Spyder Tire Preasures

[Tim Harman]

Tire Preasures: What are you setting them at ? :chat:

 

[sabunim5]

20 front, 30 rear

 

[NancysToy]

20 front, 30 rear since about day three. Has worked real well, and helped stiffen it up in the turns. Shocks still set mid-way.
-Scotty

 

[bjt]

20 front, 30 rear since about day three. Has worked real well, and helped stiffen it up in the turns. Shocks still set mid-way.
-Scotty

dltang and I do the same, 20 and 30.

 

[SpyderMark]

Tire Preasures: What are you setting them at ? :chat:

There's label on the left side of the Spyder's swing arm with tire information. It reads:

UP TO MAX WEIGHT CAPACITY:
FRONT: 15 +/- 2 psi
REAR: 28 +/- 2 psi

Tire pressure should be checked/adjusted before riding while the tires are cold.

There has been much discussion about whether or not signficantly changing the tire pressure materially affects the function of the Vehicle Stability System. The manual reads:

!WARNING!

Tires that are not the recommended type, damaged, worn down below the minimum tread wear limit indicator or improperly inflated can cause loss of control.​

Regards,

Mark

 

[AMTJIM]

I have 28 up front and 25 rear...felt too gooey at 20 up front.

 

[NancysToy]

There's label on the left side of the Spyder's swing arm with tire information. It reads:

UP TO MAX WEIGHT CAPACITY:
FRONT: 15 +/- 2 psi
REAR: 28 +/- 2 psi

Tire pressure should be checked/adjusted before riding while the tires are cold.

There has been much discussion about whether or not signficantly changing the tire pressure materially affects the function of the Vehicle Stability System. The manual reads:

!WARNING!

Tires that are not the recommended type, damaged, worn down below the minimum tread wear limit indicator or improperly inflated can cause loss of control.​

Regards,

Mark

IMO 15 up front is too low, and 15 minus 2 psi would be below the rated minimum for the tire, as printed on the sidewall. I know what their engineers say, but I am more concerned about what the tire manufacturers say. let's not forget the Ford Explorer mess. More comfortable erring on the side of caution. As far as vehicle stability goes, more pressure seems to have helped the Spyder, rather than hurt. No problems with VSS kicking in thus far.
-Scotty

 

[Twodog185]

I set my front up to 20 also. On several occassions it felt like the fronts were rolling over on the sidewalls. I'd rather go through more sets of tires than pull one off the bead in the turn. The back has washed out too, but only on 2 or 3 occassions. No change on the rear though.

 

[Trypod]

Adjusted my front to 20 psi and rear to 32 psi today. Went for 60 mile test ride on a few curves, straight roads, traffic....and experienced a lot less tire "roll" on cornering steering seems a good bit more responsive. After I got back home pulled it in the garage and checked the tread. The contact area stops at the corners of the tire tread now and none over the edge toward the sidewall. I think I've found my tire pressure "comfort zone" and don't plan on adjusting the shocks from 3 setting for now as the ride seems to be just stiff enough for me. Happy :spyder: 'in. Oh, and Happy Independence Day!!!!!!!

 

[WaltH]

Currently, I am doing 25 front and 30 rear. It seems to be working just fine.

 

[Way2Fast]

Been running 20-22 front and 32 rear with shocks set one up from midway. Factory pressures are way too low unless you want a bump free mushy ride, poor gas mileage and like to buy replacement tires on a regular basis !

 

[SpyderMark]

Factory pressures are way too low unless you want a bump free mushy ride, poor gas mileage and like to buy replacement tires on a regular basis !

On what do you base this claim? I would assume BRP took the time to test the tires chosen at different pressures to determine the best compromise between performance, ride quality and tire mileage.

I've read many articles about the fuel saving benefits of higher tire pressure; in theory it sounds good, but in practice you may gain three percent (maybe one mpg for us Spyder ryders). BTW, that three percent gain is comparing recommended pressure to twenty percent under-inflation -- I've yet to find any research claiming gains in fuel mileage from OVER-inflating your tires. Google "tire pressure vs fuel mileage" or read this.

There are many downsides to over-inflating your tires, and while there are SOME benefits, those benefits are usually only applicable on a race track. From what I've read, the experts agree the BEST compromise between performance and safety is to follow the manufacturer's recommendations. This article covers the issues pretty clearly.

