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Road tyres / Pressures and different constructions & Compounds

924Srr27l

New member
PSH Hi Roger
This is the first set that I've had, I'm usually a 'Goodyear' man but alas they are no longer available in my size for a symmetrical directional pattern. These have been on the car for nearly two years (12,000 miles) with no real signs of wear, they are brand new in the picture. The fronts have worn but that's my fault for not getting the geometry sorted quick enough after the rebuild, in my defence I had my son's wedding to go to in Devon which took priority.
Pete



Ok, so that's quite impressive then with all that Torque! as the Compound or treadwear number as the America Rating is low / soft @ 140
A toyo R888 Track tyre is Rating 100 and as a comparison my current Michelin Pilot Sport 3's are rating 320.

The bridgestone and Michelin constructions and compounds are like chalk and cheese,

I've always preferred for road use a Michelin Tyre because it has a Soft thinner Sidewall and a harder compound which is essential
when a soft sidewall generates so much heat, otherwise the tyre would wear excessively. I've found this set up also allows for a stiffer chassis (Higher damper bump & rebound & Bigger ARB's) and then let all the give, compliance & rock and roll occur in the tyres, a bit like F1 to a degree (Without trying to digress too much) very stiff suspension & minimal travel but a big sidewall profile on 13" Rims.
F1 tested 18" low profile tyres and they were a nightmare to drive, and 12+ seconds a lap slower! (Another related discussion on profiles!)

A Bridgestone construction has a thicker stiffer sidewall which copes much better with HEAT and hence they can reduce the compound
grade and make the Coefficient Of Friction higher with a softer shore & treadwear rating but because the sidewall is stiffer the suspension settings could need softening otherwise stiff everywhere is too much for the road and several characteristics occur.

My current Michelin set up is very good, but I like many desire to constantly develop and test new things I'm keen to try a Stiffer sidewall Bridgestone with a softer compound.

Especially after a run in the car a couple of weeks ago when I had pumped the tyres up to 40psi over winter to avoid flatting them. I went out for an hour run in the pi$$ing rain in North wales and couldn't be arsed to reduce the pressures, being fully aware of this and driving more gingerly than normal, however the car felt good, so I pushed more and found it was still had impressive traction off the line and no loss of cornering grip either when pushed (which I was expecting) should of been the case as previously I'd been running 26psi! which is the ballpark for a lightweight car @ 1110kg. (Inc driver & Fuel)

Tyre Pressure is usually dependent on load / weight and the tyre width & profile. hence why Commercial vehicles are up in the 45 - 60psi+range and the pesky MX5 and Lotus Elise etc...are down in the 26's.

But there are exceptions to this rule when Wide and / or higher profile tyres on some heavy cars like big jags are not that high because the section width and volume evenly distributes the pressure per square inch.

EG:
A Jaguar XKR V8 4.0Turbo 1998 model has 245 & 255 wide tyres with pressures 32F & 29R psi
A ford Fiesta 1.25L 1999 165/70/13 is 30F 26R psi !

If anyone has any part worn So2's in 205/55/16 i'm after a set of 4 to test? (they will be getting an application of Tyre Softner)
or Kumho V70A's ?

R


 
There are many reasons why just switching to an 18" wheel on an F1 car will result in it being slower, this article touches on some of them http://www.autosport.com/news/report.php/id/114907 With lower profiles and longer travel suspension they could have have much more control, currently a large part of the suspension movement is in the tyre and is therefore un-damped and relatively uncontrolled, this creates its own headaches. The size of F1 wheels is down to the rules and the rules only.

For what its worth in 17" my personal favourite 944 road tyre is Dunlop sp9000 at 32psi cold all round, After trying from memory Bridgestone S02 N-rated, Goodyear eagle (F1?), Michelin pilots N-rated, some pirellis - cant recall the model. Have some toyos to try. The Dunlops have similar feel to the Bridgestones possibly slightly looser at the rear, similar grip levels better wear and more progressive breakaway. Think I went Michelin/pirelli/goodyear/dunlop/dunlop/dunlop/michelin (came with the cab) and I have a set of new toyos (well actually a few years old now but unused).

