There are times when it is great to be a big guy. Like when you get a toe down and save a big high-side down a hill-one of those deals where you would have plummeted if you were 1 inch shorter. But then there are theater and airplane seats, compact cars and most modern dirt bikes. Manufacturers build for an "average" guy, and that doesn't suit big guys any more than it does short folks. I get a lot of mail asking what I do to make bikes fit my grande chassis, and now that Derek Steahly is on board, he'll be receiving the same sort of inquiries. At just over 6 feet 1 inch and 210 pounds, I am right on the edge with a lot of bikes. I can make adjustments and ride them stock. Steahly is roughly the same size as me, but he is faster, so he generally needs stiffer springs. But this story is more for riders who are completely outside the design window of a stock bike.
Matt Robinson is 6 feet 2 inches tall and claimed he was in the 280-pound range. He is a good off-road guy who likes playing at the track. He'll probably play more at the track now that his bike is more capable, but he has literally never been able to jump anything unless he was able to perfectly downside the landing ramp. Robinson is a dedicated rider, but finding gear and a bike to suit him is a never-ending process of frustration.
Together we focused on two areas. We wanted to open up the riding position so it would be easier for Robinson to move around on the bike, and we wanted to personalize the suspension so he could ride the bike closer to its limits and his abilities. Here is the route we took in making a 2003 Honda CRF450R a big-boy toy.
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1. We began with the Race Tech web site (www.race-tech.com). It has a spring rate calculator (found under your specific bike) that helps to get you in the ballpark. The calculator said this for fork springs:
2003 Honda CRF450R
A. Select Type of Riding:
B. Enter Rider Weight (without gear): lb or kg
We answered: Motocross, 280 lb
The Site Calculated Spring Rate: 0.508kg/MM(use closest available)
Stock Fork Spring Rate (measured): 0.470kg/mm (stock)
Available FRSP 4349 Series Springs are:
2.We used the same method to determine a starting point for a shock spring, and we got this information:
Type of Riding: Motocross
Rider Weight: 280 lb
Recommended Spring Rate: 6.06kg/mm (use closest available)
Stock Shock Spring Rate (measured)5.5kg/mm (stock)
Available SRSP 6727 Series Springs are:
 3.We obtained the indicated springs from Race Tech and headed out for some back-to-back testing to see if springs alone would work. We checked the sag with the stock spring, and even with no bike sag at all, the race sag wasn't even close. We were able to remove the pipe, loosen the subframe and slip the shock out through the side of the bike after removing the shock bolts. |  4.It was then easy to loosen the shock preload rings, slide down the shock bumper, pop down the spring collar and remove the snap ring (shown here). The old spring comes off and the new one goes on. Reassemble the shock in reverse order with the new stiffer-rate spring in place. |  5.Unfortunately, the 6.0 Race Tech shock spring wasn't enough. Before we could get the right amount of sag, the bike was nearly topped out with no bike sag. At that point we had Robinson ride the bike. He claimed it was a big improvement, but we could see that the bike was far too soft. We didn't bother with the fork springs, since it was obvious that stiffer springs would be only half the answer. We also had Robinson check his weight, which actually turned out to be 310 pounds-so that explained the sag being off. |
 6.Race Tech wrenches pulled apart the overworked shock, and we found that the oil was all foamy and bubbled over like a warm soda. This shock had never been disassembled before, and there is no way it could have worked properly with this much air in the oil. |
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