bearing preload

[Psychosis]

does anyone know how to calculate bearing preload (specifically wheels)? tried books, google and bearing manufacturers websites. im stumped!

cheers

[Jersey Tom]

Try talking to someone in technical sales from your bearing manufacturer?

[terra_dactile]

Hi psychosis,
i am current finishing an 8 month cooperative session with SKF in Montreal Canada,
preload is difficult to accurately select, in most cases it is commonly known that a slight preload will increase rigidity of the assembly and increase life, up to a certain optimal value, the problem is after this value is reached, any more preload will cause for increased friction and consequently heat which will decrease life exponetialy as it expands under heat and causes more preload, for these reasons most commonly used wheel hubs (Tapered roller bearings), are designed to have a small amount clearance, with a calibrated spacer to ensure that bearing life does not decrease under changing temerature situation. With a small clearance, the life is not at its maximum but it is in a safe range. If you look in any SKF bearing catologue you should see a graph which compares bearing life with either clearance or preload. If you need any more specific answers to you questions, give me a call at work and i will be glad to help you.
Toll Free 1-800-905-5230 EXT 314


Jude Berthault
ETS FSAE 2003-Current
Steering and Brake System Leader
SKF Applications Engineering

[jsmooz]

Jude hit the nail right on the head. Basic rule of thumb on tapers is snug the nut then go a little more, maybe 1/8 turn. (That's the mechanic in me.) Everything should spin for a while and slowly come to a stop. We (SAE teams) don't really put enough wear on wheel bearings to have to worry about life.

Jude - I also work for SKF in Michigan at the NATC (Testing Engineer). Nice to see the company recognizes the value of SAE people at other locations too.

[Psychosis]

thanks guys http://fsae.com/groupee_common/emoticons/icon_smile.gif
we're sponsored by INA bearings (no offence to you guys!). our stubs and hubs guy chose a pair of these bearings per wheel:
Double row ina bearing (http://medias.ina.de/medias/en!hp.ec.br.pr/30..-B-2RSR_FAG*3008-B-2RSR-TVH_FAG;aEZii-J0O1Xc)
they're double row, so id think any extra pre-load would result in one row being under more load than the other. hence your snug + 1/8th turn would seem to be spot on Jim. they discontinued the wheel bearing we used last year http://fsae.com/groupee_common/emoticons/icon_frown.gif they were only 160g each rather than 250g.

[jsmooz]

Psychosis - That's pretty much the same thing we use just different brand and slightly different size. You really can't preload this type of bearing by tightening the nut because the rows share a common ring. The way you preload this type of bearing is the interference fit between the OR and housing and/or IR and pressed in journal. If you have to much press fit you can easily see what it does when you try to spin the bearing....it's hard to do.

I usually make our housing a thou or 2 bigger than the bearing OD and our journal is purchased and slides right into the ID. Doesn't result in much preload but the bearing is kinda already in preload as assembled. But this then gets back to the "we don't drive enough to wear out a bearing" statement.

[Psychosis]

cheers man, thats a big help and laid my mind to rest. ive always been used to putting back together road cars where correct bearing preload is pretty important, but as you say the units are kinda preloaded at manufacture so i just need to make sure theres no play.

thanks again

[jsmooz]

You hit the nail in the head. Glad to see that my work knowledge is being used on SAE stuff. Usually it's the other way around. http://fsae.com/groupee_common/emoticons/icon_smile.gif