Xtreme Kermit
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| posted on 16/7/09 at 09:03 PM |
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Tyre pressure - stupid question
So everyone quotes tyre pressures - but are these hot or cold.
Tin top pressures are cold I know, but how about our light weights?
I have been recomended 22 ish at the front and 24 ish at the back for my Xtreme. But this seems high compared to locosts and the like.
So do you think these are hot or cold temps?
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eccsmk
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| posted on 16/7/09 at 09:06 PM |
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i may be well off the mark but i run 16 psi (cold) all round in my little indy
[Edited on 16/7/09 by eccsmk]
[Edited on 16/7/09 by eccsmk]
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Steve G
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| posted on 16/7/09 at 09:06 PM |
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I'd always do them cold myself. It does sound a little on the high side - i'd say start at 18psi all round and go from there. Try
adjusting one end at a time until you find what suits you.
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alistairolsen
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| posted on 16/7/09 at 09:09 PM |
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most people quote cold but you really need a thermometer and a track to tune them, then measure the pressure hot.
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Xtreme Kermit
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| posted on 16/7/09 at 09:20 PM |
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The Xtreme does weigh a little more than your indy I guess because of the stainless monocoque chassis.
I will try dropping them down a bit. It does seem to understeer less with the fronts at a lower pressure.
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smart51
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| posted on 16/7/09 at 09:20 PM |
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It doesn't matter so much whether you do it hot or cold as long as you measure when they're the same temperature.
I ran mine at 20 PSI which is higher than most on here. I tested the car on the track starting at 16 and working up. Each 0.5 PSI gave me a couple
more MPH round Gerards at Mallory Park until I didn't dare go any faster. Tyre wear was even, allowing a bit for -ve camber, not just worn in
the centre so I assume they weren't over inflated.
edit: 195/50/15 Toyos and 530kg kerb weight.
[Edited on 17-7-2009 by smart51]
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miikae
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| posted on 16/7/09 at 09:57 PM |
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18psi cold all round for me, next time a go for a thrash i must check them when i get back, i do know that the tyres where damn hot today when i
checked them as where the brakes too.
Mike
If it can be done it i will be done .
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procomp
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| posted on 17/7/09 at 07:01 AM |
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Hi
It's amazing how everyone starts recommending all these very low tyre pressures without ever taking into account exactly what tyres are being
used. Also amazing that so many people are using these low pressures to mask that the cars are too stiff on dampers and springs.
Just my 2P's worth.
Cheers Matt
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nick205
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| posted on 17/7/09 at 08:27 AM |
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quote:
Originally posted by procomp
Hi
It's amazing how everyone starts recommending all these very low tyre pressures without ever taking into account exactly what tyres are being
used. Also amazing that so many people are using these low pressures to mask that the cars are too stiff on dampers and springs.
Just my 2P's worth.
Cheers Matt
Matt,
I take your point here and you're correct that no one correlates pressures in relation to specific wheel/tyre combos, car weights or indeed
spring rates.
In your experience should tyre pressures be generally higher for lager/lower profile tyres or the other way around?
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procomp
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| posted on 17/7/09 at 09:48 AM |
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Hi
It was not necessarily the exact tyre profile i was getting at. More the sidewall construction. Tyres such as the YOKO 048's have sidewall
construction to be able to run down at 20-24psi. As do some others but the majority do not.
The majority are running low pressures to mask wrongly setup cars dampers and springs. This means that they are not necessarily making full use of
the mechanical grip from the tyres.
Cheers Matt
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andyd
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| posted on 17/7/09 at 11:02 AM |
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Matt, is there a way of figuring what spring rates are best for a certain weight of car?
I'd reckon most people have just either guessed or got what they can for a particular budget.
I'd like to be able to at least get somewhere close to an ideal rate for my build.
Any advice, links etc.?
Andy
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alistairolsen
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| posted on 17/7/09 at 11:42 AM |
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you can work it out on the basis of cyclic frequency but you need to know the car weight, distribution and unsprung weight of all 4 corners to
calculate the effective rate, and then the inlination and attatchment points of the dampers to get to true spring rates.
Most people seem to make an educated guess, and then try and tune it to a greater or lesser extent by trial and error while watching laptimes, or
subjectively measuring ride quality
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will121
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| posted on 17/7/09 at 11:51 AM |
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quote:
Originally posted by procomp
Hi
It was not necessarily the exact tyre profile i was getting at. More the sidewall construction. Tyres such as the YOKO 048's have sidewall
construction to be able to run down at 20-24psi. As do some others but the majority do not.
The majority are running low pressures to mask wrongly setup cars dampers and springs. This means that they are not necessarily making full use of
the mechanical grip from the tyres.
Cheers Matt
agree with above my track day tin top running toyo road tyres (generic weak side walls) run upto 34psi to also restrict tyre roll. but on track tyres
currently Silverstone FTZ run down to 22psi as side wall extreemly firm like R888s ect
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Ninehigh
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| posted on 17/7/09 at 07:16 PM |
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How can you tell if it's too high or too low (before the uneven wear kicks in)?
My tintop says 30 and 33 but if I did them, say 40 and 43 would I be able to tell? I've had them down to 22 before (not on purpose!) and not
noticed them looking flat..
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Dave Ashurst
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| posted on 18/7/09 at 09:00 AM |
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I set mine to give equal temperature across the tread.
(It seemed logical to me - but it might not be !! )
I used an infrared thermometer from maplin.
I set damping rates by allan staniforth method, i.e. wind the damping adjusters fully soft, drive on a test run and progressively stiffen up until the
car feels too hard over bumps then back off.
Concentrate on each end independently.
d
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David Jenkins
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| posted on 18/7/09 at 10:16 AM |
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I did almost exactly the same thing, also with a maplins remote thermometer!
I use 18psi with my 185/70 x 13" tyres, and it seems to handle well. Tried 16psi and found it too 'slushy', and 20psi was too
harsh.
I should probably set the fronts to 20psi as there's more weight there... maybe I'll experiment when the weather's better.
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alistairolsen
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| posted on 18/7/09 at 10:34 AM |
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thermometer linky please!
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David Jenkins
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| posted on 18/7/09 at 11:05 AM |
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This is the one I've got
Maplins
But mine was £19.50 when I bought it! They do have others...
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