An interesting take on tyre pressures [Archive]

slofox

20th October 2010, 16:33

Was in discussion re tyres t'other day and was told as follows:

"The reason back tyres square off is because riders use too low a tyre pressure. The user manual recommendations are not that good - the manufacturer of the bike doesn't care about tyre wear. A higher pressure will give the tyre better shape and it will wear longer. Go with the tyre manufacturer's pressures not the bike manufacturer's..."

So I've done a heap of reading about tyres in the last couple of weeks and have found the odd thread that might support this assertion. But opinion seems to be pretty evenly split - in fact miles apart at times and this from opposing "experts" claiming either a million years in the tyre industry or dealing with bike tyres. There ain't no agreement out there.

I suspect that the quote above may be at least partially true. But I also suspect that higher pressures may lessen grip to some extent. The only time I rode with a reeeeally high back tyre pressure the bike was all over the place.

I feel pretty sure that underinflation may well cause the tyre to lose its profile under certain road conditions. And that might lessen grip as well

Incidentally, I have not found any tyre makers' pressure recommendations to compare with the bike makers pressure recommendations despite trawling gazillions of websites. My own thoughts are that it must be nigh on impossible to cover the wide range of loadings any given bike may have and come up with a "correct" pressure...

So, I thought to draw upon the collective wisdom of KB, seeking out the opinions of all our local experts...:whistle:

What say you?

Bike makers pressures too low?
Does this cause poor wear patterns?
How does this affect grip?
Etc etc etc?

Grubber

20th October 2010, 16:54

My 2c worth.
I run 190's on the rear of my Daytona and i usually run it at around the 40 to 42 psi when riding at a reasonable pace on road. If i decide to have a fast day out i tend to let it run around 36 to 38 psi.
Track day i run around 32 or 34 for obvious reasons.
I am around 11000k on this set and no rounding to speak of. Still seem to have a ton of grip too.

how's that for ya!

yachtie10

20th October 2010, 16:59

I Think it has more to do with the riding you do
obviously pressure has an effect on wear but if you spend a lot of time on straight roads then they will square off no matter what you do

Guys I know who just ride the twisties dont square off there tyres because they are worn out before that is an issue

AllanB

20th October 2010, 17:21

slofox

20th October 2010, 17:38

Interesting.

I run a lower pressure in the rear than the factory recommendation of 42 - I run 39 as I found 42 to be too harsh. Fronts fine at 36.

No issues with squaring off, though obviously a rear tyre will naturally wear quicker in the centre as you spend the greater % of your ride there and you tend to squirt more power through it when vertical.

However to clarify, most of my rides involve a good set of corners to fang around so the sides get a fair bit of use up and above someone who uses their bike as a daily commute.

Just fang it harder in the corners!

Back to the theory - on a car :facepalm: too high pressure will wear the centers of the tyre faster, unsure how I can apply this to a bike though.

interesting post.

One of the things I read said that the maximum pressure on the tyre (42psi in your case) is NOT the recommended but the MAXIMUM pressure you can run it at. Should only be used when "fully laden" (whatever that means).
So if you are a lightish sort of person, and don't load up with luggage, you wouldn't run it at maximum.

I might try going maybe two psi higher on the next set of tyres and see what happens...

Usarka

20th October 2010, 18:01

Conti suggest that you follow the bike manufacturers guidelines.

http://www.conti-bike.co.uk/default.asp?pid=27 Probably a gigantic case of buck passing.....

Gremlin

20th October 2010, 18:01

It also depends from bike to bike.

The hornet sits at 36F 42R (honda recommendations), and tyres like PR2, Strada, etc, have all been happy, and excellent life, 15k or more from rear, more than that on front. Bike is used used almost entirely for commuting, motorways, so a lot of centre wear.

