Front tire pressure

[Mr. Rick]

I'm running that Avon AM 20 Roadrunner 90/90 on the stock WM 2 rim.
Yesterday I pulled out for a test drive around the block without checking the tire pressure and noticed a dramatic increase in front brake stopping power.
Back home, found the pressure was down near 20 lbs, far from the recommended 29 and my usual of 26.
Obviously, the increased size of the contact patch is very helpful.

So the question is: How far down can I go without blowing the handling or violating some safety margin?

 

[MexicoMike]

Optimum handling TP is totally dependent on your riding style. For example, on my BMW R1200RS, the best pressure for ME and my riding style is 6 PSI below what the manual says. The bike handles best at those pressures for me which is approx 33/35PSI. On my Norton Commando, Avon 4.10/19s, the factory specs seem to work best for me. SO...unfortunately, the only way you can determine the best TP for what you do is adjust and ride and do so until you figure it out.

HOWEVER, 20 PSI is awfully low and, IMO too low for safe operation for several reasons: you could hit a pothole or something similar and blow out the tire/bend the rim due because of the insufficient pressure. Emergency braking could cause the tire to rotate on the rim, tearing the valve from the tube and causing a blowout. Also, at those pressures, under hard cornering there will be so much tire squirm that a tire could actually roll off the rim.

 

[Stephen Hill]

Unless you were locking up your front wheel with the front tire at 26 pounds, I don't see how decreasing the tire pressure to 20 pounds is going to improve your braking. You will have increased the contact area on the road, but in terms of braking, it normally wouldn't make any difference. At pressures around 20 pounds and less, you are going to notice a decrease in how the bike handles in the corners.

Stephen Hill

 

[comnoz]

That sounds a little unusual.
With my twin disks I could raise the rear tire off the ground with a 90-90 AM20 with 34psi.
I would never run under 30 psi cause the tire wears out too fast. I suspect I have more weight on my front than normal though.

 

[Hobot]

hobot by accident or on purposed explored this to say that even stunt stoppie guys lower front pressure below what is safe for public road speed handling. 'Best' tire pressure is compromise of how rough surface is and how secure stable tires are high-ish speed, power loaded or unloaded nil throttle turns.

'Best' is when forks seem the least effort to work, which in my case every bike, Honda 250 scooter, SV650 120/180 non DOT race tires and Trixie with old vintage 110/110 tires, Peel with 110/120 new dual sport tires, always came out 2 lb less in front, regardless of base line PSI. Trial error d/t pilot mass cargo and sense of security and tire compound on width of rims fitted will guide ya to your own conclusions. BY FAR the best handling I've experienced was 60 PSI rear/58 front for ice skater like traction/handling on Ms Peel but not practical d/t harshness on common rough American roads, nor tolerated by over rigid moderns or too flexy Commandos. Most hard to follow cycle I've followed, short of life death squid spanking in same twisites was an 850 with big guy and camp cargo, just laying over some rolling on right theFk out of there with me seeing his rear visibly smashing down some on the apexes. I asked him what pressure, told 28 rr/26 fr, d/t better feel thru tights, exactly same as I came to use on all my above examples. Let us know what you like best.

 

[Mr. Rick]

Thanks for the quick replies, you guys.
Just to be clear, I was not out there on the open highway, or even out there at all with 20 lbs on purpose. Both tires lose pressure as they sit.

And I don't think I can lock it up at 26, not sure I wanna try, either...

I'm gonna run 24-25 for a while, see how it goes until I get the sleeved MC fitted, then test some more.

 

[Hobot]

The risk of too low air while just easy going is sudden need to dodge or brake so tires distort enough to flip ya down. Its great for rough off road play. Learning sense of low air is vital for two reasons, one a slow leak will not surprise you by sudden stem pull out/blow out and two, handling distorting tires is exactly same skill as elite racers use to fight bike stable in dangerous maxed out turns or sudden dodging of downed pilots. Can develop stunt to racer skill set in short time by 1st lowering front till too obnoxious hard to control, then air front and lower rear till calling uncle enough. Then lower both tires till enough. Worse is right before about to put foot down, can give sudden whiplash head to tail plop down.

Do Note, tire wear affects Commando Significantly more than any other type cycle so until fitting new tires one can not really assess isolastics set up or best tire pressure and balance, just compromising till renewing to baseline.

