Weight difference btwn oem 16" and YZF 17"rear tire assembly

[Pat Conlon]

We know that unsprung weight is the best type of weight to remove from our bikes. You can run less preload and thus lower compression/rebound settings on your suspension allowing a faster, smoother response from your suspension.

Today I was putting new rubber on my '92, getting ready for our WCR, and SWMBO bought a new digital scale (yes honey, it "appears" that you've lost weight)
I had my oem '92 tire/rim assembly handy so what the hell...

1) 1992 FJ1200 oem assembly with 150/80-16 Dunlop, 40 tooth steel sprocket/cush drive and oem brake rotor: 41.0 lbs
2) 1997 YZF ThunderAce 5.5x17 with a 180/55-17 Pilot Road 2, 40 tooth steel sprocket/cush drive and Galfer Wave rotor:  36.0 lbs

A 5.0lb weight savings with better tires....That's a no brainer.  
Thank you folks for talking me into it and showing me how.....

[Firehawk068]

Pat,
I was in the garage today and started disassembly of the rear suspension.
While I was out there, I looked at my digital postal scale, and the thought occurred to me. I should weigh them both, and find out the difference.
My Findings surprised me. I ended up with exactly the opposite of your results.



1st, I weighed the original 16" wheel with a severely worn 160/80-16 Avon Azarro, with brake rotor bolted on. Bearings/spacer installed.
  It weighs 30lbs,14.4oz
Next, I weighed my 17x5.5 FZR1000 EXUP wheel with a brand new 180/55-17 Pirelli Angel, and set a spare rear brake rotor on top. new bearings/spacer installed.
  It weighs 35lbs,13.8oz
So I ended up with a 5lb increase in unsprung weight. I didn't have a spare set of rotor bolts, but I imagine they only weigh a couple ounces. After reading your post, I went back and rechecked them again to make sure i didn't reverse my readings when i wrote them down. I didn't include any cush rubbers, cush drive, or sprocket as I figured they would equal out.
Just in case anyone is wondering, a stock rear brake rotor weighs 3lbs,2oz.

Maybe if there was more tread on the Avon, it might have weighed more, but I have no clue how much?




I also measured the circumference of each.
The worn 160/80-16 Avon Azzarro measured 80 inches. with full tread it would probably add an inch or so more.
The brand new 180/55-17 Pirelli Angel measured 78 inches.

So at 60 miles per hour, the old 160/80-16 would be turning 792 rpm's
The new 180/55-17 would be turning a little over 812 rpm's.

Anyway. maybe after machining my cushdrive, and switching to a Galfer wave rotor, I can get closer to the original weight.

[Pat Conlon]

1st, I weighed the original 16" wheel with a severely worn 160/80-16 Avon Azarro, with brake rotor bolted on. Bearings/spacer installed.
 It weighs 30lbs,14.4oz

Hey Alan, if you were to add the FJ cush drive and steel sprocket I wonder if you would get closer to 40-41lb reading I got. Also, the 150/80-16 Dunlop on mine was almost new. You have a more accurate scale than I, but before weighing, I checked my scale with a 20lb hand weight, and the scale read exactly 20.0lbs

Next, I weighed my 17x5.5 FZR1000 EXUP wheel with a brand new 180/55-17 Pirelli Angel, and set a spare rear brake rotor on top. new bearings/spacer installed.  It weighs 35lbs,13.8oz

I do not know the weight difference between my YZF rim and your FZR rim.
I do know that the rear rotor on the YZF is a smaller diameter rotor than the FJ rotor. There is a ~1 lb difference between the oem YZF rotor and the Galfer Wave rotor, and of course a savings with the aluminum vs. steel sprocket.

I stand by my #'s.  Picking up the wheel assemblies by hand, you can feel a weight difference. It's real.

[andyb]

We know that unsprung weight is the best type of weight to remove from our bikes. You can run less preload and thus lower compression/rebound settings on your suspension allowing a faster, smoother response from your suspension.

Actually no, removing weight between the suspension and the ground means no change to the preload at all.  Arguably you'll have less inertia from the moving bits and need added damping rather than less, while you're at it. 

Helps in just about every other part of riding though, so that much is right

[Firehawk068]

I'm sure most of the difference in our two findings are in the wheel itself.
I would guess after I add the cushdrive, and rubbers, and sprocket, I would be right around the 40lbs that you found for the stock setup.
I'm sure your Thunderace wheel is lighter than my Exup wheel.
I don't doubt your numbers, especially since my 16" tire has so much tread missing. It's gotta count for some weight. Maybe not 10 lbs, but some.
and I'm sure a Galfer wave rotor weighs maybe half what an oem does.

[Pat Conlon]

Actually no, removing weight between the suspension and the ground means no change to the preload at all.  Arguably you'll have less inertia from the moving bits and need added damping rather than less, while you're at it. 

Lighter wheel = less inertia; ok I agree, but less inertia = need for more damping?  I disagree.

[andyb]

Lighter wheel = less inertia; ok I agree, but less inertia = need for more damping?  I disagree.

Pfft, you're the one that said it changed the preload

Less inertia between the springs and the ground requires something to staunch their movement, which is what damping is for.  Isn't a requirement, just means things can be tuned farther in that direction.