Tire pressure recommendations

[BoilerAnimal]

I've been trying to find info to support the 18-20 PSI argument for a real car tire on the rear of a Spyder. This is the best I could do. The last sentence is particularly interesting.

This is from a pdf file downloaded from www.lehmantrikes.com/assets/docs/uploads/Manuals/techbook-master.pdf

THE IMPORTANCE OF PROPER TIRE PRESSURE-TECHNICAL ARTICLE WHAT IS THE CORRECT TIRE PRESSURE FOR MY TRIKE?

There has been a lot of confusion and misinformation out there when it comes to tire pressures for trike riders. Most all trikes have a motorcycle tire up front and automotive tires in the rear. The motorcycle compliance label has a recommended pressure for both the front and the rear tires. Now that your motorcycle is a trike are these still the pressures to use? Since we are trying to clear up the confusion and misinformation… the answer is yes and no! Let me explain more fully. We, Lehman Trikes, have always recommended that you maintain the same pressure the motorcycle manufacturer lists on the compliance label for the front wheel. There is no reason to change this pressure. That’s the “yes”. The “no” is a bit more involved. First of all, the two automotive tires like those installed on the rear of your trike are a completely different design than the single motorcycle tire they replace. Now for some history. Lehman Trikes has been building and riding trikes for 25 years. Our founder, John Lehman, and many of the dedicated trike riders that work here have experimented for years trying to find what air pressure in the rear tires gives you the best ride, handling and tire life. What they found and recommended for years was an air pressure in the 20 to 22 psi range worked best. So why, if you look at a current Lehman Trikes Owner’s Manual or the Owner’s Manual for a H-D Tri Glide, do you see a 26 psi recommendation for the rear tires? When I came to Lehman Trikes several years ago one of the things I was asked to do was to confirm with the manufacturer of our tires that they would support our recommendation of 20 to 22 psi air pressures for our application. What I learned is that no tire manufacturer will recommend anything less than 26 psi for standard automotive tires.

Where the 26 psi number came from is an interesting and somewhat involved story. There is a regulatory organization called the Tire and Rim Association (T&RA) which, of course, standardizes specifications for all different applications for tires and wheels (rims). One of the things that they provide is a load carrying capacity for each tire size at different air pressures. In their old reference books they listed load carrying capacities for tire pressures all the way down to 20 psi. I don’t know what year they changed but in 1999 they still listed load carrying capacities down to 20 psi. Do any of you remember the big public fight that went on between Firestone and Ford Motor Co a few years ago? As I recall, people were rolling over in their Ford Explorer’s and Ford and Firestone were vigorously pointing the finger at each other. The final out come was that it was determined that people were reducing the air pressure in their tires to improve ride quality. That would not have been a problem but they failed to increase the pressure when the vehicle was more heavily loaded. As a result, the T&RA elected to eliminate the lower pressure ratings from their reference books. In support of the T&RA, the tire manufacturers will not support running their tires at anything less than 26 psi. So how much difference does it make? Why not just run them at a higher pressure? Running the rear tires on your trike at a higher tire pressure has a dramatic impact on how the trike rides and handles. For each additional psi of pressure you increase the rigidity of the sidewall. At maximum pressure the sidewalls of your tires are quite rigid. Rigid sidewalls will increase the occurrence of the low speed “head shake” inherent in all three wheeled vehicles. They will also transmit more of the bumps in the road to you and your passenger. As you reduce the tire pressure it allows the sidewall to provide additional “cushioning” when riding over irregularities in the road surface. Certainly you do not want to reduce the air pressure too far because that will adversely affect the handling of the trike.

The “cushioning” effect of the sidewalls is, of course, reduced if you are using a tire that has very little sidewall. For example, those 18 or 20 inch rims that look so cool on the back of your trike do all the wrong things for ride comfort and low speed head shake. A standard 15 or 16 inch rim with a properly sized, properly inflated tire will give you the best ride quality and the least amount of head shake. The most commonly used tire on the rear axle of a Lehman Trike is the P205/70R15. As a point of interest, in the 1999 T&RA reference book it lists a load carrying capacity of 1146 lbs for a standard P205/70R15 tire with 20 psi of air pressure.

[missouriboy]

The above touches on a point I wanted to explore, but then the other thread went off the rails... sidewall flex.

It seems to me that all radial tires are designed to flex a little; that is the feature that differentiates them from prior bias-ply tires, and causes them to give their superior ride quality while delivering their optimal economy and safety. So............

I posit that the following statement is true, and could be a reliable guide to proper PSI for any radial tires, in any application (except 2-wheelers):

Inflate radial tires until the sidewall bulge appears the same as it would on the heavier vehicles the tire is intended for.