The KTM is recommended to be 31F 31R, I run on 32F 36R or thereabouts. Bike carries more weight than stock, too soft and it was ripping up the tyres. Too hard and they wouldn't grip properly. KTM does very little commuting and I wear the edges of the front tyre faster than even the centre of the rear. Usually turn the front triangular and wear away the edges of the blocks. Supposedly, its because the tyres are too soft... Mileage varies a little, but usually around 7500km for a set of Pirelli Scorpion Syncs. Going to try a set of Angels shortly and see how I go.

Motu

20th October 2010, 19:34

I'm a low pressure sort of guy...maybe riding around on trials bikes with 3 or 4 psi has distorted my thinking....low pressures to me mean traction,and I'm all for traction.I don't ride an expensive powerful bike with really expensive tyres,but I'm on a tight budget,and buying tyres hurts.

On my streettracker setup I use Dunlop K70's,a tyre from the '60's,and I run them at the pressures they used in the day - 25psi rear,20 front....recommended pressures for the bike are 36 and 32.They do wear fast,but I love the grip.I feel nervous using my standard tyres with standard pressures,the bike seems to be on a knife edge and runs wide.

A month ago,after not riding the bike for some time I went for a ride,after getting settled in I really enjoyed the ride,had great confidence in the bike,it never felt nervous or ran wide.Getting home I see there are no chicken strips,it's right down to the edge when I normally have 20mm.A check on tyre pressures show 8 psi in the rear.It takes all kinds - don't worry,I'm happy.

Corse1

20th October 2010, 20:27

I wrote a letter to spannerman a while ago re tyre pressures. I had recently wasted a set of pirelli diablo stradas on the ST4s in 10000km's. I was running the Ducati recommended pressurs of 32 front 36 rear.
The reason i had written the letter was that the triple came with Triumph recommended pressures of 36 front and 42 rear.

Didn't really get a straight answer, rather some questions re visual properties of the tyres to confirm his recommendations.

My own findings are that the 36/42 Triumph pressures work great on the triple and to let you know how I ride the PR2's on it now have 5500kms on them now with no squaring off at all and with a pretty much even wear with tread depth being between 2-3mm left all over the tyre. Now I am worried about getting 10k km's out of the set.

Now i am running higher pressures on the 4s ....about 35 front and 39 rear and the wear seems to be more even which would support the statement that higher pressures prevent square off on the rear.

What I have noticed however is that while the higher pressures on the lighter triumph give me full confidence at all lean angles, if the heavier bike has the same pressures the front end does not have the same grip and is a little nervous.

This seems to me to be the opposite effect of what I would think:blink:

Soooo there are a lot of variables involved such as suspension set up etc (heavier bike has higher quality suspension..??? go figure).......

All the tyres I run are more sport tour than sport. I can't get my head around 5000km replacement costs...i mean I cant get my wifes head around the costs.

Really i think kiwi roads are that rough that they will chew out tyres at alarming rates on any bike. Ameriacan riders get 10 m 15 thousand miles out of the same tyres I get 10k km's out of.

Back to the thread... i would recommend using pressures closer to the higher end than lower.
Track days yes I run 30 - 32 or 32-34 depending on temp and who gives a toss if they wear faster. But there are plenty of racers here to give you their advice.

Tyres tyres tyres tyres tyres .... al little bit like oil questions:facepalm:

davebullet

20th October 2010, 21:10

HenryDorsetCase

20th October 2010, 21:13

I was thinking about this the other day. I have been experimenting with the front tyre pressure on the Scrambler. New front tyre last week (Bridgestone DeathWing OEM size. Manuel says 30 psi, I am happily running 26.

rear recommended either 30 ir 32, happy at 28. I am light-ish, and usually ride solo, and I presume the recommendations are for two fat americans running flat out across Death Valley.

grip is fine, turn in good, no worries.

Mishy

20th October 2010, 21:15

So this is an interesting question - what pressures ? and why ?
I go entirely from a reccomendation supplied by the tyre manufacturer, and have found this to be pretty much dead right. They are also TUV approved, so this tells me that they have been tested outside the factory as well.

