Sumo 3 light front end

[steve14]

I have recently purchased a Sumo 3 fitted with a Rover V8, all reports I've read say it should be heavy on the front mine isn't in fact it's unervingly light. It has Serria running gear with Spax adjustable shocks fitted all round. The rear end is set to the max neg camber setting (tried it on mid position and it feels awful to drive) but I'm not sure about the front it doesn't self centralise from full lock tho.
In short I get no feed back at all and it doesn't inspire confidence when I push it on a bit, I'm looking for suggestion from anyone to try and put it right maybe somebody out there has had similar problems.
P.S excuse my ignorance but whats steering bump? I've seen it mentioned in a couple of reports.

[TINKA]

Hi Steve and welcome to the club. I don't own a sumo so can't help on that side of things but bump steer is when because the front suspension is not set up properly in relation to the steering rack, when ever you hit a bump or the front suspension is compressed the wheels actually turn without you moving the steering. There are many posts on this subject with a way to cure this plus loads of other info too. Try using the search system, will keep you buisy for ages

[Noel]

Hi Steve,

What is your chassis number (it will tell you when the chassis was made, the first 4 digits after the letters "PS") after a certain date the bump steer issue was solved by Pilgrim and you can verify this by measuring the posts that the steering rack sits on. As I remember 10cm is the magic length. Look at posts made by Sidecarbod, he has investigated this at great depth.

If the steering is that light and it does not self centre I would guess that the tracking is way off, it should be set at 0 degrees toe-in and would be easy to rectify/experiment with.

Noel

[stevee8]

Hi Steve and welcome to the forum.

The Rover engine is very light so what you have read has probably related to cars equipped with Chevy or Ford V8's. Some Chevy / Ford Cobras are fitted with power steering because the front end weight with the wide tyres provides too much of a workout for the arms.
You probably have the standard Sierra rack which, in combination with the light engine, will give comparatively light steering. If you wish to have a heavier feel to the steering, there are faster racks (fewer turns lock to lock) which are available.
What tyre pressures are you running? - if they are hard at the front this will give a light feel. 18 to 20 psi should be about right. I initially had some lack of self centering but that seems to have eased off with a few thousand more miles use - how many miles has your car covered?
Otherwise it is dependant on the steering geometry setup and you will be a little limited on what you can do to adjust this out.
As Tinka suggests, a trawl through the site may yield some info but if not then let us know and everyone will try to help you get it sorted.

[dave]

Doesn't self centring have more to do with castor angle?
Check the top wishbones are on the right way around (If they are not symetrical).
Also check:-
Tyre pressures.
Camber etc.

[Sidecarbod]

The front end should not be overly light with a RV8 fitted, infact Pilgrim recon that this is the ideal setup with 50/50 weight bias. I bet that you've got toe out as this will make the steering very light and horrible!

I spent ages sorting out the bumpsteer on my car and it did make a big difference. If you've got a MKII then it will make any even bigger difference. I think that not all of the MKIII's had the Pilgrim mod which still isn't enough to fix the problem. I did tell them about the work that I've done but they did not seem very interested.

I believe that the MKII and early MKIII's have pillars that the rack sits on which are 120mm high, the late MKIII's are 110mm.

You need to cut another 8mm off either the pillar of the bottom of the rack. (Both is a bit of a pain on a fully built car but its DEFINATLEY worth doing).

Be careful as the rack mounting bolts will now be slightly too long to torque up, you need to make a couple of 10-15mm spacers. (I drilled the threads out of a couple of nuts and used them!).

To give you an idea of how bad the bump steer was, over the full suspension range the front wheels would cause a metre long length to move 25mm laterally after the rack mod this reduce to zero.

The bottom pinch for the steering UJ will now be very close to the chassis, check the steering before driving off! You will need to slacken the pinch bolts whilst you move the rack so that the steering coloum can set its own length.

As someone has pointed out it is the caster that causes the self centering effect. I have not messed about with this yet and my steering just about self centres but its not brilliant. Doing this and the caster will mess up the toe in which is one reason my I haven't bother yet.

The tracking is set to zero toe in but you can't use the rear wheels as reference (not easily anyway) because they toe out even though this is bad....loads of threads about this kicking about.

I'm surprised that your car is better with maximum neg camber on the rears, mine looked like only half the tyre was on the road. I've had a quick check with an infrared temp gauge on my rears and with min camber the inner edges still run 5 degrees hotter than the outer edge, this indicates that the inner edge is providing more of the grip at the moment.


