The pot plants are too big and the fireplace needs cleaning.

Not sure what you mean about 'vague' on descents

As in steering like a canal barge!

Each to their own....

what's the, erm, worst that could happen? 😛

why not, y'know, just fix your puncture?

MrNutt - there are lots of ways to get round the obstacles in life. just because it is obvious doesn;t make it right.

I can't fault your logic! 🙂

You do realise that after all of this messing around on 'tinternet and measuring things taking photos and messing around with them then uploading them and finally posting them just to get an answer has taken longer than it would take for me to drive from Birmingham realise the air from your forks and check if the tyre would hit then fix your puncture and drive back to Birmingham.

Sorry for the lack of punctuation.

But then what would we discuss on the forum 😉

you're all beginning to sound over tyred,

perhaps you need a lay down? 😆

Right thats me Im off for a ride on my totally un-niche 26" wheeled 6" FS bike.

Have a fun night.

Ones Crown might hit ones tyre if one was riding ones land when ones corgi runs under ones wheel causing one to go over ones handlebars. And no one wants to damage ones jewels.

"I guess I am safe" maybe not, something else to consider -

the leverage on the crown area is increased when you fit 29" wheels to 26" forks - the radius is larger so the leverage is higher than the manufacturer may have factored in. Fox recently put out a notice warning about the danger of doing this, and although there is a saftey margin built into the design of all bike parts, you shouldn't risk having the crown seperate from steerer or stanchions.

Your risk, but i couldn't ride that set up hard with confidence.

and it has the same effect on your headtube / down tube weld... it's on a few-years-old alu frame too...

As I was the one that brought about the worry in the first place WCA, should probably chip in with the measurements you've given for everything, and the knowledge that your forks can't get within 15mm of use of the full stanchion length showing, you *should* be fine even under full compression running this wheel. Though if the wheel deflects because of a hard hit (they do this you know!), it could be tyre into the brace time which would equal instant stoppage!

*I do not take any lawful responsibility should anything bad happen!

As others have said though, there's lots of reasons not to do it. I can understand your thinking that where you're riding, it should be fine for the most part as they're not that hilly trails etc. Personally, I'd want some bloody mud room between my tyre and the fork brace. I've managed to stop a 2" front tyre rotating inside a fork with loads of mud clearance, due to the ridiculously gloopy mud we get where I live. Not a problem now I'm running upside down forks at least!

Oh, and I also don't like running silly thin tyres, especially not on the front. If you're riding Afan at the weekend, and haven't done so before, I'd fix the puncture on your 26" wheel and slap it back in personally! To me a 2" tyre is narrow though, I like a bit of cushioning, and we're all different.