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MG MGB Technical - DIY Tracking Setting
|When replacing the rack I just used a stick between the wheels to set the tracking back to where it was previously. Now wanting to check it properly I fancied a DIY method.|
Can I run this past you and see if we can see any problems,
Mark a point on the inside edge of each front tyre tread 5" above ground and in front of the car.
Measure the distance between the points.
Roll the car backwards til the marks are now 5" above the ground at the rear of the front wheels.
Measure the distance between the points.
At 5" height the tyre is 20" across. Using the toe angle found from the BMC tracking figures of 1/16" to 3/32" at the wheel rim, this gives new figures to adjust to of 1/12" to 1/8" at 20" distance.
A rod or piece of wood with a steel rule taped to the end would make for easy measurement and the 5" height is chosen to allow free passage of this under the car. A helper would be needed to hold one end.
Any off-truth of the tyre and wheel should be cancelled by using the same point on the tyre (as opposed to measuring 2 different points without rolling it back). The greater size of the new measurements should make measuring slightly easier.
Any thoughts before the wife puts her overalls on?
|Rich, I've been trying to work this out for years and think that your idea might work. However, as you point out at only 5" above the ground measurement becomes a little critical and would be difficult to set accurately. If you get one of those telescopic aliminium clothes poles you could cut it to length so that it would be adjustable around the 20" length and it might just be possible to mark a centre point on it so that parallelism could be set. Lines scribed each side of this could then indicate toe in/out and it would be an easy matter to use this device between the rims. However it would be specific to one car only to suit the wheel combination. |
Now it is normal to check the alignment twice rolling the wheels by 180 degrees to take into account possible buckle etc. This could be achieved by using two sets of different coloured marks.
Whilst I accept that this method could work I wonder if we could develop it a bit further as it is a bit of a pain having to crawl underneath to do the checks unless of course you have access to a ramp.
|I used a method described in the archives of running two pieces of thin wire from the rear wheels to the front. I fixed them to the rear of the leaf springs and ran them flat against the outside of the rear wheels, at the same height near the wheel centre, to a pair of heavy car ramps in front of the car. The ramps (or whatever you have to hand) allow you to keep the wires taught and to move them to be parallel with the front wheels. Turning the steering to make sure you have the same gap between the wire and wheel on both sides, you can quickly adjust the tie-rods as required. I'll find out how valid this method is in a few thousand miles!|
|That sounds a pretty reasonable idea Steve it will also show up if the rear axle is offset from the front. However rear axle location is not exact being only located by holes in the spring insulator blocks and if it is slightly out of line say on one side only then the error will be multiplied considerably before it reaches the front. Perhaps this should be checked by measuring the wheel centre distance before carrying out this method.|
|FWIW - I've been using a gunson's Trakrite for the last 15 years or so on most of my family's cars. It's not expensive, is easy to use, and every time one of the cars is checked somewhere else they've always been either dead right or close enough. It's worth the investment imho.|
|Rich, Your method will work. I think the car should be rolled forward rather than back. It may be easier to stick some tape near the center of the tyre treads and mark an x on the tape. Measure between the center of the x marks to determine toe in/out. |
I use strings rather than wires as Steve suggested. It's pretty accurate if carefully done. The strings will indicate if there is a front to rear wheel alignment problem. As Iain said if the rear wheels are off center this method will not be accurate.
Another method that works is to use a plumb bob. Place an x mark on the tire tread at about center hub height on each front wheel. Make sure the wheels are pointed straight ahead and hang the plumb bob line over the mark center and mark the floor at the bob point. Do the other wheel and roll the car forward so the tire marks are at the rear of the wheel at the same height. Drop the plumb bob and mark the bob points. Roll the car enough to clear the marks and measure the distance the between the rear marks and record the reading. Measure the front distance and record. If the front reading is less than the rear the wheels are toed in.
After using a cheap tracking bar for several years I constructed a tracking bar from some 1" square steel tubing, 1/4" round stock, a flat bar 1/8" x 3/4" and some nuts bolts and a pop rivet. It works well without help and is accurate if the front tires are scribed and measurements made between the scribe marks. You can see the bar in my Yahoo photos, I hope you can open them. I use the buble level to check camber.
|Thanks for the input and ideas.|
I used a straight plank-edge from the rear wheels to set the fronts ahead when fitting the rack. Like the string, it's a good way to check overall alignment but i wonder how accurate it would be for setting toe-in as it relies on the rear wheels and tyres being true and the F/R track width is not the same on all cars.
