Project "Marginal gains..."
Turbo Mini Forums

Just to add, the lightest caliper isn't always best when braking performance is concerned...I have heard people comment they could see their Minisport calipers flex when having a friend press the brake pedal.

In that respect I like the specialist components monoblock item. I sure hope they stick to machining them from 7075 when making them available again early next year. 7075 is 15% heavier than the 6082 KAD machine theirs from with much higher strength to weight.

http://www.makeitfrom.com/compare/6082-AlS...A97075-Aluminum

Edited by Evoderby on 18th Dec, 2016.

Firstly, yes I agree 100% the lighter caliper wont necessarily be the best as far as stiffness / pedal feel etc goes...

Very likely that your standard 'S' caliper will deflect less than any of the 4 / 6 pots on offer, not just the material properties difference but mainly the size of the bridge / opening with a 2 pot having less of an opening compared to 4 / 6 pots etc. So if caliper stiffness is your priority stick with the 'S' caliper.

As with any component it's the balance of stiffness:weight and strength:weight which we are willing to make

However 7075 wont offer as much (if any) of a reduction in deflection over 6082 as you think when all else is equal, deflection in a materials elastic / linear region is determined by material stiffness and this is given by the various measured moduli a material has, using the data you linked to it gives:

Elastic Modulus is 72 GPa for both (A typical stiffness indicator)
Shear modulus is 27 vs 26 Gpa for 7075 over 6082 (3.8%)

Unless massively overpressured the higher strength that 7075 gives wont really show in the caliper behaviour and even then it's related to the plastic failure. Any properly designed caliper should be way below it's chosen materials yield / failure point.

Considering the 15% weight penalty quoted for 7075 you could probably have a stiffer caliper from 6082 by putting material back in say 10% more and still be lighter.

It's very common that people think stiffness and strength are the same, T45 is a good example, a T45 cage is no stiffer than a good quality steel cage of the same dimensions, so the car will handle the same as far as any added torsional or bending stiffness either cage gives, but T45 will take a bigger wack to permanently bend or fail it in a crash.

Cheers

Edited by Aubrey_Boy on 18th Dec, 2016.

Std hub and kad hub for comparison. Sorry the arms are on the KaD one, did not want to disassemble

Attachments:

1.38mb

1.36mb

Thanks very much for taking the time to photograph them together, very interesting more difference than I expected, I see you have the lower ball joint 'extension' - is that a KAD part? Looks like ally? Have you done a test with and without the LBJ extension? Feel any difference?

The KAD knuckle looks better for clearance for CV boot and retaining clip than the Minisport part, I have tried a HD CV from one of the 16V Mini vendors which I probably won't use, one (of a few) reason/s being the lack of clearance for the CV boot to knuckle with the Minisport knuckle

Thanks again

Edited by Aubrey_Boy on 18th Dec, 2016.

Hi. Happy to be of assistance. The extension is ally, from KAD. Not done much testing at all with this unfortunately.

More on the car they where meant for here: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=264092

Edited by miniminor63 on 18th Dec, 2016.

I didn't know this was your build, I have plenty of photos from your build on my laptop as inspiration.... shame you didn't get to race it around some of Sweden's lovely circuits... Anderstorp being my favourite, you should do a track day tour with it finished!

Such a shame you got shafted on the regulations you were building the car for.....

Semi trailing arms and all...

That inspired me to do some further reading on the subject, you're indeed right.....learning all the time, thanks!

No problem,

This graph better shows what I mean:



The black line could be 6082, the badly added red line is what 7075 would look like, the linear region (Rise/run) is the same gradient for both (Modulus - stiffness) but the plastic deformation occurs at a greater level of stress / strain for 7075, so yield and ultimate strength is higher but normal linear deflection / stiffness would be the same for both.

Cheers

Edited by Aubrey_Boy on 5th Jul, 2017.

Again thanks, very insightful!

So cast irn is probably not all that bad then. At least it's stiff.

Beralcast 363 seems interesting although the beryllium gives me the heebeejeebies

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Yeah cast iron can be good using the higher Modulus stuff...

Never encountered Beralcast 363, it's modulus seems to be in the region of 200 GPa

But the Daddy is aluminium Metal Matrix Composites "MMC", very stiff, very light and difficult to consistently manufacture....

I remember using it in the 90's but I think it was banned soon after even in F1, I recall a pair of Touring car / WRC 6 pot calipers was circa £7000

It depended of the aluminium alloy and the specific type of matrix reinforcement used but IIRC it had a Modulus of elasticity of over 350 GPa... 7075 ally is 72 Gpa ! Available physical property data was sketchy to say the least....

