Speedo accuracy

I'm thinking of moving to a slightly larger tyre size. 5% larger in fact. My speedo currently reads about 5% fast, so the larger tyres would compensate for this & the speedo should read accurate.

But, if were to throw caution to the wind and go to 10% larger tyres, my speedo would then read about 5% slow. How does this leave me from an MOT point of view - ie, would I need to recalibrate the speedo? What's the allowed tolerance for MOT purposes?

Thanks, David

Reply to
David French
Loading thread data ...

Bonza. Thanks.

Reply to
David French

Speedo is not part of the MOT test.

Reply to
mark solesbury

However, a correctly reading speedo is a requirement of the Construction and Use regs, meaning you could be fined if a VOSA official takes your vehicle for an inspection. And it is not a defence in law against speeding either.

Alex

Reply to
Alex

Does a GPS count as a working speedo in the eyes of the VOSA people?

My speedo is dead at the moment, but ive got a gps fixed onto the dash instead. GPS tis probably more accurate anyhow!

Reply to
Tom Woods

Not a chance - you have to have a working speedo - GPS would not count. You would be looking at maybe £30 fine after a Court Appearance.

A
Reply to
Andrew Renshaw

I hate speedo's. Never work properly in my landy! I shall put it on the list of jobs right after fixing the exhaust back together properly! The speedo worked perfectly for a couple of months after my last rebuild efforts. It was even accurate! It had a new cable and head then too.

Reply to
Tom Woods

A bicycle speedometer costs under 10UKP and usually is adjustable for both wheel diameter and miles/kilometres. I can't imagine there is a requirement for a *specific* type of speedometer to be fitted, although you might have to rig some sort of night time illumination for it.

I bought some for the children's bikes that were around 5ukp per set. they'd need to be modified for the Landy (mainly by lengthening the cable, but it's readily do-able - it's only a reed switch at the far end). Use screened, audio-type cable to minimise ignition interference (but mine's Diesel, so even that doesn't matter!). Personally, I'd fit it to a rear wheel, or better still the rear prop shaft close to where it exits the centre diff. You only have to glue a tiny magnet on somewhere to actuate the switch. If you know the rear diff. ratio you can calculate the effective wheel diameter easily.

Gotta be worth looking at the ones in Asda...

(*now* you can laugh)

Regards,

Simonm.

Reply to
SpamTrapSeeSig

I know someone who failed SVA on a kit car because they used this speedo, and it got to about 60ish and stopped reading. The speedo has to be capable of displaying the top speed of the vehicle.

Also, when you change the batteries, if you leave it too long, the mileage disappears, and it can be reset.

Probably be worth talking to a friendly MOT tester....

-- Simon Isaacs

Peterborough 4x4 Club Vice Chairman, Newsletter Editor and Webmaster (how much more....)

3.5V8 100" Hybrid, now LPG converted Part owner of 1976 S3 LWT, currently under restoration Suzuki SJ410 (Girlfriend's) 3" lift kit fitted, body shell now restored and mounted on chassis, waiting on a windscreen and MOT Series 3 88" Rolling chassis...what to do next 1993 200 TDi Discovery (the Pug 106 is dead, long live the Pug)

Peterborough 4x4 Club

formatting link

Reply to
Simon Isaacs

The main reason for a GPS not being a valid speed measuring device is that it doesn't work in tunnels. On a slightly less major point the multipath radio propagation effects can effect the positional accuracy on a sample to sample basis such that the speed could be significantly in error.

Reply to
Phil Gardiner

Not quite true. The speedo has to be capable of reading to 70mph on an SVA test and (from memory) within -0% to +10% of actual speed. I know this as I have the SVA speedo test certificate for my non land rover vehicle (it was very marginal as at 70mph it was reading 76mph). As the SVA is a subset of the Construction and Use Act i suspect that providing the bike speedo can read up to 70mph then you will be complying with the act. There is no requirement for any sort of type approval for a speedo.

Reply to
Phil Gardiner

Reply to
Neil

So does an analogue speedo - they are damped so that the needle doesn't go careening all over the dashboard.

P.

Reply to
Paul S. Brown

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.