Therefore, weaker Kendas would require more PSI, car tires on a Spyder would take less. Right?

So I now ask whether you agree or disagree, and why? (Perhaps a YES/NO poll should be created, if there is enough interest.)

[Bob Denman]

There's a HUGE difference between a Lehmann conversion; and a Can Am Spyder.
Virtually nothing that they say applies to our bikes.

[AeroPilot]

"Therefore, weaker Kendas would require more PSI, car tires on a Spyder would take less. Right? "

Yes.

Beyond that generalization, your ryding style and requirements and biases are your choice.

I value longer wear life as we dont ryde agressively or need maximum grip. Any choice is a trade-off between wear life/ fuel economy and the "grippiness" or comfort of the ride.

Your ryde, your choice.

[BoilerAnimal]

There's a HUGE difference between a Lehmann conversion; and a Can Am Spyder.
Virtually nothing that they say applies to our bikes.

Bob, I don't want this to devolve into a pissing contest for ANY reason. I am fully aware that there is a difference between a delta and a tadpole trike. My intent was not a comparison of the two but rather to show what they had listed for the weight capacity of a comparable size tire that we use on our Spyders. That said, the performance of similar tires will be similar for a vehicle with the same number of tires.

I don't want this to be construed as a directive for mandatory tire pressure. Far from it. After all the vitriolic arguments back in forth between the different camps for rear tire pressure and the claims of "no science", I found this and thought it did lend credence to the 18-20 PSI point of view.

It may not be absolutely scientifically proven but it is the closest I've found so far, one way or the other. I did think that the mention of the weight carrying capacity of 1146 pounds for one tire was rather significant. That is more than the weight of an entire RT. Now throw in the extra capacity of two additional tires and you have far exceeded the carrying capacity of an RT.

[BoilerAnimal]

2dogs, if everyone shows at least a modicum of respect and maturity, this thread will not be like so many of late.

[2dogs]

2dogs, if everyone shows at least a modicum of respect and maturity, this thread will not be like so many of late.

I certainly hope so. Keep up the good faith.

[IdahoMtnSpyder]

Reading the Lehman comments I take it that tire manufacturers did not stop showing loads for pressures below 26 psi because lower pressures are not valid, it was because average Joe and Jill American did NOT keep the pressure up where it needed to be for the loads they actually were carrying. Not listing load capacities for pressures less than 26 was a defensive move on their part to offset people's laziness, incompetence, or ignorance in running the correct pressure for their situation.

I'm sure no tire manufacturer is going to come tell us that 18 psi is OK for a car tire on the rear of the Spyder simply because some idiot will take it to mean they should be able to run 22 psi safely in the tires for their baby-sized car. I wonder what Elio is going to be able to publish, with tire manufacturers consent, if and when they actually start production. What does Vanderhall say, or Morgan?

[bikerbillone]

There's a HUGE difference between a Lehmann conversion; and a Can Am Spyder.
Virtually nothing that they say applies to our bikes.

Spot on Bob Denman.

[IdahoMtnSpyder]

Spot on Bob Denman.

Bob has been long gone from the forum. You responded to a 3+ yo post.

[bikerbillone]

Whoops, should have checked the date, my bad.

[DGoebel]

I just want to say it's easier to set my digital tire inflator to 18 lbs and fill all three tires to that before riding and my non- kenda tires have gone three times farther now than my original rear kenda did. The fronts were still OK treadwise, but changing them smoothed out my ride.

[2dogs]

[Docster]

Yes, this again....

[Mikey]

LOVE IT!!

[Peteoz]

I just want to say it's easier to set my digital tire inflator to 18 lbs and fill all three tires to that before riding and my non- kenda tires have gone three times farther now than my original rear kenda did. The fronts were still OK treadwise, but changing them smoothed out my ride.

Yeah, I do the same now, DGoebel.....and I get a 15% increase in tyre psi after an hours riding, which is close to fitting the 4psi rule that Peter A and others refer to. I’m happy
Pete

[SteveLaoyster]

The above touches on a point I wanted to explore, but then the other thread went off the rails... sidewall flex.

It seems to me that all radial tires are designed to flex a little; that is the feature that differentiates them from prior bias-ply tires, and causes them to give their superior ride quality while delivering their optimal economy and safety. So............

I posit that the following statement is true, and could be a reliable guide to proper PSI for any radial tires, in any application (except 2-wheelers):

Inflate radial tires until the sidewall bulge appears the same as it would on the heavier vehicles the tire is intended for.

Therefore, weaker Kendas would require more PSI, car tires on a Spyder would take less. Right?

