Rear wheel weight, drum vs disc (my XS 650)

[Dvsrd]

Not my RD350, but definitely related and applicable, if scaled appropriately.

My stock 2.15x18 77 XS650 rear spoke/drum brake wheel, with axle, adjusters and a 60% worn Pirelli MT60 120/80 weighs 17.35 kg.
My 2.50x18 wheel for the XS, with a Talon MX hub, a 250 mm disc, Brembo caliper, caliper bracket, axle, adjusters, and a new Avon AM26 120/90 tyre weighs 15.55 kg.

That is 1.8 kg or 4 lbs less unsprung weight, when fitted with a SIGNIFICANTLY heavier tire.
IIRC, the weight difference between these two tires is close to 2 kg, or another 4 lbs.....

So, surely, with a 200 mm-ish disc, one could easily save somewhere between 3 and 5 lbs from an RD rear wheel. And there will be additional weight savings from the brake pedal/pivot as well.

[m in sc]

with a Talon MX hub

^ this makes a difference.

I went from xs400 mags (same as daytona) to spoked RD hubs front and rear, same exact discs as were on the cast wheels. But went with wider rims, and tires which added a LOT of weight i saved, so it about washed out.

on the lightweight, the drum assembly stock rd wheel vs mag was on par with a mag, actually a bit lighter, but used rearsets and simple linkage. .02

[Dvsrd]

Yes, the weight savings is definitely due to the Talon hub. It is for a KTM500 MXer, and for the same 20mm axle diameter as the XS.
And neither the stock XS hub nor the Talon hub have a cush drive.

If I found a cush drive disc brake hub from a smaller MXer, I'd definitely would be tempted to convert my RD to rear disc brake.
In the meantime, I will convert the stock drum into cable actuation. I just ordered a cable for a 75 KX 400 from Venhill in the UK, outer sheath length for this cable is 480 mm. That will allow both TR3 style setup, and a lower cable run  as well.
Will work out the exact details when I get the cable. Then I can make some lightweight muffler brackets to replace the stock setup, and save some weight that way. Passenger pegs are not very useful on an RD with rearsets anyway.......

[m in sc]

thats why i went with nicks rear-set setup.
i found that there was no weight-savings gain going cable from a rod with a direct rod to the rearset linkage (not the heavy stock stuff).

I do like cable rear brakes though. look for small kawasaki triple cables, s1/s2. pre made and good length. .02

[Czakky]

FWIW my XS-1 front drum wheel w/fresh Avon Roadrider weighed 28.5lbs. I'd be interested to hear what an RD350 front wheel weighed.

[1976RD400C]

FWIW my XS-1 front drum wheel w/fresh Avon Roadrider weighed 28.5lbs. I'd be interested to hear what an RD350 front wheel weighed.

I just weighed a RD350 front wheel with brake disc, tire, bearings, no axle       23 pounds

[m in sc]

Thy aluminum hooped rd one on mine was def well under that, i have the weights somewhere i think. the fzr rotor helped as well.  .02
i think it was int he 18-19 lb range but i could be way off.

[Dvsrd]

Thy aluminum hooped rd one on mine was def well under that, i have the weights somewhere i think. the fzr rotor helped as well.  .02
i think it was int he 18-19 lb range but i could be way off.

Yes, that stock rotor is 7 mm thick, so very heavy. Modern discs are mostly 4 or 5 mm thick.

[Czakky]

Plus a caliper... either way I always wondered what the weight difference would be.

Thanks

[m in sc]

i think in my lightweight the front brake differences wound up being over 4lbs alone.

another reason i went with drum on the back was no sub 250 lbs street bike needs a rear disc, sorry. 

[1976RD400C]

Just because I had one laying around:  RD350 front wheel with drum brake, everything but the axle (wheel, tire, brakes shoes and backing plate in the wheel, arms and linkage)    21 pounds

[m in sc]

rear wheel? you said drum. 

[1976RD400C]

rear wheel? you said drum. 

Oops, 1973 RD250 front. Was it called a RD then?

[m in sc]

if it's an rd front drum, and north america market, its 73 or 74 250. or ds7 or r5.

[Dvsrd]

Just weighed a bone stock front wheel with equally bone stock and undrilled disc, from my 1974 RD350A.  The tire is a less than half worn Conti 112 in 3.00-18.
10.75 kg or 23.7 Lbs. Without axle and speedo drive.

Currently I have a drilled stock disc and shouldered Akront 1.60 alloy rim on the front wheel I'm using. It may be 0.5 kg or 1 pound lighter at best. For unsprung weight reduction, the caliper and the fender is where I have lost most weight.