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Author: Subject: Front upright kit
v8kid

posted on 17/4/10 at 05:04 PM Reply With Quote
Front upright kit

Some time ago there were extensive discussions on a custom front upright kit mainly lead by Rorty if I remember right.

Is there still an interest in lightweight kits of parts for members to assemble their own uprights?

I have been working on Rorty's design for myself and have modified it quite extensively stiffening it in buckling, bending and torsion whilst not adding weight.

The advantage of a weld it yourself kit of parts are that the location of the lower and upper pick up points can be determined to suit yourself - handy if you are running extra high or extra low ride heights. Another advantage is that the kpi and ackerman angle are easily adjustable at the welding stage.

What range of adjustments would members like to see? I am very content with cortina geometry - around 5 degree kpi and 80mm scrub but aware that we all have our own directions to follow.

Cheers

David

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russbost

posted on 17/4/10 at 05:33 PM Reply With Quote
Any links to previous discussions?





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cymtriks

posted on 18/4/10 at 12:20 PM Reply With Quote
The Elise has:
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

The MX5 (Miata) has zero scrub

Mass makes have been using high KPI and low scrub for a long time. Why on Earth would you want to copy anything from a Cortina? I've heard that parts are getting harder to source to.

Why did you feel the need to change Rorty's design?

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iank

posted on 18/4/10 at 12:41 PM Reply With Quote
quote:
Originally posted by russbost
Any links to previous discussions?


http://www.locostbuilders.co.uk/viewthread.php?tid=33544

http://www.locostbuilders.co.uk/viewthread.php?tid=34565





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v8kid

posted on 18/4/10 at 03:59 PM Reply With Quote
Thanks for posting the links Ian. It all started with this article which addresses the subject of ideal spindle geometry. The questioner postulated that zero scrub and zero kpi seemed a good idea and Mark Ortiz made the case against it.

www.auto-ware.com/ortiz/ChassisNewsletter--January-February2005.

To paraphrase it and add my own interpretations:-

Steering with little or no trail will go light before the point of tyre breakaway – excellent for a commuter vehicle not so hot for a sports car. Trail also improves turn in. So we need some trail.

A car with little or no scrub radius tends to be numb and uncommunicative so we need some scrub please. Commuter cars have very little because it increases vibration and braking feedback through the steering wheel – I think car engineers call it NVH and it is paramount to the sales chappies - even in the Elise. Scrub also helps to unload the rear wheel in tight corners – handy if you have a LSD

The camber change associated with caster is good and caster combined with scrub helps turn in for slow corners particularly in cars with LSD so a dollop of that as well please

The kpi’s used in modern cars are more due to packaging considerations necessitated by MacPherson struts which in turn are required to get widely spaced mounting points on a pressed steel frame. They also make up for inattentive drivers and none of the above applies to us does it! So not so much kpi for us.

All in all a persuasive case for not adopting suspension uprights from heavy saloon cars designed for commuting rather than spirited driving. It is hardly surprising however that the humble Cortina has some of the attributes we are looking for – it did not have strut suspension, power steering or any compromises forced on it by NVH requirements. Just because it is old does not justify decrying a design based on sound engineering principles and constraints.

The question is exactly what values to use and this is where an upright kit that could easily be configured to individuals requirements comes it.

What was wrong with Roarties design? Nothing it was perfect for an off road buggy with lots of kpi and zero scrub to reduce steering feedback on rough surfaces. We want an upright for a road sports car.

Also the design was a little weak in torsion and it was difficult to get the bottom outer balljoint far enough outward – ideally we want it just clearing the disc. Also the balljoints were vertical and its easier to package them close to the rim (bottom outer balljoint again!) if they are horizontal.

So that’s where I am coming from and am interested if this is a common problem and if so what range of values people would be looking for. On the other hand it may be just a bee in my bonnet.

Cheers

David

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Ahdammit

posted on 19/4/10 at 04:23 PM Reply With Quote
Didnt the original 7 use the Triumph upright?
I dont know the geometry or dimensions,but if it saved re-inventing the wheel,what about using the same scrub/kpi but redesigned for modern fittings?

