Alfa Romeo Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
2,729 Posts
Discussion Starter #1 (Edited)
I'm running 195 45 16, thinking of going to 205 40 16....??
car is track setup
Purple powerflex bushes all round, I've got a complete set of black series to put on but not sure if that's a good idea, as its used on the road
AHM springs
Koni sport shocks
stripped out
was running at 33psi, a bit crashy, now 29psi, better, do I go lower than recommended for standard size?
https://toyotires-1524598101.netdna...ication_of_load_inflation_tables_20151020.pdf
im a little lost
 

·
Registered
Joined
·
1,481 Posts
Usually the recommended minimum values are determined for a specific load
that the tires must handle without abnormal deformation on either
the sidewalls or the contact surface.

Nowadays cars using 16" tires are often more heavier than the 33s were, even with fully packed,
so I think the recommended minimum pressure for a given 16" tire will be bit much for the 33.

It's an uncharted territory, since there's no factory pressure recommendation for tire sizes
above 14", which leaves experimenting as the only option.

IMHO with reduced load on the tires you can reduce the pressure too.
The original tire load index was 82 with 28.4 psi which is rated for ~1050lbs weight per tire.
 

·
Registered
Joined
·
2,661 Posts
My closest experience is with a race/rally sud running 195/50-15 road legal race tyres (grooved slicks). These were probably set at somewhere around 22-24psi cold. I assume you're running road tyres so will probably need a bit more than that but as Lonewolf says your wheels/tyres are somewhat large for the car, so trial and error is your best bet.
 

·
Registered
Joined
·
2,729 Posts
Discussion Starter #4 (Edited)
Thanks for the replies guys, Michelin Pilot Sport 3 PS3 84V XL TL, Load index:84 = max 500 kg / 1102.31 lbs

I found this interesting article
https://www.mycarforum.com/topic/13...article-on-air-pressure-load-index/?p=6146137
post #94

Single Load per tire in pounds
LI 82
LBS 694 728 753 772 805 828 838 871 915 924 948 0981 0995 1014 1047

LI 84
LBS 728 772 793 805 849 871 882 926 959 973 992 1036 1048 1069 1102

PSI 022 023 024 025 026 027 028 029 030 031 032 0033 0034 0035 0036

https://www.mycarforum.com/index.php?app=core&module=attach&section=attach&attach_id=203402


Standard 1040kg 2292Lbs roughly, 637kg 1404Lbs front axle and 397kg 875Lbs rear axle, do you divide by 2 to get 1 wheel?
What do you think the weight of my car is, maybe 910kg total, 60/40 split 546kg 1203Lbs, 364kg 802Lbs
Doesn't add up
if using your "The original tire load index was 82 with 28.4 psi which is rated for ~1050lbs weight per tire."
that = 838lbs and equivalent on LI of 84 = 26psi...
 

·
Registered
Joined
·
1,481 Posts
Well, the load index is depends on the allowed maximum axle load of the vehicle.
In case of the 16V FWD 33s this is 800kg on the front and 900kg on the rear axle
according to the manual(*).
This means 400kg maximum static load per tire at the front and 450kg at the rear.
(As you wrote dividing the axle load by 2 to get the load on one wheel/tire.)
Some safety margin is also needed in case of cornering, due to the weight transfer
between the sides. Plus imagine hitting a pothole during cornering,
this also needs to be added to the effect of weight transfer.
IMHO this justifies the original 82 load index.

(*) the maximum allowed weight is 1410kg, axle loads must be distributed accordingly,
so it is not 800+900=1700kgs, this is a whichever comes first situation.
Therefore static load weight figures are somewhat smaller in real life,
but the safety margin still needs to be considered.

The post was interesting. I think the XL part is not relevant here.
It's a bit late for me, and I guess I couldn't follow completely the description.
The starting point in your case 28.4 psi (2.0 bar) of inflation
and 1050 lbs or 475 kg per tire (factory spec),
but I didn't understood how to get the pressure figures for a +2 size tire to
support the same load... :disappointed:
 

·
Registered
Joined
·
2,729 Posts
Discussion Starter #6 (Edited)
Using the Load Index that the tyre has, no matter the size, you inflate to the PSI that corresponds to the weight you want to support.
400kg front 882Lbs Li 84 = 1.9 bar = 28 psi
450kg rear 992Lbs Li 84 = 2.2 bar = 32 psi
That makes no sense as i thought fronts are a higher pressure than the rears?
 

·
Registered
Joined
·
1,481 Posts
That makes no sense as i thought fronts are a higher pressure than the rears?
And this would be the factory recommendation too, at least for everyday driving.
A trunkful of concrete slabs may require increased tire pressure
at the rear axle, but normally there's more weight on the front axle.
 

·
Registered
Joined
·
2,729 Posts
Discussion Starter #8 (Edited)
You are saying that factory is, higher at the rear?
I've alwaye known it to be higher at the front and 3 psi lower at the rear.
185/60R14 H 82 1.8 BAR / 26 PSI 1.6 BAR / 23 PSI
I think i will start with 28f 25r... what do you think
 

·
Registered
Joined
·
1,481 Posts
No, the front tire pressures should be a bit higher normally.
For 14" rims 2.0 bar (28.6 psi) @ the front and 1.8 (26 psi) at the rear.
These values also worked fine for me on my 15" rims till my
tires got old.

Sidewall deformation was not right below 1.6 bar pressure at the front
while at the rear 1.5 bar seemed normal in my case with these tires.
But I used to keep 1.8 bar anyway at the rear.

28f/25r sounds good to me.
 

Attachments

·
Registered
Joined
·
2,729 Posts
Discussion Starter #10
Much better at 28f 25r, no under-steer in the wet but still a little crashy on bumps, I will try 26f 23r, remember my car is stripped out.
 

·
Registered
Joined
·
2,729 Posts
Discussion Starter #11
I didn't lower it anymore, parking as it is, is a pita lol, am I being a wuss? I have no power steering btw :rofl:
I did turn up my koni sports to full hard, omg wow, brings back memories, wont keep it like that on the road as it pulled a rear shock through the top of the turret in a previous 33.
 
1 - 11 of 11 Posts
Top