New OEM Sized 20" Hoosiers for GT3 (WARNING PIC HEAVY)
 

Hey guys, well after finishing off the Michelin Pilot Sport Cup 2's a few weeks back, I'd anxiously been awaiting getting the OEM sized Hoosier R7's for our GT3.

I've been racing and winning with Hoosier Tires on our Race cars for 10+ years, and so when I learned that Hoosier was releasing 20" sizes this year, I reached out to my contacts within Hoosier to discuss doing some early tire testing in return for some contingency wins earlier in the season.

First off, here's the complete list of 20" Hoosiers that are currently in production (though not all are presently available, more and more will be throughout the year).
46955R7 P245/35ZR20 R7 - $399.00 ea
46965R7 P265/30ZR20 R7 - $410.00 ea
46975R7 P285/30ZR20 R7 - $425.00 ea
46985R7 P305/30ZR20 R7 - $499.00 ea
46995R7 P335/25ZR20 R7 - $510.00 ea

I've heard of a few people running the 265 front and 335 rear... but the 265's have rubbed on the few cars that have ran them, so I wanted to wait to try the 245/305 setup.

I recently received the 245 front and 305 rears, and went to the garage to proceed with mounting and balancing them. The 245's are perfectly sized at 245mm on the caliper and fit the 9" front wheel very squarely.

I then proceeded to mount up the 305's... and was in for a bit of a surprise... as they are almost a full inch narrower than the Michelin 305. And Porsche already 'stretches' that rear tire... across a 12" wide wheel (pics below).

https://cimg3.ibsrv.net/gimg/rennlis...8a6f9c3a6a.jpg
https://cimg2.ibsrv.net/gimg/rennlis...c156d4c3d2.jpg
https://cimg1.ibsrv.net/gimg/rennlis...643245a7ee.jpg
https://cimg6.ibsrv.net/gimg/rennlis...7b6eb3faa9.jpg

So I took a caliper pic of the '305' and realized it was closer to 285, and just wasn't going to be the best fit for the rear. I reached out to Hoosier, and after showing the caliper pics of the Hoosier and the Michelin, it was determined the 335 Hoosier, is actually spot on for the 12" Porsche rear wheel, and within 5mm of the 305 Michelin in overall width, while being the exact same height! So it is the 'natural' best tire for the rear. (Pics below)

As for 'tire weight' the Michelin's are VERY LIGHT and I had expected to save a few lbs with the Hoosiers, as we do on the race cars... but the Hoosiers and Michelin's we're negligible in any weight difference!

I've got some solid lap times in from the Cup 2's and will be testing the new Hoosier 20" R7's next weekend out at AMP.

In summary, the rear tires are already available today, (335/25/20) for our cars, and as you can see in the pics are almost identical to our 305/30/20. The Front 245/35/20's should be available in the coming weeks, and I'll be able to report back very soon on how they worked, but for overall 'size/fitment' I strong recommend the 245/35 front matched with the 335/25 rear.

https://cimg5.ibsrv.net/gimg/rennlis...712f6b1bb4.jpg
https://cimg8.ibsrv.net/gimg/rennlis...c8edc45462.jpg
https://cimg7.ibsrv.net/gimg/rennlis...f47ed98d1e.jpg
https://cimg5.ibsrv.net/gimg/rennlis...bf852ed09a.jpg
https://cimg4.ibsrv.net/gimg/rennlis...e0a7234d69.jpg
https://cimg9.ibsrv.net/gimg/rennlis...4aa255d0cb.jpg
https://cimg6.ibsrv.net/gimg/rennlis...4f45ba41d7.jpg
https://cimg2.ibsrv.net/gimg/rennlis...3a5539e28f.jpg
https://cimg1.ibsrv.net/gimg/rennlis...e0532331fc.jpg
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https://cimg3.ibsrv.net/gimg/rennlis...50582935db.jpg
https://cimg4.ibsrv.net/gimg/rennlis...5088865737.jpg

I'll plan to update the thread next weekend with track times and overall impressions.

