Please Help: Slick Tyre Issue

[ja9]

I'd like to start by saying I'm stumped and have no idea what to do next.

So I purchase a set of Dunlop slicks last December and ran them for the first time at the FOSC meeting that month. I wasn't impressed with them as the times were nothing to right home about. I did discover I had an alternator problem so I put it down to loss of hp due to an electrical issue.

I was at WP today quietly hoping for a PB and to dip into the 1.09's. Well that didn't happen and to my surprise I was 2 seconds slower in the morning. I played around with tyre pressures and all I could manage was 0.7 seconds slower than my PB. I was aiming for 28 hot.
Now I was under the impression that slicks should give you approx 2 sec. Lets be a little realistic, surely 1 sec should have been a possibly.

Now you're probably thinking the track was off etc but the bloke next to me managed a PB which rules out a slow track.

MY QUESTION IS: to optimise the slicks should I have altered the set-up?
I'm currently running
-4 degress camber
7 Degress castor (makes for really heavy steering)
Front:1mm toe out
Rear: 1mm toe in.

Any suggestions much appreciate. Car is an NB8A and is a dedicated race car.

Cheers - John

[oztrackdays]

If you think about it, Slick tyres have more static grip so actually cost you horsepower in a straight line.

Braking and Carrying corner speed is where they more than catch up.

I was about 2 seconds a lap quicker on Dunlop slicks, the compound can make a difference.

Have you got any VBOX files of before and after, you will need to drive a little harder to
make the slicks work for you.

[Magpie]

Did you heat cycle the slicks?

What tyre pressures? Hot and cold?

What are the inside, middle, outside tyre temps of each tyre? Both when cold and when hot?

When you took the temps was there a cool down lap and any sharp turns coming into the pits etc?

Tyre temps and pressures will also give you feedback on your alignment. In addition have you been keeping a log of previous tyres temps pressures at the tracks you run at?

[Hellmun]

Just to add more questions if you don't have any pyro reading for temp can you at least describe what the surface of the tyre was like? Were they getting up to temperature so they actually beaded and started shedding a little rubber or did they stay smooth? Did they get really wrinkly and heat distorted? What was the weather like on the day? How much did the pressure change after each session?

[MattR]

And what size were they, new or second hand, what were they built for, light sports car, lighter formula car or big heavy taxi?

What were the starting pressures and what pressures did they get to? Are they radial or cross ply slicks?

What are the desired cambers to use? Some slicks like not too much camber, some are designed for around -6deg camber.

Slicks won't "cost you power" in a straight line, yes they are stickier and grip better than semis and this is where you make up time, you can brake a lot later and carry a lot more corner speed. If you don't get them up to operating temperature they will be slower and feel terrible.

Radial slicks, when warm are awesome and you won't want to go back to treaded tyres, however when they let go it is with next to know warning. But to get the best out of them you really have to push harder. In a lot of cases with very standard cars it isn't worth the effort to go to slicks unless you make a lot of changes to the suspension as well to take full advantage of the grip available to you.

[ja9]

Firstly thank you to those who responded. It certainly gives me more to think about. Now for some answers.

Did you heat cycle the slicks?

What tyre pressures? Hot and cold?

What are the inside, middle, outside tyre temps of each tyre? Both when cold and when hot?

When you took the temps was there a cool down lap and any sharp turns coming into the pits etc?

Tyre temps and pressures will also give you feedback on your alignment. In addition have you been keeping a log of previous tyres temps pressures at the tracks you run at?

Tyre pressures were 22 cold and 28ish hot. The ambient temperature for the day was 28 degrees. No other information at this stage and no previous info.

Just to add more questions if you don't have any pyro reading for temp can you at least describe what the surface of the tyre was like? Were they getting up to temperature so they actually beaded and started shedding a little rubber or did they stay smooth? Did they get really wrinkly and heat distorted? What was the weather like on the day? How much did the pressure change after each session?

Now this is something I should have remembered from my racing days. Seems when I'm trying to diagnose my own issues my brain goes into melt down. The tyres were smooth which would suggest they weren't working very hard. Does this mean more or less tyre pressure? Or is it more of a suspension adjustment.

And what size were they, new or second hand, what were they built for, light sports car, lighter formula car or big heavy taxi?

What were the starting pressures and what pressures did they get to? Are they radial or cross ply slicks?

What are the desired cambers to use? Some slicks like not too much camber, some are designed for around -6deg camber.

