Tyre pressure for Uniroyal Rainsport 3's

Tyre pressure for Uniroyal Rainsport 3's

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Discussion

black_potato

Original Poster:

280 posts

174 months

Friday 2nd February
quotequote all
I'd be curious to know what pressures people have tried and their experience of these tyres.

When originally fitted they came at something like 35PSI and not having checked them at the time they felt pretty good in what was in effect a blind test pressure wise.

Since then I was advised to drop the pressure to 24PSI all around by "somebody in the know" and now the car feels pretty squirmy and less positive, especially under acceleration which I can only assume is down to sidewall flex. So my current thinking is to ~30 PSI front and rear and see how that works out.

What have others experienced are and what have you found the best pressures are with these ?

ianwayne

1,873 posts

203 months

Friday 2nd February
quotequote all
The handbook suggests 24 psi rear and 22 psi front on a Chimaera / Griffith. I've always used this and thought it fine. When I took mine off the road for a winter in 2016, I put 33 psi in them to resist permanent deformation. I forgot in the Spring and for a couple of days, the car was all over the place until I lowered the pressures.

Others who do track days lower their pressures even more. These are very light cars (comparatively) for the tyres that are fitted so 30 psi + is unnecessary.

If you've gone up to 17" or 18" wheels then perhaps more pressure is needed but I can't comment on the effect.

Yex 450

4,315 posts

155 months

Friday 2nd February
quotequote all
I run 24 rear and 22 front on my 17 "rims fitted with 215/40/17 front and 225/45/17 rear on Yokohama AD08R and the car handles beautifully thumbup

black_potato

Original Poster:

280 posts

174 months

Friday 2nd February
quotequote all
Thanks for that. Its interesting to know everybody else is wrong. rolleyesrolleyes

350Matt

3,564 posts

214 months

Monday 5th February
quotequote all
With the uniroyals I too found I needed another 3-4 psi over the 'stock' settings
a very soft sidewall
but well suited to my Wedge
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black_potato

Original Poster:

280 posts

174 months

Monday 5th February
quotequote all
Interesting you had the same experience. I think that's where I will likely end up. I pushed them up to 26 PSI all around and it felt better, still need to play a bit more with the pressures, damper settings and rear ARB...

Whilst I was jesting a little in my last post its key to appreciate that different tyres require different pressures to operate well, it often isn't just a case of reading the handbook as that was based on the tyres we originally sold the car with (what ever they were). I'm not surprised the ADO8R work at that pressure though, they will have very stiff sidewalls. The RS3's though are pretty soft in the side wall so may well want a bit more.

Anyway, You can all laugh at me when I leave the road backwards into a hedge !

ianwayne

1,873 posts

203 months

Monday 5th February
quotequote all
Tyre pressures can be a bit of an obsession but the most important thing is that they are the same on each axle.

Its only 3C here today and the average tyre pressure will be 3-4 psi lower than on a hot summer's day at 30C or after some prolonged driving.

Track day enthusiasts often lower them even more to below 20 psi because very hot tyres increase the pressure quit a bit!


Classic Chim

8,499 posts

84 months

Tuesday 6th February
quotequote all
Not so much in this weather but 22/24 during the summer months can warm and increase to 26 easily enough.

21 on the front is possibly the best I’ve found for steering tracking etc which is the recommended psi anyway biggrin

I use 17 in rims allround so tyre wall isn’t so high
If I was on smaller wheels id likely go up with base pressures using Rainsport.




mk1fan

9,400 posts

160 months

Wednesday 7th February
quotequote all
Things to consider when setting tyre pressures;

Weight of the car.
Size of the tyre.
Sidewall stiffness.

black_potato

Original Poster:

280 posts

174 months

Wednesday 7th February
quotequote all
And...

Compound
Geometry
Suspension rate
Spring rate
Bush material and age
ARB stiffness
Intended use
Driving style
Weather


I'm sure there are a few others that are escaping me

Byker28i

13,708 posts

152 months

Wednesday 7th February
quotequote all
ianwayne said:
Track day enthusiasts often lower them even more to below 20 psi because very hot tyres increase the pressure quit a bit!
When I was involved in Caterham racing, we used to measure the tyre pressures after the car had warmed up and done a few laps. Inside tyres always got hotter as did the rears so pressures were always different when cold on all 4 tyres.

On the Cerbera on Eagle F1's with 17" wheels I run 24psi all around

mk1fan

9,400 posts

160 months

Wednesday 7th February
quotequote all
black_potato said:
And...

Compound
Geometry
Suspension rate
Spring rate
Bush material and age
ARB stiffness
Intended use
Driving style
Weather


I'm sure there are a few others that are escaping me
If you're such an expert, why start the thread?

