Spring rates and body roll ?? - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 64 (permalink) Old 12-05-2015, 12:03 AM
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The tyres can accept 1 to 2 degrees of negative camber by deformation of the side walls so the wear is not from running down the straight unless of course you have 5 or 7 degrees (excessive) or you have pumped the tyres too high, but that combined with negative camber will wear half the tread not the inner edge only. Over pressure causes the tyre to bulge the centre of the tread out.

The negative camber is to stop the outside edge of the outside tyre wearing by presenting a full tread width to the road in cornering. You try to set the camber to what the car rolls in the corner and the camber gain plus the initial negative camber presents the tyre perpendicular to the road.

It is not the heat that causes the wear but the scrubbing. You will always be sliding some in a corner at the limits of grip. It may be a lot if you have poor handling setup or very little if you are almost perfectly set up but you will be scrubbing the tyres. They are trying to get a mass at speed to change direction are they not. On a circuit with mostly long straights tyre wear is not an issue normally, its only on the tight and twisty circuits tyre wear becomes a worry.

This is our local circuit. (Clock wise)

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post #32 of 64 (permalink) Old 12-05-2015, 05:47 AM
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Great info everyone......

Now....93 164s, 91 164s, 91 164L, 79 spider, '31 Ford model A Rat Rod, 88 Milano 3.0, 87 testarossa, 05 SL600 twin turbo V-12, 82 GTV6-3.0, Dodge Ram
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post #33 of 64 (permalink) Old 12-05-2015, 08:34 AM
Richard Jemison
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Spring rates

Remember that regardless of the "Spring Rate (inlb)" the angularity of the spring results in a lower percentage of that rate measured at the point of the spring at the lower A arm. As well the point of attachment at the A arm is again a lower percentage due to the attachment point as a percentage of the arm length from the inner pivot point to the center of the wheel. Computing this gives you the spring`s "wheel rate" which is the needed information.

The "Knuckle-riser" is a patch that only helps the camber issue in a small manner if the lower A arm isn`t level. These were used in early mid `60s cars with Spindle uprights that were shorter from the spindle position to the upper arm`s ball joint mount point.

On most race car spindle mods I do, both the spindle is dropped (actually raised by extending the lower section, and the upper section lengthened and moved slightly inboard to facilitate correct geometry. This raises the roll center substantially.
Below is a cut & paste from my website:

Quote:
Dropped Spindles & Steering Arm Modifications



The correct way to lower without crapping the roll center!

The most "drop" that can be done, is dependant "physically" by the clearance of the lower ball joint body in a 750/101 suspension, and the ball joints' threaded taper & nut on 105/115 and the 116 type cars.

Optimally, the suspension would be designed so that with the lower arm level (key to suspension design), the rotational part of the ball joint would be barely clearing the designed rims' inner shell. (see pictures of the RJR GT-R on my website) However, doing this requires the rest of the suspension points be designed into the car so that geometry is functional.


When working with compromised suspension designs on existing cars, only a limited amount of change is possible, or you have to go into pick-up point modifications (typically not legal). On the Alfas' you have to consider the distance between the pick-up points on the body for the upper & lower inner pivots. That is about 12 inches . On the stock car the outer ball joints are almost exactly the same, relying on a shorter arm to give camber change (less than can be optimized for performance). By adding to the length of the upright (dropping the spindle) with the car situated with the lower arm level, the upper arm outer ball joint will be higher in relationship to its' inner pickup point. The result is a lower car, without a terrible roll center drop, with more camber change as the wheel moves up & down. This gives better compensation as the car rolls into a turn (moving negative on the outside wheel & positive on the inside wheel. Since the lower, longer arm is "level" it has less movement "in & out" than the upper which enhances the camber change, Even when the lower arm is not level the camber change is enhanced, but not as perfectly.
The other consideration is body clearance which is also an issue, & that has to be accommodated. On my wide body 101 racecar the spindle drop is 1.5 inches. Typical drop is a 1 inch drop as they go on a lowered, stock fender vintage car. The steering arms are dropped to eliminate bump steer since most are lowered to get the arm level by shorter high rate springs. The amount of steering arm modification is dependant on the total drop of the car. The Ackerman is adjusted as well, so that the car does not need to be set with initial toe out to eliminate initial understeer. The toe can be set at "0" toe for less wear, AND better braking stability ( a big plus!).

Some samples of "Dropped Spindles":

Richard Jemison
RJR Racing

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post #34 of 64 (permalink) Old 12-05-2015, 11:15 AM Thread Starter
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Alfanutsmurph,

While you may be right regarding why your inner edge of your inside tyre wears on this track there is one problem with your theory that Alfa/Autodelta created the knuckle riser for this tyre wear reason.

