Tracking and Tires and Pressures
10-16-15, 06:21 AM
#16
Pole Position
Thread Starter
I did put chalk marks on the tires (foot powder spray actually) and I
clearly saw the roll over happening on the fronts so I did not lower the pressure. If you look at my 1st post you can see the triangular marking in the zoom image in the upper left.
clearly saw the roll over happening on the fronts so I did not lower the pressure. If you look at my 1st post you can see the triangular marking in the zoom image in the upper left.
10-16-15, 06:57 AM
#17
Are you saying the RC-F has no camber adjustment, or no camber adjustment BEYOND stock parameters? I could bet my house the former is not true, but you probably meant the latter, correct? I'll get under my car tomorrow to see if I can adjust the stupid parking brake myself (goes all the way to the carpet without holding the car much), and will look for camber and toe adjustments for myself. They're usually adjustable thru an eccentric nut/washer with limited adjustment (same for the toe).
What I meant is that there is NO camber adjustment whatsoever out of the box. There's toe adjustment though. Like I said, if you find otherwise, let me know, because the car needs more negative camber up front.
Very good point. Forgot to comment about that. Usually you run LOWER cold pressures at the track, not higher. 40 should be the highest HOT pressure indeed, not 50. But I have NO previous experience driving a 4K-lb whale aggressively, so optimal tire pressures might be different. Will continue to read other more experienced owners for the best cold tire pressures for aggressive driving
40psi +-5psi is about right from my research and experience too. Basically as low as you can go before you start to roll over on the sidewall. I don't think PSS sidewalls are quite as stiff as other tires like the DZ-II or RS3 so you may need a few extra pounds of pressure. You really have to experiment while you're at the track though.
The car is front grip limited, so along with less weight on the rears, it doesn't get much of a work out. I'm running 31psi cold out back without any rolling over, which makes oversteer a bit smoother and more predictable.
Last edited by rage2; 10-16-15 at 07:03 AM.
10-16-15, 07:19 AM
#18
Here's my g-meter readings from this week's driving. While it's street driving, I do run on some really open back roads, so it's fairly aggressive compared to your typical street driving.
Comparing to rjmalm's graphs, you can see the difference in our braking styles, even though we're just looking at peak #'s. I'm harder on the brakes in a straight line but I don't trail brake as much. I have a lot of off camber corners, and the RC-F suffers from a trail braking oversteer there, so I'm pretty easy on the brakes at turn-in.
I'm driving harder out of corners tho, but he was only driving 8/10ths, so it's not really a fair comparison. It'd be interesting for others to pull up their G meter history to see how they look.
Comparing to rjmalm's graphs, you can see the difference in our braking styles, even though we're just looking at peak #'s. I'm harder on the brakes in a straight line but I don't trail brake as much. I have a lot of off camber corners, and the RC-F suffers from a trail braking oversteer there, so I'm pretty easy on the brakes at turn-in.
I'm driving harder out of corners tho, but he was only driving 8/10ths, so it's not really a fair comparison. It'd be interesting for others to pull up their G meter history to see how they look.
10-16-15, 12:36 PM
#19
Very interesting discussion. The first thing track drivers need to do is swap the factory DOT3 brake fluid for a quality DOT4. With such a heavy car, the brakes have to work a lot harder than a lighter car, and would boil DOT3 fluid much quicker. I'll also switch to DOT4 when I bleed the brakes in a year or so.
Just checked my front tires, and there's obvious sidewall rollover on both, with the right a bit worse, since I pulled 0.9G on a left curve once. Did many curves at 0.8G on both sides. The rears look absolutely perfect. By the way, had the equivalent of 34 psi cold up there. Next time I need to increase tire pressure by 2 psi at home to compensate for the 20ºF difference at the mountains. It's also over twice as high as well. Will take my pressure gauge and pump to see exactly what's the gauge difference up there. TPMS said 37, but I agree it should be in the 40s hot for optimum grip and to minimize wear.
Hey Rage2, will check the front for alignment adjustments. I repeat that I agree with you there won't be adjustment beyond stock, but it'd be the first car ever without camber adjustment to bring all wheels within spec. The only adjustment I've seen omitted is caster (needing shims to adjust, if necessary), but that's it. Will call Lexus and ask for a master tech and see what he says too.
