TVR tyre pressure not the usual question....

[alexcurtis]

Hi all

So this is not the usual what tyre pressure should I run my TVR at.

The general view for Toyo T1-R’s is 24psi at the front and 26psi at the back?

I was discussing this with a friend who took issue, and what he said made a lot of sense and the tyre wear that he then showed bore this out. On a front engine Fwd the tyre pressure is always higher at the front than the back, due to weight of the engine and braking, the same for a front engine RWD. The rear tyres are lower as there is less weight and just “roll” along on a fwd, on a rwd they obviously have more to do!

After further thought and discussion can understand why the rears may be higher as if the pressure was low then the torque could start to distort the softer side walls and cause issues of wear and “interesting” handling under acceleration where you need everything to be turning in parallel without any torque twist…

It does not solve the front though which on my Griff 500, you can see the shoulders are wearing and the middle is not suggesting that the tyre is being “lifted”in the middle. Therefore I am considering raising the tyre pressure at the front to 25-26psi to get better adhesion / contact and wear.

Lastly my car was and has just been fully set up camber / caster / toe, with general road set up, at Aline in Dudley, so it is not a geometry issue.

Would welcome people thoughts discussion, I feel like I am missing a blindingly obvious simple answer....

Thanks Al

[bobfather]

Front tyres are supposed to flex laterally so that when cornering the tread area can absorb issues that work to break adhesion. Without this, the first stone chip or poor road surface would loosen the grip sending the tyre into snap understeer. Also tyre treads like to follow ruts and sometimes white lines causing tramlining, allowing the tyres to flex laterally means the car can maintain a reasonable stable direction while the tread wanders from side to side all be it a very small amount.

In summery raising front pressure increases the likelihood of snap understeer and tramlining. I agree that the pressure needs to be sufficient to support the mass on the front axle but there are opposing arguments so a balance needs to be found.

I should add that front pressure being to low will cause progressive understeer

[jesfirth]

alexcurtis said:

Hi all

The general view for Toyo T1-R’s is 24psi at the front and 26psi at the back?

those pressures are back to front. you want lower pressures at the rear

[alexcurtis]

26 front 24 rear would seem more sensible to me also but the general view and what the handbook says is lower pressure front higher rear...

[rick.e]

bobfather said:

In summery raising front pressure increases the likelihood of snap understeer and tramlining. I agree that the pressure needs to be sufficient to support the mass on the front axle but there are opposing arguments so a balance needs to be found.

I should add that front pressure being to low will cause progressive understeer

Make your mind up Bob!

General wisdom as applied by those who set cars up for the racetrack is lower pressure gives larger contact area therefore better grip. (Forget all this talk of flexing). So by increasing the front pressure you will reduce front contact area, reduce front grip in relation to rear, moving the balance of the car towards understeer. More relevant to road use is that higher front pressure will also shift brake balance from front to rear (due to reduced front grip), which is not a good thing to do. In reality however, I don't believe the average driver will notice 2psi difference!

No doubt a Physicist will be along in a minute to tell us that the effects of increased contact patch is cancelled out by reduced pressure and therefore frictional force is unchanged, which is true enough with uniform surfaces under laboratory conditions, but that's not what we have on the road!

[rick.e]

...Then again, a quick Google of T1R uneven wear, throws up a number of people with different car types all wearing out the shoulders while there is still 5mm of tread in the centre. Sounds like it might be a feature of the tyres.

[ClassiChimi]

Lower pressures would increase the likelihood of wall flex so causing the tyre to roll over more in hard cornering, easily compensated for on track with more camber but on a road car that's not so easy!

I've got T1R's on my car and one trackday took the edge off the corners a little, I've increased the camber all around 1/4 degree since and on the road I'm getting even tyre wear.

I'd check what camber you've got in combination with the tyre pressures
I'm often running 22 cold all round on the roads during the summer as they naturally gain a few psi in the sun.