Thread: Talk to me about Tyres & Towing

Kev, here's the difference is rolling diameter;

265/70-16 30.61 (777.4) mm


255/70-16 30.06" (763.4) mm

1.8%

Kev, here's the difference is rolling diameter;

Yes BUT.
The 255.70x16 on my car makes the speedo about 3% slow and the odo 5% out, so my assumption and measurement is that the tyres are about 5% different to stock. Mine has 255.55x18 stock.

Adding another 1.8% doesn't sound much BUT it is enough to lose more power.
Also you may lose a bit of lock as I think 265s may hit the leading arms on full lock , but maybe not. The 18 inch cars came with longer lock stops but I think this was to do with most of them having ACE , which mine doesn't and I was able to shorten them quite a bit.
Do you have ACE? If so AFAIK the pipes run along the outside of the RH chassis and may foul.
Regards Philip A

Originally Posted by Redback

Kev, here's the difference is rolling diameter;

265/70-16 30.61 (777.4) mm


255/70-16 30.06" (763.4) mm

1.8%

Thanks Baz .... better yet, look at it this way ....

Std tyre size which the D2 speedo is calibrated for is 235/70*16. The Classic Country came with 255/65*16 which for all intent & purposes are the same size as a 235/70*16 (it's actually 0.41% or 3mm bigger) ... (and 255/55*18 off the Classic Town are the same size again as the 255/65*16).

Working from the std 235/70*16 as the base starting point ...

255/70*16 are 3.8% oversize

265/70*16 are 5.7% oversize

... 1.9% is the difference between these two oversized tyres .... Td5 seems to carry the 3.8% oversize OK ... 5.7% is starting to IMHO stretch the friendship ... then add the extra towing weight ....

... which is what bought me to this point in the proceedings.

You can re-gear for 32s with the 3.75 CW/P From Ashcrofts...

If I increase the tyre size 1.9% do I correspondingly reduce my engine rpm by 1.9% ... ???

????

Originally Posted by Disco Muppet

You can re-gear for 32s with the 3.75 CW/P From Ashcrofts...

No, sorry Mup' ... 32's are currently nowhere in my future ...

... Stop complicating things !!

By 32s I mean 265/75s
Mild map, re-geared and you get awesome towing ability and awesome off-road ability.
Best of both worlds.
Go on....
Or fit a VNT and be done with it!

Phillip. With the 255/70*16 fitted (3.81% oversize), and using a calibration factor of 3.8% on the Nanocom Evo for road speed, when my GPS says 100 and the Nanocom says 100 my speedo reads pretty well at 95-96km/hr.

My odometer, when compared to the GPS, reads approx' 3.6% under ... ie: odometer says 100km travelled, GPS says 103.6km. Dam close to the 3.8% tyre oversize.

So AFAIK with std tyres the D2a speedo & odometer are spot on !