A question on tyre pressures

[ARCHIVE_Joker]

Contact info?

Anyone got the contact info for Fuelr that the could PM me. Id like to get intouch with him.
Josh

 

[ARCHIVE_kawasaki-krazy]

Josh

I presume you've tried the members list?

KK

 

[Stormy]

Hey guys,

I'm after what tyre pressures I should run in my tyres.

I've quizzed the local motorcycle shops, etc about it and I've hit a bit of a conundrum (that's a big word for this time of the day!!!). I feel, what I've been told, is a bit of rear tyre, sidewall flex, it's very apparent when I hook into any left or right corner, it feels like the rear wheel is in a slight power drift (...but it's not) and it's a bit unnerving sometimes, I've even given the bike to one of the guys to ride to see if I'm imagining it, and he can actually feel it too.

I've asked the local motorbike shops for their recommendations for tyre pressures and the answers vary greatly.

Some say, 36psi front / 38psi rear, other's say, 38psi front / 40psi rear, some other's say 38psi front / 42psi rear.

The Good Book recommends for the OEM tyres;

Front : Dunlop Tubeless F17, 100/90-56H @ 33psi
Rear : Dunlop Tubeless K425, 160/80-15 74H @ 40psi

I'm currently running;

Front : Michelin Commander, 100/90-18 56H @ 38psi
Rear : Michelin Commander, 150/90-15 74H @ 40psi

The max. recommended pressure written on the sidewall of both new tyres is 41 psi.

In the latest issue of "Motorcycle Cruiser" magazine, in the letters section, a person wrote in with a similar question and the guy replied that if you subtract 3psi from the maximum rated pressure (in my case 41psi), you'd be close to the tyre manufacturers recommended normal riding pressure, so using that information, my tyre pressures should be 38psi all round.

I've found even though the front and rear tyres responds well enough on the bitumen, it's like skating on ice on gravel roads (I travel about 3 kms of gravel / dirt from the bitumen to home) and I thought it would have something to do with the tyre pressures, personally, I think 38psi front / 40psi rear is a little on the hard side, but I'll get better tyre tread wear.

I'd really like your opinion on this and what pressures you put in your bikes and how your bike responds to your pressures.

Mick.

 

[furchin]

tire pressure

Stormy, Not going to say much here other than I always run the tire pressure that is listed on the sidewall of the tire. This info is provided by the manufacuturer for a reason I believe. And one last thing I don't know that street tires were intended to perform well in the stones. I know I don't like riding is stones at all. :nonono:

 

[marki]

I know its a different bike but my 600 running Bridgestones is 36 front and 39 rear as recommended by the tyre maker. Much higher than the continentals I had on before which were 29 front and 33 rear.

 

[Blagadán]

I feel, what I've been told, is a bit of rear tyre, sidewall flex, it's very apparent when I hook into any left or right corner, it feels like the rear wheel is in a slight power drift (...but it's not) and it's a bit unnerving sometimes

Are your rear shocks ok stormy? If you have a 160 on the rear then the sidewall shouldn't flex much. I have been told by my bike shop guys over the years that you will start to get flex if you start goin oversize, makes sense really, if your squishin an oversize tyre onto a narrow rim, the bead is squished in and could allow for movement..
(I hope I dont offend you boys with the oversize rubber on the back here!!! )

Thats kinda why I didnt go ovesize with my last rear tyre, I HATE having insecurity when I'm cornering.

I run with 36psi in both tyres and have a 160 on the back. I can lean right over to the edge of the tyre going into corners with no twitching. I know if you push the ZL really hard, you will get some "interesting" handling, I dont think they were designed for hard cornering but general enthusiastic driving should feel solid.

It might be an idea to jack the rear wheel off the ground and give it some lateral movement to see if you have some bearings/bushings in trouble either in the wheel or the swingarm?? dont know, just throwing in a few ideas...?

blag

 

[Stormy]

yeah, blag, I've got a 150 section tyre on the back, not a 160.

The rear shocks are fine, actually I've just replaced and re-filled the oil in the rear shocks to spec and I usually check the air dampening pressure before I go on a ride (10psi) and checked the swing-arm bushes for lateral movement or play, and they checked out fine, no lateral movement or play anywhere within the arc of travel and both the rear wheel bearings were replaced about three or so weeks ago.

I think I've worked it out, I was having a close inspection of the rear tyre and I reckon the cross section profile/curve of the tyre is slightly parabolic? rather than completely spherical, in other words, the centre of the tyre is slightly higher, if you looked at the curvature of the tyre in a cross-section, whereas the front tyre has a more evenly rounded (spherical) curve.

The old tyre I had on before this tyre, never did this, as it was a typical near worn out, rear tyre, virtually no tread in the middle and pretty good tread depth on the edges, and slightly elliptical in shape, so maybe it's just the shape of the new tyre.

If my assumptions are correct, time will tell, as the feeling will eventually disappear as the centre tread of the tyre wears down.

Sometimes I'm too analytical for my own good.

Mick.

 

[marki]

A few times when I've changed tyres I felt there was something wrong. The bike feels twitchy in corners, almost like its going to fall over? It felt like it was dropping too fast when I leaned over.

The other thing I noticed was that it would track the white lines in the middle of the road, you know, if I rode over a line in the road the bike would almost steer itself to follow the line rather than pass over it?

Its always been down to the shape of the new tyre and how worn out the one it replaced was.

 

[Stormy]

A few times when I've changed tyres I felt there was something wrong. The bike feels twitchy in corners, almost like its going to fall over? It felt like it was dropping too fast when I leaned over.

The other thing I noticed was that it would track the white lines in the middle of the road, you know, if I rode over a line in the road the bike would almost steer itself to follow the line rather than pass over it?

