Buggy tyre pressures

[Tiger37]

What is the advice on Kenda midi tyre pressures please?

[jhn.holgate]

I think I run about 15 - 18psi in my midi's. 8 - 10psi in the bigfoots - a bit more if you're on a smooth surface and you want to get rid of some of the wobble. And somewhere around 18 - 20psi in the barrows or a bit more. That seems to work ok for the surfaces I generally ride on (I tend to be on the side of comfort rather than speed). I usually like a little bit of 'give' when I stick my knee into the tyre.

[Tiger37]

I think I run about 15 - 18psi in my midi's. 8 - 10psi in the bigfoots - a bit more if you're on a smooth surface and you want to get rid of some of the wobble. And somewhere around 18 - 20psi in the barrows or a bit more. That seems to work ok for the surfaces I generally ride on (I tend to be on the side of comfort rather than speed). I usually like a little bit of 'give' when I stick my knee into the tyre.

Thanks John. Am new to midis having barrows on my PL. Recently bought Johnny's Sysmic S2 and started with 20psi which was great on ovals in Canberra but will let them down a bit for beach runs. Down the coast at Broulee this weekend.

[Slartibartfast]

I crank my Kenda BeachRacers pretty hard generally running 30-35psi. I find that if I let the pressures drop too much they start 'beating' at high speed, as in you start feeling a rhythmic bump-bump-bump as they turn. I see no advantage to running soft tyres so I reckon you might as well pump them as tight as you think they'll handle

I know some believe low pressures offer better traction but I'm not convinced, so I say "Go Hard"

[Clive]

I run my kendas at about 10-12, as Slartibartfast suggests you could run them harder, but I've not found any issues with them at the lower pressure at 70 Khr, however on my other bug a homemade one I did on the front, I actually put this to frame design and strength as it doesn't thappen on the libre at all.

Of note the front tyre isn't a kenda but a duro, if I pump this up to 15psi it swells and rubs on the plastic guard, so I'm guessing the manufacturer hasn't allowed for high pressures on their tyres.

The beach racer type tyres are " balloon tyres and will swell accordingly, MIDIs are a harder tyre, my suspicions are slightly more pressure than beach racers, a little softness gives a nicer ride for me, if you are of the heavier variety maybe more pressure helps.

It's all suck it and see what works for you.

What speed did you notice cavitation Slartibartfast ?

[jhn.holgate]

My Kendas say 'do not exceed 36psi when seating bead'. I take that to mean that they're not designed to run at that pressure Still, you've had yours pumped pretty hard for a while and nothing's exploded yet..... fallen off and gone rolling down the beach, yes, but exploded, no.

edit: ps Clive, mine start getting a little wobbly around 50kph at low pressure.

[Slartibartfast]

What speed did you notice cavitation Slartibartfast ?

Cavitation? Do you mean the "beating" I was talking about?

I'm not quite sure what speed it comes in at as it kind of creeps up on you but you start to wonder "what on earth is that?" I'd guess that at perhaps 40-50km/h it becomes noticeable. It's no doubt similar to the experience people have when they put thorn protecting slime in there tyres. I first noticed it on the Kingston clay pan and thought there was something seriously wrong with a wheel. I went back and noticed one of the tyres was significantly down on pressure so I gave them all a good whack with the compressor and was amazed at just how much better the buggy ran

I'm not sure what the pressure was down to but possibly 10-15psi or something. It looked fine to the eye but if you pressed it you could definitely feel the lack of pressure. Other than suspension is there any reason for running low pressures? Personally I'd much rather suffer the bumps and take the gains of reduced rolling resistance

On a different note I know it's recommended to let the tyres down on a 4x4 whenever you drive on sand but this is for reasons that really don't apply to kite buggies, mainly because we have "rolling" wheels as apposed to "driving" wheels. Essentially what we care about is sideways traction where as a 4x4 cares about driving traction. Also you know, we aren't trying to make 2 tons of steel 'float' on soft sand

[Clive]

The "beating" you describe, was this the front or rear tyres?

[Tiger37]

Well I've certainly opened a can of worms! As usual it all seems to be down to personal preference. However, I looked at my Kenda midis and interestingly on the tyre it has printed "maximum pressure 28psi"! Looked at Popeye the Welder's website and there is a similar interesting discussion but people in UK are debating between 8 and 15 psi.

[nigel]

Cavitation? Do you mean the "beating" I was talking about?

I'm not quite sure what speed it comes in at as it kind of creeps up on you but you start to wonder "what on earth is that?" I'd guess that at perhaps 40-50km/h it becomes noticeable.

I think you might find it's because the wheel is out of balance.

My barrows tend to go a little nuts once you hit 50kph, but settle a bit the faster you go.

It still causes the buggy to be a little jumpy though.

If your on sand, go back and find your tracks, if your tyre marks go wider then narrower and back to wide, this is a clear indicator that they are out of balance.

Balanced wheels will have a two fold effect, they will provide a smoother ride (safer), and as a result, allow you to push harder (more speed ).

