Changing Track Width (on my car - not a circuit)

[Woofly]

Technical Vintage Question

I have found a new front axle for my car (1922 Fiat)that has front brakes (probably a good idea) I have to weld up and redrill the spring mounts so that the centres are 28mm closer together but that will still leave the new track width 6.3" wider than the old front axle and the rear axle. Any suggestions on how this is likely to affect handling? I could narrow the whole thing but that would need a cut and shut on each side outboard of the springs and I woud also have to shorten the perrot shafts and track rod!

All suggestions welcome - before I cut up the axle , I told you so after the event will go straight to room 101

[zefarelly]

wider track will improve cornering, but thats not really the issue with a car of that age surely ?

you could always offset the rims . . . .some nice 20" Bazza racer alloys perhaps ?

[Woofly]

actually cornering is important particularly on mud and loose surfaces. This photo is very very rare - the hood is up (to protect the brides hair do) and its clean and shiny!. The car is entered for a sprint at Elvington in August and a week later is going to Ireland to compete in a couple of hill climbs. Principally it is a trials car. It has been very successful in the past and is currently being prepared for a bash at a number of trials this winter. This photo might be more useful for identifying FiFi when she is out and about:

[zefarelly]

ahh . . .well increased track at the front will help the stability no end . . .but be warned that it'll put more strain on the rear end probably, and if the performance is upped too much probably the chassis as well.

its a credit to you that the car is used properly, not fluffed up in a garage for sunny days only

[BugEyed]

Mike

Changing the track will not have a huge effect on handling. More significant effects will be things like the change in unsprung weight (presumably up quite a bit thanks to the brakes), the need to change the front wings (to cover the wider track), and whatever changes in the steering geometry occur (based on any differences in steering arm lengths and angles).

Do you have a cunning plan to control the location of the front axle under braking loads?

Duncan

[Woofly]

umm no! but niether did Fiat, these axles were fitted to the last of the 501's in 1925 / 26. I will use all of the track rods steering arms etc from the wider axle, that should solve steering geometry probs as the steering box did not change position from the early to the late cars.

Unsprung weight has gone up - I know from the effort required to pick up the components. I plan to use the braked front axle during winter for trials when the 4wb will really help especially descending muddy tracks. During the summer will refit narrow unbraked axle for sprints / hill climbs / DT's.

The wheels should mostly be covered by the guards (well they were when I left home officer, they must have spread!)

[BugEyed]

Mike

I'm confused (which isn't unusual ) about the changes in the 501 that resulted in the differences on the axle. Presumably the location of the front springs changed - did they spread the chassis at the front? Is the position of the steering box the same? Are the springs stiffer for the heavier axle, and could you mount those on your earlier chassis? Do you have a compensator mechanism for the front/rear brake balance, or do you plan to run uncompensated?

It strikes me that you need to fully understand the issues before changing the axles over. Alternatively you could change the whole chassis over.

Duncan

[Woofly]

Duncan,
2 things happened with the 501's (as far as I can work out). Fiat produced a colonial model that had a wider track (1400mm) and the springs mounted outboard of the chassis, these cars had braked front axles which cannot easily be fitted to the narrow cars. They also produce domestic market cars with FWB's on narrow chassis (ie standard width) cars. They then produced the 502 and 503 on which the chassis rails were 28 mm further apart at the front but in all other respects the same (same engine, gearbox, steering box etc). These cars used the 1400mm wide axles as opposed to the original 1240mm ones but had the springs conventionally mounted under the chassis rails. I have done a lot of research and can find no other differences - I have the springs and other bits off both axle types they are all the same.

The fiat brakes are cable operate from the cross shaft through the gear box. The actuating arms are exactly the same except there is a top one (for the rear) and bottom one (for the front) on each side on the late type and just a top one on each side for the early cars. I assume the different lengths of the arms is calculated to balance the load front to rear?

[BugEyed]

Mike

So your axle is effectively a 502-3 axle? Hence the difficulty of mounting it.

At least FIAT in their wisdom haven't bothered fitting compensators and different springs to further confuse the issue.

It doesn't look as if the axle has a specific "pad" to locate the spring on - just holes drilled to locate the bolts. If so, I think your first suggestion of drilling new holes is the simplest. However, if there are specific pads you could always chop the offending 28 mm out of the centre of the axle and re-weld it.

Duncan

[Woofly]

Yes Duncan, well done for being patient enough to wade through the obscurity of some of my posts - sorry they weren't intended to be like that. It is probably a 502 axle but at least its Fiat and save for the extra width is just the same as a braked 501 and its complete from hub cap to hub cap making it easy to change over with the unbraked front axle.

The axle does have pads but they are big enough to accomodate a 14mm shift on each side, BUT on reading the eligibility rules again I note that increasing the track makes my car a "special" and obviously this is undesirable unless I was going to upgrade all sorts of other things too. I think therefore the best thing will be to take 75mm out of each of the perrot shafts, 150 out of the track rod, 3 bits out of the axle (28mm out of the centre, and 61mm each side outboard of the spring mounting pads). All much more complicated than I first envisaged but at least it will all then look right. Please god it should all work once its together!

[BugEyed]

Mike

That is an awful lot of work to achieve your target, and personally I'd be worried about the integrity of the welds outboard of the springs given the loadings they'll receive. Could you not "just" swap the complete stub axle assemblies between the two axles or did FIAT beef up the kingpin assemblies when they went to a braked axle?

Duncan

[Woofly]

Duncan,

great idea, sometimes you get caught up following a simple idea as it gets more and more complex! I don't know is the simple answer whilst sitting in my office but I should be able to get a front axle (unbraked) and put it on the bench next to the braked one I have just stripped down for comparison. Probably not until the weekend but will let you know the outcome in due course.