Preston Petty No-Dive.

[Nathan S]

Good idea, snake oil, or just an answer to a question that nobody asked?

Current market value?

[BAHNZY]

Have one fitted to my 78 125C and don’t mind they way it behaves.
"Back In the Day" they had their place where it suited a certain rider’s style and bike configuration but with today’s available technology (i.e. PD Valves) they have no specific advantage.
As an example Stephen Gall had them fitted to his YZ’s and took a likening to them on certain models whereas Mike Landman had essentially the same spec bike and hated the system, horses for courses I guess.
What they are worth is totally what someone wants to pay as they have no market value as such. One piece of advice that I could pass onto the seller/buyer is that you have to get the complete system if it is coming off a bike, i.e. the left side fork leg & the brake backing plate as they are modified to a point where you’re unable to return them back to the original specification. If you are buying a "new in the box" system then find yourself a sacrificial fork lower leg and brake plate to re-work just in case you’re not happy with the end result.

[Slakewell]

About as usefull as as an extra Bra clasps

[Swiss]

I built one in the '70s after Petty announced them and then took months to actually produce units for sale.  I liked the magazine test results and wanted one but couldn't get one.  Also since they were pretty much bike specific they were almost like custom units.  I used mine for Enduro/Trail riding on my custom Honda XL350/403 bike and liked it.  Really great for BIG downhills where everyone else was off their bike and "bulldogging" their bikes down the mountains and I could just clamp on the front brake and ride it down with full suspension travel available and no tucked in compressed front end threatening to toss me over the bars!!

Here is an old picture from the mid '70s of my Honda with the homebuilt anti-dive front end.  I improved on the Petty design by stepping the upper collar around the fork tube.  That put the forces directly in line with the lower fork clamp and not in shear like the Petty design.  Also lucked out and found a lightweight throttle rod off of a Huey Cobra Gunship that was just the right length and sitting around our Supply Room.  It had been mis-ordered and no one claimed to have a use for it!  HA!HA! 

The conversion that I did on the front hub was reversible and I mounted an aluminum block between the lower arm and the hub with two countersunk screws.  Simple to remove the screws and the hub would still fit to the fork leg for normal brakes.  In the late '70s I built a custom double leading brake backing plate that worked with the Anti-Dive conversion.


The major complaints that I read about were that the "Pro" Factory riders did not like that the front end did not "tuck in" in tight turns and thus slowed the steering down.  Riding Enduros and woods this wasn't a problem for me and I really liked using it.  I only took it off when I went to 12" of front wheel travel and that wasn't good for the arc travel of the lower arm.  I am converting back to about 11" of travel now and may think about re-fitting the system to the new inverted 21"KTM 85sx front end.

Swiss

[mx250]

  Also lucked out and found a lightweight throttle rod off of a Huey Cobra Gunship that was just the right length and sitting around our Supply Room. 

Knowing the price of aircraft parts the No Dive was probably worth more then the rest of the bike  .

Interesting comments. I've always being interested. They seem to make a lot of sense. I'll have to try one some time. Your comment about the lack of dive not changing the rake during the 'turn in' phase is an interesting one. I understand it in theory although I have not experienced it to understand just how effective the dive is in assisting the turn in. In part it could be compensated by set up and steepening the rake.

Thanks.

[Swiss]

Just wanted to add that with any of the older VMX bikes there is no problem with the amount of fork travel and the rotational arcs for the brake backing plate are acceptible.  Thought about it and on one of the newer long travel bikes it could be possible to use a linkage system to change the amount of arc travel of the backing plate arm vs. the travel at the lower steering head/triple clamp.  So you could either build an arm that mounted off the top of the lower fork tube (conventional fork) or the bottom of the upper fork tube (USD) to change the leverage and the arc travel.  Basically a second arm pivoting between the Petty style lower arm and the upper fork leg mount. 
Just something to think about.
Swiss

[TeeBone]

I understand it in theory although I have not experienced it to understand just how effective the dive is in assisting the turn in. In part it could be compensated by set up and steepening the rake.

Thanks.

Next time you set up for a corner, try dragging the front brake a little and see how much more the front end can dive and assist turn in - you'll be amazed!
Disclaimer - not a universal panacea for ALL corners and soil types!

[Swiss]

Yea, actually when I typically set up for a corner it is with the throttle dialing how far around the back end comes.  Does away with most of the front end steering problems!  HA!HA! 

Swiss

Friend once told me that my front end comes up too easily when coming out of corners.  He was a 2-smoke 250MX rider and I figured that he lacked a little finesse on his throttle control...  Mostly either full on or shut off!

[cheapracer]

You guys use brakes??   

[Swiss]

Yea, we use brakes!  Our bikes are fast enough to need them!!!  Of course for the rear we just shut off the throttle and let the engine stop the knobby down to nothing, then use the throttle to spin it back up again!

Swiss