27 replies to this topic

[Andrew aka Stuwy]

 

I have never questioned your knowledge or expertise but remember when dealing with us plebs not get wound up, if you don't want to help, don't.. No one is making you post.

 

stop getting so emotional about it...

 

my first post was to make people think, nobody learns anything being spoon-feed.

 

to answer one question though, yes, I could point you at people who can do this work, the problem with that is I will know doubt be chastised for advertising somebody and not another, and the list of people I would not want to name is vastly longer than the ones I would...

 

as the paying customer, I would expect you guys to start asking the right questions of your preferred supplier and make an informed decision.

 

Sorry, little confused how I'm getting emotional?

 

Ok so you made people think, and then they wanted answers.

 

We all have favourite suppliers/garages/tyre/shops ect. and if said Tesco and you said Sainsbury's I would try out Sainsburys to see how I get on. 

 

Also calling up a geo place and asking lots of questions that they don't know will get their backs up. I know that's your point right there that obviously you don't use them, but what for instance they are like you and get your nickers in a twist when people ask questions? They know there stuff but come across rude.  

 

Another point is, if you explain a few basic points, we can then ask these questions to our Geo places to know they are not just bullshitting us. Because at the moment I can call up "insert name here" ask them, "do you check bump this and that" and they say Yes.. how am I to know with out learning. I love learning, 4 years ago I knew nothing about cars, other then I like that and I don't like this. Now I still know (comparable to you nothing) but enough to basically take my VX to pits and put it back together. Just about   

 

I hope that makes sense...

[VXT Tim]

Is it not firstly important to know what bumpsteer is and more importantly, what too much or too little (or not the correct amount for the application) has what effect on the car and causes it to do/feel xxx?

 

 

[Scuffers]

Is it not firstly important to know what bumpsteer is and more importantly, what too much or too little (or not the correct amount for the application) has what effect on the car and causes it to do/feel xxx?

 

 

not a stupid question, however the answer is not that straight forward.

 

first thing to consider is you cant just say too much or too little, the scale is from too much negative to too much positive, with an approximation of zero somewhere in-between (and more importantly, not in the middle).

 

(the plot Arno posted up kind of shows the issue, once you get near the edges, it can all go to sh*t too...it's not a straight line).

 

at the rear, you want some toe in on bump to 'bias' the tyre a but, this is done on a lot of cars, some makes tried to call it passive rear steering - which it kind of is, but not how people would think of it.

 

if you have it set close to zero, then it's not disastrous, just less than ideal, (at this point I should say that this varies from tyre to tyre too to some extent), if you have it toe out on bump the car will become very unstable, going into oversteer as soon as you try to lean on it.

 

I see this all the time where people have had fitted motorsport toe link kits and not got a clue what they are supposed to do with the shimms.

 

Upside to the rear is that although it does make a difference if you change the ride hight, it;s not as drastic as the front, ie. if your only going 10-15mm change in height, then you don't have to worry too much about it (assuming it was right in the first place!)

 

The front is a completely different story, get this wrong and the car will not want to go in a straight line, fidget on bumpy roads, and either understeer like a b1tch or turn in so violently that the rear just wants to swap ends.

 

on a std car the way to adjust this is to move the rack up/down in the chassis, Lotus did two 'plates' to pre-define a high and low position for this, although in the chassis itself, it's a slot.

 

ideally, you want toe out on bump at the front, this means when you stamp on the brakes into a corner, the front toe will go from what it's statically set at (should be ~0.5-1mm out) to further out, this should make it slightly less nervous under braking and make initial turn in more responsive.

 

if you go too far, then the car will start to wander in straight lines as the road surface undulates, it also means than when you apply power out of a corner, and start to lift the front (with weight transfer) the front can go into toe in, and understeer like a pig.

 

if you go the other way, so you get toe in on bump, this get's 100 times worse, car will feel very darty, with very un-predictable turn in, massive understeer (usually followed by snap oversteer as you try to fight it).

 

once again, different tyres also have an effect on how little/much you want.

 

Lastly, to give you some idea, doing a full geo from start to finish is a good days work (assuming nothing is seized up/broken), anybody that says they can do all this in a couple of hours is talking crap (that said, I can usually tell you in <5 minutes if it's wrong just by looking at it).

[VXT Tim]

Fantastic..... genuinely. But why this?

not a stupid question.

Assume all q's from here/me are stupid? Can't help it? Am I being too emotional about it?

[Andrew aka Stuwy]

 

Is it not firstly important to know what bumpsteer is and more importantly, what too much or too little (or not the correct amount for the application) has what effect on the car and causes it to do/feel xxx?

 

 

not a stupid question, however the answer is not that straight forward.

 

first thing to consider is you cant just say too much or too little, the scale is from too much negative to too much positive, with an approximation of zero somewhere in-between (and more importantly, not in the middle).

 

(the plot Arno posted up kind of shows the issue, once you get near the edges, it can all go to sh*t too...it's not a straight line).

 

at the rear, you want some toe in on bump to 'bias' the tyre a but, this is done on a lot of cars, some makes tried to call it passive rear steering - which it kind of is, but not how people would think of it.

 

if you have it set close to zero, then it's not disastrous, just less than ideal, (at this point I should say that this varies from tyre to tyre too to some extent), if you have it toe out on bump the car will become very unstable, going into oversteer as soon as you try to lean on it.

 

I see this all the time where people have had fitted motorsport toe link kits and not got a clue what they are supposed to do with the shimms.

 

Upside to the rear is that although it does make a difference if you change the ride hight, it;s not as drastic as the front, ie. if your only going 10-15mm change in height, then you don't have to worry too much about it (assuming it was right in the first place!)

 

The front is a completely different story, get this wrong and the car will not want to go in a straight line, fidget on bumpy roads, and either understeer like a b1tch or turn in so violently that the rear just wants to swap ends.

 

on a std car the way to adjust this is to move the rack up/down in the chassis, Lotus did two 'plates' to pre-define a high and low position for this, although in the chassis itself, it's a slot.

 

ideally, you want toe out on bump at the front, this means when you stamp on the brakes into a corner, the front toe will go from what it's statically set at (should be ~0.5-1mm out) to further out, this should make it slightly less nervous under braking and make initial turn in more responsive.

 

if you go too far, then the car will start to wander in straight lines as the road surface undulates, it also means than when you apply power out of a corner, and start to lift the front (with weight transfer) the front can go into toe in, and understeer like a pig.

 

if you go the other way, so you get toe in on bump, this get's 100 times worse, car will feel very darty, with very un-predictable turn in, massive understeer (usually followed by snap oversteer as you try to fight it).

 

once again, different tyres also have an effect on how little/much you want.

 

Lastly, to give you some idea, doing a full geo from start to finish is a good days work (assuming nothing is seized up/broken), anybody that says they can do all this in a couple of hours is talking crap (that said, I can usually tell you in <5 minutes if it's wrong just by looking at it).

 

 

Thank you, I understand the affect it has now and why its important   its also interesting to know what affect breaking has on the front wheels.

[rob999]

I'll let you know my thoughts on machine geo v top engineer setup next week....

[Exmantaa]

OK, I skipped over/ignored a few postings here, but thank you for the info in post #23. 

This is not spoon feeding, but it explains the mechanics and importance behind bump steer. And like Arno said, this real-world info is very hard to find for our cars...

[FLD]

To sum up,

thats good sh*t!