Quick thought/question… I don’t think we would ever get to the point that we are breaking bearings (may be wrong). My question is more around rotational mass. I think that minimizing this will always help especially in a lower HP kart (206’s) but what’s the return? .025 at best?
People that have the funds, will always turn into weight weenies for an edge. The 500 they will pay for bearings would be better spent on 10 practice days.
Kinda, Yes they will eventually fail likely around 200mph on a kart… However, you will get losses from bearing weight come at higher RPM so on a 206 where max speed might be 70 its a non factor. On a shifter at 125mph its a bigger deal. (50x80 bearing) higher losses on a 40x80 (Larger balls)
Karts are hard on bearings for a few reasons. 1 No preload on the bearing 2. Loaded bearing isn’t square to race its nearly 90 degree loaded into the groove. (Corners) 3. Little tires = Large bearing rpm 4. Leveraged load, like a TQ multiplier the space from bearing to outside of tire is larger then most vehicles. 5. Bearing is single row. Every, car bearing I have ever seen angular contact or Deep Groove is twin row setup.
A rocket scientist (literally) explained to me that the original grease in bearings acts as a shield from dirt intruding into the race. I do not lube either the front bearings or rear bearings on my karts. Solvents, such as the carrier in WD40, dissolve the grease and allow grit to enter. My bearings roll smoothly, without noise, and I’ve been doing this for years in Arizona without failures of any kind. The feed back should be interesting… No flames, please!
Greg,
It is not about just RPM. It is RPM x the running diameter in the bearing. 15,000 RPM for a crank bearing is nothing, as the diameter is small. 15,000 on a 75+ mm diameter machine tool spindle is completely different.
If you are wondering about drag and bearings, do the Engineering math. Remember that energy can not be created / destroyed, just transformed. So if you have bearing drag, what does that energy become?
Noise and HEAT.
OK. So lets say you are utterly convinced that axle bearing drag is slowing you down. Let’s say you conclude it is sucking 0.4 HP. Where is that 0.4 HP of energy going? It is becoming heat. Power is just an energy rate. So convert HP (which is an energy rate) to BTUs per hour (which is a different type of energy rate).
BTU / hour = HP x 2545. 0.4 x 2545 = 1,018 BTU/hour. Which is a bit of heat to be acting right at your bearing races. 0.12 BTUs will raise 1 LB of steel by one degree F. 1,018 BTU/s per hour is .283 BTUs PER SECOND. So if you have 2 LBs of steel in the bearing, and assume it is well insulated…0.4 HP is going to initially heat the bearing by a little more than 1 degree F PER SECOND +/-. Of course the steel in a bearing is not insulated, so it will transfer heat. But it had to develop a differential (get hot) in order to transfer heat. Basically, if your bearings are not noticeably hot…then you are not losing anything measurable to bearing drag.
I recently took Jamie’s advice a splurged on a set of japanese bearings at $169 a set. It was pricey, but holly hell the difference is night and day. I had no idea. I might pick up half a second or more. I used to only get 10 seconds of revolution if I spun it by hand, now I’m getting a solid 60 seconds of spin.
Thanks Jamie.
I bought the last set of Japanese bearings they had in stock. Not to say they cannot get more.
I like your optimism.
Yep, I have done more bearing research and have a background in Tribology. There is something to be gained by bearings but not like most people understand.
A unloaded bearing free spin is absolutely irrelevant to a loaded bearing. I could go into deep dive but basically a quality manufactured all steel bearing is the way to go in 206, with very few exceptions.