Best Regards,
Dave

Great info well done thanks

N spec 305 cup2 tires run very wide. They really aren't 305. They are more like 325, so what you found makes sense. 19" 305 Re71r tires on 12" wide wheels are stretched. Very difficult to find alternative tires for this car. Just wish Hoosiers were better for more than just a couple heat cycles...

Not sure what your reference is... R7's are good for way more than that, at least 8, but usually 10-15. I used one set with good results 20 heat cycles on a track that was easy on tires. True enough they can be set up to have a great second cycle after a scrub and 24 hour rest, but the remaining cycles are still good and within 95% of the performance. We run a spec Hoosier tire in our SRF3 and likewise they are not a two cycle tire, construction and rubber are different than R7's, but we usually run at least 8 on those as well. Interestingly, there is no real peak with these early, some have done their best laps on the last heat cycle.

Thanks for the info Dave.

I am not sure how I feel about running a 35 series tire in the front and a 25 series tire on the rear. I have never seen this done before.

What are your thoughts on this?
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I ran a set of R7s once on the GT4 and they were great for about 6 cycles and then started to drop off quickly afterwards. Maybe I did something wrong.

Great question, aspect ratios can be very confusing... a 25 series tire and a 35 series tire can have the exact same sidewall size/diameter actually. This is because the aspect ratio, is the 'Percentage' of the width of the tire. So, what you actually get is a 245/35 a 305/30 and 335/25 that all have the exact same actual sidewall size (aspect ratio). All of them coming in at about 42 - 45 mm. I took some detailed pics of the sidewall and will upload them shortly to show the comparison of the 3 different tire sizes.

I don't see why it would, these are DOT legal tires, the car comes from the factory with Cup 2 DOT Legal racing tires as well. It could possibly void the 'wheel' warranty (possibly?) but anything else... I don't believe there would be any issues. Frankly the cars can pull higher g's on 'Cup 2's and 'banking' than Hoosiers and a flat track' (like we have in AZ).

I think it depends on each persons definition of heat cycle. If 6 heat cycles are 6 20 minute sessions.. that is getting up there... but I've gotten closer to 10 to 12 and typically lose about a second. The most notable difference in the heat cycles for me, is they just end up taking longer to come in, ie may take until lap 3 or 4 to be 'working'. I typically only do TT sessions with my Hoosiers (except for the NASA National Championships, where I run race and TT). And for me.. I can easily get 10 sessions with little fall off... but I'm only doing 3 to 4 laps max each session.

I do believe these tires will last every bit as long as the Cup 2's (I only got about 12 sessions out of them)... and these should be considerably faster through their life cycle.

Sidewall pics coming next!

Best Regards,
Dave

Sidewall Pics:
https://cimg6.ibsrv.net/gimg/rennlis...eab5e57485.jpg

MPS4S 305/30/20 with a 62mm sidewall from rim lip to contact patch
https://cimg7.ibsrv.net/gimg/rennlis...55576199fc.jpg

Hoosier 335/25/20 with a 62mm sidewall from rim lip to contact patch

https://cimg2.ibsrv.net/gimg/rennlis...e3f28c3678.jpg

MPS4S 245/35/20 with a 57mm sidewall from rim lip to contact patch.
https://cimg3.ibsrv.net/gimg/rennlis...6c5f6c63dc.jpg

Hoosier 245/35/20 with a 57mm sidewall from rim lip to contact patch.

Best Regards,
Dave

Excellent info! This makes me feel better about those sizes.

Thanks Dave.
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User's manual says clearly that if you put slicks on car the warranty is voided.
Practically for the whole as tires are responsible for loads for suspension but the drivetrain as well.

But it doesn't change the fact I would be eager to check how they go with road car.

Slicks are not DOT legal. Hoosier R7's are a DOT legal street tire. While Hoosier has gotten their 'DOT' street tire, looking very closely to a slick, it isn't one. ;) Hoosier/Pirellii/Michelin 'Slicks' have considerably more grip.

Best Regards,
Dave

Cant wait for your update on how the R7's did. I'm itching to try em