 

[baz]

A lot of the original tyre pressures quoted in manuals are a bit out of date now I run my tyres at 34 psi on the back and 32 on the front these are roadriders.
Never really thought about the bike braking better with lower pressure in the front tyre I suppose you could experiment with lower pressure and see how it affects the bikes handling

 

[Hobot]

Front tire patch mash down distinctly tolerates more brake before lock up let go and less fork chattering tire skipping so another compromise of braking vs handling ease. Stunt stoppie guys'gals run pretty low front air for better braking w/o lock up security. Also helps noise dive down to get rear air born. Stoppies are not the fast way to stop until only a few mph speed.

 

[Danno]

I know a lot of people that are continually fiddling with their tire pressures, depending upon the type and place of the riding.

For what it's worth, a Bridgestone MotoGP tire tech told me you should never run less than 4psi under the recommended cold max on the street, not because the tire wouldn't perform, but due to the possiblity of damaging the tire on ordinary road hazards, potholes etc. All my bike and cage tires are set at max cold recommended.

 

[ashman]

The orginal K81s were recommended to run 30psi on the rear and 28psi in the front but todays moden tyres run a higher pressure I run my RR tyres at 35psi on the rear and 32psi in the front and it seems to be the best handling pressure for my Norton, I check my tyres when they are cold and use the same gauge, don't trust garge gauges as they get knocked about all the time from abuse, when the tyres are hot they will be about 3psi higher than cold .

Ashley

 

[comnoz]

Thanks for the quick replies, you guys.
Just to be clear, I was not out there on the open highway, or even out there at all with 20 lbs on purpose. Both tires lose pressure as they sit.

And I don't think I can lock it up at 26, not sure I wanna try, either...

I'm gonna run 24-25 for a while, see how it goes until I get the sleeved MC fitted, then test some more.

I do not think you will get any decent handling from an AM20 until you get over 30 PSI. Newer tires need a lot more pressure than the old ones. I would suggest 32 to 35 on the front of a stock Commando. Jim

 

[Mr. Rick]

There was a memorial service here in Sacramento today for Hubert Kriegel of Timeless Ride fame. He had lived here with his wife Lorraine for the past year, after being on the road for ten years, going everywhere in the world. He was in the process of fixing up a van, to take Lorraine out on the U.S. roads, when his heart gave out unexpectedly on the 24th last month. She and his daughter Jessica hosted a reception at the beautiful House Kitchen and Bar on the Capitol Mall. There were probably close to 100 people there from all over the place. RIP Hubert.

So some of the Motomeeto guys met on Freeport and rode together in beautiful weather downtown to the reception, and on the long way home I did notice (in the turns) the mushy feeling one wd expect from lower (25) pressure. Although not very confidence inspiring, it wasn't horrible either. Of course this was all in the city, so I never got over 60. The braking payoff is definitely there, but as soon as the stock brake MC is modified, I plan to get the tire back up near 29, and maybe more if the braking pans out.
Thanks again for all the feedback!

 

[Hobot]

There is distinct conflict of whats best for tire vs pilot ease/security. I agree with highest pressure one can stand the shocks of road surface texture as give ice skater like accuracy sense but will jar harshly if on lumpy/broken surfaces and will dump you too fast to know what happened on much braking or slightly poorer traction encounter like dust/grit/moisture/grass/bugs/blood/spills/frost/mud, so over mid 30's PSI is counter productive unless in ideal turn pike motorway hwys.

Peel tale to skip past
At times mud so deep long to get to pavement had to lower to 18 rr/12 front or tires sunk in too much for each to act like rudders pointed in wrong directions for instant crisis to stay upright. Ms Peel was fully tri-linked tested to direct steer handling, to finally encounter her last pecking order test case, Ducati 900's turning off main Federal hwy onto my commute to work Hwy 21. I happened to turn in ahead of them so waited till they got up to illegal thrill speed, to keep upping Peels annoying them till only one emerged from the pack willing/able to hang with Peel, at which point I let her hair out in fairly mild river valley curves, the Duc could not match Peel though 45ish lean sweeper turns, so in 1/2 mile open I slowed behind a car 50's mph to let em see what I was on, they pulled up even for an instant, I felt / saw pilot jerk shock, so next instant they essentially wheelied away, so I tried to snick down to 2nd but ended in 3rd, Peel worse ratio to accelerate, hearing strange sounds but still quick enough to run right back on their tail before apporaching 35 mph turn then had my own surprise forgetting about the low tire pressure, thank goodness for the tri-links, even half crippled Peel could hang with the Duc pilot laying over on throttle knee down like a seasoned racer, cool. Got to my village square to see long hair of girl on the Monster, asked if had track time, she said yes, but visibly miffed on such nil advantage against such obsolete POS. I aired up tires and we took off again with Peel leading through the better twisties but got out hp'd topping 100 in an open but caught back up in next set of more dangerous twisties but then had trouble shifting till got stuck in 4th, crap, so pulled over and flagged one of the laggard pilots to say tranny trouble so gal would know why the road dance ended. At home found a lot of teeth missing on both 3rd cogs.

