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  #21 (permalink)  
Old 11-14-2018, 05:09 AM
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I have 315's on one car and 335's on the other. Can't really tell the difference. Would depend on compound and a lot of other factors. Even the test day Richard is referencing would change and change the results. For a tire that large getting heat into it or the right compound could be a large factor. For the rims supplied 335's would be largest imo.

Those early cars I don't believe were the pullrod rear suspension models, that could play a big part in the skid pad numbers.

I did some hand fitting of the front rockers and improved the movement quite a bit from the way the cars were delivered, no reflection on Richard. The up and down movement of the rockers is very fast even on a seemingly smooth road, reflection on Richard.

I'd put my cars up against any of the previous mentioned cars, just the design itself tells the tale.

And one of the cars is a dry sump, so we can rule that little niggle out.
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Last edited by vector1; 11-14-2018 at 05:18 AM..
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  #22 (permalink)  
Old 11-14-2018, 07:57 PM
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Originally Posted by xlr8tr View Post
Curious Richard, would the 295 and 355 kuhmo's fit on the JBL? Section widths of 12.1 and 14.2" respectively. One would think with current state of the art tires the numbers would be even better, assuming you could keep oil in the engine
The Comp chassis would accept the section widths that you quote as there is room for the increased wheel width while maintaining the same outside dimensions and therefore the motion ratios would still be correct. (Just add the required 2 inches to the backspacing)

More contact patch does indeed equal more grip if the suspension geometry is correct for the tyre construction. I am not familiar with the Kunmo sidewall design so I cannot give you a honest opinion on how they might work on the JBL.

The camber curves were designed for the Hoosier radials of the time and by good fortune the Michelin Pilots of the era were very close on the sidewall angle deflection numbers. The tyre pressures required were quite different between the two brands because the Michelin sidewalls were much stiffer than the Hoosiers.

And to Mark's comment "The up and down movement of the rockers is very fast even on a seemingly smooth road".

He nailed the reason for the front end rocker design there. The motion ratio is about 1.2-1 on the rockers. This was to increase the damper shaft motion and speed as very short shaft displacements are extremely difficult to valve for and control.

There are other reasons for this motion ratio as well that have to do with creating a rising spring rate curve that worked with the very high moment around the design roll axis.

This same philosophy was finally applied to the rear of the later cars with the introduction of the pull rod design.

Since Mark has examples of both chassis possibly he could comment on the differences that he feels in the dynamics of the two designs.

The pull rod car should give a much more stable transfer of weight and rotation about the roll axis. Transition from one direction to another should be quicker and more predicable as well.

Of course things being as they are when doing vehicle design, the best laid plans of Mice and Men etc...................
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Old 11-15-2018, 02:11 PM
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very interesting Richard! Adding 2" to backspacing would not mess up scrub radius?
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Old 11-16-2018, 03:26 PM
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Originally Posted by xlr8tr View Post
very interesting Richard! Adding 2" to backspacing would not mess up scrub radius?
Good catch. If done the way I stated it would indeed alter the scrub radii and wheel rotation would be difficult due to the wheel/upright interference drag induced by the clamping force of the lug nuts.

What I should have stated is that one would add 1" to both the backspacing and the offset on the front (split the increase) and one would add 2" to the backspacing on the rear.

The front with the standard offsets currently has 2.75" positive scrub radius with 11 degree SAI on a tyre dia. of 24.5".

Therefore the increase in backspacing would change the SR to 1.75" which should still give the desired steering feel and centering effect. Note: the design calls for 2 degrees castor or less as the camber gain required is in the geometry and jacking effects are therein minimized as they are extremely detrimental dynamically.

This would necessitate a toe (static) change to offset the reduced torque on the contact patch under braking. Probably would change from .040 to .070 out but once again tyre construction is the biggest factor here.
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Old 11-16-2018, 04:11 PM
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Positive scrub of 2.75 plus a spacer of 1 = 3.75.

You already have positive and adding a spacer.

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Old 11-17-2018, 12:25 AM
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Positive scrub of 2.75 plus a spacer of 1 = 3.75.

You already have positive and adding a spacer.

Gary
I was not clear in the last post.

I am not speaking of any spacers but rather the width of the wheel to fit the tyres that xlr8tr was speaking about and its offset relative to the stock wheel.

And I misspoke on the SR since I was referring to an additional inch on both the inboard and outboard barrels and that would not alter the SR at all.

Sorry. Not paying attention to my details in the response. It should not happen. I hate bad information.
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Old 11-18-2018, 09:43 AM
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Excellent info thx Richard, goes to show how many interactions are going on in suspension design
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Old 11-25-2018, 01:08 PM
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Originally Posted by Richard Hudgins View Post
I was not clear in the last post.

I am not speaking of any spacers but rather the width of the wheel to fit the tyres that xlr8tr was speaking about and its offset relative to the stock wheel.

And I misspoke on the SR since I was referring to an additional inch on both the inboard and outboard barrels and that would not alter the SR at all.

Sorry. Not paying attention to my details in the response. It should not happen. I hate bad information.
Ah yes, I see what you mean Richard, sorry for my confusion.

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