FL2 tyre sizes

300bhp/ton said:

The only thing is "modern" speedo's have really been the norm for about 30 years now. You'd probably do well to find many vehicles on the road that use a speedo cable.....

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Craig_mate said:

I have about 3mm..

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GrumpyGel said:

If there's a 12.6% difference across factory tyres, then the speedo must be calibrated to the tyres installed on the vehicle when it left the factory or else some of them would be illegal.

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Nodge68 said:

It depends on the wheels and tyre combo fitted.
Mine has style 2 17" wheels, which have 5 pairs of spokes and Chinese Jinyu tyres (I know but it came with them and they don't want to wear out)
This combination gives about 8mm at the rear, and 12mm at the front, between the side walls and strut tube.

If it's very close to the Mass damper on the rear strut, then it's probably broken loose from it's rubber and needs replacing or removing.

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Kevm said:

I was quoting UK law....it may differ in other countries.

Under UK law a speedometer can not read low therefore the assumption would be that a manufacturer would have the speedometer calibrated for the largest tyres that the vehicle takes ( legally ).

As the tyre size could vary by up to 2% and tyre wear could give another 2% then it would be expected that an accurate speedometer could vary from actual speed by up 4% dependant upon tyres.

Also the accuracy of sat nav speed readings can be very variable.... it depends upon the accuracy of the road on the map and uphill/downhill can affect it as well.....my personal record is 220mph along a newly built road.

Although in general along a good flat road sat navs can be quite accurate......well at least as accurate as the radar gun that got me.

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300bhp/ton said:

Running at 72mph on the motorway is illegal too. But I bet anyone who has driven on a motorway has done it. Even if they didn't know or by accident. But I bet people also aren't persecuted for it.

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300bhp/ton said:

looking at the factory sizes there is a 12.6% speedo difference across the tyre sizes.

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Craig_mate said:

I'm trying to upload a picture of my shock/tyre situation and it says I don't have permission....?

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GrumpyGel said:

Had an interesting 1 today at work.

Couple dropped off their campervan. Its an old 'budget' / 'backpackery' type van - 2004 Toyota Hiace van conversion - done over 350k miles.

Anyway, they asked to be reimbursed for the 2 speeding tickets they got because the speedo was showing under. Said the speedo was showing 50 and they got nicked for doing 62.

Thought they might be pulling a fast one, so I drove it with another fella following in another van, sure enough, I was doing an indicated 50 and the fella following had to do 60 to keep up - felt faster than 50 as well.

I did my prechecks on the van after it got back and even though there's a '45 psi' sticker over every wheel, they were pumped to 50 psi, but I don't suppose that could make the speedo read 20% slow!

Van had had a COF just before they picked it up - a 'commercial' (more stringent) version of the WOF (MOT). Would have thought they would check the speedo accuracy.

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kermit_rr said:

Speedo isn't checked in the MOT, only for obvious defects eg broken needle etc

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GrumpyGel said:

Had an interesting 1 today at work.

Couple dropped off their campervan. Its an old 'budget' / 'backpackery' type van - 2004 Toyota Hiace van conversion - done over 350k miles.

Anyway, they asked to be reimbursed for the 2 speeding tickets they got because the speedo was showing under. Said the speedo was showing 50 and they got nicked for doing 62.

Thought they might be pulling a fast one, so I drove it with another fella following in another van, sure enough, I was doing an indicated 50 and the fella following had to do 60 to keep up - felt faster than 50 as well.

I did my prechecks on the van after it got back and even though there's a '45 psi' sticker over every wheel, they were pumped to 50 psi, but I don't suppose that could make the speedo read 20% slow!

Van had had a COF just before they picked it up - a 'commercial' (more stringent) version of the WOF (MOT). Would have thought they would check the speedo accuracy.

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Kevm said:

Something is probably not original and is throwing the reading off....

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