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Post by team-art on Nov 24, 2011 9:48:11 GMT
"Check how nerdy I’ve been today."
Hi Kay, That’s dedicated, Gold Star nerdy. ;D So nerdy that I’ve saved the image. (how nerdy is that?)
The 47.5mm width doesn’t match my (nerdy) results on a 30mm outside width rim…can you check at 65psi? And perhaps try 80?psi….
Cheers Rich
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Post by team-art on Nov 24, 2011 10:18:58 GMT
Hi Lee, I will order some Big Apple 305’s next week and measure them on various rim widths. I suspect they will be too narrow, at least on “standard” rims (approx 25mm internal), but I could be wrong! Cheers Rich
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Post by andy on Nov 24, 2011 10:31:57 GMT
Good morning to you too ! I think the rims are 35mm internally..... Must admit, I was feeling a bit left out on the Nerdy stakes so have just put a 54-305 city jet on a 24mm rim and ramped it up to 70psi .. measures over 50mm width, but does look a bit precarious ! I wouldn't want to put a lot of lateral load through it.
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Post by team-art on Nov 24, 2011 11:08:06 GMT
“I was feeling a bit left out on the Nerdy stakes” Get a beer, pull up a chair, you’re in.
Here’s an interesting (quite nerdy?) fact. If I measure the width at various different points round the tyre at 65psi with no load applied, it varies between 51.6mm and 53.8mm!
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Post by andy on Nov 24, 2011 11:21:55 GMT
Art.......Following on from your test, I just did a quick check of the wheel I have....here are my results:-
I took 100 measurments round the cicumference of the wheel and found a variation of 1.56mm between the maximum and the minimum width.
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Post by leew on Nov 24, 2011 13:02:04 GMT
I wonder how accurate the measurements by the scruterneers will be? Will we see 1/1000mm micrometers in action?
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Post by roo4 on Nov 24, 2011 13:05:59 GMT
You 2 have to much time on your hands.
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Post by andy on Nov 24, 2011 13:16:33 GMT
YES, you do !.............
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Post by Scottish Cartie Association on Nov 24, 2011 13:27:16 GMT
Will we see 1/1000mm micrometers in action? Only if you're actually going to be there.
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Post by leew on Nov 24, 2011 13:34:37 GMT
Well I'm thinking about it, but for me it's 400 miles, and I don't want to have to go home again without running just because my tyres are 49.9785mm wide.
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Post by andy on Nov 24, 2011 13:45:24 GMT
Check how nerdy I’ve been today. As you can see the city jet is loads fatter, only slightly heavier (when built into wheel) and very strangely has a very similar footprint despite being loads fatter and only half the pressure. Not sure why this is but I tested it loads of times and it is. Jedi mind tricks !
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Post by brillo451 on Nov 24, 2011 13:49:10 GMT
Iam quite puzzled that you all seem to be surprised to find such a difference on the width of these tyres. They are designed for a pushbike after all that will spend most of its time traveling at a max of 30MPH Not a Cartie doing 60+ so there is no need for the tyre manufacturer to tighten up their tolerances on these types of tyres, the tolerances on expensive 700c tyres are much tighter...
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Post by leew on Nov 24, 2011 14:00:08 GMT
Yes but we can not use 700c tyres as 1: they are not allowed and 2: if they were allowed they would most likley end up pringle shaped.
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Post by andy on Nov 24, 2011 14:29:59 GMT
Brillo has a point there.....about the quality and the tolerance levels of these tyres....must admit the last pair of City Jets I bought were of very dubious quality.......although they looked the same as others I have, they felt as though they had been made from chewing gum.......I have not used them......I had a fairly high speed blow out at CSEx 2010 ...front left just exploded coming through the finish line....If it had happend a few hundred yards further up the track, through the right kink over Allt Mor Bridge, there's a strong chance I would have ended up in the scenary............and that wouldn't have be much fun.
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Post by andy on Nov 24, 2011 14:38:48 GMT
I believe Gerry '' where's me spanners'' Quinn was watching the race when I lost the tyre.
