Kumho rear tire air pressure?

[BLUEKNIGHT911]

Question: How much does the air pressure in the tire affect it's ability to remain seated on the bead of the wheel?
(Is there a point where too little pressure might become dangerous?)

I posted about this last year , here's the short version ...... My Michelin Hydro-edge rear tire was drivable at 8 psi, ... it did feel slightly squirrely, so I checked it and added air....... Everything Peter wrote is valid ,imho ...... Mike

[Grayfox]

I posted about this last year , here's the short version ...... My Michelin Hydro-edge rear tire was drivable at 8 psi, ... it did feel slightly squirrely, so I checked it and added air....... Everything Peter wrote is valid ,imho ...... Mike

I did what Blue Knight said and set my tires at 16 on front and 18 rear on my 2012rts. I thank it rides better and hugs curves better, thanks for the info

[BLUEKNIGHT911]

I did what Blue Knight said and set my tires at 16 on front and 18 rear on my 2012rts. I thank it rides better and hugs curves better, thanks for the info

I'm glad you like it ( only if you switched to CAR tires - right ) .... they will work better this way if it's wet .... annnnnnnnnd your ride will be more comfortable because they will help ABSORB road irregularities ............. Mike

[nealperkins]

So what is the recommendation for the pressure in the original Kenda's? (Other than get rid of them...)

[Peteoz]

So what is the recommendation for the pressure in the original Kenda's? (Other than get rid of them...)

18 and 28, Neal.

[nealperkins]

Well, that's what I've got.
Thanks

[malibu_dan]

Y'all make me want to wear out the Kendas so I can put some real tires on and get some traction to go with the new Elkas!

[AY4B]

I wore out my rear Kenda before it got to 4000. I wore out the Yokohama S at around 10,000 because I kept 28 pounds in it. Wore out the center. My second Yokohama, I'm running 20 and may take it down to 18 after reading this thread.

[spyderfish]

I'm the Mike ( of Mike and Peter ) and if you are using a car tire ( any brand ) you will be safer and enjoy the ride better if you lower the REAR psi to .. 18 ( cold ) .. I'm sure Peter will agree with this . I know this may seem too low, but remember that tire will increase at least 3 psi after about 3 miles of driving ....... Mike

Mike and Peter,

With you folks all the way on this one. Kumho Ecsta on rear, original OEM on front, 19K miles. Looking for traction, longevity is secondary. Everything I have read everywhere indicates that lower pressure increases traction, A LOT. Limited of course by tire damage due to underinflation and too much sidewall flex.

So, simple and easy, 18 pounds all around.

Spyderfish

[BLUEKNIGHT911]

Mike and Peter,

With you folks all the way on this one. Kumho Ecsta on rear, original OEM on front, 19K miles. Looking for traction, longevity is secondary. Everything I have read everywhere indicates that lower pressure increases traction, A LOT. Limited of course by tire damage due to underinflation and too much sidewall flex.

So, simple and easy, 18 pounds all around.

Spyderfish

The Kenda's because of their construction perform better at a higher psi than any car tire..... if you have very good alignment they will last like a car tire also....... Personally I'm not impressed with the Kumho , many here have reported that it's wet road abilities decrease considerably at about it's half -life point. Try 18 psi, ( rear ) I think you will like that for many reasons, ............ Mike

[JP58]

I will go with 18. Sounds like most here agree. I have the Michelin Premiers on my Nissan Sentra. Expensive but they get better traction as they wear do to the Sipes get wider as they wear is what they say.

[Bob Denman]

I wore my Kumho down to within a couple of hundred miles of needing replacement: it performed consistently for the entire 12,300 miles.
(The last 100 miles was in a rainstorm: no signs of hydroplaning, or loss of traction!)

[BLUEKNIGHT911]

I wore my Kumho down to within a couple of hundred miles of needing replacement: it performed consistently for the entire 12,300 miles.
(The last 100 miles was in a rainstorm: no signs of hydroplaning, or loss of traction!)

Bob, I never investigated an accident below 15 mph that I attributed to " Hydro-planning " ........ Mike

[Peteoz]

Bob, I never investigated an accident below 15 mph that I attributed to " Hydro-planning " ........ Mike

Cheeky bugger

Pete

[wrb3004]

I never new about the 4psi rule until I read this thread. Since then I have read other threads about it and have also googled it and read some interesting articles.

Based on many discussions about tires and tire pressure I am running Federal Formoza's on the front at 15# and I am running a General Altimax on the rear at 20#.

