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Taller trials tire--do I need more sag?

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I'm now running a trials tire on my 09 ktm 250 sx that is revalved/sprung for woods duty and HS racing. The tire (Dunlop 803) is noticeably taller than a knobby--you can really feel it in seat height and stance of the bike. Should I run more sag to compensate?

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You can try to run a little more sag. That will bring the rear lower. Be careful about adding too much preload to the rear spring though.. You don't want to change how it behaves.

How much air are you running? any more than 8lbs and you won't get the full benefit in my opinion. The tire will bubble and will lower the back.

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To get full benefit from the 803 you need to run lower pressures than most run in knobbies, the lower pressure will also lower the tire height. The TT is only about 1/2" taller than a low profile knobby but if you run lower TP you can mitigate some of the height, so try that before resetting sag. The 803 is a Radial tire and low pressure makes for a longer contact patch and the radial belt helps maintain even contact pressure, the result is super traction and improved sharp bump absorption. I suggest you start lowering TP to find a sweet spot; I run less than 4psi on my Trials bike for wet clay (cleans mud from the tread) but it only weighs 165lbs, I run 6psi in the 803 on my dirt bike. The caveat is low TP provides great traction but can make the bike squirrely at speed. As you'll find the TT has more traction than a knobby but breaks loose more suddenly, also the transition to side slip is more abrupt making it harder to control brake slides into corners.

Edited by chuck4788

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I'm running 8 psi. Any less and the wallowing in corners is too distracting. Are you sure the trials tire is only 1/2 inch taller? I'm running 105 mm sag now, and the bike is so tall I sometimes feel like a kid trying to ride an adult bike. I have a 30" inseam. It's been a while since I had a knobby on the bike, but it was definitely lower as I did not have so much trouble touching.

I'm currently debating getting the suspension lowered, or trying a professional seat modification, perhaps combined with the "X bushing". I'm reluctant to modify the suspension, as I have been very successful racing with the current revalve/spring setup. Any thoughts?

Edited by rpt50

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at 105mm rider sag you are not running enough sag. The KTM has 13.2 or 335mm of travel. You want 34% of availble travel in rider sag (11% static sag on linkage suspension, about 12% or less static on PDS, I ran 38mm). You are looking for about 114mm (+-2mm) in rider sag. That will help greatly with the trials tire also.

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Thanks. I think I took the 105mm setting from an MXA article. I'll try a little more and see how it feels.

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Don't believe everything you read in Magazine articles. They are no better riders than we are. If they were they would be professionals. I take everything I read with a grain of salt. Sometimes they are right and many times they are wrong. LOL

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