So I now ask whether you agree or disagree, and why? (Perhaps a YES/NO poll should be created, if there is enough interest.)

I also hope this thread stays clean. There is already good information here. Thanks BoilerAnimal. As for sidewall bulge missouriboy, I think that might get you in the ballpark. But knowing what pressure you are at and using the 4 psi rule is probably the best peace of mind for every rider. Thanks for the info everyone!

[canamjhb]

Far, far away and long, long ago, I heard of a way to make sure each tire under any application was aired up correctly. Makes no difference if the tire is on a 40' RV, motorcycle, trailer, or whatever. That guideline is that the tire should increase 10% in pressure from dead cold to operating temperature. Don't know the source and don't know if it's true, but sounds good.....

[PMK]

Far, far away and long, long ago, I heard of a way to make sure each tire under any application was aired up correctly. Makes no difference if the tire is on a 40' RV, motorcycle, trailer, or whatever. That guideline is that the tire should increase 10% in pressure from dead cold to operating temperature. Don't know the source and don't know if it's true, but sounds good.....

That seems very reasonable in that each type of vehicle weighs a much different amount than the others.

Myself, I always considered the 4 psi increase subjective to the vehicles weight and cold tire pressure.

A 10% increase on tires with cold pressure of 20 psi would see 22 psi hot.

A 4 psi increase on a cold tire at 18 psi still comes in at 22 psi.

A car tire at say 35 psi would show 38.5 psi vs 39 psi.

If we use a motorhome at say 60 psi cold it would be 66 psi vs 64 psi.

Granted small differences, but the 4 psi increase on the 18 psi cold tire is over 20% increase, on a light vehicle which to me seems excessive.

I have no formal training in tire pressure selection and found the pressures I preferred, on the roads I ride, based on stability, cornering feel, and ride smoothness.

It is accepted that tires with lower pressures will generate more heat. Also tires more heavily loaded will generate more heat. Payload, meaning a rider or riders, plus baggage, can vary a huge amount between two identical Spyders. This alone may find variances in what owners deem as a best pressure for them.

Chassis mods, such as swaybars or higher performance suspension, even subtle variances in how true the wheels are aligned when loaded with payload can induce more tire scrub, adding heat.

Possibly, if I feel motivated to get the gauge out after a ride, I can see how close we are to 10%.

[wingit3611]

bump

[Peter Aawen]

OK, at the risk of writing another epic tome, I've used the 4psi rule as outlined above on a whole range of vehicles and a whole range of tires over the last 50 or so years, and I've found that using the 4psi rule basically works across the board to get the best balance across the range of a tire's behaviour & performance... doesn't matter if it's heavy haulage truck tire, a thumping great off road tire, your mum's passenger car tire, or a tiny little motor scooter tire - aim for a 4 psi increase after an hours use & you'll get better performance across the board in every factor & feature & be very close to the optimal pressure for that tire in those particular conditions... and that's been confirmed by comparison to the calculations & testing done by a number of tire design & test engineers from a variety of tire manufacturers over the years too, some that I've worked for/with and some that I haven't. When you look for where all the lines reflecting changes in each factor of behaviour/performance as pressure changes on their charts, the place all the lines cross at is on or within a smidge of the pressure that gives that 4psi increase!!

Where it came from originally, I don't really know, but I first learnt it about 40 years ago from a 'tire guru' who'd looked after the tires for an international GP Race team back in the 50's & 60's, and since then I've seen it referenced & used in & by all sorts of companies & people... I even found a document written in the early 1890's referencing aiming for a 4psi increase after riding (a bicycle!) for an hour; and if you search you can find it referenced somewhere in pretty much every decade since! In most of the tire manufacturing company's that I've worked with/for, all the calculations & testing that goes into creating the charts & graphs they use to produce the tables of 'pressure for given load' that they publish often either hang off or are at some stage compared directly to the 4psi rule; lots of TPMsystems have settings that at a very basic level somewhere use the 4psi increase as a benchmark or trigger; many tire manufacturers & top level car racing teams either use it directly to help them 'fine-tune' their pressures or use it in their testing and development; it's been used widely either as a referenced factor or directly across pretty much all industries & activities that use pneumatic tires; and when I was a youngster, all the best tire companies & fitters used & recommended applying the 4psi rule to get the best from their tires.... And quite a few existing & reputable tire manufacturing companies still use &/or refer to it, some even still publish it for purchasers of their tires to use! For whatever reasons, it seems to me that it's probably only the last 20-30 years or so that the 4psi rule has receeded from the forefront of 'general knowledge' about tires in the passenger car using population; when I was a kid just about every tire fitter would either use it themselves when setting customer's tire pressures or they'd tell & help their customers in using it to get the best from their tires....

