Trans Am Tires

[Eunos_Cosmo]

GT7 could definitely use some historic tire compounds. First time out with the Porsche 904 I bought from LCD, I was shocked out how stiff and grippy it felt. It came on RH tires! I'm not even sure the 904's suspension components could even take the forces of modern race compounds. I put it on CS tires immediately afterward, but as @Marcus Garvey notes, these still don't feel right.

 

[hawkeyez]

GT7 could definitely use some historic tire compounds. First time out with the Porsche 904 I bought from LCD, I was shocked out how stiff and grippy it felt. It came on RH tires! I'm not even sure the 904's suspension components could even take the forces of modern race compounds. I put it on CS tires immediately afterward, but as @Marcus Garvey notes, these still don't feel right.

I could have swore I have that car stock and it had CS on it. It slides around a lot for me?

 

[Eunos_Cosmo]

I could have swore I have that car stock and it had CS on it. It slides around a lot for me?

Maybe I am misremembering, but I felt like it handled on rails when I first drove it.

 

[hawkeyez]

Maybe I am misremembering, but I felt like it handled on rails when I first drove it.

You can just add sheet in the settings page and see what tires it throws on it as that reverts it all back to stock.

I wouldn’t say it handles like it’s on rails, but I would say it’s very predictable in its handling even though it doesn’t have a ton of traction. Or perhaps I just drive it harder than I need to. Lol

I love that car at goodwood, lots of predictable drifting.

 

[Marcus Garvey]

Haven’t gotten around to trying comfort mediums yet. Is that 2600lbs correct?n I thought that was the weight of the Sunoco Camaro that they were told to never bring it to the track again? I thought they were more in the 2900lbs range?

The 1967 car they got down to 2550 lbs that they were told not to bring back, they kept running through 1968. They just swapped the nose so it looked like a 68 lol. They would swap number plates to run the cars through tech to avoid rolling thr lightweight car over the scales. Even after all the teams got caught acid dipping by 1968, they just slowly reintroduced lightweight parts over time to get the cars back where they were by 1969. Even in 1970 the Autodynamics Challenger driven by Sam Posey got nabbed dipping. That was part of the popularity in vinyl roof coverings on the cars, to hide the oil canning. Sam talks about it in this interview - start around 2:20 and then Sam begins talking about his car at 3:00.

Attached are a couple of excerpts from The Unfair Advantage detailing some of their efforts in getting the lightweight cars through. Apologies for the cell phone pics of the book lol

By 1969 the SCCA rulebook had the trans am cars at 2900lbs, though as you'll see in Sam's interview I linked, they were running much lighter cars in the races. Iirc the Penske's secondary car was around 2700lbs, not quite as light as the primary car. Nowadays SVRA rules put the Camaro at 3000lbs for historic trans am, but they're well over 500hp.

I think CM are closest to real life but CS are probably the sweet spot for the most drivability.

 

[hawkeyez]

The 1967 car they got down to 2550 lbs that they were told not to bring back, they kept running through 1968. They just swapped the nose so it looked like a 68 lol. They would swap number plates to run the cars through tech to avoid rolling thr lightweight car over the scales. Even after all the teams got caught acid dipping by 1968, they just slowly reintroduced lightweight parts over time to get the cars back where they were by 1969. Even in 1970 the Autodynamics Challenger driven by Sam Posey got nabbed dipping. That was part of the popularity in vinyl roof coverings on the cars, to hide the oil canning. Sam talks about it in this interview - start around 2:20 and then Sam begins talking about his car at 3:00.

Attached are a couple of excerpts from The Unfair Advantage detailing some of their efforts in getting the lightweight cars through. Apologies for the cell phone pics of the book lol

By 1969 the SCCA rulebook had the trans am cars at 2900lbs, though as you'll see in Sam's interview I linked, they were running much lighter cars in the races. Iirc the Penske's secondary car was around 2700lbs, not quite as light as the primary car. Nowadays SVRA rules put the Camaro at 3000lbs for historic trans am, but they're well over 500hp.

I think CM are closest to real life but CS are probably the sweet spot for the most drivability.

Well I may buy another Camaro next time it comes up and copy what I have and then lighten some more just to compare.