 

[The Buckeye Rider]

There is distinct conflict of whats best for tire vs pilot ease/security. I agree with highest pressure one can stand the shocks of road surface texture as give ice skater like accuracy sense but will jar harshly if on lumpy/broken surfaces and will dump you too fast to know what happened on much braking or slightly poorer traction encounter like dust/grit/moisture/grass/bugs/blood/spills/frost/mud, so over mid 30's PSI is counter productive unless in ideal turn pike motorway hwys.

Peel tale to skip past
At times mud so deep long to get to pavement had to lower to 18 rr/12 front or tires sunk in too much for each to act like rudders pointed in wrong directions for instant crisis to stay upright. Ms Peel was fully tri-linked tested to direct steer handling, to finally encounter her last pecking order test case, Ducati 900's turning off main Federal hwy onto my commute to work Hwy 21. I happened to turn in ahead of them so waited till they got up to illegal thrill speed, to keep upping Peels annoying them till only one emerged from the pack willing/able to hang with Peel, at which point I let her hair out in fairly mild river valley curves, the Duc could not match Peel though 45ish lean sweeper turns, so in 1/2 mile open I slowed behind a car 50's mph to let em see what I was on, they pulled up even for an instant, I felt / saw pilot jerk shock, so next instant they essentially wheelied away, so I tried to snick down to 2nd but ended in 3rd, Peel worse ratio to accelerate, hearing strange sounds but still quick enough to run right back on their tail before apporaching 35 mph turn then had my own surprise forgetting about the low tire pressure, thank goodness for the tri-links, even half crippled Peel could hang with the Duc pilot laying over on throttle knee down like a seasoned racer, cool. Got to my village square to see long hair of girl on the Monster, asked if had track time, she said yes, but visibly miffed on such nil advantage against such obsolete POS. I aired up tires and we took off again with Peel leading through the better twisties but got out hp'd topping 100 in an open but caught back up in next set of more dangerous twisties but then had trouble shifting till got stuck in 4th, crap, so pulled over and flagged one of the laggard pilots to say tranny trouble so gal would know why the road dance ended. At home found a lot of teeth missing on both 3rd cogs.

Write On Hobot, Write On
Dave

 

[xbacksideslider]

I run tire pressure according to the roads of the day's ride. Slow roads, lower pressures. Fast roads, higher pressures.
As Hobot says, the quality of the road matters too. Lots of cracks, ridges, sharp bumps - lower. Smooth as glass - higher.
Lower pressures really do help the suspension, especially when compression damping is too strong.
Generally, canyons lower, highways higher.

Too low pressures overheat the entire tire because the carcass is flexed more, the tread squirms and overheats too.
Too high pressures overheat the tread layer because only that part is flexed and the tire wears more in the center.
Both conditions result in excess wear.

Riding the canyons of Southern California, I care more about the tire's road holding than its rate of wear.
Low pressures present a larger contact patch to the road and help the suspension deal with road irregularities.
Average canyon riding speeds might be 30 - 50 mph, depending on the road.
Yes, on straights, I will go faster than that but throw in those slow corners . . . . and you get a low average, and most of the time - in the corners - the speeds are lower.

The only downside, for me, with lower pressures is high speed instability.
So, I set pressures high enough to prevent that, but that means that I run lower pressures.
I trade an occasional and slight high speed weave for great traction.


I've settled on these tires/pressures for the slower canyons near my home:
Avon 100/90V19 Super Venom AM18A - Front
A53 Soft Compound - 28-30 psi cold, 31 - 33 hot
Avon 120/80-18 Super Venom AM18 - Rear
A31 Hard compound - 25-27 psi cold, 28-30 hot

For the smooth and much faster, occasional triple digit, national forest roads, I'll add three psi to both front and rear.