As you noted this tyre wear situation happens with your friends 1750 GTV also and my, and others, understanding is from the 1750 on wards Alfa incorporated the geometry of the knuckle riser as standard:
Quote:
Originally Posted by Mound Dawg
... the later 1750 onwards cars had different uprights which effectively include the knuckle riser so the roll centre is higher on these which evens it out a bit but it's still not good
We can therefore conclude that the knuckle riser did not improve tyre wear in this situation.
Pete

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post #35 of 64 (permalink) Old 12-05-2015, 12:33 PM
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The statement re: 1750 and later spindles/uprights is not quite correct.

The early spindle/upright is about 9" tall and was fitted with a 2.5" knuckle riser for a total height of 11.5".

The later spindle was about 10" tall and was fitted with a knuckle riser about 2 1/8" tall for a total length slightly more than 12".

When running 13" wheels the later 10" spindle/upright was used with a riser that was about 1 5/8 tall for a total length of about 11 5/8".

Thus, while the later production uprights did incorporate some of the geometry improvements, they were a long way away from the geometry that was fitted on the Autodelta prepped cars.

A drop spindle will deal with the roll center issue but will not have the same effect on the camber curve geometry - aggressively increased camber on bump.

Interestingly enough back in the day Monzeglio apparently did usually not use knuckle risers. It would be interesting to know whether they used drop spindles then ... it's too bad as the only Monzeglio car I have had opportunity to closely examine is an ex-Autodelta car which happens to have knuckle risers. Anybody have an original ex-Monzeglio car?

Another interesting piece is that the knuckle risers were actually never mentioned in the FIA homologation papers. It is my understanding that homologation was not necessary, as the original suspension mounting points and original spindles were maintained and the risers were essentially considered just a spacer.

In that sense modern historic racing takes quite a different tack on this part as was the case back in the day .... sliding block on the other hand is in the homologation papers.

QUOTE=Mound Dawg;6634258]
Quote:
Knuckle risers and sliding block axles are verboten in U2TC racing as they weren't homologated until after 1966 so we're not allowed those .... Knuckle risers and sliding block axles are verboten in U2TC racing as they weren't homologated until after 1966 so we're not allowed those.



The roll centres were horribly mis-matched in these early cars, the later 1750 onwards cars had different uprights which effectively include the knuckle riser so the roll centre is higher on these which evens it out a bit but it's still not good
[/QUOTE]

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from the 1750 on wards Alfa incorporated the geometry of the knuckle riser as standard:
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post #36 of 64 (permalink) Old 12-05-2015, 05:00 PM
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We can therefore conclude that the knuckle riser did not improve tyre wear in this situation.
Pete
How could less camber not have an effect on tyre wear.

Lets have a look at camber with a knuckle riser in place. Same dimensions as previous sketch.

A lot less camber change. Interesting is it not.

Allegeritta

Some interesting pages for you.

Here is page 222 from the book Allegerita. It is a page of the homologation papers of the 1967 GTA 1300 junior. There is a picture of the knuckle riser on that page. It is also visible on page 233. Part of the 1970 GTA 1300 junior homologation papers
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post #37 of 64 (permalink) Old 12-05-2015, 05:17 PM
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Never homologated for GTA 1600 but used extensively.

More aggressive camber curve in bump, eg outside wheel - as in your picture but less in droop, e.g. inside wheel - the less imporatant one. Without the extended bumpstops suspension will go into positive camber on droop with knuckle risers.

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Originally Posted by Alfanutsmurph View Post
How could less camber not have an effect on tyre wear.

Lets have a look at camber with a knuckle riser in place. Same dimensions as previous sketch.

A lot less camber change. Interesting is it not.

Allegeritta

Some interesting pages for you.

Here is page 222 from the book Allegerita. It is a page of the homologation papers of the 1967 GTA 1300 junior. There is a picture of the knuckle riser on that page. It is also visible on page 233. Part of the 1970 GTA 1300 junior homologation papers
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post #38 of 64 (permalink) Old 12-06-2015, 12:18 AM
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Nobody cares what the inside wheel is doing, only the outside wheel that is doing the cornering work.
Pete
I am not so sure that this statement is true. There is a lot of work being put into the grip available from the inside tyres.

Just think about this. If the tyre is on the ground and there is a load on it there will be "grip" to prevent sideways motion from the contact with the road by a certain factor multiplied by the load on that wheel.

If you keep the car as flat as possible and present all tyres to the road they will all provide a resistance to sideways motion i.e. "grip"

Why is it the optimum to get the roll centre as close to the centre of gravity? Less body roll maybe? Less weight transfer?

A tyre offers only so much grip and when that is exceeded you loose traction and go sideways, i.e. slide. Four tyres offer more grip than two.

