another question....i know from experience rotating mass from wheel and tire combo makes a huge difference...wondering about the gain from say billet aluminum hubs...it computes to about 2.5 # per wheel....yet thinking about it the rotating mass is at the center not the outside of the wheel tire combo....anyone have any real world experience playing with this?? dyno results maybe. or is the only benefit strength? thanks.
olddog
Another benefit is that cast wheels crack when impacted too hard, but billet will bend. Could be the difference between a flat tire or not.
Those hubs are unsprung weight. Back when I was young I was knee deep in dirt late model cars. I recall talking to a group of the shock experts at a racing conference. Back then one thing they all agreed upon (and not much else) was that taking unsprung weight off of the race car was a big deal. The figure I remember was 1 lb. of unsprung weight off the springs was the equivalent of 10 lbs of sprung weight removed.
So dropping 2.5 lbs off of each corner of the car is a big deal using that theory.
So dropping 2.5 lbs off of each corner of the car is a big deal using that theory.
Even though hubs are unsprung weight but since hubs don't rotate they they are not considered in rotational mass calculations. They count just like sprung weight. Unsprung weight generally applies to all components that are not supported by the suspension which most components do rotate but not all (axle tubes, hubs, brackets, etc.
Items that affect HP via rotational mass are transmission gears and shafts, drive shaft, diff gears, axles, brake rotors, wheels, and tires. This is why wheel HP is always less than engine HP.
Items that affect HP via rotational mass are transmission gears and shafts, drive shaft, diff gears, axles, brake rotors, wheels, and tires. This is why wheel HP is always less than engine HP.
I was considering the hub as the fixed part the axle goes through and that the bearing is pressed in to. I think that may be called the carrier. if you are referring to the part that the brake rotor bolts to you are correct, it rotates.
I think there is an issue here with nomenclature. The hub is the rotating part that the wheel bolts to, the carrier or knuckle is the part that houses the bearings and attaches to the suspension.
Also, any component that is part of the suspension and on out to the tire is unsprung weight. (Shocks are usually a 50/50 split) Anything that rotates with the axle is rotational mass. The further out from the centerline of the axle this mass is, the more it will affect things. I’d be far less concerned about weight in hubs and brake discs than I would in wheels and tires.
Also, any component that is part of the suspension and on out to the tire is unsprung weight. (Shocks are usually a 50/50 split) Anything that rotates with the axle is rotational mass. The further out from the centerline of the axle this mass is, the more it will affect things. I’d be far less concerned about weight in hubs and brake discs than I would in wheels and tires.
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Couldn’t say if it’s worth the $$ but all the sand drag cars in the utv sand outlaw series run aluminum hubs
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Speaking of sprung and unsprung weight. I have a rzr 570, yes the 45hp machine. I had "upgraded" from a stock setup to 27x9x14 setup. I had no idea how heavy everything was, I just wanted 2 inch taller tires to give my machine a bit more ground clearance. After feeling a significant power loss, I upgraded the clutch thinking it was the increased tire diameter. The Dalton kit worked great to breathe in some extra midrange, but top end suffered. I started digging and came across something similar to what's being discussed. The upgrade I had put on weighed close to 62lbs per corner. With a 45hp machine that was a huge deal. I decided to do more research and find a setup that gave me a taller tire but a weight close to stock. The setup I have now, the wheels each weigh 22lbs and each tire weighs 21lbs and measure 26.5 inches tall. Unsprung weight was a few lbs less than stock with almost 2 inches of tire diameter increase. 19lbs off each corner is very significant especially when you don't have ponies to spare. I hit my rev limiter at the same speed I did when it was stock. Dalton clutch now just helps it get there quicker.
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If you look at this like you are taking 10 lbs of unsprung rotating weight then if you are on a quest for losing both then "worth it" is a decision you will have to make. I think the bang for the buck is really on you.
Saving 2.5lbs per hub would not even be noticable as far as power is concerned. Power related to changing tire diameter and weight is significantly different than the rotational mass of a hub. The further away from the center of rotation the greater effect mass will have. Billet hubs are nice upgrade for strength but HP difference no.
To add onto this question I wonder what strength you lose with a carbon drive shaft. They actually recommend I go with a chromoly instead of the carbon for my rock bouncer
Carbon is a great drive shaft option for many applications. But in high repeated shock load applications a steel chromo shaft will normally survive longer. That's probably why they are recommending a chromo. I would check out kb3 for drive line stuff.
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