marc_w Posted December 5, 2003 Report Share Posted December 5, 2003 Thought of something last night. With the weight bias of the truck - the tires aren't equally loaded. The fronts carry more weigh, obviously. They look 'squished' down closer to the ground. I'm not sure if it's just an illusion, but I'm basing this all off of the idea that diameter of the wheel is smaller up front, compared to the rear, at the same pressure. I'm not sure if a difference in diameter of a tire will effect the circumference as much as it obviously would for a 'solid' object. I put in 35psi up front, and I'm running around 32.5 out back. This brought the diameters of the tires closer to each other. (just eyeballing here, I didn't pull out the 32" micrometer. ;) ) I noticed "less" drivetrain noise this morning, when making those sharp low speed turns. Was it a fluke, or does this idea float? Link to comment Share on other sites More sharing options...
wutrbonc Posted December 5, 2003 Report Share Posted December 5, 2003 I think it was a fluke. In your theory if the front tire is a smaller diameter than the back then the front is spinning faster than the back at the same speed. The only problem is, if I am not mistaken, when you turn your vehicle the outside wheel spins faster than the inside wheel. My truck only makes the sound when I am turning, louder on right than on left. Link to comment Share on other sites More sharing options...
marc_w Posted December 5, 2003 Author Report Share Posted December 5, 2003 I hear ya... I was thinking along the lines that with the tires smaller than the front... when we take a tight turn, the front has to swing all the way around and take the long way, while the rears cut across the inside. With the front wheels already spinning more (theoretically), and then they have to travel more around the outside of the turn... I was thinking that puts some stress on the drivetrain. I'm not sure about how MUCH stress - depends on how tight the AWD system is. Enough to cause the groaning noise. In the past, I thought the reason you couldn't drive on asphalt or make tight turns with full time 4x4, was because of the stress between the pairs of tires... Like side to side - like I'd snap an CV joint or something. I was told a number of different ways that it's actually the link between the two axles - the transfer case, which takes the most abuse.. Link to comment Share on other sites More sharing options...
detjoe Posted December 6, 2003 Report Share Posted December 6, 2003 I see the front tires look'n low too, I am going to give it a try and maybe keep them 5psi over. Hopefully it will make the noise less loud i'll post the results. Link to comment Share on other sites More sharing options...
marc_w Posted December 6, 2003 Author Report Share Posted December 6, 2003 Cool... Thanks! I can say that mine was definitely quieter yesterday... I just don't know if it was having a 'good day' or not. There's a bunch of snow on the ground now, so it'll be a few days before I can really test it again. Link to comment Share on other sites More sharing options...
deezel Posted December 7, 2003 Report Share Posted December 7, 2003 I think increasing the front tire pressure does 2 things for us. It makes the tires easier to turn (steer) because the contact patch is slightly smaller. This reduces stress on the CV joints and thus, that low speed sharp turn noise. In the past I have increased front tire pressure to reduce power steering noise. I also agree with marc's theory of reducing the AWD noise by balancing front/rear tire diameter. You would think GM would account for things like this in the design of the AWD transfer case. But, I suspect that no matter how its balanced, the viscous coupling style t-case will always have an operating range where it makes some noise. After reading marcs post I went out and put my rears at 34 and fronts at 38 (was at 36/36). Going up in the front reduced the CV noise in low speed, sharp turns. Going up-front/down-rear seems to have reduced the slight groaning noise at cruise (45-60mph). I plan to try a little more tweaking with the front/rear pressure balancing to see if the AWD noise can be reduced further. Definitely some sharp guys on here! Keep the good ideas coming! Link to comment Share on other sites More sharing options...
pharmb Posted December 10, 2003 Report Share Posted December 10, 2003 I went out and put my rears at 34 and fronts at 38 (was at 36/36). Have you noticed you can feel every single hair-line crack in the asphalt with 38lbs in the fronts? Link to comment Share on other sites More sharing options...
deezel Posted December 10, 2003 Report Share Posted December 10, 2003 Have you noticed you can feel every single hair-line crack in the asphalt with 38lbs in the fronts? Its only slightly worse than at 34 lbs in front. The tires make a little bit different noise at higher pressure - they make more of a snap/crack/pop (rice krispies?) sound over road seams - but the feel in the cabin and steering wheel is not much different. Link to comment Share on other sites More sharing options...
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