I think my point has been lost in the side tracking. My issue is overtaking at speeds over 55mph. Now in most cases this wasn't an issue but yesterday for example on the M6 there was a quick lane closure with no warning which meant I had to merge into my right lane. I indicated and moved but the car in the lane I was moving into was forced to break and I was unable to accelerate to keep the flow of traffic. It's only in circumstances like that & inclines at speed which cause an issue. The gears you'd use for off roading are absolutely fine and it is great but 4th and 5th feel underpowered.
Thanks for your replies
Based on
your experience, your problem would appear to be the gearing, which as has been discussed ad nauseum is affected by the increase in tire size. It's not that the power isn't there, but, the "multiplication factor" provided by the transmission has been altered.
The simplest way to deal with this is to switch to a smaller tire, another option is to "re-gear" - it might be possible, if you have a manual transmission vehicle to swap in the transfer case from an automatic as that has a 1.32:1 reduction in high range, whilst the manual has none. Similarly the axles from the automatic can be used as that has lower gearing (4.3:1) than the manual (4.09:1).
I believe another post in the discussion mentions that the increase in tire size is around a 7% change, based on my experience with larger tires, anything over a 5% change will be noticeable - for what it's worth, this experience is on a 2.0 liter Grand Vitara, with no added weight, just swapping the tires for larger ones and repeating the process.