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iank

posted on 19/4/10 at 05:11 PM Reply With Quote
quote:
Originally posted by Ahdammit
Didnt the original 7 use the Triumph upright?
I dont know the geometry or dimensions,but if it saved re-inventing the wheel,what about using the same scrub/kpi but redesigned for modern fittings?


Caterham still do iirc.





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ettore bugatti

posted on 19/4/10 at 09:04 PM Reply With Quote
Caterham use only the geometry of the Triumph upright. They changed the bottom trunnion for a balljoint (if Im correct).

A nice alternative could be the Mustang II upright. The hotrodders in the USA use them, widely available and the KPI is 11-12 degrees.

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Neville Jones

posted on 20/4/10 at 08:58 AM Reply With Quote
The Wilwood uprights are good value, and geometry is useable.

The axles need reshaping for RD hubs, or custom hubs for UK bolt patterns.

Cheers,
Nev.

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cymtriks

posted on 20/4/10 at 09:19 PM Reply With Quote
quote:
Originally posted by v8kid
A car with little or no scrub radius tends to be numb and uncommunicative so we need some scrub please. Commuter cars have very little because it increases vibration and braking feedback through the steering wheel – I think car engineers call it NVH and it is paramount to the sales chappies - even in the Elise.

The kpi’s used in modern cars are more due to packaging considerations necessitated by MacPherson struts which in turn are required to get widely spaced mounting points on a pressed steel frame. They also make up for inattentive drivers and none of the above applies to us does it! So not so much kpi for us.

All in all a persuasive case for not adopting suspension uprights from heavy saloon cars designed for commuting rather than spirited driving. It is hardly surprising however that the humble Cortina has some of the attributes we are looking for – it did not have strut suspension, power steering or any compromises forced on it by NVH requirements. Just because it is old does not justify decrying a design based on sound engineering principles and constraints.


The Elise :
KPI 12.0 degrees
Castor 4.25 degrees
Trail 4mm
Scrub radius 10.5mm

The MX5 (Miata) has zero scrub

The Honda S2000 has minimal scrub and high KPI but I don't have the numbers.

Are you seriously suggesting that These cars, and many other very fast and capable machines, have got it all wrong?

None of the cars I've mentioned have high KPI to accomodate strut suspension as they use double wishbones.

On the other hand your claim that the Cortina upright is based on sound principles and modern stuff is compromised by catering for struts is just not right. Cortinas were not noted for handling and were designed to cater for the fleet and family workhorse market from the outset. There is no evidence at all that the geometry was chosen to give some double wisbone handling perfection, or even anything other than good use of available tooling and parts.

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Livio

posted on 21/4/10 at 09:24 AM Reply With Quote
I think one should take in consideration which parameter influences which properties for designing an upright.

-The bigger your scrub the heavier to steer the wheel in a corner. – this must be an important issue in a car without ps. At the same time with increasing scrub the load of the steering mechanism will increase too.
-The more kpi you have the more +camber will be gained by steering the wheel. –does not sound very good
-Trail helps self aligning of course.
-With caster you can gain –camber by steering the wheel.

Usually the limit of reducing scrub and kpi is defined by the brake disc and other packaging constraints. The ET of the wheel has heavy effect on these parameters too.

Of course every parameter is in connection with many other properties and parameters and I just wanted to mention a few from the most important relations.

Correct me if I am not right.

I am curious about the new design.

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posted on 21/4/10 at 04:58 PM Reply With Quote
Too much about a lot of things that make very little difference except to your Mum's shopping car.

For those who think modern cars are the ducks nuts got to a Historic sedans race meeting and vice versa.

For those who think 5 degrees KPI is great I'll show you winners with 15 and vice versa.

Same for caster.

Trail is the most underated yet very important part of the whole equation for feel and more.

Often when people add caster to their cars they think it handles better for the wrong reasons, it's usually the trail gain thats giving them better feedback and earlier slip angle saturation.

