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Tyre Pressures

Discussion in 'R1200RS Tyres/Tires' started by Spiky, Aug 30, 2015.

  1. Jim Evans

    Jim Evans Well-Known Member

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    Nothing to do with pressure, mate - that's just too bloody cold for the rubber!
     
  2. Peter Burridge

    Peter Burridge Well-Known Member Contributor

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    When I've been on track days its been emphasised that lowering pressure isn't to get greater grip at a lower pressure, its because the tyres run hotter and the pressures go back up to where they should be.
     
  3. Grumpy Goat

    Grumpy Goat Well-Known Member Contributor

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    Agree with this ... lower pressures result in higher temperatures. I pay particularly close attention to this with my travel trailer which is at max payload and so the tires have to be at maximum pressure. If too low the tires will overheat and the risk of a blowout goes up significantly. My tire pressure monitoring system (on the trailer) tells not only pressure but temperatures.
     
  4. KOCook

    KOCook Active Member

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    Would be careful with that sort of advice. Recommended tire pressure is different for cold (68 deg F) than hot off the warmers (170 deg F) and should be so stated which is which. That is the only differentiation to be make for temp. But both are only about getting the biggest contact patch while still providing sufficient support to the sidewalls and crown of the tire so it can do its job. As I stated in my earlier post, 36/36 cold is lowest recommended by Michelin NA's race rep/distributor for the PR4 on a R1200RS. Since there is no benefit to putting street tires on warmers, only cold temps are available.
     
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  5. Richard230

    Richard230 Well-Known Member Contributor

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    Last weekend my tires were set at 34 psi front and 38 psi rear as I left home according to the computer. After riding for 30 minutes on the freeway they were up to 36 front and 40 psi rear, per the on-board pressure checker.
     
  6. Aussie Import

    Aussie Import Well-Known Member

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    When I did the California Superbike School a couple of years ago, the instructions were to set the cold pressure of both tyres to 30 psi. I had no difficulty on the track (given my skill set....) but on the street I found it did not work as well as 36 / 41 that I have used normally. These pressures are "cold", or at least room temperature -- basically the IQ of motorcyclists:D.
     
    Last edited: Nov 27, 2015
  7. Peter Burridge

    Peter Burridge Well-Known Member Contributor

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    The
    To put my comments into context. It was guided track sessions for street bikes with street tyres. No specialist track bikes or tyre warmers allowed. The advice was very well qualified.
     
  8. runnerhiker

    runnerhiker Well-Known Member Contributor

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    About 3 years ago I spent considerable time researching this. The best info I found was on the Dunlop website, and given how much time has passed, I don't know if the info is still there. The bottom line is that "recommended" pressure are for 69 def F and for maximum load carrying capacity. For best performance, a lower pressure works better, given lawyers all over the place, they did not give a specific lower pressure. The key, indisputable fact here, is that recommended tire pressure are for load capacity.
     
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  9. Richard230

    Richard230 Well-Known Member Contributor

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    Not only load capacity, but I believe maximum load capacity at the highest top speed that the tire is rated at. I am pretty sure that a 165 pound solo rider sticking to typical speed limits should find a lower tire pressure well within the tire's structural limits, and experience more secure cornering and a more compliant ride. I might add that the tire and motorcycle manufacturers used to provide solo riding tire pressures in their publications that were typically about three or four pounds lower then their maximum recommended tire pressures for that particular motorcycle model, but they no longer provide that detailed and useful information. I'll leave it to your imagination why not. :rolleyes:
     
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  10. KOCook

    KOCook Active Member

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    Such as tires of today use new advanced materials in carcass construction and design than those of yesteryear? Maybe advances in suspension quality relies less on the the air pressure of tires for ride comfort? And what about new tread designs--lower air pressure will cause the sipes to close, thus dramatically reducing their ability to move water? Those are just a few changes that immediately come to mind that would have a significant influence in recommended tire pressures.
     
  11. KOCook

    KOCook Active Member

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    Still, it was misleading info. Pressure rise from temperature increase caused by friction is a factor, but that is taken into account with the manufacturer's recommendation in the first place. Generally, you will get a 1 psi rise in pressure for every 10 deg F change. You can use this to adjust your cold pressures where 'cold' equals 68 deg F.

    If you lower the pressures from the manufacturer's setting, sidewall flex will increase causing much more friction from carcass/crown squirm and higher temps than expected. So, lowering the pressure is last thing you would want to do if you are worried about pressure growth from temp rise. I have measured a lot of motorcycle tire temperatures on/off the track. You are going to have to be pushing those street tires to their absolute limits to where you are sliding through nearly every turn (see photos I posted from my track day with the RS on PR4s) to worry that your tire temperatures will be significantly different on the track as they are on the street when running pressures where the manufacturer recommends.

    The only reason you would lower the pressure on motorcycle tires is to reduce sidewall support so that you get a bigger contact patch. Of course, you are compromising the tire's ability to support the weight of the motorcycle and all that extra sidewall flex will contribute to early tire wear, and failure if done regularly.

    Note, that for cars on the track, the recommendation is to INCREASE pressure to add sidewall support. The contact patch is not affected because the crown is straight (parallel to the road surface).
     
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  12. David Evans

    David Evans Member

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    Whe
    I work with Team Bike endurance team and our rider Stephane Mertens came with some Pirellis and we ran them down in the low twenties and they transformed the bikes,we won at Magny cours and the Bol dor,taught us a few things about tyre pressures.
     
  13. Peter Burridge

    Peter Burridge Well-Known Member Contributor

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    I read your report. Excellent stuff!
     
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  14. David Evans

    David Evans Member

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    Whoops,it was Dunlops at the Bol....honest.
     
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  15. Jim Evans

    Jim Evans Well-Known Member

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    Seems like we need an official statement from Michelin or Metzeler: which will say " stick to recommended pressures"! My comment on the temperature being too cold for the rubber was based on winter tire recommendations for cars: they say only winter tire rubber works properly below about 6C. I don't suppose they use that stuff on bike tires.
     
  16. KOCook

    KOCook Active Member

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    We are talking about street tires at a trackday. You want to talk racing tires, then that is a whole different topic.
     
  17. Kurt

    Kurt New Member

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    I
    I ride 34 FRONT 36 REAR one up no luggage Weight 78 KILOS
     
  18. folagana

    folagana Well-Known Member Contributor

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    First of all let me say compliments for the way you destroyed your tyres.

    I have experience with many tyres. I think 36 psi is quite high for the track. I typically use 32 on the front and 33-34 on the rear if the tyres are design to ride on road.
    The lower pressure is very useful during the braking.
    For sporting tyres, the pressures could be even lower.
     
  19. wildoat

    wildoat Member

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    With respect, I think these tyres may have been getting too much temperature!
    Reckon your pressures were too low!
    cheers
     
  20. KOCook

    KOCook Active Member

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    36/42. And temp was just fine. It is a track event with very aggressive cornering and speeds. So the surface rubber does melt off. That is how fresh rubber is presented to the high traction track surface for max grip. Is very normal. Have a look at the tires on a race bike (or car) after a race & you will see the same sort of balled rubber. What you can't see in the photos is the spots of melted rubber that is slung inside the fenders. That too is normal.
     
    Last edited: Jul 3, 2016
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