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Post by team-art on Nov 24, 2011 14:46:34 GMT
Iam quite puzzled that you all seem to be surprised to find such a difference on the width of these tyres. They are designed for a pushbike after all that will spend most of its time traveling at a max of 30MPH Not a Cartie doing 60+ so there is no need for the tyre manufacturer to tighten up their tolerances on these types of tyres, the tolerances on expensive 700c tyres are much tighter... I think that’s all very true and pretty much spot on. I didn’t use a CityJet on the front of the Trike because I couldn’t even find a round one!!!!!!!!!!! What tolerances? ;D Competitors still need to find out if tyre x is legal. Yes or No. Up to 2mm difference? The event wants a quick pass/fail. Preferably a pass. Not a competitor arguing, “I’ve got a fat bit round ere somewhere guv”
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Post by kingkay on Nov 24, 2011 18:25:12 GMT
Well after being blown up for 24hrs the tyre has expanded slightly to 49.5 / 50mm depending where you measure it. So hopefully that would be OK.
However it does beg the question – seeing as how so many people have pointed out how crap they are – Can you really say that a cart running on egg shaped tyres that explode, but are 50mm wide, are safer than skinny tyres that are obviously designed to run a bit faster and truer?
Also was there a reason why the magic sizes of 50mm below 460mm and 45mm above were decided on? Anyone looking at anything under 406 is really struggling for choice. You can get some but they are all a bit low grade and slow and, from the sound of it, dangerous. So really what it comes down to is don’t go small. Was this actively sought? Or could it simply be that all the people making the decisions are running 406’s and didn’t think about how much it could mess people about?
All things being equal, smaller wheels are stronger and therefore safer wheels too.
“Without deviation from the norm, progress is not possible.” Frank Zappa.
And there’s a man who knew all about soapbox racing.
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Post by peasnbarley on Nov 24, 2011 19:12:06 GMT
;D Just love it! ;D
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Post by Scottish Cartie Association on Nov 25, 2011 9:08:46 GMT
My goodness but you've all got your panties into quite a bunch about this haven't you?
The overall objective here is to reduce the exposure to risk of the organisers so we can get it down to a level where we're comfortable to run the event at all. Once we've done that, the decision about whether or not this matches the level of risk that you want or will accept is entirely up to you.
What we're trying to achieve with the tyre size restrictions is;
1) A reduction in top speeds. 2) Less fragile tyres.
The effect of wider and heavier tyres has on speed is not huge, but the physics is clear even if peoples' understanding of it isn't.
The main concern is that the light and skinny stelvios, kojaks, etc that are becoming increasingly popular are just too fragile for Cairngorm. You need to brake very hard before the The Switch and if you lock up your wheels you will burn through them in about two seconds. Even if you don't shred them instantly, you'll have severely weakened them.
Nonetheless, we don't want to make it prohibitively difficult for you to find tyres, so we'll be releasing a new version of the rules in the next few days which reduces the minimum width for all wheel sizes to 44mm.
Where there is any doubt as to the suitability of the tyre, we're going to take the actual real life width measurement as the basis of the decision. This is because we need a test which is quick, easy and unambiguous, and we'll make up a fixed width guage to check them. If it's in spec' anywhere on the tyre it'll pass, but if we can spin the tyre in the gauge and it doesn't touch anywhere then it's a fail.
(As an aside; it seems that the only thing we get to chose is what we get moaned at about. It'll either be "my tyres are 1mm too small" or "her tyres say they're 1.8 inch but they're actually 43mm". Hey ho.)
As usual, if you are only marginally out of spec' then we may offer you the opportunity to take race but without being eligible for silverware. But if you have super light and skinny tyres you'll need to find some new ones.
That should help most of you find tyres, but I think I probably doesn't help TDR much - really sorry about that, but I think you already know you've got some problems with your tyres as they couldn't really cope at Dalby either.
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Post by leew on Nov 25, 2011 9:52:16 GMT
Do you consider 24" (ISO 507) wheels too fast? In CSEx 2011 the top 3 teams were all running 16" (305 or 349) which seggests smaller=faster. Theraetically a larger wheel has less rolling drag but as speeds increase the air drag caused by the larger wheel overides the reduction in rolling drag. I notice you have made the max wheel size just slighly smaller than a 507 wheel with a 45mm tyre, was that intentinal? Several teams were running 507 wheels in previous years and they seemed OK. 507 wheels are generally used for Downhill mountain biking and thus can be strong, being built to withstand 10 foot drop-offs etc. I would seggest it be a good idea to up the max diameter to about 627mm (allowing a 507 rim with 60mm tyre). This would still rule out 26" and 700c sizes which are prone to pringling. Maybe say that the wheels have to be fit for purpose or something like that. You can get lightweight road bikes with 24" wheels but they use a diffrent rim size (ISO 520) for which only skinny tyres are made.
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