After about an hour of driving the fronts read 16# and the rear reads 23#(per the FOBO). So the fronts rose about 1# and the rear rose about 3#.
I can drop the cold pressure on the rear to maybe 18# or 19# and see if I reach the 4psi but I'm not sure I could reach the 4psi rule on the fronts without going quite a bit lower than 15#. From everything I have read 15# seems to be a good number.

Thoughts on this? Thanks Wayne

[hypurone]

I was gonna skip this thread completely but someone has to point out that with any maximum tire pressure there is a minimum. Although the minimum is not as clearly defined as the maximum is (listed right on the sidewall of the tire)...

This is from the Kuhmo website but you can find it on any tire manufacturers' site as well:

The importance of maintaining the proper air pressure cannot be overstated. Under-inflation can lead to excessive heat build-up and structural stress and can cause a tire to fail. Over-inflation can cause uneven tire wear in the center portion of the tread pattern and can also lead to vehicle handling problems.

Granted our rides are much lighter than cars but you can still get there....

Having had been in the business for 20+ years I have seen what that looks like firsthand..... I would prefer to lose a few hundred miles of wear over having a failure due to heat buildup and structural failure.

The very first thing I noticed once switching to "car" tires and being able to run higher pressures without the tires getting all squirrely and actually losing traction like the Kendas would, was how EASILY the bike accelerated & rolled down the road.... Also, my DPS actually feels like DPS! Now mind you, I am not running car pressures but I am not in the "teens" of air pressure either....

To each their own, but I just had to say my piece.... ;-)

[Bob Denman]

There's no doubt that running a bit more air in the tires will reduce rolling resistance...
But there will be the inevitable trade-offs as well.
The ride will probably seem harsher, and Traction MIGHT BE decreased...
So dance with the Devil of your choice.

[Peter Aawen]

Hypurone, I can only agree that you are absolutely right about there being a Minimum Pressure as well as a Maximum, & that it's a helluva lot harder to define than the Max. But I believe the most significant issue for us as Spyder Ryders is that many people are either sticking with the pressures required for the very lightly constructed Kendas & using it in the car tires they are now running, or that they are running car tires and continuing to run the pressures those tires needed under something waaayyy heavier!! That's why there is so much discussion about what pressures to run in car tires under a Spyder & why some of us are advocating that we should drop our tire pressures to something more suitable, but not too low as to be dangerous!

At the risk of preaching to the converted &/or saying it all again (again!).... Car tires under a Spyder are carrying a far less load than these tires are capable of supporting at their labelled Maximum pressure, & just like similar sized tires under a small car rather than a big car require somewhat less pressure in them than they would under that big car in order to do the job properly & SAFELY, (a big car which might weigh in much closer to the tire's published max load & therefore need a pressure closer to the tire's max pressure) then so the same sized tire under an even lighter vehicle like our Spyders requires proportionally less pressure in it to do the job safely & properly than it does under the small car! And that is reflected on the pressure/load charts & tables that just about every tire manufacturer will have produced somewhere - except very few of them ever expected a vehicle load as light as our Spyders, so they generally don't go that low with their published pressure/load figures!! But if you ask them nicely, possibly after searching for & finding the right person in their organisation, you can sometimes get them to either show you the 'lower loading' figures or get them to do the calcs for you to provide the appropriate pressures for your Spyder's loads. And some have done that - the pressures Mike & I have been suggesting reflect that!

Not only that, but since people started running car tires on their car rims under their Spyders instead of running the very poor quality controlled Kendas, there have been literally millions of miles of On Road/Real World Testing conducted absolutely free of charge to BRP, (some of us have even meticulously checked pressure increases & tire temperature increases just to make sure that the pressures being used are not harming the tires & are within or at the recommended/optimum rates) There are 'tools' & 'rules' that I (& some others?) have previously mentioned that you can use to help make sure the pressures you are running are appropriate, & we've made suggestions about what pressures work & what doesn't. However, Pretty much all of this has confirmed that not only are car tires capable & safe under our Spyders but also, when run at the lower pressures that have been previously mentioned (without going to low) they will provide significantly better ride, traction, wear, handling, etc than the Kendas do, basically excelling at all those things that most Ryders are searching for from their Spyder tires & telling BRP the OE tires just don't do for them....