 

[wheelhp]

without reading too much I'd honestly try to tune for a tyre swap. Something like CS front and SH rear. Or SH front and SM rear then make the rear swing out more on turns with ballast and suspension changes, install a differential but make it very poor and open, that should do it. You're correct that GT7 tyres do not hook up at all realistically. This is a fault of the physics engine and tyre model

 

[hawkeyez]

I’d do that but then if I want to run it in our room with pp and tire limits, I’d have to open up the tire restriction.

It’s pretty good now, I’m getting used of it. Another couple weeks and I’ll probably share it. Hard part with be getting the challenger and boss to match. I’m sure they’ll come in a little under in pp.

 

[hawkeyez]

It’s been a minute but I think I have sorted them out now. Camaro, Challenger and Mustang.

Don’t think I could manage much faster than that. Track to myself, palms sweating trying to maintain control. But they’re not bad, you just can’t go flooring it out of a corner until you straight out.

In case anybody wants to give them a go. I don’t really know much about suspension tuning. They all seem to handle ok. You can get them sliding entering a corner, like inducing oversteer and then throttle out.

I like how they handle. Reminds me a little of Project Cars 2, maybe a bit easier to drive and some differences here and there. Happy with how they turned out. Only tested at Laguna Seca. Probably try them out at Watkins, Road Atlanta and Spa. My favourite tracks.

I ran the Camaro at Goodwood and thru St Mary, I can almost be completely sideways for the right and then again for the left. Pretty much every lap too.

 

[hawkeyez]

Tried to go by specs I found online for the Camaro and then do my best to just match the other two to that. Obviously using lap times mostly versus performance points. But they’re still pretty close in pp. I think the Camaro ends up a bit higher because it’s a small block, doesn’t have the same torque.

 

[Marcus Garvey]

I needed a weekend off from racing myself, so I spent the weekend at the IROC revival exhibition with a close friend of mine who runs a 65 Mustang in the SVRA historic trans am group. The cars are making over 600hp, and the class almost exclusively runs Hoosier TDs. I know I am repeating myself a little, but I figured I would provide an update after verifying for certain what I had posted previously.

The SVRA cars, while looking mostly historically accurate (less safety and comfort/convenience features like fire systems and cool suits and garmins) are making a lot more power than they did when raced originally, but they are handicapped by narrow tyres and wheels and limited compound options.

 

[Mafio]

^That Avy to screen name ration is blowing my mind right now.

 

[hawkeyez]

I needed a weekend off from racing myself, so I spent the weekend at the IROC revival exhibition with a close friend of mine who runs a 65 Mustang in the SVRA historic trans am group. The cars are making over 600hp, and the class almost exclusively runs Hoosier TDs. I know I am repeating myself a little, but I figured I would provide an update after verifying for certain what I had posted previously.

The SVRA cars, while looking mostly historically accurate (less safety and comfort/convenience features like fire systems and cool suits and garmins) are making a lot more power than they did when raced originally, but they are handicapped by narrow tyres and wheels and limited compound options.

If I threw another 150hp at these they’d for surely be undriveable. Aiming for more historic than a throwback Thursday but like a retro version.

The problem is most of the specs you find online I feel like are mostly guesstimates and then there’s different track layout and also tire differences.

I think they’re sorted now. Might have to tweak gearing for different tracks. We ran them at Spa and I took the Boss tuned to match, my friend took the Camaro tune, two others took the challenger. Turns out the challenger was topping out, I may have forgotten to send the transmission sheet, can’t remember if I tweaked any of it. But I was only slowly gaining on the Camaro and I think that’s because I had just ran a ton of laps in all three of them and they’re a little bit to get used of.

I focused on Laguna, but I think a lot of the other tracks will just need some gearing changes or tweaks.

They’re the same weight, same tires, close to the same horsepower. Torque is the only thing differing between them. Which can be an advantage on the straight getting up to speed but it can be a bit of a disadvantage trying to get power down.

They feel similar in handling but different, I like the playfulness of the Camaro, the boss feels a bit more stable, the challenger feels heavier even though it’s the same weight, but I think it had more torque so it kind of makes up for it.

