Syncro Wheel and tyre weight

Syncro G:

This wheel weight issue has got me thinking so I got the scales out and went looking for wheels that weren't on a vehicle. I measured them on a mechanical bathroom scales, readable to about 1kg and by no means super accurate. Did the first couple by difference with me and also on their own, didn't seem to make a difference so I did the rest on their own. Everytime I weighed myself and it came out about the same too so they seemed to be consistant and always on smooth surface - thats the fair test bit over...

1) BFG AT 27x8.50R14, 11mm tread on 6J14 = 24kg

2) Goodyear Xtra Grip 7.50-16, <2mm tread on 5.5F16 (tubed) = 26kg

3) Goodyear Wrangler m+s 7.50R16, 3...4mm tread on 5.5F16 (tubed) = 27kg

4) 5.5F16 rim only = 12kg (by difference)

5) Goodyear Xtra grip 6.50-16 tyre only = 11kg (by difference)

6) Colway 205R16 (retread), 5...9mm on 5.0F16 (tubed) = 29kg

7) Unknown m+s 205R16 spare, 4mm tread on 5.0R16 (tubed) = 26kg

8) BFG Trac Edge 7.50R16, 3...4mm on 5.5F16 (tubed) = 31kg

Things I find surprising is how heavy the colway retreads and the BFG tracedges seem to be, good few kg more than other simular sizes.

I switched from 6 to 8 on my landy, it rased the gearing by nearly 10% as you'd expect but there hasn't been a noticeable drop in mpg on the unaltered odometer unless the tank was mainly used in hilly areas, whereby I wouldn't say it was 10% worse than the Colways so is therefore a saving. They've really killed its acceleration (gearing) but when up to speed it holds it quite well, handleing is poorer though - seems like those 2kg a tyre is quite noticeable (Big squidgy sidewalls don't help the handling either so its hard to pin the cause on weight or tread, it is much worse than the Colways though!) I think what I'm gonna do next is try the Wranglers to see if I notice the difference with significantly lighter wheels without gearing change, and what it does to mpg, though if I do that I think my dad will cut up the trac edges to make a garden path.

I've heard lower profile tyres past a cirtain ratio can actully weigh equal or more than higher profile ones as the sidewalls need more reinforcement (though I wouldn't have thought the high aspect ratios we use will be in that region, that said it mught explan why BFGs are so heavy?) so bigger rims for the same dia. might not save much weight. Rims won't make as much difference as tyres as they are closer to the axis, remember the spacers if used on alloys - Alloys are in theory lighter but I doubt by much, they are usally done for style rather than weight saving (except for the mega expensive performance magnesium types on track cars).

HarryMann: Worthwhile data there Glen. It's the wheel and tyre inertias we should ideally be measuring, 2nd Moment of Mass, so they'd need to be suspended on axle and accelerated, using a given torque to determine that experimentally. However, one can deduce the MoI to soem extent form the size and weight