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Reducing understeer in the rain?

Old 08-18-17, 02:19 AM
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Reducing understeer in the rain?

So, yesterday I had a track day in the wet and my FD had fairly heavy understeer which actually made it pretty easy to drive, but boring and slow.

I had a hard time getting heat in the fronts. The rears were reasonably warm, all considered.

I was wondering whether I should have increased or decreased the tire pressure to get more heat in the tires. Which way actually works better?

It seems like less pressure would allow more heat to build up from the tire's deformation, but the pressures are already lower than normal because they don't heat up as much. OTOH, less pressure generally means more grip, which could have meant they'd be even more likely to stay cold.

Increasing the temperature would help prevent hydroplaning, but I didn't have any hydroplaning (the tires are still fairly new). OTOH, they would have probably slided even more with more pressure, which could have increased heat in them.


Are there any other things you can change at the track besides tire pressure and sway bars (although mine aren't adjustable) that can adjust balance?
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Old 08-18-17, 10:11 AM
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Tread?

i would think you'd have oversteer when wet not understeer
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Old 08-18-17, 10:55 AM
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No, you have terrible understeer first in standing water because the front tires hit the water first and have to evacuate it all.
The rear tires benefit from the front tires having evacuated/dispersed the standing water.

Well, its the same with gravel, dirt or anything else on the track surface. First terrible understeer as the front tires get in it and then hopefully oversteer once the rear tires get in it so you can rotate the car to keep it on track.

Of course you can also provoke oversteer as in the wet easier than in the dry, but that is easy to drive around- you don't just have to slow down like with understeer.

Last 5 lap kart track event I was at it poured just for my run group so I didn't have time to change wheels/tires so I was stuck racing on my 295/30-18 slicks front/rear.

On the low speed track like I was on you just have to e-brake or otherwise provoke the rear out to initiate the corner with oversteer otherwise you get the death understeer right off the track.

Saw one of my favorite super clean cars hit the tires that day from death understeer.

I actually want to set up a hydraulic e-brake and practice the reflex of yanking it when the front washes out for such occasions as surprise dirt and puddles on the track as I have been in this predicament several times now.

Watching the Video Options/Hot Vesion professional drivers and they all have this e-brake reflex learned.

Over inflating the tire or over cambering the tire is commonly used up front in the rain as it decreases the tire's contact patch which mean more vehicle weight load per area of contact patch and it is able to push down to the pavement through the water easier.

If you have just enough time to change 2 wheels and tires to rain and not all 4 then just do the fronts so you can safely juggle the oversteer around the track.
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Old 08-18-17, 12:34 PM
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Generally speaking you are pretty screwed. Drive off the racing line, maybe drop pressures slightly in the rear and increase in the front, but there is not much you are going to do without switching to rain tires. You'll never get heat in the tires to get mechanical grip.

All the aero grip in the world does not help if the front slides along the pavement and wont respond to input.

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Old 08-19-17, 04:24 PM
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Come to think of it I could have lowered the front ride height a little bit.
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Old 08-19-17, 06:39 PM
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Looser rear diff.
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Old 08-19-17, 07:46 PM
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Originally Posted by peejay View Post
Looser rear diff.
The stock helical is about as loose as they come.
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Old 08-23-17, 10:59 PM
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just disconnect one side of your front swaybar.
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Old 08-24-17, 12:51 AM
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Originally Posted by racingdriver View Post
just disconnect one side of your front swaybar.
I had actually considered doing this. I assume you should zip tie the free link out of the way. Sure it's not too much of a change?
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Old 08-29-17, 08:51 AM
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honest question because I don't know the weather patterns in Japan: how often are you going to track it in the rain? Are you trying to run TT, race, or be competitive in the rain? or just having fun and learning car control?

If you're trying to compete then I'd explore things like adjustable sways (which you said you didn't have), diff tuning and more complicated matters. If you're just having fun and learning, then use shock settings and tire pressures and don't over-complicate it. It'll never perform the same way in the rain as it does in the dry.

Also, if you really want to drive regularly in the rain the single biggest change you could make over ANYTHING, would be buying a set of dedicated rain tires.
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Old 08-29-17, 01:02 PM
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In the rain I used to soften the shocks front and rear by two clicks each. Tokico Illumina 5 ways. Let the suspension lean and absorb the lateral g's instead of transferring that load to the tires that are not up to the task.

As for your understeer, you could try getting off the throttle earlier to shift more weight to the front earlier before turn in, in addition to everything else mentioned already.

More tire pressure = more heat in the tire. But in the rain you really need a super soft sticky treaded rain tire. And sometimes a new pair of shorts.
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Old 08-30-17, 02:10 AM
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Originally Posted by Smokey The Talon View Post
honest question because I don't know the weather patterns in Japan: how often are you going to track it in the rain? Are you trying to run TT, race, or be competitive in the rain? or just having fun and learning car control?

