Tyre pressures are one of the most argued-over subjects on the forums, and the threads run from 2005 to 2019. The short version is that most owners on the road run about 24 psi at the front and 26 psi at the rear, measured cold, which is lower than the handbook. Some Turbo owners go a couple of psi higher, especially at the rear, and track day pressures are a separate subject, because they are set when the tyres are hot.
Standard wheels and tyres
From the Vauxhall TIS, for all models. The TIS says the rims are magnesium, held to the hubs by five bolts, with security bolts fitted as standard.
| Wheel | Inset | Tyre | |
|---|---|---|---|
| Front | 5.5 J x 17 | 26 mm | 175/55 R17 |
| Rear | 7.5 J x 17 | 39 mm | 225/45 R17 |
The standard front tyre is no longer available, so owners fit 195/45 R17 instead, which they say works fine. It isn't a standard size, so the TIS gives no pressures for it, but the recommended pressures are the same as the most common road figures below: 24 psi at the front and 26 psi at the rear, cold. Many owners also fit aftermarket wheels. The threads mention 16 inch fronts with 17 inch rears, for example 205/45 R16 at the front with 225/45 R17 at the rear, or 195/50 R16 with 225/45 R17 on Team Dynamics wheels. For other sizes and makes the right pressure depends on the tyre as well as the size, so use the figures below as a starting point.
The factory pressures
These are from the Vauxhall TIS. The table is headed "full load", and we don't have a separate figure for a lightly loaded car.
| Car | Front | Rear |
|---|---|---|
| NA (Z22SE) | 1.8 bar (26 psi) | 1.9 bar (27.5 psi) |
| Turbo (Z20LET) | 1.8 bar (26 psi) | 2.1 bar (about 30 psi) |
Both are for the standard 175/55 R17 and 225/45 R17 tyres. Owners quote them as cold figures, though the TIS text we have doesn't say so. They match what owners posted from their manuals: 26/27.5 for the NA, and 26/30 for the Turbo, which has no separate owner's manual but has a handwritten Vauxhall entry in at least one. As a rule of thumb, multiply bar by 14.5 to get psi.
One 2005 poster gave the NA figures as 1.9 bar front and 2.0 bar rear. That was wrong: the TIS confirms 1.8 and 1.9 bar.
Several owners also said the factory figures are too high for the car: "You might find those pressures are too high for the VX even though the manual shows them." One poster said 24/26 isn't the book figure, just the pressures that give the best overall performance. Another view was that a road car should use the factory figures, because the engineers spent time and money testing them, and that this only changes for a race or track car.
What owners run on the road
| Front / rear (psi, cold) | Who and what |
|---|---|
| 24 / 26 | The most common answer by far, in every thread from 2005 to 2019. One owner in 2012 said it was what the majority use. Posters with standard wheels and Bridgestones, with AD08s on 16/17 inch wheels, and with Continental tyres all gave it. |
| 22 / 24 | The recommendation of a geometry specialist ("Scared Stiff") in 2005, for their own set-up. Another poster said it is a suggested cold pressure for the track, and too low as a hot pressure. Other owners found it soft on the road, with heavy steering and less response. |
| 24 / 27 | One owner, depending "which way the wind blows". |
| 23 / 26 | One Turbo owner, with "whatever feels best". |
| 24 / 28 | Two Turbo owners in 2005. One was running it, and the other planned to try it because the front skipped over the road at the dealer's 26/30. |
| 25 / 28 | One owner on the road, with good even wear all round. |
| 25 / 24 | One owner on 205/45R16 front and 225/45R17 rear tyres, chosen to get even wear across the tread. |
| 26 / 28 | One owner who said it felt better than 24/26, though he had also just fitted new tyres all round. |
| 27 / 29 | One owner, posted without explanation. |
| 28 / 30 | One owner when he used the car, and another who said he has always been unhappy with the lower pressures and runs about 30 at all four corners. |
| 25 / 27 | Given as typical for the Yokohama AD08R in a 2019 thread. |
| 24 / 26 | Given in the same thread as typical for Toyo R888s, measured cold. |
A few owners gave their reasoning. One runs 22 front and 23 rear on R888s for low-speed B-road driving, because it gives more grip and lets the tyres soak up poor surfaces, and 24 and 26 for higher speeds and A-roads, which makes the car bounce more but stops the tyre deforming at speed. Another summed it up as: lower pressures give more comfort, higher pressures give less movement of the tyre in corners, so experiment and find what works for you. A third said sidewall strength, the number of plies and the profile all affect how much the tyre flexes, so the right figure depends on the tyre.
NA or Turbo
One owner said the Turbo wants slightly more at the rear, with 27.5 as his example, and the TIS agrees: 2.1 bar at the rear for the Turbo against 1.9 for the NA. In practice, Turbo owners in these threads mostly gave 24/26 anyway, and some went to 26/28 or 28/30. The 2008 track threads found that a Turbo handled better on higher pressures when hot, which is covered below.
Checking and setting them
- Measure cold, before you drive. Posters stressed that the pressure changes a lot between the cool of the morning and the heat of the day, and that the side of the car in the sun gains a couple of psi.
