As per my other posts I’m up to my neck in suspension design, having committed myself to building a, one-off, midi with custom suspension and uprights. Although it has no effect on geometry I do need to finalise the rose joint sizes I’ll use because it has design effects on brackets, wishbones etc.

I’m guessing a finished weight of around 400-450kg and as a two seater it could therefore have a total rolling weight of about 600-650kg. The car will be used on both road and track. Whilst not wanting it to be fragile I don’t want to get sucked into the ship building approach of overbuilding each component because I fear this can just domino through the build i.e. an overly big/strong joint needs equally overly big brackets/tube to accommodate it, keep making these choices and what could be a 400kg car could become a 500kg car.

At one extreme is the likes of Tony Pashley (How to build bike engined race cars) obviously he’s talking about slightly lighter single seaters but these are highly stressed vehicles being used ‘full chat’ on slicks with corresponding suspension loadings. Anyway I digress, he suggests 7/16th of an inch (11mm) on the lower outer (the most highly stressed) and only 5/16th of an inch (8mm) for the least stressed inner upper joints. Despite believing in the maths that say this is strong enough, bigger joints should wear better over time (a consideration for the road)

So I was thinking possibly 12mm (or ½ inch equivalent) for the outer joints and 10mm for the inner joints. I’m happy to pay to get decent quality. The other factor is I’ll probably go metric, I know this will be slightly more expensive.

What are peoples opinions on these choices?

Hi I would speak with mcgill motorsports, they gave me excellent advice and service


http://www.mcgillmotorsports.co.uk/


Tony

+1 for McGill. sizes sound about right, but dont buy their cheapest for susp joints, they are fine for other items (column hanging etc), but they will advise the spec required for susp joints. If poss, standardise the size joints, along with bolts, then its only a case of having a couple of spares 'in stock' if you find any wear particularly badly.

I used 1/2" rose joints on my upper wishbones (used poly bushes on the lowers) and quickly realised that you need some good quality ones, even for gentle road use. My first set failed after a couple of thousand miles but after I replaced them with some high quality ones from McGill Motorsport they seem to be holding up well after 4 years of road use.

I would say that the weight penalty of a larger, stronger rose joint is well worth it unless you really need to save a few grammes.

[Edited on 7-1-11 by RazMan]

quote:

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Originally posted by t16turbotone
Hi I would speak with mcgill motorsports, they gave me excellent advice and service


http://www.mcgillmotorsports.co.uk/


Tony

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I am doing just the same worrying as you. My car is slightly heavier say 900kg and has 750BHP to contend with through 10/14" wide slicks. I am not using threaded joints because it appears impossible to avoid bending loads. I am turning up my own wishbone ends and will use stake in bearings. I have been angsting about sizes and have decided to trust the maths! I am going with 3/8" top and bottom at the inside front. I would have used 5/16 but haven't got any! The outside bottom front has nasty loads for a ball joint so I am probably going to 1/2". Undecided for the rear.

I take your point about wear but there is an obvious trade between the weight and long life of the bearings. I would design for load rather than wear but then treat the bearings as a service item and check them regularly. Mr McGill's prices are such that it is fairly economical to make regular changes.

I would not go metric if I were you. Imperial measurements are still the standard for aircraft so you get a much better choice of sizes. Metric threads are generally coarser than the equivalent UNF sizes. You can buy aircraft quality bolts that can give you the confidence to go smaller and lighter. They are not silly expensive - see LAS Aerospace website (link anybody? Beyond me)- great people.

If you are going more upmarket than McGill try Nick Skidmore's website - he will sell staking tools or do it for you.

If you go with make your own housings look at ADR Engineering - Adrian does great wishbone components and his cars are similar to your specs.

I have bunked off for the day and am off to machine up some wishbone ends!

I certainly can't comment on sizes, but being that the car is not going to be an out nd out race car it would surely make sense to standardise on a single size/spec of joint for the whole car. The weight penalty will be nothing in relation to the overall vehicle weight and easily outweighed by getting bettter prices on bigger volumes of parts including spacers, nuts, bolts and washers. You can then standardise on bracket dimensions as well which all helps as will only having to carry minimal "common" spares for the car.

i used m18 on mine because i wanted them to last more than 5 mins

1/2" outer and 3/8" inner is fairly standard, although most use 1/2" all round for reasons given by nick205.

As long as you dont expect to pay £5 a piece and them to last you'll be okay.

Hi.

Personally i would go for 1/2" x 1/2" all round and sleeve down for smaller bolt sizes on the inner joints. These are the most commonly available size in high quality items and the larger ball size will give a longer life. As mentioned 3/8" is common but on race cars with slicks in the order of 10"R and 8"F they can give roughly a one year life span on a car around the 550 Kg in weight IE Chevron B8's . But that's a car seeing a lot of hard use in endurance racing.
Also remember to use high angle items on the outers to enable full articulation of the upright vertically in movement. And always use a UNF threaded item as it gives far smaller increments of adjustment / more accurate setup compared to a metric equivalent IE a 1/2" UNF thread is 50 tho of adjustment per 1 turn / 25 tho per half turn( i think !! It's getting late ).

Cheers Matt

[Edited on 7/1/11 by procomp]