R100S tire pressures

[montmil]

I'm trying to determine working tire pressures for the Metzeler Lasertec tires on my R100S. The OEM handbook and shop manuals provide pressures for older style tire construction; even going so far as to recommend a higher air pressure in the front tire.

The bike is a naked 1978 R100S rolling on 110/90-front and 120/90-rear.

I've been to the Metzeler site but, with our litigious society here in the US, there's no help from the manufacturers. "Follow your handbook recommendations." D'oh.

Right now, I'm running 32/34 psi, front/rear. Am I close or what? Any recommendations from R100 owners would be appreciated.

 :-/

[Red_Hen]

32 sounds good for front
38 good for rear

I was running 38 up front on my K75 & ride was real stiff & bouncy.  32 made bike ride a lot nicer.

[tvrla]

I think you're pretty close.

Factors that come into play are temp, speed, your weight and style of riding.

I'd heard the way to check is to shoot for a 10% rise over cold pressure. I think I read somewhere that the rear should increase by 15% or some such. For long high speed runs in the summer it's a good idea to run pressures up higher.

[Barry]

Monte

This is from Metzlers UK site. They only give pressures for the sizes they recommend so it's no use filtering by tire size. I know yours is an S but they recommend the same tires and pressures for all airheads including mine. Most will probably say they are too low but I use them or at least treat them as a minimum by inflating a touch higher at 2.2 and 2.4  to allow for the slow leakage before the next pressure check.

Using the cold/hot pressure rise check and starting at 2.1 and 2.3 I got 9.5% and 17.4% increase which was close enough for what I understood should be 10/20. Certainly didn't indicate I should be increasing the pressures.

Maybe you would get better handling with higher pressures but ultimately it's the tire temperature that counts which is how the F1 boys do it. If pressures are too high they won't warm up enough but other than saying they should be distinctly warm to the touch I don't know what that temperature should be. I think if you analyse to death what the optimum tire pressure should be, you conclude there is no one set pressure that suits all circumstances.

[Crossrodes]

I always use the pressure that is stamped on the side of the tires for my Goldwing and my R65.  Years ago I used the pressure recommended by the manufacturer of the bike (which was lower) and found that the tires would start to cup.  Since I have been using the pressure stmped on the tires I have experienced no cupping.

[Bob_Roller]

Try different tire pressures and differential pressures between front and rear to see if it makes things better or worse from your viewpoint .

I've gone as high as 40 psi (2.7 bar) front and rear on the R65, the handling 'feels' quicker, it's probably due to less tire in contact with the road surface .

[montmil]

As is often the case in Boxerworks Land, my concern generated some healthy discussions. This is a good thing as it keeps one's mind working in considering opposing viewpoints. There are some very bright people in our Airhead communities. Respect 'em all.

For your enlightenment, edification and enjoyment, I have -so far- received six solid recommendations -all very close in each individual's preferred tire pressures.

By averaging the six responses, the recommendations are: 33 psi front & 36.5 psi rear.

However, four of the six front tires run 32 psi. The rear pressures run from 34>40 psi with some higher pressures dictated by the riders personal weight.

I plan to initially use 32F/36R and see what the bike's handling performance feels like. I may also reduce the pressure in the R65s rear tires.

Again, thanks to all for your assistance.

[Barry]

healthy was a polite way of putting it.

That was quite a pointed exchange about the side wall pressure. It's a safety critical issue so I suppose it's going to generate strong views.

My 2 cents is that when the manufacturer puts a pressure on the sidewall they are most definitely not advising everyone to run at that pressure. They are just saying it is safe to that pressure at the rated load specified.  


Airhead tire load ratings codes will be typically 51-57 for the front tire and 64 for the rear. That means the front tire can support 430 - 507lbs and the rear 617lbs. Except for fully loaded touring most riders will not subject their tires to any where near these loads so common sense suggests running proportionally lower pressures. And that's just what the manufacturers advise at least where the lawyers allow them to.

As an aside the combined front and rear tire load ratings usually exceed the permitted maximum gross vehicle weight (877lbs for airheads) by some margin so there should no circumstances when the side wall pressures are needed.

[tvrla]

As always - Barry comes up with some very good points.

As for the pressure on the sidewall - isn't that the max allowable?

I've run the max on long hot high-speed stretches. I also pumped the pressure up last time I needed to get 600 more miles out of a tire worn past the wear bars.

But as already mentioned, the max pressure makes for a stiff ride besides insufficiently heating the tire, resulting in less traction - not to mention, a reduced contact patch. But higher pressures (along with minimal right wrist action) will net better fuel consumption.

As with anything, there's a positive and negative and quite often we're not given the complete data to decide for ourselves the best action for the current conditions.

Too little pressure causes over heating, softer ride, but less cushion making it easier to bend a rim.

Perhaps there may be a time you'll want to lower the pressure to gain one of the positive effects by doing so. On the R80G/S on really rough roads I'll lower the pressure to 20 lbs for better traction, control and ride. But once back on pavement, the pressures goes back up to 30 something.

Or you may bump pressure up to the max and slow way down to ensure making it to the next gas station.

I always use the pressure that is stamped on the side of the tires for my Goldwing and my R65.  Years ago I used the pressure recommended by the manufacturer of the bike (which was lower) and found that the tires would start to cup.  Since I have been using the pressure stmped on the tires I have experienced no cupping.

[Red_Hen]

I was clueless until taking my bike to the track & instructor told us to reduce TP - it was at that moment I felt how much better the K75 felt & handled - I'd be running 38 up front which was really too high. It is a feeling kinda thing.

Maybe I should start a thread on the best oil to use  

[bruce_launceston]

Crossrodes, the  maximum pressure on the sidewall is for the maximum load. In theory you need to weigh the load on each tyre and divide the maximum weight by the actual weight and then divide the maximum pressure by the same percentage.

IMHO just go with the BMW recommended pressure and add 4 or 5 psi for the modern tyre construction.
Running them too low may make for a soft, confortable ride but it will squirm through corners, get hotter and wear faster.

For what its worth I run 33/34 in the front and 38/40 in the rear on my R65, it's ridden hard and mostly 2-up so I keep the rear tyre pressure set at the higher range even when commuting solo.
It handles better and the tyre wear should be better with the higher pressures.

[Barry]

....until taking my bike to the track & instructor told us to reduce TP  

That's normal practice even when starting from correct road pressures. Track pressures are usually lower than road pressures as the tires will be worked harder on the track and the pressures will rise more than they would with road use so you have to start off a bit lower to end up with the same hot running pressures.  It doesn't mean you should run track pressures on the road.


On a related issue many riders report better mileage with higher pressures.  Why should that be? You would think the reduced contact patch would wear faster. Perhaps that is more than compensated for by the tire running cooler and is that a good thing from a grip point of view.  

It all goes to show that which ever way you come at this topic it always comes back to tire temperature. If the tires don't come up to the right running temperature (whatever that is) then the cold pressures are too high.

[Red_Hen]

Barry's correct.

Track instructor said to lower TP but after track day, I pumped tires back up when I got home - it was on the ride home that I noticed how much smoother the front end felt and handled w/less TP.  I didn't mean to suggest to ride all the time with lower TP when riding on a track.  The reason, like Barry says, for lowering TP is all the cornering heats up the tires.