Vantage tyres

[graham 500]

I've been offered a set of rear tyres but they are 295x30x19. Anyone fitted these or is it not advisable?

[taylor172]

seems considerably wider than the norms, they might not seat properly, can get away with narrower tyres but im not sure that much wider wouldnt cause an issue

[Cockernee]

Same size as V12V

[yvr]

Make sure the circumference is close to what you have on the front, otherwise you could have traction control or ABS issues.

[graham 500]

yvr said:

Make sure the circumference is close to what you have on the front, otherwise you could have traction control or ABS issues.

295x30x19 81.58
235x40x19 82.94

1.36 difference, would that be too much?

[graham 500]

yvr said:

Make sure the circumference is close to what you have on the front, otherwise you could have traction control or ABS issues.

295x30x19 81.58
235x40x19 82.94

1.36 difference, would that be too much?

[Cockernee]

255/35 on the front of a V12V, I would look at the comparative differences in width. You have upped the rears by 20, but not the fronts.

[Simon T]

yvr said:

Make sure the circumference is close to what you have on the front, otherwise you could have traction control or ABS issues.

how so?

[yvr]

Simon T said:

how so?

Wheel speed differentials. Smaller circumference on the rears will mean the back wheels are spinning faster than the fronts. At some point (maybe not at 1.6% difference?) I think the computer will start applying rear brakes to stop the "slippage".

Perhaps vankypanky will chime in with his experience using undersized rears -- as described above.

[Simon T]

yvr said:

Simon T said:

how so?

Wheel speed differentials. Smaller circumference on the rears will mean the back wheels are spinning faster than the fronts. At some point (maybe not at 1.6% difference?) I think the computer will start applying rear brakes to stop the "slippage".

Perhaps vankypanky will chime in with his experience using undersized rears -- as described above.

I reckon it would be a long way off that for the TC. ow would it impact the ABS as the wheels have to stop rotating for that o be impacted

[DB9VolanteDriver]

Simon T said:

yvr said:

Simon T said:

how so?

Wheel speed differentials. Smaller circumference on the rears will mean the back wheels are spinning faster than the fronts. At some point (maybe not at 1.6% difference?) I think the computer will start applying rear brakes to stop the "slippage".

Perhaps vankypanky will chime in with his experience using undersized rears -- as described above.

I reckon it would be a long way off that for the TC. ow would it impact the ABS as the wheels have to stop rotating for that o be impacted

ABS works the same way. If one wheel is slowing faster than the others, ABS releases pressure on that wheel to allow it to speed up to match the others. ABS doesn't wait for the wheel to stop rotating. We're not talking about all out emergency stops where you've got your foot to the floor.

The real issue is not if the front and rear diameters match, it is how the R/F ratio is now different than what is programmed into the system.

The OEM R/F ratio is 1.01. You are proposing to change it to 0.98. This is a 3% change in the OEM ratio of rear to front diameters. Is 3% too much? Don't know, but I have heard that on many cars that 3% may be on the edge of screwing up TC and ABS. Kinda' all depends on how aggressive the TC and ABS systems were programmed.

[KarlFranz]

The tire you are proposing (295/30) is actually smaller in diameter than the standard OEM tire (275/35) by 0.6 inches. Is that a lot? Not necessarily, but consider this:

The tread depth of a new OEM tire is 10/32in and a fully worn tire is 2/32in. This means that a fully worn OEM tire's diameter is still larger than the diameter of a brand new 295/30 with full tread.

Being a larger tire, the OEM wheel will make 17.8 revolutions less per mile than the proposed tire. If you compare it to the Sport Pack tire (285/35) it's 25.6 revolutions less per mile. Since vehicle speed is usually determined from one of the rear ABS sensors, your speedometer will register about 2.3% faster speed than true vehicle speed (3.3% vs. the Sport Pack tires).

More concerning, while the OEM rear tires are approx. 0.18in larger diameter than the fronts, the proposed tires are actually 0.43in smaller than the fronts. So for the OEM tires, the fronts revolve 5.1 miles more than the rears each mile. With the proposed tires, the fronts will revolve 12.7 times less than the fronts. This 17.8 revolution swing from front bias to rear bias, may be enough to screw up the ABS braking determination.

[graham 500]

Great summary, I take it is a no then, thanks for all your input.....