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Old 10-26-2010, 11:33 PM   #1
DRONE OP
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Front tire pressure

Being new to hacks, I've asked around about front tire pressure. Everybody I talked to has basically suggested running the air at about the same pressure as on a bike. In other words--high! I'm not sure I understand this.

I understand about contact patches and friction and whatnot on a leaning motorcycle. But on a hack the front tire doesn't lean. This means the front tire basically has the same job to do as a car front tire--steering and braking. That said, it seems I should run my front tire softer than on a bike in order to increase the size of the contact patch. My screwed up logic suggests this will result in better braking and steering, and improved mileage too.

I'm not talking about ridiculously soft so that you risk damaging the rim. I'm talking about softer than HARD. Like on my GSA, the recommended 2-up front tire pressure is 36 lbs. So why not run it at around 26 lbs?

Some of you guys who are wearing out tires real fast right in the middle of the tread, wouldn't you get better performance and more mileage if you bled out some of the air?

I suppose this discussion applies to the rear tire and the sidecar tire too, for that matter, since none of the tires need to lean. Like I said, I'm new to hacks, so please explain why my logic is messed up. I'm forgetting something, right?
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Old 10-27-2010, 06:38 AM   #2
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I've wondered about this myself and surely an expert will chime in. Maybe a softer front tire coupled with the slight tow-in of the sidecar tire allows some sort of ying yang affair causing a wobble. I was told that by slightly adjusting front tire air pressure that the wobble could be nearly eliminated. After I did trail reduction with the triple trees the wobble was gone so now no need to fool with it.

Haven't seen pics of your rig on here!!!

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Old 10-27-2010, 06:51 AM   #3
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Great Question DRONE.

Im all ears on this one

On our gsa sidecar In the dirt we run
24 in the front
the rear 25,
and 15 in the sidecar tyre.

On the tar we run
35 in the front
the rear 35
and 20 in the sidecar .

The same psi as tar for rocky tracks

It seems to work out ok for our sidecar .

But i think every sidecar set up would have different settings .

It would be interesting to hear what others run.

Cheers Ian.
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Old 10-27-2010, 06:53 AM   #4
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I`ve found on my Urals that if the front tyre pressure is too high,the front wheel will 'tuck in' or skid sideways when pulling away from junctions especially when turning right...on mine,that is turning away from the sidecar.

I used to run the fronts at about 34psi-36psi but they are better at 30psi-32psi.

I run the sidecar tyres at 34psi-36psi and the rears at 40psi-42psi.

Many Urallists seem horrified that I run such a pressure on the rears,as they all seem to have been advised to run at around 28psi but the bike feels like a marshmallow at that,and my pressures feel and work just fine for my useage.

Bear in mind that the Urals are running with narrow 4.00x19 tyres and not fat low profile ones.
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Old 10-27-2010, 09:20 AM   #5
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More Information ?

This is a subject that has been a constant in sidecar circles for as long as I've been involved. When using motorcycle tyres in times past, i.e. tyres size wise not unlike used on modern Urals, it seemed fine to use pressures close to solo recommendations. A few pounds increase perhaps for increased loads.

Now we have a more complicated situation, with much wider bike tyres, and certainly very different profiles and rubber. To add to the dilemma, there's the complexity of using car tyres ranging from relatively narrow stuff of ancient French 2CVs (125 x 15") up to modern mega wide, low profile car tyres.

The spectrum of opinions on tyre pressures has become confusing. Personally, I operate on what some would view as on the high side with the three different sized car tyres fitted to our outfit. This stems from advice from Dutch guys back in the early 80s. In comparison, I know of others who run similar tyres to me operating on pressures that appear way too soft.

Would be nice to hear some objective guidance, possibly taking into consideration things like weight on each wheel, volume within the tyre, or such like.

For what it's worth, I'm perfectly happy with the pressures I use, but would appreciate objective views for doing otherwise.
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Old 10-27-2010, 10:38 AM   #6
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Just to clarify the initial question, I'm asking about motorcycle tires on a sidecar outfit, not automobile tires on a sidecar outfit. The effect of air pressure on the automobile tire contact patch I think is pretty well understood.

