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MG Midget and Sprite Technical - Negative Camber Top Trunnions

Does anyone have a Peter May negative camber top trunnion and is able to measure the dimensional offset between the king pin and trunnion bolt holes.
I believe a value of 1" should provide a 1 deg negative camber although on car measurements vary through range of suspension travel.
Thanks
S G KEIL

If I have remembered correctly the distance between top and bottom trunnion centres, 1 degree is approx 4mm.

If you want the precise measurement, to convert small angles (less than 6 deg) to linear measurement the magic number is approx 57.3 (which is 360 deg divided by 2 x pi). For most of our purposes for quick mental calcs 60 is close enough, as our measurement resolution is not precise enough to worry about the difference. In this example the difference between 60 and 57.3 is only a few thou linearly or 0.05 deg.

So if you want to calculate the exact offset rather than rely on my memory of what the trunnion to trunnion distance is (which would be most prudent!) then measure from the centre of the top trunnion to the centre of the bottom trunnion and divide that by 57.3 on a calculator or 60 if doing it in your head. The result is the sideways offset required to change camber 1 deg.

You can also use this method to measure your camber with a spirit level held vertically by the wheel, provided the car is on level ground.
Measure the offset from vertical between the top and bottom of the rim, divide by the distance between your two reference points, then multiply the result by 57.3 (or 60).
If the car has a lean due to tired springs or whatever you might like to jack the lower side a little to bring the chassis to level first.


Paul Walbran

Yep 1" is way too much, it'd be more like 0.1"per 1deg.
Nothing to do with midgets but. The old std type wheel alignment shims that we used to pack the Ford/GMH top arms were 1/8" 1/16" and 1/32" and they were roughly good for 1 1/2 and 1/4 degree.

willy
William Revit

Are you seeking to make your own negative camber trunnions?
Daniel

I have already made a number of sets of negative camber top trunnions based on the Aldon version that I would describe as suitable 'for fast road use' together with some current prototypes intended for use with increased size brake discs and incorporating a ball thrust race to replace the original bronze thrust washer.
It is the actual dimensional offset between the king pin and trunnion bush holes for which I was seeking clarification where the value is around 1" but may need to be marginally greater (1-1/16").
On car measurements over the total range of suspension movement (full bump to rebound) give much greater camber angles of up to 5 deg so difficult to ascertain at what ride height/angular position of lower wishbone the trunnion offset really needs to be established; probably with a normally loaded car complete with fuel, driver and passenger but will change with length and stiffness of coil spring.
S G KEIL

By the way my trunnions take poly bushes !
S G KEIL

Original negative camber trunnion prototypes with poly bushes and needle roller thrust bearing to replace standard trunnions together with comparison between avaiable units,





S G KEIL

Very interesting. I have a Frontline kit and Peter May negative camber trunnions and at the right height of my car, the negative camber is what I want.

For my car, in the pursuit of a small weight saving (albeit an unsprung saving), I plan on modifying the frontline top arm to increase negative camber to the extent where I can use the lighter standard trunnion.
Daniel

Found this stashed away, might help-? or not
looks like 1/4"/degree


William Revit

Daniel, do I understand correctly that you have the Frontline kit and the Peter May negative camber trunions on your car at the same time?
Isnt the Frontline kit alreadt 2 negative so isnt that enough or is your more negative by adding the Peter May trunions?
A de Best

Hi Arie,

What Frontline never understood, even though I told them so several times, is that their kit doesn't always produce the amount of negative camber they say it will (for various reasons). On my car the trunnion is raised relative to everything else in the suspension by a spacer that's required for a big disc conversion kit. So I do indeed use the Frontline kit and Peter May negative camber trunnions (fitted with Polyurethane bushes). Page 113 refers.

I forget exactly how much negative camber I have on my car (I don't think it's exactly the same each side) but I do have a camber gauge and will check it later this year since I have recently done a full front suspension rebuild.
Daniel

Hi William
Thanks for sketch however marked values cannot be correct at 0.250/0.375 and 0.500.
I would estimate a standard trunnion at 0.750" between respective hole centres however your values could be those of inside edge of bush bore to centreline of kingpin as I measure 0.25" for standard trunnion that I understand provides a slightly positive camber angle.
Could the sketch values relate to the increase in offset required to provide the 1, 1-1/2 and 2 degree negative camber angles i.e. 0.250"/degree.

Hi Daniel
Your use of double camber provisions for increased disc diameter is noted and for which I am actually seeking an offset dimension but for fast road although a variant for potential track use would be a useful value to cater for any possible situation.
What disc diameter, the modified Spitfire disc used with MGB caliper ?
S G KEIL

As you say, I agree these figures must be in addition to the std. measurement and relate to the amount of camber change for each measurement---unfortunately there's no mention of the std. measurement and the std. base camber would depend on the ride height of the particular car--sorry I can't help further, just found that sketch and thought it might be useful-----maybe
Cheers
willy
William Revit

I haven't got around to measuring disc diameter yet and might need a reminder.

In my stash of spare parts I have a single used Peter May negative camber trunnion which has been fitted with an offset bronze bush and drilled and tapped with a small allen grub screw (not what I had in mind but it was a favour). I was of course looking for something else when I found it. . .

Do you want to make me an offer to take it off my hands for a lot less than half the cost of a new pair?
Daniel

Hi Daniel, sorry for late reply, I was on holliday with the family and the famaly-classic.

Funny you mention that with the FL kit its not always automaticly 2- camber.
before Kconversion my 13 inch tyres would wear out more on the inside becuase of the position of the wheels (Michelin tyres)

After conversion to Kengine they dont wear out in that shape anymore or say hardly...
Change was also 14inch wheels but -2 camber is what it is so shouldnt change by just wheel size...?

No longer run the Michelin type tyres but Yokohama A... kinda forgot my the brand&type of my tyres on the midget.. im getting old! LOL

A de Best

After last lining out the wheels they found that the lhs is almost 2- and the rhs is 1-
Will see if I can find the lining rapport with the actual nr's.

Probably because the midget kissed the rail on the nurnburg Ring while therhs wheel was sticking out trying to manouvre out of the slip I was in..
Had to reline the wheel just by eye on the parking of the Ring before driving home. :(

I was lucky and so was the midget: a bit paintdamge, mirror broke off and a squecking wheel.
Only found out last year that one spoke on the minilite replica had a tiny crack too, must be from then I guess... its now my spare wheel in the boot.
A de Best

Yokohama A539
A de Best

This thread was discussed between 18/07/2024 and 22/08/2024

MG Midget and Sprite Technical index

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