Sure, some Ryders may go a tad lower than possibly ideal in order to benefit from the increased traction that allows, at the cost of a spongy ride & the less direct steering that results; while some may keep their pressures a little higher than ideal in order to maintain the firmer ride & more direct steering/less rolling resistance that higher pressures can deliver, at the cost of less traction & harsher ride; but that's their choice & hopefully most have now come to terms with the concept that running pressures that are too high in a car tire under their Spyder WILL compromise ride, wear, & traction, but (until the limits of traction are reached) the lesser rolling resistance will give you some pretty direct steering; while going too low WILL compromise wear & give you a spongy ride & sloppy directional control as well as markedly improved traction (at least until that 'hold the tire on the rim' level is reached/passed) & maybe the tire overheats. Hopefully....

That's why some of us here have been suggesting pressures that would allow people/Spyder Ryders to try for that 'ideal compromise' & aim for the best mix of all outcomes, but it is all a game of compromises -
* stick with the Kendas & their recommended pressures, the compromise is that you'll hafta accept crappy performance, wear, handling, etc (noting that experience has show these tires are sooo poorly constructed that varying pressures makes NO difference at all & some are so badly made that you can't avoid the vibration, wobbles, crappy traction, or sloppy steering they provide);
* fit car tires & run car pressures, & the compromise is that while you'll get really direct steering you also get a pretty harsh ride, accelerated centre of tread wear, & poor traction, especially in the wet;
* fit car tires & run the pressures some of us have been suggesting, & the compromise is that you'll get pretty good steering response (but not the overly direct response offered by higher pressures), you'll get a great ride (but not too soft & spongy, & not to harsh & firm), & very even wear with reasonable if not long tire life as well as great traction; or
I suppose you could also choose to...
* fit car tires & run pressures that are really too low & run into the tire life & safety issues hypurone mentioned..... but I don't know why you'd choose to do that, unless maybe you think choosing tires & pressures is sorta like living in Goldilock's land!

Sorry about the epic (again!) but it's not a straightforward & simple subject, nor is it easy to discuss when you have such a wide ranging audience, altho there are a few points that I hope are now clear to those who weren't previously sure!

[Peter Aawen]

....After about an hour of driving the fronts read 16# and the rear reads 23#(per the FOBO). So the fronts rose about 1# and the rear rose about 3#.
I can drop the cold pressure on the rear to maybe 18# or 19# and see if I reach the 4psi but I'm not sure I could reach the 4psi rule on the fronts without going quite a bit lower than 15#. From everything I have read 15# seems to be a good number.

Thoughts on this? Thanks Wayne

Wayne, the 4psi rule is a 'rule of thumb' aimed at helping you consistently determine the optimum pressure for your tires under varying loads & conditions. It's not something you hafta slavisly or mindlessly adhere to, it's a repeatable & relatively easy to use guide aimed at helping you get the best (your best) from your tires & vehicle, & to help you make informed (more informed? better informed?) decisions about what pressures you might choose to run in your tires.

Broadly speaking, higher pressures than it suggests will come at a cost in traction & tire life but likely give you more direct steering & firmer ride (at least until you get OTT too high!) & lower pressures than it suggests will come at a cost in fuel economy & handling but likely give you more traction & 'flotation' on poor surfaces.... and YOU get to decide which way you go, or even IF you go either way!!

That said, the front end of our Spyders really don't carry a great load, & if the tires you are running provide YOU with 'acceptable to you' adhesion & steering response at 15psi, then I'd suggest you stick with that pressure, altho it might pay to add a psi or maybe even two if you are heading out on a long & laden ride. I generally run somewhere between 14 & 18psi up front depending upon the ambient temps, the roads I'm planning on riding on, the speeds I'm planning on travelling at, how hard I'm gonna hit the twisties, &/or the load I'm putting aboard my Spyder (or car, or truck.... ) Use the 4psi rule for a while, or even just watch how your tire pressures vary from this sort of difference in the what where when & how of your riding & you'll quickly learn what pressures suit YOU best!

As for your rear tire pressure, if you are happy with the ride & handling you are getting from your General Altimax while it's running 20psi (cold) in it, then I see no reason to change that just cos you don't quite get a 4psi increase - after all, it's just a guide, intended to HELP you schoose what pressures to run!! Maybe you should watch carefully for increased tread wear in the centre of the tread, cos that is an identified risk of running too high; & certainly, if it looks like raining you might want to drop another lb or too out of your rear tire to minimise any chance of hydroplaning; OR maybe you could take that 'ONLY a 3psi increase' as an indication that you could ride a bit harder, corner a bit faster, brake a bit later or heavier, etc without creating any significant tire concerns - adjusting the tire pressure is only ONE of the ways you can vary how much your tire pressures might increase from their cold start levels!

