Front Hub Load Input and Modeling
Front Hub Load Input and Modeling
(OP)
Would anyone care to share what they know about loading of automotive hubs for front suspension applications? I am interested in knowing if anyone has done testing during racing condition to see what sort of load spikes can be expected when a driver decides to drive over the berms during corner entrance and exit.
There are at least 3 types of loads seen by a hub: thrust, moment load from the tire gripping the ground, and radial load from the normal force on the tire surface from static weight and weight transfer. Obviously tire stiffness plays a significant role when impact loading is considered so, for conversion's stake, lets assume we are dealing with 35-40 series tires on 17 or 18" wheels. If anyone has any metrology data they are willing to share or out put from an ADAMS model I would be most appreciative. Thanks in advance.
-Joest
There are at least 3 types of loads seen by a hub: thrust, moment load from the tire gripping the ground, and radial load from the normal force on the tire surface from static weight and weight transfer. Obviously tire stiffness plays a significant role when impact loading is considered so, for conversion's stake, lets assume we are dealing with 35-40 series tires on 17 or 18" wheels. If anyone has any metrology data they are willing to share or out put from an ADAMS model I would be most appreciative. Thanks in advance.
-Joest
RE: Front Hub Load Input and Modeling
on a few designs ive done ive used 4g from a bump during cornering.
Also dont forget about brake loads, and also to a lesser extend acceleration.
Jakub
RE: Front Hub Load Input and Modeling
Thanks, that's a good start. I've seen 3-5g quoted elswhere. How about lateral loading? As you probably know, the moment load on the bearing caused by a lateral force at the tire contact patch is the largest hurdle. Assuming full weight transfer of a heavy car (> 3000lb), a 275/40/17 tire, and 1g cornering, the lateral force can be as much as 1300-1500lbf, hence moment = rolling radius X lateral force = 12.5" x 1500lbf = 18750 in-lbf. I'm curious to know if this can spike higher such as when a driver curbs the outside tire on a berms such as that typically used on circuits to keep cars off the edges of the pavement.
Cheers,
-Joest
RE: Front Hub Load Input and Modeling
RE: Front Hub Load Input and Modeling
Thanks for sharing some of your experiences. They are useful. I'm pretty sure that the load is kept within reason since the tire sidewall has give to it. I wouldn't expect it to be more than 0.5g increase lateral. We discuss many topics here on Eng-Tips, but often it is difficult to get specifics on the subtleties of suspension metrology data.
-Joest
RE: Front Hub Load Input and Modeling
If you mount the inside kerb, the wheel is already partly unloaded, so the loading in any but vertical planes is irrelevant.
If you ride up the outside kerb while sliding towards, the wheel alredy is loaded, and the maximum side and vertical loads that can be applied on a smooth surface will already be there. The extra traction obtained by both the vertical acceleration of the wheel, and the raising of that corner of the car relative to the other side, will have a substantial effect on both vertical and lateral loads
eng-tips, by professional engineers for professional engineers
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Front Hub Load Input and Modeling
for a kerb strike, 4g lateral.
for a bump or pothole, 3g longatudinal at effected wheel and 4g vertical.
These are more for consumer cars, not race cars, but it may give an idea. There was a post on here recently discussing suspension design and loadings for testing and how long it would last under those loadings, might try a search for that. It was along the lines of 3,2,1 which i assume is 3g bump, 2g corner, 1g longitudinal (although i would put more longitudinal), again production cars not race.
Jakub
RE: Front Hub Load Input and Modeling
I picked up 3-2-1 for designing suspensions from two people who have designed a lot of suspensions- both for road and race cars. I suspect this means it is actually a bit excessive for race cars.
The peak loads for kerb strike, sqaure edge pot-hole and chuck hole events are also very event specific - hitting a 5 inch kerb square on will typically rip the suspension off after four goes, whereas a 2 inch step will be hit several hundred times during a standard durability test, with no significant effect.
I'd happily use 3-2-1 for bearing loads, but might want to get a bit cleverer if trying to optimise aluminium arms and things like that.
Cheers
Greg Locock