Spoke vs Mag Wheel Weights, rotor weights

[Guest]

I just did some weighing while doing some work on my '78 GS750. I have read a lot of posts in the past about whether the stock mags or the stock spoke rims (750 steel rims, not alloy GS 1000) wheels are lighter. I have seen it claimed both ways, some says mags are lighter, some say spokes. Well, I'm here to tell you that the mags are indeed lighter overall. With a naked front wheel, the mags weighed in at 12.4#, spokes at 11.1. Don't forget to add the weight of the tube for the spokes at 1.25#; making the spokes total 12.35#. Pretty much a wash on the front.

For the rear the mags weighed in at 14.8#, and the spokes at 16.6#, plus 1.3# tube for 17.9#. Looks like running stock mags saves nearly 3# on the rear, which surprised me!

For rotors (I have a stock dual rotor setup) the stockers ran 5# ea., while the '80-'82 slotted rotors (front GS750-1000) I swapped in ran 3# 11oz. For the rear, the stock rotor ran 5# 6oz. These are all used rotors but well within spec. Looks like swapping front rotors saved 2.6# of up front in my case.

I know the 80-82 slotted front rotors are a 'bolt on' for the rear rotors on '77-'79 750's, but does anyone run them for the rear on the 8 valve 750's, or is this a no-no?

I'm not a freak for weight, just thought some of you might find the info useful. Happy riding!

 

[postman_pat]

I think part of the confusion between mags and spokes arises because of differences between the castings. For instance, early model (77-79) GS750s have a different, heavier pattern to the later GS1000/GS1100 type. I have magazine articles from the period which mention that the GS1000 and later design was significantly lighter than the preceding cast wheel GS750.

"The front wheel weighs 5.2kg" (Two Wheels magazine, circa 1978). Hahahahaha, yeah right - maybe in the prototype stage it did, not in production form.

There can also be differences between castings of the same design. For instance, you say...

With a naked front wheel, the mags weighed in at 12.4#, spokes at 11.1. Don't forget to add the weight of the tube for the spokes at 1.25#; making the spokes total 12.35#. Pretty much a wash on the front.

Well, a 1980 GS1000 front wheel I found in the shed weighs 5.895kg bare, which is 12.99lbs. Big difference, and that's supposedly two castings of the same design. Incidentally, a supposedly "heavier" GS750 cast wheel from 1978 weighs 5.835kg (12.86lbs). Wait, what? That's the nature of foundry work, I suppose.

I know the 80-82 slotted front rotors are a 'bolt on' for the rear rotors on '77-'79 750's, but does anyone run them for the rear on the 8 valve 750's, or is this a no-no?

They're not really designed for use with twin opposed-piston calipers. From personal experience I've learned they tend to flex...significantly. That's not to say you can't use them there, but just make sure your rear caliper is in perfect working order, and that neither piston is "stuck".

 

[sharpy]

Mag wheels on GS750/1000 unless stated "Tubeless Tyre Applicable" should NEVER be run tubeless. Only the front of the 850 (in Australia) came as tubeless if i recall. I started fitting bike tyres professionally in 76. There are enough things out there trying to kill you besides your own stupidity. The answer that you have run those rims tubeless dont wash with me, EVER. With nearly 30 yrs working in a motorcycle tyre shop make me say this. You at your own risk.

 

[tkent02]

How much lighter are the GS1000 spoked rims than the chromed steel ones on the 750s and 550s? I put the 1000 wire wheels on my 550 but never weighed them first. I don't want to remove the tire to find out. They did feel a lot lighter but that can be deceptive.

 

[tkent02]

Mag wheels on GS750/1000 unless stated "Tubeless Tyre Applicable" should NEVER be run tubeless. Only the front of the 850 (in Australia) came as tubeless if i recall. I started fitting bike tyres professionally in 76. There are enough things out there trying to kill you besides your own stupidity. The answer that you have run those rims tubeless dont wash with me, EVER. With nearly 30 yrs working in a motorcycle tyre shop make me say this. You at your own risk.

Have you seen any of them actually fail from doing this? Or is this a theoretical lesson?

 

[Sandy]

Have you seen any of them actually fail from doing this? Or is this a theoretical lesson?

Not theoretical at all. The safety bead for tubeless tires is there for a reason, to keep the tire bead seated in the event of loss of air or hitting an object like a piece of wood or pothole. You've done a lot of dirt riding and how times have you come back and had to pick stuff out from under the tire bead? If you didn't have a tube that would have been an instant flat. Most of the time you get away with running tubeless on tube type rims but I wouldn't want to have maintain control of a big heavy bike that ran or got run off the road by somebody and then the tire instantly deflated from hitting something like a rock or curb and dislodging the bead. Hard enough to keep it upright in a situation like that, even harder with flat front tire. We are free to make our own choices though.

 

[tkent02]

O k