Topic: Wheels weight optimization

[aminemed]

Hi everyone

I'm looking for weight reduction for my CB 750 K2 and was wondering if anyone has an idea of the weight of stock wheel rim. I would like to know how much moving to an alu rim would save vs keeping stock.

What about the rear rotor ? any idea of its weight ? would drilling holes into it reduce some weight ? can also rear Hub be swapped for a lighter one ? Any ideas are more than welcome

thank you for your help

[slikwilli420]

You can get a general idea by looking at the weight difference of steel vs aluminum via a factor. Don't quote me, but aluminum is something like half the weight of steel.

As to rotors, the rotors on our bikes are ridiculously heavy and lots can be done to slim them down. The best method is to have the rotor thinned, then drilled. The drilling won't save a ton of weight but will make the rotor work more efficiently. Its in the thinning that weight is really saved.

If you goal is reducing unsprung weight, hollow axles help and are stronger than solid ones. Our bikes have heavy antiquated brakes as well so there is room for improvement there as well.

The rear swinger is steel and pretty heavy so replacing with an aluminum one would help.

[aminemed]

steel vs aluminum is about 2.5 times (from Internet). Do you have an idea of the stock wheel rim weight ?

As for the rear swinger, I guess the cost of changing it is quite expensive I guess, right ?

[Don R]

 Aluminum rims aren't usually inexpensive either.  The cb750A came with aluminum rims and should bolt on your bike. I got one that's 17" in the rear for my dragbike project.

[aminemed]

what inexpensive options do I have ?

[slikwilli420]

None. Go fast parts cost money. Aluminum rims are around $200 a piece or more and spokes are $100 per wheel. Then having it all put together, trued, balanced, bands, tubes, tires. You could get to a grand pretty easy.

Thinning rotors is done with specialized equipment and costs $80 or so per rotor, plus drilling if you don't have a drill press.

Replacing stock components with lighter ones is not for the faint of heart or wallet. A swingarm that is appreciably light will set you back $600 or so unless you adapt something else, but that takes machining and fabrication skills that if you don't have, will need to pay for.

[evanphi]

Aluminum rims aren't usually inexpensive either.  The cb750A came with aluminum rims and should bolt on your bike. I got one that's 17" in the rear for my dragbike project.

I have them on mine, too. Front and rear.

[754]

 Mags are sometimes cheaper than new rims, but may need adapting. some mags like lester are not superlight, and due to demand tend to be pricey...they are however bolton..

[Kickstart]

I actually just measured the weight of my stock rear steel rim compared to my new excel aluminum shoulder rim two weeks ago.  It's not apple to apples as I got a wider aluminum rim (18 x 2.5 vs. the stock 18 x.215 steel rim), but it gives you a general idea.

Not super accurate, but I hopped on the scale holding the steel rim, and then hopped on holding the aluminum rim: total weight savings was 1.8lbs. 

I know, I thought it would be more.  I assume you'd save a little more weight if you stick with the stock size... maybe a little more if you get the non-shouldered rims... not sure?  But, I wouldn't expect a huge weight savings - I'm guessing 2-3 lbs savings max.

All that said, saving 2lbs of rotational mass around a 18" diameter is pretty significant.

[aminemed]

2lbs in comparison to the amount invested is not much I know that the stock wheel, front or rear is around 40 lbs, alu rim should decrease this number a bit, but what about other solutions? is there a way to drop this to 25 lbs ? I know that some CB 750 are around 400 lbs and part of this weight shaving is coming from some great savings in wheels, but I m not enough experienced to know how

[754]

 Morris mag knocks a lot off Scottly runs them with custom frame and weigjs around 410.

[aminemed]

do the Morris mag equip any modern bike and can therefore be found in used good condition ? is there as well any modern bike direct bolt on ?

Now I'm running 19 in the front and 18 x 450 in the rear..maybe I should start by changing this to 350