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MG MGB GT V8 Factory Originals Technical - caster wedges, worth the effort & expense?
|recently in a topic regarding the wedges by Frontline, a topic related to the reduction of steering effort at speed was discussed. would someone explain the mechanics of these wedges and advise if i have a reasonable understanding. according to other research, 7 degrees positive caster (castor) is designed into the front thru the std. mounting of X-member & kingpin inclination. due to advances in tire technology, the caster is too much now and can be reduced to require less steering effort at speed. another article indicated a reduction of 3 degrees puts the caster at an optimum angle of +4 degrees. this is accompolished by the caster wedges available from Frontline. i believe the wedges install from the front of the X-member (reducing + caster). a discussion also indicated washers could be used to achieve this funtion and gave the specs to be used. |
i have a slightly heavier steering effort due to addition of 148# (Ford 5.0 V-8 EFI & P205-60-16 tires). the front gained 148# and rear lost 37# for net gain of 111#.
are the above statements correct?
|How much would you pay for an alignment on a modern car? How much do the shims cost? I imagine they could be installed in an hour or less. |
|the earlier discussion indicated the kit was 68 quid (whatever 68 quid is. no idea on conversion factor since the English pound is only listed in finanical news. one presumes that S&H plus the VAT would bump the price up. in the neighborhood of $60-$70 for 4 wheel alignment would a quess. the hour or two to change out is not unreasonable. would one omit the rubber pads and use metal to metal, or slip the wedges between the rubber pads? are there local suppliers or would this be sourced direct front Frontline? thanks for input|
|I seem to remember having the installation instructions for the Frontline wedges somewhere on my harddisk, I'll try and dig them out later today.|
Nearly bought them this summer but then again, will they make that much difference? (I'm running 185 width tires on 15x5.5" wheels)
|I've bought 2 sets (V8 roadster and GT) but not yet fitted them ( next weeek's job probably)|
They fit under the chassis rail,and tilt the crossmember backwards slightly, it looks like quite a simple job, just loosening the crossmember bolts, disconnecting the steering rack (it needs spacers to re-allign it) and slipping the spacers in, and tightening up.
The original mounting bushes stay on the cross-member.
The object of the exercise is to reduce the castor angle,
'The result gives a noticeably lighter steering, which does not load up or get heavier when cornering.You also get more feedback through the steering and improved directional control '.
Time will tell ....Frontline Costello have a very good reputation in the UK (it was Ken Costello we have to thank for the MGB V8 in the first place).
|Why do you need wedges?|
The front crossmember is held by two bolts perside.
The cross member sites on two rubber bushes each side, ie it's not in continous contact with the rail. Put in one spacer each side. Surely the rubber spacer will compensate for the slight angle?
|Peter, my thoughts exactly. The Frontline kit is beautifully over engineered. Two thick washers - one on each front bolt - should be all that is needed. You could even cut them from square stock to match the size of the bushings. If you made them thin, you could stack several to reach the desired caster angle. Anyone with a tinsnip could make them in a matter of minutes. |
By the way, reducing the cater angle will also reduce the car's ability to re-center the wheel after turning a corner AND will not allow the car to track as well travelling straight down the freeway. It a balancing act of finding the proper adjustment to achieve the handling characteristics you want. Stock is fine for weekend drivers, but autocross guys may want around 3 degrees.
|Kelly, here is a response I posted on another site that may add some more fuel for thought regarding the use of wider tires..or it might not...but anyway:|
The best way to minimize steering wheel effort without going to power steering is to make certain through the use of proper rim offset that the scrub radius is as close to zero as posible. "The What?" you say.
Well, if you draw an imaginary line between the center of the pivot points at the top and bottom of the kingpin (degrees from vertical of this line is the "kingpin angle") and continue this line down until it intersects with the ground - that exact point is where you want the center of the tire tread to be. That point should be equidistant from the inside and the outside edges of the tire. If that imaginary line intersects the center of the tire on the ground, then the scrub radius is Zero. If the intersection point is not equidistant, then the distance from the center of the tire to the point where the king pin angle intersects the ground is the scrub radius. By dusting off the old geometry text book you should be able to figure this out. All things being equal, the taller the wheel/tire combination, the more outboard it should be for the kingpin angle to intersect the center of the tire's contact patch.
I've never measured it, but I gotta think the MG engineers have it pretty close. The other suspension setting that can effect steering effort is Caster. Caster is the degrees that the bottom "A" arm is ahead of the top A-arm (OK... lever arm damper) when viewed from the side. Imagine that same imaginary line I mentioned above. When viewing that line from the front of the car, we see the kingpin angle. When viewed from the side of the car we see degrees of caster. More caster is what makes the wheels seek center and gives stability at high speed. Less caster reduces the effort at the steering wheel when you turn the wheel, but makes on-center feel vague and feels twitchier at speed. All well and good, but our suspension does not allow adjustment of Caster as far as I know. Someone please correct me if I'm wrong on the lack of adjustment.
Oh yeah, proper inflation and correct setting of toe-in should also help, as well as keeping the kingpins properly lubricated.
This should cover explanation with a few pics
The B was designed for skinny tyres, with a long narrow contact patch with high slip angles.
The modern wide tyre has a short wide contact patch and low slip angles. The rubber at this wide contact patch is difficult to twist.
The kit changes the castor to give better "feel" with the wider tyre.
|thanks for the additional feedback and info. since the 50 series tires have a wide footprint and negible sidewall flex; i will try the Frontline kit and see. They (Tim Fenna) has been very helpful; also provided additional material. these caster wedges costs $127 USD incl S&H. They also take credit cards so the exchange rate is handled in the transaction. may take a while to get time to install, but i will have a objective trial and note the results. anyone having questions can ck back with me later (Jan. 06?). |
thanks again for info.
|Paul, What a fabulous web-site that is, thank you for mentioning it.|
I've just bought a VR6 and wondered about the R32 engine, the english is a bit stilted (second language ?) but pics and explanations are excellent. (oh and the description of castor was clear too )
This thread was discussed between 08/10/2005 and 22/10/2005
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