Tire Pressure Question

[headshrink]

Fact: The manual says the front should be set at 28 psi and the rear at 32 psi (cold).

History: When I got a nail in my rear and went to replace it, the dealer pointed out how my front was cupped from under-inflation. I was perplexed because I check my air at least once a week (it is actually in my Outlook calender), and always while cold. I figured the cheapo pen-type tire gauge I was using must be off, so I ordered a nice digital one that reads down to 0.5 psi. It turns out, the pen gauge wasn't really that bad.... but since I have gotten the new gauge (about 1,500 miles ago), I have been religiously keeping it to exactly 0.5 psi where the manual recommends.

Current Situation: I was just out checking my tires, running my hand over the fairly new (1,500 miles) Perelli rear tire, and I thought I may have felt the beginnings of cupping or maybe feathering..... I'm not sure, I need a second opinion, but it may be starting. Out of curiosity I looked at the sidewall.... it lists it's maximum load rating at 42 psi cold. Hmmmm.....

Qustion: Now I don't what to follow - is it the tire sidewall, or the manual?
What do you all do?

[komohana]

hey bob...i'm no tire expert, but this is what i do..
to make a long story short, i've determined for myself that the tires i've used on the bikes i've owned fall into an operating pressure range of 28 psi minimum, to between 32-34 psi maximum, under normal operating conditions. the max psi/weight information on the sidewalls i thought was for maximum tire pressures at the maximum allowed weight. my perelli sport demon rear says something like 42 psi max at 677 lbs. (don't quote me on that...memory call)
in determining what range to run the new tires at, a friend who helped me mount them suggested this: start each tire on the high end, and see how they perform, slowly taking out pressure in incriments that i would decide (2 psi) and see how this affects the handling. do this till i reach the minimum pressure and determine which pressure works. i've never felt the difference in small pressure changes like i do riding the 250.
determine why you've chosen the pressures you have. can you raise pressure to prevent cupping and still have the tire perform as you want?
you may be trading tire life for the pressures you run for a given tire. research the net if you need to determine ranges, find what works and if that pressure is allowable, and you're comfortable with it, then DO IT.

[bob706]

Follow the manual. +100 for the digital gauge. My old pen type gauge was off by 3-5psi.

[Snake]

Inflating to the max pressure on the side wall can be even worse for tire wear. The tire "baloons up" and you wind up riding on a very thin strip of tire the"chicken stripe". You can verify this by putting a small amount of dirt/dust on concrete and then ride through it and note the area of dust in the tire the "contact patch".

[OldGuy]

Originally Posted by Snake

You can verify this by putting a small amount of dirt/dust on concrete and then ride through it and note the area of dust in the tire the "contact patch".

Or, take a piece of old fashioned chalk and make two marks on the tire from sidewall to sidewall 180 deg apart. Go for a ride and look to see how much tire you are really using in the turns (old auto cross trick).

[tlhamon]

You also need to realize that while the tire pressure may be constant under any load, the shape of the tire is not. A 200 lb guy on the same bike as me at 120 lb will get more rubber. That will wear the tires differently. The OM specs are an average to go by.

[Snake]

Originally Posted by OldGuy

Or, take a piece of old fashioned chalk and make two marks on the tire from sidewall to sidewall 180 deg apart. Go for a ride and look to see how much tire you are really using in the turns (old auto cross trick).

Thanks for the trick. Much claner way of doing it!

[Snake]

Originally Posted by OldGuy

Or, take a piece of old fashioned chalk and make two marks on the tire from sidewall to sidewall 180 deg apart. Go for a ride and look to see how much tire you are really using in the turns (old auto cross trick).

Originally Posted by tlhamon

You also need to realize that while the tire pressure may be constant under any load, the shape of the tire is not. A 200 lb guy on the same bike as me at 120 lb will get more rubber. That will wear the tires differently. The OM specs are an average to go by.

With that in mind I would say do the chalk test and adjust accordingly until the best contact patch is achieved.

[OldGuy]

Originally Posted by Snake

With that in mind I would say do the chalk test and adjust accordingly until the best contact patch is achieved.

By golly I think they've got it

[Alex]

I'm not sure what the chalk test would be trying to show. Whether the tire is at 20 psi or 40 psi, it's still unlikely that someone will use the tire right to the absolute edge on the street, either front or rear. Seems to me that the amount of chalk that would be rubbed off it only related to how much lean angle the rider uses on that particular short ride, right? On a car tire I can see more benefit, as the chalk test would let you know if you've overinflated the tire and the contact patch becomes only a smaller portion of what should be firmly on the road when properly inflated.

As some have said in this thread, the max psi rating on the tire sidewall has nothing to do with the optimal psi once it's mounted on a particular bike. It's exactly what it reads, the max psi that the tire can be expected to withstand without risking a failure. The owners manual (or the swingarm sticker) on a bike state the recommended pressures that Kawi has determined to be appropriate for the OEM tires on that bike. That said, the world doesn't end if you go up or down a few psi based on your particular preference. Perhaps going up a few psi in front might lower the risk of cupping the tire, but on the other hand some tires are prone to cupping no matter what the pressure.

