To be more specific:

I have just changed SWMBO's A2 17's with 205/40 rubber (with the sport suspension like riding in an Asda trolley) for 15" audi pepperpots with 185/60 all season Kleber quadraxers. The effects of this on economy have been outstanding as the 17's weighed in at 40lb a piece and the replacements only 30lb a piece (+22mm on the roling circumference). Handling in the dry is predictable and comfort levels are vastly improved (with the added benefit of the rattles have got quieter or gone completely!).

My octy 4x4 came with 288's as standard but I upgraded the fronts to 312's after trying different pads and disks I came to realise that the OEM Pagid were the best performing (I did not try DS2500 so please dont get all defensive about them) I spend most of my time plodding around the motorway system of the UK visiting customers and rarely drive my car in anger (was hoping to get to Castle Combe on saturday but not lookling likely) so I am considering going back to 288's when the disks need replacing and changing to 15's with 195/65 four season rubber.

the difference in economy on the A2 was equivalent to approx 35-40% improvement so giving this some serious consideration as money is tight and need to focus finances on other things besides the skip

Edit:

Forgot to add that the Octy RIDE 16's with 205/55 rubber also weigh in at 40lb a piece I also have a set of TT 5 spokes that weigh 37.5 that may find their way on if I don't go for the 15's

Edited 7 September, 201213 yr by karlbar2k

Different makes of tyre weigh different for the same size. Also, there's a 6.5x16 steel for the Octy (one resting in my boot as I type).

I'm just trying to help with other factors you might want to consider.

Finally, if you do mostly long constant speed tags, reciprocating mass reduction won't save anything like 1/3 on your fuel bills.

Yes 15s fit over 288s fine

so is the improvement in economy more to do with the reduction in width from 205 to 185, the rolling resistance and the slight increase in radius/circumference?

so is the improvement in economy more to do with the reduction in width from 205 to 185, the rolling resistance and the slight increase in radius/circumference?

When changing wheels/tyres, your rolling circumference should stay the just about the same.

Any increase in fuel economy should come from less rolling resistance from decreased width, or lower weight of smaller wheels.

I have 288 rotors,and yes 15 inch wheels will fit.

Need to find another set of pepperpots then

Rolling resistance at 70mph is maybe half your total drag; if we assume that rolling resistance is a direct function ot tyre size, that means that going from 205s to 185s saves about 5% of cruising fuel consumption.