Tyre size calculator

[DVR]

I dunno if there is already a link to something like this on this forum, so I apologize straight up if there is. OK?

I found a handy calculator here for working out tyre size differences.

Here

You give it the standard size and what size you considering and it overlays the two tyres in the screen to illustrate the size difference and spits out a few details like tyre diameter and such. It also tells you how far out you can expect your speedo to be out.

 

[Aussie Frontier]

Kool
here is the one I have been using
Tire Size Calculator - tire & wheel plus sizing

However the more the merrier

 

[Al]

thats the one i use also aussie

 

[Yakka]

Here's one for the mathematicians out there....... If my speedo is now out by 5.3% (reads 100kms is actually 105.3kms) does that mean that at a reading of 50kms on my speedo I am actually traveling at 52.65kms? Thats how my logic works anyway, am I right?????? (by the way, I haven't bothered to try this on a calculator. Just an excuse for a post I guess!)

Now. How, using the above noted adjustment, does this affect my mileage???

If I travelled an actual distance of 1000kms at a constant speed of 100 and then did the same at 50, would the final trip meter reading be the same??

Just something to ponder.....

 

[Dion]

Here's one for the mathematicians out there....... If my speedo is now out by 5.3% (reads 100kms is actually 105.3kms) does that mean that at a reading of 50kms on my speedo I am actually traveling at 52.65kms? Thats how my logic works anyway, am I right?????? (by the way, I haven't bothered to try this on a calculator. Just an excuse for a post I guess!)

Now. How, using the above noted adjustment, does this affect my mileage???

If I travelled an actual distance of 1000kms at a constant speed of 100 and then did the same at 50, would the final trip meter reading be the same??

Just something to ponder.....

Yes, that would be right. On both counts.

Two problems though. The ADRs specify that a speedometer should be accurate to within 10%, but cannot underread. So you are unlikely to have an underreading gauge like the one you have described unless you have upped your tyre size.

Problem two, in the real world your speedometer's inaccuracy is not that linear. Unfortunately if you have an inaccuracy of 5.3% at 100km/h, it's unlikely though not impossible that you will have an inaccuracy of exactly 5.3% at 50km/h, though you could use that figure as a good rule of thumb.

 

[Aussie Frontier]

Not sure what its like on D21 or D22 but on the D40 going to the larger tyres actually brings the speedo close to accurate.Well sorta anyway. I run the 265/70/R17 and when the speedo reads 100 its actually close to correct. The odometer is still way out though

 

[Al]

navaras d22 and i guess the d40s have an electronic speedo so the inaccuracy will be out by the same % regards of speed.

 

[Dion]

navaras d22 and i guess the d40s have an electronic speedo so the inaccuracy will be out by the same % regards of speed.

Your point is valid, an electronic speedometer is far more linear in its accuracy than mechanical speedometers, which sort of suggest that "you're kind of moving at about x speed but maybe a bit less, don't really know...".

However tyres change in temperature, and therefore pressure, and diameter at different speeds. Without a radar/laser/GPS sensor, it's very difficult to design a perfectly linearly accurate/inaccurate speedometer.

 

[Aussie Frontier]

As far as I know the speedo uses an averaged out speed from all 4 ABS sensors

 

[Handyman72]

Engine Rev's

Hey There,
I'm new to this forum and just have a couple of questions.
Cruising at 100 on the highway my QD32 sits around 3000 rpm, has anybody on here done any mods to decrease the rev's such as larger tires or diff ratios.
If so what were the results.
Thanks in advance for any advice.