Slicks Vs Semi's - Need Some Help With Tyres

[No Crust Racing]

I need some new rubber for the S13. I'm currently running 235/45/R17 Bridegstone Semi's on 8.5" Front and 9" Rear rims (the fronts might be 8" I need to check)

MPC is selling the Mini Challenge Slicks which are 215 45 R17s but Troy thinks they will be too small for my rear rims. He's suggesting I go some 225 Pirelli slicks he has on hand instead.

I'd prefer to keep the same tyre size all round for rotational reasons.

A few questions.

Are slick widths the same as Semi Slick widths? I ask because the 235 Semi's I have seem to be as wide as 245/255 road tyre in width.

Will I still come out in front grip wise If I go a 225 Slick all round (assuming I'll get better grip due to bigger contact patch on the slicks).

Should I just stay with 235 Semi's all round instead of worrying about slicks. Newer semis will give me more grip anyway as the currents are pretty much bald in some spots.

Sorry for multiple tyre threads, just trying to get all my ducks in a row before I buy.

[Marlin]

In my opinion, a set of 235/45/17 Dunlop O3G's will outperform those Dunlop slicks in 215/45/17.

If you run slicks, in my experience you'll need a lot of camber increase to get the most from them. (maybe I can't get enough front camber on mine to make slick really work well).

[No Crust Racing]

Well it seems like the 215s aren't really an option for me as I want the same tyre all round and he doesn't think they'll fit the rears. I'd have to go the 225 Pirellis instead.

How much camber are you running? I'm only running about -2 to -2.5 or so

[warps]

With the price of wheels these days, is it feasible to get another 2 rims for the back to accommodate the 215's? Then you can have all the cheap slicks you want. Surely in the long term this would pay off?

Is it a track only car, or does it do daily duty as well? If it's track only, what does it matter if the front and rear rims don't match?

Do you need 9" rims on the back?

Your car is probably lighter than the minis, and unless you're pushing 500hp, do you need a 9" rim on the back?

If you run the same size rim front and back, then tyre rotation becomes easier again.

[No Crust Racing]

Yeah wheels are cheap but my budget is not so great right now, just built a house.

I got these Volks track rims a while back for a good dollar and I doubt I could find some matching width rears. Other option is I sell these rims and get diff ones, lots of stuffing around though.

Car is primarily track only but road reg'd I have a second set of rims for road driving though.

9" might be big for a partly stripped S13 but the car is very light in the rear so extra tyre contact is not a bad thing, the tyres fit under the guards so why not?

The cheapest thing for me to do is just buy some tyres and head to the track. The 225 Pirelli slicks are no more expensive than the 215s and will fit all four corners. So it really just comes down to whether I'll get as much grip out of a 225 slick as 235 semis- thoughts?

[zebra]

I had 235/45/17 Dunlop Formula R slicks, they were wider than the 255/40/17s I have on the back of my soarer.

A 215 slick would fit a 9" rim with maybe a little strectch...but you say you want to rotate the tyres front to back...will the 9" rims fit under the front?

[Marlin]

I run 2.8 front, 2.2 rear, its the most I can get from Targa legal bushing mods.

[No Crust Racing]

I had 235/45/17 Dunlop Formula R slicks, they were wider than the 255/40/17s I have on the back of my soarer.

A 215 slick would fit a 9" rim with maybe a little strectch...but you say you want to rotate the tyres front to back...will the 9" rims fit under the front?

I'll probably go with the 225, dont want stretch on a track car. When I say rotate tyres I mean actually flip them on the rims so I get even wear from both sides etc. The rims stay where they are.

I run 2.8 front, 2.2 rear, its the most I can get from Targa legal bushing mods.

That's a fair bit from bushings, I'm just using the camber adjustment from the top of the coilovers.

Is -2.5 front and -1.5 rear going to be enough when using slicks? Are any other suspenion changes needed?

