Tyre pressures for Mk IV

[NZ XR6]

I've just fitted a set of Bridgestone Potenza RE001 tyres on 17" wheels. My tyre shop recommends 46 psi and the handbook says 32. So I thought I'd ask what pressures those of you with 17" wheels are running?

Initial thoughts after a few kms is that the steering feel is noticeably improved and the tyre noise on smooth roads is actually reduced compared to the standard 16" Goodyear Excellence(!) tyres. The tyres do thump more over cats eyes, etc. but they are lower profile, performance tyres. I'll take it easy for a few hundred km to allow the tyres to bed in, or at least I'll try to do so!

[svo supporter]

I'd be running them between 32 and 36 PSI. 46 PSI is way to high. I even think it's way over the bridgestones maximum pressure for the tyre.

The best way to judge, is start at 32 PSI and at every rotation, check the tyres for feathering on both inner and outer edges. If you do have this, bump the pressures up by 2 PSI, until you end up with even treat wear across the entire face.

That's about the best way to judge what would be the ideal pressure for your car and driving style. The drivers manual is a rough guide, not really gospel.

Final thing. I'd be heading back to your local tyre dealer where you got the tyres from and tell them to look at the side wall of the tyre. That actually has the maximum allowable pressure for the tyre, located near the bead of the tyre and get them to read it. I'm sure the maximum pressure is 40 PSI. Then ask them why they'd recommend such a high pressure.

Good luck with it all

[cammag]

Thing to remember with the book and placards, is that is the pressure recommend for the best ride/comfort.

Higher pressures means the harsher the ride, lower rolling resistance and increased fuel economy, with in limits of course.

Tyre guys generally know more about this dealers.

But 46psi does seem a little high. And over inflation leads to a whole heap of other problems.

I am running 38 front and 36 rear and I am happy with wear and ride. The dealership had them at 28 psi which was way too soft.

Cheers.

[NZ XR6]

Thanks for your replies. I've dropped them back to 36 psi front and rear, which certainly feels better than 46!

I note that the handbook recommends 41 psi for high speed (> 160 km/h) and full load, which is probably a reasonable upper limit. It's interesting to think that Mondeos in Europe are regularly driven above 160 km/h!

I'll post a review on the tyres when I've put a few km on them. But they are certainly a revelation, and make me realise just how good the handling of a standard Mondeo is. An XR5 with 18s and the sports suspension must be something else again!

[NZ XR6]

Well, I've now done well over 1,000 km on the tyres, although much has been on motorways. I've experimented with the pressures, and am now running 35 psi front and 32 psi rear. I tried 40 psi front and rear, but the ride became noticeably harsher and the steering lighter but with less feel. However, for the best road holding and tyre performance, this is the way to go.

The ride is definitely harsher than with the OE Goodyear Excellence 16" tyres. Tyre noise is less on smooth roads, but slightly louder on the very coarse chipseal that is used on main highways in NZ. I suspect that some of this is simply a function of changing from soft, touring tyres to performance rubber.

The car feels far more stable on the 17s and the steering feels more direct and responsive. I'm not conscious of having to "steer" the car around corners - the car is much easier to drive.

So, overall I'm pleased with the wheel / tyre combination. It certainly feels much safer, and hopefully next time a truck driver who's driven far too many hours pulls out right in front of me on a wet road, it won't be nearly as much of a drama to stop in time.

[NZ XR6]

I've now settled on the recommended pressures (32 front and rear). The ride quality and road noise on chip seal are certainly better at this pressure. But if I was heading for a Sunday drive on a winding back road, I'd put them up to about 38 psi...