Tony Posted July 2, 2007 Report Share Posted July 2, 2007 wim set this beast last week...... Which was hurt in the chassis. The owner phoned me on his way home and said "it's still vibrating".... I thought hang on he never said anything about vibration before..... Apparently one of his complaints was violent wheel wobble at 40mph..... I suggested he has the balance checked at a place local to him... Seemingly they had been balanced before but he would try another company just to be sure.... He did and the vibration remained. What was concerning was the low speed the violent vibration occurs 40mph... Wheel imbalance is a frequency easily absorbed by the suspension to 60 or 70mph especially on a beast like this.... Then i twigged the problem.... I phoned him and said.... "your wheels are aftermarket"........ yes.......... "and you have spacers"........... yes......... "are they hub-centric?"............. a what? I invited him back today and the problem is the spacers... Basically the spacers (male) inner ring needs to have a snug fit in the wheels centre (female) this ensures the wheel is located and not off-set as the wheel nuts are tightened... A simple solution.... He needs some of these. Quote Link to comment Share on other sites More sharing options...
Tony Posted July 9, 2007 Author Report Share Posted July 9, 2007 I spoke to the owner today and he now has "hub centric" spacers fitted and the vibration has gone But the car handles absolutely pants :angry: I've not re-measured the car yet although i think i know why it has problems. The scrub radius is incorrect. The wheel off-set and the SAI no longer correlate, meaning the tyre contact patch is to far inboard so acting directly at the steering during any perturbations... Subject to measuring i forecast one of two choices.... Remove the spacers or change the wheel off-set. Quote Link to comment Share on other sites More sharing options...
jon Posted July 10, 2007 Report Share Posted July 10, 2007 Surely changing the wheel offset to match that of the wheel + spacer would leave the car feeling the same as the spacer simply extends (well, reduces in numbers) the offset. Quote Link to comment Share on other sites More sharing options...
Tony Posted July 10, 2007 Author Report Share Posted July 10, 2007 Surely changing the wheel offset to match that of the wheel + spacer would leave the car feeling the same as the spacer simply extends (well, reduces in numbers) the offset. The spacers were fitted purely for looks not to accommodate wheel fitment If he wants to keep the spacers then he needs wheels with the correct negative off-set. Currently the scrub radius is inside of the steering pivotal point hence the poor handling. Quote Link to comment Share on other sites More sharing options...
jon Posted July 10, 2007 Report Share Posted July 10, 2007 Imagine the first of the 3 wheels with a spacer the size of the positive offset, this means the first 2 wheels would feel exactly the same as you've the same result through different means. If he's spacing the wheels out for looks then he'll always have the scrub radius issue unless he moves the hub? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 10, 2007 Author Report Share Posted July 10, 2007 Imagine the first of the 3 wheels with a spacer the size of the positive offset, this means the first 2 wheels would feel exactly the same as you've the same result through different means. If he's spacing the wheels out for looks then he'll always have the scrub radius issue unless he moves the hub? The scrub position is determined by an imaginary line through the steering pivotal points and true vertical at the tyres centre. The intersection of the two lines concludes the scrub-radius. Key: Red: True vertical Blue:SAI (steering axis inclination) White: Tyre Most modern cars have a zero SR. It is possible to change the SAI if the camber adjuster is on the lower wishbone. This in reply changes the position of the SR but with a consequence.... The camber will also change. By whatever method the SR needs to be within the steering pivot point and as close to zero as possible. Quote Link to comment Share on other sites More sharing options...
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