ddd4114
forum member
Just like almost everyone else in TT, I'm always looking for (relatively) easy ways to shave off a couple tenths per lap, and after finding little improvement with messing around with suspension setup, I'm tempted to reevaluate my tire selection. If you're interested in hearing my experience and "logic" for this, see the following wall of text. If not, you can skip to the Cliff's Notes at the end.
First, some background to explain how I arrived at this point:
I've been driving my 2011 GT in TT for a little over 4 years, and most of that time has been on Hoosier R7's. When I first started, I ran the car in TTB at ~3800 lb (including me), and I started on 275mm NT-01's. Soon after, I decided to shuffle points and try the "compound always trumps width" concept and switched to 245mm R7's. This isn't quite a fair comparison because a 245mm R7 is actually only 5-10mm skinnier than a 275mm NT01, but even still, I immediately dropped ~4 seconds per lap without any other changes. The 245mm R7's were definitely overloaded and noticeably lost grip in long braking zones, but they were surprisingly consistent for an entire 15 min TT session. Some of my best times were set on laps 4 or 5, which admittedly could just indicate incompetence. Lighter cars would destroy me in the corners (where I struggled to maintain more than ~1.3g), but I made up the difference with a lot of power, and it showed that the less-than-ideal setup at least had a fighting chance against prepped S2000's and STI's on more open tracks.
Fast-forward to 2017, and NASA got rid of TTB. Knowing a 3800-lb Mustang would be cannon fodder in TT4, I moved to TT3. That allowed me to switch from 245mm R7's to 315mm R7's and go aero crazy. The 315mm R7's were definitely an improvement - by almost 0.1g, which is a lot. However, even with wider R7's, another 36whp, and hundreds of pounds of downforce, my lap times weren't *that* much better than in TTB. For example, my best Mid-Ohio Pro Course time was 1:36.5 in TTB, and now it's 1:33.2 in TT3 even with way more grip, more power (yet more drag), and more experience. Three seconds is a lot, but... I really struggle to compete with well-built Corvettes, and I don't give up easily.
This summer, I made the switch from 315mm R7's to 315mm A7's. On R7's, even if I was aggressive on the warm-up lap, the first hot lap was always way off pace. Even pushing it, I would be 2 seconds off my lap 2 times, and typically there was still a little improvement on lap 3. As expected, the A7's were basically ready to go by the end of the wam-up lap, but I still noticed that my lap 2 times were at least 0.5 sec better than lap 1. That wouldn't be such a big deal, but there were two huge downsides of the A7: they were TOAST by lap 4 (if not sooner), and they were at the cords - and way more exciting to drive on - after 15 heat cycles when R7's would be good for 30 heat cycles. I would be somewhat accepting of these compromises if the A7 was much faster than the R7, but it wasn't. When I compared lap times and data to my recent events with R7's, there was basically no difference. Hoosier actually told me this would happen when I consulted them about tire selection a couple years ago, but since people always claim how much better A's are than R's, I had to try them. Who would have thought Hoosier would be right???
Here is where I stand now:
Since Hoosier has an excellent contingency program for TT, I'd really like to stick with their tires (no pun intended). I'm pretty convinced that a 315mm A7 is not a superior tire to a 315mm R7's with this much weight and aero loading. I talked with Vorshlag to see what would be required to run their 11"/12" wheel package - or better yet, a 12" square package - but it sounds like this will not be a bolt-on affair. I already need a 1/2" + 3mm spacer in the front to keep the coilovers from chewing the tires, and they already stick out of the fenders by ~1/2". Wider tires will actually be a considerable expense to do it right: flares, maybe spacers, new wheels, more expensive tires, maybe some inner fender clearancing... It's also certainly more drag. That got me thinking: if "compound always trumps width" worked in TTB, maybe it could work now...
I looked into my point assessments for TT classification, and here are the two options I have:
1) Keep running a DOT tire as wide as I want at 3751 lb min weight. Right now, I cross the scales at ~3800 lb, so a small diet wouldn't hurt.
2) Switch to a non-DOT tire (probably an S80) no wider than 265mm and run it at 3831 lb min weight. Considering where I am now, this is really only another 40-50 lb with some buffer.
I called Hoosier to ask about this, and they advised against running a smaller tire on this heavy of a car even for a short TT session. They also said a non-DOT tire will take way too long to warm up, but I was a little skeptical about that. The Pirelli DH compound is somewhat common in TT, and people seem to make them work even though they're designed to last WAY longer than a 15-min TT session and tend to heat up slowly. Also, everyone I've talked to said they provide a noticeable improvement in grip over an R7. I've also read on the internet (which MUST be true) that a Hoosier S80/S100 provides similar or more grip than a DH but doesn't last as long. My hope was that running an overloaded 265mm S80 would warm up within 2 hot laps and still provide more grip than an R7 - at least within a narrow window. For sure I'll be on the wrong side of the load sensitivity curve and a lighter car will get much more grip out of them, but as long as it's more than an R7 - even by 0.05g - it might be enough of an edge to justify the change if I can win tires through contingency. Speaking of - another downside of an S80/S100 is that they're ~$50 more per tire. Whatever the case, it would be silly to ignore Hoosier's advice about their own tire, but I also have to consider that I'm playing with a somewhat uncommon setup compared to most of their customers. I imagine that most of their experience is with much more restrictive classes, and I just need to make something work really well for 1-2 laps even if it sucks everywhere else.
Cliff's Notes:
What will provide more grip for just one lap of a 10-15 min TT session: a 315mm Hoosier R7 or a 265mm non-DOT slick (preferably a Hoosier S80/S100)?