My research shows that over-inflated tires can lead to premature wear as quickly as under-inflated tires. I've also learned that tire inflation affects sidewall stiffness and the size of the contact patch, both of which affect a vehicle's performance. A too-stiff sidewall will not allow proper "give" and could result in a tire "bouncing" over permutations in the road instead of it riding over them while remaining in contact. Obviously, if your tire is not in contact with the road you have NO traction; how would that affect performance?

My assumption is BRP conducted testing and selected a tire pressure to suit the weight and expected side loads generated by the Spyder. The pressure chosen ensures the tire flexes and maintains the optimum contact patch for optimum performance and tire wear.

I'm not saying BRP is infallible, obviously mistakes are possible. Given the issues, tire inflation is most definitely a safety item; I'd like to know my tires are properly inflated. Are you privy to data that says BRP's tire pressure recommendations lead to poor performance and premature tire wear? If so, please share your source.

Regards,

Mark

 

[NancysToy]

On what do you base this claim? I would assume BRP took the time to test the tires chosen at different pressures to determine the best compromise between performance, ride quality and tire mileage.

I would hesitate to assume anything. Vehicle engineers recommend pressures based on numerous factors, including ride comfort. The Ford Explorer tire recall, and subsequent change of the recommended tire pressures for that vehicle, is a classic example of getting it wrong. In this case, there is adequate reason to wonder, since the BRP recommendation includes pressures below the minimum stated on the tire sidewall! I certainly would not recommend running pressures outside the tire manufacturers requirements, no matter what BRP engineers may have recommended.
-Scotty

 

[SpyderMark]

I would hesitate to assume anything. Vehicle engineers recommend pressures based on numerous factors, including ride comfort.

Right, which is why I asked for DATA. If someone knows for sure BRP's testing (or lack thereof) is flawed as regards their tire pressure recommendations, please share the DATA and the SOURCE.

In this case, there is adequate reason to wonder, since the BRP recommendation includes pressures below the minimum stated on the tire sidewall!

I would argue BRP's recommendations on tire pressure SEEMS appropriate given the relatively light weight of the Spyder. I haven't actually looked at the sidewalls to confirm, but I would guess these tires are capable of carrying a great deal more weight than they do in this application. The number on the sidewall tells you the minimum allowable pressure when the tire is carrying its maximum load. I would estimate the Spyder's front tires are carrying 350 lbs or so when loaded to maximum capacity.

From this article, Oscar Pereda, an engineer for BFGoodrich, offers a rule of thumb for a "realistic starting point" to determine an appropriate tire pressure for a given vehicle.

(Vehicle Weight in lb/100) + 2 psi at heavier end + 2 psi all around if suspension and alignment are stock.

Example: Stock Porche 911, 3,000 lb.
(3000/100) = 30 psi
Add 2 psi all around = 32 psi
Add 2 psi to heavy end = 34 psi at rear

IF the Spyder had four wheels, we would get:

(800/100) + 2 + 2 = 12 psi (the front is the heavy end)

The denominator in the forumla represents the four wheels. Since the Spyder only has three wheels, I'll subtract 25% from the denominator and re-apply the formula. In this case we get:

(800/75) + 2 + 2 = 14.7 psi

Based on this rule of thumb, BRP's recommendation for front tire pressure doesn't seem too far off the mark to me. (I'm not sure how they arrived at the rear tire pressure, but I assume -- there's that word again -- it has something to do with sidewall flex under acceleration and is based on performance testing.)

The Ford Explorer tire recall, and subsequent change of the recommended tire pressures for that vehicle, is a classic example of getting it wrong.

I know some vehicle manufacturers in the past (Ford most notably) have based tire pressure recommendations on factors other than vehicle performance and safety, however, I find it difficult to believe BRP would make the same mistake -- especially in light of the decision to incorporate the VSS. THAT decision tells me BRP is VERY interested in vehicle safety (and presumably avoiding litigation).

