40mm or 50mm Rear Axle

I didn't interpret the question that way.
I thought he was asking if you had the wheels the same distance from the cassette bearing but you had a different hub that allowed a longer axle to protrude out another inch or so how would that affect how the axle works?
 
The question is how wide are you running the rear with your current axle and if you put in an axle at 960 would the hub hang off the end. If so there would be handling difference. If not it will be the same. I know much of Canada has a 50" max width rule so a 960 axle likely would have the hub hanging off.
 
FYI, for WKA Gold Cup (4 cycle sprint racing) the maximum overall width is 55 1/8", with 7.10 rears.

For road racing with a CIK style chassis it's 50" minimum and 55 1/8" maximum. Also for the CIK LO206 Sprint class in road racing we must run 7" minimum width rear tires.

Back on subject...we road race and it doesn't seem to matter much whether you run a 40 or 50 mm axle. But for sprint racing, I'd go with the 40. I road raced a TopKart with a 50 mm axle and my Son's Ignite has a 40, both with 206's. The Ignite rolled a "bit" freer through the turns. So I'd suspect for sprints the 40 might be a little freer. I'm no expert by any means, but I don't know of any North American made 4 cycle CIK style chassis' made with a 50 mm axle. It just seems for the low HP stuff, the 40 makes more sense. Of course other chassis setup spec's will make a huge difference too.

Many of you know much better the me...these are just my observations.
Good discussion,
Clark Gaynor Sr.
 
A 50mm will be inherently stiffer than a 40mm, but potentially more fragile (thinner wall for same stiffness). I just get annoyed with the 50's that the hub is no longer able to slide in past its' own width. (The axle dia. is close to the bolt circle, so they can't slide further in.) Loss of tuning. It seems the prevailing theory with the 50mm is that they'll leave the width alone, and affect the rate of lift and timing by adjusting front end geometry. If a big swing is needed in tuning, they'll swap axle. This is different than the philosophy I use with the 35 / 40mm axles where I'll slide the fronts in until I get the balance F/R I want, then both sets in until it bicycles and then edge back out. It seems the modern high HP sprint Euro chassis like a relatively stable untouched rear, then use the front geometry to tune... But I could be wrong.
 
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