If anybody has experience with experimenting with things like this and is willing to share, I would definitely appreciate the advice. I know it wouldn't be difficult or expensive to test a set of used S80/S100 slicks or even Pirelli DH slicks, but since I don't know how much slower they would be compared to stickers, I'm afraid the test would be misleading.
Thanks,
Dan
First, some background to explain how I arrived at this point:
I've been driving my 2011 GT in TT for a little over 4 years, and most of that time has been on Hoosier R7's. When I first started, I ran the car in TTB at ~3800 lb (including me), and I started on 275mm NT-01's. Soon after, I decided to shuffle points and try the "compound always trumps width" concept and switched to 245mm R7's. This isn't quite a fair comparison because a 245mm R7 is actually only 5-10mm skinnier than a 275mm NT01, but even still, I immediately dropped ~4 seconds per lap without any other changes. The 245mm R7's were definitely overloaded and noticeably lost grip in long braking zones, but they were surprisingly consistent for an entire 15 min TT session. Some of my best times were set on laps 4 or 5, which admittedly could just indicate incompetence. Lighter cars would destroy me in the corners (where I struggled to maintain more than ~1.3g), but I made up the difference with a lot of power, and it showed that the less-than-ideal setup at least had a fighting chance against prepped S2000's and STI's on more open tracks.
Fast-forward to 2017, and NASA got rid of TTB. Knowing a 3800-lb Mustang would be cannon fodder in TT4, I moved to TT3. That allowed me to switch from 245mm R7's to 315mm R7's and go aero crazy. The 315mm R7's were definitely an improvement - by almost 0.1g, which is a lot. However, even with wider R7's, another 36whp, and hundreds of pounds of downforce, my lap times weren't *that* much better than in TTB. For example, my best Mid-Ohio Pro Course time was 1:36.5 in TTB, and now it's 1:33.2 in TT3 even with way more grip, more power (yet more drag), and more experience. Three seconds is a lot, but... I really struggle to compete with well-built Corvettes, and I don't give up easily.
This summer, I made the switch from 315mm R7's to 315mm A7's. On R7's, even if I was aggressive on the warm-up lap, the first hot lap was always way off pace. Even pushing it, I would be 2 seconds off my lap 2 times, and typically there was still a little improvement on lap 3. As expected, the A7's were basically ready to go by the end of the wam-up lap, but I still noticed that my lap 2 times were at least 0.5 sec better than lap 1. That wouldn't be such a big deal, but there were two huge downsides of the A7: they were TOAST by lap 4 (if not sooner), and they were at the cords - and way more exciting to drive on - after 15 heat cycles when R7's would be good for 30 heat cycles. I would be somewhat accepting of these compromises if the A7 was much faster than the R7, but it wasn't. When I compared lap times and data to my recent events with R7's, there was basically no difference. Hoosier actually told me this would happen when I consulted them about tire selection a couple years ago, but since people always claim how much better A's are than R's, I had to try them. Who would have thought Hoosier would be right???
Here is where I stand now:
Since Hoosier has an excellent contingency program for TT, I'd really like to stick with their tires (no pun intended). I'm pretty convinced that a 315mm A7 is not a superior tire to a 315mm R7's with this much weight and aero loading. I talked with Vorshlag to see what would be required to run their 11"/12" wheel package - or better yet, a 12" square package - but it sounds like this will not be a bolt-on affair. I already need a 1/2" + 3mm spacer in the front to keep the coilovers from chewing the tires, and they already stick out of the fenders by ~1/2". Wider tires will actually be a considerable expense to do it right: flares, maybe spacers, new wheels, more expensive tires, maybe some inner fender clearancing... It's also certainly more drag. That got me thinking: if "compound always trumps width" worked in TTB, maybe it could work now...
I looked into my point assessments for TT classification, and here are the two options I have:
1) Keep running a DOT tire as wide as I want at 3751 lb min weight. Right now, I cross the scales at ~3800 lb, so a small diet wouldn't hurt.
2) Switch to a non-DOT tire (probably an S80) no wider than 265mm and run it at 3831 lb min weight. Considering where I am now, this is really only another 40-50 lb with some buffer.
I called Hoosier to ask about this, and they advised against running a smaller tire on this heavy of a car even for a short TT session. They also said a non-DOT tire will take way too long to warm up, but I was a little skeptical about that. The Pirelli DH compound is somewhat common in TT, and people seem to make them work even though they're designed to last WAY longer than a 15-min TT session and tend to heat up slowly. Also, everyone I've talked to said they provide a noticeable improvement in grip over an R7. I've also read on the internet (which MUST be true) that a Hoosier S80/S100 provides similar or more grip than a DH but doesn't last as long. My hope was that running an overloaded 265mm S80 would warm up within 2 hot laps and still provide more grip than an R7 - at least within a narrow window. For sure I'll be on the wrong side of the load sensitivity curve and a lighter car will get much more grip out of them, but as long as it's more than an R7 - even by 0.05g - it might be enough of an edge to justify the change if I can win tires through contingency. Speaking of - another downside of an S80/S100 is that they're ~$50 more per tire. Whatever the case, it would be silly to ignore Hoosier's advice about their own tire, but I also have to consider that I'm playing with a somewhat uncommon setup compared to most of their customers. I imagine that most of their experience is with much more restrictive classes, and I just need to make something work really well for 1-2 laps even if it sucks everywhere else.
Cliff's Notes:
What will provide more grip for just one lap of a 10-15 min TT session: a 315mm Hoosier R7 or a 265mm non-DOT slick (preferably a Hoosier S80/S100)?
If anybody has experience with experimenting with things like this and is willing to share, I would definitely appreciate the advice. I know it wouldn't be difficult or expensive to test a set of used S80/S100 slicks or even Pirelli DH slicks, but since I don't know how much slower they would be compared to stickers, I'm afraid the test would be misleading.
Thanks,
Dan