 

[Marcus Garvey]

Yeah there is really no way to properly duplicate either the current historic trans am cars or the period configurations of the cars with the tyre and modifications options in game. Many of the cars can't make the kind of power they make now, and those that can do so with waaaay more torque than the cars ran in real life. Either due to our options being big blocks instead of 5.0 litre, as well as the in game tuning options, camshafts, etc all produce a ton of low end torque that wasn't available with the cam profiles and induction systems they were using at the time.

Pretty much back to make the cars look good and drive as well as you can if you want to build a series around them.

 

[hawkeyez]

Yeah there is really no way to properly duplicate either the current historic trans am cars or the period configurations of the cars with the tyre and modifications options in game. Many of the cars can't make the kind of power they make now, and those that can do so with waaaay more torque than the cars ran in real life. Either due to our options being big blocks instead of 5.0 litre, as well as the in game tuning options, camshafts, etc all produce a ton of low end torque that wasn't available with the cam profiles and induction systems they were using at the time.

Pretty much back to make the cars look good and drive as well as you can if you want to build a series around them.

I think I can make the cars handle better and be more competitive but that was really the point. I wanted them more loose feeling, a bit harder to drive but fun.

You can almost tune the handling characteristics right out of a car in this game if you really want to. I think what helps the most is no camber or toe on the rear. Almost feels slower to get away on you which makes more sense to me, more tire contact to the pavement.

I like how you have to start your corners a tad earlier, get them drifting some for a better corner. Which is what I’ve seen on a lot of older footage, sliding around the corners, a little loose coming out when on the throttle. They’re not speed demons but they’re not exactly slow either.

Yeah I wish we could engine swap in small blocks into the challenger and boss. Biggest pet peeve with this game for me is the cars they give you, while you’d think they’d be competitive with one another, they really aren’t and it requires so much tuning and testing.

I get they can’t be perfect, but why’d we get a dodge challenger demon, a ZL1 both 2018 but a 2016 GT350R? Most companies all make cars each year that are almost exact in testing.

I remember reading about the latest cars in some magazines and 0-60 times were all within .1-.2 of one another, top speeds were maybe 5-10mph different. Track times were for the most part relatively the same. Was more like pick your flavour. But PD gives us the P4 but then the slower GT40. So you’re left tuning to try and match them up and who wants to go tuning $4-$20 million cars haha

 

[jrbabbitt]

Forgive me, but when the OP mentioned TransAm tyres all I could think of was "Bias-Ply" tyres. You remember before Radial tyres...

 

[hawkeyez]

Forgive me, but when the OP mentioned TransAm tyres all I could think of was "Bias-Ply" tyres. You remember before Radial tyres...

Yep, I know they’re different, the post was trying to figure out which tire would be closest but it was said probably somewhere between two of the tires and even then it’s not totally accurate so I just had to roll with something. Ended up going comfort soft as sports hard seemed a little too gripped and comfort medium was just really hard to put the power down.

When I was younger we had a 68 EL Camino that still had some bias ply tires on it haha. Might not be the best tire but holy durable. Had a weird size rating like G60-15 or something like that. Very squared off looking tires too.

 

[jrbabbitt]

Yep, I know they’re different, the post was trying to figure out which tire would be closest but it was said probably somewhere between two of the tires and even then it’s not totally accurate so I just had to roll with something. Ended up going comfort soft as sports hard seemed a little too gripped and comfort medium was just really hard to put the power down.

When I was younger we had a 68 EL Camino that still had some bias ply tires on it haha. Might not be the best tire but holy durable. Had a weird size railing like G60-15 or something like that. Very squared off looking tires too.

Yes, bias-ply were sort of squared off, their side walls were stiffer than the newer radials of the day, I can remember when my Dad bought a set of radials for the 71 Skylark and after they were on they looked bulged out and looking like they were almost flat!
Correction:
(From Wikipedia)
Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stabilizer belts directly beneath the tread. The belts may be cord or steel. The advantages of this construction include longer tread life, better steering control, fewer blowouts, improved fuel economy, and lower rolling resistance. Disadvantages of the radial tire are a harder ride at low speeds on rough roads and in the context of off-roading, decreased "self-cleaning" ability, and lower grip ability at low speeds.

Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees. Successive plies are laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.

 

[LSFDRX]

Very interesting conversation. Makes me want to get into replicating the same characteristics for myself, although it has been said that these trans-am cars and many other classic race cars operated within a WIDE range if slip angle that GT7 is notoriously unforgiving with.

I don't know if it has been mentioned, but the reasoning behing these cars needing to be set at 0 toe and camber in the rear is because they are live axle vehicles. The rear is a solid axle and does not allow for adjustment. I always set any car in game with a solid rear to 0 for posterities sake, but I do not know if this truly replicates the physics of a true live rear.

Unfortunately all of the hard work done in replicating these setups may be all for nought as we are likely to see a marked change in tire physics in the update tomorrow.

Regardless, great conversation and wonderful history!

 

[hawkeyez]

Very interesting conversation. Makes me want to get into replicating the same characteristics for myself, although it has been said that these trans-am cars and many other classic race cars operated within a WIDE range if slip angle that GT7 is notoriously unforgiving with.

I don't know if it has been mentioned, but the reasoning behing these cars needing to be set at 0 toe and camber in the rear is because they are live axle vehicles. The rear is a solid axle and does not allow for adjustment. I always set any car in game with a solid rear to 0 for posterities sake, but I do not know if this truly replicates the physics of a true live rear.

Unfortunately all of the hard work done in replicating these setups may be all for nought as we are likely to see a marked change in tire physics in the update tomorrow.

Regardless, great conversation and wonderful history!

They’re not bad. I think the 0 camber and 0 toe actually helps widen the slip angle. Could be me. I can drift the Camaro thru St Mary at goodwood no problem. Right then left.

Marcus Garvey gave the tip about the straight axle.

Try them out. I like them.

 

[hawkeyez]

Hey Marcus, I tossed Comfort Medium on the Camaro and ran it at Laguna Seca. 1:45 I believe I managed, so right in that lap time range you mentioned. Unfortunately I think the front end pushes too much and the rear tires heat up very quickly exiting the corner. I can drive it, you definitely have to work the throttle a lot. So definitely have a good idea of where to aim. Just lack the proper tires I believe, as you had mentioned.



Hey LSFDRX
*** On another note, I think I stumbled across something with that low slip angle gran Turismo situation. I think most of it stems from tires heating up. Which explains the high horsepower cars being prone to send off. Haha

At a certain temp they just don’t grip at all and this is just before the red outline shows up in GT7, I’m using SimHub to see the tire temps. If you see the red border around the tire, it’s too late. Haha

I think the issue arises because when they’re hot, there’s literally no grip. It’s not like the car gets very loose, its that it behaves like the rear tire(s) are on ice.

Somebody had mentioned it’s like the rear tires are like a massive flywheel and won’t stop spinning. Which they are, but you should be able to let off, disengage power to the wheels (stupid no working clutch in GT7 as this would help) and work at saving it. I think that’s the severely heated tires becoming greaseballs causing the feeling of not being able to do anything. I’m talking about when the cars tail end start coming around, you let off, lightly pump the brakes, countersteer like a mad man and it just keeps turning on you. Maybe if we had a proper working clutch we could stab the clutch and completely remove power to the rear wheels!

I was watching the tire temps running the comfort mediums with those tunes, and they heat up a bit but at a certain point it’s not as gradual and it just sky rockets. That’s the poor slip angle of Gran Turismo. Some of my friends that have played a lot of sims have mentioned this, “it’s hard to push the car and know when you’ve gone to far until it’s way too late”. It all makes sense now. Because those tires can heat up in the blink of an eye.



Hopefully they fix that in this latest update. No compounding interest for tires heating up haha and a proper working clutch so you can instantly remove all power to the wheels.

 

[LSFDRX]

They’re not bad. I think the 0 camber and 0 toe actually helps widen the slip angle. Could be me. I can drift the Camaro thru St Mary at goodwood no problem. Right then left.

Marcus Garvey gave the tip about the straight axle.

Try them out. I like them.

I'm sorry, but I'm not exactly sure what you mean by "them".