If you're trying to compete then I'd explore things like adjustable sways (which you said you didn't have), diff tuning and more complicated matters. If you're just having fun and learning, then use shock settings and tire pressures and don't over-complicate it. It'll never perform the same way in the rain as it does in the dry.

Also, if you really want to drive regularly in the rain the single biggest change you could make over ANYTHING, would be buying a set of dedicated rain tires.
I'm more or less good on car control.... I just want to go faster.

Japan has a rainy reason, and it apparently rained in that area for several track days in a row, but I don't actually do as many events as I used to so I only occasionally drive in the rain.

I would really like to get corner-weighted properly since I'm leaving a lot of braking power on the table as one of my front tires locks up first consistently.
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Old 08-30-17, 09:42 AM
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get the baseline sorted first, that will help a lot. Otherwise you're chasing your tail. Then just use tire pressures and shock settings for the rain. Keep notes/records on what you do and what works. Then get a 2nd set of wheels with rain tires and you'll enjoy the rain much more.
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Old 08-31-17, 12:28 AM
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Originally Posted by Smokey The Talon View Post
get the baseline sorted first, that will help a lot. Otherwise you're chasing your tail. Then just use tire pressures and shock settings for the rain. Keep notes/records on what you do and what works. Then get a 2nd set of wheels with rain tires and you'll enjoy the rain much more.
I would but the only shop with weight scales refuses to do it the right way (they want to use preload instead of ride height on a car with full-length threaded shocks) and charges a little too much to come pick up my car, corner weight it, and align it (probably $300+).

I actually know someone who owns scales but won't let me borrow them.

The other shop that has scales is two hours away and doesn't have a proper alignment machine (just dunlop gauges), so no guarantees on how accurate thrust angle is.

If I lost 80 pounds or so the car would probably brake better. There's just too much weight on the front left and rear right (RHD car). The same applies to my MR2.

I'm wondering if I need new rear sway bar links because one of them is rubbing on the shock and I suspect it's the cause of a weird clunking noise in the rear.
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Old 08-31-17, 07:49 AM
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My experience with corner weighting the car 3 times now is that if you set ride heights closely to the same height each corner that the weights are very close. Close enough to save you the trouble of using scales if it's that difficult.

Set your ride heights within 1/4" of each other WITH your body weight in the driver's seat. That will get you close enough. Then make sure to have it aligned properly, also while you sit in it ideally or have your weight in the seat.
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Old 09-19-17, 11:35 AM
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There are a couple ways to get heat in the tire, whether wet or dry:
1. Increase the load on the tire - in this case, heat is generated by the internal flexing (side to side, up and down) of the rubber, belts and tread. Snow tires have sipes to generate friction at the tread surface for added heat. If you can generate more grip, you create more load and more heat.
2. Slide across the road surface - in this case, the friction between the road and the tire creates the heat. Consider that sliding may create less heat than loading. This depends on item 1. You can slide a lot on a low friction surface and not create heat. Sliding on a high friction surface generates much more heat. More grip = more heat = more grip until the tire starts to break down.

In the rain, you also have the high cooling effects of the water carrying away the heat.

I don't know of any hard and fast rule that says more pressure means more heat. Less pressure creates more internal heat inside the tire compound due to increased flex. Remember the Explorer/Bridgestone debacle?

What I do know is that more pressure creates more heat in the center of the contact patch and less pressure creates more heat on the edges. Also, more pressure reduces the size of the contact patch which increases the load per unit area. This MIGHT offer more grip in the rain because there's more load pressing the tire into the peaks and valleys of the road surface. On the other hand, less pressure MIGHT offer more grip because the tire is allowed to flex more, offering softer more compliant grip and less slip angle sensitivity.

In other words, you just have to try it and see. Make large adjustments in pressure, like 5psi at a time. Once you can see the general direction, you can narrow in on your preferred setting.
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Old 09-19-17, 12:01 PM
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As for car set-up, anything you can do to soften the front and stiffen the rear will transfer the balance of grip to the front. Disconnecting the swaybar in the front is a good quick and easy solution. And yes, it might be too much such that you have a hard time putting the power down. Again, you just have to try and see.

You do want to zip-tie the link to the sway bar or the suspension link, depending on what makes the most sense. You don't want that flopping around and hitting other parts of the suspension as it moves in the opposite direction to the suspension travel on the disconnected corner. You can also remove the link entirely if you don't mind the extra work.

And finally, there's the question of driving technique. Do you drive the same in the wet vs. dry? Same line? Same inputs? You'll do best to smooth out your inputs as much as possible. Use more trail braking in the rain to load the front tires at turn-in. Earlier turn-in while progressively adding steering down to the apex will give the tires time to build up the cornering force. It's very easy to shock the tires in low grip conditions. Remember, more load generates more grip which allows for more load. If you try to generate a lot of load before the suspension has time to load up, then you artificially reduce the cornering capacity of the tires. The same applies to braking.

