rake angle vs handling

[jimmyhackers]

ive recently replaced my front forks. this appears to have given me more "rake" i think.

as you may of guessed my handling seems a bit foobared hence asking.

my symptoms are....it doesnt seem happy going straight. like im riding on the ridge of a roof and it keeps wanting to pull either left or right.

the bearings are fine n smooth with no play. nothings bent or twisted. so this is purly rake angle i think.

i can raise the rear or lower the front or a combination of both to reduce rake. will this help?

thanks in advance

jim

 

[4bound]

Foobared was a new one on me Jim, but worked out it was a version of "fubar"ed which means f'd up beyond recognition apparently! Can you sho0w us a photo? Are the new forks a different shape to the old ones or just a different length? Or maybe a different material?
In the meantime you might find this page informative http://sheldonbrown.com/rinard/forklengths.htm

 

[Nealh]

Did you fit a crown race, If not you need to fit one. With out one the steering will pull to one side or the other and feel like torque is pulling it.

 

[jimmyhackers]

yep. crown races fitted either end. As i said though theres no play and all is good and turns smooth as butter.





heres a pic of the forks before and after. ignore the fact that the first pic has a heightend (more than standard) rear suspension to accomodate the old motor. its the other way now and is lower than standard.

the difference between the forks is one is cheap and chinese and one is a old but good set of beefier rst 381s i think they're downhill bike forks. same length/front ride height but more travel and nicer ride comfort, they really soak up the bumps nice.

the front shocks are slighty moreso set forward from the crown 2 or 3 mm compared the the old set.

the main difference seems to be the front axle mounting point. its infront of the shocks now and on the black shocks it was below.

all i can adjust is the front down or the rear up. ill put the rear back to standard tomorrow and see if it helps.

thanks for the help

 

[trex]

...
my symptoms are....it doesnt seem happy going straight. like im riding on the ridge of a roof and it keeps wanting to pull either left or right.
...
jim

it sounds like wheel flop.

 

[martin@onbike]

I think It'll be down to your handlebar position....you've gone from steering over the centre of the wheel to now steering from behind the centre of the top of the steerer tube....if you put a short stem on to pull it in front of the steerer, I think you'll feel a difference....or at least straight bars in line.( you could even rotate your bars to rake forward and see if it makes a difference as a first port of call) Looks like you'll be pushing to steer rather than pulling.

 

[trex]

@Martin: I don't think the handlebars position is responsible for what the OP describes as 'like I'm riding on the ridge of a roof and it keeps wanting to pull either left or right', his problem is instability, not pulling or pushing to steer - the trail of the bike determines the stability when riding hands off to a large extend and the wheel flop to a smaller extend. Trail is a function of head angle, rake, and wheel size. These haven't changed much or at all, leaving wheel flop as possible candidate. Increasing the trail (the distance that the front wheel ground contact point trails behind the steering axis ground contact point) may fix his problem.

 

[jimmyhackers]

thanks for the info.

i raised the rear end today. this didnt help much :s if at all
just read your post TREX. By rasing the rear end am i right in understanding i reduced my trail?

and your saying i should go for more trail?

i can lower the rear again and probably go up 10mm on the front . after that im stuck for a simple fix, and for some reason i dont think itll make it work

i think i can see now with help from your diagram that the problem lies when going from my old to new forks i have increased the rake a fair amount which has inturn rather drastically shortened my trail.

i could...... spin the shock mounts 180degrees. this should give me pretty much no rake like my old forks and inturn give me more trail.

gonna try this.... see what happens.

thanks for the help

 

[jimmyhackers]

my fix fixed it...... twisted my fork holder/mounts 180 to give me minimal rake.

bike handles like a dream now

thanks again guys for the help, couldnt of done it without yams

jim

 

[jimmyhackers]

just thought id show the new side angle photo. so you can see how i sorted it