Hey LSFDRX
*** On another note, I think I stumbled across something with that low slip angle gran Turismo situation. I think most of it stems from tires heating up. Which explains the high horsepower cars being prone to send off. Haha

At a certain temp they just don’t grip at all and this is just before the red outline shows up in GT7, I’m using SimHub to see the tire temps. If you see the red border around the tire, it’s too late. Haha

I think the issue arises because when they’re hot, there’s literally no grip. It’s not like the car gets very loose, its that it behaves like the rear tire(s) are on ice.

Somebody had mentioned it’s like the rear tires are like a massive flywheel and won’t stop spinning. Which they are, but you should be able to let off, disengage power to the wheels (stupid no working clutch in GT7 as this would help) and work at saving it. I think that’s the severely heated tires becoming greaseballs causing the feeling of not being able to do anything. I’m talking about when the cars tail end start coming around, you let off, lightly pump the brakes, countersteer like a mad man and it just keeps turning on you. Maybe if we had a proper working clutch we could stab the clutch and completely remove power to the rear wheels!

I was watching the tire temps running the comfort mediums with those tunes, and they heat up a bit but at a certain point it’s not as gradual and it just sky rockets. That’s the poor slip angle of Gran Turismo. Some of my friends that have played a lot of sims have mentioned this, “it’s hard to push the car and know when you’ve gone to far until it’s way too late”. It all makes sense now. Because those tires can heat up in the blink of an eye.



Hopefully they fix that in this latest update. No compounding interest for tires heating up haha and a proper working clutch so you can instantly remove all power to the wheels.

I agree with most of this, but I don't think tire temps are affecting the ability to slide. That might be an issue for some when a slide get's away from them, but I have the opposite issue. They're only in the red range well into wheelspin, and the problem for me is not getting the car to slide, but maintaining a slide in opposite lock, then smoothly transitioning out of it with throttle modulation and opening the steering back up.

There is still the issue that you mentioned of the drive wheels acting like a flywheel and seemingly continuing to apply power after throttle is dropped, but having clutch control isn't necessarily the way to remedy this. Yes, pushing the clutch in will disengage power, but cutting throttle also does. Dropping throttle in gear should also cause the drive wheels to actively decelerate due to compression braking, which also doesn't seem to happen in most cases.

The biggest issues for me since GT7 released is the crazy narrow window in which opposite lock exists and the rapid, sometimes random, timing of the tires gripping back up. In the real world, maintaining opposite lock in a car is much easier than in the game, and most tires have a much more progressive return to grip when beyond traction limits. I've done my fair share of track days and drifting and even with R compound tires there are rarely moments when you get into sawing back and forth at the wheel to straighten a car out that happens so often in GT7.

Even in this latest Time Trial with the LFA (granted its on sticky SS tires) there are moments where you'll be coming out of oversteer and straightening the car out on throttle, and just when you're about to settle back in the car all of the sudden wildly steps out again. Instead of smoothly powering out of a sweet slide, relying on the increased load on the motor that comes with speed to tamper wheelspin, the tires will just break free out of nowhere. It really makes no sense. It's like the physics model adds little clutch kicks into acceleration, which is a fundamental physics issue.

After many hours in the game I am used to the physics and can slide cars at will with little issue, but there are still many messy looking moments where the car is still trying to come around when it shouldn't. It would be nice if we could comfortably slide cars and keep them in feint yaw without scrambling to keep steering lock. ACC is much more realistic when it comes to this.

While not the best example in the context of classic, low-grip racers, here is an example of purposeful drifting in a high-horse RWD Mercedes GT-R. You'll see that the tires only get into the red well into the slides, and them being "hot" doesn't really effect the angle of or ability to maintain a drift. The issue, as always, is the tries transitioning to 100% grip very suddenly, ruining the angle and forcing me out of the drift. I wish the steering animation reflected the actual steering input needed to do this!





I'm really looking forward to the update tonight since GT has been working with the people at Michelin. I'm very hopeful that some talented drivers have spent some time in game, found the same issues we have, and assisted in fixing them. GT7 has gotten much better physically since it's release, but there is still much room for improvement.