The more grip you can get from the inside tyres by less weight transfer the better your cornering speed would be. Flat would be the quickest.
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post #39 of 64 (permalink) Old 12-06-2015, 12:29 AM Thread Starter
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Quote:
Originally Posted by Alfanutsmurph View Post
How could less camber not have an effect on tyre wear.
Agree, but you need to also take into consideration the fact that the inside tyre is unloaded so less temp or scuffing.

Now I think we can all agree that the primary reason was the roll centre lifting, but yes maybe there were other favourable reasons such as less camber change. Whether this related to less tyre wear I think is debateable. All I can conclude is "maybe"

I think you and your mate with the 1750 are in a unique position in doing some back to back tests. The 1750 does have a longer spindle so should have less camber change for the inside wheel during body roll than your older car. Would be great if you could both start a meeting with brand new front tyres. Of course there are many other variables ...
Pete

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post #40 of 64 (permalink) Old 12-06-2015, 03:10 AM
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Now I think we can all agree that the primary reason was the roll centre lifting, but yes maybe there were other favourable reasons such as less camber change. Whether this related to less tyre wear I think is debateable. All I can conclude is "maybe"
Some food for thought!

Did "Luigi" (race engineer) know about roll centres or did he know about camber gain? Did "Luigi" have a problem with tyre wear and then did a problem solving knuckle riser camber gain fitment?

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Originally Posted by PSk View Post
I think you and your mate with the 1750 are in a unique position in doing some back to back tests. The 1750 does have a longer spindle so should have less camber change for the inside wheel during body roll than your older car. Would be great if you could both start a meeting with brand new front tyres. Of course there are many other variables ...
Pete
I have later 2000GTV spindles fitted so that I can fit BMW four pot calipers. (huge improvement) We both have the same height spindles.

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post #41 of 64 (permalink) Old 12-06-2015, 08:48 AM Thread Starter
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I'm reasonably confident they would have known about roll centres as Alec Issigonis did when he designed the original Mini.

But we are back in the maybe territory ...
Quote:
Originally Posted by Alfanutsmurph
I have later 2000GTV spindles fitted so that I can fit BMW four pot calipers. (huge improvement) We both have the same height spindles.
So as these spindles are longer you should have less camber change during roll ... and yet you still have tyre wear, hmmm ... I'm confused again
Pete

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post #42 of 64 (permalink) Old 12-06-2015, 02:10 PM
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cornering

Before the risers, before the sliding block, on its 165HR14, in the heroic days, the camber was like this
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post #43 of 64 (permalink) Old 01-12-2016, 10:57 AM
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Nobody cares what the inside wheel is doing, only the outside wheel that is doing the cornering work.
Pete
yes thats what the MR2 mk2, 348, and lotus elise use to think until they had to do a $$$ redesign of the the suspension geometry. newer update revamped the jounce travel to provide more positive camber to aid tire contact with the inner tire

of course it matters. those privateer race engineers clowns on fchat for the 348 challenge cars dont have a clue why the rear pick up points updates were done for.

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Originally Posted by Mound Dawg View Post
In an ideal world no, you want all four wheels on the ground. This is why a 250 cc go-kart will always set a faster lap time than a 250 cc motorbike with the same engine.
yes and no... fast corners yes but in a tight corner you want to pick up the rears in a kart since it has a lock rear end to rotate the kart otherwise it would push and bind up like an old 4x4. next time you see a kart, before getting into it, turn the wheel to full lock. you will see the rear inner pick up cleanly off the ground. this is done with adding massive castor on the fronts. ever notice how much more castor modern cars are running compared to the old cars like the 105? you can do that easily now virtually every front engine car is equipped with pw steering

we entered race car design competition, one of the judges said our car wouldnt handle right without understanding the suspension geo. its ended up winning the Goodyear Outstanding performance award. you know who that judge was? Carrol Smith author of the "tune to win" book series. now they test the cars before the static design event to save the embarrassment of the so called expert judges and their theories.

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Cornering speed is all about tyre contact patch but the load is on the outside wheel, so sorry don't agree that you need to worry about the inside wheel or keep it on the ground.

A car, or go-kart, setup properly has a considerably larger outside wheel contact patch than any motorcycle because that wheel stays closer to vertical than the motorcycle and therefore more of the tread surface is in contact with the ground. Plus lower CoG and roll centres, etc. ... a motorcycle does not stand a chance.

If you picked a single corner and put the skinniest low grip wheel on the inside front of a car and timed it through that corner it would be very similar in time to when it had its normal wheel on that inside front of the car. After all look at a F1 car; often that wheel is bouncing over a kerb or has ridiculous negative camber ... but the designers don't care, 99% of the work is being done by the outside front wheel.

