Suspension suggestions?

[SeverAMV]

such a large post... i'll read it when im not tired after work at 4am in the morning.

i guess i did swap to much wider profile tyres. i think the stock tyre width for an ed6 is 145? im currently using 195, so yeah, big difference. and its not so much torque steer, my car doesnt have enough torque for torque steer due to some engine issues atm. i'd like to fit my coilovers as soon as possible, but most mechanics are closed over christmas. right now, my dead shocks borderline dangerous. i can feel my front left shock compress, but take a few seconds to decompress. the hovering scares the shite outta me.

[JohnL]

such a large post... i'll read it when im not tired after work at 4am in the morning.

I specialise in long posts! You think thats long? You should see some I've posted on kart racing forums when discussing weight transfer theory, pages and pages, you guys here are getting off lightly!

i guess i did swap to much wider profile tyres. i think the stock tyre width for an ed6 is 145? im currently using 195, so yeah, big difference. and its not so much torque steer, my car doesnt have enough torque for torque steer due to some engine issues atm. i'd like to fit my coilovers as soon as possible, but most mechanics are closed over christmas. right now, my dead shocks borderline dangerous. i can feel my front left shock compress, but take a few seconds to decompress. the hovering scares the shite outta me.

If you read my post carefully you'l notice I said that torque steer affects can occur even when only light power or braking forces are being applied, you don't need to be pushing any pedals through the firewall or have a high torque output motor. Torque steer will tend to be stronger when trying to accelerate (or brake) hard, and with a more torquey motor, but can be noticable even with low power or braking inputs, if the steering geometry and tyre width work to create a strong tendency toward torque steer.

Torque steer can supposedly be generated by driveshafts of unequal torsional stiffness (typically if one shaft is a lot longer than the other), meaning one shaft will tend to wind up more than the other, but in this case it requires a high torque input or hard braking effect to significantly cause any twisting of the shafts. This used to be 'accepted wisdom' in the days when front drivers mostly had unequally stiff drive shafts, but these days this fault is much less common.

In any case I do have some doubts about this theory, IMO its not likely to have more than momentary significant affect due to the affect of the differential accounting for this unequal shaft wind up, though it might cuase the steering to be more twitchy under hard acceleration / braking rather than 'torque steering' for more than a moment or so. Geometric affects associated with scrub radius and uneven road surface seems much more likely to me to be responsible for what most people would understand as torque steer as felt by the driver.

I could be wrong, but I'm suggesting that what you are percieving as bump steer may instead be momentary manifestations of torque steer associated with the increased tread width, and that you don't need big torque for this to occur. If I'm right the problem would tend to diminish or disappear if you just allowed the car to coast rather than holding speed with light throttle.

It sounds like you're increase in tyre width might be enough to cause at least some increase in torque steer affects on uneven roads, but your problem may be more associated with the blown damper(s) causing a wheel(s) to momentarily unload excessively. Sounds to me like you still have rebound but have lost bump damping, which would explain the lag in 'decompressing', keeping in mind that the bump stiffness of other dampers (most probably the damper on the diagonally opposite corner) may contrive to 'hold down' that corner of the car with the blown rebound.

[SeverAMV]

nah, even when coasting, bump steer manifests itself. its effects are probably enhanced by the bad wheel alignment that bridgestone did on my car. once i fit the coilovers, i can see if it was indeed the dead shock causing the bump steer. if it isnt, then its back to the rather expensive drawing board.

[JohnL]

If your effective scrub radius has been increased enough to cause noticable torque steer like effects at each steered wheel, and considering that when traveling in a straight line on a smooth road these torque steer effects will be in balance side to side (and hence no pull to one side), then a bad damper causing one tyre to excessively unload in bump might cause the still loaded wheel on the other side to no longer be in 'torque steer balance' with the unloaded wheel and for a torque steer from the still loaded wheel to be felt and a momentary pull to one side that feels like bump steer??

That's a lot of words with no full stops, apologies for the poor punctuation!

Anyway, the short of the above is that it's not unlikely that a blown damper might at least be excacerbating any problem that may exist (even if it may not be the actual cause), and new dampers may reduce the symptom to a degree that it's not noticable.

