Almost sold my Tuscan due to poor handling! Fixed for £20!

[Chad speed]

My experience is that the steering arm length and outer wishbone position is completely independent of BS. The only important thing is the relationship between rack end location and upper and lower inner wishbone pick-up points. Again I recommend the book ' Race and Rally Car Source' by Alan Staniforth - it will all become clear.
Modern day Formula cars, F1 to F3 plus hill climb etc negate the BS issue by making the rack length the same as the upper wishbone inner pick-up points and locating the rack at the same elevation as the upper wishbones. Fine for a single seater, not so a road car.
Its a mine field and rather like tuning a piano in the case of the Tuscan

[Basil Brush]

Maybe you've misunderstood what I was saying, or I wasn't very clear.

I was referring to track rod length not steering arm length. The inner track rod end is in line with the lower wishbone inner pivot and the later post 2001 track rods are the same length as the wishbone. The problem is that the outer track rod end is much higher than the lower ball joint when mounted above the steering arm, meaning the track rod moves in a different arc to the wishbone. On bump, the horizontal effective length of the track rod shortens quicker than the wishbone, due to this angle mis-match, leading to toe in on bump.

This was changed on the sag by modifying the steering arms so the outer track rod end is mounted lower, making the track rod level and parallel with the lower wishbone.

[Phil Tudhope]

Don't spacers reduce the heat dissipation from the brakes? Or is there little conduction of heat into an alloy wheel?

Phil.

[Chad speed]

Basil Brush said:

Maybe you've misunderstood what I was saying, or I wasn't very clear.

I was referring to track rod length not steering arm length. The inner track rod end is in line with the lower wishbone inner pivot and the later post 2001 track rods are the same length as the wishbone. The problem is that the outer track rod end is much higher than the lower ball joint when mounted above the steering arm, meaning the track rod moves in a different arc to the wishbone. On bump, the horizontal effective length of the track rod shortens quicker than the wishbone, due to this angle mis-match, leading to toe in on bump.

This was changed on the sag by modifying the steering arms so the outer track rod end is mounted lower, making the track rod level and parallel with the lower wishbone.

Basil B, I think we are talking about the same thing - I think? probably a bit difficult for either of us to understand what we are trying to describe without a drawing to show us. What we realy need is a drawing with acurate dimmensions of the Tuscan front suspension geometry. Plotting every degree of say 3" bump and 2" of droop would reveal all.
Having driven the car a bit more today, a lovely blat to Goodwood at 7.00am, I think stability under breaking is improved as well around the twisties. Just that damn tram-lining and floaty feel when cruising in a straight line to sort.

[Full SP]

Chad speed said:

Just fitted some cheapo 3mm spacers to my Mk1 Tuscan as I was quite intrigued by this one and a little bit sceptical. Sceptical because its supposed to work for all tyre sizes and the intersecting point of king pin inclination and centre of contact patch most definitely changes if the rolling radius changes, as it does with different tyre widths and aspect ratios's (I have 225/35ZR18's).
The result? Well, round the twisties its much improved and inspires more confidence, it's almost even chuckable. But, and so far it's a big but, high speed wander and tram-lining is worse, as though the front toe settings are parallel or even toeing out (it may be worth looking at rear toe as well).

What is your geometry set up? And OF COURSE it's worth checking the rear geo (and not just the toe)

As per my previous posts, having correct tyre pressures and geo/ ride heights is a prerequisite for getting the best out of your Tuscan and 225/35 18 is the worst possible front axle set-up on a Tuscan. Thanks for taking our spacers idea and spending your money elsewhere. Really appreciate that Chad!!

When you get 235/40 18 tyres on the front (assuming your set-up is good) you'll find your car is where you'd hope it will be. Perhaps then you can drop us a cheque in the post for commission ;-)

Edited by Full SP on Monday 28th June 10:16

[dvs_dave]

In terms of suspension geometry, spacers alter scrub radius, nothing else. Too little or too much either way is not good. Generally road cars should be set-up to have a negative scrub radius, although not too much as then you then get a large imbalance of forces either side of the steering axis. Tyre width doesn’t affect the centre of the contact patch or the scrub radius. Tyre rolling radius/aspect ratio does alter the scrub radius.
See this wiki for a simple explanation.

In the case of the Tuscan, I believe it runs too much negative scrub, hence the darty steering over bumps and wobbly braking. The scrub radius can be tuned by adjusting the camber to reach a reasonable compromise, but to get it right without spacers means getting into undesirable camber angles. Running tyres that are too low profile (e.g 225/35’s as opposed to 255/35’s and 235/40's) makes the situation worse as it causes even more negative scrub.

Bump steer is a different matter all together, however an incorrect scrub radius can be confused as bump steer (the steering kicking and deviating from straight ahead), especially if the car already suffers from an amount of bump steer.

Edited by dvs_dave on Monday 28th June 12:09

[JR]

dvs_dave said:

In terms of suspension geometry, spacers alter scrub radius, nothing else. Too little or too much either way is not good. Generally road cars should be set-up to have a negative scrub radius, although not too much as then you then get a large imbalance of forces either side of the steering axis. Tyre width doesn’t affect the centre of the contact patch or the scrub radius. Tyre rolling radius/aspect ratio does alter the scrub radius.

