Tracker RTX Kingpin upgrade

[Glenn S]

All of the Tracker RTX trucks that I have purchased (about 10 total), the kingpin in all of them was a Grade-8 3/8" Hex Head Cap Screw with 24-thread that was 2" in length.

But I think a 2 1/4" length kingpin is best for the RTX. This little bit of extra length is especially helpful when using Tracker Stimulator Bushings that are usually around 9/16" to 5/8" in height. I prefer using the full height for both the top and the bottom bushings. Also, If you are planning on using the new Radikal Bushings in your RTX (and using the full height of 9/16" for both bushings top and bottom) the 2 1/4" kingpin would again be the better alternative over the stock 2" kingpin.

Here is a technical drawing of a Grade-8 3/8" Hex Head Cap Screw with 24-thread in 2 1/4" length:


Of interest for some of you out there (especially after reading the paragraph below this), a quick upgrade for a deck with both an RTX front and RTS rear, I have found that of the three RTS's that I bought all of them had 2 1/4" kingpins. So you could just put the stock 2 1/4" RTS kingpin into your RTX and then put a new longer 2 1/2" kingpin back in your RTS. Since the RTS is usually a back truck which is ran flat to de-wedge the kingpin will not be sticking out as much. And if you wanted to use full 5/8" height of Stimulator bushings, and even 9/16" height of the new Radikal bushings, for both the top and bottom bushing in the RTS a 2 1/2" kingpin would be better.

If you go to the local hardware stores you will generally not find a 2 1/4" length in 3/8" Grade-8 cap screws. Most general hardware stores and automotive supply stores only carry 2" length then make the jump to 2 1/2" length skipping the 2 1/4" length altogether.

Sure, you can just use a 2 1/2" length for your RTX's (that is easy to purchase from any local hardware store) but the 2 1/4" length is an exact fit for the RTX when using 5/8" Stimulator bushings. Also, a 2 1/2" kingpin in a front RTX with a good amount of wedge would stick down very close to the ground if you ever decided you wanted to use a 62mm wheel like the cambria.

You can purchase 2 1/4" length cap screws from http://www.mcmaster.com , just put in the part number 91286A254. However, you have to purchase a box of 25 cap screws. But this is only $7.50 or so for 25 plus the ground shipping. And you could sell or give the extras to your friends to fix up their trucks. Single 2 1/2" cap screws at your local general hardware stores can cost 70 to 95 cents each, so this is not a bad deal.

I was emailed and told that Indy 101's are also 2" kingpin stock and could benefit from a 1/4" longer kingpin too if using taller bushings.

[Paul Howard]

Hey! I've recently replaced some kingpins in Tracker RT's and after talking to the person at the hardware store, they told me Grade 5's have more shear strength and being less hard and thus less brittle, they're more likely to bend before snapping than a Grade 8, though the grade 8 has much more tensile strength. If any metallurgically minded people have thoughts on this I would like to know your thoughts. Thanks- Paul Howard.

[Pat Chewning]

Grade 8 bolt capability in yield (stretch) = 130,000 lbs / in2 x .03349 in2 = 4354 lbs minimum
Grade 8 bolt capability in tension (failure) = 150,000 lbs / in2 x .03349 in2 = 5024 lbs minimum
Copied from : http://www.rockcrawler.com/techreports/ ... /index.asp


Grade 5 bolt capability in yield (stretch) = 92,000 lbs / in2 x .03349 in2 = 3081 lbs minimum

Grade 5 bolt capability in tension (failure) = 120,000 lbs / in2 x .03349 in2 = 4019 lbs minimum

Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.

[Rich Stephens]

I've never broken a skateboard kingpin or axle in my life, vert or street. What kind of action can put over 3000lbs. on a kingpin? Just wondering...

[Paul Howard]

Thanks Pat, Glenn, and whoever else gave me feed back. I did put in Grade 5's and have now replaced them with Grade 8's. When I cut the Grade 8's(from 2 1/2" to 2 1/4") they didn't seem any more difficult to cut with a USED hacksaw than my memory of the Grade 5's. They had the same markings and brass/gold sorta color as the 2" stock kingpins that came in the Tracker X and S baseplates as stock. The drawer they came from in the hardware store said " May contain items from India, Indonesia, China......USA......." so I'm wondering even though they say Grade 8, could there be some metallurgical trickery going on? And if I replaced them for a 3rd time with genuine USA Grade 8's, is that a risk to the baseplates as I'm using a 5 lb Hammer and wood blocks for a punch and a wood stump for an anvil? or am I safe at 165+/- lbs cranking thru cones with the "hopefully Grade 8's" I've got in them at present? Thanks - Paul Howard

[Glenn S]

Paul,
Cutting the 2 1/2" down is definitely a good idea for anyone not having alot to change out. And not wanting the kingpin close to touching the ground on a front truck with a good amount of wedge. Glad you mentioned that. I'm lazy though. Do you use cutting oil while hacking saw?

But I would think sure you could get bad stuff from out of country. Hey Mark McCree got Titanium that was out of spec here in the US. Do the bolts have all the hash marks of a grade 8 bolt?

