Tyre pressure on new gen tyres

[g6089 10]

I was always wondering if tyre pressures recommended by factory almost 30 years ago should still be the same today with the new tyres fitted on cars being different in structure and built. My guess is since todays tyres are better built, better reinforced, better threaded, better compounded than 30 years ago, which makes then also firmer, the tyre pressure recommended 30 years ago should get some reconsideration. Talking mainly for the g60 version where the recommended tyre pressures of 30 years ago was 39/35 (half load) and 41/36 (full load ). Used to have from new a g60 back in 1990 and remember the ride was not as harsh as today's. Well this also had to do with the fact that oil shocks were fitted from factory but anyhow I think that a drop to 35/32 half load and 37/33 full load should be more than safe today.Talking for 195/50/15 tyres as the later fitment of 205/50/15 had no issues and pressures were down to usual todays specs for such type of a car. This is also strane, for a mere 1 cm more in width and .5 cm in height, the 205/ tyres were down to 33/29 pressure! Come to think, maybe instead of playing with pressures on a 195 to get a 205 and be fine!

[Dox 22]

Its the air pressure inside the tyre that keeps the tread flat and it's derived from the weight on that axle, under inflation (or adding extra weight) leads to the outside edges of the tyre wearing (as the centre of the tyre buckles away from the road surface), over pressure leads to the centre of the tyre wearing because the becomes more rounded (balloon like).

 

Try to inspect a Uniroyal Rainsport off the rim, they have really flimsy sidewalls.

[g6089 10]

New tyres are more rigid and do not deform as the old ones. Must be taken into account that those pressures were relevant to the tyres built 30 years ago. Unless we fit a tyre similar to those, which is impossible, the tyre pressure on new fit tyres for the specific car should be lower. New tyres are built taking into consideration they are made for heavier cars, as safety and extra equipment and features as well increase in dimensions made the cars heavier, but the G60 Corrado at abt 1140 kg is considered light compared to, say, the current Golf at abt 1300 kg, when back in 1988 the Golf weighted much less that the Corrado. Obviously tyre pressure of 39-41 for the front is way too high for todays tyres and for a car of abt 1140 kg. If you also take into consideration that replacement shocks are mainly gas shocks, which are good for handling and endurance but not for comfort, the combination of the two makes for a punishing result for the driver and most importantly for the car's body integrity as todays tyre with high pressure and gas shocks combination offer little if any absorbance.

[Dox 22]

There's a lad on here who does TPMS surveys and data collation, maybe he will comment?

 

A little survey I found, I got 15 / 20 - I don't ride mopeds and got most of the "What percentage of" wrong due to poor guess work.

 

https://www.tyresafe.org/tyre-safety-test/

[fla 9]

i keep mine at 36/32 on 17s. Seem to get fairly even tyre wear but welcome any suggestions on making a proper assessment of what should be correct

[Dox 22]

i keep mine at 36/32 on 17s. Seem to get fairly even tyre wear but welcome any suggestions on making a proper assessment of what should be correct

 

According to Tyresafe you're on the money with those figures

 

https://www.tyresafe.org/check-your-pressures/

[g6089 10]

Since VR6s from factory were set for 33/29 for 205 tyres on 15s, I think 36 is a bit high for 17s for the weight of the car. My guess would still be 33/29 as per factory's 205 on 15s considering today's 17s tyres are more rigid than 15s of 25 years ago. It would make a difference also in comfort. Best judge is yourself as long as you don't go overboard with the numbers.

[g6089 10]

According to Tyresafe you're on the money with those figures

 

https://www.tyresafe.org/check-your-pressures/

 

Cant say if its accurate, it gives 34/30 for my G60, unless it takes into consideration what I was saying about new tyres and pressures vs old tyres and pressures.Looks logical to my standards of today but far from factory specs of 39/36.

[GrahamU 5]

You are probably correct that the tyre you have fitted now should be adjusted for pressure.

 

I have customers that for exactly the same car with same size tyres the pressure changes depending on if it has Pirelli or Michelin fitted, then also depending on if the Pirelli are Pzero or trofeo so yes, different compounds do get set at different pressures.