Rear tire mileage is poor . . . . but worth it.

 

[Hobot]

Hot Dam backslider you're encouraging juvenile delinquent behavior risking Commando isolastic hinge onset I have no counterpoints against but accepting could die over doing multiple road orgasms. SERIOUSLY if not working up to actually on purpose slipping out on rear or front traction to know survival limits/hinging horrors then always facing holding back for unknowns with wise fear or daring to fling past that to see what ya can get away with to respectfully brag about surviving fine later.

MOTHER LOVING FATHER KILLING OEDIPUS COMPLEX CIMAXING life/death kix on un-tamed-tri-linked Commando hinging horrors, exbackslider ability to nail down heating loading of skinny Commando tires to racer temps demos mastery to jaw dropping remarkable honorable mention to disregard in confidence risks of family morning ya demise out the blue on mere joy ride because ya ain't really tested what it takes to max out routinely on iso Commando and brag about it later. i've seen expbackslder mistakes going wide across lane, just like me, but smart enough in rural hwy to be reasonable risk enjoying limit thrills with devil may care intelligence.

Tri-linked Peel or Mcrae's tri-swash plate tamed isolastic flying carpets is beyond comprehension to discuss on ordinary Commando, Seleely, Irish ITT, supermotard trials racer cripples but my Trixie Combat is bone stock expect for rear sets fouling limits and brake cable safety spring. I've worked up tire heat and nerve on 110 fr/rr in good banked places to over power in leans to skip rear out a tire width w/o hinging, AS LONG as could keep power on to keep suspension/frame in tension but required some fighting control back on let off relaxation slack but expected so no problemo. My best PSI base line on 500 lb pilot ful0l IS gas tank ordinary dangerous Commado was 30 rear 28 front. Best on Ms Peel 60 rr/57 front to give a sense of what even racers missing out on as too ridig crippled or flexy to tolerate approaching.

 

[xbacksideslider]

Thanks Steve.

Back when we raced in Griffith Park (where speeds were low, the pavement was slurry seal, and the ripply/cracked surface was often complicated by patches of sand and pine needles) the best tires were K81s. I ran a 3.60-19 K81 up front and a 4.10-19 K81 out back. After regular schooling by an old timer - Mr. Bob West - one day he took pity on me and told me his secret - low pressures. After that, I was proud that I could hold him off. He'd still "show a wheel" on me though. Settled on 17psi rear and 19psi front.

We didn't know about the swing arm and heim joint iso fixes, just torqued em down, rode the difference, and suffered the vibes. Slow speeds helped. Late in the game, I bought a Fontana 4 shoe brake; that thing liked low psi. Wish I still had it. lol

 

[Hobot]

Gosh dang exasssendslider I want what you felt back then but can't conceive doing it on hard surface with such low pressure, hot damn I got a lot to catch up on. I have hung with track trained Ducadi Monster pilot on 18 r/12 front - to cross half foot mud underground springs turned to quick sand to enocounter the Monster squadron on way to work, but worked/worried the shit out of me trying to control the tire squirming. Still can't ignore your report which has front 2 PSI higher than rear which I found on slow leaks ain't pleasant but never tired in anger so will have to experiment and see.

D/t THE Gravel travel I don't view front as main steering mostly hindering and dangerous to use to turn so depend on front giving way to rear authority so not to interfere with rear steering which takes front extending/lightening power to do - but only so much that lets off ain't so fast fork suddendly acts like a rudder in conflict with rear. Will have to re-think/try you oppositic success - which scares me to contemplate.

We know good/bad tires matter a LOT as does pressure so I plan to experiment/adapt pretty easy anywhere d/t Peel air supply station.

I work up to either rear or front or both sliding groin spiking lets goes to know limits to avoid, which is scary to me as I need to know or not press handling surprises or expect to have reflexes for surprise hazards nothing to loose but life if not going bezerk on handling loads avoids/saves.

Realize when feeling frisky there are more tire sounds over engine sounds. We survived so far making memories so carry on w/o me if worse happens.

 

[concours]

Unless you were locking up your front wheel with the front tire at 26 pounds, I don't see how decreasing the tire pressure to 20 pounds is going to improve your braking. You will have increased the contact area on the road, but in terms of braking, it normally wouldn't make any difference. At pressures around 20 pounds and less, you are going to notice a decrease in how the bike handles in the corners.

Stephen Hill

This.