. The first thing track drivers need to do is swap the factory DOT3 brake fluid for a quality DOT4. With such a heavy car, the brakes have to work a lot harder than a lighter car, and would boil DOT3 fluid much quicker. I'll also switch to DOT4 when I bleed the brakes in a year or so. Just checked my front tires, and there's obvious sidewall rollover on both, with the right a bit worse, since I pulled 0.9G on a left curve once. Did many curves at 0.8G on both sides. The rears look absolutely perfect. By the way, had the equivalent of 34 psi cold up there. Next time I need to increase tire pressure by 2 psi at home to compensate for the 20ºF difference at the mountains. It's also over twice as high as well. Will take my pressure gauge and pump to see exactly what's the gauge difference up there. TPMS said 37, but I agree it should be in the 40s hot for optimum grip and to minimize wear.
Hey Rage2, will check the front for alignment adjustments. I repeat that I agree with you there won't be adjustment beyond stock, but it'd be the first car ever without camber adjustment to bring all wheels within spec. The only adjustment I've seen omitted is caster (needing shims to adjust, if necessary), but that's it. Will call Lexus and ask for a master tech and see what he says too.
10-17-15, 12:11 PM
#20
I only know the cars I've owned but the RC-F is the first one I've owned with no camber adjustments whatsoever. Talking to my mechanic he says 1/3 of the cars out there don't have camber adjustments out of the box.
10-18-15, 09:49 AM
#21
Great stuff...many thanks for the information on optimizing performance.
10-19-15, 05:18 AM
#22
The extra camber I was able to get in my IS350 was good for 2-4 seconds at Mid-Ohio this past weekend. Obviously, it's not a direct comparison to those driving an RCF but still similar enough IMO. My corner speeds increased, understeer was much more manageable (still bad), and consequently my lateral accelerations increased. Previous peaks at 0.98-1.02G, now 1.05-1.07G. I didn't lose any of that "easy to drive" tendency either, still very neutral. We didn't have ideal weather conditions either, frosty 28F in the morning with a high of 45F in the afternoon. It was very hard to manage the tire temperatures, but I ended up around 43psi upfront (heavy *** instructor, probably 4000lb gross weight at least).
Aaron
Aaron
10-21-15, 08:24 PM
#23
I've spent the last month trying to find the optimal setup on the RC-F, and here's what I've ended up with. The car struggles with front grip, rear was pretty easy to dial in, but fronts was a nightmare. First thing I did was add 20mm spacers up front. No rub, even under hard compression, lots of room for it. This helped improve front traction.
On the alignment side, my final setup after 6 alignments messing with toe was 0 toe L/R fronts, and 0.01 toe in L/R rear. For the rears, it's slightly off from factory range (min 0.04) but the rear was much more predictable and allowed a bit of slippage using throttle even in faster corners, which helps with rotating the car with the throttle. A disclaimer, I'm at 3700ft elevation, so my car makes less power than at sea level, so the minimum factory range may be ideal at sea level. For front toe, even though factory range allows -0.08 degress toe out per side, it was way too much, washing out the front, understeering on turn-in significantly. 0 was the optimal from my experiments.
Tire pressures, I started with what the car was delivered with, 34f/34r cold, and it was rolling over quite a bit up front where it wore out the damn tread indicator arrows. The rears weren't anywhere near the tread arrows on the PSS's, and now that I've dropped them to 31psi cold (~35psi hot) they run right to the tread arrow indicator. The fronts, now that's a bit of a nightmare. Had it as high as 40psi cold (46psi hot) and it was still rolling over too much. Slowly worked it down from there, and the point of diminishing returns on this setup was 37psi cold, which works out to 42psi hot.
Some visual data. Took the car out tonight to my usual hard driving route, warmed the tires up (42f/34r hot), pulled over, and chalked the front tires. I took a 3rd gear flat elevation corner at 2 different speeds (0.8g and 1.0g), rolled into the corner gently so that there are no excessive G spikes, and here's how it looks.
0.8g turn, and chalk mark:
At 0.8g's, the tire is running pretty much right at where the arrow starts if the arrow didn't get melted off.
1.0g turn, and chalk mark:
At 1.0g's, the tire is rolling over past the edge, at the end of the tread block near the end of the arrow marker if it was still there.