Furthermore, load and grip cause the tire to flex and the flex creates the slip angle. You need slip angle in order to create cornering forces (just as a bridge bends to support a load). In the dry, you can build up the slip angle quickly with quick inputs. The rain requires slower, smoother inputs to build up slip angle.

Finally, are you driving the line with the most grip. The dry line is typically smoother from many tires wearing it down - good for slicks, not so good when wet. It also has a lot of rubber laid down, which gets oily and slick in the wet. You can try braking just off the dry line, turn in slightly later to cross the dry line and stay at least a half car width away from the apex. This works better in some corners than others so just go with trial and error.
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Old 09-20-17, 01:08 AM
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Originally Posted by Quickshoeracer View Post
As for car set-up, anything you can do to soften the front and stiffen the rear will transfer the balance of grip to the front. Disconnecting the swaybar in the front is a good quick and easy solution. And yes, it might be too much such that you have a hard time putting the power down. Again, you just have to try and see.
I only say that because even a few millimeters of ride height adjustment makes a huge difference on the FD.... driving without parts attached might end up being like driving with a broken suspension.



And finally, there's the question of driving technique. Do you drive the same in the wet vs. dry? Same line? Same inputs?
lol, no.


Furthermore, load and grip cause the tire to flex and the flex creates the slip angle. You need slip angle in order to create cornering forces (just as a bridge bends to support a load). In the dry, you can build up the slip angle quickly with quick inputs. The rain requires slower, smoother inputs to build up slip angle.
Basically, if you feel like you're driving on the rails, you're not going fast enough.


Finally, are you driving the line with the most grip. The dry line is typically smoother from many tires wearing it down - good for slicks, not so good when wet. It also has a lot of rubber laid down, which gets oily and slick in the wet. You can try braking just off the dry line, turn in slightly later to cross the dry line and stay at least a half car width away from the apex. This works better in some corners than others so just go with trial and error.
Basically I avoid rubber, puddles, and rumble strips.


I discovered that now I have a GT wing, my front and rear tire temperatures (235 front, 255 rear) are MUCH closer than before (and sometimes the fronts are actually hotter). That's the upshot to having understeer, I guess.
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Old 09-20-17, 11:30 AM
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Originally Posted by Valkyrie View Post
driving without parts attached might end up being like driving with a broken suspension.

...

I discovered that now I have a GT wing, my front and rear tire temperatures (235 front, 255 rear) are MUCH closer than before (and sometimes the fronts are actually hotter). That's the upshot to having understeer, I guess.
I don't think it'll feel like a broken suspension. You'd likely feel the increase in roll and it may feel like it's pitching over the outside front tire in the dry. However, in the wet, you have lower cornering forces, less roll and so less effect.

The wing would certainly be a cause for understeer. Do you have anything on the front to balance it? Splitter? Airdam?
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Old 09-20-17, 11:40 AM
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Do you have an adjustable front swaybar, ie Tripoint or old Racing Beat? If so you can loosen up the front a little bit. I wouldn't take it off though. Yikes.

If not, maybe a less aggressive one up front? I may be wrong but I'm pretty sure the 93 has a bit bigger swaybar in the front than the rest of the USA FDs. If your car's a 93 maybe a bar from a 94 would help.

EDIT: Actually read through your entire post. lol.

Someone bring back the adjustable FSB!

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Old 09-23-17, 11:09 AM
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Originally Posted by Natey View Post
I wouldn't take it off though. Yikes.
you never know until you try. if its a stock or near stock bar, the actual contribution to the spring rate is pretty small, especially compared with any spring a coil over comes with.
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Old 09-25-17, 06:25 PM
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Real full-tread rain tires in a narrower width with tall flexy sidewalls makes a big difference

IME shock settings matter more than bars, if the tire is on the pavement rather than hydroplaning the chassis still needs balance. Otherwise lowering the overall ride frequency (Hz) with softer matched springs is the next best thing.
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Old 09-26-17, 09:58 AM
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In my experience in the wet, yeah, you get push. Degree of push indicating degree of lack of grip, so it's a good heads-up at corner entry.
Originally Posted by Valkyrie View Post
The stock helical is about as loose as they come.
Is it? I *think* that helicals can act practically locked in low-traction conditions, until TBR is exceeded... For sure the stock Torsen in my S2000 is very obvious in its operation on the street, scrubbing quite a bit around tight corners vs. the 1.5-way OSGiken clutch-type in my FD which is totally unobtrusive.

