Speed Camera between Gungahlin Dr and Ellenborough Street

c` said :

…how else do I calculate the rolling circumference? Genuine question.

You cheat -> 2154.4mm according to http://www.1010tires.com/TireSizeCalculator.asp

Very Busy said :

caf said :

The difference between old and new tires can definitely be in the ballpark of a 10% difference in indicated speed (with new tires causing the speedo to indicate slower).

The difference in overall circumference between a new tyre and an old tyre is nowhere near 10%. 1% or 2% max could be possible. The original poster has stated that the car is fitted with original spec tyres so speedo error is almost certainly not to blame here. If the speedo is wrong it could only be due to a non factory spec differential or gearbox fitted.

Or, of course, a faulty speedo, nylon speedo gear or dodgy cable 🙂

Very Busy said :

This case is a very good example of my utter disapointment with the pathetic efforts of our authorities regarding law enforcement and road safety. Many will probably shoot me down here, but I would say that it is infinately safer to travel at 90kmh on that stretch of road than it is to travel in any 80kmh zone while talking on a mobile, failing to use indicators, failing to give way etc.

Yep, I’ll agree with this, particularly regarding the camera/s that have pinged the OP.

Sidewall height has to be added to wheel radius to calculate the total wheel/tyre radius.

Very Busy said :

c` said :

Tyres are 215 65 r16

16 in diameter rims. Tread Width 215 mm. Sidewall 65% of Tread Width.

Radius is

8in (20cm) + .65 * 21.5 = 34cm

circumference = 106

circumference @ 32.5 = 102

This is around 3.75%.

So my speedo should read 3.75% slower. That’s right, isn’t it?

Anyway, that might be a contributing factor but in the end means little in defence of my situation.

No, treadwidth and sidewall % are irrelevant, but yes it has nothing to do with your predicament.

Unless I’m riding on steel how else do I calculate the rolling circumference? Genuine question.

Very Busy: Circumference is directly proportional to radius, so an X% difference in radius results in an X% difference in circumference. If you can’t see that, I don’t think you have anything useful to contribute to the discussion.

I’m a sofa king. circumference is 2*pi*r. The good thing is the ratios remain the same.

c` said :

Tyres are 215 65 r16

16 in diameter rims. Tread Width 215 mm. Sidewall 65% of Tread Width.

Radius is

8in (20cm) + .65 * 21.5 = 34cm

circumference = 106

circumference @ 32.5 = 102

This is around 3.75%.

So my speedo should read 3.75% slower. That’s right, isn’t it?

Anyway, that might be a contributing factor but in the end means little in defence of my situation.

No, treadwidth and sidewall % are irrelevant, but yes it has nothing to do with your predicament.

Very Busy said :

This case is a very good example of my utter disapointment with the pathetic efforts of our authorities regarding law enforcement and road safety. Many will probably shoot me down here, but I would say that it is infinately safer to travel at 90kmh on that stretch of road than it is to travel in any 80kmh zone while talking on a mobile, failing to use indicators, failing to give way etc. Yet, what are the stats – How many infringement notices have been handed out for each offence over the last year? I’ll bet that the speeding infringement is 100’s of times more often. After all it doesn’t take much effort to pull in those $ does it? That is why it’s called revenue raising.

Couldn’t agree more. In fact, I’m willing to wager that on that particular stretch of road, a vehicle being driven at 100km/h by an attentive driver, in good conditions, with little to know other vehicles around, is safer than a person doing 50km/h on many of our residential streets. Yet, how many fixed speed cameras are on residential streets? How many mobile cameras can be spotted on residential streets? How many police radaring has anyone spotted on residential streets?

There are so many contradictions in ACT speed limits it is hard to list them all. My favs, the 80km/h limit on the northern end of the Monaro, a favourite for police. Limited access for the majority of it’s length, no U turn bays… vs Yamba drive between the Yarra Glen round about and the hospital… traffic lights everywhere, passing within close proximity to schools, intersections with give way signs… also 80km/h.

GDE between Glenlock and Belco Way, 80km/h, a single carpark exit northbound, otherwise limited access, central barrier, limit widely ignored by many. Turn onto Parks way between Glenlock and Holt, 90km/h zone with traffic lights, 3 intersections with passive traffic control, no central barrier, and indeed no median for a fair chunk of it’s length. How does that make sense?