[OldGuy]

Agreed that tire pressure does not affect contact patch on our tires to the extent that it does on a cage, and I would certainly defer to the resident experts on this issue.

However, from my limited experience on the Ninja, and from what I have read, tire pressure can have a significant influence on how the bike "feels" and that in turn could affect how aggressive / comfortable a "newer" rider might be in using the available contact patch.

Without a track to go out and really learn how to wring it out and see how hard you can take it into a corner with minimal danger to yourself, your bike, and those around you it would seem that combining changes in tire pressure with chalk marking could help one find the happy balance.

Remember guys I'm the flat-lands disadvantaged rider without any "real roads" to work things out on.

PS - And an old fart too

[Alex]

Originally Posted by OldGuy

However, from my limited experience on the Ninja, and from what I have read, tire pressure can have a significant influence on how the bike "feels" and that in turn could affect how aggressive / comfortable a "newer" rider might be in using the available contact patch.

Absolutely agreed! Tire pressure, even just a few psi, can have a large effect on how a bike feels, no question about it.

Originally Posted by OldGuy

Without a track to go out and really learn how to wring it out and see how hard you can take it into a corner with minimal danger to yourself, your bike, and those around you it would seem that combining changes in tire pressure with chalk marking could help one find the happy balance.

I just don't see how chalk markings would vary significantly, if at all, under the different pressures (assuming we're not testing 0 psi and 100 psi), and it seems like any variations that we did see in the chalk would be more likely due to the max lean angle used on that particular test ride rather than any noticeable change in the contact patch from the pressure change.

[OldGuy]

Originally Posted by Alex

Absolutely agreed! Tire pressure, even just a few psi, can have a large effect on how a bike feels, no question about it.
. . . and it seems like any variations that we did see in the chalk would be more likely due to the max lean angle used on that particular test ride rather than any noticeable change in the contact patch from the pressure change.

Bingo - as a new rider if I have a tire pressure that makes the bike feel more comfortable I'm most likely to input more lean angle than one that is a little squirrely in a turn and bites me.

If nothing else its an easy way of monitoring how much lean angle you are inputting (and makes for a good discussion right?).

[VeX]

For commuting air up to 34psi. For a weekend ride go down to 28PSI (cold). Whenever I go up to L.A. I usually air up to 30-32PSI cold and when I get up there I'll drop it to 28PSI (well 30 PSI because the tires are warmed up at that point). The last time I had my tires changed they put 40 PSI in the tires and I thought I was going to die. I could feel EVERY little bump in the road and the bike handled horribly. At 28PSI (cold) the bike literally performs 100% better.

[headshrink]

Thank you all for your input.

Since I didn't really have the new gauge until I go the new rear, I think I should keep that EXACTLY at OEM specs for the life of the tire to get better "sample data." The front, since it is the original tire still, probably won't reveal much from the change since it was already damaged. I'll revisit the possibility of airing up a little either if the rear starts getting badly cupped, or at the next tire change if necessary.

[Dr Shorty]

Originally Posted by Snake

Inflating to the max pressure on the side wall can be even worse for tire wear. The tire "baloons up" and you wind up riding on a very thin strip of tire the"chicken stripe". You can verify this by putting a small amount of dirt/dust on concrete and then ride through it and note the area of dust in the tire the "contact patch".

Maybe I am misunderstanding what you wrote here, but I think you are confused about what a chicken strip and what a contact patch are.

A chicken strip is the small unused portion on the edge of a tire. It is called a chicken strip because the rider is too "chicken" to lean over far enough to use it. It is not the portion of your tire in contact with the road, as you seem to have suggested.

A contact patch is the portion of your tire that is in contact with the road at any given instant in time. This patch is about the size of a postage stamp for each tire, it does not encompass the whole circumference of the tire as your post suggests.

Sorry, had to do it.

[tlhamon]

I guess the only real solution is to fill your tires with Stuff insulation or replace them with the hard plastic kind on big wheels.

I'm not sure it's something the average rider really needs to worry that much about. If you are riding really hard, then I would go to someone that is a professional rider and ask them flat out. You may also try sending an email to the company and trying to track down a rider, not just a computer jockey. I've had good success talking to the people at Buell when I had questions.

[KJohnson21]

The pressures listed in the manual are a good rule of thumb, but one of the ways that you can fine-tune how your bike handles is by adjusting the tire pressure. The rider's weight directly affects it, so what works for one rider might not be right for another. As VeX said, what type of ride you're going on is important. The pressure you use for a long, twisty, mountain ride, should be different than the pressure you'd use for a long freeway/interstate/highway ride. That's because the tires aren't doing the same thing in those situations. I wouldn't necessarily change the pressure for short trips, but it depends on what you're doing.

Here's a good article: Tire Pressure-Not a Lot of Hot Air

If you keep the pressures correct for your normal driving conditions you can improve the life of the tires and keep them from getting weird wear patterns.

