Racing In The Rain

[GTS4WD]

On this thread, to save me starting up a couple of other threads, I just have a couple more questions:

Tyre Temps in the wet - Should I be aiming for the same as dry by ramping up pressure?

How much should tyre temps differ accross the inner middle and outer of the tyre? I understand inner may be hotter because of static camber, but how much difference should there be between the three areas of the tyre?

Boxheadmr - Thanks for the reply, this gives me ideas..

[Beer Baron]

you will never get the same tyre temp in the wet with the same type of tyre used in the dry. that is why you bring the starting pressures up. it's all about getting the pressures right, don't worry about the peak tyre temp too much. chasing a number won't work.

as far as temp across the face of the tyre you want it to be pretty much even across the whole width of the tyre. if it's not that is telling you that you are not using the whole tyre properly and need to adjust your camber settings and general suspension set-up. measuring the temps across the face will tell you lots of things, like is the tyre over infalted? under inflated? too much camber? not enough camber etc.

[GTS4WD]

as far as temp across the face of the tyre you want it to be pretty much even across the whole width of the tyre. if it's not that is telling you that you are not using the whole tyre properly and need to adjust your camber settings and general suspension set-up. measuring the temps across the face will tell you lots of things, like is the tyre over infalted? under inflated? too much camber? not enough camber etc.

Thats right.. its very important data, thats why I wanted to know how close the three areas of the tyre should be to make the most of the contact patch

[Scando]

I'm from Tassie so we get plenty of practice racing in the rain

The mega high tyre pressures work really well on karts in the wet. When I first started racing the car we thought it would work well there too. We were wrong. We've had best results starting about 3-4 psi higher than normal but nothing over the top. We generally aim for about the same hot psi in the wet as we'd aim for in the dry now. I'm in the same boat as you and haven't been able to afford a second set of tyres for the wet but as Duncan said, soft compound DZ03G Dunlops work very well. As the other guys have said, try to get as much heat into them as possible in the warm-up lap. If you drive slightly on the agressive side throughout the race then it helps keep the temps up.

Disconnect both sway bars. If the car has a natural tendancy to understeer then try just disconnecting the front bar, if it has a natural tendancy to oversteer then try just the rear bar. If you can, try softening up the suspension. Generally, the more you can get the car to roll around the better.

With lines, on tracks with old surfaces there is usually a high rubber build up on the dry racing line. This can be very slippery in the wet. Often there are certain corners where running mid-track through the corner or keeping it tight on the exit can provide a lot more grip by keeping off the rubber. It's all trial and error here to work out what to do on which corners but as with anything, look at what the quick guys in similar cars are doing (ie. the lines of an Evo might be a lot different to an RX-7). When I raced at PI last year we didn't have any wet races but the track surface seemed quite clean so I'd expect it to be quite grippy in the wet, even on the normal race line.

Hope my ramblings provide some help.

[GTS4WD]

Yeah shane, they do,

But disconnecting swaybars completely seems like a drastic change! I have never driven a car with a disconnected swaybar, but Im assuming it would be a massive change!

[Scando]

If the car has adjustable bars you could try just softening them up. It's all about weight transfer in the wet. In corners you want as much weight as possible on the outside two wheels. It's all to do with transferring the load through a smaller contact area as you mentioned in a previous post. So you're try to get all your grip from the outside two wheels rather than all four. Another thing to note is that my car was nicer in the wet when I ran 15x7's than it is now I'm running 17x9's.

On my car I just disconnect the front bar because it has a natural tendancy to understeer. I'd imgaine the RX7 would be pretty well balanced so i'd definitely try both bars. I just take the linkage out of one side so it's easy to change back to a dry setup in a hurry if need be.

Here's the link to the first time I drove my car in the wet. Both swaybars connected. and high tyre pressures. I'm in the 240Z and did a best time of 1:19, 2 seconds off the quickest 2WD car and 7 seconds off Leigh Finlayson in his Evo.

http://www.natsoft.com.au/cgi-bin/results....2/2007.BASK.R18

This is the second time I drove my car in the wet. Front swaybar disconnected and didn't change anything else from the dry setup. This time I did a best of 1:15 which was the quickest 2WD car and this time only 1 second of Leigh Finlayson in his Evo.

http://www.natsoft.com.au/cgi-bin/results....9/2008.BASK.R35

[GTS4WD]

hmm.. I need to push for a wet test day..

[GTS4WD]

You say that by disconnecting the swaybars your getting more weight transfer to the outside wheels, but wouldn't you get more with them connected as part of the weight is transfered from the inside to the outside wheel through the swaybar?