It's not impossible that when coasting the rolling resistance in the tyre might be enough to trigger an affect as described above, even with no engine or braking torque involved (?), but I might just be trying too hard to defend my theory!

PS,
Just noticed your sig. You mustn't have driven a well sorted carburettor set up, DCOE Webers (and other good carbs) can make very good power! Though you may not get quite the same 'drivability' as with a good EFI set up.

[JohnL]

Do you know what true bump steer is and what causes it? I ask because its a geometric thing that won't change because of a rim and / or tyre change, you need to alter something (a few things will affect it) in the geometry for it to exist where once it didn't. Bump steer can't be caused by bad dampers, though they could make it more obvious.

[SeverAMV]

If your effective scrub radius has been increased enough to cause noticable torque steer like effects at each steered wheel, and considering that when traveling in a straight line on a smooth road these torque steer effects will be in balance side to side (and hence no pull to one side), then a bad damper causing one tyre to excessively unload in bump might cause the still loaded wheel on the other side to no longer be in 'torque steer balance' with the unloaded wheel and for a torque steer from the still loaded wheel to be felt and a momentary pull to one side that feels like bump steer??

That's a lot of words with no full stops, apologies for the poor punctuation!

Anyway, the short of the above is that it's not unlikely that a blown damper might at least be excacerbating any problem that may exist (even if it may not be the actual cause), and new dampers may reduce the symptom to a degree that it's not noticable.

It's not impossible that when coasting the rolling resistance in the tyre might be enough to trigger an affect as described above, even with no engine or braking torque involved (?), but I might just be trying too hard to defend my theory!

PS,
Just noticed your sig. You mustn't have driven a well sorted carburettor set up, DCOE Webers (and other good carbs) can make very good power! Though you may not get quite the same 'drivability' as with a good EFI set up.

bad dampers in conjunction with a bad wheel alignment (courtesy of bridgestone port adelaide) could cause bump steer tho, right?

oh and i havent updated my sig in a while, i was just messing around with the factory setup at the time. i've done the tweaks to the keihin cv carbs already. currently, im waiting for my high compression kit to arrive, as well as new camshaft, valvesprings, retainers, which should get my compression ratio in the 11s, if not the 12s.

i've also got a pair of dual sidedraught skracing carburetors sitting around waiting for a manifold to be made. theyre dcoe 40, and apparently combine the weber and mikuni designs, so they shouldnt be too bad. once all that is done, i dont think my car will be making monstrous power, but it should have a notable increase in midrange and topend response. i find that the drivability of carbs can be better than efi in some respects, but thats just a personal opinion. most of the efi cars i've driven have lacked bottom end response, including a quad throttle ae101 sprinter, but carbs seem to have plenty of bottom end response, even when theyre tuned for top end. but this is just an opinion, and comparing carbs to a quad throttle sprinter in regards to bottom end response is flawwed as quad throttles are generally aimed at top end power and response.

[JohnL]

bad dampers in conjunction with a bad wheel alignment (courtesy of bridgestone port adelaide) could cause bump steer tho, right?

From my understanding bad dampers and / or poor alignment couldn't be a (significant) cause of bump steer, but might increase the severity of an existing bump steer.

To understand why we need to understand what bump steer actually is. True bump steer is caused by dynamic toe change with bump or rebound (which is different to momentary torque steer effects that might feel similar to bump steer). This is typically caused by the steering rack being mounted too high or low, the tie rod end being mounted too high or low, or the tie rod itself being too long or too short. Any of these conditions will cause bump steer in some degree, from severe to not noticable. And, some of these things might only need to a bit 'off' to cause a noticable problem, and that problem may manifest to a greater or lesser degree depending on other factors such as tyre characteristics (i.e. a less directionally sensistive tyre will be less affected by a given bump steer / toe changes because it will 'smother' small steering inputs due to being unresponsive in nature).

