SEX!! actually toyo r888 tires pressure help

CM sport · Postby **CM sport** » Tue Nov 11, 2014 10:12 am

Hi guys now that I have your attention. I'm running a set of 195/50 15" toyo r888 on my rally car and our stages are only a few klms long. Wondering what pressures guys are running on these tires when doing sprints , hillclimb etc. I know they will only just be getting up to temps as we cross the finish line so was thinking of starting on a slightly higher pressure rather than going low straight up.
Any points in the right direction would be great.

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plohl · Postby **plohl** » Tue Nov 11, 2014 10:39 am

I haven't ran the r888s, but I have done a bit of dirt sprint stuff which are a standing and flying lap of ~2km long course. I have been running hankook rs3's and for tarmac stuff I aim for 31psi hot, at the dirt sprints I aim for about 28-29psi and start them at 26psi. I found the car less skatey with the lower pressures.

Magpie · Postby **Magpie** » Tue Nov 11, 2014 11:35 am

Lower than normal tyre pressure will cause the tyre to heat up faster and it will 'flex' more. If you are trying to get heat into the tyre then this would suggest to run them a little less than normal cold. However this will increase rolling resistance, always a trade off somewhere...

Whilst you are asking about pressures the question is really how to get heat into the tyres faster on a hill climb. R888's work best between 70° and 105° http://toyotires.com/sites/default/files/imce/Spec_Miata_R888_Setup_Guidelines.pdf. Whilst the article does say to start at 32 PSI hot, I have found that R888's perform better at lowever pressures like 26-28.

Do you have access to a tyre pyrometer? An infrared (non contract) is a good indication, but it only gives a surface temperature, not the temp a few mm's into the tyre.

A suggestion could be to run the wheels that will get worked more 2 PSI less than the others. Just my thoughts...

Postby **beavis** » Tue Nov 11, 2014 2:08 pm

30psi hot

manga_blue · Postby **manga_blue** » Tue Nov 11, 2014 3:01 pm

What Beavis and magpie said. I've used a few sets of R888s for circuit sprints. Aim for 30-31psi hot. The lower the starting pressure the faster you can heat them up.

The best you can do with them on short (5 minute) sprints is to start at around 22-24psi cold on a coolish morning or 24-26 in the heat of the day and weave like buggary on the out lap. That gets them up to a vaguely workable heat within 1/2 - 3/4 lap, i.e. after 40-50 secs.

For longer sessions they're best after about 5 laps if you build them up slowly to it instead. I think it's a question of getting the carcass evenly warm throughout.

If you start with high pressure (say 28+) then they just refuse to get the contact area hot enough. They don't develop proper grip and they squeal like people instead.

Hope this helps to figure out how you can use them for hillclimb/rally. Exacly how long are the stages?

MattR · Postby **MattR** » Tue Nov 11, 2014 5:15 pm

When you say rally are we talking tarmac type events like the targas or dirt????
Might be me being stupid and not understanding, but R888's would have to be one of the worst tyres for dirt rallying, that's why they have rally tyres.

For tarmac rallies the stages are usually a few kilometres long so just set them up to get to about 30 psi hot, I start my R888's at 25psi cold for a track day and they get to 30psi hot.

For a hill climb where you have to be on it from the word go and no warm up I used to set my Toyo RA1's to 24psi cold on my 240Z, 200rwhp and 1060kg with me in it. They were a better tyre than the R888 for hill climbs as the tread blocks were smaller so would heat up quicker, but the hill climb is short enough not to overheat the tyre, unless I left 100m long stripes from the start with two small gaps as I changed gears...... :lol:

CM sport · Postby **CM sport** » Tue Nov 11, 2014 7:01 pm

Wow thanks for the quick response guys. It's for the twilight Tarmac rally series in Sydney. The stages are approx 4-5klms long from the info I have been given.
I'm still used to bigger cars where the weight of the car will make the tires heat up much faster so was curious to see if you guys were going any lower than what I thought to counteract the light chassis of the mx5.
Its more of a testing what will and won't work for us at the moment . we are using our spare chassis to race in this night series while our ground up build for targa is being done.
Looking at the weather for next weeks event it is supposed to be over 40 deg during the day so it will be interesting to see how the tires react to the temp changes. Also I will have a temp gun to keep an eye on temps after each stage.
Thanks for your feedback guys.

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