So yea, that's the best I can do in terms of setup on this car. It needs some negative camber up front badly. Next year, I'm going to move to the 265/35-19 PSS to see if I can improve things a little more, and retry the setup from the start.
On the alignment side, my final setup after 6 alignments messing with toe was 0 toe L/R fronts, and 0.01 toe in L/R rear. For the rears, it's slightly off from factory range (min 0.04) but the rear was much more predictable and allowed a bit of slippage using throttle even in faster corners, which helps with rotating the car with the throttle. A disclaimer, I'm at 3700ft elevation, so my car makes less power than at sea level, so the minimum factory range may be ideal at sea level. For front toe, even though factory range allows -0.08 degress toe out per side, it was way too much, washing out the front, understeering on turn-in significantly. 0 was the optimal from my experiments.
Tire pressures, I started with what the car was delivered with, 34f/34r cold, and it was rolling over quite a bit up front where it wore out the damn tread indicator arrows. The rears weren't anywhere near the tread arrows on the PSS's, and now that I've dropped them to 31psi cold (~35psi hot) they run right to the tread arrow indicator. The fronts, now that's a bit of a nightmare. Had it as high as 40psi cold (46psi hot) and it was still rolling over too much. Slowly worked it down from there, and the point of diminishing returns on this setup was 37psi cold, which works out to 42psi hot.
Some visual data. Took the car out tonight to my usual hard driving route, warmed the tires up (42f/34r hot), pulled over, and chalked the front tires. I took a 3rd gear flat elevation corner at 2 different speeds (0.8g and 1.0g), rolled into the corner gently so that there are no excessive G spikes, and here's how it looks.
0.8g turn, and chalk mark:
At 0.8g's, the tire is running pretty much right at where the arrow starts if the arrow didn't get melted off.
1.0g turn, and chalk mark:
At 1.0g's, the tire is rolling over past the edge, at the end of the tread block near the end of the arrow marker if it was still there.
So yea, that's the best I can do in terms of setup on this car. It needs some negative camber up front badly. Next year, I'm going to move to the 265/35-19 PSS to see if I can improve things a little more, and retry the setup from the start.
10-21-15, 09:21 PM
#24
Thank you very much for that detailed report. Without adding negative camber, no sense in doing anything else IMO. You can put a 305 tire in front, and you'd still have the brunt of the car's weight on the same narrow outside patch of the tire as right now, leading to very little improvements IMO. Same with spacers, which only add stress to the suspension IMO (not enough to make a difference). My car shows exactly the same rollover problem at 0.8G as yours, and I had my tires at the equivalent up there of 34 psi cold. The front is the problem, so no sense in making the rear even grippier IMO, so I'd just leave the pressures alone. My car was very neutral up to the 0.8G. Just got it up to 0.9G once, and it started plowing, even after transfering some of the weight rearward with throttle steer (and yes, TVD in track mode). Not close to losing grip, for what I could tell (steering is precise, but not very communicative), but not fun anymore, and not worth eating your tires up IMO. I bet at 1G, it wasn't fun anymore with the understeer, was it?
As a final comment, this is a VERY HEAVY car to even be doing anything at a track. So we have to keep in mind that. But it's disheartening that a simple alignment job could elevate this car much higher than it's already accomplished level, with hardly any cost. Without the ability to adjust negative camber to the level it should have come from the factory (heck, even my Hyundai Azera Limited beater travel car has -1.5 camber in front), Lexus did a disservice to itself and all RC-F owners. Hopefully they'll correct that in the near future. Even more disturbing is that it reportedly has NO camber adjustment at all. I still find that hard to believe, but will have to wait for an oil change to verify it myself
. And yes, curious what the heck is the current alignment on my car. Anyway, thanks again for all your hard work. And you should consider waiting for a camber kit instead of throwing your money away in spacers, wider tires, etc. Good luck, and please keep us posted on your improvements.
