Mark, I'd like to see some closeups of your front end. I've been contemplating a couple different designs on a project quad of mine and whether it will be worth the effort or not....

 

Since we got some good conversation here with some people that seem to know what is going on, I would like to shift gears a little and ask a question about front end rake. I am a little different and race Mojaves. I have been making a arms, swing arms, stems, and frame mods to the mojaves we race. I am currently modding a frame to narrow the front and some other stuff to practically eliminate bump steer. I would like to add some rake to my frame while in the process. The Mo has some rake but it needs a little more. Can any of you guys tell me the angle of rake of the 250r and the 400ex. Just looking at most aftermarket frames it looks like the 250 has more rake than the 400. what is the optimal amount of rake (ballpark, as I know wheelbase and such may change it) for MX? do the aftermarket frames have a different rake than the stock 250r?

 

I don't know the rake of a 250R, but I'm sure someone is going to wonder why not put in a lot of rake. As you increase rake, you increase brake dive. One way to counter brake dive is to have the rake of the upper A-arm slightly more than the lower. This increases caster as the suspension moves up. The rotational force on the suspension during braking is trying to twist it the other way therefore driving the A-arms down. The negative to that is decreased caster at full droop so if you land on your nose off a jump, there is increased chance of the wheels getting ripped to one side. Just some food for thought. It is all a balance.

 

I don't have an LT or a Mojave, but this is a great thread! We need more of this, and less of my raptor80 is faster than your 250ex...blah..blah...blah.


Keep up the good work guys.

 

Yea, its that balance that I am looking for. I know that a little more rake will help my Mo, but not sure how much. Since a 250R seems as close to that perfect balance as anything so far, I was interested in its rake. And just from a visual it looks like some aftermarket 250r frames have more rake than stock. Could even more than the stock 250r has be better without excessive dive? I prefer to keep the a arms at the same rake and keep my caster constant. I will be adding more camber change through the travel with my new setup because i am adding more length to the lower arms(narrower frame) than the upper, but i don't think that is nearly as critical as the caster changing.

 

Mark, are you sure the Honda 250R is set at 15 deg?

I've measured the 400EX at 15 deg and the 250R appears to have a steeper angle (in respect to the main lower frame rails, considering they should be parallel to the ground). Although I haven't measured it myself, I have heard the number 22 thrown around. I hope to get a rake measurement on the Cannondale soon, but it appears to be about the same as a 250R or LTZ400 (which both appear to have about the same rake)

Also, on your idler setup, do you run into any trouble with tie rod bind due to the shorter length?

I've got some tie rod binding on my EX already at full suspension extension at wheel lock with my PEP ZPS shocks and stock length control arms - and shortening the rods would only make it worse.

 

JB, Thanks for checking the R for me. Adding the rake will not affect my plastic as I am taking a section out of the vertical frt tubes just above the top a arm mount tubes. I don't use the stock upper shock mounts anyway. I will measure the mo tonight but I feel sure it already has more than the 7 degrees of the Yamis. I will check the difficulty in going to 15.

Did I understand you to say that the bottom arm mounts are at 15 degrees rake and the top are more than that on the R? I wonder if this is necessary at 15 degrees to counter braking dive? I was looking at the photos of the Lone Stars on there web site and the 250r looks to have much more rake than the 400. It also looks like the 250r upper and lower are close to the same but that is real hard to tell in a picture.

 

bigal, someone was just saying to me the other day why they were not coming to this board anymore, too many lounge chair racers.

JohnnyBravoWPG, who has 4+1 wheels? 3+2 is the biggest offset 10x5 you can get from Douglas. I run a 4+2 which moves the tire center in 1/2" over the 3+2. Hiper-Technology fronts are 4+1, but I am waiting for more feedback on those before shelling out that kind of cash.

1986atc250r, I dont know if the idler thing is really worth it, especially if you are narrowing the A-arms. I was just saying it is the only way to attain 0 bump steer. Even then it takes a huge amount of of design thought and tweaking to get perfect. Hopefully with your longer arms, you can attain the travel you want without the steep angles though.

If you still were going to do it, there is a way you can guarantee no bind on the inner ends. Instead of mounting two ends to the idler arm, you have the inner tie rod pivot on the idler arm and extend past it with a clevis on the end. The outer rod would have a hiem on the inside connected to the clevis with a horizontal bolt instead of vertical.

Not much can be done on the outers because they have to be able to take a lot of angle in two planes. One thing is to somehow angle the outer tie rod since the angle is steeper at full droop than full compression. Basically the way the ball joints are angled to the A-arms. The tabs on the spindles should have been angled in the first place. If you bend the tie rod, you would then have to make adjustments in full turns. If you were using male threaded tie rods, you could use a male thread hiem on the inside and a coupler so all your toe adjustment is at the top. I would put it on the inside so it is sprung vs. unsprung weight. You could also just pull the bolt to make half turn adjustments at one end.

 

Good thread, two posts between the time I started typing and finished.

I mixed up mojaveaddict and 1986atc250r, but you get the picture
[img]i/expressions/face-icon-small-blush.gif[/img]

 

Yep, shocks are a tad long... I'll probably leave it until the next rebuild though - not sure yet, just have to watch tie rod wear closely for now...

Lazarus Sommers has 4/1 Douglas wheels in stock (although they are not truly 4/1, they should be better than 3/2 - but I don't have exact measurements yet). I can get you contact info if you like.