Pros/Cons of different wheel hub designs?

[Tim G.]

Hey guys,

I'm curious as to why one would want to use a fixed (bearings are attached to upright and hub spins inside them) vs. non-fixed (bearings are attached to the hub and spin around the spindle) hub design?

What are the pros and cons of each design in your opinion?

Thanks

[Tim G.]

Hey guys,

I'm curious as to why one would want to use a fixed (bearings are attached to upright and hub spins inside them) vs. non-fixed (bearings are attached to the hub and spin around the spindle) hub design?

What are the pros and cons of each design in your opinion?

Thanks

[RacingManiac]

from our experience, at least with the hub in the upright design, we were able to make stiffer upright/hub combo due to the better installation stiffness without gaining too much weight as the upright is more optimized in geometry.

[Marshall Grice]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">from our experience, at least with the hub in the upright design, we were able to make stiffer upright/hub combo due to the better installation stiffness without gaining too much weight as the upright is more optimized in geometry. </div></BLOCKQUOTE>

what exactly does "hub in upright design" mean?

live spindle or fixed spindle?

[John Grego]

A couple times now we've broken spindles and lost wheels while running....should tell you how we feel about em

[Matt N]

As far as maximizing stiffness, whichever solution offers the largest diameter at the smallest corner/radii will be stiffer (from your moment of inertia calculations). The live spindle solution offers this. As far as avoiding ultimate failure that TA&M describes above, make sure that your wall thicknesses and treatment of stress risers (fillet from spindle into upright...) is reasonable for the forces involved.

If you are really good at designing multitasking parts, you can design so that the tripod joints run inside of the rear live spindles, and do away with a handful of parts (and joints between them). This was seen on many cars this past year. Wisconsin, TU Graz, TU Fast, I'm sure there are more.

Matt

[Brett Neale]

Our reasons for running a full live spindle is modularity and weight. The spindles are the same front to rear (CV housing mounts and all), and the spindle can be made with a smaller wall thickness by relocating the brake disc to the inboard side of the upright, which reduces space between the upright and wheel center, hence reducing bending loads on the spindle. We also have the CV housings completely inside the upright on the rear, which helps out with reducing our close-to-marginal driveshaft angle.

All these things we couldn't have done with a fixed spindle.

[SR-Mike]

To give a balanced debate some cons for the live spindle design are –

* Potentially higher wheel assembly moment of inertia as you have at least one more rotating component
* More complex, more expensive and possibly heavier upright

It is difficult to compare the mass of the 2 set-ups as the component packaging requirements are so different but I would guess that a higher stiffness/system mass ratio could be achieved with a live spindle design. Although I'm all for simplicity and ease of manufacture so I wouldn't completely rule out the dead spindle option.

Mike
Strathclyde Uni 02-06

[Christopher Catto]

At UH I think the past 2-3 cars had fixed spindle at the front. While this was strong enough, the 2004-05 car had a monolithic hub so that the brake disc and wheel were mounted through the same studs. This part was a bit expensive to machine out of alum alloy. Previous designs had hubs with two mounting faces but no reinforcement between the two faces and also different bolts: more weight and bolts were held by a thin portion of material hence prone to bending since no studs were present and wheel torque was reacted by the bolts (bad but ok in the front wheels)

In hindsight I think a rotating shaft would have been a better solution. Most production cars have a fixed spindle and taper roller bearings because this is a cheap solution and bearings can be easily replaced and the pressure on them adjusted via the nut on the spindle. Most formula cars (including F1) have rotating shaft/hub. However, decisions in FSAE cars must be appropriate to the function, not just to follow motorsport trends or fashions.

I would say wheel deflection is more to do with bearing stiffness. Sure, if the bearings are inside the upright and well spaced apart this should be stiffer. Bearing type, fit tolerance and other params are quite important. Again at UH, some students in 05-06-07 have tested the stiffness simply by putting a long bar mounted to the hub and pushing on it. Simple test that can be done on all your past cars. You can write some reports on this if a team member is interested in instalation stiffness of suspension components. Sort of stuff Claude likes to know that you have improved from year to year to get your slip angles as accurate as possible (etc etc.)

