Hoosier 20 x 7.5/ 13

[Silente]

Hi averybody!

I was looking to hoosier site and i have seen the informations about these tires.

I have seen they show a resonable diameter on the website, but they say they have a section width of 9.4", which is a lot more than the 8" of the 20.5 x 7/13.

Does anybody use these tires on his car? Are they so big?

Does anybody knows about their weight?

Thank you very much!

[Silente]

Hi averybody!

I was looking to hoosier site and i have seen the informations about these tires.

I have seen they show a resonable diameter on the website, but they say they have a section width of 9.4", which is a lot more than the 8" of the 20.5 x 7/13.

Does anybody use these tires on his car? Are they so big?

Does anybody knows about their weight?

Thank you very much!

[MalcolmG]

We used to use these on the rear of our car, they have a tread width of 8", compared to 7" of the 20.5x7.0's. Weight is about 300 grams per tyre more, from memory. They're not that big, but if you have a normal sized FSAE car you may very well struggle to get sufficient temperature into them.

Those tyres were tested in Round 3 of the TTC, so there's comparative data between them and the 20.5x7's if you want to have a look at how they behave.

[Silente]

you say 300 grams more than the 20.5 x 7 / 13?

Do you know the actual weight of both? I've checked on TTC data but i was not able to find tire weight...

[blister]

Stuttgart used them on the rear in Germany and Italy last year. At least they were not slower with this tires ;-)

I wonder how many have looked at the new tire data. quite interesting tire!

[Silente]

nobody knows where i can find their weight?

[Rex]

You could possibly email Tim or Jeff at Hoosier about the weights. I've always found them to be very helpful and responsive.

I run the 7.5" on the rear of my car now, and yes they are noticeably bigger than the 7.0" (to the point that they rubbed the exhaust and it had to be slightly rerouted). I have no comparitive data to make any performance gain/loss claims vs. the 7.0", but so far I'm happy with them.

[Silente]

do you have an address of Tim or Jeff?

[Rex]

I probably have them around here somewhere, but they are also listed on the Hoosier FSAE webpage (along with ordering info, etc). That would be much faster than waiting on me.

[MotorCity1]

Hello everyone,

My name is Hesh and I'm leading the suspension design for Wayne State University FSAE (Warrior Racing). This upcoming year will be my 3rd as a FSAE participant, 2nd as suspension design captain. And this is my first post on the forum!

I've been diving into the TTC data over the last month with the help of OptimumTire, and found some interesting results - specifically regarding the Hoosier 20.5x7.5 - 13 and how it compares to the 20.5x6 - 13 and the 20.5x7 - 13 tires.. I'd love to hear anyone/everyone's feedback.

Let me just quickly say...Last year, the extent of my tire data research was determining peak SA at each corner for a given weight distribution and TLLT. This pointed me in the right direction for choosing a % ackerman to implement into front geometry. That's about all I did..13" wheels were chosen based on ease of packaging, and tires choices were carried over from the year before (I know, I know...). I spent the majority of my time focusing on kinematics, without realizing how the kinematics impact the tires. But, 2 full months of testing is what I took advantage of to find the a decent set-up for each of our drivers.

I used the Pacejka 96 model and generated some basic curves to analyze. Its clear to me that the 7.5" tires provide the most Fx and Fy, (again, compared to the 20.5x6 and 20.5x7 tires).

FY vs. SA - For a given tire pressure, the cornering stiffness (CS) of the 7.5" tire is higher (on 7 in wide rims as well as 8 in rims), and the downward slope of the curve once peak SA has been reached is much steeper. These characteristics should correspond to increased response to lateral acceleration due to decreased relaxation length, at the expense of correctability and control at peak SA (please correct me if I'm wrong). The 7" and 6" wide tires have lower CS, even when mounted on 7" rims, and do not give up as much lateral force after peak SA, hence giving the driver a better chance correcting US/OS behavior, at the expense of turn in response. So in my opinion, the takeaway from the FY/SA graph for these 7.5" tires is that they can generate the highest peak lateral forces for a given Fz and P and they provide better turn in response, but the driver would need some time in the car to maximize the capability of the tires and get used to how the car handles.