Having the correct tyre pressure in the rear tyre certainly has a huge impact on tyre life, and being a few psi off can have a much greater influence than most people think - as in 7% (roughly) less life 2 psi short of optimum, up to 15% less at 4 psi short, and 25% or more at 6 psi short.
Heat is what causes the extra wear, and a higher pressure keeps the heat build up in check.

Most Jap road bikes with radial tyre sizes would want 36 F, and 42 R as a start point. If you are carrying a load, then put 2 psi extra in, and if you are doing sustained high speed, then add 2 psi more !
All of this helps keep the heat down, and the wear in check when you have a bigger load on the tyre, or extra speed causing extra heat build up.

The "max load at 42psi" mark refers to the max load, not the max inflation pressure, and just tells you that to carry that load, you have to have at least 42 psi in the tyre.

I think that most manufacturers are reccomending pressures pretty close to what the tyre manufacturers are, so I would be surprised if there were many huge differences with large modern bikes - I'd interested to hear if anyone has come across an example.

Corse1

20th October 2010, 21:17

I am light-ish,

:drinkup::drinkup::drinkup::drinkup::drinkup::drin kup:

Be interested to see how your tyre wear progresses. Maybe your light but those are pretty low pressures.

Ok I am jealous:facepalm:

Corse1

20th October 2010, 21:23

Having the correct tyre pressure in the rear tyre certainly has a huge impact on tyre life, and being a few psi off can have a much greater influence than most people think - as in 7% (roughly) less life 2 psi short of optimum, up to 15% less at 4 psi short, and 25% or more at 6 psi short.
Heat is what causes the extra wear, and a higher pressure keeps the heat build up in check.

Most Jap road bikes with radial tyre sizes would want 36 F, and 42 R as a start point.

Yes I think my bad experience with the higher pressures was when I had the wife on the back :shutup:. I am slowly getting the duc pressures back up to the 36-42. Not sure why the would have even recommended the 32-36 pressures.

AllanB

20th October 2010, 22:04

New front tyre last week Bridgestone DeathWing.

I'm not sure if that is the coolest name I've ever heard for a tyre or a scary nickname relating to it's grip!!!!

:laugh::laugh::laugh::laugh:

HenryDorsetCase

20th October 2010, 22:09

I'm not sure if that is the coolest name I've ever heard for a tyre or a scary nickname relating to it's grip!!!!

:laugh::laugh::laugh::laugh:

Its called a Bridgestone Trailwing. OEM. Its perfectly adequate for the bike's intended use, and the way I ride. I think the DeathWing name came about from the guys who punt them about aggressively offroad. I ride mine on shingle roads, and NZ chipseal, and they're fine.

Best part: $180 fitted. Compared to Diablo Corsa's that were on the Hornet I had, a freakin' bargain!!

I'm 74 or 75kg ready to ride

ellipsis

20th October 2010, 23:57

....bloody tyres....

21st October 2010, 03:13

I run 40 front and 42 rear on the Beemer.
The bike is rather heavy and I am no "slim-jim" at 100kg...

TimeOut

21st October 2010, 05:14

YellowDog

21st October 2010, 05:23

The next question is, how accurate are your tyre gauges!

I've found a 5 psi difference even in the same make/model of gauge.

I checked mine against the local bike shop who have there's calibrated regularly

Great Point !

I've not had any problems with squaring off however I do enjoy my cornering, which may account for that. IMO - The tyre manufacturers are in the business of selling more tyres and also have a legal responsibility over the advice they give, hence it will not be performance related.

I have spoken to many about tyre pressures and have come to a trial and error agreement that the recommended 42 rear is reduced to 39 and the recommended 36 front is reduced to 34. For long motorway journeys I bump back up to the recommended pressures.

The Gas stations are dangerously inaccurate, as are the pointy needly thing on the home pumps. Worst off, they tend not to be consistently inaccurate so you can't accurately guestimate.