As an e.g.;
Looking at a double wishbone suspension from front on we'll see the upper and lower arms pivotted on the chassis pivots, and each arm will rise and fall with the outer end describing an arc (and these arcs will be different depending on the length of the arm). We'll also see the tie rod rise and fall pivotted at the rack end joint, and the tie rod end describing an arc. The arc in which the tie rod end rises / falls should match the arc of the suspension at the point on the strut or upright at which the tie rod end attaches to it. To achieve this the rack and tie rod end must be at the correct heights and the tie rod at the correct length (though this is typically more or less impossible to acheive exactly due to toe being adjusted by means of changing tie rod length, though it will typically be quite close to the correct length within the range of likely toe adjustment).

If any of the above is wrong then bump steer will occur because as each component rises and falls in arcs the effective distances (of the ends of the arms and tie rod) from the centres of pivot become laterally longer or shorter, and if these distances don't become longer or shorter in a manner that is 'matched' to the arcs of the other components then the ends of the tie rod will move in or out (laterally) relative to the steering axis and the toe will change with bump and / or rebound. Got that?! This is hard to describe!

Possibly the most likely reason for introduction of excessive bump steer is modification of suspension / steering geometry. E.g. if you substantially increase caster by moving the top of a Mac strut or upright (of a double wishbone suspension) backward then you'll also tend to lower the height of the tie rod end because you will have 'rotated' the strut or upright around a point centred on the lower ball joint, which will cause the end of the steering arm to be lowered to some degree. On the other hand if you increase caster by moving the bottom of the upright or strut forward then any increase in bump steer will be less because you move the strut / upright in an arc centred on the top of the strut or upper ball joint, and the end of the steering arm will lower a lot less (maybe not at all, depending...) than if we'd moved the top of the strut or upright backward.

It's very difficult to design and build a suspension / steering set up that has absolutely no bump steer at all (with some suspensions it's utterly impossible, e.g. front trailing arms on old VWs where the suspension doesn't move in arcs but straight up and own but with the tie rods moving in arcs), but the designer will (should) attempt to achieve as close as possible to zero or minimal bump steer at / near the static ride height. Due to manufacturing tolerances it wouldn't be unlikely for a car to have some degree of significant bump steer from the factory, but unlikely to be a substantial problem most of the time (especially with less responsive tyres fitted). Having said that, a lot of effort might be put into dialling out any significant bump steer on a chassis intended for serious competition.

Even on a well set up car it wouldn't be unusual though for bump steer to become significantly worse the further into bump or rebound you go. So, if you have a bad damper you might expect to see more adventures deeper into bump (and rebound to a lesser degree), possibly resulting in noticably increased bump steer.

Poor toe alignment could in theory cause the tie rod to be too long or too short, and thus introduce some bump steer, but I suspect it would have to be quite a lot wrong to cause a significant problem (I could be wrong). Soft suspension bushes might also increase bump steer tendencies, though the mechanics aren't the same as above, it's more to do with the bushes compressing and allowing whole suspension arm to move inward and outward while the tie rod end doesn't.

i find that the drivability of carbs can be better than efi in some respects, but thats just a personal opinion. most of the efi cars i've driven have lacked bottom end response, including a quad throttle ae101 sprinter, but carbs seem to have plenty of bottom end response, even when theyre tuned for top end. but this is just an opinion, and comparing carbs to a quad throttle sprinter in regards to bottom end response is flawwed as quad throttles are generally aimed at top end power and response.

I think it's more to do with the nature of the set up. All else being equal, carbs with very large venturi will tend to be pigs at lower rpm, but scream in the top end. This is a problem for single throat carbs like the DCOE Weber and similar clones (more or less clones) such as DHLA Dellorto etc, i.e you can set them up with smaller venturis and get good bottom end / mid range, poor top end, or with larger venturis and get good mid range / top end, but poor bottom end. Splitting the difference might give good mid range with acceptable bottom and top. Despite having been used fairly successfully on a number of higher performance road cars (mostly Italian!), this sort of carb probably isn't the ideal choice for a road car, the design is primarily intended by Weber for racing applications.

In any case, even good carbs are archaic technology these days. EFI should be able to outperform carburettors on all fronts (power, tractability, economy) so long as it's in good condition and been correctly set up for the application.

