Greater-Than-Average Dirt Bike Rider Setup - Dr. Dirt - Dirt Rider Magazine | Dirt Rider

Greater-Than-Average Dirt Bike Rider Setup - Dr. Dirt - Dirt Rider Magazine

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.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:

  • Desert/Enduro/Trail

  • Motocross

  • Arenacross

  • Supercross
    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:

  • FRSP 434949
  • RT FRK SP
  • 42.7x493mm .49kg $109.992.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: * SRSP 672760 * RT SHK SPR 66.9x64x267mm 6.0kg $109.99

17.While the bike was apart for suspension work, we made the riding position more open. The ideal way to go here, since Robinson had always adjusted to the small feeling of the bike, was with a ProTaper P3 top triple clamp ($169.95, www.protaper.com). The P3 offers up to five positions for the handlebar mounts. These photos illustrate the range of adjustment available. We opted for the furthest position forward that didn't let the edge of the clamp extend past the forward edge of the triple clamp.18.In addition to the five handlebar clamp positions, ProTaper offers different height clamps. Again, this photo shows the available range with optional height clamps. Most triple clamp manufacturers have a variety of handlebar placement options. We used 45mm risers ($59.95).19.Another option for opening up the rider compartment is to change to a footpeg that is lower or moved back. There are not a lot of available options here. We used Fastway Evo F3 pegs ($109.95, www.fastwayperformance.com).The portion of the peg that the pivot pin goes through is not cast into the peg. It is a precision-machined sleeve, and it can be inserted from either direction. The result is that you can have the footpegs in the standard position (top) or you can reverse the sleeve, swap sides with peg return springs and the footpegs will be located down and forward from their normal location. These photos show the relocation. Since Robinson wears a size 13 and he bottoms the bike fairly often despite the stiffened suspension, we opted to stay with stock pegs and peg height.20.The final area of the rider compartment that we addressed was the seat. A taller seat ($105.99) and, for a heavy rider, one with firmer foam can greatly ease the transition from sitting to standing. The easiest fix is to call SDG (www.sdgusa.com; 800/743-3734 ) and get one of its complete seats. We ordered a tall, firm model, and it came as a complete seat, including a nonslip cover. It even has the correct brackets. Just bolt it on. Enduro Engineering (www.enduroeng.com) is also a great source for KTM riders. You can choose from Guts (www.gutsracing.com), Factory Effex (www.factoryeffex.com), Ceet (www.ceetracing.com) and a few other companies for seat foam. Be sure to check the parts book; some models have taller seats available from the manufacturer.21.If you have been doing the math, we spent a bit of cash modifying the bike, but for a big guy to be able to ride at his potential, there really aren't many cheap shortcuts available. There is one for moving the handlebar up and forward. Thumper Racing has these adapters ($89, www.thumperracingusa.com) for tall riders that use the standard bar. These work great on bikes such as the Honda XR250R, 400R, 600R and even the 650R. Those bikes tend to have ergonomics that force the rider into a sit-down mode, and these clamps can change that in an economical way. The applications are limited but work well on the bikes for which they are designed.When the mods were completed, Robinson had a little trouble adapting to the spread-out riding position, but he soon acclimated and enjoyed the customizing. He took no time at all to appreciate the personalized suspension upgrades. He rides with more confidence and aggressiveness off-road and on the track. He is able to seat-bounce jumps and hammer into jump faces for the first time in his riding history. He literally has never had a motorcycle that worked correctly before. He is quickly unlearning the timidity that has come from a constant diet of frightfully undersprung motorcycles.When I found out I would be the lab rat for this story, I tried to keep my expectations reasonable. Secretly, though, I had this fantasy result in mind of how good the suspension would be and how much of a difference it would make in my riding. The final result blows away those fantasy expectations. I couldn't even imagine the difference that correct suspension setup made. I'm still adjusting to the suspension, and as I learn what the bike will do, I have tried stiffer adjuster settings, and it just keeps getting better. I'm able to experience riding in a way that I never have before. I've even started passing riders and having battles on the track. Now I realize that I was trying the equivalent of riding motocross with trials suspension. I can land short and not crash and even overjump without fear. A big part of the trust in the suspension comes from opening up the riding position. I'm a working man/kid on a strict budget who only buys used bikes. But if I had known how valuable these mods were going to be, I'd have scraped up the money somehow, some way and a long time ago!
-Matt Robinson/6'2"/310 lb/Novice (but learning fast)

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.

7.Race Tech felt that Gold Valve suspension pistons ($159.99 for either front or rear) and new shim stacks at both ends would be required for best results. The Gold Valve shock piston is installed with a new piston band. Race Tech has video instruction on how to do all this shock and fork service as well as the tools to accomplish the work. For sure, the shock mod is best left to confident mechanics, and the fork requires special tools and knowledge. Race Tech charges $100 for the shock and $110 for the fork.

8.The next step is to select the shim stacks. Race Tech\'s Ronnie Williams has worked with another fast motocross rider who is living large, so he had a good direction for the shims he wanted to use. The Race Tech piston and shims are on the left, and the stock valving and piston are on the right. These are the compression stacks, and it is hard to see much difference. The size and thickness of the shims are not the same, and this shock will be much stiffer.

9.These are the shock rebound shims, and again, the Race Tech ones are on the left, and it is hard to detect much difference without measuring each shim.

10.These are the fork parts. Here the stock parts are on the left and the Race Tech parts and Gold Valves are on the right.

11.These are the pistons from the midspeed valves in the fork. These pistons are not replaced, but Race Tech laps the sealing surface to make sure it is flat and will seal well. The one on the right has been surfaced.

12.Finally, the parts are cleaned and readied for reassembly. Note that the shock shaft has a new shock bumper ($18.99) installed. As with any other rubber that has an extreme life and exposure to sun, heat and chemicals, it wears out.

13.Williams pointed out that the bumper is beginning to come apart inside. Obviously, this bumper no longer works as it was designed to.

14.Before final assembly, the 6.0kg/mm shock spring had one coil cut off, and the end of the spring was reshaped. This required machining a spacer for the spring to allow the preload adjuster rings to work correctly. Race Tech offers this service for $50, and it stiffened the spring rate to 6.2kg/mm. It would be better to begin with a stiffer spring, but we didn\'t have that option.

15.After the shock was assembled, Williams assembled the revalved fork and filled the outer chamber with the proper quantity of oil. A quart for each leg at $24.99 each.

16.Once the bike was back together, we had the sag numbers we wanted, and the Honda looked balanced instead of squatted-out in the rear.

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.

Back

Middle

Forward

Related Content


Latest


Videos