I'm starting to think I should just stick to 235 semis, the car seems to use those well and was working well on them. It was only that the slicks keep popping up cheap.

[Marlin]

My experience (limited) on slicks is they love camber. On Giant's Evo, I went nearly a full second quicker when I dialed it from 3 degrees (front) to max (say, 6 degrees?). It used the tyre a lot better too, it was flogging the outside edge hard. They were on Porshe Cup front slicks..... maybe you should try and get those? We ran them on 34GTR rims (9")

Edited February 25, 2011 by Marlin

[No Crust Racing]

Not sure where to get those from. I can't run any more camber than I have without more parts so if they need a stack more camber then I won't be able to give it to them.

Might see what 235 semi's are around instead, I know they fit, know they grip well enough, and the car is currently set for them and was happy enough.

[Marlin]

Sure thing. If set up correctly, you will get more life from slicks. The Evo did 160 odd laps at Bathurst, a bit of a test and flog at QR, and I finally killed them with about 80 laps at Lakeside. Bloody good value out of a tyre I reckon! lol

[No Crust Racing]

Yeah that's good, was that extended sessions though as I do like 10 laps at a time so they would get heat cycled a bit and I thought slicks didn't like that.

Any idea where those porsche slicks are?

[Marlin]

Never bought 2nd hand ones, try Troy, if he doesn't have he may know. I think Duncan (R35 forum section) uses them?

[Tektrader69]

whats the weight distribution front/rear of your stripped out S13 ?

Edited February 25, 2011 by Tektrader69

[No Crust Racing]

S13, and no idea.

Stock they weigh about 1200-1250?

All the rear interior through to the boot is removed, only seat is FRP Velo for the driver, no stereo or any air con at all. Dry Cell in the boot.

So i'd say about 1200 if it weighed 1250 to start with or 1150 if it was 1200 to start with.

At a guess I'd be thinking 55:45

[Duncan]

My experience (limited) on slicks is they love camber. On Giant's Evo, I went nearly a full second quicker when I dialed it from 3 degrees (front) to max (say, 6 degrees?). It used the tyre a lot better too, it was flogging the outside edge hard. They were on Porshe Cup front slicks..... maybe you should try and get those? We ran them on 34GTR rims (9")

agreed, but that is simply due to more roll due to better lateral grip.

all things being equal better tyres need more anti-roll bar, more spring or more camber. preferably the first

[Nee-san]

agreed, but that is simply due to more roll due to better lateral grip.

all things being equal better tyres need more anti-roll bar, more spring or more camber. preferably the first

+1

Think about your friction circle of your tyre and how the increase in grip effects the attitude of the car and you see that Duncan is right. Moar ARB.

[wrxkilla]

Never bought 2nd hand ones, try Troy, if he doesn't have he may know. I think Duncan (R35 forum section) uses them?

where can you get the new porka cup tyres from?

Any idea of cost?

Cheers

Michael

Edited February 25, 2011 by wrxkilla

[Angus Smart]

where can you get the new porka cup tyres from?

Any idea of cost?

Cheers

Michael

Hey mick, I think you may be able to get them directly from Michelin themselves.. i was speaking to them at bathurst fosc last year and they had many 18x10's from the fronts of the porsche cup cars for sale. (used however for 50 a piece) i'd say you'd be able to get new ones from them if you tried.

[handbrake]

Trevor Schumack from 'European technique/track tyres is the distributor for Michelin slicks. Not so sure about any advice you'll get from him (unless you are in a Porsche) but he has always delivered tyres on time from Vic to Qld and is reliable.

As marlin says, you will need lots of camber. Requirements vary from cat to car but I tun about 4.5 front and 2.5 rear. Pyrometer is your friend, run outside 5-8 degrees C cooler than inside to have camber right ( assuming you are measuring temps after really pushing the car hard- otherwise your readings won't be relevant).

There us a Michelin PDF on slick set up/ pressures/camber/temps on the web. Search Michelin slick setup or something similar.