Very Busy said :

BTW, for the record I have never had an infringement from a red light or speed camera.

Ditto.

Tyres are 215 65 r16

16 in diameter rims. Tread Width 215 mm. Sidewall 65% of Tread Width.

Radius is

8in (20cm) + .65 * 21.5 = 34cm

circumference = 106

circumference @ 32.5 = 102

This is around 3.75%.

So my speedo should read 3.75% slower. That’s right, isn’t it?

Anyway, that might be a contributing factor but in the end means little in defence of my situation.

caf said :

15mm of tread depth difference on a 320mm-radius tire seems like a pretty fair figure, which gives a 5% difference. It will obviously vary significantly depending on your tire size, but I’d say 5% is definitely “in the ballpark” of 10%.

On a 4WD tyre perhaps, but not on a car tyre. I don’t think most car tyres would even have 15mm of tread on them when brand new. I think it would be perhaps 2.5%, as an educated guess.

caf said :

15mm of tread depth difference on a 320mm-radius tire seems like a pretty fair figure, which gives a 5% difference. It will obviously vary significantly depending on your tire size, but I’d say 5% is definitely “in the ballpark” of 10%.

LOL – Can you please enlighten me as to what road tyres have a usable tread depth of 15mm. Please – the speedo difference is determined by the circumference, not the radius. A 5% difference in radius will not generate a 5% difference in the speedo reading.

15mm of tread depth difference on a 320mm-radius tire seems like a pretty fair figure, which gives a 5% difference. It will obviously vary significantly depending on your tire size, but I’d say 5% is definitely “in the ballpark” of 10%.

caf said :

The difference between old and new tires can definitely be in the ballpark of a 10% difference in indicated speed (with new tires causing the speedo to indicate slower).

The difference in overall circumference between a new tyre and an old tyre is nowhere near 10%. 1% or 2% max could be possible. The original poster has stated that the car is fitted with original spec tyres so speedo error is almost certainly not to blame here. If the speedo is wrong it could only be due to a non factory spec differential or gearbox fitted.

This case is a very good example of my utter disapointment with the pathetic efforts of our authorities regarding law enforcement and road safety. Many will probably shoot me down here, but I would say that it is infinately safer to travel at 90kmh on that stretch of road than it is to travel in any 80kmh zone while talking on a mobile, failing to use indicators, failing to give way etc. Yet, what are the stats – How many infringement notices have been handed out for each offence over the last year? I’ll bet that the speeding infringement is 100’s of times more often. After all it doesn’t take much effort to pull in those $ does it? That is why it’s called revenue raising. BTW, for the record I have never had an infringement from a red light or speed camera.

C, your only real chance of reducing the pain is to plead your case through your good driving record. A carefully worded letter to the RTA may result in at least one of the fines being changed to a caution. The offence will still stand but the fines may be waived. Good luck!!

Interestingly enough, that very model of camera is used in the UK in literally thousands of locations. The UK courts/government have deemed the radar in those cameras as too inaccurate to be used as evidence in court. As a result, in the UK, the camera must take two photos exactly .5 seconds apart. The speed of the vehicle is then measured by the number of dashes marked on the road that the vehicle has passed. The distance travelled over .5 seconds is the only evidence admissable in court. Radar evidence is not.

I raised this issue with the NRMA when I first noticed these cameras being installed a few years back. They took it up with the ACT Gov, who’s response was essentially, we’ve tested the units and they are accurate, end of story. Naturally NRMA having little spine, did not demand clarification, nor further testing on this.

So, somehow, ACT GovCo has deemed their testing of a handful of units, more accurate than many years of real world experience of the UK government with thousands of units. Or they have simply chosen to ignore the UK’s results for other convienience$.

I’m not filled with confidence about these cameras accuracy, thus you’ll all forgive me for slowing to 10km/h below the speed limit when passing Gatso units 🙂

The difference between old and new tires can definitely be in the ballpark of a 10% difference in indicated speed (with new tires causing the speedo to indicate slower).

I was more thinking of going to a reputable workshop than doing it yourself with a GPS, although that should give you a rough indication. I just think it’s more likely for the inaccurate equipment to be the one in your car rather than the one in the speed camera.

caf said :

Might be worth getting the speedometer in your car recalibrated.

