Speedo accuracy

[robbom3]

Hi all,

Quick question. I collected my Superlight on Saturday, and overall I'm delighted with it. One impression I'm getting (and so far I haven't verified this), is that the speedo is massively inaccurate. Basically, it appears to be reading a fair bit quicker than the car is going.

So :

a) Are Caterham speedos usually fairly accurate ?
b) If so, then what is the problem likely to be ?

[ewenm]

Mine (when it works at all) reads about 10% over all the time. A lot of people fit a digital cycle speedo for a more accurate reading. Do a search on Blatchat for ideas and instructions.

[Cat7SuperLight]

Hi Rob

It is very common for the speedo to over read. If the speedo has a digital mileage readout you can adjust the settings by the dip switched on the back see Blatchat for settings. If the speedo is the old mechanical type you need to send it back to speedy cables and they can calibrate it for you this is what I am about to do as my speedo reads 160 mph at 130 mph so not good for a limited mileage policy mind you it has taken me over 2 years to finally get my arse in gear and sort it.

Nathan

[dalongbloke]

I understand that is the LAW for speedos to over read slightly. Can u imagine how many legal cases threre would be along these lines .... "My speedo said I was doing exactly 30 officer...."

[Sam_68]

dalongbloke said:

I understand that is the LAW for speedos to over read slightly.

That's pretty much the case... at least they are not allowed to under read.

They are allowed to be spot-on accurate, and they are allowed to over-read by up to 10%, so manufacturers usually set them to over-read by between 5-10% to take account of variations in tyre diameter, tyre growth at speed, and the risk of being sued when someone loses their licence.

[MarchHare]

It will also be affected by wheel/tyre size. My car was supplied with 13 inch wheels but big,fat CR322 tyres. Once I switched to lower profile Avon CR500's the speedo over reads significantly. I don't know if Caterham bother to calibrate speedos for tyre sizes but depending on the set up there must be all kids of variables such as dif ratio, wheel size and tyre size.

[robbom3]

Thanks for all the responses guys. Think I'll get someone to shadow me ina more conventional car to see how inaccurate the speedo actually is. Not sure at the moment if it's that inaccurate, or if the car is just bloody quick !!!

[Fat Arnie]

Try a Sat Nav unit or GPS if you want to be dead on. The cars with the older VDO gauges are notorious for inaccurate speedos, some overreading by as much as 50%! The newer (can't remember the name ) gauges I think are configurable in terms of turns per mile.

A Stack is the best solution. Just enter the rolling circumference of the tyre in setup mode. This data is available for Avon CR500s on their website.

[iguana]

Checked mine at the wk end vs sat nav, speedo is 10 mph over reading at 60 & 70 & 20mph optimistic at 130 on the clock.

[Rokay]

First post on Pistonheads so be gentle.

Anyway speedos. Been through this exercise myself. Comparing my speedo gauge to the Origin B2 camera detector thingy i found i was over reading by as much as 15mph or so at the top end of things.
What concerned me however wasn't the mph over reading so much but the mileage that was being recorded. After all mileage is everything on a car like a Caterham.
Give you some idea i did a run where i recorded 44miles on the speedo trip however actual mileage recorded on the B2 was 32 miles. Now with figures like that i wanted to sort things out sooner rather than later.

Speedy Cables here we come. Four to five week turn around time i was told on recalibration although what with bank holidays it was nearer six in the end. Anyway after a long wait the gauge returned and i now have an error of no more than 3 or 4 mph with a vast improoved mileage trip recording. Infact the sort of error i now get on the Caterham speedo is certainly no worse than any of my day to day cars i have driven in the past. Good enough for me.


Gordon.

[henrywilliams]

With our speedo on the 7 it is not only inaccurate but it also fluctuates over a reading of about 10-20mph (depending on how fast you're traveling)

If you're wanting an accurate speedo (and am not sure about a stack dash) then you could try fitting a bike speedo - it's what we've done.

Admittedly it doesn't look amazing - but it does seem to fit our ethos towards a 7! It's nice to be able to glance at something a bit more accurate when approaches speed cameras! Doesn't really overcome the problem of the mileometer over reading though