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Pirelli Tire Pressures

17K views 21 replies 14 participants last post by  Salt flats 
#1 · (Edited)
Hey Guys: Hope this isn't a re-post. Since purchasing my HP-4 on 8-1-14, I've loved the engine and brakes. I've hated the handling. (only person in the world that doesn't like it, right?) At 205-210 in gear, the suspension has been unduly harsh, transmitting every road irregularity through the bars and frequently bouncing me a good ten inches out of the seat on what should have been minor bumps. :eek: As delivered, front and rear preload were full soft. Based on an article in Sport Rider magazine, I set the the forks at -5 and the rear at -4 compression and rebound. Huge improvement but no real joy when riding fast. I've always suspected the recommended tire pressures for the Pirelli Super Corsas were way too high. When racing, pressures were always in the 28-32 range. There was one thread here where someone said Nate Kerns recommended 27-27 on the track. A quick search brought up this info:

Diablo Racer.com • View topic - Pirelli Tire Pressures

"These pressures are general pressures for both DOT's and Slicks. Pirelli works with pressures in the only truly accurate way and that is once the carcass has been heat soaked. You should think twice about any tire tech or vendor that simply tells you to set cold pressures and be on your way. This goes for all tire brands. There are way to many variables in working simply from cold pressures such as ambient temp, track temp, humidity, track surface, cloud cover, nitrogen and the list goes on. The best way is to start with a base cold pressure of around 29psi front and 26psi rear. Warm the tires as suggested in the Tire Warmer Post and then set the pressures once again coming off the warmer.
The range for the front tire is 30-34psi and the rear is 25-28psi. Pressures should be checked everytime the bike comes off the track. Record the prssures and adjust if needed to get final hot pressure. Once this is done, you can allow the tires to cool to ambient and check cold pressures to get a good base number for the you and the bike on that day at that track. Be sure to keep an eye on track temps. It's amazing what even some clouds can do!
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Tuning the tires:
This is not an exact science but here are some good hints. The range of the front is 30-35 hot. A higher pressure will give the rider a firmer feel under breaking and turn in but the level of grip tends to decrease as the pressure increases. The tire will feel more precise and offer more or even too much surface feedback. Pressures on the lower side will offer maximum grip but will feel less precise on turn in and may tend to move around more under breaking. Most riders tend to prefer 32-23 as a true hot pressure. Riders who prefer running the tire in the higher end of the pressure range should consider testing a harder compound tire at a lower pressure. Riders who tend to run the front tire in the lower pressure range should consider testing a softer compound tire at a higher pressure. People are often mistaken in thinking a harder compound tire has a stiffer sidewall or different carcass when really the main difference is that a harder compound is exactly that. It's harder and tends to move around less on the actual carcass giving the feeling of a stiffer carcass or sidewall. Keep in mind that the stiffer set up could also cause chatter.
The rear tire should be run in a range from 25-29psi. The tire may start to spin and feel greasy above 30psi.
Ideal pressures for sprint racing tend to be around 26psi Hot! The chasis may need some work if the tire feels squishy to the rider at these pressures but set up and correct it. Keep in mind that the squishy feeling of a soft pressure will go away as the tire builds heat and the pressure rises during a session or race."

I'm going to try the 29 front/ 26 rear cold recommendation tomorrow. I'm hoping now suspension adjustments will do some good without the ridiculously high 36/42 ( probably 40/46 hot) recommended by BMW. Hopefully this will help anyone else struggling and considering the 6K move to Ohlins front and rear. ;)

On a side note, I never liked the geometry with the zero spacers. I installed the +3mm ride height spacers. I plan to raise the forks 1-2 lines on the triple clamps as well. :)
 
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#2 ·
Are you talking street pressures or track? If street, then you also must consider the possibility of bending the front rim if the pressures are too low. And also your HP4 is a std not a comp, in other words not ddc? Can't tell from your description, sorry.
 
#5 ·
I'm running F26/R26 on trackdays medium speed with 220lbs in gear and F34/R36 on public roads - works great, smooth tyre picture if you control your throttle. The faster you go, the more you have to reduce the pressure either because heat can add up to 6psi and then you are out of the recom. range :eek:
 
#11 ·
with those street pressures you have to be eating up some rear tires. that of you must avoid straight roads/highways like the plague

I understand track pressures but for the street the rear seems like you'd give up TOO much mileage for grip.

I run roughly 34f 36r street. provides excellent grip for going around corners nearly double speed limit and i guess saves some rubber when i have to slab it on the highway to work.

by all means im not a pressure guru just seams like that rear is really low for street riding. each to his own tho, have fun stay safe
 
#9 ·
Old thread I know but just wanted to add to this.

I've been making a heap of changes to this HP4 track bike over the last six months or so to try and find more confidence under braking, where I felt like the rear started to squirm too much.

To 'fix' this I have done the following:

- added stiffer springs front and rear
- then removed DDC altogether and fitted Ohlins
- lengthened wheelbase
- professionally re-setup suspension

I really thought I had it nailed with the Ohlins but no, although the bike definitely works better this squirming rear still came back to haunt me. Anyway, I generally run 25 Rear, 32 Front on the warmers. The rear has to be 25 hot or it starts to move too much for my liking but the front can be 31-33 and I'm happy enough.

So last weekend I did a track day and in the penultimate session i noticed that the bike wasn't squirming as much if at all, just figured I was riding better or not as hard. When I came off the track I checked the pressures and the front was 36/37. I dropped it back to 33 and the bike was back to squirming in the last session. So after all that I'm hoping that I might have finally found the problem - it wasn't the rear, it was the fact the front was squirming that was making the whole bike move.

Is anyone running the front at 36 hot or higher? These are Pirellis SC1 slick fronts. Looking forward to running these higher pressures at the next race day.
 
#10 ·
On super abrasive tracks I'll run the from higher to avoid some hot tearing. The pressures are also going to be dependent on track temp and track condition.

A sc1 rear is pretty soft, but has a sh1t ton of grip, and needs the track to be pretty warm to avoid issues, if it starts tearing then Your riding on the little rubber pellets coming off the tire and not the tire itself.

My typical pressures are 33f, 27r for the tracks I run, 1 pound either way can adversely effect tire wear and handling.

Tried the rear sc1 with 25 on a 95 degree day at a solid pace and was hot tearing the tire. Bumped it 2 pounds and it cleaned up nicely. Now on a colder day the 25 might have worked.
 
#14 · (Edited)
This is a general guideline I use.

Seems to work pretty well but of course it's dependent on many factures. Ambient temp, tire temp when heated, rider weight with and without gear plays a role.

Being 250 lbs with gear is a big difference for me than someone who weighs 160-180 lbs. I find that the numbers are pretty darn close. I run 32 psi front and 30 psi rear at temp, street riding. With me the bike is working harder because of my weight and this gives me the best traction, confidence and feel.

If you can't read the numbers that well, send me a PM and I'll shoot it over actual size via email. The 98 KB resizing is a pain.

Hope this helps. Ride safe.
 

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#22 ·
Tire inflation

Running on the Salt, there is no way to really do warm up laps, your lucky to 3-5 runs on the course an usually anywhere from 45 minutes to in excess of an hour between runs. With that being said, after watching our data from over 25 passes, I run 44 in both to start an adjust downward from there !
 
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