Suspension Geometry and Camber Change

[Jas1159]

Hi all,

The question i have may not be best suited for this forum but i always seem to get sensible answers here! I have not found an answer too this after searching and searching...

If my Rear geometry provides better performance in roll than in bump in comparison to my front axle, firstly is this acceptable for track/road use and secondly would it be better or advisable to have more of one or the other on the rear?

below i explain how i met this question.

Now my first question would be its a mid/rear engined vehicle, in general terms should i be making the rear camber change better in roll or bump/droop? or keep it the same as the front steering axle?

My problem is I want to make my rear roll centre higher based on advice and literature say 70mm (+23mm on front). The rear track = 1300mm so as both track and RC are directly effecting my swing arm length it automatically means the swing arm is shorter than the front and therefore worse in bump but better in roll!

Roll is something i can understand being needed on the front as it is the steering axis but the rear? it seems every car i look at has a higher RC on the rear and therefore would almost always be worse in bump and better in roll than the front axle.

is it acceptable to induce better cornering performance into my rear geometry? making it better in roll but worse in bump?! what would you advise for a mid/rear engined vehicle for track / road use?

 

[xxChrisxx]

We needs to get an automotive subforum.

Ranger Mike is the one to ask, as he has huge experience with suspension setups. There is a good suspension thread the was originally a series of tutorial/lectures, but has become a setup surgery.

It may be worth you reading the first couple of pages of that.

 

[Jas1159]

Thanks for the reply chris, I actually PM'd mike after reading his thread! the information within is priceless however it didnt quite answer my specific question.

Hopefully mike or others can provide there opinions.

 

[Ranger Mike]

Jas , welcome..i got he message and replied..hope it helps...and curious to see what the other racers advise..

 

[ncracing]

I have a question about 3 link asphalt latemodels. What would be a good starting point on correct angles for the trailing arms and 3rd link? With what I am using now the car has good entry but gets a little push in the center of the corner and is loose coming off the corner. Thanks, NCRACER

 

[Ranger Mike]

welcome..I am out of town on business this week.

do not have notes wioth me..
May I suggest you read
Race Car Suspension Class posts in this forum


questions about rear end set up..
see post # 132 page 9 for 4 link info, post 116 page 8 for rear steer, post 81 page 6 for top link info, post 253 page 16 for 3rd link info and post 261 page 17 for 3rd link spring rate

i will be back this week end ifin i don't have chassis set up duties at the local bull ring
rm

 

[mender]

Depends what you anticipate for track conditions. If you can't make them the same (which is normal) I'd tend towards making the back better in roll to keep the rears planted as cornering force builds.

I usually don't have much choice in the matter though.

NC, what angles are you running now? How far into the corner do you consider entry? Does the car start to push as it takes a set, before, after? How close is the loose tied to the throttle? How much stagger and what size track? Locker type?

 

[Kozy]

WRT to the OP: So far as I have been able to determine, the reason for higher rear RCs is that the load transfer through them is instantaneous, where the same transfer through the elastic route is not. This allows the rear tyres to react to changes at the front tyres at a faster rate, improving steering response. The trade off for this is of course increased camber gain in roll, which may or may not be of benefit to you.

So far as I can see though, if your rear axle on an MR car has better roll camber than the front then you are less likely to encounter an unstable roll oversteer situation as the front tyres will de-camber faster in a turn tending towards a gentle push.