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View Full Version : Slicks, What Air Pressure should I run?



Pumba
29th July 2008, 20:34
Hey, as the title says.

Managed to pick up a set for my FXR project, fitted them, and just wanting to know whats a good starting pressure to run them at, at Mt Wellington.

I was thinking about 20-25 PSI, am I wright or wrong.

gammaguy
29th July 2008, 20:41
as a rule of thumb when i race i look for a 4psi pressure rise from cold to hot.(when using air)starting as a baseline you sound about right but i have not raced a bucket for a loooong time.the seat of the pants counts for a lot too

CB ARGH
29th July 2008, 20:46
From what I have been told by a bird in a tree...

The lower the pressure, the quicker it heats up, and more of the wheel will be on the surface. However if it's too low, it will drag along the road, potentially slowing you down and becoming very poor with fuel economy. This is better for riding in the wet.

The higher the pressure, the slower it is to heat up, less of the wheel will be on the surface. However, the less drag it will have on the road, and potentially more fuel economic.

Don't take my word for it though. There's some smart guys on this forum who could help you a lot more, just adding my two cents worth though.

Churr!

STEVE

Ivan
29th July 2008, 20:49
Depends what tires you are running. Dunlops

are arpund 28 rear 22 front I think cant remember fully aint done tire pressure on 125 in ages

But I mean some tires using example here COnti Race attack 22PSI rear tire and 28 PSI front

Buckets4Me
29th July 2008, 20:50
I was always told that it is a psi or 2 above the presure that lets the tire slide easily:gob: or something like that
i would shit myself trying to find that point (i got this backwards it use to be you added pressure till they slid then backed it of 2 psi)


but am sure that they run 18-20 psi in the slicks at Mt wellington {bit more air when it is wet so the tire presses down threw the water}
it is a lot lower than for road tires like tt900's

then the fast guys on slicks are mad

just ask a few next time you are there they have a compressa just take a tire pressure tester with you
best to use your own and use the same one every time

SHELRACING
29th July 2008, 21:53
Hey, as the title says.

Managed to pick up a set for my FXR project, fitted them, and just wanting to know whats a good starting pressure to run them at, at Mt Wellington.

I was thinking about 20-25 PSI, am I wright or wrong.



Assuming you have removed the Tubes. Most riders run at 19 - 20 PSI. I've run 19 PSI at 3 different tracks and that works best for me.

The only problem you'll have is if you are still using tubes 19PSI is not enough to stop tubes moving and eventually punctures.

Got any pics of the bike ??

Buddha#81
29th July 2008, 22:05
i was running 24-26psi in slicks on my FXR, last meeting I was recomended to go up to 28psi front and rear and the bike felt pretty good.

I think below 20 psi you will be running into troubles.

nudemetalz
29th July 2008, 22:19
I run around 22psi front and 25 psi rear in the slicks on Lady P.

Pumba
30th July 2008, 08:21
Thanks guys, you have just confirmed what I already thought


Got any pics of the bike ??

No finished pics, still got to do a bit of tidying up with the wireing. Doesnt look to didferent from a standard FXR at the moment though

Buckets4Me
30th July 2008, 08:32
tubes 19PSI is not enough to stop tubes moving and eventually punctures.

heavy duty tubes for dirt bikes
dont ask me where you get 17's from
and also grinding the spokes down so they dont poke threw to far lol
and lots of rim tape's

come have a talk to every one next time
they will tell you all the secrets and where to get stuff from
cycletreds is always a good start and they are good with info 2

k14
30th July 2008, 13:08
On the RS125 I run between 27 and 29 psi in my slicks. I do the same on the bucket. I think 20psi is way way too low for one of those tyres (not that I have any proof of that though). I think if you run too low pressure it will effect both the handling and straight line speed, too much drag and the tyre is too deformed on the surface. If anything I would tend to run closer to 30psi on a bucket cause a RS125 is 30+kg lighter than my bucket. Each to their own though.

xwhatsit
30th July 2008, 13:18
heavy duty tubes for dirt bikes
dont ask me where you get 17's from
From what I've read (and seen people do), tubes seem to be pretty tolerant to being used as the `wrong size'. Plenty of offroad bikes out there with 18" rims -- I don't think using an 18" tube in a 17" tyre is going to be too much hassle.

F5 Dave
30th July 2008, 14:52
ok time for the definitive answer, and just to be a prick I'll finish with a question.

The chch guys are right for their tracks you run more pressure, the speeds are much much higher. I'd dispute the same as RS as the speeds are lower. At the BOB I was running pretty low pressures & the tyres were not marking up like they were working, but the 50 is very light (less than an RS) & it was stupidly cold.

At kart tracks you get away with running tyres too soft so they are actually deforming. Some of the light guys on 50s on old Yokos used to run 16psi! They ran tubes & threw them away often.

19-20 on Bridgestones seems good for me & I run a pound or so more on the Dunlops. Less if freezing cold.

But I'd also add a pound or two if you are, um how can I put this? :innocent: or your bike is a porker. Then try it, add & subtract & see what you like. Try & determine the diff between squirm & slip.

OK the question. . .um, no I don't really have one.