FWIW, the front tire on my GSA mounts to a 2.5x19" tubeless rim. I'm currently running a standard 110/80/19 motorcycle-type tire.
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Old 10-27-2010, 10:44 AM   #7
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Like Sidecar John said this topic has gone on just about forever. Franly I do not think there is any definate answer as all outfits will vary somewhat as will driving conditions and driving styles.
So much does depend on what tires are being run also.
Many of the guys who run th e195 car tires on the front are saying they run low air pressures to help curtail the tire's tendancy to follow road inperfections and grooves. Others say no to this....go figure.
Those running more conventinal bike type tires on the front also differ in opinions from time to time. Some say that too little pressure will cause a headshake whille other say just the opposite. I am not so sure either camp is right or wrong as personal experience has seen both work or not work...lol.
Yes, too much pressure will usually prompt an understeer situation in turns away from the sidecar with the power on. But...too little can have a similar effect.
All in all I kinda feel that if one starts out with whatever pressure is indicated on the side of a given tire and then is diligent to experiment some he or she will mabe come upon what is best for their own situation.
There may be some absolutes related to sidecar setup etc but tire pressure is not one of them.
Lot of words to sday nothing huh?
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Old 10-27-2010, 10:46 AM   #8
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Quote:
Originally Posted by DRONE
FWIW, the front tire on my GSA mounts to a 2.5x19" tubeless rim. I'm currently running a standard 110/80/19 motorcycle-type tire.
Bear in mind that you may well get weird effects due to the more rounded profile of a traditional bike tyre,as opposed to the slightly (or very) squared profiles of 'traditional' sidecar tyres like the Ural ones and Avon SM tyres and car tyres.

Also any effects created due to the load rating....many solo tyres aren`t sufficiently load rated for a combo.

Do you have leading links or other trail reduction,because if not,any effects felt may not actually be due to tyre pressure per se.


This is assuming that you`re having problems of any kind,instead of just thinking too much about a problem that doesn`t exist.

The simple answer to the complicated question is to experiment with your own tyre pressures,then study changes in handling,fuel economy and tyre life ....and select what is best for you.
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Old 10-27-2010, 10:54 AM   #9
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Quote:
Originally Posted by Tarka
I`ve found on my Urals that if the front tyre pressure is too high,the front wheel will 'tuck in' or skid sideways when pulling away from junctions especially when turning right...on mine,that is turning away from the sidecar.
This sideways skid you describe is what got me thinking about this in the first place. I've only driven my rig once (from the seller's house to my house - a 1500 mile trip) and I skid twice on right hand turns--once on dirt in Oregon and once on pavement in Nevada. In both cases it felt like the front wheel just couldn't get enough grip so inertia simply carried the rig towards the outside of the turn. I think we call this "understeer." No oncoming traffic either time, and I recovered before going off the shoulder both times so no harm no foul.

Maybe I didn't have my load optimally configured, and maybe with a little front brake I could have loaded the front tire and got more grip, but I'm a noob and IN ANY CASE I want more grip on that front tire!
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Old 10-27-2010, 10:58 AM   #10
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Originally Posted by Hackpirate
Haven't seen pics of your rig on here!!!

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I bought it used, so if I posted pics, they would be pics of HIS rig, not MY rig. I'm working on my mods now, and will post pics when my initial round of pimping is finished. I can report, at least, that I've given her a name.
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Old 10-27-2010, 11:01 AM   #11
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Quote:
Originally Posted by DRONE
This sideways skid you describe is what got me thinking about this in the first place. I've only driven my rig once (from the seller's house to my house - a 1500 mile trip) and I skid twice on right hand turns--once on dirt in Oregon and once on pavement in Nevada. In both cases it felt like the front wheel just couldn't get enough grip so inertia simply carried the rig towards the outside of the turn. I think we call this "understeer." No oncoming traffic either time, and I recovered before going off the shoulder both times so no harm no foul.

Maybe I didn't have my load optimally configured, and maybe with a little front brake I could have loaded the front tire and got more grip, but I'm a noob and IN ANY CASE I want more grip on that front tire!

