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Correct slick tyres pressions

 
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SPRINT
Alfa Arna


Joined: 03 May 2003
Posts: 12
Location: Barcelona-Catalunya-Spain

PostPosted: Mon May 19, 2008 6:10 pm    Post subject: Correct slick tyres pressions Reply with quote

Hi! a friend uses slick tyres Camac 205 /48 -13 on 13x7" rims, in his Alfasud 1.7 with a pression of 1.7 bar, and he don´t feel good sensations with them, the back of the car goes to the front!!! where is the problem??? any ideas??? We test our cars during 30 minutes at the Formula 1 track Circuit d Catalunya, near Barcelona, and we hope retunts to test our car with best results another day, thanks! SPRINT



My Marangoni front left tyre:



www.sprintmania.com
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mt
Alfa Sprint


Joined: 19 May 2005
Posts: 177
Location: Portsmouth

PostPosted: Fri May 30, 2008 9:31 am    Post subject: Re: Correct slick tyres pressions Reply with quote

SPRINT wrote:
Hi! a friend uses slick tyres Camac 205 /48 -13 on 13x7" rims, in his Alfasud 1.7 with a pression of 1.7 bar

Hi, i'm not an expert by any means and have only ever driven 33s as a road car, not a race car, but that sounds like there's not enough pressure in the tyres. 1.7 bar is a lot less than the road cars, and as you use wider, lower profile tyres than a road car you should have even more pressure in the tyres.
This is backed up by the pic of the tyre being scrubbed on the outside, there's not enough pressure to hold the wall steady under cornering so it's rolling under itself.
I'd go up to 2.5 bar as a starting point and see if that feels better, it should feel a lot more solid.
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Fri May 30, 2008 10:57 am    Post subject: Reply with quote

hi,
there is no correct pressure for slick tires.
it depends too heavily on the track, on the car, on the driver, on the tire itself.
bottom line is, pressure shall remain between 1.8 and 2.0 bar
when you start from cold, after a few laps, the pressure will have risen dramatically. It is then time (as soon as you get off the track) to de-inflate the tire until pressure drops around 1.8 -2.0 bar. Run a few laps again and repeat the operation.
Beware : if for some reason (lunch?) you let the tires cool down be sure to drive carefully during a few laps to allow the tires to heat properly. If you drive home in the evening with your tires (not recommended) be sure to REINFLATE the tire cause road use will not heat it enough to reach 1.8 - 2.0 bar pressure.

regards,
zp
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SPRINT
Alfa Arna


Joined: 03 May 2003
Posts: 12
Location: Barcelona-Catalunya-Spain

PostPosted: Wed Jun 11, 2008 12:27 am    Post subject: Reply with quote

Thanks for the comments! more photos:















I hope you like it!! SPRINT
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Eddie_W
Alfasud


Joined: 08 Aug 2007
Posts: 74
Location: New Zealand

PostPosted: Wed Jun 18, 2008 10:27 am    Post subject: Reply with quote

That road tyre doesn't look too bad to me, I.ve seen them with all the edges of the tread blocks rolled when used on the track. The only recent experience I've had with slicks is on two single seaters, one a Ralt Formula Holden (read F 3000) and a Mcrae F5000 and they ran between 18 and 21 psi hot(1.2 to 1.4 bar approx). The rears are pretty wide of course with the Mcrae at something over 600hp.
Incidentally the Mcrae will be running at a classic meeting at, I think, Brands in the next week or so and later at the Goodwood festival . In between it's doing Zandvoort. If anybody is going to any of those meets, it's bright yellow no 22. Stu is building a hotshot injected motor for it but couldn't get it done in time so he'll be down in power on a few of the others. I think he got a 2nd or 3rd at Silverstone the last time he had the car in Blighty. One of my other friends ( the Ralt man) is going over with him but I couldn't bloody afford it. Bugger.
Regards Eddie
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Eddie_W
Alfasud


Joined: 08 Aug 2007
Posts: 74
Location: New Zealand

PostPosted: Thu Jun 19, 2008 11:52 pm    Post subject: Reply with quote

Adendum to my above post, the Mcrae will be running at Zolder not Zandvoort.
Regards Eddie
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SPRINT
Alfa Arna


Joined: 03 May 2003
Posts: 12
Location: Barcelona-Catalunya-Spain

PostPosted: Tue Aug 05, 2008 9:56 pm    Post subject: Reply with quote

New tyres Toyo Proxes R888 195-60/15 on my Sprint 1.7 QV:















Ending september I hope return to the tracks, ciao! SPRINT
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richard33
Alfasud


Joined: 29 Jun 2005
Posts: 40
Location: Somerset, UK

PostPosted: Wed Aug 06, 2008 6:00 pm    Post subject: Reply with quote

I saw the original post sometime back and it puzzled me somewhat!

Having raced both Suds and 33s in recent years, I found the the references to oversteer a bit surprising to say the least. A fundamental handling characteristic of the Sud (and less so on the 33) on the track is understeer. I can't claim to have fully mastered the technique of getting the backend out on entry to a corner to allow earlier application of full power.However, I have worked on trying to get the backend of the car to 'move about a bit'.
Dependant upon the tyre regulations for whatever race I was doing - used either List 1b road legal tyres (e.g. Dunlop D98J) or Michelin slicks. Initially, I started with fairly conventional track pressures e.g. 28psi front and 26psi rear. At one meeting at Pembrey about two years ago, I found out that many people were running much higher rear pressures (e.g 33psi) to induce a bit of skittishness into the rear. I tried it in the second race and was immediately two seconds a lap faster! Since then I have stuck with F27/R32.
I too have now just bought a set of Toyo 888s, size 195/50-15, which is now the control tyre for both the Toyo Tyres Racing Saloon series and the Alfa Romeo Championship.
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