Hub Carriers

[StuartBowes]

hi all, I'm not actually a Caterham owner, I'm currently trying to design a full spaceframe to suit my mini, FR layout, Vauxhall redtop 2ltr

anyway, long story short I need to work out what Hub Carriers I'm going to use, to know what the geometrics of my wishbones are going to be, so here's my query;

what hub carriers do caterhams use, and if anyone is in the garage tonight and has a tape measure to hand, would they be so kind as to measure the distance from the top mount to the bottom mount please? Ideally a picture would be awesome as well, or a link to one somewhere else on here, I've tried googling etc but not knowing what brand of hub carrier I'm actually looking for is restricting me somewhat!

that's all, Thanks

[StuartBowes]

as an additional note, just to get the ball rolling I measured my boss' F4 hub carrier and found that it was 220mm, top to bottom

but also, when viewed from above, the upper mount was actually set in towards the center of the car by about 30mm, and the steering bracket was level with that, if you see what I mean.. presumably to move it in slightly to clear the wheel. if that is the case a +/- 10mm estimation of that distance would also be awesome

Cheers

[TheLastPost]

StuartBowes said:

...to know what the geometrics of my wishbones are going to be...

...what hub carriers do caterhams use, and if anyone is in the garage tonight and has a tape measure to hand, would they be so kind as to measure the distance from the top mount to the bottom mount please?

'Normal' Caterhams have de Dion rear suspension, so don't have hub carriers with top and bottom pickups suitable for double wishbone IRS. The actual bearing carrier is Ford Sierra, I think, but it's bolted to a machined alloy plate that forms the 'ears' of the de Dion axle.

The Caterham CSR uses a (very expensive) custom upright to Caterham's design. I doubt you'll find accurate dimensions for it without buying and measuring one yourself.

Front suspension on both cars uses a modified version of the old Triumph upright (modified to use a spherical bearing at the bottom instead of the trunnion on the original).

I'd suggest that if you're looking for a rear upright/hub carrier for your project, you'd be better off getting a copy of the Haynes Roadster 'build yourself a sportscar' book and creating a fabricated steel upright similar to the one shown in the book (which also utilises the Ford Sierra bearing carriers). Other cheap and readily available options you might want to consider include the Mazda MX5 (CAD files for the uprights on which are available for free download on the internet, if you hunt around).

[StuartBowes]

brilliant, thanks for that, very helpful. to be honest I just assumed the Caterham had double wishbones all round, obviously not then..

I will get me a copy of that book then, I've seen it on sale and often thought it looked interesting, thanks for the suggestion

if anyone else knows of a carrier that is suitable for double wishbones or that is commonly converted as such, please feel free to chip in, but it sounds like I have the answer I need

Cheers

[StuartBowes]

also in terms of front /rear, I was planning to use identical bits front and back, only at the back I'd turn them the other way and use the steering arms to connect adjustable rods to the upper wishbones, should mean adjustable toe and ease of replacing parts etc

[TheLastPost]

StuartBowes said:

also in terms of front /rear, I was planning to use identical bits front and back, only got the back I'd turn them the other way and use the steering arms to connect adjustable rods to the upper wishbones, should mean adjustable toe and ease of replacing parts etc

In that case, you'd probably be looking for front uprights from a front wheel drive car, because you'll need suitable king pin axis/caster/steering arm geometry to work at the front, but the ability to fit a driveshaft and 'live' stub axle at the back. If you look at the Triumph/Caterham front upright (or the Mazda MX5, or any similar front upright from a RWD car), you'll see that they have a fixed stub axle that forms part of the upright (this is actually a Cortina upright, but they're all the same principle), which carries the bearings that the hub rotates on:



What you want is an upright - preferably from a car that has double wishbone front suspension, though there are ways of adapting the upright from a strut suspension - where the stub axle is 'live' and rotates inside bearings carried by the upright (this is a bare Mini upright):


It's not impossible to use the same uprights and suspension geometry front and rear (several cars have done it with Mini uprights for example - though usually with the Mini engine mounted at the rear; the original GTM kit car used this approach), but it does make life a bit more difficult in terms of getting the basic balance of the car right - you're limiting yourself to having the roll centres at the same height front and rear, for example, whereas normal practice is to have an inclined roll axis as one of the design tools for establishing the basic weight transfer characteristics of the car.



Edited to add: you might be better off asking the Mods to move your thread to either the Kit Cars forum or the Suspension and Drivetrain forum, if you want more detailed advice: the Caterham forum is mainly inhabited by people whose technical knowledge is limited to putting together the automotive equivalent of an Airfix kit (one of the ones suitable for 5-11 year olds).