 

The thing you should look at is the load rating which is how stiff the sidewall is, I dont know what the original tyre specs were for load but that could be why you are noticing a difference in ride comfort.

 

The problem with tyre pressures is that unless the temperature is the same every time you set them, you wont set it the same on different days, then there are the inaccurate gauges on garage forecourts.

 

Lots of things will affect what happens with your tyres, do you drive on your own or with pasengers (different weight distribution), do you have any or both the air ducts for the front brakes (cooling of tyres aswell as brakes) do you have coilovers and are they set correctly (one corner set higher will put more pressure on a tyre so more heat/pressure) just to name a few.

 

 

To sum up, I always recommend that people start with what VW state (but that should be set at 20°C), and use their own gauge to check them. Then keep an eye on the wear pattern and adjust accordingly. There is a tolerance because as with all things in the car world, the OEMs have to compromise for all the different conditions around the world.

 

My biggest bug bear is to see someone ask what pressure others set their tyres to and get a load of answers with a huge variation, all of them saying they are correct. No one else can tell you what pressure you need for your car because that is what they run. Them and their car is probably different to yours especially if its been modified.

 

Some of the bluetooth TPMS systems that show on your phone are quite cheap now and are accurate (at least the ones I have tested are) so for a small investment you can keep an eye on the pressure and temperatures then set them the same every time, you could even calculate the adjustment your pressure to the temperature in the same way Porsche and Bugatti do :) (that is what I do on my Golf and will on the corrado when its back on the road).

[Jon_vr6 1]

You are probably correct that the tyre you have fitted now should be adjusted for pressure.

 

I have customers that for exactly the same car with same size tyres the pressure changes depending on if it has Pirelli or Michelin fitted, then also depending on if the Pirelli are Pzero or trofeo so yes, different compounds do get set at different pressures.

 

The thing you should look at is the load rating which is how stiff the sidewall is, I dont know what the original tyre specs were for load but that could be why you are noticing a difference in ride comfort.

 

The problem with tyre pressures is that unless the temperature is the same every time you set them, you wont set it the same on different days, then there are the inaccurate gauges on garage forecourts.

 

Lots of things will affect what happens with your tyres, do you drive on your own or with pasengers (different weight distribution), do you have any or both the air ducts for the front brakes (cooling of tyres aswell as brakes) do you have coilovers and are they set correctly (one corner set higher will put more pressure on a tyre so more heat/pressure) just to name a few.

 

 

To sum up, I always recommend that people start with what VW state (but that should be set at 20°C), and use their own gauge to check them. Then keep an eye on the wear pattern and adjust accordingly. There is a tolerance because as with all things in the car world, the OEMs have to compromise for all the different conditions around the world.

 

My biggest bug bear is to see someone ask what pressure others set their tyres to and get a load of answers with a huge variation, all of them saying they are correct. No one else can tell you what pressure you need for your car because that is what they run. Them and their car is probably different to yours especially if its been modified.

 

Some of the bluetooth TPMS systems that show on your phone are quite cheap now and are accurate (at least the ones I have tested are) so for a small investment you can keep an eye on the pressure and temperatures then set them the same every time, you could even calculate the adjustment your pressure to the temperature in the same way Porsche and Bugatti do :) (that is what I do on my Golf and will on the corrado when its back on the road).

 

What TPMS systems do you recommend?

[g6089 10]

Tyre pressures back in 1988 were set basis the suspension at the time which was oil shocks, when today we are using gas shocks we should also use tyre pressures adjusted not only basis the harsher dumping action of gas shocks but also basis the stiffer todays tyre

walls. Its a no win situation as our cars, talking for g60s, were built basis an oil shock suspension, which admittedly did a landmark job and set a reference for handling and comfort. Don't know if also the vr6s were factory equipped with oil shocks, but the factory tyre pressure for their 205 50 15 tyres of 33/29 would most probably indicate that gas shocks were used.

[GrahamU 5]

What TPMS systems do you recommend?

