Higher Tire Pressure = More Suspension Compliance?

[Huladog_imp]

Just wanted to run this by you guys to see if I'm nuts or not.

When the CB1100 suspension starts to feel harsh and jarring (and I start thinking of fiddling with the preload or worse, spending $ for replacement shocks) I remember to check the tire pressure.

Find out they're both maybe 5-6 pounds low, so I pump them back up to 36 front/42 rear and then the stock suspension seems relatively plush, compliant and composed again.

Seems sort of counter-intuitive if you ask me.

Higher (proper) tire pressure seems to make the ride compliant as if the road shocks are now able to be absorbed by the suspension as designed. Low tire pressure and the ride seems harsh like the road shocks don't get transmitted to the suspension although you would think the softer sidewalls would absorb road shocks.

Am I nuts?

On my previous BMW R1200RT it was sensitive to tire pressure and turn-in/handling definitely improved running higher that spec'd pressures. Before that my Street Glide needed proper tire pressure just to turn-in at all.

Just wondering if anyone else noticed something similar?

Aloha,
Huladog

 

[the Ferret]

Hmmm I've always felt the ride kind of stiff even though I have mine set on full soft front and rear. I was wondering if dropping a few pounds in the rear tire, especially since I never carry a passenger, might soften the ride even more. Guess not .

 

[CIP57_imp]

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

 

[Pterodactyl_imp]

I guess it's very individual. Also riding style and road conditions affect how the suspension should be set. I have 2nd ring for the front, 4/5 for the rear (2nd hardest) and tyres at 36/42.

I think CIPs got it with:

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

It's funny I have always regarded the CB as a soft ride. Softer (preload) front assists turn in so I go that way. I keep the tyre pressures up as I often ride loaded and some of our country roads have pot holes that would swallow a Mack truck. I hope that this will limit sidewall damage.

Cheers

 

[mininsx_imp]

The recommended tire pressure for a given motorcycle is so that you get the proper "footprint" from the tire and has nothing to do with suspension compliance. Personally, I think my 2013 CB is on the soft side, suspension-wise; I adjusted the front pre-load one full turn harder.

 

[the Ferret]

Funny thing about tire pressures

My ST calls for 42 front and 42 rear (whether single or double up)

My 750 Nighthawk called for 36 front and 36 rear .... unless carrying a passenger then 36 front and 42 rear

My FZ-1 called for 36 front and 39 rear (whether single or double up)

My Majesty calls for 29 front 36 rear (whether single or double up)

My Triumph T 100 called for 33 front and either 38 or 41 rear depending on the source... owners manual or service manual (whether single or double up)

The CB calls for 36 front 42 rear (whether single or double up)

My trailer calls for maximum 50 pounds when loaded for 1360 pounds. If I have 50 pounds in the tire and only load 500 pounds on it, it will bounce like a ball on every bump. so if I am hauling just 1 motorcycle I only run 45# per tire.

Yes I have a chart on the wall so it's easy reference when checking tires lol

Tire pressures are however "recommended" and the pressure can be safely varied within a few pounds or manufacturers wouldn't stamp "maximum pressure" into the sidewall which some people take as the "only" pressure they can use.

Tire pressure gauges can also vary...I have 3, an analog, a digital and a pencil gauge, that between them measure over a 3 pound range..one will measure 35, one 36 and one 37 pounds on the same tire measuring with one after the other.

Maybe on my CB I will put 42# in the rear but measure it with the low gauge

 

[AzBob_imp]

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

Pre-load has no effect on compression damping (and therefore brake dive). If we had fully-adjustable forks up front, you'd want to up the compression damping to combat brake dive, but we don't, so all you're really doing is reducing your ride height and reducing your fork's range of travel. I'm not sure if we have progressive springs, but if we do, you may also be unnecessarily increasing the harshness of your ride by pushing the spring into the stiffer progressive rate sooner.

I run recommended tire pressures (36psi front), with front pre-load set for my weight (220+lbs w/gear, right at 2nd line) and experience very little brake dive.

