Finally got to take the Spyder out, the "feels like" finally went below 100. Hadn't checked the tire pressures in a while. Normally kept 18 F and 20 R on auto tires. Everybody saying 16 & 18 are great. When I checked the pressures on the TPMS, they were about 15.8 F and 17.5 R. Close enough. Found out it had a shimmy up to about 45 - 50. As the tires heated up, shimmy eased up. Going to go back to 18 & 20.
Air pressure ( psi ) can't balance an un-balanced tire .....Nor can it un-balance a balanced tire. ....Air pressure doesn't cause or fix, " shimmy ". I have successfully Drag Raced my Spyders at 12 psi REAR with 45 psi FRONT, these amounts are way more disparate than yours. And I had no issues with Shimmy. ..... Mike :thumbup:
:agree: . As most here would expect, I gotta agree with Mike on this Baron, your tire's air pressure isn't likely to be the '
cause' of any shimmy you're experiencing at either pressure! :lecturef_smilie:
But without seeing/feeling them & maybe doing a few other checks on them, I'd
guess that by earlier running your front car tires at 18 psi, ie. a pressure that's most likely too high for the (light) load your Spyder places on them, your tire's contact patch was concentrated in the middle 2 inches of the tread except when cornering fairly hard, so you've probably at least started an adverse sawtooth wear pattern on one or both of the outside edges of each of those front tire's treads.... :gaah: . Then when you ran these tires with dodgy wear patterns at a lower pressure (marginally
under the suggested 'good for most' 16 psi up front) for the first time the whole of the tread face contact patch was actually touching the road surface for most of the time (as it should
) and that 'shimmy' you felt was feedback from the sawtooth wear on the outside edges of your tires created by the dodgy wear due to the previous over-inflation! :sour: . And then as the tire heated up after ryding on it for some time (as it should and
needs to do to some degree) the tire carcass expanded (probably heating up a little more than strictly ideal.... cos it's pressure started out a bit lower than ideal
) and you were once again left running on a narrow strip of tread down the middle of the tire, leaving the sawtooth wear on the edges barely in contact with the road surface and reducing the 'shimmy' feel again!! :shocked:
Now that you've started that adverse wear pattern on your tires, you'll never really be able to change it much (at least not without some extensive running at dangerously low pressures; or by getting the tire tread shaved down so that it's all even & your tire's & their treads are properly shaped again - loosing a bunch of tread depth & therefore tire life in the process!
) so that even if you do continue running a more appropriate 16psi from here on in, you'll
still probably hafta put up with that shimmy until the tire warms up each time you ryde, maybe for the first 10-15 mins or so of each ride... but at least you'll be getting the most life out of whatever tread you've got left on those tires
and you'll be running on a much safer to ryde on width of contact patch that's close to as wide as the tread face! So I reckon that's what
I'd be doing - running the 16 psi up front & putting up with the 'shimmy' for the first bit of 'warm up the tire's' ryding to minimise the tread wear & let your tires work as best they can for your ryding safety!
hyea:
However, if you choose to go back to running that too high 18 psi up front, not only will you likely be running mainly on an unsafely narrow strip of tread down the middle of your tires, you'll also be accelerating the dodgy tread wear down the edges of your tires
as well as increasing the wear rate on the middle strip of tread that's the only bit of tread face touching the road surface for most of the time! All up, you'll likely get less shimmy, but it'll be at the cost of not so safe ryding and an accelerated tread wear rate on your front tires!! :yikes:
Just Sayin'
. From what you've told us, that'd be my guess about what's happening & my musings on how to get the best from whatever tread you've got left. But it is your ryde & they are your tires.... :thumbup:
