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