top arm angle on very low cars
Turbo Mini Forums

Hi James, I am happy to share the standard cone data as that is data I have measured for myself, to be honest it duplicates data which Robert has already measured, other data I have measured or had measured was at the request and cost of others so I'd need agreement to share but my guess is they'll say no as it's still relevant to any current Historic / Miglia etc running on rubber cones, standard or otherwise.

Measuring the dynamic rate of rubber parts is neither easy or cheap.

The rate I have measured is constant over 25mm of cone compression which exceeds what is used in normal use

The rate measured is the static rate of the cone, that is to say it is typical of the rate below 1Hz (1 loading cycle per second) this rate (averaged over several tests of the same part and several different parts) is just under 3000 lb/in. It will also vary with how we restrict the shape change of the cone.

What I will say is that depending on how 'bumpy' the surface is that we drive or race over it is safe to say that we do not load rubber cones at the static rate (i.e. below 1 Hz) the frequency of input needs to measured and will change track to track and is quite varied. So suspension potentiometers are needed along with a data logger, This is before we consider temperature effects and age etc.... Tracks like Thruxton (Or how it used to be pre 2000) have a much higher frequency input than some of the 'smoother' circuits.

Thanks for sharing! The reason I asked was because I'm trying to find an alternative to the modified rubber cones on the front of my gtm coupe. Due to the front end being a lot lighter, but it seems switching to coilovers might be the way to go!

It's just the practicalities of getting it all in. The knuckle joint doesn't line up with the centre of the cone (well not when using hydro arms), so you need a decent length of hi-lo to make the angle work.

Depends how much you move it I guess.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

mines moved up an inch or so and I retained the rubber cones . hi-lo is shortened loads, and welded a caphead to the rear of the threaded section so now to adjust I use a tool(home made extra long allen key) thro the subrame hole like old hi-los that allowed me to shave away the adjusting nut too.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

That's clever.. Did u use a lock nut

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yeah but IIRC Mine only went up about 30mm or so, with 50mm i dont know if youll squeese a locknut in. had a dig but dont have any pictures of what I did. suppose you could use a grub screw thro the side of the hilo to lock the thread, is a bit sketchy tho, not sure id be too happy about it.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

What sort of front sill line height are cars that run this low?

I've set mine up so that the suspension bottoms out with the belly of the car about 1 1/2 inches off the ground. The ride height will just be set up as low as is reasonable without hitting things.. And without hitting bump stops. Something that'll be experimented with I guess when the cars going. Even with all the stuff moved up when the driveshafts are horizontal the cars not as low as it used to be when I just had it riding on bumpstops.

I cant really comment as im on metro (k series) hubs which have the top balljoint about an inch higher than the mini hubs all things equal, i did it mostly to get back to normal angles my cars not very low atall.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Had a go at measuring and modeling up my suspension geometry today.

Loosely reassembled the subframe, wishbones and wheels at the approximate ride height to get some basic measurements:





Then plotted them into the excel available from here: https://sites.google.com/site/porschersk718/step8a:design



As expected, when you wind on the bounce / bump, the additional negative camber is a little scary, just aswell there isnt much travel!:



Raising the upper and lower pickup points and extending the top arm improves things massively, albeit raising the top pick up by almost 100mm! :


but this tool doesnt do bumpsteer unfortunately. This seems to: http://www.racingaspirations.com/apps/susp...try-calculator/ but im still getting to grips with it before paying the £2.80 to unlock bumpsteer calculations and a few other features to see where the rack theoretically needs to be and if thats going to be physically possible..

Be interesting if anyone else fancies putting their car into the spreadsheet to see how things compare .

Blimey is that really what angle your arms are at when on the car?

Interesting that the top arm can fit at 30mm, and even 50mm movement. I think the fact that I use hydro arms made it look wrong when I looked at it.

the above is really low to start with. As I said before I never set mine lower than the bottom arms level, and it was ok.

I guess if you're running this low at the front you need some serious body mods at the rear to keep the angle of attack sensible.

Look like 8" rims too? I found even on 7" rims the cars are close to tipping rather than sliding, maybe this extra grip is why you feel you need to go lower?

What tyres are you using (4-ply front 2-ply rear)? Are they 8" on the rear also?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Having tried to measure on car hard point positions several times I can sympathize with how difficult it is to get accurate measurements, but some of the values don't seem quite right here.

