Topic: Hollow axles?

[Franken750]

Hi All.

Has anyone used, or know of, hollow axles on/for 750's?

Better still, are there any alloy axles in use anywhere (suitably heat treated grade of alloy of course)?

This is to further reduce unsprung weight on my FrankenBike.

Cheers

Franken.

[bwaller]

TTR400 offers 20mm hollow axles in SS for sale. I have one on my race bike.

[Steve_K]

Hollow axles are possible if care is taken for strength considerations.  Note that most hollow axles have larger diameters than in the CBs.  They do look cool.
Steve

[Franken750]

Thanks for the replies guys.

My '72 XL250 (in '73) had a hollow (large dia) rear axle. By the time I'd changed to a lighter hub and replaced all the steel spacers, adjusters etc with alloy ones, plus a duralumin sprocket, the rear wheel was 8lb lighter. The improvement in traction on choppy surfaces was mind blowing.

Cheers

Franken.

[HondaMan]

To go whole hog...have someone gun-drill the OEM axles 50%, then get them heat-treated to 45 RC. It almost doubles their strength!

[jaguar]

To go whole hog...have someone gun-drill the OEM axles 50%, then get them heat-treated to 45 RC. It almost doubles their strength!

Really?

[crazypj]

Yep, really
 Axles are mainly in shear (particularly if you have a good fork brace)
Probably easier to visualise if you think about stress 'lines' going through axle section
 With solid axle, stress can go in a straight line through it.
 If you gun drill and ream (or polish, needs to be smooth inside) stress 'lines' have to go 'around' center hole and, in effect, travel further

[70CB750]

Heat treated means heat up and cool down rapidly? Like a knife only not that hard?

[BobbyR]

I think a few weeks on Ultra Slim Fast will save more weight when you are on the bike that messing with the axle.

[Rigid]

Heat treated means heat up and cool down rapidly? Like a knife only not that hard?

Maybe,  heat treating is a science, temperatures are varied, time at specific temperatures are varied, cooling is very tightly controlled to obtain specific desired metal properties.  The same alloy can be soft, brittle, ductile, etc... based upon its heat treatment.  Much research would be required to do an axle correctly for a first timer.  The nice thing about hollow axles is if you find yourself in a fire fight, you can safely look through the axle while hiding behind the bike.  Just one of the many benefits.  maybe it would be better, as mentioned above, to slim the wasteline about 2 lbs.   

[Retro Rocket]

I think a few weeks on Ultra Slim Fast will save more weight when you are on the bike that messing with the axle.

Not necessarily so my man, its the unsprung weight thats important, wheels, swingarm, brakes and all parts below the suspension, lightening these parts will help a lot in the way a bike's suspension works....

[70CB750]

I was just making sure I understand right. I had several semesters of metalurgy in college - Typicaly the material and treatment is prescribed by the designer, hollowing and treating existing part is probably based on some empirical knowledge.
Also the steel is either created for the heat treating, or Carbon or Nitrogen has to be difused in it to allow additional hardening.

[bwaller]

Granted it may not seem like much weight on a street bike considering all the other factors. Just for the info, on my race bike the hollow rear axle is 1.75 lbs lighter. I didn't record the front but even at 20mm diameter it was also very significant.

[BobbyR]

I think a few weeks on Ultra Slim Fast will save more weight when you are on the bike that messing with the axle.

Not necessarily so my man, its the unsprung weight thats important, wheels, swingarm, brakes and all parts below the suspension, lightening these parts will help a lot in the way a bike's suspension works....

Granted, what does a stock axle weigh?

[scottly]

K1 750 front axle, with nut= 285.4 grams
K7 750 front axle, with nut= 311.5 grams
(compulsive calorie counter  )

[70CB750]

I remember from my windsurfing days that one kilo off the board is worth 5 kilos of the windsurfer -  means, I guess, that dead weight is more significant.

[scottly]

Just for the info, on my race bike the hollow rear axle is 1.75 lbs lighter.

A stock K7 750 rear axle weighs 794.4 grams (1.7513 lbs).

[BobbyR]

Just for the info, on my race bike the hollow rear axle is 1.75 lbs lighter.

A stock K7 750 rear axle weighs 794.4 grams (1.7513 lbs).

So, if that is correct you could save 1/2 lb at most. I will keep my opinion on Slimfast. 

[scottly]

I will keep my opinion on Slimfast. 

Feeling chubby these days Bobby? Putting on fat for the coming winter?

[BobbyR]

I will keep my opinion on Slimfast. 

Feeling chubby these days Bobby? Putting on fat for the coming winter?

Yeah, I could add a lot of HP to my 750 if I dropped a few. A few 10's 

[scottly]

If I dropped a few 10's, there wouldn't be much left of me, just like if Brent actually dropped 1.75 lbs from a rear axle.

[bwaller]

Now I realise this is getting trivial, but I feel like I need to defend my honor.  Long story short it seems I have embellished the numbers however and couldn't live with myself without a correction.

The stock 78 550 rear axle/axle spacers/CB350 steel bearing spacer (using 350 rear hub) is 1219grams. Hollow axle/alloy axle spacers/ replacement alloy bearing spacer is 590grams. So 629g's or just under 1.4lbs. Not even apples to apples, but for arguments sake.

The 78 CB550 front axle and spacer is 381grams vs the 20mm hollow axle @430. But considering the smaller ID wheel bearings and alloy bearing spacer it'll be a wash, but have a much stronger axle in the end.

There, now I can sleep at night!  On the street hardly worth the effort, but some of us can't leave well enough alone.

[scottly]

There, now I can sleep at night!  On the street hardly worth the effort, but some of us can't leave well enough alone.

Sorry if I kept you up last night! Still every gram adds up, and I can attest that a 401 pound (no fuel) 836 is a bit of fun on the street, compared to when the same bike weighed about 70 pounds more.

[crazypj]

There are newer bikes using hollow axles of smaller diameter.
 Check out some of the MX bikes from 1995~ on.
 You'll probably find rear axles and swing arm pivots in correct diameters.
 I have a couple 17mm diameter but can't remember where I got it or what bike it's out of? 
 One is  front axle, about 8.5" un-threaded, the other 12.5" un-threaded with about an inch of threads plus the bolt head on the other end.
 I think they may possibly be out of Suzuki RM's

[scottly]

Good call, PJ. My '82 Honda CR480 has a hollow axle. Not sure about the diameter where it meets the races, but the threaded end looks to be 18mm. It's about 13" over all in length.
Franken, the stock rear 750 wheel, with the drum brake and steel sprocket is very heavy. My rear wheel is quite a bit lighter than a stock one, but I won't say how much, since I don't recall exactly. Lets just say it was in pounds, not grams..