This is a thread that I started last summer:-

http://autos.ninebean.com/cobraclub/...709&highlight=


Run the tyres at 18 psi all round (Give or take a couple to suit yourself, but not 26 like most tin tops)




Regards,

Pete

[steve14]

Originally Posted by Noel

Hi Steve,

What is your chassis number (it will tell you when the chassis was made, the first 4 digits after the letters "PS") after a certain date the bump steer issue was solved by Pilgrim and you can verify this by measuring the posts that the steering rack sits on. As I remember 10cm is the magic length. Look at posts made by Sidecarbod, he has investigated this at great depth.

If the steering is that light and it does not self centre I would guess that the tracking is way off, it should be set at 0 degrees toe-in and would be easy to rectify/experiment with.

Noel

Noel thanks for the info, I'm not that technically minded and bought the car to drive. The chassis number was made up by the builder but I have the full history and the chassis was delivered in April 96. I noticed someone else in the Sumo tech section had their suspension geometry set up by a company in Wakefield which isn't far from me so I may take it there.

Steve

[Sidecarbod]

Originally Posted by "steve14[/quote

Noel thanks for the info, I'm not that technically minded and bought the car to drive.

Steve

I don't wish to worry you but you've bought a hand built kit car...you will end working on it whether you like it or not!

You will get loads of help here and these cars a pretty simple.

Regards,

Pete

[steve14]

Originally Posted by Sidecarbod

The front end should not be overly light with a RV8 fitted, infact Pilgrim recon that this is the ideal setup with 50/50 weight bias. I bet that you've got toe out as this will make the steering very light and horrible!

I spent ages sorting out the bumpsteer on my car and it did make a big difference. If you've got a MKII then it will make any even bigger difference. I think that not all of the MKIII's had the Pilgrim mod which still isn't enough to fix the problem. I did tell them about the work that I've done but they did not seem very interested.

I believe that the MKII and early MKIII's have pillars that the rack sits on which are 120mm high, the late MKIII's are 110mm.

You need to cut another 8mm off either the pillar of the bottom of the rack. (Both is a bit of a pain on a fully built car but its DEFINATLEY worth doing).

Be careful as the rack mounting bolts will now be slightly too long to torque up, you need to make a couple of 10-15mm spacers. (I drilled the threads out of a couple of nuts and used them!).

To give you an idea of how bad the bump steer was, over the full suspension range the front wheels would cause a metre long length to move 25mm laterally after the rack mod this reduce to zero.

The bottom pinch for the steering UJ will now be very close to the chassis, check the steering before driving off! You will need to slacken the pinch bolts whilst you move the rack so that the steering coloum can set its own length.

As someone has pointed out it is the caster that causes the self centering effect. I have not messed about with this yet and my steering just about self centres but its not brilliant. Doing this and the caster will mess up the toe in which is one reason my I haven't bother yet.

The tracking is set to zero toe in but you can't use the rear wheels as reference (not easily anyway) because they toe out even though this is bad....loads of threads about this kicking about.

I'm surprised that your car is better with maximum neg camber on the rears, mine looked like only half the tyre was on the road. I've had a quick check with an infrared temp gauge on my rears and with min camber the inner edges still run 5 degrees hotter than the outer edge, this indicates that the inner edge is providing more of the grip at the moment.


This is a thread that I started last summer:-

http://autos.ninebean.com/cobraclub/...709&highlight=


Run the tyres at 18 psi all round (Give or take a couple to suit yourself, but not 26 like most tin tops)




Regards,

Pete

Hi Pete

Thanks for the info, like I said to Noel I'm not that technically minded and bought the car to drive, having said that I don't consider myself a dimbo!
I'll check the rack and look at the mods you suggest, thinking of having the geometry set up professionally, your right it does run on the inside of the rear tyres and wears them from the inside out (in about 8000 miles just put 2 new rear tyres on) but there is a big difference in the handling when I change the fixings to the mid hole as Pilgrim suggest, may be this is down to the front set up being out.
I've been running the tyres at 24 rear and 22 front, I'll drop this all round as you suggest and see if there's any improvement.

Regards

Steve

[steve14]

Originally Posted by Sidecarbod

I don't wish to worry you but I've bought a hand built kit car...you will end working on it whether you like it or not!

You will get loads of help here and these cars a pretty simple.

Regards,

Pete

Pete

Thats fine I don't mind working on the car, gives me sommat to do, as I see it thats what owing a car like this is all about its worth just for the heads it turns when I'm out.