Hi all

Been working on these for a while now and thought its about time to share my efforts and get some feedback

Going to try and make pictures work, havnt done it before so bare with me if it dose not work first time

Looking forward to your thoughts

Upright are 2" CDS tube with an EN16T stub axle and 6082 ally inserts at each end to take tapered ball joints.

geo is:
0 deg Kpi
7 deg Caster (steering arm needs moving slightly to allow for this)
36mm Scrub radius

Thanks Tilly



[Edited on 17/3/11 by tilly819]

Dam no pictures i managed to upload them to my archive tryed linking them to the post but no luck any help???



Front Upright 1



Front Upright 2

[Edited on 17/3/11 by tilly819]

There we go figured it out eventually

your thoughts??

tilly

Hi,

Good to see someone taking a different design route, very interested in the thought behind the geometry, is the scrub genuine scrub or is it assuming zero offset wheels, i.e. will that figure come down once wheel offset is factored in?

I now have most of the parts to start messing with my design so maybe we should meet for that beer!

Cheers
Peter

Hi peter

The scrub is the actual scrub taken from the center of the tyre contact patch on a 215 tyre.

iv drawn it all out in front view and can package every thing in the wheel just. got some lovely double deep groove sealed bearings and il make some ally hubs to suit

That beer sounds good lol

tilly

Very slick. Do you have any pics of the assembly?
With 0 kpi there is only 110mm to pachage the hub/wheel center or caliper/wheel center in so it will be tight

Cheers!

oops should have said 143mm

Hi david

It is indeed tight but everything just fits, like i said in a u2u if i fit a bigger disc it actually makes packaging easier slightly.

here is a rough front elevation so you can get an idea, iv got on the static roll center lines as well, ball joints are not shown but the wishbone lines come from there center of rotation



Front Upright front elivation

cheers tilly

I think you are making a mistake here.

King pin inclination should be incorporated, and should, generally, be between 7 and 9 degrees. KPI makes the steering self centre, reduces steering effort and improves feedback to the driver.

quote:

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Originally posted by designer
I think you are making a mistake here.

King pin inclination should be incorporated, and should, generally, be between 7 and 9 degrees. KPI makes the steering self centre, reduces steering effort and improves feedback to the driver.

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I applaud your thinking and don't want to be critical as, after all, I do what I want to do and I look forward to you proving me wrong.

But, my thoughts are that I have never come across a performance car with zero KPI.

http://www.shedworks.eu/tips.html

Second column five down.

quote:

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Originally posted by designer
I applaud your thinking and don't want to be critical as, after all, I do what I want to do and I look forward to you proving me wrong.

But, my thoughts are that I have never come across a performance car with zero KPI.

http://www.shedworks.eu/tips.html

quote:

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That statement is probably true, but then again, you might want to take a close look at a current LM car. or open wheeler.

KPI is only there on production cars for packaging and to reduce/minimise scrub. Scrub causes kickback, not something you would design into any car.

Feedback comes from caster, and the resultant trail thereby induced. As much as some may argue otherwise.

Think about it.

Cheers,
Nev.

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designer - 18/3/11 at 11:37 AM

I would never considered the McLaren F1, or the Elise 111S as production cars, all the LM cars I have seen, along with the Audi R18, have KPI and I have never seen an open wheeler without.

But, I stand to be corrected.

Scrub transfers feel to the driver, but if kept at a maximum of 25% of the tyre width 'kickback' is negligable.

Yes, castor does effect self centreing, but it's main purpose is straight line stability as without, when a car travels in a straight line the front wheels have a natural tendancy to splay outwards.

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tilly819 - 18/3/11 at 02:50 PM

If i may take a little from both of your comments

1) Kpi is there for packaging reasons (I agree)
2) Kickback is negligable when less than 25% of the tyres width ( i dont now, but i like the sound of this if it is indeed the case since my scrub is only 16%)

thanks for the input your views are recived greatfuly

tilly

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Neville Jones - 18/3/11 at 04:51 PM

quote:

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Originally posted by designer
Scrub transfers feel to the driver, but if kept at a maximum of 25% of the tyre width 'kickback' is negligable.

Yes, castor does effect self centreing, but it's main purpose is straight line stability as without, when a car travels in a straight line the front wheels have a natural tendancy to splay outwards.

---

So, 2.5" scrub on a 10" tyre is acceptable???? Not likely! That would rip your arms off at speed hitting a slight bump or hole.

You've been looking in the same places as that ships engineer guy from scotland.

The rest of the design world, and moreso those who drive the quick cars and set them up, will tell you different.

Think about what castor does to the contact patch as the wheel turns, then what scrub does, relative to steering axes and suspension. Then tell us which one you would design in, and which you would design out.

Cheers,
Nev.

[Edited on 18/3/11 by Neville Jones]

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tilly819 - 18/3/11 at 05:12 PM

quote:

---

Originally posted by Neville Jones

quote:

---

Originally posted by designer
Scrub transfers feel to the driver, but if kept at a maximum of 25% of the tyre width 'kickback' is negligable.

Yes, castor does effect self centreing, but it's main purpose is straight line stability as without, when a car travels in a straight line the front wheels have a natural tendancy to splay outwards.

---

So, 2.5" scrub on a 10" tyre is acceptable???? Not likely! That would rip your arms off at speed hitting a slight bump or hole.

You've been looking in the same places as that ships engineer guy from scotland.