I've taken the hard points shown in your pics and I get the same results as you have here, i.e. 130mm front roll centre height etc but this is the sort of roll centre height you what get roughly from a Mini at standard static ride height, the roll centre height for your heavily lowered car will be much lower, less than 60mm if not even lower.

Also the figure shown as 'Upright length = 203mm' this is basically the linear distance between the top and bottom ball joint, this figure is too high, it should be nearer 150mm. Assuming it's a standard Mini A series knuckle without a lower ball joint extender? Apologies if this isn't the case but are you sure you're estimating the centre of where the actual ball joint is and not where the taper goes through the arm?

All of this causes the predicted camber of -6.6 Deg for 40mm of bump travel to be way too high, this is effectively a camber change of 5.6 Deg for 40mm of bump travel which converted into a number I am more used to looking at is 3.6 Deg camber change per inch of bump travel and from memory this figure should be more like 1 Deg per inch or less for standard Mini subframe hard points, lowered or otherwise.

The positions of the inner wishbone hard points you have used suggests the car is lowered 110 - 120mm from standard does that sound right, do you have a front sill height measurement?

None of this is to try and criticise what you've done, but just to try and help make the predictions more useful from the software that you're using

Cheers

Yes, the ride height is maybe even a little lower than that once its on the car. you can just about make out the arms on the 2nd pic on the first page.

The rear has had some serious surgery yeah. Chopped out and raised shock pickups, coilovers, beam and diy tube swing arms.

Rims are 8inch, but i run 7.5" A15 compound avon slicks on the front and really soft A92 7.2" on the rear. When i first fitted them years ago before lowering the car, it went up on 2 wheels at a tight hairpin which combined with wanting to get the cog as low as possible resulted in the major lowering going on.

@Aubrey - im under no illusions that the measurements are bang on , nothing was bolted up tight either so this was just to get me started and see if i could work out how to use the software and get a ballpark figure. Next step was as you say to measure the calculated figures like wishbone length and upright length to validate the x and y points used. They are probably some way off, but 50mm for the upright does sound odd as the hub is standard.

re the centre on the balljoint vs the taper, i was measuring to the taper. Should i measure as if the ball joint was sitting vertically?

Agree that the -6.6 is a little off, especially as the wear pattern /melted rubber on the tyres is pretty good in terms of it covering the majority of the contact patch and people often comment about how good the car looks out on track compared to other saloons, and its not too shabby to drive either.

I dont have a record of what the car is lowered compared to standard or what the sill height was when it was when i originally set it up but the overall ride height was around 50mm in the lowest places.

Edited by nky_84 on 31st Dec, 2016.

The red line being the centreline through the taper and the ball joint and the yellow cross being the approximate centre of the ball joint itself.



This is the point you should be trying to measure as this the centre that the wishbones pivot about

In the past I have cut a Mini ball joint assy in half to help me estimate where the centre of the ball is so I could compare Metro A series and Mini A series knuckles.

So would 50mm ride height be to the lowest part of the floorpan, say the footwell indentations?

Edited by Aubrey_Boy on 31st Dec, 2016.

Yes, I run A92, but the 4-ply fronts was the biggest change to the handling and stipping it tipping.

I only runs 7s, but that offers sufficient grip.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

just thinking out the box here.... what might work well is...

Metro K series hubs,

the bottom joint is outboard of the hub so should move the outer lower pivot point out and down, reducing scrub radius and allowing lower ofset rims, also longer arms can be used,

a lot of work though...

also, another thought, moving the top arm pivot straight up as a few people have done, might introduce bump steer, essentially moving that pivot changes the inner angle between the pivots, and hence puts the inner track rod end in the wrong place.

I tig brazed a lower steering arm onto my hub today to make a parallel plate type design. Purely to test how the wheel moves when it moves up and down. You couldn't do it like this in reality because when you drill out the tapered hole its on the wonk compared to the hub face (as you can see by the nut not sat properly at the top. The other reason its isnt ideal is im not sure I'd trust the braze to hold the arm in actual use. That said, it reduces the toe movement as the suspension travels significantly. You could tune it further by moving the rose joint up and down to optimise.

The annoying thing is i cant figure out how to do this properly, without handing over a squillion £ to carl for his parallel hubs.

Any ideas?

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Is there anyway whatsoever to move the rack up in the toeboard?

Just a thought, rather than raising the top arm could you not raise the subframe itself into the body a bit, drop the engine in the frame to keep closer to original go but lowering the car?

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Just a thought, rather than raising the top arm could you not raise the subframe itself into the body a bit, drop the engine in the frame to keep closer to original go but lowering the car?

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis