peejay

My stock crossmember and oil pan would beg to differ.

The bumpsteer on that thing looks REALLY scary. Will someone who does not work for CP Racing install a strut without the spring and check bumpsteer over the suspension travel?

edit: Need to add... yes you know what the steering lock to lock is but that doesn't mean anything significant, what you want to know is what is the amount of rack travel vs. steering shaft rotation. THAT is the kicker. You can have a rack that is 2 turns lock to lock but if it only moves 2 inches per turn then you are going to have slow steering (and not much of it!). What is the rack travel to turns ratio, then compare that to the center link travel to turns ratio of the stock RX-7 boxes.

Also... you guys talk about a "dead spot" on center as if that is a bad thing. When you are bombing down real world roads, it helps to not have so much kickback over bumps. Helps the driver control the car better. When you reengineer the suspension to have zero scrub radius, then kickback isn't such a problem... assuming you don't have bumpsteer to mess things up.

TexasGunRunner

My understanding is that it is US$550 for stage 2, or US$350 for stage 1

Also, for those frustrated by the information presented here, please understand that nothing I say is official. It is all based on personal emails between me and CP racing for my benefit. I might misinterpret or make a typo.

The real wonder is that you too can send email to them and they will respond, answering your specific questions. That might be better than making decisions based on what somebody else was told in response to a totally different question.

FWIW, I never heard of these guys (CPR) before this came up...I am just grateful they continue developing cool products for FBs.

--BTC

inittab

peejay, can you explain bumpsteer? Does the current steering setup have bumpsteer and how do you measure it? I assume this is something that is quantitative in nature so side by side comparisons between this mod and stock can be made. Thanks!

'85 GSL 302

"bump steer" is a term that referse to a cars tendancy to make unintentional steering inputs due to a bind in the steering/suspension components. Bump steer origionates from steering links that aren't perfectly paralell to the control arms. If you ever have your car on a lift, when the wheels are strait the LCA's and the steering links are 100% parallel. If you mount a steering rack to low or to high, then the difference will cause binding. When an arm sweeps up and down on a fixed point, the outside point makes an arc in the air. If you mount two arms at different points, the diferent arc will cause the wheel to turn forwards or backwards. Basically when the suspension compresses or extends, the wheel turns without the rack moving. IE, bump steer. It's a bad thing. Personally I don't like the way the CP kit looks in pictures, but it may just be the camera angles.

TexasGunRunner

For those complaining about the price, you can get it for $500 online at eBay:

Stage 2 Kit on eBay

I am still not totally clear on bumpsteer, or what I would be measuring, assuming I had the kit installed, and the time to remove a spring to take measurements for somebody else.

The difference in the arc causing the wheels to be pulled/pushing out of sync and to different degrees makes sense...but I don't see why a lower mounting necessarily causes that. If the rack is level, with respect to the tie-rods and even between them, then there shouldn't be any problem whether it is high, low, or perfectly at level. Maybe I don't understand what you are saying well enough.

Thanks,
BTC

inittab

When I drive my RX-7 on the highway I feel like I'm playing tug-of-war with the steering wheel. I hold the wheel straight but the grooves in the highway tug the car from side to side. Is that bump steer?

virfighter

inittab,

How wide are your tires? That is something that usually happens with wider and/or high performance tires (I have that issue with my 7 on falkens).

Bump steer usually occurs when going over bumps, like you go over a bump and the car will jerk to one side or the other... at least this is what I usually refer to as bump steer, but then I might be talking about something else.

'85 GSL 302

Tires following the road is a multi problem symtom. Usually the result of too much possative caster and sticky tires. It's something you just have to live with if you have a performance set up on your car.

Bump steer is different. It's the result of the suspension movement changing the toe, making the car turn when you don't want it to. The effect is similar to the road pull you mention, just differnt things cause it.

To prevent this from happining, the rack must be mounted in such a way that the lower control arms and the steering tie rods sweep the same arc. In the RX-7 that means that they must be parrallel to each other. IE when the LCA is perfectly 90 degrees to the ground, so must the steering tie rod. They should always be the exact same angle to the floor pan when the wheel is straight.

peejay

Bump steer is when suspension motion causes toe in or toe out.

It is caused when the suspension moves in a different arc than the tie rod end. Generally speaking, for a rear steer car, if the tie rod is too short (poor pivot placement) then you will get toe out as the suspension moves up or down. If the inner pivot is placed too low, for example, as the suspension moves upwards (bump) you get toe-out and as it moves downwards (droop) you get toe-in.

I've measured the bump steer on my '80 and it was not measurable on my alignment rack. The stock steering system is very good, and the geometry is simple because the outer pivot is in line with the ball joint and the inner pivot is in line with the line described by the control arm bushing and the strut rod bushing. (Note how the center link is shaped like a flattened U in order to get the inner tie rod pivots in an advantageous location yet also clear the engine) The tie rod end doesn't necessarily have to be parallel for there to be zero bumpsteer, it depends on the specific suspension and steering design. (For example, if you had a double control arm suspension with a difference in angle between the upper and lower control arms, and the steering met the knuckle in the center of the knuckle, the angle of the tie-rod would want to be roughly splitting the difference between the angles of the control arms, same for length. After you find the TRUE pivot axes, of course!)

Nibbling on rough pavement isn't bumpsteer, it's called tramlining and is generally caused by tires with stiff sidewalls, which negate some of the advantage of having radial tires.

abeomid

I agree with peejay. I am worried about the bumpsteer as well. Any better pictures? cause from the pictures I see there will definitely be some problems.

MikeLMR

For all those RHD hopefulls, Got an E-mail the other day from CP , the kit will NOT fit a RHD car

Mike

TexasGunRunner

Since bumpsteer is measureable and quantifiable, why don't you ask CP make the measurements?

I know you said you wanted somebody else to give you the answer, but the kit has only been available for a week or so, and, at least for myself, even if I measured it I am not sure the measurement I would give you would be correct or accurate because I have no experience doing it. (not to mention I don't have it installed yet)

Your desire for somebody outside of CP to tell you appeared to be motivated by their generic response about it not being too low. In this case, you would be asking for a specific measurement, not an opinion. They will be honest about that because it is verfiable later by others. Further, it might lead to improvements in the kit, if necessary.

I would ask, but I don't know enough, or understand enough about what you wrote to ask an intelligent question. Besides, I wouldn't be able to interpret the results or follow up. Please...ask them.

-BTC

peejay

I ask someone else because judging from past experience with other companies, they often don't even MEASURE the suspension geometry, they just say "It's better than stock" or "It's not that much worse than stock".

Perhaps they did measure it... in which case, they are really insulting the intelligence of potential buyers by not posting the bumpsteer curve. Even a fake one would suffice :grin:

abeomid

Any news on this? I mean I don't need it as I already have 2nd gen suspension on my car. But there are bunch of potential buyers on west coast which would like to know about the geometry on this thing, like actual numbers, not if it's better or same as stock. These guys are racers, so they don't know what stock feels like.

TexasGunRunner

I wish one of y'all who truly understand what you are talking about would just ask them. Since you are asking for a specific, quantifiable measurement, they are not going to lie to you (too easy to disprove later).

Geez, just buck up and ask...they won't bite your hand.

This is exactly the sort of detailed technical information that should come from an authortative source (i.e. the vendor); not y'all waiting for somebody else to act as your own personal guinea pig.

Rant OFF

--BTC

Pedestrian X

I recall this issue coming up before. But it was back before the tubular design came to the table. Apparently it was perfect.

J Oliver

Please contact CP Racing so all questions and concerns can be answered and put to rest.

Thank you
J.Oliver

purple82

So, has anyone installed it yet?

Spinner-D(eluxe)

+ $50 shipping. (Same total as directly from CP).

smnc

I'm getting mine sometime in November... now that I have a new car to put it in

purple82

If no one has installed it yet, what's the hold up? Funds, slow shipping, fear?

TexasGunRunner

Funds. I already have two Rabbit racks. I plan to buy one kit in November, or December at the latest. The other one will probably be in the Spring.

Brian T. C.