It works because it's based upon the changes that occur in the air that the tire contains while it's being used, so it doesn't really matter if it's the tire carcass flexing or the tread working, if the tire itself gets hotter, the air inside the tire gets hotter, either as a cause or as an effect, and looking for a 4psi increase allows a tested & proven standard change to be measured & aimed for. But if a particular user wants to target saaay fuel economy over tread grip/traction, they can (& some do) make an informed decision on aiming for saaay 2psi instead of 4. Want to enhance traction over tire life? Then they can aim for 6 psi. And since it's the air inside the bag (tire) that is actually carrying the load, it doesn't matter if it's a lightweight bicycle tire under your Spyder or a heavy duty M&S tire under your Spyder, aim for the 4psi increase & you'll be much closer if not exactly on the optimum pressure for that tire under that load to hit the optimum spot where all the lines on the chart cross!! The lightweight tire NEEDS MORE air in it to keep the tread on the road, the tire on the rim, & the rim off the road; while the heavy duty tire NEEDS a whole lot LESS air in it to allow it to flex & conform to the surface & absorb any road shocks & flex enough to reach it's ideal operating temp, cos the strength of the tread & sidewall is so much that any more air than results in that 4psi increase would have the tread not flexing at all & it'd be like riding on a steel railway bogie wheel.... and leave you either riding on a 1" wide strip down the middle of the tread cos the tire's blown up like an over-inflated balloon or you'll be cornering on the very edges of the tread with the rest of it lifted right off the road surface as the Spyder leans so much that it'll either skid off the road or maybe just play dead ants & flip over to lie on it's back rather than letting the sidewalls flex enough to keep the tread on & gripping the road during cornering!!

Dunno if I've answered all your questions, but I've got a large collection of bunf gathered during over about 40 years of study, including my own & others notes & calculations, essays, presentations, documents etc that address every point I've ever seen raised on this; I can't & won't reproduce it all here, but you're very welcome to come visit & go thru it to your hearts content (altho my Wife would dearly love to get rid of it all!! What possible benefit can I see in collecting musty 100 year old papers, stuff like the scribbles I made on the back of a lunch wrapper about the temp & air pressure changes that occurred while I was putting down 1000 miles in 12 hours on a circle track & skid pan more than 20 years ago, or the notes re other's tire pressures & tread wear that I made on our Spyder ryde last weekend!! )

[Cobwebs]

Wait till the new airless tyres hit the scene then we'll have some debate.Compressor values are going to tank for one.Kenda will probably skimp on the honeycomb.ssc_hidingsofa2.gif

[IanB]

I have a newly purchased 2017 F3-S with 4000km on it. I just changed the front tyres to Conti Premium Contact 2 tyres 175/55-15 and, based on many forum updates, plan to run these tyres at 16psi cold.
I'll wear out the stock Kenda rear tyre before replacing it with a car tyre. The Spyder F3 owners manual and service manual both recommend 28psi for the Kenda tyre. I see several updates mentioning 18psi for rear car tyres. My question is, what pressures are people running in the stock Kenda? I guess it would be somewhere between 18 and 28, but cannot find much on this.
IanB

[BLUEKNIGHT911]

I have a newly purchased 2017 F3-S with 4000km on it. I just changed the front tyres to Conti Premium Contact 2 tyres 175/55-15 and, based on many forum updates, plan to run these tyres at 16psi cold.
I'll wear out the stock Kenda rear tyre before replacing it with a car tyre. The Spyder F3 owners manual and service manual both recommend 28psi for the Kenda tyre. I see several updates mentioning 18psi for rear car tyres. My question is, what pressures are people running in the stock Kenda? I guess it would be somewhere between 18 and 28, but cannot find much on this.
IanB

From what I've learned on this Forum, the Kenda's are garbage weak tires - Period ..... I would stick with 28 psi for the rear ( only ) .....( for auto tires 18-19 psi works best )... there is no magic psi ( for Kenda's that will change the " Wear " outcome...... Mike

[mikthebik]

I had an order in at Tire Rack for the same Contis, but the shipment they expected didn’t arrive after 10 days, and then became ETA unknown. Changed to Yokohama Avids which were the only tire in the 165/60 or 175/55 range for the F3 available. They’ve been strongly recommended by one or more forum pundits, so am hoping their $20 per tire cost is worth it. They arrived yesterday, one day after ordering. I’ll go with 16 psi cold also, unless convinced otherwise. Still have brake flush/pads, front sprocket and the tires before the “new” lady comes off the stands for her first post delivery ride.