As a final comment, this is a VERY HEAVY car to even be doing anything at a track. So we have to keep in mind that. But it's disheartening that a simple alignment job could elevate this car much higher than it's already accomplished level, with hardly any cost. Without the ability to adjust negative camber to the level it should have come from the factory (heck, even my Hyundai Azera Limited beater travel car has -1.5 camber in front), Lexus did a disservice to itself and all RC-F owners. Hopefully they'll correct that in the near future. Even more disturbing is that it reportedly has NO camber adjustment at all. I still find that hard to believe, but will have to wait for an oil change to verify it myself
. And yes, curious what the heck is the current alignment on my car. Anyway, thanks again for all your hard work. And you should consider waiting for a camber kit instead of throwing your money away in spacers, wider tires, etc. Good luck, and please keep us posted on your improvements.
10-22-15, 07:01 AM
#25
Pole Position
Thread Starter
at my track worn tires and replaced the fronts. Lexus did not have the RC-F alignment specs and the alignment check report shows IS-F numbers.
The result of a .5 difference in camber between the left and right can be seen in my images after tracking. In the upper left photo you can see my chalk mark
is gone after the vertical stripe. You can see the R groove is worn more with -.2 camber than the outside tire edge of the front left (camber -.7).
Last edited by rjmalm; 10-22-15 at 02:23 PM.
10-22-15, 07:29 AM
#26
Thank you very much for that detailed report. Without adding negative camber, no sense in doing anything else IMO. You can put a 305 tire in front, and you'd still have the brunt of the car's weight on the same narrow outside patch of the tire as right now, leading to very little improvements IMO. Same with spacers, which only add stress to the suspension IMO (not enough to make a difference). My car shows exactly the same rollover problem at 0.8G as yours, and I had my tires at the equivalent up there of 34 psi cold. The front is the problem, so no sense in making the rear even grippier IMO, so I'd just leave the pressures alone. My car was very neutral up to the 0.8G. Just got it up to 0.9G once, and it started plowing, even after transfering some of the weight rearward with throttle steer (and yes, TVD in track mode). Not close to losing grip, for what I could tell (steering is precise, but not very communicative), but not fun anymore, and not worth eating your tires up IMO. I bet at 1G, it wasn't fun anymore with the understeer, was it?
I don't think anyone makes camber plates or anything for the front yet. I've only been able to find rear camber arms, but that's pointless until the front is fixed.
Last edited by rage2; 10-22-15 at 07:42 AM.
10-22-15, 03:37 PM
#27
) info. I did my experiment at the end of my run, so obviously with hot tires. You'd have experienced that big time at 1G with hot tires as well. And keep in mind it wasn't even hot up there. On a hot track, you'd destroy these tires in short order with that ridiculous alignment.
10-22-15, 05:37 PM
#28
WHAT?!? No alignment specs after a year of production? And did you see the freaking tolerance? That's absolutely insane. WIthout alignment adjustments, car is going to be all over the f***ing place, like yours is. Only -0.2 in a sports car? And the spec is from -0.1 to -1.6? This is an absolute joke. The rear is similarly bad at -0.8 to -2.3. You clearly said IS-F specs, but this car being based quite a bit on the IS, I'd guess they'll be similar. Will call my friend (salesman since Lexus started) and see what he has to say about that; he's extremely knowledgeable on this car. I want to know the freaking specs, and the adjustment issue to see what we can do about that. Thank you for that (disturbing) info.
I did my experiment at the end of my run, so obviously with hot tires. You'd have experienced that big time at 1G with hot tires as well. And keep in mind it wasn't even hot up there. On a hot track, you'd destroy these tires in short order with that ridiculous alignment.
) info. I did my experiment at the end of my run, so obviously with hot tires. You'd have experienced that big time at 1G with hot tires as well. And keep in mind it wasn't even hot up there. On a hot track, you'd destroy these tires in short order with that ridiculous alignment.
I would recommend you guys get in contact with FIG or some other automotive company for an aftermarket solution. FIG offered to make custom upper control arms for +-$500, so it should be feasible with the RCF. But even with adjustable arms you may run into clearance issues with the spindles.
Don't forget that the PSS is not a track tire, although it can be used at the immediate level. You may need to get an extreme summer tire with stiffer sidewalls (DZII, RS3, etc.). PSS will most likely get greasy, chunk, and/or roll-over before the other tires. Of course you'll sacrifice a lot of road manners compared to the michelins. The wear in your pictures look pretty good, but I'd imagine the inside of the tires are not getting to optimal temperature even so.
