Saturday, January 25, 2014

Alpinestars Bionic 2 vs Thor Impact Rig Protection Jackets / Compression Suits.

I've been wearing a Thor Impact Rig SE for a while and decided it was time for a change.  The Impact Rig has been great, but I wanted to try something else, preferably something just as light and with higher CE ratings. A couple jackets I tried were really warm and/or heavy (like the Leatt) and so I rejected them. The Dianese Light Wave jacket also looked very nice, but the back protector features an aluminum honeycomb that crushes during an impact and isn't reusable. Very cool for the street, but not so good in the dirt where I crash regularly.

For reference, I'm 140 lbs and 5'5". I wear a 36 short jacket.

Thor Impact Rig SE
size S/M
This jacket has served me well.
Some notes:
I weighed it: 52 oz. The jacket fit me very well and I like that the shoulders felt slim and close. I always wore thin synthetic sports shirt under the Impact Rig and if it was cold I wore a turtleneck underneath. I wore my jersey over the Rig but it was impossible to tuck my jersey into my pants as the Impact Rig would get in the way. I had no trouble wearing a hydration backpack on top of everything. When I first bought it I had been aware from reviews that the zippers holding the kidney belt on would come undone, and sure enough it was a problem. I just sewed them permanently closed. I also found that the kidney belt would sometimes creep up over my rib cage. I liked the off center zipper because it allowed a full chest plate. The back protector is removable, but I've never removed it.
I've owned the Thor long enough that I've had to figure out how to clean it. The solution I found was that I just hosed it off and then hung it to dry. That seemed to work adequately.
The Thor web site claims the Impact Rig SE is CE "approved" but provides no specs. Frankly, the padding is thin. It worked fine in my tumbles, but I really wanted to upgrade to something more protective.

Alpinestars Bionic 2 Protection Jacket
size S
I was shocked when I weighed the Bionic 2 that it was also 52 oz, no heavier than the Thor Impact Rig. The shoulder and elbow protection is CE certified. And the removable back protector has level 2 CE certification. The main zipper divides the chest plate in the center... I was a bit unhappy with this and it leaves the center of your chest unpadded. When I first tried on the size "small" Bionic 2 it felt very snug, almost too tight, but I soon decided it was just the right size for me. (If you are larger than me go for the "medium").  Compared to the Thor, the shoulders feel bigger but disappeared as soon as I started riding. The fabric between the protective pieces is an open mesh which promises to be cool and breezy.
I've now ridden with the Bionic 2 a couple times for several hundred dirt miles. I wear it as I did the Thor, over a synthetic sport t-shirt or turtleneck and under my jersey. The back protector ends up going over the rear belt line of my pants and the Jersey is untucked. No problem wearing a hydration backpack.  I've taken a couple falls and one hard blow to a shoulder and I've been very pleased with the protection. It does appear to be superior padding compared to the Thor. While the shoulders feel bit bulkier, they disappear when riding. I spent two full days riding and hanging out wearing the Bionic 2 last weekend while at a riding school and had no comfort problems. Frankly, I didn't even think of it, which is perfect. I didn't even take it off for lunch, although it was obviously a bit more awkward in a chair.

I think both of these jackets worked fine for me. The zippers on the Thor's kidney belt need to be sewed up so they don't come loose. In my opinion, the Alpinestars Bionic 2 seems to offer better impact protection, except in the center of the chest where the zipper is. Neither jacket offers much protection for your your lower sides, except for the fabric of the kidney belt. The Bionic 2 might be a bit cooler in hot weather due to the open mesh fabric.

Thor from the front.

Alpinestars from the front. Note the split center and that the shoulders seem a bit wider.

Thor back:

Alpinestars protector seems to go further down the back:

PS: Living in warm San Diego I've seen street riders wearing these instead of a real jacket... that is a big mistake! These provide some impact protection but don't help with abrasion. I suspect in street fall the protection would be torn off or holed within a few feet of sliding so get a leather jacket to wear over it on the street!

Monday, January 13, 2014

Suspension Lowering: KTM 350 EXC-F

I had George at Suspension 101 near San Diego, California help lower the suspension on my 2013 KTM 350 EXC-F.

I'm very happy with the work George did, I highly recommend his business. And I learned some interesting things in the process.

The difference in the "new ride height" vs the "amount of travel removed from the suspension" is interesting to note.

The thing I learned was that there is a measurement difference between shortening your suspension travel and lowering the bike's ride height. This means if you shorten the suspension 30 mm, the ride height will NOT be reduced a full 30 mm!

So, If you want to reduce the ride height by 30mm, you will have to shorten the suspension my more than 30mm! (- at last in the rear of the bike, more on that later.)

Some explanation
When you set the rider sag on the bike, you want to set it at a specific fraction of the total suspension travel. When you reduce the suspension travel you thus reduce the target rider sag. For example, if you want your rider sag to be 1/3 of the suspension travel and your original travel is 300mm, your original rider sag target is 100mm. If you reduce the suspension travel to 270mm, your new rider sag target will be 1/3 of 270 = 90mm.The new rider sag is 10mm less than the original rider sag. So, when you shorten the suspension 30mm, the ride height in this example only goes down by 20mm after you correct your rider sag.

Now, with most dirt bike forks, setting the front rider sag is tricky because stiction makes this very hard to measure. Also, the front fork rider sag is usually set to a smaller number than the rear, and thus the sag effects the lowering equation by less. Additionally the forks are at an angle, so the change in the length of the fork effects the height of the bike a bit less than you might think (Look up your trigonometry!) But you are concerned with the change in ride height, not just the length of the suspension.

What I did to my KTM
I wanted the bike lowered 30mm.
-The stock rear suspension travel is 335mm and the stock rider sag 1/3 * 335 =  111mm.
- If we shorten the rear suspension travel by 40mm to 295mm the new rider sag will be 1/3 * 295 = approximately 98mm.
- So the change in rider sag will be 111mm - 98mm = 13mm
- So shortening the rear suspension 40mm results in the ride height being 40mm - 13mm = 27mm lower. Close enough for me!

On the front fork, given the stiction issues and the smaller sag differences, we shortened the fork travel by 30mm AND we changed to a spring that was 30mm shorter but the same spring rate. Thus the fork was 30mm shorter, but with the same preload the sag should be approximately unchanged because the spring rate is the same. Upon measurement of the rider sag after reassembly, the front ride height was approximately 30mm lower.

Be aware that if you shorten your suspension 40mm, after properly setting your sag the bike's ride height will not be reduced by the full 40mm. Check your target rider sag and see how that effects the height before starting the project.

Here's a pic of my bike after the lowering. Also note my shaved seat.

I also had to shorten the side stand of the KTM to match the lower bike. Conveniently the KTM side stand is a hollow tube and has a removable foot. I pulled the foot off and cut the end of the stand off. You can see the removed piece has a flared end for strength, so my cut stand will be a bit weaker than original, but seems fine so far. Also, the inside of the tube has a bit larger inside diameter in the end to accomodate the foot. So I had to grind down the male part of the foot to get it fit in the new end of the stand.

Shortened stand with the foot re-installed.