I have noticed at work now that the rear bearings of our sportscar are much weaker than the toe geometry (we have a good toe link installation). a bit disappointing really after having designed an manufactured some really nice uprights and wishbones. its nice that in FSAE you can use whatever bearings you wish so long as they are not hugely expensive. in the real world of making and selling, the type of bearings, their price, and the way they fit to an existing OEM hub (number of studs and PCD) is of paramount importance.

I would personally go for rotating shaft inside the upright. It makes your upright quite light if you have big diameter bearings because you will have a great big hole in the centre of the upright. this then makes it easy to make a design with webs (or ribs depending on how you call them) that joint to the brake calliper mount.

About the bending moment, I think for outboard brakes this is dictated by the depth of the calliper rather than anything else. I dont understand why spindle or not would make a difference of more than a few mm. I would personally never have brakes inboard of the uprights because the discs will be smaller in diameter and the gains are small. You will just need to stamp on the brake pedal harder or have softer pad compound. How many cars have inboard brakes? And guess why? Design is always a compromise between ultimate performance and common sense. Common sense says to me that good brakes are better than a few Nm of bending moment.

[Drew Price]

Remember that brake rotors placed inboard of the upright will likely be easier to keep cooler than ones buried inside of the wheels....

Probably most important at West (ambient was around 105*F/41*C all weekend).

Best,
Drew

[Christopher Catto]

any temps or comparisons between teams/cars to confirm this??

theoretically maybe but practically with wheels with multispokes I doubt the difference is much. for 10" disc wheels I can see there would be a difference.

i guess you mean that the discs are more in the airstream during driving. thats possibly true although the aero around wheels and brakes is a bit complex.

[RacingManiac]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Marshall Grice:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">from our experience, at least with the hub in the upright design, we were able to make stiffer upright/hub combo due to the better installation stiffness without gaining too much weight as the upright is more optimized in geometry. </div></BLOCKQUOTE>

what exactly does "hub in upright design" mean?

live spindle or fixed spindle? </div></BLOCKQUOTE>

Sorry, live spindle is what I meant, similar to what Brett mentioned about their car, we use homologated CNC steel hubs on all 4 wheels(with CV feature and whatnot). Each riding on 2 preloaded deepgroove ball bearings spaced ~1.5" apart(inside edge to inside edge). Uprights themselves are hollowed steel weldment. I think the overall assembly(on the front at least, as this was the only end on the car that had fixed spindle design back in 2003) is heavier compare to the fixed design(also with steel weldment, but was basically a 1.5" x 1.5" stock tube dimension, with aluminum hub), but is definitely stiffer as the drivers and engineer can notice the setup changes better(and driver are not complaining of seeing the upright deflect). Would've gone to a aluminum hub(which would bring the weight pretty close) if we don't have concern over wear(as we've had in 2005), or if we have enough budget to have several sets of spares...

[Drew Price]

Christopher,

Carroll Smith discusses it a fair bit in 'Tune.' Our rotors are obviously much thinner than what the information is meant for, and we likely do not build up nearly as much heat due to our confined track space, but I think the point is still valid.

Will it necessarily have a negative effect on performance? I can't say, I was just pointing out pros/cons.

Depending on wheel design, with the rotor buried in the wheel the inboard side will receive more cooling air than the side in the wheel, and you will have a nice gradient across the width of the wheel.

Mr. Smith also gives us a drawing of a nice little ventilation housing oin 'Tune' (I will get the page # when I get home) that mounts around the rotor, sort of like a caliper, that feeds cool air to the rotor via a duct, and scrapes the heated boundary layer away from the surface of the rotor. Inboard diff-mounted rotors on the rear would be the application we see that I think would benefit the most.

We use nearly solid centered Al wheels with round slots around the outer circumference like older circle track cars, so for us I feel it is an issue.

Best,
Drew

[Christopher Catto]

hmm.

if you have a guy who is not too keen on building the car but is into fiddling around and doing r&d (assumes a big-ish uni with some cash) then I would recommend

buing a 2kw (?) electric motor
fitting a wheel with hub and brake rotor
heating the rotor in an oven (really hot!!)
pointing a big fan onto the wheel
varying the offset of the rotor
checking temperature dissipation

Has anyone ever done this? Are any unis organized enough to do this kind of work, maybe in july august time before commencing design. I know at my uni we were never really that close to old teams to plan seamless development.

I am interested in opinions on this. Brake cooling. I will search old posts