Tyre Pressures

[Guest boggie]

Hi All,

I have an EXMO with 195/50 VR15 Yokohamas all round and was wondering if any of you guys have advice on what tyre pressures to use.

As the load on each corner is (I guess) around 175 KG they don't want to be too hard and it was suggested that I should try running them at 15 - 20 PSI but I find this makes the steering rather too heavy. I put 25 PSI in them this evening and that seemed better but does anyone have any informed knowleage as to the correct pressure?

Cheers, Boggie.

[Big Jim]

I run 195/65's and put 21psi in, it's a matter of choice, too soft and like you said, the steering is "lumpy" too hard, and the ride is harsh and the grip seems to be reduced. Suck it and see what's best for you.

[Guest trevor hooley]

ive got an exmo running 195 / 50 /15 yoko a539s on 71/2" rims, and my local expert reckons 25 front and 27 rear!! seems about right as well

[Big Jim]

Which local expert is that? The one that tightened up the wheel nuts? 27 lb is way too hard, you'll need new false teeth if you drive it for long at that pressure.

 

(Mind you, we've not seen this Robin Hood yet.....................)

 

[Guest boggie]

I have now talked to both Yokohama and Goodyear tech advice people. Yoko man told me to refer back to the car builer, when I told him I was the builder he said he could not help. Goodyear man was more forthcoming, he suggested starting at a pressure of 28 lbs (which should be about right for this tyre size and corner weight), accurately measure the treadwear across the wull width of all four tyres, drive it for a while and re measure the depth. If they are wearing more in the middle then drop them by 2 lbs, if the outsides are wearing then increase the pressure by 2 and repeat the whole procedure. This will (eventually) obtain the correct pressure for tyre wear with the weight of this car. However he suggested that the best way to set them up for handling would simply be a suck it and see affair.

So I have been experimenting and if I use much less than 25 lbs I get tyre squirm, heavy steering and vague handling, if I go as high as 30 the ride gets a little harsh and the car understeers when pushed hard. I am now back to 25lbs all round and this seems about the best for my setup. I might try sticking a couple more pounds in the rears as suggested by Trevor to see how it feels.

Jim: I think you must have stiffer springs than me as my teeth don't seem to mind. My rear coils are from a 100,000 mile 2.0 ghia model and the fronts are standard RHE.

Boggie

[Shandylegs]

Boggie

 

I have 195/50/15 Goodyear Eagles fitted all round and have found that 18psi seems to suit my 3a best.

i.e. Plenty of grip with mild progressive oversteer when approaching the limit (Of course only on my personal private testing ground.....officer ).

 

I would guess that there is no definative answer to this question as different people have different requirements from their cars.

 

Regards

Shandylegs

[Guest Daz]

When I went to get my tyres fitted to my 195/55 wheels for my 2b, the guy who did the job thought I was extracting the urine when I asked for 17psi. He did not believe that any car would be OK running that low a pressure so he put about 27psi in instead and said it would be fine. It was like riding in a boneshaker. The first time I took it out the ride was harsh and the car was skittish to the point that I thought I had ballsed up the suspension completely. After about 2 weeks, and as an afterthought, I went round and reduced the pressures back to 17psi all round to see what difference it made. It was like a different car altogether - bags of grip and a comfy(ish) ride on long journeys. I still haven't got to the point of investigating over/under steer yet, after all it was me that made it!! but I am having bloody good fun so far. And I do not find the steering too heavy at all, even with the leather-bound shirt-button that came in the kit.

 

In summary, try the tyres at a higher pressure and see what you think. Trial and error is the way to go.

 

Daz

[Guest Peter n the better half]

An old racing pal of mine used to swear by the following for setting up his stripped out cars. As there is less weight on the tyres due to reduced body bits and no interior he started by measurig the tyres to be used for swashed width at the bottom ofthe tyre wall to wall. Then as a starting point he'd inflate to this mesurement. Although the series he raced in only allowed 60 profile tyres it should be the same for all others.

 

Im not saying this is the correct way to do things but it does give you a starting point rather than the too high or too low system.

 

One point though is that all makes and with that styles / types of tyre act and require different pressures so a goodyear will need different pressures to say a Dunlop / Yok' etc.

And remember The Police are pulling cars with under inflated tyres and giving the driver a ticket .

 

Peter

[Peter Bell]

Pete, does that mean the police know what pressure tyres we should be running even if nobody else does? I run about 18 front and 22 rears which is fine for me.

Peter

[Guest Dave Gilling]

I tried 25 all round, hellish understeer, all my fillings fell out and I spilt my G & T. Tried 16 front 18 rear, slight oversteer, smooth as silk, fitted cup holder to dash , no more spilt G & T. Sorted.

[Guest mickmellors]

To Boggie

 

Goodyear man seems to want to sell you a new set of tyres when all the tread is worn off during your trial and error stages !

 

Seems an expensive and long winded way of going about what should be a relatively simple task ! Even driving fairly hard in a legal way I would expect to have to drive 500-1000 miles to be able to detect tyre wear as he describes, then adjust pressures and do another 500-1000 miles etc etc - cost of replacing worn out tyres and petrol bills for that mileage would not bear thinking about - did his brother own a petrol station nearby ?

 

From talking to some of the lads at Curborough Sprint Day last year (there was obviously a spread of tyre makes, types and profiles) the general concensus seemed to be 18-24 psi dependant on type and profile and they were certainly giving it some around the track.

 

Have a look at this website - there is a lot of info on alsorts of motoring fact and figures on the site - I have targeted tyres

 

http://www.chris-longhurst.com/carbibles/t...tyre_bible.html

 

Mick M

[Guest boggie]

Cheers Mick,

I will try 20 and see how she feels.

B