[Old Crow]

I'm assuming that the 4psi rule does not apply to the OEM Kenda front tires. I'm at 14K on the original front Kendas on my new to me 13 RTS. 10 K of that is mine. I'm running 15-16 cold on the fronts and typically see a 1.5-2.0 psi increase after a long ride. Cant see reducing the pressure to get more of an increase on these.

I've got about 3K on a new Khumo 225/60-15 rear running 28psi cold. Usually see a 3.5-4.0 psi increase on it. All measured by FOBO.

Bob

[wrb3004]

Great explanation. Still getting used to this new to me Spyder RTs, especially the handling, and want to get the tires set at an optimal setting. I will play close attention based on your advice. Thanks again.

[WackyDan]

I was gonna skip this thread completely but someone has to point out that with any maximum tire pressure there is a minimum. Although the minimum is not as clearly defined as the maximum is (listed right on the sidewall of the tire)...

This is from the Kuhmo website but you can find it on any tire manufacturers' site as well:

The importance of maintaining the proper air pressure cannot be overstated. Under-inflation can lead to excessive heat build-up and structural stress and can cause a tire to fail. Over-inflation can cause uneven tire wear in the center portion of the tread pattern and can also lead to vehicle handling problems.

Granted our rides are much lighter than cars but you can still get there....

Having had been in the business for 20+ years I have seen what that looks like firsthand..... I would prefer to lose a few hundred miles of wear over having a failure due to heat buildup and structural failure.

The very first thing I noticed once switching to "car" tires and being able to run higher pressures without the tires getting all squirrely and actually losing traction like the Kendas would, was how EASILY the bike accelerated & rolled down the road.... Also, my DPS actually feels like DPS! Now mind you, I am not running car pressures but I am not in the "teens" of air pressure either....

To each their own, but I just had to say my piece.... ;-)

The Kumho site also has ZERO recommendations on PSI for the tire and rightly states to use the PSI specified by the vehicle manufacturer. The only place I've seen PSI/weight ratings is for trailer tires.

[WackyDan]

I'm assuming that the 4psi rule does not apply to the OEM Kenda front tires. I'm at 14K on the original front Kendas on my new to me 13 RTS. 10 K of that is mine. I'm running 15-16 cold on the fronts and typically see a 1.5-2.0 psi increase after a long ride. Cant see reducing the pressure to get more of an increase on these.

I've got about 3K on a new Khumo 225/60-15 rear running 28psi cold. Usually see a 3.5-4.0 psi increase on it. All measured by FOBO.

Bob

Keep in mind that all vehicles spec their recommended PSI to cold inflation. You don't fill to lower PSI in anticipation of heat.

[Peter Aawen]

I'm assuming that the 4psi rule does not apply to the OEM Kenda front tires. ...

No, it still applies Bob; it's just that the OEM tires (front OR rear) are basically pretty mediocre anyway & varying their pressures up or down won't do a great deal either way... You might (should?) get even better life out of them up front by running pressures a bit lower, possibly even get a little better ride & handling, almost certainly get better traction... but at what cost & what risk??!

They often aren't a 'well constructed' tire & the quality control where they are made seems to be seriously lacking!! Personally, from what you've told us I'd stick with what you've got now, realising that you aren't going to get anything better than OK performance out of them & knowing that as soon as they are worn out or you get sick of their lack of performance in any area, you can swap 'em out for virtually any appropriately sized car tire alternative & get significantly better ride, handling, traction, & tire life from them!

Over to you!

[Peter Aawen]

Keep in mind that all vehicles spec their recommended PSI to cold inflation. You don't fill to lower PSI in anticipation of heat.

Actually WackyDan, when it comes to vehicle tires, that management of 'anticipated heat increase' thing is pretty much WHY we run pnuematic tires where we can vary pressures & manage the changes instead of just running solid rubber rings & going with what you get!

But you are right in that you don't LOWER your cold start pressures to avoid too much heat increase, cos lowering the cold start pressure will INCREASE the proportional heat & pressure gain!!

LESS than optimal heat increase (& therefore a corresponding small pressure increase) means your cold start pressure was too HIGH, so if you want to minimise or lessen the heat & pressure gain you increase your cold start pressure;

GREATER than optimal heat increase (& therefore a corresponding larger pressure increase) means your cold start pressure was too LOW, so if you want to maximise or increase the heat & pressure gain you lower your cold start pressure!