Since you are switching out your kingpins I can only guess that your using taller bushing like Stimulators or Radikals. I really like the taller top bushing on all front trucks, it just feels better anyway, especially with the high-rebound urethane. Not sure about increased speed. But feel is important to me. And there is much better return to center.

[Dave Gale]

In slalom , I think the fine thread and long unthreaded section is more key than grade 5 vs. 8 I've used 5's and 8's for over 25 years and never sheared or bent either!!

[Glenn S]

Yeah looking at the specs that Pat posted I cannot imagine breaking a Grade 5 bolt or even coming close to its limit even if you were doing some of those sick jumps some of the skaters are doing these days, or even skating something like that giant ditch in AZ. For slalom you probably put less than double your body weight of stress on the kingpin, just a guess.

There must be a reason the manufactures spend more on the Grade 8. Maybe liability?

[Paul Howard]

Hey! Thanks Dave and Glenn for the feedback. As far as the question of cutting with a hacksaw using cutting oil, no I have not used it for metal cutting, does it improve the cut or help prolong the life of the blade? Anyhow, I feel better about the broken king pin issue so now I can go slalom in a state of serenity (sort of). As far as bushings go are Stimulators a current or old out of production bushing? I pretty much use the soft blue Doh Dohs, white soft Powell "cores", and the soft white or black Tracker "figure 8" and tall coned uppers in various combinations for now. Are the Stimulators or Radikal bushings much of an improvement? Thanks - Paul H.

[Pat Chewning]

Couple of comments:

The strengths and "capability" I posted for the bolts is when you load them straight in tension which is applied slowly. Of course, when used in a skateboard truck you also have impact loads, flexural loads, and repeated loads which can lead to fatique failures.

So I would't put much emphasis on the absolute numbers of the strength, but more on the relative strengths of grade 5 vs grade 8.

Another comment: A grade 8 bolt might be easier to cut with certain hacksaws because it is slightly harder than a grade 5 bolt -- less "gumming" of the blade might occur.

The use of cutting oil is to reduce the friction and avoid heat build up in the part and the cutting tool. Reduction of the heat prevents the part from expanding and "grabbing" the saw.

[Glenn S]

Pat,
Or anyone that knows. Why would you think that a manufacturer like Tracker and others would use a Grade 8 over a Grade 5? Grade 8's cost considerably more in hardware stores. I could only guess that they must feel that there is the possibility of failure with a Grade 5.

Paul,
Stimulators are high-rebound urethane. But I feel that they really need to have the OD trimmed down to the proper size to work right for me from the way then come stock. Look in the Geezer-X Forum here. The pictures posted recently of Eric's work show the Green Stims with the OD shaped down to approximately the size of a stock Tracker bottom bushing. And using the full height especially on top on a front truck makes the truck feel better to me at least. It looks to me that Geezer is using a 2 1/2" kingpin with those trucks. Stims start out about 5/8" tall. And I'm gunna guess from that picture he is using the full height.

The added height on top and bottom bushings give the truck much more range of turn. And with the high-rebound urethane there is good return to center. I've not yet tried Radikal bushing but I am hearing that they are basically a similar high-rebound urethane. I plan to check them out soon. The benefit of the Radikals is that they are cheaper by 1/2, $3 compared to $5-$6, plus shipping for most people.

Nick Krest said in the Radikal forum here: "Radikal bushings are indeed 9/16" high, with an OD of 1 1/8".

I've been taking my Stims down to an OD of about 1" and they look just like in the picture of Geezer's trucks, they start out stock like 1 3/16" OD. So from what Nick says about the measurements I'm gunna say that Radikal bushings will benefit from a bit of a OD trim for use with conventional trucks like the Tracker RTX/S.

==================
Sorry Nick my mistake. Because I really appreciated you telling me the measurements. lond day. quick cut/paste/spaced out

[Nick Krest]

Dave Gale said in the Radikal forum here: "Radikal bushings are indeed 9/16" high, with an OD of 1 1/8".

I wrote that, Glenn.

[Dave Gale]

Yes, butt..I can see how "Clear and Red" could be mistaken for 9/16" high and 1 1/8 O.D

[Eric Wallgren]

I just did a pile of trucks, and all the newest RTX and RTS baseplates came with 2-1/4 kingpins. I put 2-1/2s in so you can use 2 full height Stims. I'm using grade 5s lately since by the time you got to the stretch or yield point of a 5, you'd have long since ripped all the truck bolts through the deck, broken the baseplate or hanger casting, or broken your sledgehammer.

In other REALLY EXCITING kingpin news, I was given a pair of beat up old small pivot baseplates which had had the kingpins ground down pretty far. I was to see if it was possible to replace them. I've got a way to machine them out and press in bolts from the bottom, so if you have old small pivots without huge collector value...

I have the technology!

[Jeff Boswell]

Small pivot point Trackers with stimulator bushings top and bottom, sounds very intriguing. All kidding aside Eric did a great job on my Trackers. He brought an set of old trucks back to life!

[Claude Regnier]

I want to Thank Eric Wallgren for doing up my Trackers for me they look sweet. As soon as my ankle is better I'll post what can only be a great review.

They look so sweet, EH!

All the best folks.................

[Alex Walters]

I just measured my RT-X and RT-S and the X has a 2 1/4" kingpin and the S has a 2 1/2". Looks like I don't have to bother with the modification.