15 replies to this topic

[87MugenProCR-X]

A few weekends ago I got a chance to take the car out at Cal Speedway and evaluate a few setup changes including David's bumpsteer correction kit. I'll take this chance to review the product.

First of all the kit looks beautiful in its craftsmanship. The installation was very easy and the kit even included detail instructions. The only hang up I got during install was opening up the hole on the knuckle with a small rat tail file, the instructions say some knuckles may require filing. This process was easy and only set me back about 10 minutes or so. Everything else was very straight forward. The kit comes with an A, B, C(x2) and D shim, my kit currently is set with the 2 C shims and D shim between knuckle and tie rod and A,B shim between the lower jam nut and tie rod. This was the suggestion I got from David based on the data he had collected.



My experience with kit so far was great. The cars feel is improved when riding the curbs during cornering(curb bangin') and also noticably better through turn 1 and 2 at the Speedway(the oval), which has some bumps at the center. The car used to feel a bit hairy through 1 and 2 being that the car was carrying so much speed but with the corrections the car feels more confident even while wide open through this section. Over the curbing the car feels smoother and more consistant. I didn't get any improvement in braking stability which I've had a problem with at the Speedway under heavy braking(braking into the turn 3 and 4 chicane) but I feel this may be a different issue not correctable with bump correction only. Overall I'm very happy with this kit and feel my money was well spent. I don't think its worth a whole lot in lap times, but really helps with the feel of the car.

Julian

[TribalHatch]

Thats great to hear since i havend had the time or chance to put on my bump steer yet so this is awesome feed back.

[cbstdscott]

If we have not lowered out cars to the point where the control arm is now point upward, would there be a benefit to "correcting" the bumpsteer?

Scott

[RETROCRX]

There is always a benefit to correcting bumpsteer to your nominal ride height, regardless of what that is. It's just not a very big benefit unless you need a significant correction.

[firstgencrx]

If we have not lowered out cars to the point where the control arm is now point upward, would there be a benefit to "correcting" the bumpsteer?

Scott

There is always a huge benefit. It doesn't matter how much the front is compressed. Even when the front is compressed too far, the gains are great. You also need to know, that yes, it's not as desirable to have the car too low, but it's also not good at OEM ride height either. I guess what I'm saying is the geometry at the extremes is less desirable. That is where the most change is. Depending on the camber you are running, the sweet spot, in most instances, is between 1.0 and 1.5 inches of front compression from OEM position. But that doesn't mean you can't go really low. Big improvements are seen with the kit for cars that are over-lowered compared to the stock tie-rod end.

Give me some parameters Scott, and I'll give you the difference. All I need is the tire diameter you're running, the ground clearance from the front cross member to the ground (I measure from the bottom of the torsion bar tube in the front where it is the largest in diameter), and the camber you are running. This allows me to calculate how much the front is compressed from OEM position, or what the lower control arm angle is.

All my data is taken relative to the lower control arm angle. I did it that way to make it easier. You can lower or raise a car without changing the geometry of the front suspension by simply changing tire diameter. It's the position of the front suspension, or it's compressed height relative to the chassis is what I need compared to OEM.

Here is a stock OEM comparison. Remember when looking at this, Honda deliberately put a ton of under steer in the front for safety. They knew that people would feel safer with a car that resisted turning compared to one that has the ass end passing up the front.

22.6" diameter tire, 6.5" of ground clearance, OEM camber, three inches of front suspension travel to full bump:

With factory rod end, the front will experience 0.497" of total toe out.

With bump steer kit, the front will experience 0.089" of total toe change.

How about 1" lower with two additional degrees of negative camber?

22.6" diameter tire, 5.5" of ground clearance, -2 degree of camber, two inches of front suspension travel to full bump:

With factory rod end, the front will experience 0.337" of total toe out.

With bump steer kit, the front will experience 0.043" of total toe change.

Now lets over compress the front. Lets lower the car by 2.5", give it three degree of negative camber, and shorter bodied shocks so we can get two inches of suspension compression before full bump.

22.6" diameter tire, 4" of ground clearance, -3 degree of camber, 2" of front suspension travel to full bump:

With factory rod end, the front will experience 0.489" of total toe out.

With bump steer kit, the front will experience 0.069" of total toe change.

You can see above that at stock ride height, the bump steer kit helped improve bump steer by 5.58 times. The 1" lowered car with two degrees of negative camber saw a 7.84 times improvement. The car lowered 2.5" with three degrees of extra negative camber and shortened bodied struts saw a 7.09 times improvement.

Scott, the combinations are so great, you will need to feed me some information before I can help you.