 

[Pterodactyl_imp]

^^^^^. True, however I can't agree with

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

Pre-load has no effect on compression damping (and therefore brake dive). If we had fully-adjustable forks up front, you'd want to up the compression damping to combat brake dive, but we don't, so all you're really doing is reducing your ride height and reducing your fork's range of travel. I'm not sure if we have progressive springs, but if we do, you may also be unnecessarily increasing the harshness of your ride by pushing the spring into the stiffer progressive rate sooner.

I run recommended tire pressures (36psi front), with front pre-load set for my weight (220+lbs w/gear, right at 2nd line) and experience very little brake dive.

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player. Therefore Honda (and others) recommend higher preload settings for heavier loads. I found that the bike tended to "wallow", particularly leaned over and going over small road irregularities. A bit over active. Upping the rear preload one notch has made an improvement. There are so many variables to suspension set up. Most are not available on the CB. Not needed really as it's damn good as is. Thanks for that Honda.

Cheers

 

[CIP57_imp]

^^^^^. True, however I can't agree with

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

Pre-load has no effect on compression damping (and therefore brake dive). If we had fully-adjustable forks up front, you'd want to up the compression damping to combat brake dive, but we don't, so all you're really doing is reducing your ride height and reducing your fork's range of travel. I'm not sure if we have progressive springs, but if we do, you may also be unnecessarily increasing the harshness of your ride by pushing the spring into the stiffer progressive rate sooner.

I run recommended tire pressures (36psi front), with front pre-load set for my weight (220+lbs w/gear, right at 2nd line) and experience very little brake dive.

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player. Therefore Honda (and others) recommend higher preload settings for heavier loads. I found that the bike tended to "wallow", particularly leaned over and going over small road irregularities. A bit over active. Upping the rear preload one notch has made an improvement. There are so many variables to suspension set up. Most are not available on the CB. Not needed really as it's damn good as is. Thanks for that Honda.

Cheers

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player. Therefore Honda (and others) recommend higher preload settings for heavier loads. I found that the bike tended to "wallow", particularly leaned over and going over small road irregularities. A bit over active. Upping the rear preload one notch has made an improvement. There are so many variables to suspension set up. Most are not available on the CB. Not needed really as it's damn good as is. Thanks for that Honda.

Cheers Thank you p, you saved me trying to type on this iPhone

 

[Pterodactyl_imp]

^^^^^. No worries mate.

In addition I quote from Lee Parks: "For street riding it is very important not to stray too far from manufacture's recommended tyre pressures as tyres have been designed to provide the correct amount of contact patch and flexing at a given load and pressure". Parks knows a little bit more about motorbikes than I do so I think whatever he says is worth considering.

 

[the Ferret]

Define too far..2#.. 5#..8#?

 

[Pterodactyl_imp]

"Too far". Easy. I find a reliable tyre pressure gauge, adjust the pressure as close as I can get to recommended. I try to do this while the tyre is cold.

As I think you said previously tyre pressure gauge accuracy is variable. I don't own three tyre pressure gauges but the digital one I have is normally within +\- 2psi of my local service station's reading. It's often spot on. This might be because the tyre is a little warm from the (short) ride or one of the gauges is out of calibration. If I stray far from home I trust my own gauge if there is a discrepancy.

Cheers

 

[Cormanus]

How on earth does one buy an accurate—that is, properly calibrated—tyre gauge?

 

[the Ferret]

How on earth does one buy an accurate—that is, properly calibrated—tyre gauge?

Good question. when I bought my accu-guage analog it was printed right on the package guaranteed accurate within +- 1/4 pound or something (doesn't say that on the package anymore). But my brother has one too and the two gauges measure a pound different.

 

[tomas_imp]

I run the same exact pressures as CIP57 does (32 front, 36 rear). It seems to provide the best feed back results for me. Lower air pressures provide a softer ride and a wider contact tire patch, providing for better braking and turning. If the stock settings of 36F & 42R will work with two passengers and luggage on the bike, how can the ride be safe and smooth when only one rider is on the bike at a third of the weight? I think Honda has these settings set for safety reasons only, because riders are not diligent enough for checking and adjusting their tire pressures regularly. Bikes use to come with two levels of air pressures, with or without passenger. I believe Honda has these psi[/u] set at the extreme levels for two riders plus luggage, so they"ll be safe.