Personnally, I found 24psi all round fine with the Rainsport 3 on the Sag and the Tam.

black_potato

Original Poster:

280 posts

174 months

Wednesday 7th February
quotequote all
No I'm not "a great expert" but I have have Tracked/Sprinted/Raced cars for several years so I have some practical understanding that suggests it is more complex than the 3 dimensions you suggest. I was (and still am) interested to see what pressures people were running, if they had played around with them and what the results are as my experience is questioning what I'm being told.

Relax soapboxdrink

Classic Chim

8,499 posts

84 months

Wednesday 7th February
quotequote all
The type of driving your suggesting is very different from road going driving.
If your happier with 30 psi then fair enough.
I’d have thought you’ll experience poor traction and compliance over bumps and a reduced footprint let alone less braking effect before lock up but that’s just a personal opinion rather than the law wink
Rainsport have only been going onto Tvr for the last few years at best so you might be right.
Watch every Rainsport user try pumping their tyres up this weekend hehe

I’ve indeed tried everything from 18-28 ( cold)

And the grip levels don’t change very much but the ride and other behaviour does. Hard the car moves around much more,,,, well mine does thumbup

black_potato

Original Poster:

280 posts

174 months

Wednesday 7th February
quotequote all
The track stuff is in the past, at least for now and if i do get the hankering its more likely id take he lotus.

I have no plan to take the Griff on track although having a play at the limit at an airfield activity day would be fun.

The plan at the moment is just to get the planted feel on the road and good manners over bumps and in the wet for my summer road trip. At the moment i want to get a few bits refreshed that have a little play and then try and balance the damping and tyre pressure. I also think the Nitrons could do with a service but i have yet to play with them in a bid to confirm that. Its actually quite hard without much knowledge or reference for the car which after all considers it chassis a ls a big spring !

Classic Chim

8,499 posts

84 months

Wednesday 7th February
quotequote all
There’s plenty of guys using Nitrons to talk with.
Best to find out what spring rates you’re on. It should be written on them somewhere.
Often these cars are set to low on ride height with adjustable shocks which knocks the geo camber settings etc out, so I’d possibly start there as that’s something you can check at home if you have a flat floor. Whatever height you come to your happy with it’s always best to keep about a 10 mm rake with nose pointing down.
Do check you have an air spoiler underneath the front of the car too. Often these get knocked off but the car handles better with it. All imho

As a rough guide you use outrigger corners to measure down to the floor for ride height setting. Best to get it corner weighted and geo re set if you really do want an even footprint all round.
Matt Smith is your man, just him, go there and it will be as good as it can be not forgetting the spring loaded chassis biggrin
It’s the one big advantage adjustables allow us so corner weighting would be the way to go.

black_potato

Original Poster:

280 posts

174 months

Wednesday 7th February
quotequote all
Thanks, that all makes sense.

I had the basic alignment checked when I had the tyres fitted and the front was out quite a bit so I had it corrected, the rear was close to spec.

I think the ride height and front splitter ( assume this is the spoiler here https://www.racetechdirect.co.uk/car-parts/body-tr... are both a good call.

A full alignment and corner weight will happen but I want to get it all nice and tight first as if you have play in things it just isnt worth the money.


Classic Chim

8,499 posts

84 months

Wednesday 7th February
quotequote all
Sorry the link isn’t working for me.
If it’s a 900-1000mm long bit of aluminium with a 45degree angle or so stamped into it then yes smile
You can use some house hold plastic guttering or other such material which is just as effective,,, and you have spares.
I found some with the same angle 2 metre length, so 4 of them biggrin
White on under side so matches the chassis, black when looking from the front so suits the black paint hehe
I’ve bust it recently too!

Trackdays, low ride height, rock hard shocks anti roll bars blar blar

As a rule of thumb if you haven’t discovered this yet when sat stationary your front lower wishbones should be flat and level.
I prefer the car very slightly higher and wishbones just a few mm further down at hubs. Makes for a good road car. Saying that I’ve gone back to non adjustable shocks and the wishbones sit level. thumbup

Yex 450

4,315 posts

155 months

Thursday 8th February
quotequote all
black_potato said:
I think the ride height and front splitter are both a good call.
I had a splitter fitted under my car at the annual service and MOT last March (had no idea it was missing silly) and the handling difference was noticeable. Plus the engine bay stays cooler and the engine runs slightly cooler which is nice smile

Unfortunately I drove carefully over a speed hump near my house a few weeks ago but did not know there was a new pothole on the other side so a graunch and crunch later means a new one is being fitted at the service and MOT next month rolleyes

Once you get your car as you would want it come along to the regular Essex meets we have at Bicnacre and South Woodham Ferrers, ping me an email for details thumbup

Byker28i

13,708 posts

152 months

Thursday 8th February
quotequote all
Nitron charge me £150 for a service/refresh of all 4 shocks on my car.
You dont say what springs you have but I find the Eibech progressive ones good.
I have my car set quite high and soft because if this setup as I find it suits my driving and comfort requirements and absorbs the deviations in todays roads