- Check your own gauge, and check what the fitter did. One owner asked a garage for 28 psi in two new rear tyres and found them at 32 and 34 when he got home, and the ride was awful. Another had a cheap digital inflator that put in 26 psi when it was set to 21, and spent a track day with rear tyres that went off after two laps. Check the inflator or forecourt air against a gauge you trust.
- Read the wear. If the middle of the tread wears before the outside, the tyres are over-inflated. If the shoulders wear faster, they are under-inflated. One owner on 25/24 said his centre wore a little first because of wheelspin, and that 26/30 would wear the centre "like mad".
- Long motorway runs. Opinions differ. One owner took a little extra in the rear for long journeys, to stop the driven wheel's sidewall getting too stressed and hot. Another said 24/26 is fine for anything including long motorway journeys. Nobody reported a problem either way.
- Experiment properly. Change one thing at a time, in 2 psi steps, on a road you know, and write down what you did, because "you will never remember". If you end up lower than before, keep an eye on tyre temperatures. If they run noticeably hotter, add 2 psi all round.
Track days
Cold to hot
The pressure rises as the tyre heats up. Owners gave these examples, all for R888 or A048 type tyres unless said otherwise:
| Cold start (F / R) | Hot after running (F / R) | Tyre and notes |
|---|---|---|
| 21 / 22 | 25 / 28 after a 20-minute session | New Yokohama AD08s, nitrogen-filled. The owner was surprised how much they changed. |
| 24 / 26 | 28 / 32 after 10 laps at Donington | Toyo R888s on Team Dynamics 1.2 wheels. He dropped each by 4 psi and the rear felt sloppy and the front felt as if it was rolling onto the sidewall. He went back to 28 front and 30 rear and it felt right again. |
| 21 / 23 on a cold day (under about 12 to 14 °C) 18 or 19 / 20 or 21 on a warm or hot day | Not given | R888 and Yokohama A048 on a Turbo. The owner's key rule was not to let the rears go over 30 psi hot, because both tyres drop off sharply above that. |
Another owner gave a rough rule from the gas law: 25 psi cold works out at about 30 psi hot, since the air at 80 °C is about 1.2 times its pressure at 20 °C. Treat that as a rough guide only. A different post estimated the rise from cold to hot at about 5 psi.
Hot pressures owners found best
| Tyre | Hot pressure (psi) | Notes |
|---|---|---|
| Toyo R888 | 30 front, 32 rear | Reported from a Toyo motorsport tester at a Rockingham track day in 2008, working on three VX220s. Grip was noticeably better once the tread was properly hot. Another owner with TR-1s found 30/32 the best compromise on an abrasive track, though he didn't say whether hot or cold. |
| Toyo R888, Turbo | 29 front, 31 rear | Better than 24/26 hot, at Rockingham. |
| Yokohama A048 (typed "A408" in the thread, probably the LTS version), NA supercharged | 28 front, 30 rear | Best overall grip and feel, with Nitron dampers and a motorsport anti-roll bar. |
| Yokohama A048 | 25 to 28 | From an owner who says he has collected data from these cars for years. He says 30 is too much for the A048. |
| Toyo R888 | No more than 28 | Same owner. He says the R888 has a softer sidewall so needs more air than the A048, but he would be surprised if it wanted over 28. |
| Yokohama AD08 | 26 front, 28 rear | Another owner, who also gave 25/27 for the A048. |
These figures don't agree, and the owners who gave them say so. A newcomer in 2010 called the track pressure threads a minefield, and a PistonHeads thread in 2009 reported minor disagreement with the Toyo advice below. The owner who gave the A048 figures above also said tyre makers only want to avoid failures, so they always suggest higher hot pressures, and that he runs as low as 15 psi cold to reach the pressure he wants. Toyo's own figures below are much higher, and tyre failure is the risk if you go too low. Pidgeon, who races, said the 30 psi was a hot figure, and that on his race car he starts at 23 near side and 24 off side to reach it. For a track day he suggested starting at about 25 psi cold.
Toyo's published guidance for the R888
The Motorsport Manager of Toyo Tyres UK posted this in March 2008 after working with VX220s at Rockingham. It is for the R888, and it is the only manufacturer guidance in these threads.
| Vehicle weight | Cold pressure (psi) | Hot pressure (psi) |
|---|---|---|
| Very light (under 800 kg) | 17 to 22 | 22 to 29 |
| Light (800 to 1,000 kg) | 20 to 26 | 24 to 32 |
| Heavy (1,000 to 1,400 kg) | 23 to 27 | 28 to 40 |
| Very heavy (over 1,400 kg) | 27 to 35 | 37 to 40 |
- The maximum hot pressure Toyo recommend is 40 psi.
- Their ideal tread temperature, measured with a probe pyrometer, is 85 to 95 °C, with a difference across the tread of no more than 9 °C. They say tyres should have two heat cycles before hard use.
- If the day or track is cold, start with a higher cold pressure, because the tyre won't get as hot and so the pressure won't rise as much.
