Modifying suspension
Discussion
Hi I'm a new member here and it seems like a place to learn. I was reading a a discussion from April of 2013 about moving front suspension mounting points out 2 in. I'm in the process of converting a FC car to a FB car and to clear the chain I believe I will have to move out the rear suspension pick up points out about 2 in. Does anyone know what that will do to the handling? Thanks for any help
thunder287 said:
I thought you were racers maybe not.
Since you're new, I'll be nice.There are plenty of racers here, among other types, but don't expect folk to understand every acronym in your chosen field of interest. Unless you ask a question in a way that makes any sense at all, you can't expect anything other than WTF type questions and sarcasm. And if the article you were reading was worth reading, it would explain any effects of altering your suspension mounts.
Oh, to save confusion it's often easier to type two inches as 2".
Ok, to start off I have no idea of the car design you've got, so maybe posting a picture would help generate some answers.
If you are moving just the lower pick-up points outwards by 2" then my first thought would be that a couple of inches wider track might not be a major deal, but if it alters the camber of the wheel or angle of a suspension unit, then yes, it will be a big deal.
For example if it's lower link with a MacPherson strut and the top of the strut stays put, then it's changed the angle. Also the effective spring rates change with the angle of operation, as a rule of thumb moving them from the vertical usually reduces the effective rate and you need a harder spring.
A picture or sketch of the suspension design and your proposals might get more input?
If you are moving just the lower pick-up points outwards by 2" then my first thought would be that a couple of inches wider track might not be a major deal, but if it alters the camber of the wheel or angle of a suspension unit, then yes, it will be a big deal.
For example if it's lower link with a MacPherson strut and the top of the strut stays put, then it's changed the angle. Also the effective spring rates change with the angle of operation, as a rule of thumb moving them from the vertical usually reduces the effective rate and you need a harder spring.
A picture or sketch of the suspension design and your proposals might get more input?
If upper & lower arms are moving identically and it doesn't affect the camber or toe-in, then all you're doing is adding a couple of inches of extra track width. The same sort of thing people used to do to mini's with wheel spacers back in the 60s in an attempt to improve handling. Or because they wanted to fit aftermarket wheels which weren't really designed for the car in question.
Next question is if the spring angle will change significantly ? If so it will affect the effective spring rate and you might need to increase it. You can calculate the effects, +/- a few degrees isn't a big deal but if it's 15-20 degrees then it needs consideration.
Next question is if the spring angle will change significantly ? If so it will affect the effective spring rate and you might need to increase it. You can calculate the effects, +/- a few degrees isn't a big deal but if it's 15-20 degrees then it needs consideration.
All the control arms will be exactly the same length as they are now. The pick up points on the frame will be moved out 2 inches each side. I don't think it would be the same as putting spacers behind the wheels. I'm counting on it lowering the COG and the extra track increasing corner handling.
If you had given us all of the information, that you now have piecemeal, you may have had more favourable answers from the start.
Ok, so here is my 2p worth.
You will not lower the COG by increasing the rear track.
Yes, you will typically improve cornering speeds, but only if all other suspension dimensions remain the same.
The only thing is that you may well need to go to a fatter rear anti-roll bar as the effect of the increased track will increase the suspension leverage about the anti roll bar ends.
Alternatively, as you are talking about a race car, have you thought of looking in the relevant Motorsport section, there maybe more relevant experience loitering there.
Ok, so here is my 2p worth.
You will not lower the COG by increasing the rear track.
Yes, you will typically improve cornering speeds, but only if all other suspension dimensions remain the same.
The only thing is that you may well need to go to a fatter rear anti-roll bar as the effect of the increased track will increase the suspension leverage about the anti roll bar ends.
Alternatively, as you are talking about a race car, have you thought of looking in the relevant Motorsport section, there maybe more relevant experience loitering there.
andyiley said:
The only thing is that you may well need to go to a fatter rear anti-roll bar as the effect of the increased track will increase the suspension leverage about the anti roll bar ends.
Increased leverage yes, but a 4" wider track is also going to be subject to less load transfer, so in effect they should pretty much cancel each other out.OP, if you're solely moving the rear out, you'll get reduced load transfer over the rear axle in proportion to the front. The overall load transfer will be lower leading to higher cornering forces, but at the expense of increase understeer.
That is very much an 'all else being equal' situation, anyway.
If you want to have a look at the effects of track width, CG and spring/ARB changes on load transfer distributions, check out this link: http://blackartdynamics.com/Chassis/LoadTransferMX... (It won't work on Internet Explorer)
Edited by Kozy on Tuesday 11th March 16:25
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