David

[cbstdscott]

David,

Thanks for the detailed response. I am reluctant to "mess" with the suspension at this point because I am happy with what I have presently. As I have it, the car is neutral and I can induce over or under steer with my right foot.

What will happen when I change the bumpsteer geometry?

Scott

[87MugenProCR-X]

Scott,
I didn't feel a change in the balance of the car, I felt a change in the car reacted to curbs, bumps and uneven surfaces especially during cornering.

Julian

[cbstdscott]

Exactly how is it different?

[87MugenProCR-X]

The car simply felt more stable over curbs and bumps during high speed cornering. I felt more confident with the car especially through turn 1 and 2 at Cal Speedway. Honestly, its difficult to describe other than what I've already posted.

If you think about what David has shared of his data, the effect of the kit is to minimize the toe change throughout suspension compression. Now think of your car going over a curb on the inside of a corner. As your inside front wheel hits the curb it compresses, while your outside front wheel is close to static height. The benefit of the kit is you won't have a .4"-.5" toe difference between the front wheels thus helping the car feel more stable or perhaps react more linear/predictable. I hope I explained that right.

Julian

[firstgencrx]

Thanks Julian!

Scott,

Julian is right. The only thing you will feel is less toe change while going over a bump. You should feel a difference in both turning and the straights. But I would imagine in the turns is where you will experience the biggest difference.

David

[EuphoricBlue]

Scott, you ever go over a bump in a hard corner/corner at aspeed and feel the nose kinda dart to one side and then come back on course? With enough speed this causes the whole car to shimmy a bit.

That's what this kit is designed to correct.

It won't effect any other handeling characteristics, when done right it diesn't change your static alignment.

[Greg Gauper]

One issue that I have been fighting over the last two seasons is very heavy wear on the inside edge of my racing slicks as if I were running way too much camber.
This has become more pronounced the faster I have gotten i.e. I'm braking deeper and seeing more cornering loads compared to when I started out in Production.
Based on David's numbers I think the problem might be caused by toe change under very heavy braking and/or cornering.

My control arms are almost horizontal, and I'm running crazy stiff spring rates (31mm front T-bars, 21mm Mugen sway bar, OMG stiff rear springs & bar....)
I see about 1" total travel using my two high tech bump travel detectors....a tie-wrap on the shock shaft that I push down all the way before I go out and then compare how far it has moved up when I come off track, and by how much wear I get on the sides of my air dam from scraping on the ground

Granted, the car feels fine...I would just like to get more even wear out of my tires. I am running between -0.5 to -0.75 degree camber which is not excessive based on info I've gotten from other strut-based FWD racers. I've narrowed the problem down to excess bump steer, and/or possible shock tower flex causing camber change in hard cornering.

I suspect David's kit might help with the toe issue. It stands to reason that it would also help with stability under heavy braking.

Wish I had more time to test/develop before the Runoffs but this will have to wait till next season. Unfortunately I wasted this season trying to track down a mysterious loss in power that we didn't find until just last week

[firstgencrx]

One issue that I have been fighting over the last two seasons is very heavy wear on the inside edge of my racing slicks as if I were running way too much camber.
This has become more pronounced the faster I have gotten i.e. I'm braking deeper and seeing more cornering loads compared to when I started out in Production.
Based on David's numbers I think the problem might be caused by toe change under very heavy braking and/or cornering.

My control arms are almost horizontal, and I'm running crazy stiff spring rates (31mm front T-bars, 21mm Mugen sway bar, OMG stiff rear springs & bar....)
I see about 1" total travel using my two high tech bump travel detectors....a tie-wrap on the shock shaft that I push down all the way before I go out and then compare how far it has moved up when I come off track, and by how much wear I get on the sides of my air dam from scraping on the ground

Granted, the car feels fine...I would just like to get more even wear out of my tires. I am running between -0.5 to -0.75 degree camber which is not excessive based on info I've gotten from other strut-based FWD racers. I've narrowed the problem down to excess bump steer, and/or possible shock tower flex causing camber change in hard cornering.

I suspect David's kit might help with the toe issue. It stands to reason that it would also help with stability under heavy braking.

Wish I had more time to test/develop before the Runoffs but this will have to wait till next season. Unfortunately I wasted this season trying to track down a mysterious loss in power that we didn't find until just last week

Greg,

I would be happy to let you know what kind of improvement you would see in only 1" of front suspension travel. You might also find that with some bump steer correction, you could loosen up some of that front spring rate, and let yourself have some more front suspension travel. Might make the ride a little softer.

[Chris]

I am having the same issues with my racecar as Greg and think this may help solve some of the tire issues

Doodson

[arvieg]

Great review....i like