 

 

https://www.ebay.co.uk/itm/Tire-Car-Bluetooth-Tyre-Pressure-Monitor-TPMS-x4-for-iPhone-iOS-Android-Wireless/122908245522?epid=13012859850&hash=item1c9de6fe12:g:P6oAAOSwrnRaVsZZ

 

This is one of the bluetooth systems I have tried, its accurate and once you have worked out how to connect it to the phone (there were 2 sets of serial numbers in the box I got :) ) it works ok

 

Only thing I did notice was one of the app's had an odd message that said to call the police when it detected a low pressure :) (But I cant remember which set had that problem)

 

Not really tried any of the cheap RF systems from ebay as we supply our own systems for that but we are looking to move into a bluetooth system soon

[GrahamU 5]

Tyre pressures back in 1988 were set basis the suspension at the time which was oil shocks, when today we are using gas shocks we should also use tyre pressures adjusted not only basis the harsher dumping action of gas shocks but also basis the stiffer todays tyre

walls. Its a no win situation as our cars, talking for g60s, were built basis an oil shock suspension, which admittedly did a landmark job and set a reference for handling and comfort. Don't know if also the vr6s were factory equipped with oil shocks, but the factory tyre pressure for their 205 50 15 tyres of 33/29 would most probably indicate that gas shocks were used.

 

 

 

Not arguing cos I didn't have VWs back then but are you sure they didn't have gas shocks? They are after all a sports coupe and my fast fords had gas shocks

 

 

like I said earlier, if you are seeing bad wear on the tyres when set to the VW recommended pressures then adjust to suit,

 

As you are saying you think the pressures are to high then you must be seeing uneven wear in the center of the tyre

 

I've not run standard wheels or suspension on any of my Corrado's for more than a couple of weeks so cant remember what the ride was like, I set my 17s with 205/40 to lower pressures

 

Out of interest, how did you measure the pressures 30 years ago and how accurate were they once you had set them ;) I'm assuming either a dial gauge thrown around by everyone that used it or one of those tube things that extended when put on the valve

[g6089 10]

as soon as I took delivery out of the dealer in 1990 I noticed a tremble on the steering wheel at highway speeds,I went back to the dealer and it was founsd that the tyres were on 28 psi pressure all around so they fixed it in front of me to 41 front and 36 rear, those were also the factory settings on the door frame sticker, and the tremble was gone. Afterwards I set them at 39/35 as hardly ever used to drive it at full load. As for the shocks when it came time to be changed for the first time I didn't go factory but elected to go Bilstein yellow, I was alsounder the wrong impression that aftermarket was going to be better, that's back in 1996, and that's when the fitter told me that the factory were oil shocks. It didn't take me long to realize it, as my ride went quite harsh but was advised that the car would now handle better so that was the tradeoff. Apparently all I enjoyed since was the harsh ride as I did not notice any visible difference in handling, to the opposite I kind of had to learn to drive my car again. I went back to the shop and the engineer who happened to race rally cars took me for a drive with my car.I was absolutely frightened, ****ed my pants with his driving and how amazingly the car handled at high speeds and in turns but unfortunately I was not a rally driver. Yes the bilstein suspension brought the best out of the car but to do so you had to have the skills and I didn't. nevertheless I kept the set and that's how I sold the car 5 years later. However I was not able to enjoy the comfy ride and feel of the oil shocks so I had to always fiddle with the tyre pressures in order not crash the chassis everytime I was on rough roads. yes the ride got softer then,lost some of the handling but unfortunately riding 30/30 or 32/32 pressures cost me numerous visits to the wheel refurbishing shop as the 3 piece BBS that were fitted from factory were quite sensitive when in rough contact with path holes.I now have in my g60 the same wheels but do not go below 35/32 so as to minimize any risk in bending them.

 

 

Back then I used the good old gas station gauge for pressures but always doublechecked them at a tyre shop. I do the same today, only I also have in my garage an analogue and a digital gauge, seems the digital is the closest to be accurate.

Edited April 1, 2018 by g6089