[headshrink]

I'm 130-140 lbs.
Drive mostly 20-30 min. commute rides (freeway and fast city streets).
Occasional twisty and foot-hill rides.
8700 mi. in 11 months

For what it's worth.

[CodE-E]

So I decided to buy a little digital tire pressure gauge. I just went outside and measured my Ninja's tire pressure for the first time:

36 psi at the rear, 32.5 at the front. I weigh 66 kilos (145 pounds) and drive alone and without luggage.

I always found the suspension of the bike to be quite hard, and after reading that the manual recommends 32/28 (front/rear) psi, I guess the somewhat high tire pressure will have affected that hard feeling! Cornering at higher speeds on uneven roads often felt a bit unsafe with my setup - I think slightly lower pressure should improve traction in those situations.

It's already getting dark over here, but tomorrow I'll go down a little bit and try 34/30 psi, and the day after 32/28. Looking forward to testing, and I hope it'll improve the feel of the bike.

[Alex]

Originally Posted by CodE-E

after reading that the manual recommends 32/28 (front/rear) psi,

It's actually 28F/32R.

[kkim]

Originally Posted by CodE-E

It's already getting dark over here, but tomorrow I'll go down a little bit and try 34/30 psi, and the day after 32/28. Looking forward to testing, and I hope it'll improve the feel of the bike.

When I ran with stock tires (btw, what tires do you have? ) I used 28/28 doing lots of twisties. If you run mostly highway riding, just follow the manual recommendations as Alex pointed out.

Lower pressures (to a point) will definitely give you more "feel".

[headshrink]

Originally Posted by kkim

When I ran with stock tires (btw, what tires do you have? ) I used 28/28 doing lots of twisties. If you run mostly highway riding, just follow the manual recommendations as Alex pointed out.

Lower pressures (to a point) will definitely give you more "feel".

Front is still the OEM (the better one, I forget off hand), Rear is Pirelli Sport Demon.

[CodE-E]

I got IRC tires on my '09 European 250R. I keep reading that they're a bit crap, but I don't have any others to compare them to, and I probably hardly ever drive on the limit. Before I spend money on better tires, though, I need biking boots and pants.

There are loads of amazing roads around my area, through forests and mountainous areas, fast corners, tight corners, hairpins with lots of elevation, you name it. I'm so glad I went through the hassle of getting a motorcycle license - riding around here is so much fun! My daily commute doesn't have any long straight roads either. So I guess going down from my currently high tire pressure will give me a better feel.

[Alex]

Originally Posted by CodE-E

There are loads of amazing roads around my area, through forests and mountainous areas, fast corners, tight corners, hairpins with lots of elevation, you name it.

There sure are! I want to see some pics of your Ninjette on the Grossglockner pronto! And you get bonus points if you wear an outfit like we saw on this guy riding next to us up that road:

[AgentCircus]

I way 135 lb. and I'm running Pirelli Sport Demons, 110/70/17 front and 140/70/17 in the rear. Best pressure?

[headshrink]

Originally Posted by AgentCircus

I way 135 lb. and I'm running Pirelli Sport Demons, 110/70/17 front and 140/70/17 in the rear. Best pressure?

Me too, and I'm pretty happy with 1 pound over Kawi's recommended pressures. If memory serves that works out to 29psi front, and 33psi rear.

[thomason2wheels]

Originally Posted by Alex

Absolutely agreed! Tire pressure, even just a few psi, can have a large effect on how a bike feels, no question about it.



I just don't see how chalk markings would vary significantly, if at all, under the different pressures (assuming we're not testing 0 psi and 100 psi), and it seems like any variations that we did see in the chalk would be more likely due to the max lean angle used on that particular test ride rather than any noticeable change in the contact patch from the pressure change.

Just an idea....street tires are designed to run within a certain heat range. Heat builds inthe tire from the flexing of the tire's carcass. Someone has suggested that setting tire pressures so you get a 10% increase in pressure between hot and cold is a good starting point for finding optimum pressure. Since we all weigh different amounts and carry different stuff when we ride, experimentation is necessary to find that magic pressure. I am a big guy so i start out with the max pressure allowed on the rear tire and on the vstrom that was just about right....still experimenting with mr. Greenie, i have no idea where i will end up on it currently at 36 rear, 32 front.

[thomason2wheels]

Originally Posted by Snake

Inflating to the max pressure on the side wall can be even worse for tire wear. The tire "baloons up" and you wind up riding on a very thin strip of tire the"chicken stripe". You can verify this by putting a small amount of dirt/dust on concrete and then ride through it and note the area of dust in the tire the "contact patch".

However that isnt the whole story. The less flex there is in the tire carcass, the less heat generated. Heat is the enemy of street tires. Keep em cool and they last longer. The less flex there is the less the tire deforms as it rolls, and the closer its rolling radius is to the unloaded radius, that means a slightly taller effective gearing and less rolling resistance will have a happy effecct on fuel efficiency. For rolling down the slab, high pressures are a good thing, maybe not so much in the twisties.