My biggest concern regarding tire pressure is, in fact, the VSS. This safety system assumes the Spyder will roll over or slide should you exceed specific, measured performance parameters (forward speed, steering angle, acceleration, etc). The formula used to make that assumption must include some physical constants (gravity, vehicle weight, the known laws of physics, etc). I don't know for sure -- and BRP is certainly under no obligation to tell us -- but it stands to reason one of those constants is the expected, specific traction performance of the tires. The VSS can only work if the tires generate grip within a certain range. Too much grip and the Spyder will roll over before the VSS intercedes; too little and the Spyder will slide before the VSS intercedes.

I can think of no way the VSS could measure and account for changes in the expected traction performance of the tires on the fly. The fact that BRP warns the VSS does NOT work when traction conditions are changing (snow, heavy rain, off-road) reinforces my belief. Again, if someone has DATA, please share!

With the Spyder's safety systems seemingly relying on known performance from the tires, I would hesitate to disregard the manufacturer's tire pressure recommendations based on an opinion. I would absolutely LOVE for someone to prove my assumptions wrong -- then we can all go and play around with tire pressures, brands, sizes, etc until our wallets explode. Absent hard data though, I prefer to err on the side of caution...


Regards,

Mark

 

[SpyderMark]

I would argue BRP's recommendations on tire pressure SEEMS appropriate given the relatively light weight of the Spyder. I haven't actually looked at the sidewalls to confirm, but I would guess these tires are capable of carrying a great deal more weight than they do in this application.

I actually went out and looked at the front tire sidewall on the wife's Spyder. Now that I've practiced what I preach, here's what I found out...

On the tire's sidewall, Kenda says the max load for this tire is 386 lbs. The Spyder's max vehicle weight is 1240 (800 + 440 = 1240). Assuming 50 to 60 percent of that weight is on the front wheels, each wheel would be carrying between 310 and 372 lbs. I used the following formula.

((MAX WEIGHT X PERCENT = WEIGHT ON FRONT)/2 = WEIGHT CARRIED BY EACH FRONT WHEEL)

(1240 X .5 = 620)/2 = 310
(1240 X .6 = 744)/2 = 372

So that means I shot my mouth off in my earlier post without checking the information first... Yes, I know, assumptions are bad!

Kenda prints a minimum of 15 psi on the sidewall; BRP says 15 +/- 2 at all weights. At 13 psi you would be 2 psi below Kenda's stated minimum tire pressure... with the tire carrying the majority of its maximum rated load... hmmmmm.

This seems like a question best directed at BRP and Kenda. Since I made such a fuss over following manufacturers' recommendations I'll attempt to get some answers for everybody.

Regards,

Mark

 

[Way2Fast]

In the 46 years since I was issued a drivers license I have always followed the recomendation of the tire manufacturer...the info printed on the side of the tire...as to inflation pressure, and have always run it at or near the maximum. Other than a couple of nail induced flats, I have never had a tire failure.

At 15lbs front the Spyder "plows" into corners and the ride feels soft and mushy. With 20 -22 lbs the steering is more responsive, the ride a bit firmer and I'll gladly welcome the mpg increase, even if it is only slightly improved. The tires on my Spyder do not hold pressure as well as those on other vehicles I have owned. They seem to loose a few pounds every couple of weeks and I have to top them off. Those who start with 15 lbs might be surprised what the actual cold pressure is when they get around to checking it.

Richard

 

[Buelldog]

I agree with shocks set midway and front tire pressure at 15psi.....cornering felt real sloppy with a feeling of front end dive......set my front shocks to 5.....rear shock to 7.....increased front pressure to 17.5.....rear to 30 and I am now real happy with cornering stability......in fact I really would not want it much more responsive as it hugs corners as if on rails.My tires are holding pressure....zero bleed off from week to week.I agree it would be great to get BRP'S feedback on their tire pressure recommendation as this topic just won't go away from many spyder forums....it's time to get the facts and put it to bed!:read:

 

[SpyderMark]

Those who start with 15 lbs might be surprised what the actual cold pressure is when they get around to checking it.

:hun:

I thought you were SUPPOSED to check the pressures cold... Am I missing something?

Regards,

Mark

 

[Way2Fast]

:hun:

I thought you were SUPPOSED to check the pressures cold... Am I missing something?

Regards,

Mark

Of course you check the pressure "cold". Where did I say differently?

 

[smokster]

Penske shocks, 20 front, 30 back