 

[hawkeyez]

I'm sorry, but I'm not exactly sure what you mean by "them".


I agree with most of this, but I don't think tire temps are affecting the ability to slide. That might be an issue for some when a slide get's away from them, but I have the opposite issue. They're only in the red range well into wheelspin, and the problem for me is not getting the car to slide, but maintaining a slide in opposite lock, then smoothly transitioning out of it with throttle modulation and opening the steering back up.

There is still the issue that you mentioned of the drive wheels acting like a flywheel and seemingly continuing to apply power after throttle is dropped, but having clutch control isn't necessarily the way to remedy this. Yes, pushing the clutch in will disengage power, but cutting throttle also does. Dropping throttle in gear should also cause the drive wheels to actively decelerate due to compression braking, which also doesn't seem to happen in most cases.

The biggest issues for me since GT7 released is the crazy narrow window in which opposite lock exists and the rapid, sometimes random, timing of the tires gripping back up. In the real world, maintaining opposite lock in a car is much easier than in the game, and most tires have a much more progressive return to grip when beyond traction limits. I've done my fair share of track days and drifting and even with R compound tires there are rarely moments when you get into sawing back and forth at the wheel to straighten a car out that happens so often in GT7.

Even in this latest Time Trial with the LFA (granted its on sticky SS tires) there are moments where you'll be coming out of oversteer and straightening the car out on throttle, and just when you're about to settle back in the car all of the sudden wildly steps out again. Instead of smoothly powering out of a sweet slide, relying on the increased load on the motor that comes with speed to tamper wheelspin, the tires will just break free out of nowhere. It really makes no sense. It's like the physics model adds little clutch kicks into acceleration, which is a fundamental physics issue.

After many hours in the game I am used to the physics and can slide cars at will with little issue, but there are still many messy looking moments where the car is still trying to come around when it shouldn't. It would be nice if we could comfortably slide cars and keep them in feint yaw without scrambling to keep steering lock. ACC is much more realistic when it comes to this.

While not the best example in the context of classic, low-grip racers, here is an example of purposeful drifting in a high-horse RWD Mercedes GT-R. You'll see that the tires only get into the red well into the slides, and them being "hot" doesn't really effect the angle of or ability to maintain a drift. The issue, as always, is the tries transitioning to 100% grip very suddenly, ruining the angle and forcing me out of the drift. I wish the steering animation reflected the actual steering input needed to do this!





I'm really looking forward to the update tonight since GT has been working with the people at Michelin. I'm very hopeful that some talented drivers have spent some time in game, found the same issues we have, and assisted in fixing them. GT7 has gotten much better physically since it's release, but there is still much room for improvement.

I meant try my trans am tunes out, I post the settings.

What I meant is I’ve been driving down a straight I can hear the tires squealing and then it’ll start losing control and then boom, red. Might be different for other cars.

I think tire temps do play a part especially hooking up again, maybe they get hot, stay there for a certain amount of time and then cool quickly, hooking back up at the most inconvenient time? I have noticed it does not take long for hot tires to cool right back down to like 55-65 once you get on a straight or let off.

My thinking with the clutch is letting off doesn’t help, can make it worse. I remember going to the local drag strip as a teen. One Camaro let off too quickly… the rear diff locked up and he ended up rolling the car. It looked like he slammed on the rear brakes only. So I do think the clutch would help. It works on project cars 2. Kicks out, stab clutch, it comes back.

Canadian here, driving standard growing up on ice. Aka poor traction in a rear wheel drive car. The clutch was my friend. You push that clutch in and the rear end snaps back into place fairly quickly. So I do think it would help, nonetheless I’d prefer a proper functioning clutch in game instead of what we have currently, because why not, it’s not right and the game is all about having attention to detail.

It feels like a Canadian tire commercial I saw years ago, who wrote this ad? A mechanic walks up to a car with the hood open with a ratchet and a 3/4” socket and rests it on the air filter and just starts cranking. Haha, umm where is there a 3/4 nut or bolt on a classic cars chrome air filter cover? GT7 clutch operation feels like that, who designed that part of the game?

I just read the physics are suspension and tires and it looks promising that the tires are going to be more accurate!