Edited November 12, 2010 by GTS4WD

[UWAM]

You say that by disconnecting the swaybars your getting more weight transfer to the outside wheels, but wouldn't you get more with them connected as part of the weight is transfered from the inside to the outside wheel through the swaybar?

The sway bar resists the inside wheel attempting to move relative to the outside. So the load on the inside tyre is whatever it normally is, plus the torsional force from the sway bar.

[Scando]

You say that by disconnecting the swaybars your getting more weight transfer to the outside wheels, but wouldn't you get more with them connected as part of the weight is transfered from the inside to the outside wheel through the swaybar?

I can see where you're coming from, but as the cars body rolls over, the centre of gravity of the car is moved further over the outside wheels. The sway bars stop this happening.

All I can say is if you get a chance then give it a try, I'm sure you'll be pleasantly surprised

[GTS4WD]

I can see where you're coming from, but as the cars body rolls over, the centre of gravity of the car is moved further over the outside wheels. The sway bars stop this happening.

All I can say is if you get a chance then give it a try, I'm sure you'll be pleasantly surprised

Yes.. Ok.. Im on the same page as you now..

Thanks for the help mate! Very interesting ideas here.

[Scando]

No problems, good luck with it. I'd be interested to hear what you find works if you get a chance to test it.

[GTS4WD]

Yeah.. Ill def post up things like lap times in the wet, with different pressures, sway bars, driver input, spoiler settings etc. etc. etc. etc.

[Roy]

So how did it all go?

[GTS4WD]

I have interesting data to post up from todays wet ride day.

Will do it tomorrow.

CBF tonight

[Duncan]

it's tomorrow +++

[GTS4WD]

Sorry for the late post.. I have been under the pump at work to get our cars out before the end of the year.

But, this is the data collected on a ride day at Eastern Creek in the wet.

Its not alot of data because we couldn't change set ups easily in the 40min between sessions.

I will try to include as much information about the car and set up as I know to get the best information out.

Car: Mazda RX7 S8

Set up and Specs:

1mm toe out on all 4 corners (yes, not the best for the wet)

~3 deg. Negy

Spring rates unknown - Jap brand coilovers

Corner weights unknown

Total weight unknown

Roll center unknown - No roll center adj.

Standard sway bar's

Tyres: Yoko Advan's AD050's

235/45/17

S compound

Target press in dry - 32-34psi

After speaking to Bill (from Gordon Levin) from Yoko, he said the target tyre temp is 50-80 deg. C (Precise, I know)

Conditions:

Track Temp ranged between 23-25 deg. C all day.

Raining

Sitting water on track

Overcast

Wet line

Starting pressures for S1:

28/28

28/28

Psi

Hot after S1 - 7 laps:

31.5/31.5

31/31

Tyre temp after S1:

Bizmal 20-25 deg. C accross tyre

Driver complained about understeer and unpredictability.

Pressure changed to:

40/40

40/40

Psi

(cold)

40/41.5

41/42

(hot)

With tyre temps ranging from 35ish to 42ish depending on session but a nice even temp accross the tyre with little temp varience between the outer, middle and inner of the tyre

Imediately, driver was much happyer with more predictability and less under.

Dampers were all prgressivly softened throughout the day front and rear with positive results.

Swaybars were not adjusted/disconnected (although we do do this with our Porsche Cup Car and GT40 when racing in the wet)

Interpretation of data in next post

[GTS4WD]

hokay.. so what does all this dribble mean?

My interpretation of the numbers (and please correct me if I am wrong or provide other interpretations)

By increasing tyre press you are reducing slip andgle. This would make for a lower level of maximam grip (yes?) as you are reducing the amount of slip angle the tyre can provide before it begins to under/over steer. How this is better, I dont know.

Reducing dampers to allow for more weight transfer. More weight over each contact patch?

I will ponder this some more and get back to you. There is more to be said, but I have to figure out the wording first.

[warps]

Higher pressure = smaller contact patch on the road = better at dissipating the water between the tyre and the road. This is a bit like the concept of skinny tyres dissipating water better, hence less likely to aquaplane, or if you think of letting tyres down in the sand to allow the tyres to "float" better on the sand.

You can all but forget about building heat up in the tyres in the wet, so higher tyre pressure will at least get some rubber to touch the road.

[GTS4WD]

Higher pressure = smaller contact patch on the road = better at dissipating the water between the tyre and the road. This is a bit like the concept of skinny tyres dissipating water better, hence less likely to aquaplane, or if you think of letting tyres down in the sand to allow the tyres to "float" better on the sand.

That was the theory I wanted to test. That was where the thread started from.