On track Slicks were great but wore out the brakes and wheel bearings too quickly for my budget, some road legal track rubber seems like a good compromise, you can often get them used from the 911 boys once they are close to being illegal for the road - 4 spare wheels and tyres will fit inside a 944 so you can swap when you get to the track. I know some people run track rubber on the road but I tended to use my coupe all year round.
Tony



 
944Turbo said:
There are many reasons why just switching to an 18" wheel on an F1 car will result in it being slower, this article touches on some of them http://www.autosport.com/news/report.php/id/114907 With lower profiles and longer travel suspension they could have have much more control, currently a large part of the suspension movement is in the tyre and is therefore un-damped and relatively uncontrolled, this creates its own headaches. The size of F1 wheels is down to the rules and the rules only.
For what its worth in 17" my personal favourite 944 road tyre is Dunlop sp9000 at 32psi cold all round, After trying from memory Bridgestone S02 N-rated, Goodyear eagle (F1?), Michelin pilots N-rated, some pirellis - cant recall the model. Have some toyos to try. The Dunlops have similar feel to the Bridgestones possibly slightly looser at the rear, similar grip levels better wear and more progressive breakaway. Think I went Michelin/pirelli/goodyear/dunlop/dunlop/dunlop/michelin (came with the cab) and I have a set of new toyos (well actually a few years old now but unused).
On track Slicks were great but wore out the brakes and wheel bearings too quickly for my budget, some road legal track rubber seems like a good compromise, you can often get them used from the 911 boys once they are close to being illegal for the road - 4 spare wheels and tyres will fit inside a 944 so you can swap when you get to the track. I know some people run track rubber on the road but I tended to use my coupe all year round.
Tony



Yes that's a brilliant example of my train of thought also, (The F1 article, which i'd seen before back in 2014)

How many Car modification enthusiasts Not only fit stiffer shock absorbers and springs and Lower the ride height
(reduce the travel) but also fit bigger wheels and low profile tyres? LOTS !

Hence why the F1 article declared the whole chassis and suspension would have to be dramatically changed with softer suspension and more movement because it's all too (Stiff) and doesn't handle well etc...

How many modification enthusiasts do you hear of that after fitting super stiff Coil over suspension kits, lowered ride heights and
stiffer bushes etc....then go and Install Smaller diameter wheels and bigger profile tyres? NONE !

This is what I've found through 10 Years of Circuit Racing, and extensive Road testing on 10 cars over 15 years etc...
A stiffer chassis & Suspension settings work so much better with a bigger profile tyre which takes up a lot of the load compliance and absorption, you can get the best of both worlds ride quality and handling.

But the general worldwide marketed Automotive Industry want to sell product and that means Big wheels and super duper Slim profile tyres, it only takes a matter of time when a lot of people follow this Pied piper" ! I used to sell tuning parts for years and even I bought into the concept & marketing in my twenties! but twenty years later and for those that think out the box a bit more it can be an interesting advantage with this set up on the road.

I tried 17" also but they were heavier and wider and the car was noticeably slower and handled worst, so I went back to 16"

Toyo's are probably one of if not the Most marketed Boy Racer Tyre the T1S T1R etc..
I don't rate them at all, the compound is too soft the tread blocks move too much, the sidewall also is soft and
the car falls over itself and I've had them on a 4.7 V8 928 and a 944 road and track and I'm not impessed with them.

Also in Wet weather they are shocking and even the Tyre test label shows this on the rating. I've worked in the Tyre and tuning Industry since 1995 and tried just about everything going and have stopped at Michelin being the best for everything wet and dry, ride quality and feel, but I just want to try a softer compound / stiffer Sidewall like the Bridgesetone S-02

R
 

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