My examples were when moving off from stationary and crossing a road in order to ride away from the junction or filling station.

I don`t have that symptom or problem while riding bends in the road.

If you have a right hand sidecar,and given your inexperience in combo riding,it may simply be that you were not fully confident in taking the 'worst type' of corner where you are turning to the sidecar side...if you`ve backed off the throttle,the sidecar will try to overtake you and make you go straight or wide.
You should be gently but progressively powering into the sidecar side bends.

Toe-in and lean-out settings can make a massive difference in this area,too.

Much more so than tyre pressures.


You certainly don`t want to be loading the front tyre or hammering the front brake in corners and certainly not in sidecar sided turns.
That`s a good way of learning real pain by flipping the combo when the front tucks right under.
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Old 10-27-2010, 11:02 AM   #12
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Quote:
Originally Posted by claude
All in all I kinda feel that if one starts out with whatever pressure is indicated on the side of a given tire and then is diligent to experiment some he or she will mabe come upon what is best for their own situation.
There may be some absolutes related to sidecar setup etc but tire pressure is not one of them.
Lot of words to say nothing huh?
I wouldn't say your words say nothing. They kinda say what I was hoping to hear. Which is--after experimenting around with it I should decide for myself what's the best pressure for me and my rig.

Great advice!
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Old 10-27-2010, 11:11 AM   #13
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Quote:
Originally Posted by Tarka
If you have a right hand sidecar,and given your inexperience in combo riding,it may simply be that you were not fully confident in taking the 'worst type' of corner where you are turning to the sidecar side...if you`ve backed off the throttle,the sidecar will try to overtake you and make you go straight or wide. You should be gently but progressively powering into the sidecar side bends.
Yup, pretty sure that was the noob mistake I made both times. Came into both turns hot, road surface turned slicker than the previous 100 curves (oil on the asphalt; mud slime on the dirt), backed off the throttle, then started to drift . . . Oops!

But still only two major mistakes is not too bad for my 1st 1500 miles -- all on back roads! They wouldn't call it a "learning curve" if you didn't make a few mistakes along the way. That's how we learn, right?

Nevertheless, there's nothing wrong with trying to figger out ways to get more grip because mistakes DO happen.
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Old 10-27-2010, 11:21 AM   #14
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Quote:
Originally Posted by DRONE
Yup, pretty sure that was the noob mistake I made both times. Came into both turns hot, road surface turned slicker than the previous 100 curves (oil on the asphalt; mud slime on the dirt), backed off the throttle, then started to drift . . . Oops!

But still only two major mistakes is not too bad for my 1st 1500 miles -- all on back roads! They wouldn't call it a "learning curve" if you didn't make a few mistakes along the way. That's how we learn, right?

Nevertheless, there's nothing wrong with trying to figger out ways to get more grip because mistakes DO happen.



Heh heh...gotcha!


We`ve all done it and we may well do it again some time.

And the weird thing is,whenever you do go in too hot,there`s ALWAYS a vehicle approaching in the opposite direction which is in EXACTLY the spot where you`ll cross the road if you don`t make it round.

Which is why I feel it vital to learn how to fly the chair on command and be happy and confident doing so.
That will remove the novice fear of the chair lifting which makes them back off the throttle in sidecar sided turns.

Take it easy and practice,practice practice...but well done up to now and above all,ENJOY.
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Old 10-27-2010, 01:31 PM   #15
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Quote:
Originally Posted by DRONE
I wouldn't say your words say nothing. They kinda say what I was hoping to hear. Which is--after experimenting around with it I should decide for myself what's the best pressure for me and my rig.

Great advice!
You also may find that if you keep experimenting you will find that as your experience grows what you felt was ' perfect ' early on may change later. You may also find that you will vary tire pressures dependant upon loads and other factors.
The front end breaking traction is not uncommon when going from a dead stop and making a turn away from the sidecar, especially on surfaces that do not provide much traction to begin with. This does not mean that you must back all th eway off the throttle. A little finesse goes along ways when throttle control is the issue....especially on powerfull machines.
Have fun and as mentioned by others..P R A C T I C E.
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