Edited by TheLastPost on Thursday 7th March 21:35

[StuartBowes]

right yeah of course, the spindle is part of the upright.. d'oh.. I'll have to have another look at the formula4 hub, I was sure it was the same unit front and back, but now thinking about it I need to check exactly how the front wheels stay on lol if I'm right it shouldn't be too hard to fabricate my own carriers, or CAD them and have them made for me... hmmmm

the essential problem with that carrier anyway is clearly they want to minimise ground clearance for open wheel, hence distance from bottom wishbone mount to bearing is quite large, whereas I want to minimise that so I get decent ride height without having wishbone mounts sticking out of the bottom ..

good call re: roll centres, back to the drawing board on that one. glad you pointed that out

this is all one big learning curve for me, at the moment it's all being built in cad, I'm slowly feeding in all the real world dimensions for the parts I'm using, but obviously hub size / wishbone geometry is something I want to get right from the start

anyway, thanks again you've been most helpful

[TheLastPost]

StuartBowes said:

I'll have to have another look at the formula4 hub, I was sure it was the same unit front and back...

It might well be - many race cars (and the Lotus Elise, incidentally) use 'live' stub axles at the front because it gives a slightly better stiffness:weight ratio than a dead stub axle arrangement, but it's quite unusual to find on road cars.

The other thing you get on race cars is the steering rack mounted high up so that the rack ends/track rod ends coincide with the upper wishbone pickups. This arrangement would work with your suggestion that the rear track control arm could be linked to the upper wishbone, but again it's very unusual on a road car upright (and again, the Elise is the only one I know that comes close). Normally on road cars the rack and steering arm are mounted lower, and in this case you'd need separate track control arms, whose chassis pickups replicated the position of the steering rack ends at the front, otherwise you'll get horrendous bump steer.

[StuartBowes]

that's an interesting point that's been baffling me somewhat, what with the engine placement and where the axle line needs to sit, I can get the rack at the right height easy enough but the track rods would be raked backward at a severe angle that I assume will limit their effectiveness..

has anyone ever used a steering rack via a pivoting linkage, that way I can have the track rods wherever I want them.. or is that a big no no for some reason? obviously I'd make it nice and beefy so's it don't break..

[TheLastPost]

StuartBowes said:

...has anyone ever used a steering rack via a pivoting linkage, that way I can have the track rods wherever I want them...

I'm not sure what you mean by a 'pivoting linkage', though, yes, fore-and-aft positioning of the steering rack such that you have raked steering arms corrupts the Ackermann geometry. Allan Staniforth covers it in a chapter of the last edition of his book 'Competition Car Suspension', and published an SAE paper on the same topic.

Lotus used a system of bellcranks to transmit the steering around the front of the tub on the Lotus 63 (though it still had track rods that raked steeply backwards) but I think what you would gain in improved Ackermann geometry, you'd lose in extra play in the linkages.

To be honest, I don't worry too much about perfect Ackermann geometry, anyway, since people have used everything from 100% true Ackermann, via parallel steering, to Anti-Ackermann (where the outside wheel turns at a sharper angle than the inside) over the years and there has been no conclusive evidence to show that one way has a substantial advantage (other than parallel/anti-Ackermann makes your tyres squeal when tightly manoeuvring round car parks at low speed) .

If you're trying to package a longitudinal front engine into a Mini bodyshell, you'll certainly struggle - I imagine you'll have to select an upright that has the steering arms running forward rather than rearwards and then just make the best of it with fore-aft rack location.

Out of interest, why are you making life difficult for yourself with a FR engine installation, rather than going for MR?

[StuartBowes]

good question, I did actually start that way but for various reasons found it nigh on impossible to make everything fit. with my limited abilities, of course, but in struggling to find a solution I realised that weight-wise the balance would be way off unless you made it literally mid engined in which case where do you sit? then you're into moving the bulkhead forward which isn't impossible of course but would be awkward to get in and out of. plus RWD this thing is just going to be a total animal what with 185bhp on tap and a very short wheelbase, I realised that I don't think I have the driving skills to keep it on the road and out of the nearest hedge. not yet, at least..

anyway so that's basically it, for weight distribution, mainly, but also for safety. bearing in mind a rear end shunt or spinning into a tyrewall backwards at high speed would mean an engine in the back.. thought at least if it's FR then a front smash will drive the engine backwards but hopefully between the two seats, if you see what I mean.

this has been on the drawing board for years but now I'm starting to really take the cad seriously with accurate measurements from my shell, and engine etc, some of these little problems are coming to light now which thankfully is all well before the build stage therefore hopefully when I make it it might actually work! lol fingers crossed

[StuartBowes]

I suppose I really need to think does it have to be that engine, why not bike or wankel .. that is being considered but I do love the red top's raw power good revving and awesome noise

[StuartBowes]

small update, if anyone was interested, it seems VX220 hubs are the ones to go for:

http://www.elise-shop.com/images/large/A116C0002F-...

something like that, it seems, although for some reason the link suggests they are Elise hubs :$ confusing.. yet to get to the bottom of that, but that's generally the sort of size I'm looking for

thanks again for your help though mate, some really interesting thoughts provoked up there ^^ much appreciated

[Farlig]

http://www.palatov.com/products/suspension.html

Posting from iPhone so can't be bothered making a linky...

[StuartBowes]

ooo even better! cheers, I'll have a look into that