Conflicting tyre pressure information

Forgiven · Postby **Forgiven** » Sun Jun 21, 2020 11:44 am

I am going to do the MX5 Club Driver Training Day (sans training - because of COVID). At Marulan.
The advice to pump tyres up to 37, so that they rise to 40 max.
This is similar advice to what I got when I did an Advanced Driver course years ago, and when the BMW Club had a day at Eastern Creek.
I have 15" KUMHO ECXSTA HS51 in good condition.
The MX5 expert who sold the tyres recommended 27 all round. That gives good grip, with no squeal on for instance a bit of a squirt around a round-a-bout. Pump them up and they squeal.
I asked the same expert why the recommended high pressures for the inexperienced on the track, and he said that it was the squeal provided a warning to the beginner.

RS2000 · Postby **RS2000** » Sun Jun 21, 2020 3:28 pm

The high pressure is not because of being inexperienced, but because they are road tyres.
Road tyres have a soft sidewall (compared to competition tyres) & under hard cornering with low pressures they will flex. They can also overheat with low pressures.
The sellers recommendation of 27psi is more about comfort than grip.

Forgiven · Postby **Forgiven** » Sun Jun 21, 2020 8:29 pm

Thanks RS2000.
Still a little bit confused.
Tyre placard says 26 all round. For the standard 14" wheels.
What difference, if any, 15" wheels?
From 27 to 37 for the track seems like a big difference.

RS2000 · Postby **RS2000** » Sun Jun 21, 2020 10:02 pm

The placard pressure is for normal road use & has comfort built into the figure. Personally, I wouldn't be using anything less than 32psi on the highway. I'm no expert, but all the track schools say to get the pressure up on road tyres. Ordinary road tyres have lots of grooves & thus small tread blocks. Apparently at placard pressures & high cornering forces, the small tread blocks squirm, the soft sidewalls flex, & you lose steering response & grip.

Magpie · Postby **Magpie** » Mon Jun 22, 2020 7:35 am

The only way to confirm is to do pressures and temps.

In normal road driving getting a 6 psi increase will be difficult. As mentioned by others the tyre carcass construction will influence cold pressures. Further increasing tyre pressures decreases under/oversteer to a point, safer for a new person on the track.

ralt · Postby **ralt** » Mon Jun 22, 2020 12:30 pm

Hi.
You will have to arrive at a pressure to suit you. I would start at 35 lbs and using your tyre pump and guage see how you feel after a run. Inspect the tyres and adjust to what you think. This is the fun of doing it at your level.

bruce · Postby **bruce** » Mon Jun 22, 2020 2:17 pm

Yup. Just put in what the tyre placard says (32?) and see if you like it. Adjust up or down to suit your butt-comfort-meter.

Forgiven · Postby **Forgiven** » Mon Jun 22, 2020 5:12 pm

Thanks guys.
Similar conclusion from this discussion: https://www.pistonheads.com/gassing/topic.asp?t=502211. Depends on the car and the tyre, but usually up from road pressures.

project.r.racing · Postby **project.r.racing** » Tue Jun 23, 2020 11:17 am

For a road tyre. I go 4psi higher than the placard.

93_Clubman · Postby **93_Clubman** » Tue Jun 23, 2020 12:19 pm

tyre placard says (32?)

Tyre placard says 26 psi front & rear cold - as PRR says for road tyres on the road go at least 4 psi higher cold. Personally, I go 32psi cold all round for road tyres on the road, but some might find the ride uncomfortable.

madmort · Postby **madmort** » Tue Jun 23, 2020 2:24 pm

93_Clubman wrote:
tyre placard says (32?)

Tyre placard says 26 psi front & rear cold - as PRR says for road tyres on the road go at least 4 psi higher cold. Personally, I go 32psi cold all round for road tyres on the road, but some might find the ride uncomfortable.

I find 32psi just a little harsh in my NB on the road, might have something to do with older suspension. I run 29psi on the road (205/45/16) and find that a good compromise and even wearing. For track up to 40psi might be in order but I'd hate to see how they'd wear

Jeo · Postby **Jeo** » Tue Jun 23, 2020 5:31 pm

Ignore suggestions about how it will handle on the road. You've just paid for (driver) training from the club, I'd be listening to what they have to say. But also I found that ~40psi hot was right for my NA on road tyres.

madmort wrote: For track up to 40psi might be in order but I'd hate to see how they'd wear

Assuming 40psi is indeed the right pressure, I'd wager they'd wear evenly. If not, 40psi ain't right.

manga_blue · Postby **manga_blue** » Tue Jun 23, 2020 6:07 pm

For track you typically want 38-40 hot on street tyres. The hard part is knowing where to start from cold to get to the right pressure hot. Tyre flexing and sliding are what brings the heat up, which them brings the pressure up. If it's a cold morning I'd try starting from around 33-34, if it's Sam then starting from 35-36 might work. Check immediately after every run as conditions change throughout the day.

On a frosty morning I would start at 22 for R-specs to get them up to 31 hot. They needed that much flexing to get them going.

madmort · Postby **madmort** » Tue Jun 23, 2020 7:59 pm

Jeo wrote:Ignore suggestions about how it will handle on the road. You've just paid for (driver) training from the club, I'd be listening to what they have to say. But also I found that ~40psi hot was right for my NA on road tyres.

madmort wrote: For track up to 40psi might be in order but I'd hate to see how they'd wear

Assuming 40psi is indeed the right pressure, I'd wager they'd wear evenly. If not, 40psi ain't right.

Your having a bet (wager), so you obviously don't know one way or the other. Just guessing hey? If they wore evenly and performed just right, the door placard would say 40 psi, no?