The rest of the design world, and moreso those who drive the quick cars and set them up, will tell you different.

Think about what castor does to the contact patch as the wheel turns, then what scrub does, relative to steering axes and suspension. Then tell us which one you would design in, and which you would design out.

Cheers,
Nev.

[Edited on 18/3/11 by Neville Jones]

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I may be wrong here but.......*deep breath*

I agree with your point about 2.5" of scrub on a 10 inch tyre etc however i carnt help but feel that we are talking about 2 kinds of scub here....... yes 2.5" of lateral scrub (tyre moving towards/away from the car) due to suspension travel would indeed rip your arms off when hitting a bump (uk pot hole) (small crater etc)

However steering scrub radius if i am correct should not have this effect, but obviously the more scub radius the heavier the steering will become

Please correct me if i am wrong!
tilly

PS My lateral scrub with currect wishbone geo is about 4mm accross the whole of the suspension travel

[Edited on 18/3/11 by tilly819]

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designer - 18/3/11 at 07:17 PM

There is no part of a McLaren F1 or race car that is designed for 'packageing reasons'

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tilly819 - 18/3/11 at 08:00 PM

quote:

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Originally posted by designer
There is no part of a McLaren F1 or race car that is designed for 'packageing reasons'

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This is a very precise example and i would like to make an observation, take a look at the front brake calipers on said Mclaren F1 they are HUGE

http://img718.imageshack.us/i/1559.jpg/

If goran murray had used a zero KPI even with the 9" wide front wheels the scrub radius would have been massive, even with 9deg KPI it still has a scrub radius of over 16mm

Like the rest of suspension design this strikes me as a compromise made by the designer to achive his desired goals....
If that design was perfect then why dosnt everybody use it??

Yes gordan murrey could have used slightly slimmer calipers and thinner pads but this would have reduced breaking power, it all depends on what the designer is trying to achive, i personaly do not now what his detailed design goals were and doubt i will ever get the chance to ask him, however there are many cars with many alternatve setups that have all been very effective. we must assume that it was done like this for a reason and that alternative designs were done however they were done for a reason also.

the way i see it is that for everything we do there will be an opposite and as such a compromise must be made.

tilly

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tilly819 - 31/3/11 at 09:30 AM

hi all,
bit of an update, i have got some en16T for making the stub axle, some 6082 for the spigots / end caps, some mild steel billet offcuts for making the caliper mounts, and ordered some CDS for the main tube, i just need to get hold of some 20x30 box section which is prooving to be dificult.

also ordered a couple of bits for making the jig to weld it all up on.

hope to get some pictures up soon

Tilly

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britishtrident - 31/3/11 at 10:18 AM

KPI is usually the main generator of self centering, how much should be designed in depends on the weight of the car.
Unlike castor KPI generated steering stability is not affected by crosswinds.
Cars with a lot of castor tend to weather cock at motorway speeds.

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britishtrident - 31/3/11 at 11:07 AM

quote:

---

Originally posted by Neville Jones

quote:

---

Originally posted by designer
Scrub transfers feel to the driver, but if kept at a maximum of 25% of the tyre width 'kickback' is negligable.

Yes, castor does effect self centreing, but it's main purpose is straight line stability as without, when a car travels in a straight line the front wheels have a natural tendancy to splay outwards.

---

So, 2.5" scrub on a 10" tyre is acceptable???? Not likely! That would rip your arms off at speed hitting a slight bump or hole.

You've been looking in the same places as that ships engineer guy from scotland.

The rest of the design world, and moreso those who drive the quick cars and set them up, will tell you different.

Think about what castor does to the contact patch as the wheel turns, then what scrub does, relative to steering axes and suspension. Then tell us which one you would design in, and which you would design out.

Cheers,
Nev.

[Edited on 18/3/11 by Neville Jones]

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You really are such pleasant individual and you never miss the opportunity to display your limited knowledge and very limited experience.
Actually I have never driven a car with 10" wide wheels on the front but I have built and raced cars with 9" slicks on the front and a lot of scrub radius.
Excessive scrub radius isn't desirable but on a circuit racer even with a very quick ratio steering rack it isn't a major problem and as already said some scrub radius is require to give some feed back. However if I was building a Forrest rally car or circuit racer with aero download I would endevour to reduce it to a minimum.

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scootz - 31/3/11 at 11:11 AM

Crikey... this thread just highlights how little I know about upright design!

Can any of you guys point me in the direction of good reading on the subject... something along the line of 'upright design for dummies' would do!

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tilly819 - 31/3/11 at 01:50 PM

OH CRAP

looks like iv made a mistake

Iv got the decimal point in the wrong place i thought i would get -0.6 deg of camber change with 5 deg of steering actualy i get -6 deg of camber change, so i am going to need to incorperate some KIP to reduce this which could well be benifishal to the self centering also as british trident has said and also reduce any weather cocking problems that may arise.

dam time for a redesign
i have made a spreadsheet that i can enter KPI caster and steering into and it will tell me the resulting camber change.

tilly

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tilly819 - 31/3/11 at 04:14 PM

Dam excell

I didnt realise it does trig in rads turns out i was right all along, no need for a redesign.

hopefully the fact that im going for a bit of aero and a 1.7:1 wheelbase should give me the high speed stability i need
Phew

tilly

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v8kid - 21/5/12 at 07:27 PM

Hi,

How goes the design - any updates for us?

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