ubrben wrote:This is more Tom's area than mine. I'm a customer of some of the tyre testing machines discussed, but I can't devote enough time to the procedure to be an expert on what you can and can't do.
With the procedure we currently have I can test a series of tyre constructions, do vehicle simulation (moment method) and have it largely agree with subsequent on track result.
This doesn't work for compounds. My soft easy to warm up compound has less grip than my "takes ages to come in" hard on a tyre rig. The grip ranking is correct if I'm looking at a 50C track temp. Flat track rigs rank constructions not compounds.
One of the big reasons tyre rigs don't represent reality is that there's no airflow over the tyre. Unless you put the flat track in a wind tunnel you will never achieve an appropriate thermal duty cycle. People love simulation, but in terms of tyres track testing is still cheaper and quicker than simulation or rig testing.
There was a study done a few years ago where lots of tyre testing machines were compared with a selection of different manufacturers tyres. Long and the short of it - the spread of the same spec tyre across the different machines was bigger than the difference between the different tyre manufacturers.
Ben
Like I said do I spend a lot of money making the test more realistic, or do I just go straight to reality and do a track test.marcush. wrote:
as always ..in testing ..are you sure the test has any significance to what happens in reality?
so if you need air to model the cooling down ...I´d say this is fairly easy technically to solve...
But how to have the drum held at a constant temperature your tyre is worked against?..
I fully agree there.ubrben wrote:Like I said do I spend a lot of money making the test more realistic, or do I just go straight to reality and do a track test.marcush. wrote:
as always ..in testing ..are you sure the test has any significance to what happens in reality?
so if you need air to model the cooling down ...I´d say this is fairly easy technically to solve...
But how to have the drum held at a constant temperature your tyre is worked against?..
As it stands it's much cheaper and quicker to go track testing than rig test.
Even if you set up an air blower and a belt cooler - it's still a belt and the track surface isn't representative.
It's like damper dyno, you're constraining the damper to a predefined velocity profile and measuring the forces. In reality the low speed damping forces prevent a lot of the higher velocities ever being achieved - this is why 4-post rig tests are good. On a flat-track I'm forcing a tyre to follow a fixed set of conditions when in reality the forces and moments generated might cause other feedback to occur that gives the driver a totally different perspective than what you might expect.
On a flat-track the load is constantly applied. I'm sure you could do something more representative, but then you loose the generality that allows you to compare options.
People miss the point of testing like this, it's not to get as close to reality as possible, it's to have a repeatable proxy for reality that allows you to filter concepts. The only truly representative testing for most things on a race car is the race car on track.
Ben
Kind of correct. Probably more accurate to say the trying to predict in the first place is of academic interest only and requires more resources than just testing on track.marcush. wrote:so .. the compound AND construction of the tire may react to certain excitations at certain temperatures in a weird ways by behaving stiffer than anticipated leading to performance suddenly not matching the predictions anymore?
Slightly off topic, but the dyno example is interesting, I think.ubrben wrote:It's like damper dyno, you're constraining the damper to a predefined velocity profile and measuring the forces. In reality the low speed damping forces prevent a lot of the higher velocities ever being achieved - this is why 4-post rig tests are good.
Relaxation length and cornering stiffness, response, all sorts of thingsDaveW wrote:
Ben, tyre relaxation length appears to be important to a driver. Does it vary with "core" temperature? I could imagine that it is connected with JT's reference to tyres "coming alive".
As an aside, can you check and/or correct my understanding:DaveW wrote:ubrben wrote: Shims are used in some dampers to control fluid flow through piston ports. When the interface between the shims and the piston is flat, capillary forces can act between the shims and the piston to delay port opening. The characteristic is almost invisible when tested with a dyno, but can be very obvious, both subjectively and objectively when the damper is installed in a vehicle. In one case, a study initiated by a customer to confirm subjective assessments, two sets of dampers produced by different manufacturers to identical specs matched very well on a dyno, but rig tested installed in a vehicle with a 2:1 difference in PI.
ubrben wrote:As an aside, can you check and/or correct my understanding:
Ohlins: low-speed = needles, high-speed = poppet valves with face shims to control pressure spikes. I think HS control is shims in the TTX. May also have blow-off..
Penske: low-speed = needles, high-speed = shims. I think so..
JRZ/Moton: low-speed = orifices, high-speed = shims. I would have guessed needles in rebound.
Sachs: low-speed = fixed orifices, high-speed = poppet valves. Depends on the damper. The "classic" 4-way HS control is rather more clever than a poppet valve, though it might look like one.
Dynamics: low-speed = orifices, high-speed = Spool valves, now, though you may still see some old style shimmed dampers.
Ben