Slicks won't "cost you power" in a straight line, yes they are stickier and grip better than semis and this is where you make up time, you can brake a lot later and carry a lot more corner speed. If you don't get them up to operating temperature they will be slower and feel terrible.

Radial slicks, when warm are awesome and you won't want to go back to treaded tyres, however when they let go it is with next to know warning. But to get the best out of them you really have to push harder. In a lot of cases with very standard cars it isn't worth the effort to go to slicks unless you make a lot of changes to the suspension as well to take full advantage of the grip available to you.

Not sure if they are radial or cross ply (my guess is radial). Never have known the difference. I went to Dunlop and told them the specs of the car the size rim I have the type of racing I do and this is what they sold me. They were new, purchased in December. My feeling is that a 7in rim is too small for this tyre 220x15. Dunlop suggested it would be fine and is within specs. One thing I don't understand and Dunlop told me this would happen is the outside part of the trye is wearing more than you would think considering I'm running -4 degrees camber. Seems the tyre is rolling on the rim or something. The tyres are wearing evenly and look good across the tread.

Anyone with lots of experience fancy a drive.
Thanks again.

[Magpie]

I would invest in a pyro and note book to record/analyse what is happening with your tyres

http://www.circletrack.com/chassistech/ctrp_0406_race_tire_technology/viewall.html

http://www.popularhotrodding.com/tech/0311phr_tire_temperature_readings_tech_guide/

[zossy1]

220s are too wide for a 7 inch rim. You need at least 8s to run those.

You could try the Kumho 205s which are also a bit cheaper, or buy some 8's (which might actually be cheaper than new slicks!).

[MattR]

220's will be fine on a 7" rim if that's what the Dunlop sold you knowing the rim width.

I used to run 230-250 wide tyres on a 8"x18" rim and it was fine, and well within spec.

Sounds like you didn't get them hot enough if there was no "beading" of rubber on the tyre and weren't driving them hard enough to get really grippy.

Next time try 21 psi cold. I used to run 21 to 22 psi and aimed for 30psi hot. When I worked the tyre well there would be a bead of rubber near the middle of the tyre about 20mm wide and coming off the track I would get plenty of pickup sticking to the tyre. I never worried about pyrometers because of the cost at the time and relied on hot pressures when first parked off the track and "reading" the tyre.

[zossy1]

220's will be fine on a 7" rim if that's what the Dunlop sold you knowing the rim width.

I respectfully disagree... A tyre that wide, especially at a 580 profile (which is what I'm sure these must be), will just work the sidewalls to buggery. The car will wallow all over the place as the wheels work back and forth inside the wide tyre carcass. IMHO, even 8's are only barely wide enough to secure the sidewalls of the 220 properly.

Remember that a 7 inch rim is only 175mm wide at the bead.

I'll grant you, that may have something to do with my driving style though, coming from karts.

[mazmad]

220s are too wide for a 7 inch rim. You need at least 8s to run those

John most of the guys would be running 8s at least. 8in =203mm. As Zossy said 8 is probably a little small for 225s that most run but that is maximum wheel width under 2f regs at our weight.

I don't think getting heat into the tyres will be an issue for me next Wed

[Boyracer]

I always ran the 220 slicks on 7 inch rims with no problems.
28 hot sounds a bit high, I used to start at 19 or 20 cold.
This is the reason I don't buy slicks any more, the first lap you do on them is the fastest and it's downhill from there, usually about 10-15 heat cycles loses about 2 seconds, I didn't ever wear out a set, they always just ended up being really slow.
We had a set of Kumho slicks that were good for one day, the next day the car was undriveable.
If you get a set of new slicks that are a bit old they will be crap.
Just get yourself some Yoko 050 semi slicks.

[zossy1]

I'm surprised you were able to make the 220s work on 7s Lou but I take your word for it.

Does anyone out there use tyre treatment on their old slicks? From what I can gather, it's legal in all forms of our racing (it's banned in AKA karting).

[MattR]

I have used tyre treatment in the past, the RPM branded Octopus grip, on some very old and hard slicks to get one more day out of them.

It does work, but I found you then have to repeat the treatment for every subsequent use of the tyres.

To do it propoerly you need to start putting it on a few days before the event and it is also worth wrapping the tyres in glad wrap as well to help with the "curing".

[mazmad]

949 racing I think it was conducted a study of wheel size for a given size tyre and found that pretty much bigger is better. Run the max size you can. But this would be affected to some extent by car setup and driving style so not neccessarily one size fits all.