[TODA AU]

Bump steer is generally a geometry problem.
When the car is lowered beyond the limits of the standard parts, the geometry of the steering arms is compromised.
This can be cured with a variety of products.
Example: Ikeya Formula tie rod ends.


Use of these or similar products will allow you you achieve parallel steering arms & reduce if not negate bump steer on a lowered car.
Obviously the wheel alignment must be correct too, as this will only agrovate the situation.
When combined with roll centre adjusters, you can achive excellent handling when the car is set a a low ride height.
Without use of such products, it's difficult to get the most from your dampers at very low ride heights.

NB: At very low ride heights, other products such as adjustabletoe & camber arms are also advantageous to achieve desired wheel alignment.

Hope that helps
Cheers

Adrian

[SeverAMV]

Bump steer is generally a geometry problem.
When the car is lowered beyond the limits of the standard parts, the geometry of the steering arms is compromised.
This can be cured with a variety of products.
Example: Ikeya Formula tie rod ends.


Use of these or similar products will allow you you achieve parallel steering arms & reduce if not negate bump steer on a lowered car.
Obviously the wheel alignment must be correct too, as this will only agrovate the situation.
When combined with roll centre adjusters, you can achive excellent handling when the car is set a a low ride height.
Without use of such products, it's difficult to get the most from your dampers at very low ride heights.

NB: At very low ride heights, other products such as adjustabletoe & camber arms are also advantageous to achieve desired wheel alignment.

Hope that helps
Cheers

Adrian

this would only help if my car was lowered. but my car exhibits bump steering with the factory ride height and factory suspension. waiting till mechanics start working again before fitting the coilovers.

[TODA AU]

this would only help if my car was lowered. but my car exhibits bump steering with the factory ride height and factory suspension. waiting till mechanics start working again before fitting the coilovers.

Fair enough, definatly get it checked out.
(Sorry I didn't read that part earlier in the thread- my bad)
What condition are your castor rod bushes in? ED Civic right?

Also, is it bump steer that is the problem or is it more tram lining?

[JohnL]

Also, is it bump steer that is the problem or is it more tram lining?

SeverAMV suggested he may have a bump steer issue, and I questioned whether this might not be bump steer but in reality might be a manifestation of momentary torque steer that could be occuring when traversing road irregularities, and might be being mistaken for bump steer.

This is in effect a manifestation of momentary 'tram lining' which itself is a manifestation of a torque steer effect, even though it can occur with only light throttle or braking applications. Such an effect is associated with changes in 'effective scrub radius' as the average centre of loading moves laterally across the face of the contact patch as the tyre passes over bumps and along longitudinal 'trenches' in the road, and potentially being a greater problem with wider tread width than narrower tread width.

[JohnL]

Bump steer is generally a geometry problem.
When the car is lowered beyond the limits of the standard parts, the geometry of the steering arms is compromised.
This can be cured with a variety of products.

Adrian

Agreed, up to a point. If you've made substantial changes to ride height and / or caster angles then you may well end up with geometric bump steer (i.e. true bump steer, not a torque steer affect), and you may well be able to address it by arbitrarily throwing appropriate parts at the problem. However, the only way to know if you've actually cured it (other than the problem no longer being apparent when you drive the car) is to measure the bump steer.

This is done by maiking a tool that consists of two flat pieces of plywood hinged together so that they can open / close like a book. On one piece of ply you fit two pointers (can be anything, a couple of screws screwed though the ply so they protrude out the back will do fine) spaced apart so they match the rim diameter and high enough so they will be at hub centre height when you place the pointers against the rim.

But I'm getting ahead of my description. Place one 'page' of the bump steer tool / gauge on the ground near the wheel with the other page up against the wheel, and place some bricks on the 'page' that is on the ground to hold it in position while the bump steer test is performed. The pointers on the vertical 'page' are placed against the rim so that both are touching the rim. Now the car must be jacked up and down while you observe if one of the pointers moves away from the wheel rim with ride height changes, if so then this indicates a toe change with ride height change and thus bump steer.

In order to do this test you need to remove both coil springs on the front axle line in order to allow ride height change as you jack the car up and down. This is fairly easy with 'coil-overs', more of a pain with struts.