FX vs. SR - The 7.5" tires generate the most Fx at all SR up to 20%. They also do not seem to tail off as much as the 6" and 7" tires at SR above 20% (I understand that the Fx will decrease eventually, but just not as soon as the 6" and 7"). So I guess, all else equal, the 7.5" tires on your drive axles would get you from a to b the fastest, and provide the most braking torque even when you are on the verge of locking up...I haven't yet explored the effect of rim with on Fx. But I plan on it.

Tire Temps - The 7.5 in. tires have a lower operating temp. than the 7s, which have a lower operating temp than the 6s. I have read on this forum that some teams seem to struggle getting temperature into the 7.5s. But it seems to me than if you go rear heavy (lets say, 45-55 rear bias), the car is 400+ lb, and keep your tire pressures relatively low, there shouldn't be a problem getting temperature into the tires. And, based on the cornering stiffness of the 7.5" tires at 10 psi, it should maintain most of its responsiveness.

I also noticed that all the tires mentioned seem to like 0 inclination. vs. 2 deg. and up.

Some questions/additional thoughts that you all might be able to comment on...

1. Depending on the weight distribution, using 7.5" tires all around may not be the best idea. But I feel that with thought out kinematics design and TLLTD, this can be overcome by adjusting your outside tire loads during cornering to get you closer to 0 yaw moment at peak Fy (compliances neglected). Thoughts?

2. I think with enough time in the car, A good driver can become familiar with the tire behavior, especially if aligning torque is used as the primary tool for feedback to the steering wheel. Even with the high cornering stiffness that I discussed earlier, do you think this is possible? After all, the 7.5" tires do provide the most Raw grip.

3. A lot of teams go with the 7s all around. I'm going to assume that is for the drivability reasons mentioned above..among many other things. Why so little 7.5s? I noticed that the 7" tires' FY vs. SA curve changes somewhat dramatically under different tire pressures, whereas the 7.5" tire curve (in terms of shape) remains somewhat constant. The raise in tire pressure due to temperature, especially during an endurance, may cause a more dramatic change in tire behavior and therefore vehicle behavior on the 7" tires than the 7.5"...that's how I interpreted the data but I could be wrong.

Any feedback is welcome.

Thanks

[BillCobb]

By ignoring kinematic and compliance (steer & camber), you are not doing car engineering, you are playing in a sandbox with an evaluation process that is too simplified. The question for you would be how will you determine what the K&C parameter values are ? I'd advise you to get some structural analysis going and a measurement system (a machine or a mechanism) to systematically obtain the influence coefficients that modify (attenuate) the tire forces and moments at each axle).

Only then can you run the play for useful tire evaluations. Do you really think/believe that its possible to have all of your tires running up to the peak SA ? Yeah I know some will claim they have been successful with their primitive models, but it was not because of the reasoning they followed. Luck is not a continuous process.

BTW: Correlation between CS and Relaxation is generally not a very good one. Relaxation and rim width is MUCH better. There should be some relaxation measurement attempts in the next round of TTC data. And just how will/would you factor relaxation effects into your tire selection process ?

[MotorCity1]

By ignoring kinematic and compliance (steer & camber), you are not doing car engineering, you are playing in a sandbox with an evaluation process that is too simplified. The question for you would be how will you determine what the K&C parameter values are ? I'd advise you to get some structural analysis going and a measurement system (a machine or a mechanism) to systematically obtain the influence coefficients that modify (attenuate) the tire forces and moments at each axle).

I definitely agree that this evaluation process is simplified. Modeling the raw TTC data (scaled down to account for different coefficient of friction based on operating surface) is what I felt was a logical first step in understanding the general behavior of each tire. I'm aware that compliances exist everywhere and until they are accounted for, any conclusions I make will not be indicative of reality.:)


Do you really think/believe that its possible to have all of your tires running up to the peak SA ?