BTW: Have a look at your recent GTA/GTV racing photos and the inside wheel is either off the ground or very close to it and doing little, but the outside tyre is trying to be pulled off the rim .
Pete
kart and formula cars have virtually no bearing with each other in terms of suspension. especially on a F1 car were its easy negate all roll just because the cg is near or below the center of the wheels. you cant do that with and alfa or kart. though im far from being an expert on F1 cars, they intentionally put the roll center below ground in which what we are trying to cure with the 105 front end

Quote:
Originally Posted by PSk View Post
True regarding braking but once cornering, ie. you have turned in, it is all about the outside wheel whether on full power or not.

Note in your excellent photo that the inside front wheel is close to off the ground and unloading. The amount of grip that wheel is providing compared to the outside front wheel is very, very low.

Maybe we are having a misscommunication??
Pete
ps: I have not raced for 20 years, but nothing has changed. The tyre with the most load on it does the most work.

Guys this is why we race with negative camber and often lots of caster angle. If the inside wheel was more important we would race with positive camber like they used to back in the beam axle days so the inside wheel maximised it's contact patch during cornering ... we don't because there is little load on that tyre and therefore pointless.

Look at the F1 photo below. That inside wheel has a ridiculous amount of negative camber during this corner, but they don't care because the outside wheel is the important one and has the maximised contact patch under load.
not point less. modern rear set IRS set up goes in to positive chamber intentionally along with toe control during jounce. why? for more contact on the inner corner and traction. you dont have that option in a kart or solid rear axle.

Quote:
Originally Posted by Alfanutsmurph View Post
I am not so sure that this statement is true. There is a lot of work being put into the grip available from the inside tyres.

Just think about this. If the tyre is on the ground and there is a load on it there will be "grip" to prevent sideways motion from the contact with the road by a certain factor multiplied by the load on that wheel.

If you keep the car as flat as possible and present all tyres to the road they will all provide a resistance to sideways motion i.e. "grip"

Why is it the optimum to get the roll centre as close to the centre of gravity? Less body roll maybe? Less weight transfer?

A tyre offers only so much grip and when that is exceeded you loose traction and go sideways, i.e. slide. Four tyres offer more grip than two.

The more grip you can get from the inside tyres by less weight transfer the better your cornering speed would be. Flat would be the quickest.
yes on most accounts

Quote:
Originally Posted by PSk View Post
I'm reasonably confident they would have known about roll centres as Alec Issigonis did when he designed the original Mini.

But we are back in the maybe territory ...
So as these spindles are longer you should have less camber change during roll ... and yet you still have tyre wear, hmmm ... I'm confused again
Pete
all things be equal, the farther you spread pivots on the spindle while the lower arm is near horizontal of the lower inner pivot the more camber gain you will get.

its been a long time since i visited the bb. ;-)
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post #44 of 64 (permalink) Old 01-12-2016, 03:09 PM
Richard Jemison
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Camber gain

Quote:
A drop spindle will deal with the roll center issue but will not have the same effect on the camber curve geometry - aggressively increased camber on bump.
Totally incorrect.

A dropped spindle does far more than the "knuckle riser" which was , as I said a patch.
The " Dropped" spindle where the length between the spindle and ball joint receiver is lengthened both lower the car without increasing the angle of the lower arm above horizontal, and also lengthens the overall length of the upright, by a minimum of the amount of "drop", and generally on race applications the spindle`s upper receiver is both raised and moved inwards towards the car`s center to facilitate alignment.
The position of the lower arm (horizontal) rather than raised upward which happens when using shorter springs, increases the camber change caused by the greater angularity of the upper arm.
As well with the Center of Gravity lowered, the improved camber gain, the other benefits of more productive suspension settings allowed by the Ackerman changes, and reduced bump steer make the simple spindle modification far more effective.

Richard Jemison
RJR Racing

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post #45 of 64 (permalink) Old 01-12-2016, 07:24 PM
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Not.

A drop spindle just moves the stub axle and all things equal the camber curve remains identical to the standard spindle. It just changes the whereabouts of the camber curve where you find yourself. The curve does not change.

If you increase the length/height of the spindle as you are purporting to do this no longer is a drop spindle, even if you were to call it that, but rather a completely re-engineered spindle which then will certainly change the camber curve as well as other variables ...


Quote:
Originally Posted by Alfar7 View Post
Totally incorrect.

A dropped spindle does far more than the "knuckle riser" which was , as I said a patch.
The " Dropped" spindle where the length between the spindle and ball joint receiver is lengthened both lower the car without increasing the angle of the lower arm above horizontal, and also lengthens the overall length of the upright, by a minimum of the amount of "drop", and generally on race applications the spindle`s upper receiver is both raised and moved inwards towards the car`s center to facilitate alignment.
The position of the lower arm (horizontal) rather than raised upward which happens when using shorter springs, increases the camber change caused by the greater angularity of the upper arm.
As well with the Center of Gravity lowered, the improved camber gain, the other benefits of more productive suspension settings allowed by the Ackerman changes, and reduced bump steer make the simple spindle modification far more effective.
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