FROSTY
30th July 2008, 15:11
As per usual Dave beat me to it-
Short version-SLIPWAY AND MT WELLINGTON- start point 18psi front and rear.
Ruapuna and Taupo 22-24 start point.
Dug out my racenotes from way back when and on the Yoki sprints I was running 17psi at a winter meeting at mt welly
To remind this old man--Dave what happened when we ran trailbike rimlocks back in the spoked wheel days?
- I remember trying it but farked if I can remember the verdict.

F5 Dave
30th July 2008, 15:20
I think I did try when running a skinny steel rim at the rear. Decent size rim & problem doesn't exist as tyre not bowed. Inner tubes are dumb anyway.

gav
30th July 2008, 19:14
Hey, as the title says.

Managed to pick up a set for my FXR project, fitted them, and just wanting to know whats a good starting pressure to run them at, at Mt Wellington.

I was thinking about 20-25 PSI, am I wright or wrong.
What size tyres did you get? Have you got two fronts or a 125GP rear?

Buckets4Me
30th July 2008, 21:06
back to this question
as I understand it you need to worry about the tire heating up
so on a long fast track you run higher pressures 25-30 psi to stop
the tires overheating

and on a slow track (best speed i have seen is 90ish k/h)
you run lower pressures to heat the tires up
yes they do deform thats what heats them up

they need to be warm to the touch

I know at the last meating one guy tried 14 psi in his tires and they still wernt heating up (yes we did have hail and lots of it)

anyway good luck and ask soem of the good guy's
there are a few 600 racers out there they now a lot they are the fast ones
one of them was running wets in the dry last time trying to get them to heat up (he definatley wasent cooking them)

Pumba
30th July 2008, 21:12
Assuming you have removed the Tubes.

Tubes are still in. I was to cheap to take them to anyone and just did it with a few tire iorns at home


But I'd also add a pound or two if you are, um how can I put this? :innocent: or your bike is a porker.

Thanks for the info. We will say it the bike is on heavier side and it has nothing to do with my, eerrmm, solid build:apint: and put a couple of PSI in to compensate


What size tyres did you get? Have you got two fronts or a 125GP rear?

Front 95/70/17 and rear 115/70/17, Dunlops, couple of ex 125GP tires

gav
31st July 2008, 07:06
So you've mounted the rear on a standard FXR rim, 2.15 x 17? That tyre would work best on a 3.5" rim.

Sully60
31st July 2008, 08:41
So you've mounted the rear on a standard FXR rim, 2.15 x 17? That tyre would work best on a 3.5" rim.

Yeah, you'd be better off putting a front tyre(95) on that in reverse direction. The 115 is too wide for the rim and will give a squidgy feeling and you're likely to run of the tread much earlier and in a less controllable fashion.

dangerous
5th August 2008, 06:31
on all 3 buckets I run 27psi F&R never had any issues

enigma51
5th August 2008, 07:20
on all 3 buckets I run 27psi F&R never had any issues

Thats cause your dangerous! :)

Sully60
5th August 2008, 08:19
on all 3 buckets I run 27psi F&R never had any issues

You're a walking issue!

So what was the go on the BoB warm up lap, was that something other than a problem?:dodge:

k14
5th August 2008, 10:19
You're a walking issue!

So what was the go on the BoB warm up lap, was that something other than a problem?:dodge:
That was the thing sitting on the seat, nothing to do with the tyres.

dangerous
5th August 2008, 17:43
haha... farking wankers :rolleyes:

Ok so what presures would you guys reconmend on F4 and F5 bikes remembering 70% of tyres are on incorect sized rims and or to wide anyway?
(repost if already done so on previous pages)

Buckets4Me
5th August 2008, 19:46
i run slicks and wets on 2.5 and 3.5 laced rims

about 16-20 psi

short slow track
bit more at taupo 22-24 ish maby higher maby not will see

Pumba
5th August 2008, 20:01
So you've mounted the rear on a standard FXR rim, 2.15 x 17? That tyre would work best on a 3.5" rim.


Yeah, you'd be better off putting a front tyre(95) on that in reverse direction. The 115 is too wide for the rim and will give a squidgy feeling and you're likely to run of the tread much earlier and in a less controllable fashion.

Man the things nobody bothers telling you untill after youve done it :laugh:

It will do for now, you live and learn.

dangerous
5th August 2008, 21:00
about 16-20 psi bloody hell, that wont do the side walls any favours will it?

speedpro
5th August 2008, 22:19
I think with the sizes you have, rims and tyres, you are just going to have to suck it and see. At Mt Wgtn keep dropping them down till it starts tank slapping over bumps or some other misbehaving starts happening. Keep an eye on what the tyres are looking like. If they start working at 20psi then there is no need to go lower. Your rear tyre is definitely too big. I've run tubed TT900GP front 90X17 rear 100X17 at 18psi & 19psi respectively on 2.15 rims. 17psi and it was even more evil than normal and more than 1psi higher the tyres never warmed up. 23-25psi is a good point to be starting.

Buckets4Me
6th August 2008, 06:59
"bloody hell, that wont do the side walls any favours will it?"

you are trying to heat the tires up remeber
how els do you do it on a slow track :drool:

F5 Dave
6th August 2008, 16:19
I remember Pete Sales commenting about the bikes we were watching going around Palmerston North kart track & seeing the tyres noticeably deform in corners. "It's all wrong, but it seems to work on small light bikes at these speeds" I agreed. But I'd pump them up a bit on longer tracks & if running inner tubes you will notice they 'chaff'. Replace every 6 months.