Tyre Pressures

[SCOTTY]

I CURRENTLY HAVE A HF3000 V6 TYRE SIZES ARE 205 & 345. WHAT SORT OF PRESSURES SHOULD I BE USING FOR FAST ROAD USE

[Cloggie]

Hi Scotty,
What kind of tyres are you using? If it's Yoko's, I was using 21 psi on the front and 24 on the back with the same sizes you mention.

I'm now running Pirelli's and I'm using 25 psi on the front and 28 psi on the back.

By the way, are you the person that bought Phil Bishop's car?

Cheers, Cloggie/

[SCOTTY]

THANKS FOR THE REPLY COLGGIE . ITS PIRELLI'S ALL ROUND . IT WAS PHIL BISHOPS CAR THAT I BOUGHT . HE WAS USING 21 PSI FRONT & 17.5 PSI AT BACK WHICH I THOUGHT WAS FAR TOO LOW FOR THIS SIZE OF TYRE ETC . HAVE JUST BOUGHT TWO NEW TYRES FOR THE REAR AND NOW HAVE THEM ABOUT 25 PSI . I ASKED PHIL ON A COUPLE OF OCCAISIONS BUT HE SAID 17.5 PSI

[SUSIT]

Welcome Scotty
Good to see another Strat in the right end of the country. We might soon have enough for a scottish meet. Hope you get many miles of happy motoring. Have you any plans to compete in the car?

Stephen Struthers
Ex Glasgow lad

[Arthur]

Gents,

This is not strictly relevant to your specific tyres, but this is as good a place to post guide pressures as anywhere else.

I'm running a CorseI with 12-valve 3-litre Alpha. I'm running Falken GR-beta tyres all round; 205x50x16 front, and 225x45x16 rear. Chose these to give a level platform.

I've mucked about for some 4 years now, and run 18psi front, and 22 psi rear. I've put around 12,000 miles on the car, and so far the wear (predominantly road use, 1/2 degree negative camber all round, 9 minutes toe-in each wheel, 4 degrees castor fronts) is pretty much dead even.

Track days - I use exactly the same. Tyres warm up nicely without overheating, but I do suffer some balling of the tread rubber on the outer shoulders. I don't consider this a problem; if I did track days exclusively, I'd up the negative camber and check temperatures across the tread to get it right, and live with the excessive inner shoulder wear and extreme tramlining that this set-up brings on the road.

Using 345 rears - well, they look the part for sure, but I reckon for roadie use in the wet that 225's are about the most you can use and still get some power down without a panoramic view of the scenery every time you turn the front wheels or squeeze the loud pedal. Even with these on, while I can load it up somewhat on damp-to-wet sufaces, a patch of free water on a turn will signal an excursion of some 6 feet or so off-line. Not bad, all the same, the car carries on as though nothing had happened. Pity I can't say the same for the driver. (I started out using about 26 front, 28 rear - its like a goddam skateboard if the humidity exceeds 50%, never mind the road gets damp....) and oh yes, while I think, don't be tempted to control roll by stiffening up the dampers. All that happens is the tyres get unhappy, and you mostly find out about this in the wet........set it for a compliant ride, let the bugger roll if it wants to, and trust the camber compensation in the suspension, or increase the negative camber if you can live with it.

Best of luck with it.

[SUSIT]

All very helpful info, thanks Arthur.

[colin artus]

I always recommended a 6 psi differential between front and rear
(high figure on rear). On a Goodyear shod demo car we had only 16 psi at the front.

Colin

[chris.richard]

Originally posted by Arthur
don't be tempted to control roll by stiffening up the dampers.


Arthur, do you use anti-roll bars?

[David May]

I'm not convinced by this low front pressure idea. Many manufacturers do it to induce understeer, which is fine if you don't want to enjoy yourself! The logic of lower front weight doesn't hold up when you brake - then you've probably got 50% more load on the front which makes 16psi look and perform a bit flat (we're not talking F1 solid sidewalls here!)
I use 32 psi at the front and a bit more on the rears on the track otherwise I'm reduced to the point-and-squirt mode. The high pressures also soften the break-away (by reducing tyre roll?) and make it more predictable at the limit (I still spin it, but seldom where there are things to hit!)
I guess if you're running soggy suspension and only cruising, then a low pressure might improve the ride, but that's not what the Stratos was designed for...

Dave May

[colin artus]

I always found the front end too unsettled and knife edge like if the tyre pressures were much over 22 psi at the front. Mind you this is on crap UK road surfaces. On the track I have found that tyre pressure can rise dramatically due to heating and its necessary to take this into account if you set the pressures from cold.

Colin

[Arthur]

Chris,

No, I don't run roll bars.
I mostly use it as a roadie, and the tyre pressures I stated earlier are set cold. What they get to on track days I haven't a clue, but the last time I ran it at Anglesey (early last year, I'm sad to say) they got to about 50+ degrees per tyre, just too hot to comfortably touch, but pretty much even front and back.
It still turns in OK, and while it does have a tendency to understeer when pushed, that's safe enough at my driving standard, and even with the bog-standard 12V 3-litre, there's enough torque left at School (mid-turn, trying to find the braking line into the second apex) to find power oversteer in the heat of the moment. Even at the hairpin, it turns in fine (a very deep entry, and chuck it and boot) and puts a shed load down on the way out without being unpredictable.

I've found with the fronts much above about 20 psi (cold) it gets very jittery, tends to dart, and will wash out anywhere.

I suspect with the very short wheelbase that any "too-sophisticated" set-ups will be compromised by the logitudinal weight tansfer in any case, so I stick with the "turn late and use the power out" method. (just got to be careful of those bloody Caterfields using the resulting hole as a braking area when you do chuck it....)

The car is a CorseI, running on the standard springs, 350 lb/in fronts, 400 lb/in rear, with the suspension brackets set to "low ride height" and about 50% of the static weight set as pre-load. It runs about 5 inches at the flat bottom, on a level platform. I'd go lower, I just don't trust the front lower arms not to foul the lower subrame if I go any lower than this. (Its on the mod list when I can find the time....). So well different from a rally set-up. Dampers are Leda single-adjustables, about 5 or so clicks up from soft front, and 7 or 8 up at the rear - as little as I can get away with, in all honesty. Just enough to take any "boatiness" out of the ride, and that's that. Sets quickly enough going into corners, so I'm happy with it.
(During build, I first put it together with the suspension brackets at "normal" ride height, and springs just unloaded at full droop - I swear I could have walked under the car.....)

Best of luck
Arhur.

[David May]

I personally think that tyre pressures are much related to the other suspension settings and on my first events in my Corse I, I too had a very similar soft setup. I soon got embarrassed at being passed into corners by Golfs and am now up to 500 and 650 lb/in and the Ledas on full clicks (23). It's still twitchy (aren't they all) but the understeer has gone and I can hang the tail out until I run out of revs. It doesn't feel much rougher than my Smart Roadster (a modern mini-Stratos) but doesn't qualify as a comfortable cruiser either.

Dave May

[chris.richard]

Originally posted by Arthur
and about 50% of the static weight set as pre-load.

How do you set this up? Is it by measuring the cornerweight and compressing the spring the required number of inches as per its poundage?

[Arthur]

Chris,

Sorry, that was a bit misleading. The preload arrived exactly as you suspected - while setting the platform, and screwing the adjusters around, that's where it ended up - evaluating the preload it gives is just a measurement of the spring compression locked in at full damper travel based on inches compression and lbs/in of spring.
I can't see that it matters much, except as an indication that the calculated spring package on the kit as supplied was a way out.

Arthur.