 

[AzBob_imp]

^^^^^. True, however I can't agree with

I was running 32 front 36 rear with the stock tires. They are rock hard. With my setting on one line showing on the front to decrease dive when braking. The rear set on standard 2 setting, three was much to harsh. This combo seemed to work well for me. Experiment with different setting until you feel the front reacts best with the rear.

With the new tires i have bumped up air pressure to 34/38.

Pre-load has no effect on compression damping (and therefore brake dive). If we had fully-adjustable forks up front, you'd want to up the compression damping to combat brake dive, but we don't, so all you're really doing is reducing your ride height and reducing your fork's range of travel. I'm not sure if we have progressive springs, but if we do, you may also be unnecessarily increasing the harshness of your ride by pushing the spring into the stiffer progressive rate sooner.

I run recommended tire pressures (36psi front), with front pre-load set for my weight (220+lbs w/gear, right at 2nd line) and experience very little brake dive.

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player. Therefore Honda (and others) recommend higher preload settings for heavier loads. I found that the bike tended to "wallow", particularly leaned over and going over small road irregularities. A bit over active. Upping the rear preload one notch has made an improvement. There are so many variables to suspension set up. Most are not available on the CB. Not needed really as it's damn good as is. Thanks for that Honda.

Cheers

Preload affects at what force spring compression will commence. This is also affected by the load that the bike carries. With a large pillion load the bikes rear suspension will operate at lighter (external) forces than unloaded. This will delay initial displacement but, as you say, after that damping forces become the only player.
That's incorrect. A linear (i.e. non-progressive spring) requires the exact same force to compress the spring the first inch, second inch, or last inch. This value is expressed as k in Hooke's law and known as the "spring rate," expressed as a weight over a distance, e.g. 100lbs/inch.

The pre-load adjustment adds load to the spring, which increases/decreases the force the spring exerts on the bike (since it can't move the ground). Increasing it won't add more ability to the spring to absorb weight/force, so the original post about it reducing brake dive is wrong. All he did was absorb the brake dive with the pre-load (in other words, dialing it into the spring before it happens, pre-compressing it). Of course this manifests itself as appearing to have reduce brake dive, but that's not really what happened. However, it can certainly make a bike easier to ride, but at the cost of reducing spring life and having it operate outside of its design envelope.

In other words, the amount the bike dives is the same, regardless of pre-load -- he made it dive (in his garage) by an inch or two (by upping the pre-load), and then when he's out on the street, it will dive another inch or two. Let's say one inch in both places, for ease, for a total of two inches of dive. If he didn't do anything to the pre-load, the bike would still dive two inches upon application of the brakes (at a given constant speed and application) -- the same. Do you see what I'm getting at? You can't increase the damping effect of the suspension via pre-load. The proper adjustment is the compression damper adjustment, which would actually _reduce_ the brake dive without changing the bike ride height, which we don't have. He (you, me, anyone) can effectively reduce the brake dive to zero by adjusting the pre-load to max so that it hits the bump-stops. That doesn't mean the compression damping has changed one iota.

I'll say it one last time for effect: pre-load has no effect whatsoever on compressing damping. It is merely for setting the appropriate ride height so that the spring is as close as possible to its load rate, which is where it was designed to operate, regardless of the weight carried. This is why the first thing you generally do with a bike suspension that you want to work optimally is set the sag correctly. Attempting to modify compression damping characteristics by using the pre-load for other than its designed purpose is a fool's errand.

If one feels the bike exhibits too much brake dive, the only real cure is to do something to the damping of the front suspension: increase the oil weight, get new valves, or get whole new cartridges/forks.

 

[Pterodactyl_imp]

AzBob, there is one point with which I entirely agree with you:

Quotere-load has no effect whatsoever on compressing damping.
Let me give some more thought to your comments on the effect of spring preload.