Calipers are not always the most compliant part of a brake system and ally calipers can give a high enough stiffness not to significantly degrade the system feel or behaviour but give a significant weight saving, hence they are widely used on the higher end stuff

Edited by Aubrey_Boy on 20th Dec, 2016.

How stiff do you need stuff to be?
If I had a caliper that was borderline acceptable at 6061-t6, jumping to 7075 would not be my first choice; moreover I'd figure out what to do differently with the base design. My real concern is that 7075 unless I bought it from a company I trusted like Alcoa or Kaiser AND had cert papers, is that you really, really don't know what the real mechanical properties are. This is why any Chinese shop on alibaba can make a billet doohickey, but a shop making the same visual component, allegedly in the same base material, will be hugely more expensive from a shop that uses reputable sourced materials...
That said, everyone seeks to like the "billet" H beam rods that clearly are made in the China...

Edited by Aubrey_Boy on 21st Dec, 2016.

Wheelie bars:

Denis asked if I could simulate the effects of wheelie bars on a Mini, he gave me the arbitrary figure of 1500mm as a wheelbase increase....

I ran the launch as 0.75g peak longitudinal acceleration for both runs, with and without the wheelie bars

Without wheelie bars the front tyre vertical force is reduced by just over 20% at peak acceleration

With wheelie bars the front tyre vertical force is reduced by just under 10% at peak acceleration

So basically the front tyre vertical force loss is halved with wheelie bars

I modelled the wheelie bars as inifintely stiff which definitely gave front end bounce problems, I suspect the actual bars are much less stiff and the tendency to bounce will be less noticeable but probably still a consideration?

Cheers

in case it helps, here's my g forces for a 13.28 and 13.13 run overlaid ..


note the base line zero setting is .036g high for one run and .021g low for the other .

Edited by robert on 18th Oct, 2017.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Hi Robert,

Thanks for that, yeah I was looking at the zero offset, so about 0.70g peak, I took 0.75g as the highest practical longitudinal accel I could expect on road tyres (i.e. having Mu as 1.0) It's good validation of the peak chosen for the sim.

It's bit of an estimate as I don't have any real 10" tyre data and doubt than any have ever been measured for longitudinal performance.

Is the long acc measured from an accelerometer or derived from speed and differentiated with respect to time?

What's also interesting to me is the braking 'g' 0.4g, is that pretty comfortable as far as stopping after a run? (From 114 mph ish?) I have done some sims for max braking to see at what point the rear tyre vertical force reaches zero. Is there still plenty of road left to slow the car down easily?

remember that's on falken tyres with no lsd and a fair bit of one wheel wheelspin in 1st and 2nd gear .

its from a innovate aux box accelerometer connected to a lm1 .

braking wise .its reasonably hard to get into the first slip rd , if you miss it there is a second one , i would assess it as about half max braking g .

yes around that speed . prob 6200 rpm on a 3.1 diff and 165 60 12 tyres , i think i logged 19.33 mph/1000 in top.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Cheers Robert,

That answers how safe a very front biased (weight) fwd car should be under braking at the strip, it should be fine.... I had modelled 0.85g braking from 120mph (not cos that's where I think I will be but as a pretty extreme example) and it was a tad 'sketchy' to say the least but your estimate of half max braking accel is comfortable.

What do you think is the maximum accel on a drag lauch you've seen for a fwd mini?

Edited by Aubrey_Boy on 23rd Dec, 2016.

So are we at a 10%gain or 50%gain in traction? Sorry im struggling a bit to digest the figures, im reading it as a 10%gain in relative downforce on the front tyres, not sure thats worth it :/

Thankyou for taking the time !

Edited by evolotion on 23rd Dec, 2016.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Sorry if I wasn't very clear, what I am saying is that without wheelie bars on a 0.75g launch you lose 20% of your tyre vertical force (Down force as you put it)

With wheelie bars you only lose 10% of the vertical tyre force in a 0.75g launch

Vertical tyre force being proportional to or equivalent to traction, so:

Without wheelie bars you lose 20% of your available traction
With wheelie bars you lose 10% of your available traction

For me it's a massive gain in traction, trying to put it in context you would have to lower the whole vehicle vertical CofG height 90mm for the same gain in traction

I have simulated lots of what I consider to be achievable chassis changes to try and improve traction and none are even remotely close to this

Edited by Aubrey_Boy on 24th Dec, 2016.

Where's the updates from your work on it over Boxing Day 😜

The wheelie bars I've seen up close on a Honda stateside had heavy springs, and are somewhat flexible. They don't impart so much force that the rear wheels lift, but probably remove 25-35" % of static weight off the rear axle. They of course also raise once out of the gate, to reduce rolling friction. I'd have thought the benefit was very much worth it though.

Edited by robert on 18th Oct, 2017.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM