285's may be a bit big.

For example I meant that where you previously coasted a wide corner in third at about 30 -40 kmh, on the 265/70's you would be able to accelerate away still in third because the engine revs were still high enough to do so. On the bigger tyres, although the ground speed is the same, (real speed not speedo) the engine revs are lower and you need to change down to second. Same thing with 4th gear and 60 kmh, any sort of small incline now needs a blat in third instead of holding 4th.

On the brighter side, 4th is better at higher actual ground speeds than before and 5th gear rpm is dropped for highway cruising.

Do you know what your RPM's are at 'true' 110km/h in 5th

The standard tyres, 265/70's, at 'speedo' 110km/h on mine is 2750rpm

Can you give any comparisons???

cheers

I'll check them for you tomorrow versus my GPS and post back then.

Hi Guys,
I have Cooper s/t 265/75/16
at 110km/h i am around 2500rpm by my tachoCheers
waynepd
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Here we go 265/70 285/75
4th gear 70kmh 1800 1750
80 2150 2000
90 2400 2250
100 2500 2300

5th gear 90 2150 1900
100 2300 2150
110 2600 2350

These figures reflect the fact that my speedo was correct vs GPS with the 265/70's and now reads about 8% low. Actual speed is higher than indicated. My daughters note taking also meant these figures were a little awkward to decipher but should give a reasonable approximation. Wow she can scream.

I think Darren worded it better than I did in his explanation which is why I work for an Oil company instead of writing for Playboy.

Same as for Andy, Josh. I'll post them tomorrow.

The speedo and tacho say the same revs and speed as they did before Josh. I need to use the GPS to get a true ground speed of 110 ...which should be reading less on my speedo... and see what the revs are then. Prior to the swap the instruments matched perfectly.

What you have to get your head around, old son, is that the tacho(engine revs) is still connected to the speedo(tailshaft revs), nothing has been altered between them.
The relationship between the speedo and the wheel speed(ground speed) is what has been altered. Comprendi??

Laughing all the way to the ARB outlet, yes josh, nothing would change tacho to speedo,only the wallopers would see a difference in theor speed gun if you use the speedo to measure your velocity

all the bestSo many places to go!
So much work to do :0(

Josh,

This might help,

The tacho is reading engine RPM and the speedo reading is derived from tailshaft speed. Nothing has changed here.
The real difference is that the diameter of the tyres has increased.
This alters the distance travelled per revolution of the tyre, by an amount of around 10% I believe for these tyres.
( Same RPM but greater distance is travelled.)
This means that the speed indicated on the speedo is incorrect, hence the need to verify with a GPS.
By the way, most speedometers read higher than actual road speed, usually between 3 - 10%. The odometers are usually spot on. What you may find now is that the speedo is reading very close to road speed, but the odometer is now out by about 10%.

I am also looking at the 285/75/16's for my GU1 4500, so very interested in the comments about driveability,low range gearing is not the best now, it will get worse with 285/75/16's fitted. May need to fit rockhopper gears or change diff ratio's.

Regards,
Mark

Bill, What's a "Ditronic"?

The power up chip, increases HP and torque by about 20%Regds

Bill

Wow! where do I get such a chip and how much? What's the down side to them?