kb58
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| posted on 16/2/06 at 09:04 PM |
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Tire pressure
My first post here in the Driving section, after building my mid-engine Mini. The question is, what tire pressure is "about right"?
The car is 1500lbs, 80" wheelbase, mid-engine, 200hp. Weight distribution is 40/60 toward the rear. Front tires are 175/60-13, the rear
215/50-13.
I've tried 15 and 25psi... maybe 20psi is next. Haven't yet taking the car on track so I won't know what pressure is perfect, but
out on the street it's hard to tell. The capability of the car is scary good, there's no safe way around here to find the limits, which
is why I'm asking.
[Edited on 2/16/06 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Mark Allanson
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| posted on 16/2/06 at 10:15 PM |
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With such a bespoke setup, I think the only way to tell is to take it out for a scary howl and then measure the temp every 20mm across the tyre width
and adjust the pressure until it is even (scary howls are loads of fun so enjoy!)
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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russbost
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| posted on 27/2/06 at 11:12 PM |
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My axle weights are around 400kg rear & 250kg front (multiply by 2.2 for lbs) around 270bhp. I run 15psi front on 245/45/18 & 18-20psi rear on
285/40/18 rear seems to behave itself!
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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NS Dev
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| posted on 28/2/06 at 01:24 PM |
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I would concur entirely with the post above. It depends heavily on tyres used, and particularly on the front of your mini, you want the softest
sidewall tyres you can find!
15-16 psi front and 18-20psi rear would be my advice, 1 psi either way on a car of 1500lb will make a surprising difference.
Tyre sizes and profiles sound about right too, certainly wouldn't argue with any of that.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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David Jenkins
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| posted on 28/2/06 at 01:33 PM |
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I'm using 18psi front and back, but I haven't experimented. Works OK for me.
Just a thought - the original question was about mini tyres, so is what we put in our 7-sized tyres totally relevant? It might be better to ask in a
mini forum.
OOPS! Ignore me - I just re-read his post - his tyres are roughly the same as mine! 
David
[Edited on 28/2/06 by David Jenkins]
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JoelP
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| posted on 2/3/06 at 02:56 PM |
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i put 18psi cold into my tyres, and i think it was a little high because with new tyres, the bobbles wore off faster in the middle. Maybe it heated up
a lot - i had forgotten my pressure gauge so i couldnt check what it rose to. 
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Jon Ison
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| posted on 2/3/06 at 04:23 PM |
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I cant imagine other tyres are too different, yoko's advice for there 048's is 21psi when hot, in other words whatever pressure cold
brings them up too 21psi when hot.
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NS Dev
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| posted on 3/3/06 at 01:17 PM |
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Would be interesting to see what temps give what pressures.
On the grasser the outer rear starts at 18psi and 4 laps on a dry track brings that up to 21-22psi.
My only gauge of temp is that 4 laps brings the outside rear from ambient to "can just touch but not for long!"
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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