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Great video as always! I know Ramey touched on it just briefly but can you expand on the adjustable roll center and what effects it will have with the handling or the feel of the car?
Raising the roll center height up front puts the roll axis closer to where it should be (as does lowering the rear roll center with Watts or PHB relo).
We get incremental gains in rate of camber gain as well.
The feel is less body roll and quicker response in slaloms because the car "isn't teetering on a below ground roll center" point.
With the front RC too low and the rear RC too high the car actually tries to roll unequally front vs rear. Since that can't happen since the car is made of connected metal, bad handling ensues.
[CONDENSED VERSION - THE TEXTBOOK VERSION TAKES A LOT OF PAGES OF TYPING]
I know you touched on the rust issue comparing the stock to the aftermarket mount, but is there any worry about rust forming under your bracket in the "cup" where the shock mount goes through the rubber? I would assume it can drain out of the rubber cup somehow but couldn't quite tell and haven't looked at a rubber mount in a while lol.
how do you know which holes to put the bolt into? how dos lowering affect this? when lowering your car with the factory mount does that put your roll center at a better spot or make it worse
The center hole is factory location. For the customer that doesn't know why, when or if they should change roll center we would recommend the stock location and come back to making changes when the tuning is needed. A lot of things are factors when making changes like this, and this is a tuning device. For a street car run stock location. The lower hole would begin to raise the roll center, it also starts to place the a-arm in its upward arc, so as the suspension loads it can improve the camber gain. This means a customer could run less static camber because the car gains more camber in travel.
so using the upper hole raises roll center .....which is good ?
bottom hole does......???
middle hole....stock ?
The middle hole is stock.
The lower hole raises the roll center slightly which decreases body roll and increases camber gain.
You really can't go wrong choosing middle or bottom hole (i.e. it won't make the car do anything terrible).
The upper hole is seldom used but is included because some guys using Performance Trends or equivalent software and lots of research, may want to try it.
Simple summary: If you're building a handling car, use the bottom hole.
Have you guys experimented with a smaller front bar with this part? I'm assuming it's nowhere near enough of a change to go back to stock, but maybe something like a 33 or 34 hollow unit.
Have you guys experimented with a smaller front bar with this part? I'm assuming it's nowhere near enough of a change to go back to stock, but maybe something like a 33 or 34 hollow unit.
We actually have. Nate and Roger tested multiple combinations at UMI Motorsports Park on some test days this fall. I remember them commenting that it was possible to get too much mechanical roll resistance when combined with the roll center height adjustment.
If you have a specific combination question you can email nate@umiperformance.com to see if they tested it. He also knows all the tendencies.
Of course there are many, many possibilities but we haven't tested them all. Yet.
We actually have. Nate and Roger tested multiple combinations at UMI Motorsports Park on some test days this fall. I remember them commenting that it was possible to get too much mechanical roll resistance when combined with the roll center height adjustment.
If you have a specific combination question you can email nate@umiperformance.com to see if they tested it. He also knows all the tendencies.
Of course there are many, many possibilities but we haven't tested them all. Yet.
ramey
Glad to hear you have some data on it. It's not something I can use right now, but I imagine when the car goes CP this will be a cheap upgrade to the front end as a stop-gap before cutting everything out and grabbing a circle track catalog. I'll have to look into it whenever that time comes.
We actually have. Nate and Roger tested multiple combinations at UMI Motorsports Park on some test days this fall. I remember them commenting that it was possible to get too much mechanical roll resistance when combined with the roll center height adjustment.
If you have a specific combination question you can email nate@umiperformance.com to see if they tested it. He also knows all the tendencies.
Of course there are many, many possibilities but we haven't tested them all. Yet.
ramey
Hmmm, so if I'm happy with my current setup (hotchkis 36.5mm hollow, 19 solid rear bars) would I need to make some adjustments if going to the lower hole on these arms?
Hmmm, so if I'm happy with my current setup (hotchkis 36.5mm hollow, 19 solid rear bars) would I need to make some adjustments if going to the lower hole on these arms?
If happy I’d actually choose the stock mount location. Why mess with a good thing?
if the car currently has a tick of understeer at the limit then the lower holes may fix that. The beauty of it is, you can always adjust.
If happy I’d actually choose the stock mount location. Why mess with a good thing?
if the car currently has a tick of understeer at the limit then the lower holes may fix that. The beauty of it is, you can always adjust.
True, but I usually cant help tweaking on it anyway! What I'm thinking is the camber gain could be nice since I still daily drive, -2.7 camber kills my street tires. So if I could dial it back some with these and be even on the track, that will give me more miles out of my all seasons.
Thanks for the responses and thanks for the continued product development!
01-10-2019, 01:39 PM
UMI Tech video - upper a-arm mounts 