The fastest current LMP2 car in the world uses 0 scrub, 0 caster, 0 KPI, static camber to suit the day but runs a whopping 65mm of trail.

For a road car that doesn't run on silky smooth race tracks and needs suspension travel I would suggest a 2 to 4 degrees KPI , double that in caster, negative scrub of around 20mm +- 10mm and about 30 - 40mm of trail.

neg scrub is pretty easy to get these days with most wheels being for front wheel drive cars with plenty of offset that way.

By the way, Cortina uprights are available in aluminium.

Theres one way a guy did his here...I think the measurements are in the thread somewhere....
http://www.locostusa.com/forums/viewtopic.php?f=36&t=5850&start=15

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posted on 21/4/10 at 05:18 PM Reply With Quote
quote:
Originally posted by Livio
Correct me if I'm wrong...

-The bigger your scrub the heavier to steer the wheel in a corner. – this must be an important issue in a car without ps. At the same time with increasing scrub the load of the steering mechanism will increase too.
-The more kpi you have the more +camber will be gained by steering the wheel. –does not sound very good
-Trail helps self aligning of course.
-With caster you can gain –camber by steering the wheel.





More scub gives lighter steering, scrub allows the tyre to follow a radius rather than screwing rubber on the spot.

KPI gives you positive camber gain but KPI is a shimmy damper, stability and self aligning giver as well.

Trail does but it does a lot more too.

Caster does gain but only in total if it's offsetting the KPI. It's not a formula but a guide is to start with 2 x KPI.





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cymtriks

posted on 21/4/10 at 07:06 PM Reply With Quote
quote:
Originally posted by cheapracer
For a road car that doesn't run on silky smooth race tracks and needs suspension travel I would suggest a 2 to 4 degrees KPI , double that in caster, negative scrub of around 20mm +- 10mm and about 30 - 40mm of trail.

neg scrub is pretty easy to get these days with most wheels being for front wheel drive cars with plenty of offset that way.


In order to fit a disc and caliper into the wheel you are effectively forced to have a high KPI of around 12 degrees if you also have a small scrub radius.

Going to a negative scrub would push the KPI up even further given that the lower ball joint still has to be clear of the inner surface of the brake disc.

An overlooked reason to have castor on a road car is that it tends to unwind under braking. You need 4 or 5 degrees even with hard bushes to make sure that some is left under extreme braking.

So it looks as if the closest you could get to your ideal would be more like 15 degrees KPI, 4 degrees castor and 30-40mm trail.

Why do you opt for negative scrub? Positive is usually considered the choice for a sportscar (though this may be based on not a lot).

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posted on 22/4/10 at 05:56 AM Reply With Quote
quote:
Originally posted by cymtriks

In order to fit a disc and caliper into the wheel you are effectively forced to have a high KPI of around 12 degrees if you also have a small scrub radius.

Going to a negative scrub would push the KPI up even further given that the lower ball joint still has to be clear of the inner surface of the brake disc.

An overlooked reason to have castor on a road car is that it tends to unwind under braking. You need 4 or 5 degrees even with hard bushes to make sure that some is left under extreme braking.

So it looks as if the closest you could get to your ideal would be more like 15 degrees KPI, 4 degrees castor and 30-40mm trail.

Why do you opt for negative scrub? Positive is usually considered the choice for a sportscar (though this may be based on not a lot).


Firstly you can not quote KPI angles without knowing the spacing between the BJ's - I figure you read that 12 degree figure somewhere in some article. A BJ spacing of 100mm will have a vastly different KPI angle than a BJ spacing of 200mm with the same vertical offset won't it. - I just looked, starting with a 12 degree example at 100mm BJ spacing, doubling the separation to 200mm gave me 7 degrees.

I haven't had any problem getting around my ideal with various uprights I have made up over the years but I'm also not limited by items such as stone shields, stamped control arms, oversized BJ's etc.. and for years now a wide range of wheels can take care of scrub if it's an issue for you. IF.