I have got new tyres but they’re the same as the OEM spec so I can’t imagine they’d be responsible for a 10-15% variation in indicated speed. I was meaning to check indicated v GPS speed yesterday and will do so tonight. We don’t have a GPS unit but do have GPS capable phones.

Punter said :

I’m not trying to be captain obvious c’, but if you can confidently say you weren’t exceeding the limit on those occaisions when you passed the camera, then that would warrant questioning the relevant authority as to the accuracy of their equipment.

You do have a choice, there must be some fine print on the tickets giving you some options. Good luck with it.

Appreciate the clarification. I can’t say I am completely confident but it is very rare for me to speed – particularly in the urban environment.

I am afraid to report, but I regularly cruise through those cameras at 80 (sometimes 82 or 83 even) and have not received any fines from them. Not sure if I was going through on those specific days, but all the same.
It is easy to lose concentration for a few minutes and find yourself doing a dreaded 7 or 8 k over without even meaning to. Perhaps the heat or some other stresses were getting to you.

It seems like all speed cameras do to me is teach me to stare more at my speedo than at the road, or the back of the next person’s car, or other far safer things to be monitoring as closely.

I know where you’re coming from, C. As a rule, I don’t speed, and as an added precaution, often turn my GPS on around town so it will remind me of upcoming speed cameras, and use cruise control. I would be very sceptical if I got a fine.

Kinda related, out city’s finest were out in strength this morning, on Canberra Avenue in peak hour. One motorbike cop with a speed camera at Fyshwick, one speed camera van at Narrabundah and one cop car with speed camera at Kingston, all focussed on city-bound traffic. However, given that Canberra Avenue city-bound traffic generally crawls along at about 30kmh during peak house, it seemed pointless. Even if it’s a visibility campaign, surely there are more worthwhile places.

I’m not trying to be captain obvious c’, but if you can confidently say you weren’t exceeding the limit on those occaisions when you passed the camera, then that would warrant questioning the relevant authority as to the accuracy of their equipment.

You do have a choice, there must be some fine print on the tickets giving you some options. Good luck with it.

I have to say, I understand your concern. If I got a speed camera photo in the mail I would be pissed with myself, but would have to assume it was a momentary lapse in concentration. However two such lapses on consecutive days does seem unlikely (personally, I have been known to speed, but I make a point of not doing it past fixed, well advertised, cameras).

Unless the government comes out publicly with a statement to the effect that the calibration was out those days though, you might well be stuck with coincidence as an explanation.

Might be worth getting the speedometer in your car recalibrated.

I also appreciate that the obvious answer might be the correct one.

Punter said :

You really shouldn’t have to rely on a notice in the mail to know if you’re speeding. Your cars speedometer will tell you what speed you’re travelling at. I would suggest you check it as a matter of routine while driving, particularly when passing a speed camera.

Thanks Punter. I had no idea what the spinning dials in front of me were for. Now that’s cleared up….

Like I said, I’ll cop it if I have to (and I probably don’t have a choice) but given my driving record and my propensity not to speed, I am quite surprised to have received multiple infringements from the same camera on consecutive days. It may simply be a coincidence, but there could be other reasons. This is what I am asking about.

Let me guess…SUV? Ford Territory? Am I close?

You really shouldn’t have to rely on a notice in the mail to know if you’re speeding. Your cars speedometer will tell you what speed you’re travelling at. I would suggest you check it as a matter of routine while driving, particularly when passing a speed camera.

Shame about the tickets. I drive through those cameras pretty much every day and touch wood have yet to recieve the dreaded letter in the mail. People do accelerate though to get ahead as the two lanes merge(travelling into the city) and i always think people must be getting stung. 90+ though seems a little over the top as as you said its pretty obvious and everybody else is trying to stay below 80. Good luck with the photo’s.

It was me driving. I even know what I was doing on those days (coming and going from the Dickson Pool with the tin lids). Just baffled that I could be rolled twice in two days. I’m going to get the photos because I simply can’t believe that I’ve done this.

Who else is driving the car?

They were our hot days. must be twice as hot inside the box, what ever the temp was those days, I just remeber being f****** hot