I carry a pen sized pressure guage on the bike as I am quite fussy with my tyre pressures.

Whatever makes you feel confident is the right tyre pressure setting for you :yes:

slofox

21st October 2010, 07:32

The next question is, how accurate are your tyre gauges!

I've found a 5 psi difference even in the same make/model of gauge.

I checked mine against the local bike shop who have there's calibrated regularly

My practice is to use one gauge and one only. It doesn't really matter if it is not 100% accurate if you use it to set suitable pressures and stick to them...

There's a lot of discussion out there re pressures. Maybe I just need to experiment over a longish period of time and develop a set of pressures that feel right to me...

slofox

21st October 2010, 07:37

I go entirely from a reccomendation supplied by the tyre manufacturer,

Where do you find these recommendations please Mishy? I have looked all over and found none so far...

slofox

21st October 2010, 07:44

Incidentally, HERE (http://www.gixxer.com/forums/showpost.php?p=3914741&postcount=18) is a thread that I have read recently...

This is where some of the ideas being mooted here have come from. especially those relating to maximum pressures and loadings.

vifferman

21st October 2010, 08:04

My answer would be "It depends" (on tyre brand type, riding style, load, bike, etc etc.)
On the last few bikes I've owned, I haven't deviated far from the recommended pressures (usually 36F 42R) and run 36F and 40R. I've been running a bit lighter in the rear tyre lately, as although it's still just leagal WRT tread depth, the tyre has done its heat cycles and lost a lot of grip, so needs some coaxing to get up to temperature. Even then it tends to spin up if I accelerate out of corners in first gear.
The front's a different kettle of worms. VFRs tend to load the front end quite a lot, and are hard on tyres as a result. Running less than 36 means the tyre doesn't last long. Plus the current Storm tends to wander a bit (a general tendency with Avons) if the pressure's even a couple of PSI low.
The rest comes down to comfort: too much air, and you feel every little ripple and bump. Too little, and there's insufficent feedback, and the bike can feel a little unresponsive when cornering.

p.dath

21st October 2010, 08:12

One of the things I read said that the maximum pressure on the tyre (42psi in your case) is NOT the recommended but the MAXIMUM pressure you can run it at. Should only be used when "fully laden" (whatever that means).
So if you are a lightish sort of person, and don't load up with luggage, you wouldn't run it at maximum.

I think this might vary a lot with the bike. But the manual for my CBR600 says 32psi is the RECOMMENDED pressure for a single rider, and has a separate set of pressures for when the bike is laden.

p.dath

21st October 2010, 08:32

I'm guessing the actual tyre pressure to be used will depend on what you are expecting from the tyres, and what you are asking the tyres to do, and as a result any general "recommend" tyre pressure will be a compromise between several factors.

For me, I'm a sedate road rider. And I would like the tyres to last a reasonable amount of time. I use the bike manufacturers recommendations.

Other road riders might cane their bike, get the tyres so hot they can't touch them, and not care about tyre life, so they might opt for a lower cold tyre pressure.

MSTRS

21st October 2010, 08:51

I'm a low pressure sort of guy...8 psi in the rear.

You running rimlocks with that?

Pressure recommendations are as varied as 'which tyre should I get?'
If there is such a thing as optimum pressure, it is subjective to each individual bike/rider/tyre model, as we are all after slightly differing things out of our tyres.
As for higher pressures giving higher mileage? One manual I read said 36f/42r on the 750, another said 37/37. I arrived at 34f and 37r as feeling 'right' on PR2s and got over 17,000kms. Oh, and I don't change that with a pillion either.

HenryDorsetCase

21st October 2010, 08:53

My practice is to use one gauge and one only. It doesn't really matter if it is not 100% accurate if you use it to set suitable pressures and stick to them...

There's a lot of discussion out there re pressures. Maybe I just need to experiment over a longish period of time and develop a set of pressures that feel right to me...

good point that.

MSTRS

21st October 2010, 08:59

good point that.