Look at it another way, cut 2 uprights in half horizontally and join the 2 halfs with the lower ball joints together and what have you got? Here is a nothing special Miata example I cropped, it would give 0 kpi, 80mm face offset with a fairly standard 40mm offset wheel gives some their ideal 40mm pos scrub. If I add maybe 5 degrees of kpi I will have some neg scrub.

Neg scrub is far more stable in every condition especially braking, shorter lever arm in deflection and the wheel steers in the opposite direction to the deflection force helping to cancel it. I'm not sure where your sports cars have pos scrub originates from in modern times but yes it can be a packaging issue sometimes.

Just a warning, don't go less than 10mm scrub either way, crossed signs are a bad thing.

A loss of caster under severe braking isn't an issue, the tyre has well enough saturation from weight transfer to be not interested in a couple of degrees loss of camber - why a you turning into a corner under that circumstance anyway .........


[Edited on 22/4/10 by cheapracer] Rescued attachment doublehalves.jpg
Rescued attachment doublehalves.jpg






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Neville Jones

posted on 22/4/10 at 07:24 PM Reply With Quote
Top flight LM cars go for 0 everything, then dial in 'feel' as the drivers require, using castor. At least, that's how they were doing it a couple of weeks ago.

Scrub, is an evil. Wrecks the drivers arms with unnecessary movements and vibrations, and gives constant and unnecessary movements, sometimes confusing and covering up real issues.

Trail is used on supermarket trolleys, and belongs there only. Someone said somewhere that some LM car had zero everything, but used up to 65mm trail......??? Someone may also have been having his chain pulled by whoever made the initial statement. In motor racing, if you haven't seen it and measured it with your own hands and eyes, it's bovine excrement!! Motorsport is awash with the stuff. When repeated often enough, it becomes absolute truth, and everyone goes on their merry way.

KPI is optimised for centrepoint steering.( before castor is added). If you are lucky enough to be using wide enough wheels, then kpi can be as little as zero. KPI on fwd cars with Macpherson struts is usually due solely to packaging issues, and getting acceptable clearances.

Sometimes, kpi and castor can be utilised and optimised for cornering grip, or so I'm told.

Cheers,
Nev.

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posted on 23/4/10 at 05:35 PM Reply With Quote
quote:
Originally posted by Neville Jones
Top flight LM cars go for 0 everything,

Trail is used on supermarket trolleys, and belongs there only. Someone said somewhere that some LM car had zero everything, but used up to 65mm trail......??? Someone may also have been having his chain pulled by whoever made the initial statement. .


The LMP2 winning Strakka HPD uses 0 KPI, 65mm of trail and minute caster and camber to suit each track, I know a development engineer who advises to the team, I chat with him often but thanks for your input. If you find a picture of it with the bodywork off you can actually see this large offset.

The last race car I developed for a client ran 45 mm of trail on the uprights I made, best thing I ever did and my current build is over 50mm of trail.

Important to have low'ish camber thrust and a bit of KPI for shimmy damping with high trail though.





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cymtriks

posted on 23/4/10 at 10:17 PM Reply With Quote
quote:
Originally posted by cheapracer
quote:
Originally posted by cymtriks

In order to fit a disc and caliper into the wheel you are effectively forced to have a high KPI of around 12 degrees if you also have a small scrub radius.

Why do you opt for negative scrub? Positive is usually considered the choice for a sportscar (though this may be based on not a lot).


Firstly you can not quote KPI angles without knowing the spacing between the BJ's - I figure you read that 12 degree figure somewhere in some article.


No, it isn't something from a book. It is simply what you end up with when you have allowed for everything else.

Take a 205/50-15 size tyre on a wheel. Lets call it 8 inches wide.

The wheel spokes will take up the first 1.5 inches, the caliper needs some clearance say 0.5 inches and the caliper to the disc centre is at least another 1.5 inches so we now have the disc in the middle of the wheel. The lower ball joint must be inboard of that plus clearance for heat from the disc, say 1.5 inches inboard of the wheel centre.

As you correctly point out the lower pivot can be at any reasonable height but that still restricts us to something in the range 6 to 9.5 inches from the road surface.

To give zero scrub that forces a KPI of between 9.0 to 14.0 degrees.