- Hot pressures should be balanced side to side. Once cool you will find a difference, and on a track that mostly turns right the offside pressures are usually higher than the nearside.
- Because the pit-lane temperatures are lower than on track, readings that are already in their range probably mean the tyres were too hot during the session.
- Higher pressure makes the tread run hotter, because the stiffer casing makes the tread work harder. Lower pressure makes it cooler.
- The R888 comes in a standard compound and a soft compound ("SG"). Toyo say the soft one is for sprints and hill climbs of about a minute, and they don't recommend it for dry track days because it goes off quickly.
- Toyo describe the T1-R as an ultra high performance road tyre that can be used on the track, and the R888 as an ultra high performance track tyre that can be used on the road. Their advice for the T1-R is the same.
How to tell if you have it right
- Set the pressures hot, after a typical session, not cold. A track day driver can adjust between sessions. One owner was told to let the pressures down to their cold figure once hot, and found the car didn't handle as well afterwards. Another said the advice is to equalise across the axle, increase the pressure as you get faster to keep the sidewall stiff, and that low starting pressures overheat the sidewall and cause uneven wear and a tyre that feels as if it is going off.
- Chalk. Wipe chalk over the tread and the shoulders and, after a few hot laps, see where it has worn. It should just wear off the tread surface. It is no use on a damp or wet day.
- Pyrometer. Take temperatures across the tread as soon as you get into the pits. One owner relayed from the Toyo tester that if the centre is more than 2 to 3 degrees hotter than the outside the pressure should come down, and if the outside is hotter it should go up. Toyo's own written limit across the tread is 9 °C. Each tyre can need a different pressure, depending on the circuit.
- The triangle markers on the shoulder. Owners disagree. Some say they show if you are rolling the tyre over, so scuffing on the markers means too little pressure. An owner relaying Toyo's answer said they mark the tread-wear indicators for road legality and aren't a guide to wear. Another owner was told by an instructor not to wear past them, ended up with nearly 40 psi to stop it, and said one left-hander felt harsh.
- Blueing where the sidewall meets the tread was named as a sign of a problem with the set-up. One owner keeps his pressures below 32 psi as an upper limit.
- Warming the fronts. One owner said the VX220 struggles to get heat into the front tyres on cold tracks, especially after he reduced the understeer.
Road tyres on track
For standard road tyres, such as the Bridgestones, owners said there is no optimum figure. Start the first few laps at road pressure, then raise it 1 psi at a time. You will never stop road tyres wearing the edges of the tread blocks, but a little more pressure makes the outer half work more progressively. If the middle blocks start to wear faster than the outside, you have gone too high. Don't go too high to save the shoulders, because the handling will suffer badly and they will still wear if you drive hard. You can expect to stay close to your road figures.
One owner who tries new tyres, road or track, always starts at 27 psi all round. He says a soft-sidewall tyre on the front, with less pressure put in to chase grip, becomes a "horrid sloppy mess", and that starting low suits only very short events such as autocross or a one-minute hill climb lap.
Changing the handling with tyre pressures
A 2019 thread asked whether raising the front pressures would reduce a Turbo's low-speed understeer. The car was standard, on 17 inch wheels and Bridgestone RE040s, at 26 psi. Owners did not agree, and the thread ends without the owner reporting a result.
| View | Reasoning |
|---|---|
| Raising the front pressure makes understeer worse | A harder tyre is rounder, which gives less grip. "Make it softer to increase grip." The cheaper fix is the geometry. Another owner pointed out that pressures are a dynamic variable, so you should get the hot balance right, which will probably understeer more when cold, and it is a moot point on the road because you never see real hot pressures. |
| Lowering the front pressure reduces understeer | It widens the contact patch, which adds grip. Owners use it on track days in the rain. Toyo's advice agrees: to reduce understeer, reduce the front pressures or increase the rear ones, and to reduce oversteer do the opposite. These are hot pressures on a race tyre, and small changes only. |
| It's free, so try it | Set front and rear to your normal figures, go up 2 psi at the front, and note the effect on a known roundabout. Repeat, then go down 2 psi, then do the same at the rear. Keep notes. |
On the geometry, one owner said the cars are set at around 0° camber at the front, while an Exige goes to about 0.5° negative, and that removing some camber shims gives a noticeable difference without chewing the tyres, at about 0.25° per 1 mm at the front and 0.30° per 1 mm at the rear. Another uses a more aggressive 340R geometry on track, but says it is oversteer-heavy and tracks in grooves on the road, and recommends a fast road geometry for the road. See Wheel alignment (geometry) settings, including the safety warning about the shim bolts.
Some owners said to get the basics right first: check the suspension components, bushes and ball joints, set the geometry on a level floor (a DIY string check was suggested, measured carefully), and make sure the tyres are decent and matched front and rear, including their age. Then work out when the understeer happens: high or low speed, corner entry or exit, under throttle or braking, and whether it is partly down to steering inputs. One owner pointed out that more grip does not necessarily mean better handling, and that if the inside tyre lifts, more camber or a stiffer anti-roll bar would be what is needed. See also Uprated anti-roll bar.