Nope, anything as small as a crack on the track surface would attenuate the tire forces. Compliances that aren't accounted for such as Wheel rim deflection, upright deflection, etc. would have the same effect..too much heat cycling, conicity, improper care of tires, ...I think that's the idea you were trying to get at, and if so, I agree that under extremely rare circumstances, if any circumstances at all, will the tires approach their peak SA, Fy, Mz...



BTW: Correlation between CS and Relaxation is generally not a very good one. Relaxation and rim width is MUCH better. There should be some relaxation measurement attempts in the next round of TTC data. And just how will/would you factor relaxation effects into your tire selection process ?

I'll investigate those effects some more. Relaxation effects would affect transient response..so I'd say a transient vehicle model of some sort would be necessary to properly account for these effects.

Thanks for the feedback!

[BillCobb]

MC-1: I would expect, seeing that you are Wayne State and in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world and with a VERY large number of Wayne State graduates working the industry, that you could be successful in getting 'company' support for testing a FSAE car on a K&C rig somewhere without much begging. Yes, the short wheelbase usually alllows on 1 end of the car to be tested at a ime. But the folks in A2 (you know, a city full of people who think otherwise), have gotten this done on weekends with volunteer alumni support.

Since MTS also has a large Engineering and Product Support in the Detroit area, I would venture a guess that you could also get an invite to Eden Prairie and get on a machine out on the Test Floor ready to be shipped out to wherever in the World.

If you can get a simulation running, steps to open you eyes would involve 1) a car with only mass and nonlinear tires with only FY. Then add MZ. Then add some steer and camber compliances to each axle, and finally the MX. An overlay plot of nonlinear responses (understeer/oversteer, max lat, and response times) for each condition will surprize not only yourself, but quite a few judges as well.

Compliance management is the professional approach to designing a great car, including all 'race car's. You can make a great career out of this, as I did.

I always am amused when I hear 'expurts' state that MZ has little effect on the car, when I know there are no MZ steer or camber compliance parameters or mechanisms to install them in their models. Don't be one of 'them'. Why do you think worn tires tighen up a car and kill it's sidebite ??

[DougMilliken]

... in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world...
[disclaimer -- we are N. American reps for ABD]
Everything Bill said, and a mention that MTS isn't the only supplier of K&C rigs -- there is an ABD SPMM at the FCA (former Chrysler) Proving Grounds in Chelsea MI, as well as Goodyear in Akron. I know that the Goodyear SPMM has been used with FSAE cars and suspect that Chelsea has also.

[Tim.Wright]

Cue the MTS vs ABD discussion.

[Zac C]

Cue the MTS vs ABD discussion.

As far as I know there's only one person that's had extensive experience with both the MTS and ABD machines. His take is that both machines are more or less equivalent in terms of capabilities. The ABD machine is WAY better to work with in terms of required maintenance schedules though. Unless you're planning on owning and operating your own rig that's probably less of a concern.

The Goodyear machine is still an option for paid testing if you want to go that route. Sponsored testing probably isn't going to happen there.

There are also ABD setups at Morse Measurements in NC (open for private testing) and Honda in OH (probably have to know someone).

I should probably also mention that even though a somewhat large number of teams have tested on various K&C rigs I have yet to see a very strong student effort in using the data. That list of teams includes some of the international powerhouses. Maybe that's changed in the last couple years though.

[Tim.Wright]

I've used the data from both - and for basic tests my impression is that both rigs are capable of more or less the same things.

The thing with the ABD rig (for basic tests) is that I don't like the way it carries out the wheel centre longitudinal force tests. They strap the wheel to the wheel pads and apply the longitudinal force but the problem (in my opinion, correct me if I'm wrong Doug) is that the wheel pads cannot rotate about the lat and longitudinal axes so it can't control the Mx and My propery.

So in the end you don't get a pure wheel centre force - there is always a bit of a "parasitic" Mx and My there as well. The MTS wheel pads on the other hand have 6 degrees of freedom so they are able to control all 6 force/moment components perfectly.

For more detailed stuff there are a few differences:
ABD rig cannot do single wheel lift/warp inputs
ABD rig can (with a software upgrade) measure the full inertia matrix of the vehicle as well as finding the CG location in 3 dimensions.

