7SE Posted July 22, 2003 Share Posted July 22, 2003 Mine has swept wings but, as Blatman pointed out, you can't change the wheels around the car - they do rotate OK on the axle Maybe you could fix a magnet to every wheel effect of tyre warming on accuracy I'm not sure that tyre warming would have an effect, but I believe that tyre circumference grows with speed - an effect of centrifugal (sic) force. Sigma do a light that you can attach to a bike speedo, and you can get backlit ones. Quote Link to comment Share on other sites More sharing options...
oioi Posted July 22, 2003 Share Posted July 22, 2003 below is a snippet of what was about a weeks discussion and a lot of emails. read from the bottom up. Taken to the extreme, yes. B -----Original Message----- Sent: den 9 oktober 2002 11:50 To: sevens@se7ens.net Subject: RE: Re: [sevens] magnet attaching (butts in) Not quite true, If the tyre is sufficiantly underinflated to the point where the tread area is pushed inwards and you start running on the side wall (imagine it completely flat) then it will cover lass distance surely!! Pete >-- Original Message -- >From: >To: sevens@se7ens.net >Subject: RE: Re: [sevens] magnet attaching >Reply-To: sevens@se7ens.net >Date: Wed, 9 Oct 2002 11:27:55 +0200 > > >Ahh, another of my favourite topics..... > >NO, EFFECTIVE CIRCUMFERENCE WILL_NOT_CHANGE! > >You still have to drag all of the tyre surface around, only the shape of >the >tyre changes (& the height of the car). > >Bjorn > >-----Original Message----- >From: >Sent: den 9 oktober 2002 11:25 >To: 'sevens@se7ens.net' >Subject: RE: Re: [sevens] magnet attaching > > >b*****k* - if your pressure reduces in the tyre then the effective >circumference of the wheel reduces and you therefore travel less distance >per revolution of the wheel. > >Regards > > > -----Original Message----- >From: >Sent: Wednesday, October 09, 2002 10:12 AM >To: sevens@se7ens.net >Subject: Re: Re: [sevens] magnet attaching > >At 10/9/2002 103 AM Wednesday, you wrote: > >>What happens when you change tyre pressure > >nothing as the sensor is on a bracket mounted off the disc mounts that >reads exactly from the back of the >studs on the disk. That diameter is a constant, and we checked as we went > >to altitudes of 9000 ft and >down at sea level. Variance was less than .001 % > >scb > names removed to protect the angry.......... Quote Link to comment Share on other sites More sharing options...
Blatman Posted July 22, 2003 Share Posted July 22, 2003 Blatman - why do you want to power from the car batteries? 'Cos A) I don't think it's been done before, and it would be an interesting project/innovation...... and B) 'cos I'm supremely lazy....... IME with my sprint car, where we go out of the way to get the tyres as warm as possible on the start line, and keep them warm throughout the run, on a return to the paddock, I haven't ever seen more than 3 or 4psi difference, but the temps still seem significantly higher than I have ever had when driving on the road, even in the current hot spell..... Quote Link to comment Share on other sites More sharing options...
7SE Posted July 22, 2003 Share Posted July 22, 2003 it would be an interesting project 'All' that you'd need is a voltage reduction circuit or even more simply, a resistor to reduce the voltage. A bit of deft soldering inside the casing of the speedo - job done. Not that I'm an electrician But wouldn't it sap power from the engine? And the batteries in those things seem to last years rather than months... The disucssion around circumference seems to be focussing on pressure and how it doesn't change anything. But when a tyre spins it seems to 'grow' in diameter/circumference. The effect is quite pronounced on 'top fuel' dragsters, maybe its caused by the more flexible sidewalls and is not an issue on road tyres?? Quote Link to comment Share on other sites More sharing options...
Blatman Posted July 22, 2003 Share Posted July 22, 2003 But wouldn't it sap power from the engine? My Cossie has around 230-240bhp..........I'll not notice one or two of those if they go missing........ Deft soldering.......with these thumbs.......... Quote Link to comment Share on other sites More sharing options...
peterg Posted July 22, 2003 Share Posted July 22, 2003 the battery in a cycle speedo should last ages - particularly if it doesn't have a backlight version Quote Link to comment Share on other sites More sharing options...
Nick M Posted July 22, 2003 Share Posted July 22, 2003 But when a tyre spins it seems to 'grow' in diameter/circumference. The effect is quite pronounced on 'top fuel' dragsters, maybe its caused by the more flexible sidewalls and is not an issue on road tyres?? It does, apparently, happen with road tyres, but the effect is very small. The construction is also designed to minimise it as well (stiff sidewalls, steel belting, etc.) Drag tyres are designed to cope with 6,000 bhp being put through them !! They initially have to put that power down to launch the car and they then also contribute to the change in gearing as the car goes down the track. Only downside is that they can make the car a bit wayward because of the lack of sidewall stiffness. They're pretty clever bits of kit really - in common with lots of Merkin motorsport, there's a surprising level of sophistication and technical thinking once you dig beneath the surface. Quote Link to comment Share on other sites More sharing options...
Rusty Nuts Posted July 22, 2003 Author Share Posted July 22, 2003 thanx to all i wasnt thinking of driving the car without a speedo just till i put the new dashboard in with all the new switchs and dials because the speedo is not working i thought i would like to clarify the law as to where i stand if any problems with the police i can also work out the speed from the rev counter and gear calculations (without using a calculator) shindha Quote Link to comment Share on other sites More sharing options...
hilux Posted July 23, 2003 Share Posted July 23, 2003 My understanding is that a speedo must be fitted for the MOT Nope mine wasnt.... Fitted a bike speedo £23 in steering wheel, sender is fitted to front of propshaft Gives me elapsed time, av speed, max speed, trip, clock etc etc Quote Link to comment Share on other sites More sharing options...
7SE Posted July 23, 2003 Share Posted July 23, 2003 My understanding is that a speedo must be fitted for the MOT I have revised my understanding having looked at the MOT Testers Manual and there is no reference to speedo or odometer. the only instrument that is tested is the horn But the Construction and Use regs are different, unfortunately the 1986 regs are not online at HMSO but the Northern Ireland version is Motor Vehicles (Construction and Use) Regulations (Northern Ireland) 1999 and won't be any different. The UK Regs nos are 35 and 36 rather than 40 and 41. A synopsis of the regs is: 40. - A motor vehicle shall be fitted with a speedometer which shall be capable of indicating speed in both miles per hour and kilometres per hour. 41. - (1) An instrument for indicating speed fitted to a motor vehicle shall be kept free from any obstruction which might prevent its being easily read and shall, at all times when the vehicle is in use on a road, be maintained in good working order. Except when - (a) the vehicle is being used on a journey during which, as a result of a defect, the instrument ceased to be in good working order; or (b) as a result of a defect, the instrument has ceased to be in good working order and steps have been taken to have the vehicle equipped with all reasonable expedition, by means of repairs or replacement, with an instrument which is in good working order. Naturally your speedo broke just after you left home Quote Link to comment Share on other sites More sharing options...
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