Originally Posted by racingdriver View Post
just disconnect one side of your front swaybar.
Originally Posted by Valkyrie View Post
I had actually considered doing this. I assume you should zip tie the free link out of the way. Sure it's not too much of a change?
I've connected and disconnected the rear bar (and ziptied link out of the way) a buncha times on my car. Car too understeery (which it is at Thompson CT), connect it. Car to oversteery (NHMS, Watkins Glen), disconnect it. I can't say I could detect much difference either way! Stock rear bar with big stiff Speedway front bar and 13k/11k springs just doesn't make a huge difference.
Front bar, however, that would be a much bigger difference. You might disconnect both the front and the rear, I don't think I'd just disconnect front only.

Originally Posted by DriveFast7 View Post
More tire pressure = more heat in the tire.
More tire pressure => less hysteresis, should put *less* heat into tire, no?

Originally Posted by Valkyrie View Post
The other shop that has scales is two hours away and doesn't have a proper alignment machine (just dunlop gauges), so no guarantees on how accurate thrust angle is.
Get ride height where you want it front/rear left/right, then get alignment, then check cross-weights and adjust to within 0.1%. *It is possible to adjust cross-weights and corner-balance the car without altering ride height*.

If I lost 80 pounds or so the car would probably brake better. There's just too much weight on the front left and rear right (RHD car). The same applies to my MR2.
??? If front left plus right rear is greater than front right plus left rear, that's the definition of corner weights being off. So yeah, if they're way off, corner balance to within 0.1% or 30 lb. IMO probably not necessary to get "better" than that.
Originally Posted by Smokey The Talon View Post
My experience with corner weighting the car 3 times now is that if you set ride heights closely to the same height each corner that the weights are very close. Close enough to save you the trouble of using scales if it's that difficult.
This is not necessarily true. You can have cross-weights WAY off with the exact same ride height at each corner. And you can have cross-weights dead-on with the car at wonky asymmetrical ride height.
Most cars will never have ride heights the same all around anyway, as there's usually some twist in the chassis. So you average it left/right, i.e. if RF, LF, and RR are all at 25" and LR is at 25.25", you can adjust ride heights to give something like RF 25.125", LF 25", RR 25", LR 25.125" by lowering the left rear and raising the right front the same amount without upsetting cross-weights.

Set your ride heights within 1/4" of each other WITH your body weight in the driver's seat. That will get you close enough..
Again, not necessarily. You can adjust cross-weights independently of ride height. You can have ride heights all spot-on equal and have corner-weights way off. Also, you can have corner-weights spot-on with the car sitting with left/right and fore/aft rake.

Originally Posted by Valkyrie View Post
So, yesterday I had a track day in the wet and my FD had fairly heavy understeer which actually made it pretty easy to drive, but boring and slow.
I had a hard time getting heat in the fronts. The rears were reasonably warm, all considered.
I was wondering whether I should have increased or decreased the tire pressure to get more heat in the tires. Which way actually works better?
I usually run the same operational pressure or ~36psi hot, which means a higher cold pressure. No idea if that's the right approach or not. "Experts" at the track events I do have opinions that vary widely :P

I do love tracking in the rain though. It is a great exercise in car control and patience. At Palmer (new track) last year the damp-to-wet grip was so bad I was laughing out loud at how slow I had to go. Came around Turn 6 and saw a Miata WAY off the track and up in a barrier. He didn't slow down enough...
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Old 09-28-17, 09:06 AM
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I was at a wet track day once.. I had to point by a Camry. My car is USELESS in the rain with race tires.
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Old 09-29-17, 08:04 AM
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Get ride height where you want it front/rear left/right, then get alignment, then check cross-weights and adjust to within 0.1%. *It is possible to adjust cross-weights and corner-balance the car without altering ride height*.

??? If front left plus right rear is greater than front right plus left rear, that's the definition of corner weights being off. So yeah, if they're way off, corner balance to within 0.1% or 30 lb. IMO probably not necessary to get "better" than that.
This is not necessarily true. You can have cross-weights WAY off with the exact same ride height at each corner. And you can have cross-weights dead-on with the car at wonky asymmetrical ride height.
Most cars will never have ride heights the same all around anyway, as there's usually some twist in the chassis. So you average it left/right, i.e. if RF, LF, and RR are all at 25" and LR is at 25.25", you can adjust ride heights to give something like RF 25.125", LF 25", RR 25", LR 25.125" by lowering the left rear and raising the right front the same amount without upsetting cross-weights.

Again, not necessarily. You can adjust cross-weights independently of ride height. You can have ride heights all spot-on equal and have corner-weights way off. Also, you can have corner-weights spot-on with the car sitting with left/right and fore/aft rake.
.
While I get your point he stated it's a big trouble to get his car corner weighted. In my experience corner weighting 2 different FD chassis that if the ride heights were set to be as close as possible with the drivers weight in the car as a starting point the Cross weights were 0.5% or less off each time. He can use that as a guide and starting point if it's that much trouble to properly scale the car.
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