Increased tyre size

Cammo,
Have you checked manufacturer's innacuracy. Most speedo's already set too conservative at 100km/h, usually between 5 - 10 % to stop any legal action against them by customers. You may find your speedo is now accurate. Others would have checked using GPS or time over distance measures.
Rolande

I have 285/75/16's on the LC100 T/D Auto. On the trip this w/e to the Grampians we went through 2 of the speed check thingos. Both times I had the cruise running at 99kph on the speedo. First one read 101kph second one read 105kph. Go figure.

If my maths is correct the difference in tyre circumference is 5%. ie. speed would be different by 5%. As mentioned by others, speedos out of the factory usually show speeds higher that actual speed, so changing tyres sizes up should bring it back towards accuracy (or over compensate).

I'm currently working on the basis that I need to take off 5% of the speedo reading to get to actual speed. A few more trips under the speedo checks - or a dyno reading is on the short list. BTW I was told there was no fix for this so I will be following up the Marks 4WD lead ASAP.

Gaz

Hi Cammo,

Gotta agree with Rolande here, my speedo was way out.

With my original 265/70R16, the speedo read 106 km/hr at a true 100km/hr (Garmin GPS V). When I changed to 285/75R16's (increase of 7%), the speedo now reads 99km/hr when doing a real 100km/hr, much more accurate (-1% error compared to +6%) IMHO.

As my engine management also reads of this sensor (so I am led to believe), the larger tyre size actually makes it more accurate.

So, before spending money on a speedo recalibration, check out what the real speed reading is. You may find you have made it more accurate.

Cheers

Captain

Not to sure on some of the replies , I have fitted 315/75/16 to a 100 series , the speedo is around 8ks out . Vehicle seams to not have suffered any ecu problems .

The reply I am talking about is the one where the speedo read more acuratly

I have a new 100 series TD to which I have just fitted 285/75 BFG AT's. With the tyres brand new on a recent trip across the nullabor the gps indicated a steady 104 k/ph with the cruise set on 100 k/ph on the speedo.

Stuart