[QUOTE]Originally posted by Taylor-Racing
Speaking of 25T pulleys and the like, I've often wondered about their impact on suspension geometry.
For instance, if you change to the 25T pulley and use, say, a 6mm split front to rear, you must then raise the front of the chassis by 3mm to maintain (for example) an equal ride height F/R.
You have now altered the front geometry with respect to the rear as originally designed by the manufacturer, yeah?
Maybe this is generally a good idea, and possibly the effect on the manufacturers geometry balance F/R is inconsequential.
Hello Taylor, you hit the nail on the head. I touched on this in the post to kevink2 and will copy it below. But you are correct that when you start altering tire diameters while keeping the ride height or level of the chassis equal you are changing the angles of the suspension arms. This in essence changes your geomety and how the forces are applied to your suspension/car, how it react and where the different planes intersect. To viasualize this simply in your mind extend a line that is level with each of the suspension arms and see where they intersect. Now lower the suspension arms i.e. increase the ride height and you will see that all of the angles have changed and the points where the line intersect are in different positions than before. This is how you can see how your alterations to settings can affect your roll axis, roll center etc. An interesting thing is that your roll center can actualy bebelow the car (in the ground) and when cornering and the car is leaning can actualy be next to the car. This stuff gets realy complex but take some graph paper and draw your front suspension on it under different conditions i.e. accelerating, breaking cornering etc, intersect the lines and you will start to see what I mean. This stuff borders on a black art that I'm have spent a lot of time trying to learn (it's not fun). What I have found is that even full size race car designers sometimes know that having a certain geomety has a certain affect but they just don't know why! Pick up a couple of race car suspension design books, this is the best way to start learning about this.
Quote from previous post to Kevink2
Running the 25T pulley allows you to run smaller front tires i.e. larger splits (@9mm) while still maintaining an overdrive ratio of 1 (aproximate numbers here). The reason that you would do this is primarily that it raises your roll axis on the front end. Raising the roll axis means the car stays flatter through corners puts more weight on the inside front tire when cornering which is not necessarily bad as the outside tire is being loaded by the G's of cornering so it argubly makes the car corner more efficiently. Having said this, when you start talking about roll axis things are getting realy complex and it's difficult to do without drawing out diagrams to show the geometry of the suspension and how the pivot points intersect.
I'm also wondering that maybe a MRX-3, not being a Touring Car chassis, "requires" the use of smaller front wheels to "maintain" it's correct geometry balance F/R.
1/8th scale cars are designed from the start to run stagger so I would think that this was taken into account by the designers when they were developing it. Having said that though they must realise the importance of being able to alter the geometry which is why I belive they included the 25T pulley. Basicaly allows you to cahnge from a 6-7mm split to a 9mm+ split which as mentioned above changes your roll axis.
That is: Can you transfer what works on a MRX-3, directly to the MTX-3?
The geomety of the cars are different so I would lean towards saying no. However all of what we have been discussing regaridng suspension angles, roll axis, roll center etc. applies to each and every model, full size, race car etc that has suspension arms and as such the theories can be applied to each of them. Hope this helps.