[RedSky]

I recently had my local tyre fitter mount my BR's onto my new DWT atv racing rims. I balanced them myself and was surprised to find out just how out of balance they were. The Beach Racers were out of balance somewhere between 80 or 90g, but shockingly the thinner, and some may argue, better quality eurotrax bigfoot up front was out by 220g

I used to run fairly low pressures and at the moment use cambered bolts, which I much prefer for traction. The tyre fitter pumped the BR's very hard. I haven't checked the pressures but I suspect they might offer better rolling resistance. If and when the big winds return, I'll opt for a non cambered setup and high pressure for chasing PB's.

[jhn.holgate]

Nice looking rims, Tom. I see that the rims are available here but what I can't find is the bearing holder - what's that sort of hub called and where do you source it from?

[SoutherlyBuster]

Slarti, interesting, low pressure and beyond a certain speed the vibrations come on, then increase the pressure and vibrations reduce. I am suspecting the natural frequency of your tyres are at play here. Increase the pressure, increases the stiffness, increasing stiffness means the natural frequency also rises (frequency approximately equals root of stifness divided by mass), so the vibrations come on at a higher speed.

What Nigel says makes sense as well, there is a sweat spot of frequency when the vibrations like to get excited, so once you pass that frequency and go faster, the problem goes away until you reach the next mode (assuming you didn't destroy your structure whilst passing through the first natural frequency -- oops).

[RedSky]

Nice looking rims, Tom. I see that the rims are available here but what I can't find is the bearing holder - what's that sort of hub called and where do you source it from?

Thanks John,

You need DWT rims 8x8 - 4/115 + Trelgo hubs 20mm.

After much homework I found suitable trailer hubs here in the UK. They called Trelgo hubs and come with 20mm bearings, spacers and caps. http://www.trailertek.com/acatalog/Hub_Assemblies.html (scroll down 11th picture)

If you can't find similar or they won't ship, then I will ship them to you.

I'm certain you'll find some closer to home. Aus/NZ are the trailer capitals of the world. The Trelgo hubs are 4/115 bolt pattern, so make sure your DWT rims are also 4/115 bolt pattern before buying.

When they arrive throw the caps away, they're useless, you'll never get them off once you hammer them on. Instead get some ITP chrome center caps 4/110/115. Don't get 4/110 as I did. I had to velcro mine on when they arrived.

Get your local tyre fitter to fit the tyres. They're nearly impossible to fit yourself. The DWT rim specs say 8x8 but in actual fact they're 8x8.5. I hope you get these wheels as I'd love to see someone else with them.

Here are some pictures to tease you.

http://i1370.photobucket.com/albums/ag2 ... 1275be.jpg

http://i1370.photobucket.com/albums/ag2 ... 9ef404.jpg

[jhn.holgate]

Many thanks, Tom. Looks like you only need one per rim - but I assume there is a bearing in each end? Will have a look around although a Google search doesn't reveal much down this end of the world - maybe there'll be an equivalent here. Not in the market for them just yet but it's nice to know there's other options out there. The bug looks awesome btw

[Chook]

On my beach racers 21x 12, I run 4 psi in the front on a 4" rim and 3 in the rear on 8" rims.

The 21 x 12's need plenty of detergent on them when seating them and a fair bit of pressure on sysmic rims or they don't seat evenly.

It took me a couple of goes to get each one to run true. I fit them to the buggy which is on axle stands and then spin up the tyre with high pressure air gun to check for trueness. Make sure you true them before the detergent drys as they are hard to break the bead when dry.

A trick in breaking the beads on sysmic rims is pump them up to 5 psi and break the bead without letting them down. Once you have one side broken. Lube it up with detergent (no water) and then reinflate the tyre and do the opposite side. Works a treat.

This works well for quad bike and lawn mower tyres too.

I use a wall mounted bead breaker in my shed. Just jump onto the handle and they crack the bead.

At these pressures for racers, it smooths out the ruts nicely on my local beaches. On big kite days I put 6 psi in the front.

Sysmic S2 on midi XL's at Yeppoon, I run 12 psi all round. Helps soften out the sting ray holes.

[RedSky]

Many thanks, Tom. Looks like you only need one per rim - but I assume there is a bearing in each end? Will have a look around although a Google search doesn't reveal much down this end of the world - maybe there'll be an equivalent here. Not in the market for them just yet but it's nice to know there's other options out there. The bug looks awesome btw

Yes, yes and thanks!

[Clive]

I crank my Kenda BeachRacers pretty hard generally running 30-35psi.

On my beach racers 21x 12, I run 4 psi in the front on a 4" rim and 3 in the rear on 8" rims.

Yep anywhere from 3 psi to 35 psi seems to work.....

[Goz]

Sysmic S2 on midi XL's at Yeppoon, I run 12 psi all round. Helps soften out the sting ray holes.

Stingray holes aren't too bad, it's those little washouts that are 1 ft wide and 2 ft deep that wreck you

Running them a bit on the soft side does help alleviate the damage to the back. Usually my Midi XL's are around the 15 psi mark.

Tried barrows once, but I near peeled the tires off the rims on my first slide with a bit of pace.