Checking overall alignment is a good idea but toe-in at the front wheels is the only adjustment we can effect and is set independantly of anything else.
I'll try the original plan and report back. Will also take on board the ideas of doing it using 2 or 3 positions on the tyres and rolling forward and back to see how consistant it is and to see how accurately the measurement can be made. That amount should be easy enough to read on a steel rule scale.
Using the same point on the wheel for the front and rear measurement should overcome wheel buckle. They can't be measured at the rims (inside) as there's no path for the straight edge at the rear of the rim. Using a parellel position 5" up the tyre gives a greater measuring distance so should be better if anything.
I don't have ramps so will have to grovel as it's best to have the weight on the car rather than doing it jacked up as the tracking will vary due to the change of track rod angle.
|Rich; I thought the MGB has equal front and rear track widths, I was wrong. The figures I found with a Google search are rear 49.25", front 49". Not much but enough to make a difference. Since the rear is widest the string will work but would require measurements on the front and rear sidewalls of each front tire. Each additional measurement gives another chance for error creep. Let us know how your measurements come out.|
|Take great care on where the measurements are taken. This should not be on the tyre sidewalls but on the tyre seat portion of the rim. The tyre could be improperly fitted or have all manner of irregularities which would adversely affect the measurements. The tyre wall can however be used for chalk marking.|
|Another thumbs up for the Gunson Trackrite, although I wouldn't call it "not expensive". It's about £60 if I remember. I'm sure careful measurement works just as well. Rich, why did you roll the car backwards? Surely you should be rolling it forwards so the stresses and take-up of play mimics ordinary driving. |
With the Trackrite you actually drive the car, under power, slowly over the gauge and it instantly shows how much scrubbing there is on the tyre. Brilliant idea. You don't need to know the toe setting. You simply adjust until the scrubbing is eliminated.
|I borrowed Mike’s Trackrite and was so impressed I bought one. Very simple to use and very accurate.|
|I keep reading and rereading the archives and I still can't get my head around this toe in adjustment. I need to do it on my car since I have completely rebuilt the front end and steering rack and am fitting new wheels and tyres on it. Problem is I currently have the back end off for rebuilding so I have nothing to measure against. I'll just set the front wheels up parallel for now and figure it out when I get the back end done. I really want to find someone local with one of these Trackrite things. It sounds like the best way to go!|
|I suppose when you look at the cost of buying a Trakrite it isn't really "not expensive". But it will save its cost in two or three usages compared with the cost of a garage check. I now check my track at every service (it hardly ever goes out) and I don't have to worry anymore about the operator not doing a careful job.|
Well I tried it this afternoon with my daughter to hold the zero end and it works great. Measured forward of the wheels, back, rocked around, and forward again with complete consistency.
I thought the inside tyre edges were wearing which suggested toe out. I wasn't prepared for the amount though - 7mm toe out instead of 3mm toe-in!!
Reset, went for a short ride then marked both tyres in new random positions to recheck and it was exactly as adjusted.
I think the key to this accuracy is using the single point on each tyre for the measurement. It takes out any error from wheel buckle that may be present using even pro gear on the rims.
For measuring we just used a broom handle with a 6" steel rule taped to each end, and a cross of yellow tape stuck to the tyres, reading against the edge of the tape. For ease I converted the new toe in 1/12" to 1/8" measurement to 2 to 3mm and aimed to be just inside 3mm which was easy to achieve.
This time we played around for maybe 2 hours with the adjustment and drive round but, knowing how it's done, it will only take a few mins to recheck in future.
|What's the toe-in value to use with 15 inch wheels? I am guessing it will be different (slightly larger?).|
|Simon, Check across the tyre 5" up off the ground and I think you'll find it's still approx 20" across at that point so use 1/12" to 1/8" (2 to 3mm). The method is very forgiving in that area as it would only make a few thou difference even if was, say, 21" across.|
|Is there a specified angle for it? I haven't found on in any of my manuals.|
|Simon, Never seen an angle specified but you can work it out easily enough.|
The figures in the BMC manual are accompanied by a drawing which shows the measurement position to be on the wheel rim. I took this as 15" and used
SinAngle = 1/32 over 15 for one wheel.
That makes the toe-in angle for 1 wheel to be .12°-.18° = 7.2 - 10.8 minutes.
I used this angle to find the measurements at the tyre for DIY setting.
|Hi Rich, thanks. I knew I could/should work it out. Was just being lazy figuring someone else had already done it for me!|
This thread was discussed between 29/06/2005 and 03/07/2005
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