Tire lateral properties 2

[sierra4000]

Hello ,
is possible (helpful) to measure and compare the tire lateral stiffness in garage conditions?

Thank You for ideas and opinions

Radek

 

[gruntguru]

Thanks Cibachrome. Any rim width data for your model Greg?

I recall a Holden HQ racer telling me that the spec size tyre performed better (lap times) when oversized on rim width.

je suis charlie

 

[sierra4000]

from Cibachrome last post even seems that vertical stiffness is more sensitive with rim width change

how vertical stiffness affect performance?
what is benefit from vertical stiffness?

 

[GregLocock]

Yes which makes sense if you look at a cross section. As you bring the sidewalls vertical they'll be working in compression instead of bending. So I'd expect the radial rate to rise to a maximum as the rim width reached the nominal width of the tire (or a little less) and then fall away again if the rim is too wide.

Yes, I can have a look at the model tomorrow. Irritatingly I used to have some nice Goodyear training material that demonstrated the difference various parameters made to Flattrac results, but that seems to have been shredded, lost or stolen.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[GregLocock]

Anonymous tire randomly disguised, it is a 195 50 . If you look in front view the overturning moment is SLR*Fy+PSR*Fz where PSR is pneumatic scrub radius, the effective offset of the vertical laod relative to the point directly beneath the wheel centre.

So I think by lateral compliance I am talking about d PSR/d Fy

here's a graph

So, it goes -ve when the vertical load is small, and the rim width is high.

Not very sure what this means in the context of the original question though!


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sierra4000]

Thank you all, was useful discussion anyway
Happy Easter !

 

[sierra4000]

Idea,
what pressure use? can less pressure will be shown more different deflections for better comparison?
please your comments,
Thank you

 

[sierra4000]

Last actualization:

tire increase stiffnees around 10-15% with extra 1 inch rim width
total value is cca 2mm/kN
thank you for comments

https://www.youtube.com/watch?v=uj4_E38rPRY

 

[gruntguru]

Well done sierra sounds like a useful gain for you. Thanks for the update.

It would be good to have some data that could be extended to other tyres. I wonder what is the trend for lateral stiffness as you progress from under-width rims to over-width on the same tyre.

je suis charlie

 

[sierra4000]

three tests

same tire Avon crossply 10,7x21,5x15.........very low aspect ratio
recommended rim range 9,5 to 11 inch

1) 10,7 tire on 10 rim 1,5 bar average 3,08mm/kN
2) 10,7 tire on 10 rim 2 bar average 2,38mm /kN
3) 10,7 tire on 11 rim 2 bar average 2,04mm/kN

 

[GregLocock]

24550 tire @32psi

8.5" rim 1.5 mm/kN
7.5" 2.191
9.5 .809 (probably too much rim for that width- may be outside model correlation)



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[gruntguru]

Thanks guys. Great info.

Sensitivity seems to be stronger than direct proportion. Roughly ^3 for sierra's data and ^1.6 for Greg's

je suis charlie

 

[cibachrome]

A cluster-fugk of ~100 tires different brands, pressures, rims, usage and markets. Mostly sizes that you are interested in.

Yes there is such a thing as Too Much Data. Sorry, it's all evaluated at 1 Fz (530 kg), that's easy to specify at some fraction of recommended load, but for your case your car weight is the only option you have.

BTW: That seems like a LOT of deflection of wheel and chassis. How is the car anchored laterally ? Not well enough I'd say. As Claude would say "That's a LOT of compliance. And no such thing as Good compliance".

 

[sierra4000]

Cibachrome,
You are right of course,

But the test with all its errors was only to show how much the lateral stiffness of one particular tire on a different rim width is affected.

the results are repeatable and obtained on the same car (same vertical load and same chassis rigidity)

I think the results are interesting anyway

 

[gruntguru]

BTW: That seems like a LOT of deflection of wheel and chassis. How is the car anchored laterally ? Not well enough I'd say. As Claude would say "That's a LOT of compliance. And no such thing as Good compliance".

The location of the dial indicator in the video suggests that only tyre deflection was measured. There may have been some movement of the contact patch relative to the plate (squirm?).

Edit. On second viewing - there is some amplification due to angle of the dial gauge and possibly the surface where the gauge contacts the rim (not visible) is angled and/or curved.

je suis charlie

 

[sierra4000]

Gruntguru,
Yes,indicator is direct on loading plate, so other movements are more or less unimportant

 

[sierra4000]

Good notice, indicator is better hold strictly horizontally to exclude mistake