Its always been down to the shape of the new tyre and how worn out the one it replaced was.

...yep, got it in one, marki, I'm glad I'm not the only one it's happened to.

...so, I should just forget about it and enjoy the ride, I'll get used to it eventually, eh?

That's pretty much what I thought, there's nothing wrong, I'm just not use to the way the new tyres handle, no worries.

thanks.

Mick.

 

[Jarney]

Try this again - didn't post the first time - damn dial up......
Had a look at my tires this weekend:
2nd set of Bridgestones I've had:

Rear:
Bridgestone Exedra G702 170/80/15
Rated 36psi - running 30-32psi

Front:
Bridgestone Spitfire 11F 100/90/18
Rated 41psi - running 35psi

This is the second front that has shown "spiderweb" cracks on the sidewall after very little mileage. I don't use the "tire shine" chemicals. The rear looks fine. The bridgestones wear good on tread. The rear looks really good - nice looking tread pattern and it looks big and fat in the rear of the bike. I just don't care for the front. Later.

 

[marki]

Same rear as me except I run mine at 39 psi since Bridgestone told me to?

Same problem with the cracking though. The tyre wears really well and seems to grip fine but its now starting to crack / split in between the tread pattern.

 

[Stormy]

...a couple of the guys in the Ulysses Club during the AGM had problems with their Bridgestones delaminating, so maybe the cracks are the beginning of the end for those tyres.

Bridgestone are aware that there is a problem with the rubber compound during the curing process, the tread will eventually peel off (delaminate) like a truck re-cap/tread and if anyone has been behind a truck when a tyre goes, it's not fun, it's even worse when you're on two wheels not 18.

I'd get them checked out and replaced a.s.a.p!!!

Mick.

 

[zlMark]

my metzelers are doing that. hard to see it's just starting

 

[elimafreak]

Oh great, I just got a set of metzs. When did yours start showing cracks Mark?

 

[zlMark]

I just noticed on the front tire, none on back. Age of tire is unknown i have put 6000 mi on them since 05'

 

[Rocket]

Stormy, just a point on higher tyre pressures... on a car this will generally give you a longer life but on a bike it will shorten it particularly on the rear. What it does is it reduces the size of the contact patch (footprint) this in turn increases the load on that patch because all the acceleration/braking forces must now be taken up by a smaller area of the tyre. Sure, rolling resistance is greatly reduced but you'll find the tyre's centre will wear much faster. Of course lower pressures generate more heat.

When my G702 was at about %50 on the centre and %100 on the sides, I took a ride up the Putty Road and in that one 4hr stint I got the tread sides down to %30. That made me feel better about tossing the tyre out when I could see canvas on the centreline. It handled just great at 36PSI, pegs got a bit worn though. This is not my ride but it's my road, I know it like the back of my hand:

http://youtube.com/watch?v=BOipfwAi_c0&mode=related&search=
http://youtube.com/watch?v=cVDWp0boADw
http://www.star-riders.org/starcruiser/volume1-3/OldPuttyRd.jpg
http://w2.bikepics.com/pics/2006\12\18\bikepics-750217-full.jpg

Oh, and there's more than the 16km of that stuff the pic shows, the whole length of the Putty Road takes about 2hrs (if you stick to the speed limit) and the S's are at both ends and parts in the middle.

For the record I've have run these:

Rear:
Dunlop D404 160/80-15 (41PSI as recommended by the KHI dealers)
Bridgestone Exedra G702 160/80/15 (36PSI as recommended by the Honda shop where I bought the tyre)
Maxxis M6011 160/80-15 (36PSI as recommended by me)

Front:
Dunlop GT501 Arrowmax 100/90/18 56H (31PSI as recommended by the KHI dealers)
Shinko 100/90H18 56H (31PSI as recommended by the Honda shop where I bought the tyre)

Mick, I've been to your place mate, try and resist the urge to twist that grip on the dirt. I was in the Futura and it felt a bit skittish on the dirt too, but it was fun

 

[Stormy]

...hey Rocket, I loved the Old Putty Road, and always will, it's got to be one of the best bike roads in NSW (the Royal National Park down to Wollongong via Stanwell Tops use to great too...)

When I lived in Penrith, I used to do the Putty Road run and Wisemans Ferry/ St Albans or Wisemans Ferry/Spencer/ Gosford run most sundays with the MRA on the old 1980 Yamaha XV750 "Midnight Special".

I used to do the whole length of the Putty from Kurragong to Singleton every now and again, with a stop off at the halfway at Colo Heights servo, it was fairly ordinary before they did it up, now it would be unreal,.

...is it still the motorbike riding mecca on Sundays?

I know what you are saying about the tyre pressures too, the dirt road had just exagerated what was happening on the bitumen.

I've dropped the pressures down to 38psi all round and we'll see how it feels when I next go for a ride into town.

I was chatting with one of the guys in the bike shop (Spanner at Wright's) and he reckoned it's a matter of trial and error, put what you like in, and see how it feels, if it feels too hard or soft, put a little bit in or let a little bit out. The 40psi in the rear, felt too hard to me, but 38psi in the front felt good, so if I've got 38psi all round, it shouldn't be too bad.

...we'll see what happens.

 

[Rocket]

Unfortunately I usually do the trip to my parents in Bingara (6.5hrs each way) up early Friday afternoons after work (12:00 knock off). The trip back is usually dark on Sunday nights with 300 Watts scanning for Spring Loaded Bush Rats.

I don’t see bikes goin’ my way (either they can’t catch up or I can’t) but the ones I see goin’ the udder way are havin’ a ball.

 

[SnakeDoctor]

Rocket, damn sure don't want to hit any of those while on the bike, hell, they'll total a car out.