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27-09-2018, 05:53 PM | #1 |
Silver Member
Join Date: Jul 2006
Location: Poole
Bike: M900ie
Posts: 504
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Setting tyre pressures
Hi all, yes a well covered topic but I came across a theory which seems (to me at least) to have some legs. The theory is that because tyre pressures rise as the tyres heat up then the pressure can be set to suit an individuals bike/weight/ridding style etc, by noting the % rise in pressure from cold to typical running temp. So you set the pressures with the tyres cold, then do a typical run for say 20 minutes so the tyres are up to your normal running temp, then stop to measure the pressures, if the pressure has risen by less than 10% for the front and 20% for the rear, then try a reduced cold pressure setting, (and more pressure where increases are over), then repeat the proceedure. The logic is that the lower pressure will allow greater movement of the tyre which in turn generates more heat.
Has anybody else come across the theory, tried it out or is it just a load of b.....s. Bitza
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Bitza |
27-09-2018, 06:35 PM | #2 |
Dismantled
Join Date: Feb 2006
Location: East Molesey
Bike: Multiple Monsters
Posts: 2,239
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Thats almost exactly how they do it with race tires, not such a great idea for the road as no guarantee you could maintaine speed to keep the heat constant.
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27-09-2018, 07:42 PM | #3 |
Silver Member
Join Date: Jul 2006
Location: Poole
Bike: M900ie
Posts: 504
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Well glad to hear it's a sound theory, it wasn't so much that I was going to apply it thinking that I was going to get an exact setting for all occasions, but was going to apply the logic to a problem I seem to have, which is: the bike weighs 175kgs, me 92kgs, 86bhp/66ft, useing a 160/70 rear &120/70 front, with Michelin Pilot Power S2s(?) things seem pretty sound all in all considering North Wales minor road conditions (& related lower speeds), however I do seem to get minor rear twitches/sudden slides easy to control and bring back but not confience inspiring, and I'm wondering if the basic problem might be that I'm not getting the tyres up to temp, especially on my 20 min ride in/out from work, in colder damp conditions. My thinking is that using pressures like 30psi front & rear will help, not only re getting the tyre hot enough, but also increasing grip via more squadgey tyre. An alternative might be of course to use a tyre which tends to heat up more easily, although I'm not sure what that would be. All thoughts gratefully received, Bitza.
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Bitza |
27-09-2018, 08:00 PM | #4 |
Lord of the Rings
Join Date: May 2013
Location: Norwich
Bike: M900sie
Posts: 5,935
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My owners handbook says to increase the front tyre pressure (by 2 psi I think?) if rough roads are encountered.
I tried this when I thought I was getting a rough ride on my Norfolk B and C roads.... It's actually pants! What they mean is to increase the pressure to protect the rim from damage in pot holes on proper rough roads such as in Third World countries. I soon reverted to my trusty 32psi front and 36psi rear. What you probably need is an all weather tyre. I used Pirelli Diablo Strada and then Pirelli Angel ST, which are both great in the wet and/or cold. My present pair of Angels are soaring past the 7k mark with flying colours. If you are more a Michelin Man* then PR3 or 4's might suit you? * Not a reference to your 92kg...
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27-09-2018, 09:47 PM | #5 |
Registered User
Join Date: Mar 2010
Location: Beachtown
Bike: M900
Posts: 2,188
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It's a bit of a tricky thing really, certainly trying to set a lower pressure expecting the tyre to heat up to get the correct pressure on the road is never going to work well.
As Kato says, on a track it is perfect as speeds and grip surface are consistent lap after lap and you can obviously adjust them to suit the conditions. Personally I am not a fan of Michelins on my Monster (I have Pilot Road 3's on)- they have never slipped when pushing on (except for the usual wet railway crossings/manhole covers etc.) but Monsters can be a little prone to wheel spin in slippy conditions. Initially they slowed the steering making it feel very vague to me until I adjusted the suspension to suit. They do seem to be lasting forever though. Your rear tyre is undersized (should be a 170/60x17) so may be a contributing factor but under what situations are you getting it to break away?
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28-09-2018, 01:47 PM | #6 |
Registered User
Join Date: Sep 2013
Location: Glasgow
Bike: S4 challenge
Posts: 447
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PR3+4's last forever, my rear is beyond 10k and still looks good for another 10k
They are however extremely sensitive to tyre pressure, dropping by even a couple of PSI makes the front end feel horrible. So playing around with pressures is definitely not an option on the Michelin's........I still like them though, esp at this time of year when the leaves start falling. |
28-09-2018, 07:05 PM | #7 |
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Join Date: Jul 2003
Location: East London
Bike: Multiple Monsters
Posts: 9,731
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I run PP 2CTs, 180/55 and 120/70 at 35 & 32 PSI respectively on the road.
As Flip says, you should have a 5.5" rim on a 900ie, so I'd have thought you'd be running a 180 rather than 160 (170 choice will be much more limited) the 160 is usually used on 600/750 with a 5" rim. Last edited by slob; 28-09-2018 at 07:08 PM.. |
28-09-2018, 10:01 PM | #8 |
Silver Member
Join Date: Jul 2006
Location: Poole
Bike: M900ie
Posts: 504
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OK, first I have been running with a 4.5 rear rim out of choice, basically as mine is presently only a 2v giving 86bhp max so putting the power down through a 160/70 isn't going to be an issue and I gain from the lighter rim/tyre giving a more nimble feel to the bike. Having said that I am about to change to a 5.5 rim 180/55 tyre when I fit my 1100 engine over this winter, so I'm guessing that a bit more weight & power should make getting heat into the tyres a bit easier.
I'm getting the rear twitching/sudden slides in pretty random conditions, at the apex or as I lean into turns from a stand still, it's like hitting on a patch of grease, quite dramatic in the instance but easy to recover? Possibly not helped by the fact that I have clip on's/rearsets, tending taking my weight off the rear. Anyway thanks for all the comments, Bitza.
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Bitza |
29-09-2018, 07:38 AM | #9 |
Guest
Posts: n/a
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After a life of aircraft engineering, I am aware of the amount of time and money bike manufacturers put into determining what the correct tyre pressure should be.
Like everything there are tolerances, and they will take into account the effects of heat and altitudes, and even different road surfaces, to come up with something that we can all measure at a standard reference point, cold tyres. I accept that on a track, a racing team will know the given temperatures and the track surface so may optimise those pressures, but on the road? Does anyone really ride in the same temperatures on the same road surface and at the same speeds all of the time? I'll just stick to the standard pressures and the standard, very sticky, Rosso 3 tyres that our bikes came with. |
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