[MotorCity1]

MC-1: I would expect, seeing that you are Wayne State and in the center of mass of one of the largest conglomerates of MTS K&C test machines in the world and with a VERY large number of Wayne State graduates working the industry, that you could be successful in getting 'company' support for testing a FSAE car on a K&C rig somewhere without much begging....

During the design/manufacture/assembly of this past year's car, we just aimed to limit compliance as much as possible from start to finish..but never considered using a SPMM as an option, because our focus was more on completing every event at competition (which we did, for the first time in school history and had the best finish in school history in the process).

Now, this seems like something worth pursuing. Thank you all for the information.

[BillCobb]

Like many other car designers, builders and users, the transition from a paper design to a working car has to pass through reality. This means making the parts exactly as drawn, installing them in exactly the design position, and contemplation of the attachment point flexures. (Even a 'perfectly' built car can have hidden flaws in a K&C validation because the method of clamping the body/frame to the reference ground can install an artificial constraint if the frame is weak or the attachment locations are coincident with modal vibration points).

But what we see so often is careless positioning and installation of parts (i.e. your ride-steer is to be held at +- 1% at 5% understeer - symmetric by design, but as built it's -19% (oversteer) on the left front and +7% (understeer) on the right front wheel. Because of fastener stretch (as in undersized), the hysteresis in your roll camber curves puts the plots off the graphic window. Oh, and your rear roll stiffness is very nonlinear (unexpected, of course). Because of your steering input shaft design, the car has more front compliance steer than a ?? And as for wheel bearings ? I'm sure they are expensive, but did anyone check their runout after you tightened that castle nut with an air wrench ?

Seen it all. Enough for a lifetime....

[Zac C]

I've used the data from both - and for basic tests my impression is that both rigs are capable of more or less the same things.

The thing with the ABD rig (for basic tests) is that I don't like the way it carries out the wheel centre longitudinal force tests. They strap the wheel to the wheel pads and apply the longitudinal force but the problem (in my opinion, correct me if I'm wrong Doug) is that the wheel pads cannot rotate about the lat and longitudinal axes so it can't control the Mx and My propery.

So in the end you don't get a pure wheel centre force - there is always a bit of a "parasitic" Mx and My there as well. The MTS wheel pads on the other hand have 6 degrees of freedom so they are able to control all 6 force/moment components perfectly.

For more detailed stuff there are a few differences:
ABD rig cannot do single wheel lift/warp inputs
ABD rig can (with a software upgrade) measure the full inertia matrix of the vehicle as well as finding the CG location in 3 dimensions.

Yeah, I've used data from both types of machines, as well as some one offs that various OEMs made before K&C rigs were available as a turnkey solution. I'd agree with your assessment. In terms of general operation MTS machines are a pain, not just for K&C rigs, but for everything. The hydraulic systems they like to default to for almost everything require a lot of upkeep. The electric systems ABD runs require almost zero.

I'm slightly less concerned about the residual MX and MY though. The wheel pads don't rotate about the x and y axis, but you've got the 6 forces and moments measured at the footprint and the displacement coordinates for your wheel center and your contact patch. It gives you enough information to post-process out any residuals, especially if you run the test at a couple offsets or use the Y-axis to minimize the overturning moment.. There's always the option of using the rigid wheel substitutes too (this will severely limit your test throughput).

The inertia stuff is more than just a software upgrade btw. You need a special set of body clamps that have 6 axis load cells built into them and some other expensive bits. It's a pretty small subset of rigs that have this capability.

[Z]

Since I have the link from the other thread ...

https://www.youtube.com/watch?v=fVrC565ynzQ

Any thoughts on the amount or rear-wheel wobble seen at 1:08? :)

Some toe-change is visible at the left upright, but the amount of floppiness of the right rear-wheel suggest that maybe the "optimised" wheel-bearings were too optimal?

And were (what looks like) the glued-carbon-tube wishbones supposed to eliminate all compliances by making the suspension super-stiff??? :D

My guess for RR toe-change is AT LEAST 1 degree (ie. looks like +/- ~3 mm at the rim)?

