Static Loadad Wheel/Tyre Radius
Static Loadad Wheel/Tyre Radius
(OP)
Hey guys just seeking some input for a formula to work out the Static Loaded Radius of a wheel/tyre. The variables that come to mind are Tyre pressure, Unladen mass of vehicle, Strength of side wall of tyre, Stiffness of suspension. When wheel manufacturers calculate for test loads what data do they use for their tests? eg Static loaded radius of largest tyre to be used on wheel will depend on what tyre and which vehicle the data is derived from. I understand i can ascertain the STL using a FEA but am lost as to how to define the variables to a point that will be sufficient for standards testing. Any input you could give would be appreciated
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic





RE: Static Loadad Wheel/Tyre Radius
RE: Static Loadad Wheel/Tyre Radius
What I'm refering to is a figure that ill need for an equation to come up with the required test load for a Dynamic Cornering Fatigue Test. The maximum STL of the largest tyre to be used on wheel is needed to complete this equation. Also May i ask why you say the springs/ suspension do not affect the STL? I had the thought pattern that those parts play a role in force/weight absorption that would effect the downforce on a wheel and tyre. Please point me in the right direction if I'm on the wrong path.
Thanks
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
Does the suspension not support some of the weight of the car even though it is static at this point? I used the thought pattern of if i sat in my car while it was stationary my suspension would absorb some of the new added weight.
Thanks
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Static Loadad Wheel/Tyre Radius
For instance a 295/40R18 has an OD of 693 mm
Yes, the SLR varies little between brands for a given tire size. If you ask the manufacturer they should be able to give you what is known as the grown profile for each of their tires.
Admittedly that only gives you the SLR at zero load (I think) and nominal pressure. IF it is important to account for the deflection at a given load then you need the pressure/load/deflection graph for that tire - the manufacturer has that. For a passenger car tire use 200-250 N/mm at 32 psi, rate is proportional to psi, near enough.
In most cases it is a trivial exercise to measure the SLR for your particular load and inflation pressure.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
Thanks for taking the time to reply
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
Take the published radius of the largest tyre possibly used, add 10mm then do your sums.
If you are designing the thing so close to the wire that brand to brand variation and tyre pressure and temperature and wear put you over the safety limit, you are flirting with danger to save almost no metal in the wheel.
Even if you accurately factor all the most minute variables, once dynamic it will all go out the window.
Also someone might make a slightly different tyre soon after you do your meticulous calculations.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Static Loadad Wheel/Tyre Radius
Thanks guys for your help
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
I am still unclear on what your ultimate goal is.
From the conversation, I'd guess you are designing a rim. If that is the case, I'd do a literature research on testing methods of rims. That ought to point you towards methodologies that work.
BTW, I am surprised that folks didn't know that the TRA yearbook doesn't have SLR - and I'm also surprised that anyone would think that it would vary from brand to brand and not from tire type to tire type (meaning all season / high performance / etc.)
And..... if I'm correct you are designing a rim, then I understand now why you were concerned about the suspension. That would cause asymetrical loading on the rim flange area.
RE: Static Loadad Wheel/Tyre Radius
You seem very switched on i must say. I have done the reasearch on testing methods and have the the relevent AS {Australian Standard} that confirms what tests are required and how to work out the test force loads to meet TYPE approval. What it doesnt state is how to work out the SLR ( which is part of an equation to work out test force for test which i stated above). I do understand that the SLR changes over the range of tyres available to go on to a rim. so my question was how to work out the largest possible SLR of any tyre combination on a wheel.
Thanks
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
The limiting load case for the rim of an alloy wheel tends to be semi-abuse cases like potholes and kerbs. Your options there are rather limited if you are using conventional wheelweights.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
RE: Static Loadad Wheel/Tyre Radius
Does that cover it?
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
So your suggestion is to go and obtain every possible tyre that would fit a wheel, inflate each tyre to every specified pressure for each vehicle that the wheel and tyre will fit on then measure it..... Go figure
Greg,
I do appreciate the help you guys have tried to give but unfortunately you seem to have misunderstood, Australian standards requires the Static loaded radius to be known for test loads so maybe you should let all the members that played a role in the development of this standard that they can remove this part of the equation because it is such a trivial part
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
I think the cornering fatigue test is based on the SAE test. If so it is up to the manufacturer to recommend a max SLR and weight. Then you just test at that combination.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Static Loadad Wheel/Tyre Radius
One thing i cant find is an organisation who actually gives type approval for automotive products in australia. Any ideas?
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
BTW, SLR is highly variable in tires and there isn't a universal formula that will cover every conceivable combination - BUT, some educated guesses can be made. Having said that, I noticed that while there have been suggestions to use 10mm as the deflection, I also noticed that we still don't know what type of vehicle the rim is intended for. I think we've all assumed this is for a car, but that is not clear. Obviously the deflection for a truck would be different.
RE: Static Loadad Wheel/Tyre Radius
Unfortunately they are copyright so not so sure about posting the standard. Sorry about not specifying the type of wheel, your correct in assuming its a light alloy wheel. The standards I'm referring to are only light alloy road wheel applicable. I agree that the SLR is highly variable so will be working with the largest Unloaded radius possible relating to specified diameter including tolerances in the T&RA manual. By doing this it only increases the test load so the wheel will meet a standard greater than specified. that way i cant go wrong, but what I'm at a loss at is why they have used this equation instead of other equations as in UNECE or SAE.
Thanks everyone for the discussion and your comments
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic
RE: Static Loadad Wheel/Tyre Radius
I stick by my earlier statement, take the highest unloaded radius or half the stated rolling diameter for the tallest tyre available, then add 10mm to cover the possibility of taller tyres being released in future.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Static Loadad Wheel/Tyre Radius
I called Australian standards to check with them a few weeks ago for one of the test houses wanted a copy of the testing appendixes, AS explained unless it was copied for an company that is a division of the company who bought the standard its illegal to reproduce in any way. I hardly think that is fair when all it is would be the way to perform the tests and nothing that i wouldnt have to specify if i didnt copy it.
Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic