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Post by leew on Nov 20, 2011 21:34:37 GMT
Sorry kingkay, but Centra Bavaria was using 305 wheels, not 349 and there are thankfully a handfull of tyres around for that size.
Also I belive c12 made a set of 406 wheels for screwfix so they could use those.
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Post by kingkay on Nov 20, 2011 21:38:45 GMT
decent ones?
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Post by azuma on Nov 20, 2011 21:40:04 GMT
Lee - a couple of points : I agree light does not need to mean weak, but carbon fibre has to be laid up correctly or it will be weak, especially if the stress is a different direction to that intended. I do not agree with the "novice" comments though. I am not a qualified welder, but I am highly critical of my own work. My welding experience is car maintenance and kit cars and I have built my own spaceframe chassis and modified others. Iain's is much the same, but he has run his own rally cars doing the required welding and mods himself. Also, how many accidents have Team Rooket had over the years and NONE of my welds have failed. With regards to the Caterham chassis, yes it weighs about half of a road car, but it is only a basic 2 seater, with no modern features. Yes it is strong and that is testament to proven engineering i.e. "fully" triangulated. Hence if you ever see a "7" type car in an accident, they may be wrecked, but the driver often walks away. A fully triangulated chassis using 16swg 25mm box section and a braced CDS roll tube is not beyond the skills of most cartie builders and some have gone beyond this using round tube. Using heavier gauge means there may not be enough structure especially when carties become more technical with suspension and better brakes etc. With regard to ballast, I agree from a safety point, if a fixing point fails they can be deadly, but on the other hand, if it used to correct the balance of a cart then I don't see it as a problem. If using adjustable shock these can be used to tune the balance, as well. One solution for the future would be if a secondary device were in place to restrain the ballast in the event of a fixture failure i.e. ali chequer floor plate??
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Post by azuma on Nov 20, 2011 21:56:43 GMT
Regarding the point of KPI, if a fatter, tyre is used it will affect the KPI, but this can be corrected by spacing the wheel out (assuming the same wheels are used) and then spacing the brake accordingly. Neither should be challenging for cartie builders? The KPI can also be affected if the builder changes his own set up regardless of the rules, i.e. change of hubs.
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Post by Scottish Cartie Association on Nov 20, 2011 22:05:48 GMT
Kay - you can't get tyres anyway. Last time I saw you, you were fixing yet another burnt through tyre with duct tape.
Centa B decided weeks ago that they wouldn't be coming. I spoke to C12 at Belchford and he just shrugged and said "back to the cityjets then".
Red Gazelle started dropping hints on facebook about not coming about a week after the last race at Cairngorm.
It's not just about rolling resistance anyway. Other factors affecting speed are moment of inertia and drag. Fatter tyres have more drag. Smaller wheels have less moment of intertia and are therefore faster. The slightly wider tyres for smaller wheels offsets to a certain degree the advantage you get from the lower moment of inertia caused by the lower weight and smaller radius.
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Post by Scottish Cartie Association on Nov 20, 2011 22:52:31 GMT
Just a quick note about the Legs Larry data (http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm). It's not without it's problems and the experimental method - particularly the fact that the tyres where measured agains a relatively small drum - means the results are not quite as clear cut as you might think.
Interesting to note though that according to those data the 406 tyre with the lowest rolling resistance is none other than the Schwalbe Cityjet...
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Post by kingkay on Nov 21, 2011 0:15:49 GMT
You’re right we can’t get tyres. Tyres are expensive. Gaffer tape isn’t. One spare was unaffordable. To replace all 4 and afford a contingency plan is simply not an option. Add the price of rims and spokes and you could sell tickets to watch us twitch and gibber. Good cheep fun was the way we were looking at it – the best you can do with the little you’ve got. It’s possible to blag an awful lot of stuff, but you can’t afford to be fussy as to what you end up with.
The tyre data is a bit unreliable I know, it’s also pretty old and you’d struggle to get hold of a lot of the tyres listed. Other people doing the same kind of research are coming in with similar results though so it’s better than suck it and see.
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Post by team-art on Nov 21, 2011 9:20:22 GMT
I’m not doing Cairngorm 2012…and with this rule set I’m unlikely to do Cairngorm again……hopefully plenty of others will. Once the dust settles there will still be a Cairngorm. I just hope that other events don’t consider adopting “tyre restrictions” and “no ballast”. That would seriously **** me off. Rich
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Post by Scottish Cartie Association on Nov 21, 2011 10:14:44 GMT
According to the respondents to the survey we did, 70% of the carties who replied (14/20) run with 10Kg ballast or less. 50% run no ballast at all. The average ballast was 10Kg. The rest were running with considerably more - two reported they were adding 37Kg of ballast to a 38Kg cartie. Frankly, I think that's a bit unreasonable, but still within the rules as they stood at the time. Personally, I wouldn't have a problem with up to, say, 10Kg of ballast, but I also have to consider the ease and effort of scrutineering as well. If we set, say, a 10Kg limit on ballast, we have yet another thing to check at scrutineering and also monitor during the event. We have very limited time to carry out the scrutineering as it is, and the most practical way to just tell people not to fit ballast at all. I've already heard people are discussing ways to subvert this rule, and I have to say I'm pretty disappointed by this. I don't put my time into drafting the rules just to give everyone an opportunity to devise ever more devious ways to ignore them. This isn't my day job you know. Although sometimes it feels like it is.