Oddly enough the above description fits an Elise, with 12 degrees KPI and 10.5mm scrub fairly well. The McLaren F1 had wider wheels which allowed bigger offsets. It used 5/8 inch scrub and 9.0 degrees KPI.

The following is copied from the USA Locost site:

================... KPI ......... caster

Lotus Elise...................... 12° ......... 3.8° caster
Mazda Miata................... 11.3° ........ 5° caster
Ferrari F355.................... 13.16°
McLaren F1...................... 9° ........... 6° caster ...... 16.25mm scrub

Can you explain how you get around the packaging restraints that I've mentioned?

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posted on 24/4/10 at 02:48 AM Reply With Quote
quote:


Can you explain how you get around the packaging restraints that I've mentioned?


I already gave you an example above with a sectioned Miata upright and thats a very limited starting base - huge castings, huge BJ, LBJ very close to axle centerline and a very wide disc offset.

I'm sure you can use your imagination from that info.





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Doug68

posted on 25/4/10 at 08:03 AM Reply With Quote
The attached section shows a cut through my C5 Corvette model. If my math is correct that 8.3 deg KPI and 12mm positive scrub.
With a bigger tyre the scrub could be reduced further but I think a 245 on the front is enough already
Of course this is all static, this is all bound to change on the road with tyre flex, camber etc.

Also I see caster removal on braking as a good thing, anyone whos riden a motorbike will know its a good thing to aid turning in.
Frankly though I think the ammount of change that happens in a car is insignificant.

Back on subject surely there's got to be parts in the world that make it not worth the effort to make your own uprights? From my point of view I've got enough bloody work to do on the car without adding on parts just for the fun of it? Maybe I'm missing the point though. Rescued attachment FrontUprightSectionII.jpg
Rescued attachment FrontUprightSectionII.jpg






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Neville Jones

posted on 25/4/10 at 10:15 AM Reply With Quote
quote:

The LMP2 winning Strakka HPD uses 0 KPI, 65mm of trail and minute caster and camber to suit each track, I know a development engineer who advises to the team, I chat with him often but thanks for your input. If you find a picture of it with the bodywork off you can actually see this large offset.

The last race car I developed for a client ran 45 mm of trail on the uprights I made, best thing I ever did and my current build is over 50mm of trail.

Important to have low'ish camber thrust and a bit of KPI for shimmy damping with high trail though.


Pics of a corner with a wheel off, please, with a reference marker/graduated background alongside to show these things clearly.

Otherwise, just so much more garden fertiliser.

Cheers,
Nev.

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posted on 30/4/10 at 04:28 PM Reply With Quote
quote:
Originally posted by Neville Jones


Pics of a corner with a wheel off, please, with a reference marker/graduated background alongside to show these things clearly.

Otherwise, just so much more garden fertiliser.

Cheers,
Nev.


I've given you the manufacturer's name and model and where my info comes from first hand so how about you show my information is false since your the one saying it is?

If it pleases you your Majesty I'll post pics of my own simple 50+mm trail upright's as I fab them in the coming weeks.





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Neville Jones

posted on 30/4/10 at 11:13 PM Reply With Quote
Pictures of your own uprights are not pics of those you claim as running on the 'top' car.

It's quite simple; if you can't back up what you are saying with clear and concise pics of the claimed articles, then don't make the statement.

There's just far too much BS touted about as truth, and until the clear and concise pics of this LM car are put in front of me, the claims are just hearsay. Paddock BS to the agricultural among us.

I am close enough to a guy who designs this stuff, in front of me, to know when 'misinformation' is being put about.

Cheers,
Nev.

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posted on 1/5/10 at 12:37 AM Reply With Quote
So your Mate is the designer of the Strakka?

Whatever. Ok, as this is obviously going nowhere lets take it from a different angle....

As I have already stated why trail is good you can counter using your depth of knowledge on the subject - simply complete these statements...

"Less trail is better because.....

or

"Too much trail is bad because.....





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posted on 1/5/10 at 05:45 AM Reply With Quote
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