Z

[DougMilliken]

I've used the data from both - and for basic tests my impression is that both rigs are capable of more or less the same things.

The thing with the ABD rig (for basic tests) is that I don't like the way it carries out the wheel centre longitudinal force tests. ...

So in the end you don't get a pure wheel centre force - there is always a bit of a "parasitic" Mx and My there as well. ...

For more detailed stuff there are a few differences:
ABD rig cannot do single wheel lift/warp inputs
ABD rig can (with a software upgrade) measure the full inertia matrix of the vehicle as well as finding the CG location in 3 dimensions.

Tim.Wright -- I didn't want to take this thread so far off topic, just wanted to make sure that ABD/SPMM were mentioned. But since we have started--

As Zac C pointed out there are rigid wheel substitutes available for SPMM, the "Rigidity Matrix Measurement Device". I believe they do what you are looking for, but I haven't been able to get confirmation from ABD (August holiday season?)

Single wheel lift/warp inputs can be supplied on SPMM incrementally, by adding a spacer(s) on top of a wheel pad. I don't know if there has been enough demand for this to write extra software to reduce the test conveniently.

ABD worked with Morse Measurements and now have software to simulate combined Ay and Ax (turn entry or exit), as well as lateral and longitudinal separately, see this page for details, http://www.morsemeasurements.com/combined-loading-simulation-test/ I don't know if MTS offers this or not?

The new SPMM 5000 model is upgradable for dynamic testing -- up to 5Hz on any combination of axes. More details in the general spec available in a pdf linked from this page, http://www.abd.uk.com/en/kinematics_&_compliance/spmm5000

[Forbes]

Z says: "the amount of floppiness of the right rear-wheel suggest that maybe the "optimised" wheel-bearings were too optimal?"

Maybe a 'rubber' upright? NC machined uprights invariably have open sections that lack torsional stiffness

[MCoach]

Since I have the link from the other thread ...

https://www.youtube.com/watch?v=fVrC565ynzQ

Any thoughts on the amount or rear-wheel wobble seen at 1:08? :)

Some toe-change is visible at the left upright, but the amount of floppiness of the right rear-wheel sugmgest that maybe the "optimised" wheel-bearings were too optimal?

And were (what looks like) the glued-carbon-tube wishbones supposed to eliminate all compliances by making the suspension super-stiff??? :D

My guess for RR toe-change is AT LEAST 1 degree (ie. looks like +/- ~3 mm at the rim)?

Z


If you check out the LR, you can see a little more in detail of what is going on during that launch. Also, that is some seriously stiff rear suspension springs for accel...

Anyway, if you sit there and play it over and over and over again you'll notice the deflection stack up. The tire movement is huge. The wheel movement seems to be about equal. Trying to see the hub is a bit easier to figure out on the RR due to the bolt pattern being visible but it breaks down about there because the axle boot and upright obscure the inboard side, leaving a guess for hub deflection. Interesting to notice is that the upright seems to rotate counter clockwise around the LBJ. The upper control arm seems rigid (enough) and the toe link doesn't seem to show significant buckling motions, but it visibly oscillates a lot. Maybe it has something to do with the two being mounted to spherical ends and allowing relative motion to each other through upright deflection? The upright also seems to oscillate around the Z axis. (as seen from above). I might agree on the bearings, but guessing at the hub size and seeing the tripod being placed inside the upright, I would venture to say that the bearings are most likely the now "standard" 61815 75x95x10 deep groove ball bearings. These bearings have been used successfully by many teams for years and should be sufficiently stiff due to their large diameter. It's difficult to tell, but the upright looks really thin, which would make it's stiffness for resisting exactly the sort of motion we're seeing low. Perhaps the tolerances in their installation are not "optimized"? Perhaps too large of clearance in the upright or low / no preload from bearing spacer?

I think a lot of the culprit could be the (most likely M5) screws hold that bracket for the UBJ and tie rod to the upright and the bracket itself being a poor support in bending between the UBJ and tie rod. That seems about as far back as I can visibly trace the large amounts of deflection...


Getting the car on a K&C machine would open your eyes on serious differences between your designs and the actual output of the car...