08-21-16, 12:49 PM
#29
bump.
Drove my first AutoX in the RC-F yesterday with these settings and the car felt great in most situations. The fronts are still rolling over like crazy at the limit, but I could easily unload the fronts and rotate the car with just a tad more throttle, basically lightly throttle steering the car around the entire course. The only exception where I had problems were once again the off camber corners where easing on more throttle resulted in more understeer. Lifting the throttle didn't help much either so pretty much had to dial back entry speed. Another place where I had to ease off was the slalom, where the weight of the RC-F really rears its ugly head. Trying to get a little more rotation using the throttle really unbalances the car on the transition and really tank slaps the rear end and kills speed. Couldn't get greedy there.
Anyways, here's the G-Meter reading.
And here's one of the runs. Didn't get my best run on video, this one was still a bit of exploring the limits of some of the corners.
Surprisingly though, with the RC-F being classed in BS, it could be pretty competitive. With better tires (RE71Rs have RC-F sizing) and more familiarity (I drove **** poor littered with mistakes) I believe the car could break into the top 5.
Drove my first AutoX in the RC-F yesterday with these settings and the car felt great in most situations. The fronts are still rolling over like crazy at the limit, but I could easily unload the fronts and rotate the car with just a tad more throttle, basically lightly throttle steering the car around the entire course. The only exception where I had problems were once again the off camber corners where easing on more throttle resulted in more understeer. Lifting the throttle didn't help much either so pretty much had to dial back entry speed. Another place where I had to ease off was the slalom, where the weight of the RC-F really rears its ugly head. Trying to get a little more rotation using the throttle really unbalances the car on the transition and really tank slaps the rear end and kills speed. Couldn't get greedy there.
Anyways, here's the G-Meter reading.
And here's one of the runs. Didn't get my best run on video, this one was still a bit of exploring the limits of some of the corners.
Surprisingly though, with the RC-F being classed in BS, it could be pretty competitive. With better tires (RE71Rs have RC-F sizing) and more familiarity (I drove **** poor littered with mistakes) I believe the car could break into the top 5.
08-21-16, 01:44 PM
#30
Lexus Test Driver
bump.
Drove my first AutoX in the RC-F yesterday with these settings and the car felt great in most situations. The fronts are still rolling over like crazy at the limit, but I could easily unload the fronts and rotate the car with just a tad more throttle, basically lightly throttle steering the car around the entire course. The only exception where I had problems were once again the off camber corners where easing on more throttle resulted in more understeer. Lifting the throttle didn't help much either so pretty much had to dial back entry speed. Another place where I had to ease off was the slalom, where the weight of the RC-F really rears its ugly head. Trying to get a little more rotation using the throttle really unbalances the car on the transition and really tank slaps the rear end and kills speed. Couldn't get greedy there.
Anyways, here's the G-Meter reading.
And here's one of the runs. Didn't get my best run on video, this one was still a bit of exploring the limits of some of the corners.
YYC AutoX RC-F - YouTube
Surprisingly though, with the RC-F being classed in BS, it could be pretty competitive. With better tires (RE71Rs have RC-F sizing) and more familiarity (I drove **** poor littered with mistakes) I believe the car could break into the top 5.
Drove my first AutoX in the RC-F yesterday with these settings and the car felt great in most situations. The fronts are still rolling over like crazy at the limit, but I could easily unload the fronts and rotate the car with just a tad more throttle, basically lightly throttle steering the car around the entire course. The only exception where I had problems were once again the off camber corners where easing on more throttle resulted in more understeer. Lifting the throttle didn't help much either so pretty much had to dial back entry speed. Another place where I had to ease off was the slalom, where the weight of the RC-F really rears its ugly head. Trying to get a little more rotation using the throttle really unbalances the car on the transition and really tank slaps the rear end and kills speed. Couldn't get greedy there.
Anyways, here's the G-Meter reading.
And here's one of the runs. Didn't get my best run on video, this one was still a bit of exploring the limits of some of the corners.
YYC AutoX RC-F - YouTube
Surprisingly though, with the RC-F being classed in BS, it could be pretty competitive. With better tires (RE71Rs have RC-F sizing) and more familiarity (I drove **** poor littered with mistakes) I believe the car could break into the top 5.