Yep. But also, be sure that the gauge you do use returns the same reading every time. Not all do, especially those cheap little pop-up pencil types.

MikeL

21st October 2010, 09:44

For both my bikes I find the manufacturer's recommendations too low. The Honda specifies 33 and the Yamaha 36 F and R, but especially with the XJR I find 39 R is much better (I stick to 36 in the front). At 36 R the XJR wallows a bit but at 39 it's much tighter on the corners.
As for tyre pressure gauge accuracy, the worst example I came across was a gauge built into a foot pump, which showed 20 psi difference (higher) than a separate gauge (the latter was reasonably consistent with service station pressures).

HenryDorsetCase

21st October 2010, 09:54

Yep. But also, be sure that the gauge you do use returns the same reading every time. Not all do, especially those cheap little pop-up pencil types.

I have two of these: I had to buy the second one (with the flexi hose) when I couldnt get the straight one (at the top) to work easily on bikes with 17 inch front wheels and twin discs.

http://www.ghmeiser.com/dial.htm

they're called "Accu-gage" so they must be accurate, right?

I havent checked one against the other, must do that.

http://www.ghmeiser.com/dial.htm

160XGA and a H60X

White trash

21st October 2010, 10:37

19 cold in the rear, 28 in the front. Works fricken awesome. You can easily get 40 laps with those pressures before the grip level drops.

slofox

21st October 2010, 11:18

I use a digital gauge - it seems to be fairly consistent within itself.

slofox

21st October 2010, 11:25

...any general "recommend" tyre pressure will be a compromise between several factors.
.

Which is exactly what I meant in the OP when I said:

"My own thoughts are that it must be nigh on impossible to cover the wide range of loadings any given bike may have and come up with a "correct" pressure..."

Mishy

21st October 2010, 21:01

Where do you find these recommendations please Mishy? I have looked all over and found none so far...

I have all the tech guff, but I think that you can find the info you want at
conti-online.

Mishy

21st October 2010, 21:04

19 cold in the rear, 28 in the front. Works fricken awesome. You can easily get 40 laps with those pressures before the grip level drops.

You did 40 laps without skidding on your bum ? :)

slofox

22nd October 2010, 05:16

I have all the tech guff, but I think that you can find the info you want at
conti-online.

OK. Thanks. But I'm using Bridgestones...

White trash

22nd October 2010, 07:40

You did 40 laps without skidding on your bum ? :)

Not consecutively :D

Mishy

22nd October 2010, 11:27

Not consecutively :D

Ha ha ! well put :)

aprilia_RS250

22nd October 2010, 11:48

32psi on my M3s. Excellent tyres. they're sticky like a blind lesbian at a fish mongers. Still have the curve like they did when I bought them.

ellipsis

22nd October 2010, 12:13

....I run a fairly soft compound tyre on the front and a couple of pounds less than most people think is right for the front end...back end I try and keep as close to manufacturers recommendations as possible...mainly because the back end doesn't worry me a lot.....I have been getting stick from a mate who rides a similar bike, about my under pressure front end and my like of the front brakes as they are ...a little to soft for his liking...not mine.....anyway he's the one laid up for a while with pins in his leg....front end gave out under a bit of braking and loss of traction to a hard front end....downside for me is less miles from the front tyre...but I like it that way ...and I (touch wood) usually get home...

slofox

25th October 2010, 12:04

After trawling through all these most interesting posts, I decided to fart around with the pressures a little...

Raised rear from 35 to 38
Raised front from 32 to 34

Impressions? More regular turn in - easier transition from one side to t'other. Grip at least as good as usual - not that I test the boundaries you unnerstand...So I feel reasonably happy that with my own gauge, I need to go up a couple of psi both front and back. I'll sneak 'em up a couple more soon and see what happens.

EDIT: I'd hafta say that the first ride on higher pressures was pretty damn good too...:devil2: But then, that could be because I was too tired to care what happened...