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Post by leew on Nov 22, 2011 10:34:29 GMT
If I was to build a cartie from solid bar stock when hollow tube would be perfeclty strong enough, would that be allowed?
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Post by peasnbarley on Nov 22, 2011 10:50:56 GMT
Lee: If you want to build a cart out of solid bar stock, or add lengths of bar stock to an existing cart there is nothing in the rules to prevent that. The only reason for doing so would be to add weight or because the material was on hand and the individual didn't want to go out and buy tube. It's difficult once round bar stock is welded in place to tell the difference from tubular so it would be stupid to attempt to rule it out. Tube is better than solid for most applications as you well know.
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Post by leew on Nov 22, 2011 11:06:04 GMT
Another idea I had if I was to build a new cartie would be to use steel sheet for body work. A full body made from 1mm or 1.5mm steel sheet fully welded could be very strong and add quite a bit of protection, especially protection from intrusion from other carties as well as being very heavy. But having such a body may make getting out difficult if I was to mangle it.
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Post by Scottish Cartie Association on Nov 22, 2011 11:34:26 GMT
If I was to build a cartie from solid bar stock when hollow tube would be perfeclty strong enough, would that be allowed? Rule 3: Just because you can do something does not mean that you necessarily should, and building with solid bar is quite definately "trying it on". But it's a moot point, since you've already said you won't be entering.
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Post by leew on Nov 22, 2011 11:40:24 GMT
well it depends how things pan out next year and if the event is full. The way things are going it's unlikley though.
I don't want to run at 105kg all up as I feel that with be a significant disadvantage, Especialy considering that I'd have to use a number plate the same size as someone running at 210kg. Why not allow a number plate proportional to the weight? We cannot use a standard number plate anyway as they are normally made from perspex which falls foul of rule 10.1.
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Post by Scottish Cartie Association on Nov 22, 2011 12:09:50 GMT
Infinitely variable drag plates is just not feasible. We have limited time to scrutineer in the first place - approximately 9 minutes per cartie - and we do not have time for that. That idea really is an absolute non starter.
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Post by team-art on Nov 22, 2011 12:40:53 GMT
Another idea I had if I was to build a new cartie would be to use steel sheet for body work. A full body made from 1mm or 1.5mm steel sheet fully welded could be very strong and add quite a bit of protection, especially protection from intrusion from other carties as well as being very heavy. But having such a body may make getting out difficult if I was to mangle it. Centre of Gravity,Roll Centres on a narrow track cart???
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Post by SteveK on Nov 24, 2011 18:57:18 GMT
I've emailed Stephen with my concerns about this, but since I've now seen this thread I've decided to put them here. I have a specific problem with the wheel diameter rule. Those of you who know our kart (The Doc's Box-pic attached) will know we have always put safety before speed. I took steps to slow my kart down when we first got it, before I put my 12 year old son in it. Our wheels are 24" mountain bike ones. They are custom built. I don't think our kart would take 20" wheels. My point is that doesn't make our kart unsafe. I believe our kart is one of the safest around-I would welcome comments from those of you who know our kart. Would a kart fitted with say 24" motorbike wheels be less stable than one with 20" bicycle wheels? It's not as simple as small wheels good, big wheels bad is it? Attachments:
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Post by team-art on Nov 24, 2011 21:49:52 GMT
Would a kart fitted with say 24" motorbike wheels be less stable than one with 20" bicycle wheels? It's not as simple as small wheels good, big wheels bad is it? No it’s not. My Soapbox has competed twice, 2009 & 2011 at Cairngorm running on 24” Wheels. Finishing both years without wheel damage or an accident. I don’t believe 24” are likely to be the fastest (heavy and not very aerodynamic) but they needn’t be unsafe. Cheers Rich
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Post by SteveK on Nov 25, 2011 10:36:10 GMT
I don’t believe 24” are likely to be the fastest (heavy and not very aerodynamic) but they needn’t be unsafe. Cheers Rich Thanks Rich. Agree with both points.
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Post by Scottish Cartie Association on Nov 25, 2011 11:19:45 GMT
Look Steve I'm sorry you seem to have taken this so personally. We're not trying to explicitly exclude your cartie, but we are trying to get a risk exposure that we're comfortable with as organisers and also to keep the effort involved down to a manageable level.
You may well think that your 24" wheels are strong enough, and you may well even be right, but there are other 24" wheels available which are not. You're right that it's not as simple as "small wheels good, big wheels bad", but from the point of view of an organiser trying to make an objective assessment in a very short space of time, I'm afraid that's what it comes down to. We simply do not have the resources or the expertise to examine every wheel on its merits, and neither do I have the stomach for the inevitable and interminable "her 24 inch wheel is OK so why isn't mine" arguments.
We need a clear, unambiguous specification that we can test very quickly and very easily. In terms of the measurement we chose - if we have erred it is on the side of caution, and that's where we need to be at the moment. In any case, it hardly matters where we put the line, there is always going to be someone who is slightly over it.
That's not to say the maximum wheel diameter might not change in the future. It would be the decision of whoever is running the event - whoever that might be.
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