Cheers

 

[CIP57_imp]

Preload

Preload is a load placed on a spring before its used. On your suspension you may have means to apply pressure to compress the spring with out effecting suspension movement. It can be an adjuster in a front fork, or a collar on rear shocks. This loads the spring to alter the point at which the spring begins to compress. If you preload a 100 lb per inch spring one inch, it will take 200 lbs of force to make the shock spring compress it's first inch from full extension. Preload does not change the springs rate.

Bob,
I understand what your saying and have set up suspension on bikes with more advanced tuning.

Increase of preload alters sag therefore reduces brake dive until you compress the shock to equal value of what has been dialed in. So, when your braking in a corner there is less compression of the shock therefore less brake dive, hard on the brakes will have no effect on dive. Coming off in exit ramp doing 60 slowing to 0 you will feel less compression on the front end by increasing preload therefore less dive.

 

[Pterodactyl_imp]

^^^^^^. This is getting interesting. Good posts Bob and CIP. Making me think a little harder about something I thought I knew something about.

CIP, what you are saying is that, the greater the preload, the less dive. This is because spring travel is effectively reduced. But once compression begins the rate of dive is a function only of compression damping. Have I got that right?

My view on preload is basically:

1. once compression begins preload is no longer a factor. Spring rate is.

2. Ride height (static sag) is controlled solely by preload

3. Preload, correctly adjusted for load, ensures that the suspension operates within the optimum range. This is why recommendations for baseline preload adjustments are predicated on anticipated load (pillion etc.).

4. The ratio of rear to front preload affects handling in that less front means easier turn in and conversely more front resists turn in.

There is a little more but that's the basics. Point 3 is the reason that the wallow I referred to in previous posts is now reduced with preload adjustment. Further adjustment is only available through adjusting damping, quite obviously not available on the stock CB, although someone did mention changing oil viscosity. Maybe it was you CIP?

One question for you both (Bob and CIP). On the CB, does preload affect spring rate? This of course would depend on the spring itself. Straight rate or progressive rate?

Looking forward to your comments. Don't spare me, I've been around long enough to know how to cope with disappointment .

Cheers

 

[CIP57_imp]

^^^^^^. This is getting interesting. Good posts Bob and CIP. Making me think a little harder about something I thought I knew something about.

CIP, what you are saying is that, the greater the preload, the less dive. This is because spring travel is effectively reduced. But once compression begins the rate of dive is a function only of compression damping. Have I got that right?

My view on preload is basically:

1. once compression begins preload is no longer a factor. Spring rate is.

2. Ride height (static sag) is controlled solely by preload

3. Preload, correctly adjusted for load, ensures that the suspension operates within the optimum range. This is why recommendations for baseline preload adjustments are predicated on anticipated load (pillion etc.).

4. The ratio of rear to front preload affects handling in that less front means easier turn in and conversely more front resists turn in.

There is a little more but that's the basics. Point 3 is the reason that the wallow I referred to in previous posts is now reduced with preload adjustment. Further adjustment is only available through adjusting damping, quite obviously not available on the stock CB, although someone did mention changing oil viscosity. Maybe it was you CIP?

One question for you both (Bob and CIP). On the CB, does preload affect spring rate? This of course would depend on the spring itself. Straight rate or progressive rate?

Looking forward to your comments. Don't spare me, I've been around long enough to know how to cope with disappointment .

Cheers

Loading the spring is minimal on this bike .6 less than in inch. Standard position in 9mm and fully loaded is 15mm or .2"

By pre- loading the suspension you create more tension therefore need more pressure to compress the front end initially. Example: The front end will feel different to someone at 250 than 160 pounds. This is why we set sag for the rider. I'm 170 and notice a difference by pre-loading the front end. Someone who is 250+ may not notice as much because they have already loaded the front end.

Pre-load does not change spring rate, only the initial load you have created.

As Bob mentioned there are other ways to control brake dive which are more effective with a fully adjustable front end.