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  #1972  
Old 01-03-2011
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I wish I had this much time on my hands.
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  #1973  
Old 01-03-2011
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Quote:
Originally Posted by Macca2801 View Post
While this is technically correct, it is VERY extreame example! The OP was about changing the speedo readout by changing tyre pressure a few PSI not 15-20 as you need to bag out (ie significantly alter the diameter) a SB Radial.
This is totally insignificant in correcting speedo from going from a 31" tyre to a 33" tyre as the OP was attempting to do. For this to be correct the 4 PSI (36-40)difference would have to equate to a 1" difference in radius...not going to happen.
Agreed - just wanted to illustrate the principle. Since the dependency is linear, to get 1.5% speedo error you need about 6mm variance in the tyre radius. No idea how much pressure difference it corresponds with: that depends on several factors. In practice I have never noticed any speedo variance based on tyre pressure.
But this is not what this thread is about, so I'll shut up now.
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  #1974  
Old 01-03-2011
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Well, it's more 32" to 33" in my case, as the originals were the 255/75R17s not the 245s.

As to the difference in height, I could see the change in height as they went up. Slow & small change, yes, but noticeable.

oh yes, the footprint is still 15-20cm long at 40psi, so tyre adhesion isn't affected that much. At least not by lack of contact area, the increased pressure making it stiffer & bouncier, however...?

Aaaaaaanyway... on the 50km trip to work today, 50km on the GPSr equated to 49.5km on the odo, so I have made ~0.6% difference in accuracy, (and I guess rolling diameter). At 40psi, I had ~1.6% error over 100km, at 38psi, ~1% error (over 50km). Will see how the trip back affects the estimate, tonight.

DBOR bullbar due to arrive tomorrow.
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  #1975  
Old 01-03-2011
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Quote:
Originally Posted by Banshee View Post
Well, it's more 32" to 33" in my case, as the originals were the 255/75R17s not the 245s.

As to the difference in height, I could see the change in height as they went up. Slow & small change, yes, but noticeable.

oh yes, the footprint is still 15-20cm long at 40psi, so tyre adhesion isn't affected that much. At least not by lack of contact area, the increased pressure making it stiffer & bouncier, however...?

Aaaaaaanyway... on the 50km trip to work today, 50km on the GPSr equated to 49.5km on the odo, so I have made ~0.6% difference in accuracy, (and I guess rolling diameter). At 40psi, I had ~1.6% error over 100km, at 38psi, ~1% error (over 50km). Will see how the trip back affects the estimate, tonight.

DBOR bullbar due to arrive tomorrow.
4 PSI is a noticeable difference in side wall height????? NOT A CHANCE, sorry...maybe if it was 0-4psi not 36-40 PSI.
But hey goodluck with it all, as pointless as it is, what you are probably reading is the difference in distance from one side of the road to returning on the other hahhah

You do know its shorter to travel around Aust anti-clockwise dont you hahah!!

Matt.
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  #1976  
Old 01-03-2011
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You may be wasting your time here...

For about every 7 degrees the temp goes up or down the tire pressure will change also by about 2 PSI.

So if you set your pressures at say 15 degrees outside temp; then start driving around in 30 degree temps the tire pressure could have increased as much as 4 or 5 degrees... Doh....

In the US and other very cold countries with heaps of snow etc, drivers are warned not to set their pressures in the garage but at a servo because they can see as much as 30 degrees diff in temp from inside the garage and day time running temp and the tires will be substantially under inflated... because the tire cools when they venture down the street.

So in short... if you’re stuffin about over a couple of PSI you’re wasting your time...
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  #1977  
Old 01-03-2011
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replaced the front speakers and tweeters with alpine component splits, in preparation for new head unit, sounds heaps better even with stock stereo. sound bar is fitted with rockford fosgate coaxial 6.5 speakers too....
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  #1978  
Old 01-03-2011
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Quote:
Originally Posted by Nemesis View Post
replaced the front speakers and tweeters with alpine component splits, in preparation for new head unit, sounds heaps better even with stock stereo. sound bar is fitted with rockford fosgate coaxial 6.5 speakers too....
Can you get decent sound out of the sound bar now Nem, or does it still crackle at anything over low volume?
I found 90% of volume comes from my front speakers and the soundbar do very little.

Might follow your lead, Im happy with the head unit and front speakers (for now) but interested in whether replacing the rear speakers balances the massive difference in sound quality between front and rear (suspect it might also be the amp as well)

Cheers
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  #1979  
Old 01-03-2011
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Default Rear Speakers

new rear speakers make a huge difference. Plus you can stuff the sound bar with foam for more improvement - that is next.
Just get speakers that fit right in, I used another brand and had to use adapter plates, and modify them as well. Good speakers though

Quote:
Originally Posted by Macca2801 View Post
Can you get decent sound out of the sound bar now Nem, or does it still crackle at anything over low volume?
I found 90% of volume comes from my front speakers and the soundbar do very little.

Might follow your lead, Im happy with the head unit and front speakers (for now) but interested in whether replacing the rear speakers balances the massive difference in sound quality between front and rear (suspect it might also be the amp as well)

Cheers
Matt.
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  #1980  
Old 01-03-2011
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head unit is the let down now, sounds heaps better at low to mid volumes, no crackle but at high volumes the head unit craps out, i run a sub i found that made the most difference to overall quality. make sure you seal up round the speakers with silicone, especially the sound bar, that makes a load of difference.
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