I can see what the previous poster means. Unless the tyre is exactly vertical a change in tyre width will affect the centre of the contact patch and have a knock on effect on all of the angles. I do appreciate that in most cases this is bordering on splitting hairs territory.

[dvs_dave]

JR said:

.....a change in tyre width will affect the centre of the contact patch.....

Altering the width/profile of a tyre on the same rim does not alter the centre of the contact patch. How can it? To do so would mean that the tyre would have to be somehow mounted on the rim lop-sided?

A change in tyre profile however does bring with it a change in the rolling radius which has an effect on the scrub radius. E.g Between a 225/35 tyre (79mm) and a 235/40 tyre (94mm) theres an effective rolling radius difference of 15mm which when it comes to scrub radius could be the difference between good and bad.

[JR]

dvs_dave said:

JR said:

.....a change in tyre width will affect the centre of the contact patch.....

Altering the width/profile of a tyre on the same rim does not alter the centre of the contact patch. How can it? To do so would mean that the tyre would have to be somehow mounted on the rim lop-sided?

It'd be a lot easier to explain if I could master computer graphics. Try sketching out a view of the wheel, tyre and contact patch from the front of the car. If the wheel were vertical then the postiion of the contact patch would not alter but the wheel is not vertical and yes the tyre is 'lop-sided'

[dvs_dave]

JR said:

dvs_dave said:

JR said:

.....a change in tyre width will affect the centre of the contact patch.....

Altering the width/profile of a tyre on the same rim does not alter the centre of the contact patch. How can it? To do so would mean that the tyre would have to be somehow mounted on the rim lop-sided?

It'd be a lot easier to explain if I could master computer graphics. Try sketching out a view of the wheel, tyre and contact patch from the front of the car. If the wheel were vertical then the postiion of the contact patch would not alter but the wheel is not vertical and yes the tyre is 'lop-sided'

Yes you're ultimately correct, however at the camber angles typically used (-1 deg max) the effect is probably negligable. This opens another can of worms and we start talking about dynamic loadings, tyre squirm, how the contact patch moves around, and in the meantime the Earth stops spinning and the answer comes out at 42.

[JR]

dvs_dave said:

Yes you're ultimately correct, however at the camber angles typically used (-1 deg max) the effect is probably negligable. This opens another can of worms and we start talking about dynamic loadings, tyre squirm, how the contact patch moves around, and in the meantime the Earth stops spinning and the answer comes out at 42.

Which is why I originally said:

JR said:

I do appreciate that in most cases this is bordering on splitting hairs territory.

[MPETT]

Hi Everyone,

I started this thread to pass on my experiences with my totaly standard car with standard tyres (Toyo T1S) and a verified standard geo set up.

It has got rather technical in a short period of time. I actually want to learn about suspension design so I will read the quoted books with keen interest.

However, for the rest of us in simple terms, I have standard tyres/widths I added the spacers and now I am completely satisfied with the handling of my car. Without them I would have sold it because it scared me.

Cheers,
Martin

Edited by MPETT on Monday 28th June 22:07

[dvs_dave]

TVR owners are generally more technically minded than most.....they attract that sort. Any simple modification that promises big results will if course spark a technical debate as to how or why it works.....check the Speed 6 forum for proof!

[TOV!E]

Just fitted them and the affect is just mind blowing. Proper tyres on my car 225/35/18s.
All this tech stuff is doing my head in, they are less than £30 for gods sake.. How some of you spend money on buying these cars i will never know , you must be a f***ing nightmare to deal with..

[900T-R]

If there's any Dutch Tuscaneers who'd like to try them out I'll ask matt to stick a pair in an envelope for 'demonstration purposes'. I might be flat broke but it seems the £20-odd would be a good investment even though I don't have a Tuscan myself.

[TVR_owner]

Gob smacked......

[Full SP]

dvs_dave said:

TVR owners are generally more technically minded than most.....they attract that sort. Any simple modification that promises big results will if course spark a technical debate as to how or why it works.....check the Speed 6 forum for proof!

I would have thought that our layman's explanation of what TVR did to compromise the offset and how our solution reverses this compromise would be sufficient!! More owners confirming that they do actually work will undoubtedly prove the point. The deep technical discussion is of course valid, but not relevant to most, who, after all, just want their cars to handle better!

[s6boy]

Is there a link on the SP website? If so I'm not finding it.

[JR]

s6boy said:

Is there a link on the SP website? If so I'm not finding it.

Click on Full SP above your post...

[Hotwheels.]

MPETT said:

Hi Everyone,

I started this thread to pass on my experiences with my totaly standard car with standard tyres (Toyo T1S) and a verified standard geo set up.

It has got rather technical in a short period of time. I actually want to learn about suspension design so I will read the quoted books with keen interest.

However, for the rest of us in simple terms, I have standard tyres/widths I added the spacers and now I am completely satisfied with the handling of my car. Without them I would have sold it because it scared me.

Cheers,
Martin
ordered mine on fri, and can't wait to have them fitted as my car is also trying to kill me.

Edited by MPETT on Monday 28th June 22:07