E type Roll Centre and Handling

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Marquis Rex
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#1 E type Roll Centre and Handling

Post by Marquis Rex » Sun Jul 14, 2019 7:06 pm

Greetings,
I have been digging deep into vehicle dynamics in general and Roll centres in particular.
My OEM background has had me deliver various vehicle projects where Ive had a good overview but Im now digging in technically deeper. The aim is to learn mainly. If I can benefit the community by sharing what I have learned I'll be happy to do so. I'd be happy to hear from people here if this is too technical and needs to be watered down or vice versa. This forum is the sort of technical audience level I'm aiming for, I'll cover what my key take aways have been and then share the roll centres I have. The E type is a nice car to apply some of the calcs to because, it generally has a simpler set up than modern multi link suspension cars- so is easier to understand.

These are some of my take aways-

•The Steering axle benefits from low Roll Centre , long equivalent control arm lengths result in steering predictability due to minimal track change, minimal RC height change , minimal camber change etc

• High Roll Centre at the rear controls roll/yaw coupling and having a higher RC at the rear stabilizes the vehicles by causing yaw in the opposite direction to the direction of turn as the car rolls

• Total Lateral Load Transfer Distribution or 'TLLTD' at the front builds progressively with body roll. Higher rear RC means lots of nearly instantaneous geometric weight transfer from the rear end, causing transient overtsteer that compensates for other perceived sources of steering sluggishness (improves turn-in). When driving the E type- I find even at modest cornering speeds I can feel the steering load up nicely. When it was happening, I was thinking of the roll centre at the rear being higher than the front and transferring load progressively.

• Raising front roll centre improves on-centre steering feel-The E type for me seems to have a lot of 'feel' and feedback compared to my X308 XJR and even my E24 BMW M635CSi. The X308s front roll centre is under the ground at -50mm. My Porsche 993 Turbo has the best steering feel of all of my cars.


- A School of thought- as shared by Gordon Murray and practiced on the Maclaren F1- was to have the distance between the C of G and Rc the same front to rear, and keeping the Rcs both low.
By having Rcs higher rather than lower (or zero) a larger part of the TLLTD will be geometric . With lower Rcs more load will be transferred via the suspension system itself.With zero Rcs the load transfer will transfer immediately via the tyre contact patch while the rest of the Wt will pass through the springs and shocks. In addition zero Rc allows the lionshare of the vehicle dynamics tuning to be done by fine tuning the suspension. Im not sure how I feel about this one- I have no direct experience of a zero Rc (frt and rear) vehicle and suspension tuning it.

And finally



The E types roll centres seem rather high- 280 mm at the front and 146 mm at the rear. This seems weird to me-with high Roll Centres in general and the rear being lower than the front. I was corrected by a colleague in the industry, who had the E type front and rear roll centres measured- on a Kinematics And Compliance Rig. He got 60mm at the front and 150 mm at the rear. This makes more sense to me.


Ive never pushed my E type to the limit, I know it has close to equal weight distribution, and have never heard of evil handling characteristics. The steering is very 'talkative'.
I hope this post is of interest to people.
This shows a list comparison of the Jaguar E type and its roll centres compared to other modern contemporaries:

Image


Image

Image
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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abowie
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#2 Re: E type Roll Centre and Handling

Post by abowie » Sun Jul 14, 2019 10:13 pm

Marquis Rex wrote:
Sun Jul 14, 2019 7:06 pm

The E types roll centres seem rather high- 280 mm at the front and 146 mm at the rear.
Very informative, thank you.

How did you arrive at the 280mm figure, or is the maths too complex?
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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#3 Re: E type Roll Centre and Handling

Post by Marquis Rex » Mon Jul 15, 2019 1:33 pm

Its not really complicated- you get pictures, like the one I posted, and take dimensions and angles.

Im posting my diagrams of how I worked out the X308 Jaguar roll centres


Image



Image


The 280 mm number for the front of the E type is just so far out of the norm. However you can see how I arrived at it, if you project/extend the LCA arm lines and do the same for the UCA toward the centre of the car, and then project where these lines come together. Its at this projected point where it comes together, where you extend ANOTHER line to the vertical centreline of the car. Its where this line meets the centreline that is the point of the roll centre.

I do think that the roll centre importance is sometimes over stated and also bear in mind that the E type was designed when cross ply tyres were commonplace.
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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PeterCrespin
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#4 Re: E type Roll Centre and Handling

Post by PeterCrespin » Tue Jul 16, 2019 10:17 am

Thanks for that. My D uses mostly E-type front suspension plus a heavy solid back axle on 4 unequal length trailing arms with a Watts linkage pivoting off the diff cover. The car rides on correct Dunlop peg drives with very tall 16” Blockley cross-ply tyres 6.00” and 6.50” front/rear. To get the ride height in D spec the front suspension is lowered, with 1/4” packing behind the UCA mounts and eccentric spindles to keep camber sensible. What would be your guess as to the effects of these changes on handling?

BTW should I call you Rex or Marquis? I’m guessing Rex, (which is also the name of my youngest grandson)
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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#5 Re: E type Roll Centre and Handling

Post by Marquis Rex » Tue Jul 16, 2019 7:11 pm

Please call me Rex.

By lowering the UCA inboard mount you would probably raise the roll centre by between 8-12mm (you're changing the UCA angle effectively).

I don't envisage huge changes to handling by doing this. You've done the right thing by controlling the camber.

Although roll centres DO effect handling , in isolation, not significantly, they're part of an ingredient for a larger cooking recipe. In this case the finished dish is the cars handling characteristics
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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#6 Re: E type Roll Centre and Handling

Post by PeterCrespin » Tue Jul 16, 2019 11:36 pm

Thanks Rex. I deliberately chose to avoid the common use of IRS to upgrade the rear suspension. Am looking forward to a 1955-ish feel when sampling my creation next spring, with luck...
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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#7 Re: E type Roll Centre and Handling

Post by Marquis Rex » Wed Jul 17, 2019 1:18 pm

PeterCrespin wrote:
Tue Jul 16, 2019 11:36 pm
Thanks Rex. I deliberately chose to avoid the common use of IRS to upgrade the rear suspension. Am looking forward to a 1955-ish feel when sampling my creation next spring, with luck...
Sounds like an exciting authentic project
"Live Fast, Live Well, Live Free!"
1970 Jaguar E type OTS

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