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Cheshire110

Member Since: 26 Jul 2013
Location: Cheshire/London
Posts: 2760

Larger diameter tyres & computer/speedo

Is it possible/necessary to tell the computer if you’re running larger diameter tyres? To correct the speedo, trip computer etc? Given that everything is electronic anyway you’d think so... Cheers, David
Land Rovers of all shapes S3 onwards… Daily is a 110 V8.

13th Jan 2021 7:48pm

hotwheels

Member Since: 30 Jan 2021
Location: South
Posts: 20

Yes would also be interested as I’m going from 18” to 20”

9th Feb 2021 6:09am

Simon Audi

Member Since: 19 Nov 2020
Location: Newport
Posts: 544

If you are staying with standard factory sizes of the 18" and 20" tyres then the outside Diameter is 32" and rolling circumference are the same - so no need to worry on speedo . I think you can increase to 33" max (maybe some rubbing)

This is 103.5 inches circumference compared to 100.5 inch circumference - so a 3% increase...

Not worth adjusting anything for in my opinion.

9th Feb 2021 7:44am

SN

Member Since: 29 Jun 2007
Location: SK6
Posts: 729

that 3% might drag you into a conversation with plod though...

On a related question does anyone know how "accurate" the Defender speedo is?

My understanding is that speedos are generally 'over calibrated' - i.e. show higher speeds than you are actually travelling at (to save you from yourself I guess?)

On my previous vehicle my approach relied on having a separate GPS speedo visible on my SatNav screen for accurate readings allowing my traversal through 50mph Average Speed Camera zones at a GPS registered 52mph (i.e. within 5%) with In-Dash Speedo reading about 57mph.

I'm assuming the built in Pivo Pro / Digital Dash will continue with the 'over calibrated' approach? Anyone know? Steve N | 21MY Defender

| 08MY Discovery 3 (history)

| 06MY Discovery 3 (ancient history)

9th Feb 2021 12:17pm

21Rover

Member Since: 25 Feb 2021
Location: PMQ
Posts: 7

My speedo appears to show around 3km/h faster than actual speed between 60-100km/h. Or 2mph between 40-60mph. Measured by gps. ■ MY21 110 D300 SE ■ MY17 Jaguar F-Pace ■

8th Mar 2021 11:25am

SN

Member Since: 29 Jun 2007
Location: SK6
Posts: 729

Useful site if you're worried about tyre and rim sizes

https://tiresize.com/tyre-size-calculator/

I was looking at 255/70R18 Duratrac's on a set of 2nd hand 18" rims
But have settled on 255/65R19 Duratrac's on the existing stock 19" rims I have already bought

Although they're both declared at 32.1" diameter it appears that over every mile the 19" tyre will turn 630 times rather than the 629 times of the 18" tyre - so a difference of 0.01% - no impact on speedo or plod-vulnerability Steve N | 21MY Defender

| 08MY Discovery 3 (history)

| 06MY Discovery 3 (ancient history)

9th Mar 2021 5:33pm

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